2016 |
Abdrakhmatov, K. E., Walker, R. T., Campbell, G. E., Carr, A. S., Elliott, A., Hillemann, C., et al. (2016). Multisegment rupture in the 11 July 1889 Chilik earthquake (M-w 8.0-8.3), Kazakh Tien Shan, interpreted from remote sensing, field survey, and paleoseismic trenching. Journal Of Geophysical Research-Solid Earth, 121(6), 4615–4640.
Résumé: The 11 July 1889 Chilik earthquake (M-w 8.0-8.3) forms part of a remarkable sequence of large earthquakes in the late nineteenth and early twentieth centuries in the northern Tien Shan. Despite its importance, the source of the 1889 earthquake remains unknown, though the macroseismic epicenter is sited in the Chilik valley, similar to 100 km southeast of Almaty, Kazakhstan (similar to 2 million population). Several short fault segments that have been inferred to have ruptured in 1889 are too short on their own to account for the estimated magnitude. In this paper we perform detailed surveying and trenching of the similar to 30 km long Saty fault, one of the previously inferred sources, and find that it was formed in a single earthquake within the last 700 years, involving surface slip of up to 10 m. The scarp-forming event, likely to be the 1889 earthquake, was the only surface-rupturing event for at least 5000 years and potentially for much longer. From satellite imagery we extend the mapped length of fresh scarps within the 1889 epicentral zone to a total of similar to 175 km, which we also suggest as candidate ruptures from the 1889 earthquake. The 175 km of rupture involves conjugate oblique left-lateral and right-lateral slip on three separate faults, with step overs of several kilometers between them. All three faults were essentially invisible in the Holocene geomorphology prior to the last slip. The recurrence interval between large earthquakes on any of these faults, and presumably on other faults of the Tien Shan, may be longer than the timescale over which the landscape is reset, providing a challenge for delineating sources of future hazard.
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Aben, F. M., Doan, M. L., Mitchell, T. M., Toussaint, R., Reuschle, T., Fondriest, M., et al. (2016). Dynamic fracturing by successive coseismic loadings leads to pulverization in active fault zones. Journal Of Geophysical Research-Solid Earth, 121(4), 2338–2360.
Résumé: Previous studies show that pulverized rocks observed along large faults can be created by single high-strain rate loadings in the laboratory, provided that the strain rate is higher than a certain pulverization threshold. Such loadings are analogous to large seismic events. In reality, pulverized rocks have been subject to numerous seismic events rather than one single event. Therefore, the effect of successive “milder” high-strain rate loadings on the pulverization threshold is investigated by applying loading conditions below the initial pulverization threshold. Single and successive loading experiments were performed on quartz-monzonite using a Split Hopkinson Pressure Bar apparatus. Damage-dependent petrophysical properties and elasticmoduli were monitored by applying incremental strains. Furthermore, it is shown that the pulverization threshold can be reduced by successive “milder” dynamic loadings from strain rates of similar to 180s(-1) to similar to 90s(-1). To do so, it is imperative that the rock experiences dynamic fracturing during the successive loadings prior to pulverization. Combined with loading conditions during an earthquake rupture event, the following generalized fault damage zone structure perpendicular to the fault will develop: furthest from the fault plane, there is a stationary outer boundary that bounds a zone of dynamically fractured rocks. Closer to the fault, a pulverization boundary delimits a band of pulverized rock. Consecutive seismic events will cause progressive broadening of the band of pulverized rocks, eventually creating a wider damage zone observed in mature faults.
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Abrahami, R., van der Beek, P., Huyghe, P., Hardwick, E., & Carcaillet, J. (2016). Decoupling of long-term exhumation and short-term erosion rates in the Sikkim Himalaya. Earth And Planetary Science Letters, 433, 76–88.
Résumé: Understanding the relative strengths of tectonic and climatic forcing on erosion at different spatial and temporal scales is important to understand the evolution of orogenic topography. To address this question, we quantified exhumation rates at geological timescales and erosion rates at millennial timescales in modern river sands from 10 sub-catchments of the Tista River drainage basin in the Sikkim Himalaya (northeast India) using detrital apatite fission-track thermochronology and cosmogenic Be-10 analyses, respectively. We compare these rates to several potential geomorphic or climatic forcing parameters. Our results show that millennial erosion rates are generally higher and spatially more variable than long-term exhumation rates in Sikkim. They also show strongly contrasting spatial patterns, suggesting that the processes controlling these rates are decoupled. At geological timescales, exhumation rates decrease from south to north, with rates up to 1.2 +/- 0.6 mm/yr recorded in southwest Sikkim and as low as 0.5 +/- 0.2 mm/yr in the northernmost catchment. Long-term exhumation rates do not correlate with any geomorphic or climatic parameter. We suggest they are tectonically controlled: high rates in southwest Sikkim may be linked to the building of the Lesser Himalaya Rangit Duplex, whereas low rates in north Sikkim are consistent with cessation of extensional exhumation along the South Tibetan Detachment after 13 Ma. The highest apparent erosion rates recorded by cosmogenic nuclides (similar to 5 mm/yr) occur in catchments spanning the Main Central Thrust Zone, but these appear to be strongly influenced by recent landsliding. High millennial erosion rates (1-2 mm/yr) also occur in north Sikkim and may be climatically driven through strong glacial inheritance of the landscape, as attested by high channel-steepness values close to the maximum extent of glaciers during the Last Glacial Maximum. In contrast, variations in rainfall rate do not seem to strongly influence either millennial erosion or long-term exhumation rates in Sikkim. (C) 2015 Elsevier B.V. All rights reserved.
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Agard, P., Yamato, P., Soret, M., Prigent, C., Guillot, S., Plunder, A., et al. (2016). Plate interface rheological switches during subduction infancy: Control on slab penetration and metamorphic sole formation. Earth And Planetary Science Letters, 451, 208–220.
Résumé: Subduction infancy corresponds to the first few million years following subduction initiation, when slabs start their descent into the mantle. It coincides with the transient (yet systematic) transfer of material from the top of the slab to the upper plate, as witnessed by metamorphic soles welded beneath obducted ophiolites. Combining structure-lithology-pressure-temperature-time data from metamorphic soles with flow laws derived from experimental rock mechanics, this study highlights two main successive rheological switches across the subduction interface (mantle wedge vs. basalts, then mantle wedge vs. sediments; at similar to 800 degrees C and similar to 600 degrees C, respectively), during which interplate mechanical coupling is maximized by the existence of transiently similar rheologies across the plate contact. We propose that these rheological switches hinder slab penetration and are responsible for slicing the top of the slab and welding crustal pieces (high- then low-temperature metamorphic soles) to the base of the mantle wedge during subduction infancy. This mechanism has implications for the rheological properties of the crust and mantle (and for transient episodes of accretion/exhumation of HP-LT rocks in mature subduction systems) and highlights the role of fluids in enabling subduction to overcome the early resistance to slab penetration. (C) 2016 Elsevier B.V. All rights reserved.
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Aguilar, I., Beck, C., Audemard, F., Develle, A. L., Boussafir, M., Campos, C., et al. (2016). Last millennium sedimentation in the Gulf of Cariaco (NE Venezuela): Evidence for morphological changes of gulf entrance and possible relations with large earthquakes. Comptes Rendus Geoscience, 348(1), 70–79.
Résumé: The Cariaco Basin and the Gulf of Cariaco in Venezuela are two major basins along the seismogenic El Pilar right lateral fault, among which the Cariaco Basin is a pull-apart. Both basins are sites of anoxia and organic-rich deposits. To examine whether the sediments in the Gulf of Cariaco have recorded traces of historical or prehistorical earthquakes, we extracted and analyzed twelve 1 m-long gravity cores, sampling the last millennium sedimentation. We focused on analyzing the sediment sources with different techniques (particle size analysis, XRF, loss on ignition tests, magnetic properties, Rock-Eval pyrolysis, C-14 dating). The results confirm that major upwelling occurs at the western gulf entrance and makes deep water flowing from the Cariaco Basin into the Gulf of Cariaco. These flows carry an organic-rich suspended load. Furthermore, we found evidence of a particular, widespread fine-grained siliciclastic deposit (named SiCL3) within the gulf, whose age suggests that it likely formed during the large 1853 AD earthquake that stroke the Cumana city. We suggest that the earthquake-induced large submarine landslides that modified the topography of the gulfs entrance, which in turn promoted upwelling and open marine water flows from the Cariaco Basin. The layer SiCL3 would be the sediment load remobilized during this chain of events. (C) 2015 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
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Ahmed, A., Doubre, C., Leroy, S., Kassim, M., Keir, D., Abayazid, A., et al. (2016). Seafloor spreading event in western Gulf of Aden during the November 2010-March 2011 period captured by regional seismic networks: evidence for diking events and interactions with a nascent transform zone. Geophysical Journal International, 205(2), 1244–1266.
Résumé: In November 2010, intense seismic activity including 29 events with a magnitude above 5.0, started in the western part of the Gulf of Aden, where the structure of the oceanic spreading ridge is characterized by a series of N115 degrees-trending slow-spreading segments set within an EW-trending rift. Using signals recorded by permanent and temporary networks in Djibouti and Yemen, we located 1122 earthquakes, with a magnitude ranging from 2.1 to 5.6 from 2010 November 1 to 2011 March 31. By looking in detail at the space-time distribution of the overall seismicity, and both the frequency and the moment tensor of large earthquakes, we re-examine the chronology of this episode. In addition, we also interpret the origin of the activity using high-resolution bathymetric data, as well as from observations of seafloor cable damage caused by high temperatures and lava flows. The analysis allows us to identify distinct active areas. First, we interpret that this episode is mainly related to a diking event along a specific ridge segment, located at E044 degrees. In light of previous diking episodes in nearby subaerial rift segments, for which field constraints and both seismic and geodetic data exist, we interpret the space-time evolution of the seismicity of the first few days. Migration of earthquakes suggests initial magma ascent below the segment centre. This is followed by a southeastward dike propagation below the rift immediately followed by a northwestward dike propagation below the rift ending below the northern ridge wall. The cumulative seismic moment associated with this sequence reaches 9.1 x 10(17) Nm, and taking into account a very low seismic versus geodetic moment, we estimate a horizontal opening of similar to 0.58-2.9 m. The seismic activity that followed occurred through several bursts of earthquakes aligned along the segment axis, which are interpreted as short dike intrusions implying fast replenishment of the crustal magma reservoir feeding the dikes. Over the whole period, the opening is estimated to be similar to 1.76-8.8 m across the segment. A striking feature of this episode is that the seismicity remained confined within one individual segment, whereas the adjacent en-echelon segments were totally quiescent, suggesting that the magma supply system of one segment is disconnected from those of the neighbouring segments. Second, we identify activity induced by the first intrusion with epicentres aligned along an N035 degrees E-trending, similar to 30 km long at the northwestern end of the active opening segment. This group encompasses more than seven earthquakes with magnitude larger than 5.0, and with strike-slip focal mechanisms consistent with the faults identified in the bathymetry and the structural pattern of the area. We propose that a transform fault is currently in formation which indicates an early stage of the ridge segmentation, at the locus of the trend change of the spreading ridge, which also corresponds to the boundary between a clear oceanic lithosphere and the zone of transform between continental and oceanic crust.
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Akuetevi, C. Q. C., Barnier, B., Verron, J., Molines, J. M., & Lecointre, A. (2016). Interactions between the Somali Current eddies during the summer monsoon: insights from a numerical study. Ocean Science, 12(1), 185–205.
Résumé: Three hindcast simulations of the global ocean circulation differing by resolution (1/4 or 1/12 degrees) or parametrization or atmospheric forcing are used to describe the interactions between the large anticyclonic eddies generated by the Somali Current system during the Southwest Monsoon. The present investigation of the Somalian coherent eddy structures allows us to identify the origin and the subsequent development of the cyclones flanked upon the Great Whirl (GW) previously identified by Beal and Donohue (2013) in satellite observations and to establish that similar cyclones are also flanked upon the Southern Gyre (SG). These cyclones are identified as potential actors in mixing water masses within the large eddies and offshore the coast of Somalia. All three simulations bring to light that during the period when the Southwest Monsoon is well established, the SG moves northward along the Somali coast and encounters the GW. The interaction between the SG and the GW is a collision without merging, in a way that has not been described in observations up to now. During the collision the GW is pushed to the east of Socotra Island, sheds several smaller patches of anticyclonic vorticity, and often reforms into the Socotra Eddy, thus proposing a formation mechanism for that eddy. During this process the GW gives up its place to the SG. This process is robust throughout the three simulations.
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Alanoca, L., Guedron, S., Amouroux, D., Audry, S., Monperrus, M., Tessier, E., et al. (2016). Synergistic effects of mining and urban effluents on the level and distribution of methylmercury in a shallow aquatic ecosystem of the Bolivian Altiplano. Environmental Science-Processes & Impacts, 18(12), 1550–1560.
Résumé: Lake Uru Uru (3686 m a.s.l.) located in the Bolivian Altiplano region receives both mining effluents and urban wastewater discharges originating from the surrounding local cities which are under rapid development. We followed the spatiotemporal distribution of different mercury (Hg) compounds and other metal(oid) s (e.g., Fe, Mn, Sb, Ti and W) in both water and sediments during the wet and dry seasons along a north-south transect of this shallow lake system. Along the transect, the highest Hg and metal(oid) concentrations in both water and sediments were found downstream of the confluences with mining effluents. Although a dilution effect was found for major elements during the wet season, mean Hg and metal(oid) concentrations did not significantly differ from the dry season due to the increase in acid mine drainage (AMD) inputs into the lake from upstream mining areas. In particular, high filtered (<0.45 μm) monomethylmercury (MMHg) concentrations (0.69 +/- 0.47 ng L-1) were measured in surface water representing 49 +/- 11% of the total filtered Hg concentrations (THgF) for both seasons. Enhanced MMHg lability in relation with the water alkalinity, coupled with abundant organic ligands and colloids (especially for downstream mining effluents), are likely factors favoring Hg methylation and MMHg preservation while inhibiting MMHg photodegradation. Lake sediments were identified as the major source of MMHg for the shallow water column. During the dry season, diffusive fluxes were estimated to be 227 ng m(-2) d(-1) for MMHg. This contribution was found to be negligible during the wet season due to a probable shift of the redox front downwards in the sediments. During the wet season, the results obtained suggest that various sources such as mining effluents and benthic or macrophytic biofilms significantly contribute to MMHg inputs in the water column. This work demonstrates the seasonally dependent synergistic effect of AMD and urban effluents on the shallow, productive and evaporative high altitude lake ecosystems which promotes the formation of natural organometallic toxins such as MMHg in the water column.
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Alvarado, A., Audin, L., Nocquet, J. M., Jaillard, E., Mothes, P., Jarrin, P., et al. (2016). Partitioning of oblique convergence in the Northern Andes subduction zone: Migration history and the present-day boundary of the North Andean Sliver in Ecuador. Tectonics, 35(5), 1048–1065.
Résumé: Along the Ecuadorian margin, oblique subduction induces deformation of the overriding continental plate. For the last 15Ma, both exhumation and tectonic history of Ecuador suggest that the northeastward motion of the North Andean Sliver (NAS) was accompanied by an eastward migration of its eastern boundary and successive progressively narrowing restraining bends. Here we present geologic data, earthquake epicenters, focal mechanisms, GPS results, and a revised active fault map consistent with this new kinematic model. All data sets concur to demonstrate that active continental deformation is presently localized along a single major fault system, connecting fault segments from the Gulf of Guayaquil to the eastern Andean Cordillera. Although secondary faults are recognized within the Cordillera, they accommodate a negligible fraction of relativemotion compared to themain fault system. The eastern limit is then concentrated rather than distributed as first proposed, marking a sharp boundary between the NAS, the Inca sliver, and the Subandean domain overthrusting the South American craton. The NAS limit follows a northeast striking right-lateral transpressional strike-slip system from the Gulf of Guayaquil (Isla Puna) to the Andean Cordillera and with the north-south striking transpressive faults along the eastern Andes. Eastward migration of the restraining belt since the Pliocene, abandonment of the sutures and reactivation of north-south striking ancient fault zones lead to the final development of a major tectonic boundary south and east of the NAS, favoring its extrusion as a continental sliver, accommodating the oblique convergence of the Nazca oceanic plate toward South America.
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Amitrano, D., & Girard, L. (2016). Fiber bundle model under fluid pressure. Physical Review E, 93(3).
Résumé: Internal fluid pressure often plays an important role in the rupture of brittle materials. This is a major concern for many engineering applications and for natural hazards. More specifically, the mechanisms through which fluid pressure, applied at a microscale, can enhance the failure at a macroscale and accelerate damage dynamics leading to failure remains unclear. Here we revisit the fiber bundle model by accounting for the effect of fluid under pressure that contributes to the global load supported by the fiber bundle. Fluid pressure is applied on the broken fibers, following Biot's theory. The statistical properties of damage avalanches and their evolution toward macrofailure are analyzed for a wide range of fluid pressures. The macroscopic strength of the new model appears to be strongly controlled by the action of the fluid, particularly when the fluid pressure becomes comparable with the fiber strength. The behavior remains consistent with continuous transition, i.e., second order, including for large pressure. The main change concerns the damage acceleration toward the failure that is well modeled by the concept of sweeping of an instability. When pressure is increased, the exponent beta characterizing the power-law distribution avalanche sizes significantly decreases and the exponent gamma characterizing the cutoff divergence when failure is approached significantly increases. This proves that fluid pressure plays a key role in failure process acting as destabilization factor. This indicates that macrofailure occurs more readily under fluid pressure, with a behavior that becomes progressively unstable as fluid pressure increases. This may have considerable consequences on our ability to forecast failure when fluid pressure is acting.
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Angel, I., Audemard, F. A., Carcaillet, J., Carrillo, E., Beck, C., & Audin, L. (2016). Deglaciation chronology in the Merida Andes from cosmogenic Be-10 dating, (Gavidia valley, Venezuela). Journal Of South American Earth Sciences, 71, 235–247.
Résumé: In the Merida Andes, a detailed deglaciation history reconstruction is difficult to achieve due to scattered deglaciation chronologies available. This paper contributes with 24 exposure ages of glacial landforms sampled in the Gavidia valley. Exposure ages were obtained based on terrestrial cosmogenic nuclide Be-10 dating. Results indicate deglaciation mainly occurred between similar to 21 ka and 16.5 ka and the complete deglaciation occurred at similar to 16.0 ka. The glacier retreated in two different phases. The oldest one occurred since the LGM until middle OtD or the local climate event El Caballo Stadial. The youngest phase occurred at ages younger than similar to 16.5 ka until complete deglaciation. A combination of topographic features and changes in the paleoclimate conditions at the end of the El Caballo Stadial seems leaded the fastest former glacier extinction. The topographic feature which seems contributed to the fastest glacier extinction was the low valley bottom slopes. In addition, exposure ages of the Gavidia valley were integrated with deglaciation chronologies from the central Merida Andes to compare deglaciation histories. Asynchronous deglaciation histories were observed. Local paleotemperatures and paleoprecipitations contrasts, different valleys aspects, insolation and catchments steepness could explain different deglaciation histories. (C) 2016 Elsevier Ltd. All rights reserved.
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Ansberque, C., Bellier, O., Godard, V., Lasserre, C., Wang, M. M., Braucher, R., et al. (2016). The Longriqu fault zone, eastern Tibetan Plateau: Segmentation and Holocene behavior. Tectonics, 35(3), 565–585.
Résumé: The dextral Longriba fault system (LFS), similar to 300km long and constituting of two fault zones, has recently been recognized as an important structure of the eastern Tibetan plateau (Sichuan province), as it accommodates a significant amount of the deformation induced by the ongoing Indo-Asian collision. Although previous paleoseismological investigations highlighted its high seismogenic potential, no systematic quantification of the dextral displacements along the fault system has been undertaken so far. As such information is essential to appraise fault behavior, we propose here a first detailed analysis of the segmentation of the Longriqu fault, the northern fault zone of the LFS, and an offset inventory of morphological features along the fault, using high-resolution Pleiades satellite images. We identify six major segments forming a mature fault zone. Offsets inventory suggests a characteristic coseismic displacement of similar to 4m. Two alluvial fans, with minimum ages of 6.7 and 13.2ka, respectively displaced by 23 7m and 405m, give an estimate of the maximal horizontal slip rate on the Longriqu fault of 3.2 1.1mmyr(-1). As a result, a minimum similar to 1340year time interval between earthquakes is expected.
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Aristilde, L., Lanson, B., Miehe-Brendle, J., Marichal, C., & Charlet, L. (2016). Enhanced interlayer trapping of a tetracycline antibiotic within montmorillonite layers in the presence of Ca and Mg. Journal Of Colloid And Interface Science, 464, 153–159.
Résumé: The formation of a ternary antibiotic metal clay complex is hypothesized as the primary adsorption mechanism responsible for the increased adsorption of tetracycline antibiotics on smectites in the presence of divalent metal cations under circumneutral and higher pH conditions. To evaluate this hypothesis, we conducted a spectroscopic investigation of oxytetracycline (OTC) interacting with Na-montmorillonite in the presence and absence of Ca or Mg salts at pH 6 and pH 8. Despite a twofold increase in OTC adsorbed in the presence of Ca or Mg, both solid-state nuclear magnetic resonance and infrared signatures of the OTC functional groups involved in metal complexation implied that the formation of an inner-sphere ternary complexation was not significant in stabilizing the adsorbate structures. The spectroscopic data further indicated that the positively-charged amino group mediated the OTC adsorption both in the absence and presence of the divalent metal cations. Focusing on the experiments with Mg, X-ray diffraction analysis revealed that the metal-promoted adsorption was coupled with an increased intercalation of OTC within the montmorillonite layers. The resulting interstratified clay layers were characterized by simulating X-ray diffraction of theoretical stacking compositions using molecular dynamics-optimized montmorillonite layers with and without OTC. The simulations uncovered the evolution of segregated interstratification patterns that demonstrated how increased access to smectite interlayers in the presence of the divalent metal cations enhanced adsorption of OTC. Our findings suggest that specific aqueous structures of the clay crystallites in response to the co-presence of Mg and OTC in solution served as precursors to the interlayer trapping of the antibiotic species. Elucidation of these structures is needed for further insights on how aqueous chemistry influences the role of smectite clay minerals in trapping organic molecules in natural and engineered soil particles. (C) 2015 Elsevier Inc. All rights reserved.
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Arshad, M., Merlina, G., Uzu, G., Sobanska, S., Sarret, G., Dumat, C., et al. (2016). Phytoavailability of lead altered by two Pelargonium cultivars grown on contrasting lead-spiked soils. Journal Of Soils And Sediments, 16(2), 581–591.
Résumé: This study assesses the potential of two contrasted fragrant Pelargonium cultivars to induce pH and dissolved organic carbon (DOC) changes in the soil solution, Pb speciation, and their subsequent effects on rhizosphere phytoavailable Pb. Rooted plantlets were grown in special devices, floating on aerated nutrient solution in PVC tanks. This setup allows roots to be physically separated, through a mesh, from a 3-mm soil matrix layer that can be considered as rhizosphere soil. Two contrasted soils, each spiked with Pb-rich particles, emitted from a battery recycling industry, were used at total burdens of 500 and 1500 mg Pb kg(-1) in addition to a control unspiked soil. Soil solution pH, phytoavailable Pb, DOC, Pb adsorption, precipitation on roots, and Pb phases in soil and plant were investigated. Attar of Roses (Attar) cultivar acidified its rhizosphere by 0.4 pH units in both spiked soils. Concolor Lace (Concolor) was unable to change soil solution pH on soil-1 and increased it by 0.7 units on soil 2. Concentrations of Pb in soil solution from Attar plants were always higher than those of Concolor ones. DOC contents of both unspiked soil-1 and soil-2 without plants were not significantly different. In the case of spiked samples, DOC contents in the rhizosphere soil were increased by three and two times for Attar and Concolor, respectively, compared to the unspiked soil without plant. Both cultivars were able to increase DOC contents, independent of soil type and level of contamination. Accumulation of Pb in shoots and roots was higher in Attar as compared to Concolor due to enhanced available Pb as a result of pH and DOC modifications of the rhizosphere soil. Significant amounts of Pb were adsorbed on roots of both cultivars. X-ray elemental analysis of precipitates on roots revealed the association of Pb with P in cylinder-like structures. Extended X-ray absorption fine structure (EXAFS) spectroscopy revealed that Pb was present, to a major extent in the inorganic form, mainly as PbSO4 in the soil, whereas it was complexed with organic species within plant tissues. The conversion of Pb into organic species could decrease toxicity, may enhance plant tolerance, and could increase translocation. Plant-induced changes were responsible for the modification of lead phases within the soil. Immobile forms present in the source leaded particles as well as in the soils were converted into soluble species, ultimately improving the phytoavailable or soil solubilized Pb.
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Ayora, C., Macias, F., Torres, E., Lozano, A., Carrero, S., Nieto, J. M., et al. (2016). Recovery of Rare Earth Elements and Yttrium from Passive-Remediation Systems of Acid Mine Drainage. Environmental Science & Technology, 50(15), 8255–8262.
Résumé: Rare earth elements and yttrium (REY) are raw materials of increasing importance for modern technologies, and finding new sources has become a pressing need. Acid mine drainage (AMD) is commonly considered an environmental pollution issue. However, REY concentrations in AMD can be several orders of magnitude higher than in naturally occurring water bodies. With respect to shale standards, the REY distribution pattern in AMD is enriched in intermediate and valuable REY, such as Tb and Dy. The objective of the present work is to study the behavior of REY in AMD passive-remediation systems. Traditional AMD passive remediation systems are based on the reaction of AMD with calcite-based permeable substrates followed by decantation ponds. Experiments with two columns simulating AMD treatment demonstrate that schwertmannite does not accumulate REY, which, instead, are retained in the basaluminite residue. The same observation is made in two field-scale treatments from the Iberian Pyrite Belt (IPB, southwest Spain). On the basis of the amplitude of this process and on the extent of the IPB, our findings suggest that the proposed AMD remediation process can represent a modest but suitable REY source. In this sense, the IPB could function as a giant heap-leaching process of regional scale in which rain and oxygen act as natural driving forces with no energy investment. In addition to having environmental benefits of its treatment, AMD is expected to last for hundreds of years, and therefore, the total reserves are practically unlimited.
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Bajard, M., Sabatier, P., David, F., Develle, A. L., Reyss, J. L., Fanget, B., et al. (2016). Erosion record in Lake La Thuile sediments (Prealps, France): Evidence of montane landscape dynamics throughout the Holocene. Holocene, 26(3), 350–364.
Résumé: Lake La Thuile, in the Northern French Prealps (874 m a.s.l.), provides an 18-m long sedimentary sequence spanning the entire Lateglacial/Holocene period. The high-resolution multi-proxy (sedimentological, palynological, and geochemical) analysis of the uppermost 6.2 m reveals the Holocene dynamics of erosion in the catchment in response to landscape modifications. The mountain belt is at relevant altitude to study past human activities, and the watershed is sufficiently disconnected from large valleys to capture a local sedimentary signal. From 12,000 to 10,000 cal. BP (10-8 kyr cal. BC), the onset of hardwood species triggered a drop in erosion following the Lateglacial/Holocene transition. From 10,000 to 4500 cal. BP (8-2.5 kyr cal. BC), the forest became denser and favored slope stabilization, while erosion processes were very weak. A first erosive phase was initiated at ca. 4500 cal. BP without evidence of human presence in the catchment. Then, the forest declined at approximately 3000 cal. BP, suggesting the first human influence on the landscape. Two other erosive phases are related to anthropic activities: approximately 2500 cal. BP (550 cal. BC) during the Roman period and after 1600 cal. BP (350 cal. AD) with a substantial accentuation in the Middle Ages. In contrast, the lower erosion produced during the 'Little Ice Age', when climate deteriorations are generally considered to result in an increased erosion signal in this region, suggests that anthropic activities dominated the erosive processes and completely masked the natural effects of climate on erosion in the late Holocene.
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Barnes, S. J., Cruden, A. R., Arndt, N., & Saumur, B. M. (2016). The mineral system approach applied to magmatic Ni-Cu-PGE sulphide deposits. Ore Geology Reviews, 76, 296–316.
Résumé: Most magmatic Ni-Cu-PGE sulphide deposits occur within long-lived magma pathways fed by high degree partial melts of the mantle. Holistic mineral-system analysis for such deposits has some, parallels with dominantly hydrothermal systems, but also some important differences. Major provinces are associated with large volumes of magma erupted at margins of ancient Archaean cratons, and are associated with small intrusions through which large volumes of magmas have passed. There is no demonstrable association with any particular magma type, although in most provinces the ores are found associated with the most primitive available magmas, whatever these may be. Ore-bearing intrusions tend to form early in the evolution of the host province, although exceptions exist to this rule, and these intrusions typically account for very small proportions of the volumes of the province as a whole. Ore deposition is favoured by prolonged high-volume flow over a horizontal floor. This floor may take the form of the base of a channelized sill, tube or blade-shaped dyke, which account for most of the known host igneous bodies to significant ore deposits. Deposition mechanisms may be chemical or physical, but large high-grade deposits require a major component of transported sulphide liquid, initially carried as droplets. Late stage migration of sulphide liquid as gravity currents within intrusion networks, coupled with infiltration and melting of floor rocks, accounts for the common observation in mafic intrusion hosted deposits of cross cutting relationships between massive sulphides, host intrusions and country rocks. The following set of criteria is proposed in targeting and evaluating Ni-Cu-PGE sulphide systems: 1) nature of magmatism and relationship to pre-existing cratonic architecture; 2) magmatic and structural controls on the development of protracted-flow magma conduits; 3) access to crustal S sources at some point along the pathway; 4) favourable intrusion geometry and emplacement style for deposition, reworking and upgrading of sulphide magmas, and 5) favourable structural history and erosional level for preservation and detectability. These components can be translated into mappable geological criteria. At the predictive targeting scale, the key features are proximity to ancient cratonic boundaries and long-lived, trans-crustal structures, and relationship to voluminous mafic or ultramafic magmatism typically with high Mg and low Ti contents, but otherwise lacking distinctive characteristics. At the detection scale, there are two distinct approaches: recognition of high volume magma pathways with prolonged flow-through operating at length scales of km based on morphological, petrological, geophysical and structural observations; and identification of the petrographic and geochemical signals of accumulation or extraction of sulphide liquid. (C) 2015 Elsevier B.V. All rights reserved.
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Barnoud, A., Coutant, O., Bouligand, C., Gunawan, H., & Deroussi, S. (2016). 3-D linear inversion of gravity data: method and application to Basse-Terre volcanic island, Guadeloupe, Lesser Antilles. Geophysical Journal International, 205(1), 562–574.
Résumé: We use a Bayesian formalism combined with a grid node discretization for the linear inversion of gravimetric data in terms of 3-D density distribution. The forward modelling and the inversion method are derived from seismological inversion techniques in order to facilitate joint inversion or interpretation of density and seismic velocity models. The Bayesian formulation introduces covariance matrices on model parameters to regularize the ill-posed problem and reduce the non-uniqueness of the solution. This formalism favours smooth solutions and allows us to specify a spatial correlation length and to perform inversions at multiple scales. We also extract resolution parameters from the resolution matrix to discuss how well our density models are resolved. This method is applied to the inversion of data from the volcanic island of Basse-Terre in Guadeloupe, Lesser Antilles. A series of synthetic tests are performed to investigate advantages and limitations of the methodology in this context. This study results in the first 3-D density models of the island of Basse-Terre for which we identify: (i) a southward decrease of densities parallel to the migration of volcanic activity within the island, (ii) three dense anomalies beneath Petite Plaine Valley, Beaugendre Valley and the Grande-D,couverte-CarmichaA << l-SoufriSre Complex that may reflect the trace of former major volcanic feeding systems, (iii) shallow low-density anomalies in the southern part of Basse-Terre, especially around La SoufriSre active volcano, Piton de Bouillante edifice and along the western coast, reflecting the presence of hydrothermal systems and fractured and altered rocks.
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Basile, C., & Braun, J. (2016). The initiation of pull-apart basins and transform continental margins: results from numerical experiments of kinematic partitioning in divergent settings. Terra Nova, 28(2), 120–127.
Résumé: We present a set of numerical models to investigate how transform faults initiate in pull-apart basins or transform continental margins. The model represents an elastic plate with three aligned weak spots. Applying strain on the edge of the model firstly propagates extensional cracks from the pre-existing damaged spots. The subsequent evolution depends on the angle (obliquity) between the applied strain and the alignment of the damaged spots. For obliquity <50 degrees, transform faults form to connect en-echelon divergent cracks; for obliquity >60 degrees, transtensional transfer zones connect the divergent cracks and no transform fault forms. These experiments suggest that pull-apart basins do not form as previously assumed by connection of overlapping transform faults, but that transform faults form as connections of extensional areas.
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Bato, M. G., Froger, J. L., Harris, A. J. L., & Villeneuve, N. (2016). Monitoring an effusive eruption at Piton de la Fournaise using radar and thermal infrared remote sensing data: insights into the October 2010 eruption and its lava flows. Geological Society, London, Special Publications, 426(1), 533–552.
Résumé: Accurate and fast delivery of information about recent lava flows is important for near-real-time monitoring of eruptions. Here, we have characterized the October 2010 lava flow at Piton de la Fournaise using various InSAR datasets. We first produced a map of the area covered by the lava flow (i.e. Arealava=0.71–0.75 km2) using the coherence of two syn-eruptive interferograms. Then we analysed two post-eruptive InSAR datasets (i.e. monostatic and bistatic data). The monostatic database provided us simultaneously with the displacement rates, lava thickness, volume and volume flux. We found that the lava flow was subsiding and moving eastward at maximum rates of 13±0.3 and 4±0.2 cm a−1, respectively. Also, it had a mean thickness of Zmean=5.85 m, VolDRE=1.77±0.75×106 m3 (1σ) and MOR=1.25±0.53 m3 s−1. The bistatic database provided us only with the thickness and volume information (i.e. Zmean=6.00 m, VolDRE=1.83±0.65×106 m3 and MOR=1.29±0.46 m3 s−1). Finally, we used a thermal remote sensing technique to verify the InSAR-derived measurements. Results show that the monostatic and bistatic datasets were both well within the range for the DRE volume obtained from MODIS data (2.44–4.40×106 m3).
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Battaglia, J., Metaxian, J. P., & Garaebiti, E. (2016). Families of similar events and modes of oscillation of the conduit at Yasur volcano (Vanuatu). Journal Of Volcanology And Geothermal Research, 322, 196–211.
Résumé: We examined one year of seismic recordings collected in 2008 during a temporary experiment at Yasur volcano (Vanuatu). The volcano has a permanent Strombolian activity that was at a relatively high level during most of our experiment with commonly at least one explosion per minute. Associated with this activity, the network recorded intense seismicicity with hundreds of transients per day. Video recordings indicate that most of the high frequency transients are directly related to the strombolian explosions. They also outline the presence of fewer signals which are not accompanied by any surface activity. The classification of transient events recorded at a station close to the summit indicates that a significant part of the events exhibit waveform similarity. This technique allows the identification of characteristic repeating events among the hundreds of thousands of transients recorded during the experiment. Most of the families of similar events are groups of explosion quakes (EQs) but a few are groups of Long Period events related to deeper processes. By scanning the 9 months of continuous data available at the summit station with master events extracted from these families we reconstruct their temporal evolution. Our results show that several families dominate the activity with a few of them lasting for several months. We show that their temporal evolutions can be used to probe changes in the structure or activity of the volcano. We observe that a major change was induced by a M = 7.3 subduction earthquake which occurred on April 9, 2008 about 80 km from the volcano. While this,event did not change significantly the surface morphology of the volcano nor the intensity of the eruptive activity, it interrupted the families as none of them is present both before and after the event. This change in the waveforms can be explained by a drop in the seismic velocity of the volcano caused by the distal event. Numerous other transitions between families are observed, sudden or progressive. These can be interpreted as representative of changes in the eruptive dynamics. The presence of similar EQs, especially for impulsive explosions, indicates that the source mechanism is reproducible and has a stable location for some periods. This favors a source process based on the oscillation of the conduit or oscillation of the edifice in response to the explosive decompression of gas slugs at the free surface of the conduit. Our results suggest that the seismic activity of Yasur is characterized by the presence of dominant modes of resonance of the conduit which may be influenced both by external and internal factors. (C) 2015 Elsevier B.V. All rights reserved.
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Battaglia, J., Metaxian, J. P., & Garaebiti, E. (2016). Short term precursors of Strombolian explosions at Yasur volcano (Vanuatu). Geophysical Research Letters, 43(5), 1960–1965.
Résumé: The seismic wavefield associated with Strombolian activity is usually dominated by explosion quakes (EQs), tremor, and various signals generated by surface phenomena. Looking at the seismicity recorded at Yasur volcano in 2008, we found that beside the transient events which occur simultaneously with surface explosions, the seismicity includes events related to a deeper process. These long period (LP) events form a family of similar events located below the southeastern part of the crater rim at a depth of about 700-1200m below the summit. They are commonly followed by EQs with a variable delay. The examination of about 20,000 LP-EQ sequences at several stations near the summit shows that interevent delays follow distributions peaked around 11-12s. This short delay compared to the relatively great source depth of the LPs favors a causal relationship linked to pressure transfer rather than gas slug propagation after nucleation at the LP source.
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Beckers, A., Beck, C., Hubert-Ferrari, A., Tripsanas, E., Crouzet, C., Sakellariou, D., et al. (2016). Influence of bottom currents on the sedimentary processes at the western tip of the Gulf of Corinth, Greece. Marine Geology, 378, 312–332.
Résumé: We investigated the sedimentary processes that were active during the Holocene in the Gulf of Corinth, using high-resolution seismic reflection profiles and gravity cores. Seismic reflection data clearly show the presence of shallow -water sediment drifts at the western end of the Gulf, close to the Rion sill that links the Gulf to the Ionian Sea. Short cores indicate that drifts are composed of homogenous bioturbated mud in their upper part. The drift deposits flank a wide central area where the seafloor is eroded and where pre-Holocene deposits locally outcrop. The seafloor morphology in this area is marked by furrows oriented in different directions and by a depression attributed to the action of bottom-currents. The magnetic fabric of sediment samples from the drift, shelves, sub-basins and from the basin floor shows a significant anisotropy and a similar orientation of K-max axes along core. The largest anisotropy (P = 1.043 +/- 0.007) is observed in the drift and is interpreted as resulting from the action of bottom currents. The similar orientation of K-max axes in the other cores, collected from areas east of the drifts, suggests that bottom currents also affect sediment deposition in the rest of the study area, even if seismic profiles and core analyses demonstrate that gravitational processes such as submarine landslides and turbidity currents exert the main control on sediment transport and deposition. Average K-max axes for four cores were reoriented using the declination of the characteristic remanent magnetization. K-max axes show variable orientations relatively to the slope of the seafloor, between along-slope and roughly parallel to the contour lines. (C) 2016 Elsevier B.V. All rights reserved.
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Belissont, R., Munoz, M., Boiron, M. C., Luais, B., & Mathon, O. (2016). Distribution and oxidation state of Ge, Cu and Fe in sphalerite by mu-XRF and K-edge mu-XANES: insights into Ge incorporation, partitioning and isotopic fractionation. Geochimica Et Cosmochimica Acta, 177, 298–314.
Résumé: Synchrotron-based microscale X-ray absorption near edge structure spectroscopy (mu-XANES) has been combined with X-ray fluorescence (mu-XRF) mapping to investigate Ge, Cu and Fe oxidation states in compositionally zoned Ge-rich sphalerite from the Saint-Salvy deposit (France). The present study aims at improving our understanding of substitution mechanisms and trace element uptake relative to Ge isotope fractionation in sphalerite. K-Edge XANES records of various Ge-, Cu- and Fe-bearing sulphides are presented for comparison with sphalerite, and ab initio calculations at the Ge K-edge complete our experimental data. The Ge K-edge spectra of the Ge-bearing sphalerite are identical to those of germanite, renierite and briartite, indicating the presence of tetrahedrally-coordinated Ge4+. In addition, Cu and Fe K-edge spectra suggest the presence of Cu+ and Fe2+, respectively, in the tetrahedral site. No significant differences in the oxidation states of Ge, Cu and Fe were observed within or between the zoning types or between the samples. The intake of Ge4+ in sphalerite may therefore occur in the tetrahedral divalent metal site via coupled substitutions charge-balanced by monovalent elements such as 3Zn(2+) <-> Ge4+ + 2Cu(+), resulting in a strong Ge-Cu elemental correlation, or, when Ge does not correlate with monovalent elements, through the creation of lattice vacancies such as 2Zn(2+) <-> Ge4+ broken vertical bar square (vacancy). The tetravalent state of Ge is compatible with temperature-related Ge isotopic fractionation and can explain the large range of delta Ge-74 measured in the Saint-Salvy sphalerite. Moreover, the exceptional enrichment in Ge and the large variations in the 'bulk' Ge contents in these sphalerites do not appear to be related to charge effects but would instead result from the effect of temperature-related partitioning. (C) 2016 Elsevier Ltd. All rights reserved.
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Bergsaker, A. S., Royne, A., Ougier-Simonin, A., Aubry, J., & Renard, F. (2016). The effect of fluid composition, salinity, and acidity on subcritical crack growth in calcite crystals. Journal Of Geophysical Research-Solid Earth, 121(3), 1631–1651.
Résumé: Chemically activated processes of subcritical cracking in calcite control the time-dependent strength of this mineral, which is a major constituent of the Earth's brittle upper crust. Hereexperimental data on subcritical crack growth are acquired with a double torsion apparatus to characterize the influence of fluid pH (range 5-7.5) and ionic strength and species (Na2SO4, NaCl, MgSO4, and MgCl2) on the propagation of microcracks in calcite single crystals. The effect of different ions on crack healing has also been investigated by decreasing the load on the crack for durations up to 30min and allowing it to relax and close. All solutions were saturated with CaCO3. The crack velocities reached during the experiments are in the range 10(-9)-10(-2)m/s and cover the range of subcritical to close to dynamic rupture propagation velocities. Results show that for calcite saturated solutions, the energy necessary to fracture calcite is independent of pH. As a consequence, the effects of fluid salinity, measured through its ionic strength, or the variation of water activity have stronger effects on subcritical crack propagation in calcite than pH. Consequently, when considering the geological sequestration of CO2 into carbonate reservoirs, the decrease of pH within the range of 5-7.5 due to CO2 dissolution into water should not significantly alter the rate of fracturing of calcite. Increase in salinity caused by drying may lead to further reduction in cracking and consequently a decrease in brittle creep. The healing of cracks is found to vary with the specific ions present.
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Bernet, M., & Bassett, K. (2016). Quartz types of the Eocene Broken River Formation, Mount Somers, South Island, New Zealand. New Zealand Journal Of Geology And Geophysics, 59(2), 274–285.
Résumé: Quartz arenites are a very common geological feature on the South Island of New Zealand. The provenance of the quartz grains that form these arenites is not well constrained because standard point-counting techniques do not provide enough detailed information. In this study we distinguish different quartz types using scanning electron microscopy-cathodoluminescence combined with standard optical microscopy on the same individual quartz grains. This is done on a suite of samples collected from shallow marine quartz arenites of the Paleocene-Eocene Blondin Sand Member of the Broken River Formation (Eyre Group) at Mt Somers in the Canterbury basin on the South Island of New Zealand. Our results show that the volcanic quartz grains were derived from local volcanic source rocks, whereas metamorphic quartz grains may have been derived from either local source rocks of the Torlesse Supergroup or from distant metamorphic sources rocks via longshore transport. Plutonic quartz grains were exclusively derived by long-distance transport. Warm and humid climatic conditions and the presence of humic acids in the associated coal-forming depositional environment probably increased the proportion of quartz in the sampled rocks.
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Bernet, M., Uruena, C., Amaya, S., & Pena, M. L. (2016). New thermo and geochronological constraints on the Pliocene-Pleistocene eruption history of the Paipa-Iza volcanic complex, Eastern Cordillera, Colombia. Journal Of Volcanology And Geothermal Research, 327, 299–309.
Résumé: The Paipa-Iza volcanic complex is the only volcanic edifice in the Eastern Cordillera of Colombia. Zircon fission track and U-Pb data from deposits of two eruption epochs presented in this study constrain the time of volcanic activity between 5.9 Ma in the late Miocene and at least 1.8 Ma during the early Pleistocene. These ages correspond to 3.6 to 4.7 Ma zircon fission-track ages reported from tephra deposits of the Tierra Negra region to the southwest of the Paipa-Iza volcanic complex in the Eastern Cordillera. A 4 Myr period of volcanic activity is longer than the previously documented 2.5 Ma to 1.9 Ma activity in the Paipa-Iza area. Therefore, our data show that the Paipa-Iza volcanic complex was active during the entire Pliocene phase of rapid surface uplift, when the Eastern Cordillera reached its present-day elevation. Unclear is if the magma chamber of the Paipa-Iza volcanic complex was passively uplifted with the rest of the Eastern Cordillera, or if magmatism contributed to surface uplift. Hydrothermal activity and steep thermal gradients in the study area today indicate that a magma chamber is still present at depth. In both the zircon fission-track and U-Pb data of this study the recycling of zircon from underlying Mesozoic sedimentary rocks is evident in the wide age spectra. The fission-track data show that many recycled zircons were affected at least by partial annealing, but further research is needed for constraining the thermal impact of the Paipa-Iza volcanism on the Eastern Cordillera. (C) 2016 Elsevier B.V. All rights reserved.
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Besselink, R., Stawski, T. M., Van Driessche, A. E. S., & Benning, L. G. (2016). Not just fractal surfaces, but surface fractal aggregates: Derivation of the expression for the structure factor and its applications. Journal Of Chemical Physics, 145(21).
Résumé: Densely packed surface fractal aggregates form in systems with high local volume fractions of particles with very short diffusion lengths, which effectively means that particles have little space to move. However, there are no prior mathematical models, which would describe scattering from such surface fractal aggregates and which would allow the subdivision between inter-and intraparticle interferences of such aggregates. Here, we show that by including a form factor function of the primary particles building the aggregate, a finite size of the surface fractal interfacial sub-surfaces can be derived from a structure factor term. This formalism allows us to define both a finite specific surface area for fractal aggregates and the fraction of particle interfacial sub-surfaces at the perimeter of an aggregate. The derived surface fractal model is validated by comparing it with an ab initio approach that involves the generation of a “brick-in-a-wall” von Koch type contour fractals. Moreover, we show that this approach explains observed scattering intensities from in situ experiments that followed gypsum (CaSO4 center dot 2H(2)O) precipitation from highly supersaturated solutions. Our model of densely packed “brick-in-a-wall” surface fractal aggregates may well be the key precursor step in the formation of several types of mosaic-and meso-crystals. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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Bestani, L., Espurt, N., Lamarche, J., Bellier, O., & Hollender, F. (2016). Reconstruction of the Provence Chain evolution, southeastern France. Tectonics, 35(6), 1506–1525.
Résumé: The Provence fold-and-thrust belt forms the eastern limit of the Pyrenean orogenic system in southeastern France. This belt developed during the Late Cretaceous-Eocene Pyrenean-Provence compression and was then deformed by Oligocene-Miocene Ligurian rifting events and Neogene to present-day Alpine compression. In this study, surface structural data, seismic profiles, and crustal-to-lithospheric-scale sequentially balanced cross sections contribute to the understanding of the dynamics of the Provence Chain and its long-term history of deformation. Balanced cross sections show that the thrust system is characterized by various structural styles, including deep-seated basement faults that affect the entire crust, tectonic inversions of Paleozoic-Mesozoic basins, shallower decollements within the sedimentary cover, accommodation zones, and salt tectonics. This study shows the prime control of the structural inheritance over a long period of time on the tectonic evolution of a geological system. This includes mechanical heterogeneities, such as Variscan shear zones, reactivated during Middle Cretaceous Pyrenean rifting between Eurasia and Sardinia. In domains where Mesozoic rifting is well marked, inherited basement normal faults and the thermally weak crust favored the formation of an inner thick-skinned thrust belt during Late Cretaceous-Eocene contraction. Here 155 km (similar to 35%) of shortening was accommodated by inversion of north verging crustal faults, north directed subduction of the Sardinia mantle lithosphere, and ductile thickening of the Provence mantle lithosphere. During the Oligocene, these domains were still predisposed for the localized faulting of the Ligurian basin rifting and the seafloor spreading.
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Bethoux, N., Theunissen, T., Beslier, M. O., Font, Y., Thouvenot, F., Dessa, J. X., et al. (2016). Earthquake relocation using a 3D a-priori geological velocity model from the western Alps to Corsica: Implication for seismic hazard. Tectonophysics, 670, 82–100.
Résumé: The region between the inner zones of the Alps and Corsica juxtaposes an overthickened crust to an oceanic domain, which makes difficult to ascertain the focal depth of seismic events using routine location codes and average 1D velocity models. The aim of this article is to show that, even with a rather lose monitoring network, accurate routine locations can be achieved by using realistic 3D modelling and advanced location techniques. Previous earthquake tomography studies cover the whole region with spatial resolutions of several tens of kilometres on land, but they fail to resolve the marine domain due to the absence of station coverage and sparse seismicity. To overcome these limitations, we first construct a 3D a-priori P and S velocity model integrating known geophysical and geological information. Significant progress has been achieved in the 3D numerical modelling of complex geological structures by the development of dedicated softwares (e.g. 3D GeoModeller), capable at once of elaborating a 3D structural model from geological and geophysical constraints and, possibly, of refining it by inversion processes (Calcagno et al., 2008). Then, we build an arrival-time catalogue of 1500 events recorded from 2000 to 2011. Hypocentres are then located in this model using a numerical code based on the maximum intersection method (Font et al., 2004), updated by Theunissen et al. (2012), as well as another 3D location technique, the NonLinLoc software (Lomax and Curtis, 2001). The reduction of arrival-time residuals and uncertainties (dh, dz) with respect to classical 1D locations demonstrates the improved accuracy allowed by our approach and confirms the coherence of the 3D geological model built and used in this study. Our results are also compared with previous works that benefitted from the installation of dense temporary networks surrounding the studied epicentre area. The resulting 3D location catalogue allows us to improve the regional seismic hazard assessment, more particularly in the south of the Argentera massif and in the Ligurian basin. (C) 2016 Elsevier B.V. All lights reserved.
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Bievre, G., Jongmans, D., Goutaland, D., Pathier, E., & Zumbo, V. (2016). Geophysical characterization of the lithological control on the kinematic pattern in a large clayey landslide (Avignonet, French Alps). Landslides, 13(3), 423–436.
Résumé: Lithology variation is known to have a major control on landslide kinematics, but this effect may remain unnoticed due to low spatial coverage during investigation. The large clayey Avignonet landslide (French Alps) has been widely studied for more than 35 years. Displacement measurements at 38 geodetic stations over the landslide showed that the slide surface velocity dramatically increases below an elevation of about 700 m and that the more active zones are located at the bottom and the south of the landslide. Most of the geotechnical investigation was carried out in the southern part of the landslide where housing development occurred on lacustrine clay layers. In this study, new electrical prospecting all across the unstable area revealed the unexpected presence of a thick resistive layer covering the more elevated area and overlying the laminated clays, which is interpreted as the lower part of moraine deposits. The downslope lithological boundary of this layer was found at around 700 m asl. This boundary coincides with the observed changes in slide velocity and in surface roughness values computed from a LiDAR DTM acquired in 2006. This thick permeable upper layer constitutes a water reservoir, which is likely to influence the hydromechanical mechanism of the landslide. The study suggests a major control of vertical lithological variations on the landslide kinematics, which is highlighted by the relation between slide velocity and electrical resistivity.
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Blanc, E., Komatitsch, D., Chaljub, E., Lombard, B., & Xie, Z. N. (2016). Highly accurate stability-preserving optimization of the Zener viscoelastic model, with application to wave propagation in the presence of strong attenuation. Geophysical Journal International, 205(1), 427–439.
Résumé: This paper concerns the numerical modelling of time-domain mechanical waves in viscoelastic media based on a generalized Zener model. To do so, classically in the literature relaxation mechanisms are introduced, resulting in a set of the so-called memory variables and thus in large computational arrays that need to be stored. A challenge is thus to accurately mimic a given attenuation law using a minimal set of relaxation mechanisms. For this purpose, we replace the classical linear approach of Emmerich & Korn with a nonlinear optimization approach with constraints of positivity. We show that this technique is more accurate than the linear approach. Moreover, it ensures that physically meaningful relaxation times that always honour the constraint of decay of total energy with time are obtained. As a result, these relaxation times can always be used in a stable way in a modelling algorithm, even in the case of very strong attenuation for which the classical linear approach may provide some negative and thus unusable coefficients.
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Bouchon, M., Marsan, D., Durand, V., Campillo, M., Perfettini, H., Madariaga, R., et al. (2016). Potential slab deformation and plunge prior to the Tohoku, Iquique and Maule earthquakes. Nature Geoscience, 9(5), 380–+.
Résumé: Megathrust earthquakes rupture hundreds of kilometres of the shallow plate interface in subduction zones, typically at depths of less than 50 km. Intense foreshock activity preceded the 2011 M-w 9 Tohoku-oki (Japan) and 2014 M-w 8.2 Iquique (Chile) megathrust earthquakes. This pre-earthquake activity was thought to be generated(1-6) by slow slip in the seismogenic zone before rupture, but where this slow slip originated and how it spread rapidly over long distances are unknown. Here we analyse seismic activity deep in the subduction zone before the Tohoku-oki and Iquique ruptures, as well as before the 2010 M-w 8.8 Maule earthquake in Chile. We find that, before each of these megathrust earthquakes, shallow seismicity occurred synchronously with bursts of seismic activity deep (similar to 100 km) in the subducting slab. The extensional mechanism of these deep shocks suggests that the slab was stretched at depth. We therefore propose that, before these megathrust quakes, the slab might have started to plunge into the mantle below part of the future rupture zone. We speculate that synchronization between deep and shallow seismicity may have marked the nucleation phase for these three giant earthquakes.
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Boue, A., Lesage, P., Cortes, G., Valette, B., Reyes-Davila, G., Arambula-Mendoza, R., et al. (2016). Performance of the 'material Failure Forecast Method' in real-time situations: A Bayesian approach applied on effusive and explosive eruptions. Journal Of Volcanology And Geothermal Research, 327, 622–633.
Résumé: Most attempts of deterministic eruption forecasting are based on the material Failure Forecast Method (FFM). This method assumes that a precursory observable, such as the rate of seismic activity, can be described by a simple power law which presents a singularity at a time close to the eruption onset. Until now, this method has been applied only in a small number of cases, generally for forecasts in hindsight. In this paper, a rigorous Bayesian approach of the FFM designed for real-time applications is applied. Using an automatic recognition system, seismo-volcanic events are detected and classified according to their physical mechanism and time series of probability distributions of the rates of events are calculated. At each time of observation, a Bayesian inversion provides estimations of the exponent of the power law and of the time of eruption, together with their probability density functions. Two criteria are defined in order to evaluate the quality and reliability of the forecasts. Our automated procedure has allowed the analysis of long, continuous seismic time series: 13 years from Volcan de Colima, Mexico, 10 years from Piton de la Fournaise, Reunion Island, France, and several months from Merapi volcano, Java, Indonesia. The new forecasting approach has been applied to 64 pre-eruptive sequences which present various types of dominant seismic activity (volcano-tectonic or long-period events) and patterns of seis-micity with different level of complexity. This has allowed us to test the FFM assumptions, to determine in which conditions the method can be applied, and to quantify the success rate of the forecasts. 62% of the precursory sequences analysed are suitable for the application of FFM and half of the total number of eruptions are successfully forecast in hindsight. In real-time, the method allows for the successful forecast of 36% of all the eruptions considered. Nevertheless, real-time forecasts are successful for 83% of the cases that fulfil the reliability criteria. Therefore, good confidence on the method is obtained when the reliability criteria are met. (C) 2016 Elsevier B.V. All rights reserved.
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Boue, P., Denolle, M., Hirata, N., Nakagawa, S., & Beroza, G. C. (2016). Beyond basin resonance: characterizing wave propagation using a dense array and the ambient seismic field. Geophysical Journal International, 206(2), 1261–1272.
Résumé: Seismic wave resonance in sedimentary basins is a well-recognized seismic hazard; however, concentrated areas of earthquake damage have been observed near basin edges, where wave propagation is particularly complex and difficult to understand with sparse observations. The Tokyo metropolitan area is densely populated, subject to strong shaking from a diversity of earthquake sources, and sits atop the deep Kanto sedimentary basin. It is also instrumented with two seismic arrays: the dense MEtropolitan Seismic Observation network (MeSO-net) within the basin, and the High sensitivity seismograph network (Hi-net) surrounding it. In this study, we explore the 3-D seismic wavefield within and throughout the Kanto basin, including near and across basin boundaries, using cross-correlations of all components of ambient seismic field between the stations of these two arrays. Dense observations allow us to observe clearly the propagation of three modes of both Rayleigh and Love waves. They also show how the wavefield behaves in the vicinity of sharp basin edges with reflected/converted waves and excitation of higher modes.
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Bouligand, C., Coutant, O., & Glen, J. M. G. (2016). Sub-surface structure of La Soufriere of Guadeloupe lava dome deduced from a ground-based magnetic survey. Journal Of Volcanology And Geothermal Research, 321, 171–181.
Résumé: In this study, we present the analysis and interpretation of a new ground magnetic survey acquired at the Soufriere volcano on Guadeloupe Island. Observed short-wavelength magnetic anomalies are compared to those predicted assuming a constant magnetization within the sub-surface. The good correlation between modeled and observed data over the summit of the dome indicates that the shallow sub-surface displays relatively constant and high magnetization intensity. In contrast, the poor correlation at the base of the dome suggests that the underlying material is non- to weakly-magnetic, consistent with what is expected for a talus comprised of randomly oriented and highly altered and weathered boulders. The new survey also reveals a dipole anomaly that is not accounted for by a constant magnetization in the sub-surface and suggests the existence of material with decreased magnetization beneath the Soufriere lava dome. We construct simple models to constrain its dimensions and propose that this body corresponds to hydrothermally altered material within and below the dome. The very large inferred volume for such material may have implications on the stability of the dome. (C) 2016 Elsevier B.V. All rights reserved.
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Bouligand, C., Gillet, N., Jault, D., Schaeffer, N., Fournier, A., & Aubert, J. (2016). Frequency spectrum of the geomagnetic field harmonic coefficients from dynamo simulations. Geophysical Journal International, 207(2), 1142–1157.
Résumé: The construction of geomagnetic, archaeomagnetic or palaeomagnetic field models requires some prior knowledge about the actual field, which can be gathered from the statistical properties of the field over a variety of length-scales and timescales. However, available geomagnetic data on centennial to millennial periods are too sparse to infer directly these statistical properties. We thus use high-resolution numerical simulations of the geodynamo to test a method for estimating the temporal power spectra (or equivalently the autocovariance functions) of the individual Gauss coefficients that describe the geomagnetic field outside the Earth's fluid outer core. Based on the spectral analysis of our simulations, we argue that a prior for the observational geomagnetic field over decennial to millennial periods can be constructed from the statistics of the field during the short satellite era. The method rests on the assumption that time-series of spherical harmonic coefficients can be considered as realizations of stationary and differentiable stochastic processes, namely order 2 autoregressive (AR2) processes. In the framework of these processes, the statistics of Gauss coefficients are well constrained by their variance and one or two timescales. We find that the time spectra in the dynamo simulations of all Gauss coefficients but the axial dipole are well approximated by the spectra of AR2 processes characterized by only one timescale. The process parameters can simply be deduced from instantaneous estimates of the spatial power spectra of the magnetic field and of its first time derivative. Some deviations of the Gauss coefficients statistics from this minimal model are also discussed. Characterizing the axial dipole clearly requires a more sophisticated AR2 process, with a second distinct timescale.
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Bovy, B., Braun, J., & Demoulin, A. (2016). Soil production and hillslope transport in mid-latitudes during the last glacial-interglacial cycle: a combined data and modelling approach in northern Ardennes. Earth Surface Processes And Landforms, 41(12), 1758–1775.
Résumé: The relative efficiency of various hillslope processes through Quaternary glacial-interglacial cycles in the mid-latitudes is not yet well constrained. Based on a unique set of topographic and soil thickness data in the Ardennes (Belgium), we combine the new CLICHE model of climate-dependent hillslope evolution with an inversion algorithm in order to get deeper insight into the ways and timing of hillslope dynamics under one such climatic cycle. We simulate the evolution of a synthetic hill reproducing the slope, curvature, and contributing area distributions of the hillslopes of a similar to 2500km(2) real area under a simple two-stage 120-kyr-long climatic scenario with linear transitions between cold and warm stages. The inversion method samples a misfit function in the model parameter space, based on estimates of the fit of topographic derivative distributions in classes of soil thickness and of the relative frequencies of the predicted soil thickness classes. Though the inversion results show remarkable convergence patterns for most parameters, no unique solution emerges. We obtain five clusters of good fits, whose centroids are taken as acceptable model solutions. Based on the predicted time series of average denudation rate and soil thickness, plus snapshots of the soil distribution at characteristic times, we discuss these solutions and, comparing them with independent data not involved in the misfit function, we identify the most realistic scenario. Beyond providing first-order estimates of several parameters that compare well with published data, our results show that denudation rates increase dramatically for a short time at both warm-cold and cold-warm transitions, when the mean annual temperature passes through the [0, -5 degrees C] range. We also point to the overwhelming importance of solifluction in shaping hillslopes and transporting soil, and the role of depth-dependent creep (including frost creep) throughout the climatic cycle, whereas the contributions of simple creep and overland flow are minor. Copyright (c) 2016 John Wiley & Sons, Ltd.
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Braun, J. (2016). Strong imprint of past orogenic events on the thermochronological record. Tectonophysics, 683, 325–332.
Résumé: Using a simple solution to the heat conduction equation, I show how, at the end of an orogenic event, the relaxation of isotherms from a syn-orogenic advection-dominated geometry to a post-orogenic conduction dominated geometry leads to the creation of a thick iso-age crustal layer. Subsequent erosion of this layer yields peculiar age-elevation profiles and detrital age distributions that cannot be easily interpreted using traditional techniques. I illustrate these points by using a simple analytical solution of the heat equation as well as a transient, three-dimensional numerical model. I also demonstrate that the age of the end of an orogenic event is so strongly imprinted in the thermochronological record that it erases most of the information pertaining to the orogenic phase itself and the subsequent isostatically-driven exhumation. The concept is used to explain two thermochronological datasets from the Himalayas and demonstrate that their most likely interpretation involves the sudden interruption of extremely fast exhumation accommodated by movement along the South Tibetan Detachment in the Higher Himalayas around 15 Ma. (C) 2016 Elsevier B.V. All rights reserved.
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Braun, J., Stippich, C., & Glasmacher, U. A. (2016). The effect of variability in rock thermal conductivity on exhumation rate estimates from thermochronological data. Tectonophysics, 690, 288–297.
Résumé: To infer exhumation rates from thermochronological data requires knowledge of the temperature field in the Earth's crust, which is principally determined by a balance between heat conduction and heat advection during exhumation. The rate of heat conduction is set by the thermal conductivity which is known to strongly vary among rock types and to be a function of depth, pressure and temperature, among other factors. Despite this, most methods used to extract exhumation rate from thermochronological datasets neglect the effect of the observed variability in conductivity. Here we have computed the effect of assuming a linear variation in thermal conductivity with depth, rock type and temperature on estimates of exhumation rates based on the interpretation of thermochronological data. We show how the relationship between depth and temperature is affected by variations in rock conductivity for a range of exhumation rates. Assuming that the conductivity is a linear function of depth but is not affected by rock advection leads to very large variations in apparent exhumation rate, especially in low exhuming environments. This case is to be considered where effective conductivity may be a function of pressure, or porosity or affected by pore fluid circulation. If the conductivity is a function of initial depth (a proxy for rock type) and is advected with rock motion, the perturbation caused by a linear change in conductivity is much less important. In this situation, we show that it leads to a systematic yet small over-estimation or under-estimation in exhumation rate, when the conductivity is assumed to decrease or increase with depth, respectively. We also estimated the effect of the temperature dependence of rock conductivity on thermochronologically-derived measures of exhumation rate and demonstrate that neglecting the temperature dependence of conductivity leads to an approximate 20% underestimation of the true exhumation rate. (C) 2016 Elsevier B.V. All rights reserved.
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Brax, M., Causse, M., & Bard, P. Y. (2016). Ground motion prediction in Beirut: a multi-step procedure coupling empirical Green's functions, ground motion prediction equations and instrumental transfer functions. Bulletin Of Earthquake Engineering, 14(12), 3317–3341.
Résumé: The strike slip Yammouneh fault is the longest fault in Lebanon, crossing the territory from South to North. It was responsible for major historical earthquakes like the 1202 A.D. earthquake, estimated to M(s)7.6. This paper presents a site-specific estimation of the ground motion caused by a potential M(w)7.5 earthquake on the Yammouneh fault, similar to the 1202 event, for various sites within the Beirut area. The empirical Green's function technique EGF is used to estimate the median and the standard deviations of the seismic ground motion at the reference station BHL, taking into account epistemic and aleatory uncertainties related to source parameters. These uncertainties were quantified through a sensitivity analysis of the position of the rupture nucleation X-nuc, the slip roughness parameter K, the corner frequency f(c) and the magnitude M-c of the EGF. The rock ground motion is then transferred to various other sites within the Beirut area, using instrumental Fourier transfer functions. Site amplification factors are next deduced by computing the ratio between response spectra at sediment sites and at a reference rock station. Considering the limits of the EGF method in the near field of extended sources, the EGF approach is considered only up to a magnitude M-w of 6.5. Selected Ground Motion Predictive Equations are then used to simulate a M(w)7.5 event at a reference station. By applying the amplification factors, the response spectra at the different sites of Beirut are also calculated and compared with the actual response spectra used in the Lebanese regulations.
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Brenguier, F., Kowalski, P., Ackerley, N., Nakata, N., Boue, P., Campillo, M., et al. (2016). Toward 4D Noise-Based Seismic Probing of Volcanoes: Perspectives from a Large-N Experiment on Piton de la Fournaise Volcano. Seismological Research Letters, 87(1), 15–25.
Résumé: Noise-based seismology is proving to be a complementary approach to active-source or earthquake-based methods for imaging and monitoring the Earth's interior. Until recently, however, noise-based imaging and monitoring relied mostly on the inversion of surface waves reconstructed from correlations of mostly microseismic seismic noise (around 5 s of period). Compared to body-wave tomography and considering similar wavelengths, surface-wave tomography succeeds in retrieving lateral subsurface velocity contrasts but is less efficient in resolving velocity perturbations at depth. Recently, the use of large-N seismic arrays has proven to be of great benefit for extracting body waves from noise correlations by stacking over a large number of receiver pairs and by applying array processing. In this article, we describe a recent large-N array experiment that we conducted on Piton de la Fournaise (PdF). Our main goal was to extract body waves traveling directly in the vicinity of the active magma reservoir located at similar to 2:5 km depth below the summit crater using noise correlations between arrays of seismic sensors. Within this article, we provide technical information about the Vol-cArray experiment, which consisted of the deployment of 300 seismic nodes during one month on PdF. We also present data-quality measurements and show how the short-period seismometers that we used compare to standard broadband seismic records. Finally, we show noise array beamforming results to study the content of seismic noise at frequencies between 1 and 12 Hz and discuss the ability to use these data to recover body waves between arrays from the correlation of ambient seismic noise.
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Brenguier, F., Rivet, D., Obermann, A., Nakata, N., Boue, P., Lecocq, T., et al. (2016). 4-D noise-based seismology at volcanoes: Ongoing efforts and perspectives. Journal Of Volcanology And Geothermal Research, 321, 182–195.
Résumé: Monitoring magma pressure buildup at depth and transport to surface is a key point for improving volcanic eruption prediction. Seismic waves, through their velocity dependence to stress perturbations, can provide crucial information on the temporal evolution of the mechanical properties of volcanic edifices. In this article, we review past and ongoing efforts for extracting accurate information of temporal changes of seismic velocities at volcanoes continuously in time using records of ambient seismic noise. We will first introduce the general methodology for retrieving accurate seismic velocity changes from seismic noise records and discuss the origin of seismic velocity temporal changes in rocks. We will then discuss in a second part how noise-based monitoring can improve our knowledge about magmatic activity at a long (years) to a short (days) time scale taking example from Piton de la Fournaise volcano (La Reunion). We will also mention ongoing efforts for operational noise based seismic monitoring on volcanoes. Further, we will discuss perspectives for improving the spatial localization of detected velocity changes at depth with a special focus on the use of dense seismic arrays. In the last part, we will finally explore the complex response of volcanic regions to seismic shaking with an example from Japan and show how imaging seismic velocity susceptibility allows characterizing the state of pressurized fluids in volcanic regions. (C) 2016 Elsevier B.V. All rights reserved.
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Brothelande, E., Lenat, J. F., Chaput, M., Gailler, L., Finizola, A., Dumont, S., et al. (2016). Structure and evolution of an active resurgent dome evidenced by geophysical investigations: The Yenkahe dome-Yasur volcano system (Siwi caldera, Vanuatu). Journal Of Volcanology And Geothermal Research, 322, 241–262.
Résumé: In this contribution, we focus on one of the most active resurgences on Earth, that of the Yenkahe dome in the Siwi caldera (Tanna Island, Vanuatu), which is associated with the persistently active Yasur volcano. Gravity and magnetic surveys have been carried out over the past few years in the area, as well as electrical methods including electrical resistivity tomography (ERT), time domain electro-magnetics (TDEM) and self-potential (SP). These investigations were completed by thermometry, CO2 soil gas measurements, field observations and sampling. This multi-method approach allows geological structures within the caldera to be identified, as well as associated hydrothermal features. The global structure of the caldera is deduced from gravity data, which shows the caldera rim as a high density structure. Large lava fields, emplaced before and after the onset of resurgence, are evidenced by combined gravity, magnetic and resistivity signals. In the middle of the caldera, the Yenkahe dome apparently results from a combination of volcanic and tectonic events, showing that lava extrusion and resurgence have been operating simultaneously or alternately during the Siwi caldera post-collapse history. There is a clear distinction between the western and eastern parts of the dome. The western part is older and records the growth of an initial volcanic cone and the formation of a small caldera. This small caldera (paleo-Yasur caldera), partially filled with lava flows, is the present-day focus of volcanic activity and associated fluid circulation and alteration. The eastern part of the dome is presumably younger, and is characterized by intense, extensive hydro thermal alteration and activity. Its northern part is covered by lava flow piles and exhibits a shallow hydrothermal zone in ERT. The southern part has hydrothermal alteration and activity extending at least down to the base of the resurgent dome. This part of the dome is built up of low cohesion rock and is thus potentially prone to gravitational landslides. Lastly, while self-potential and temperature data suggest that widespread hydro thermal circulation occurs throughout almost all of the caldera, and possibly beyond, the most active parts of this hydrothermal system are associated with the dome. The presence of this active hydrothermal system is the clearest indicator that these methods can provide of a potential shallow magmatic body underneath the dome. (C) 2015 Elsevier B.V. All rights reserved.
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Brothelande, E., Peltier, A., Got, J. L., Merle, O., Lardy, M., & Garaebiti, E. (2016). Constraints on the source of resurgent doming inferred from analogue and numerical modeling – Implications on the current feeding system of the Yenkahe dome-Yasur volcano complex (Vanuatu). Journal Of Volcanology And Geothermal Research, 322, 225–240.
Résumé: Resurgence, defined as the post-collapse long-term uplift of a caldera floor, is commonly attributed to a renewed rise of magma. The Yenkahe dome (Vanuatu) exhibits a common morphology – elongated with a graben on top – among resurgent domes, and is also one of the most active structures of the kind. In this study, we performed a joint analysis based on analogue and finite element numerical models to (1) constrain the width and depth of the long-term deformation intrusive source of the Yenkahe dome and (2) discuss the close association between the Yenkahe dome and the active Yasur cone. We consider the resurgent deformation at the surface to be driven by the uplift of a magma reservoir roof in depth. As the edifice deformation response depends on the medium and the source properties, the mechanical behavior of the upper crust and the nature of the source are modeled using two very different sets of hypotheses. Analogue modeling uses silicone putty, an analogue for a large viscous magma body, intruding a sand-plaster mixture reproducing a Mohr-Coulomb behavior for the crust. Numerical models consider the vertical displacement of a rigid indenter, allowing the conservation of a flat-shaped roof, into an elastoplastic material. Numerical and analogue models show different resurgent dome structures at depth but similar dome and graben morphologies in the surface. Inverse faults – or equivalent shearing zones – delimiting the dome provide an explanation for the confined nature of resurgent doming and the persistent volcanic activity on the dome border represented by the Yasur volcano. Analogue and numerical models together provide an estimation range of 1-1.8 km for the intrusive deformation source depth, and 1.3-2 km for its width. The proposed association between the Yenkahe dome and the Yasur volcano is compatible with such a shallow depth of the magma reservoir, and argues for a discontinuous resurgence process. (C) 2015 Elsevier B.V. All rights reserved.
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Budi-Santoso, A., & Lesage, P. (2016). Velocity variations associated with the large 2010 eruption of Merapi volcano, Java, retrieved from seismic multiplets and ambient noise cross-correlation. Geophysical Journal International, 206(1), 221–240.
Résumé: We present a study of the seismic velocity variations that occurred in the structure before the large 2010 eruption of Merapi volcano. For the first time to our knowledge, the technique of coda wave interferometry is applied to both families of similar events (multiplets) and to correlation functions of seismic noise. About half of the seismic events recorded at the summit stations belong to one of the ten multiplets identified, including 120 similar events that occurred in the last 20 hr preceding the eruption onset. Daily noise cross-correlation functions (NCF) were calculated for the six pairs of short-period stations available. Using the stretching method, we estimate time-series of apparent velocity variation (AVV) for each multiplet and each pair of stations. No significant velocity change is detected until September 2010. From 10 October to the beginning of the eruption on 26 October, a complex pattern of AVV is observed with amplitude of up to +/-1.5 per cent. Velocity decrease is first observed from families of deep events and then from shallow earthquakes. In the same period, AVV with different signs and chronologies are estimated from NCF calculated for various station pairs. The location in the horizontal plane of the velocity perturbations related with the AVV obtained from NCF is estimated by using an approach based on the radiative transfer approximation. Although their spatial resolution is limited, the resulting maps display velocity decrease in the upper part of the edifice in the period 12-25 October. After the eruption onset, the pattern of velocity perturbations is significantly modified with respect to the previous one. We interpret these velocity variations in the framework of a scenario of magmatic intrusion that integrates most observations. The perturbation of the stress field associated with the magma migration can induce both decrease and increase of the seismic velocity of rocks. Thus the detected AVVs can be considered as precursors of volcanic eruptions in andesitic volcanoes, without taking their sign into account.
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Bureau, H., Auzende, A. L., Marocchi, M., Raepsaet, C., Munsch, P., Testemale, D., et al. (2016). Modern and past volcanic degassing of iodine. Geochimica Et Cosmochimica Acta, 173, 114–125.
Résumé: We have monitored iodine degassing from a melt to a water vapor during decompression (i.e. magma ascent). Experiments have been performed by combining diamond anvil cells experiments with synchrotron X-rays fluorescence analysis. Partition coefficients D-fluid/melt(I) measured for a pressure and temperature range of 0.1-1.8 GPa and 500-900 degrees C, range from 41 to 1.92, values for room conditions D-fluid/glass(I) (quenched samples) are equal to or higher than 350. We show that iodine degassing with water is earlier and much more efficient than for lighter halogen elements, Cl and Br. Iodine is totally degassed from the silicate melt at room conditions. By applying these results to modern volcanology, we calculate an annual iodine flux for subduction related volcanism of 0.16-2.4 kt yr(-1). We suggest that the natural iodine degassing may be underestimated, having possible consequences on the Earth's ozone destruction cycle. By applying this results to the Early Earth, we propose a process that may explain the contrasted signature of I, Br and Cl, strongly depleted in the bulk silicate Earth, the most depleted being iodine, whereas fluorine is almost enriched. The Earth may have lost heavy halogen elements during an early water degassing process from the magma ocean. (C) 2015 Elsevier Ltd. All rights reserved.
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Carrapa, B., Robert, X., DeCelles, P. G., Orme, D. A., Thomson, S. N., & Schoenbohm, L. M. (2016). Asymmetric exhumation of the Mount Everest region: Implications for the tectono-topographic evolution of the Himalaya. Geology, 44(8), 611–614.
Résumé: The tectonic and topographic history of the Himalaya-Tibet orogenic system remains controversial, with several competing models that predict different exhumation histories. Here, we present new low-temperature thermochronological data from the Mount Everest region, which, combined with thermal-kinematic landscape evolution modeling, indicate asymmetric exhumation of Mount Everest consistent with a scenario in which the southern edge of the Tibetan Plateau was located > 100 km farther south during the mid-Miocene. Northward plateau retreat was caused by erosional incision during the Pliocene. Our results suggest that the South Tibetan Detachment was a localized structure and that no coupling between precipitation and erosion is required for Miocene exhumation of Greater Himalayan Sequence rocks on Mount Everest.
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Causse, B., Spadini, L., Sarret, G., Faure, A., Travelet, C., Madern, D., et al. (2016). Xanthan Exopolysaccharide: Cu2+ Complexes Affected from the pH-Dependent Conformational State; Implications for Environmentally Relevant Biopolymers. Environmental Science & Technology, 50(7), 3477–3485.
Résumé: The conformational impact of environmental biopolymers on metal sorption was studied through Cu sorption on xanthan. The apparent Cu2+ complexation constant (logK; Cu2+ + L- <-> CuL+) decreased from 2.9 +/- 0.1 at pH 3.5 to 2.5 +/- 0.1 at pH 5.5 (ionic strength I = 0.1). This behavior is in apparent contradiction with basic thermodynamics, as usually the higher the pH the more cations bind. Our combined titration, circular dichroism and dynamic light scattering study indicated that the change observed in Cu bond strength relates to a conformational change of the structure of xanthan, which generates more chelating sites at pH 3.5 than at pH 5.5. This hypothesis was validated by the fact that the Cu sorption constants on xanthan were always higher than those measured on a mixture of pyruvic and glucuronic acids (logK = 2.2), which are the two constitutive ligands present in the xanthan monomer. This study shows the role of the structural conformation of natural biopolymers in metal bond strength. This finding may help to better predict the fate of Cu and other metals in acidic environmental settings such as aquatic media affected by acid mine drainage, as well as peats and acidic soils, and to better define optimal conditions for bioremediation processes.
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Causse, M., Dalguer, L. A., & Mai, P. M. (2016). Variability of dynamic source parameters inferred from kinematic models of past earthquakes (vol 196, pg 1754, 2014). Geophysical Journal International, 207(3), 1837.
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Chandra, J., Gueguen, P., & Bonilla, L. F. (2016). PGA-PGV/Vs considered as a stress-strain proxy for predicting nonlinear soil response. Soil Dynamics And Earthquake Engineering, 85, 146–160.
Résumé: In this paper, a relationship proxy for predicting the nonlinear soil responses is proposed by mean of monitoring the variation of shear wave velocity along vertical array. The recent seismic interferometry by deconvolution method is applied to extract the shear-wave velocity profile throughout the soil column. Using synthetic modeling, this method is shown to be a relevant and an efficient solution for assessing the Vs profile along a vertical seismic array. The ratio between particle velocity and the equivalent linear shear-wave velocity, v*/Vs*, is computed between two successive sensors, and is assumed to be a proxy for strain. The particle acceleration, a*, versus v*/Vs* is proposed as a stress-strain representation for nonlinear analysis of soil response. Using centrifuge tests, v*/Vs* is shown to be a good representation for soil strain, and analysis of the variation of v*/Vs* as a function of a* allows the nonlinear soil response to be determined in an earthquake situation. These relationship proxies are finally applied to the Japanese K-NET and KiK-net in-situ data, where Vs(30) is used instead of Vs* for practical purposes related to site classification recommendations. (C) 2016 Elsevier Ltd. All rights reserved.
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Chaput, J., Clerc, V., Campillo, M., Roux, P., & Knox, H. (2016). On the practical convergence of coda-based correlations: a window optimization approach. Geophysical Journal International, 204(2), 736–747.
Résumé: We present a novel optimization approach to improve the convergence of interstation coda correlation functions towards the medium's empirical Green's function. For two stations recording a series of impulsive events in a multiply scattering medium, we explore the impact of coda window selection through a Markov Chain Monte Carlo scheme, with the aim of generating a gather of correlation functions that is the most coherent and symmetric over events, thus recovering intuitive elements of the interstation Green's function without any nonlinear post-processing techniques. This approach is tested here for a 2-D acoustic finite difference model, where a much improved correlation function is obtained, as well as for a database of small impulsive icequakes recorded on Erebus Volcano, Antarctica, where similar robust results are shown. The average coda solutions, as deduced from the posterior probability distributions of the optimization, are further representative of the scattering strength of the medium, with stronger scattering resulting in a slightly delayed overall coda sampling. The recovery of singly scattered arrivals in the coda of correlation functions are also shown to be possible through this approach, and surface wave reflections from outer craters on Erebus volcano were mapped in this fashion. We also note that, due to the improvement of correlation functions over subsequent events, this approach can further be used to improve the resolution of passive temporal monitoring.
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Charlet, L., Baham, J., Giraldez, J., Lo, W/, Aristilde, L., Baveye, P. (2016). Éloge de la méthode: A tribute to Garrison Sposito on the occasion of his retirement. Frontiers in Environmental Science, 4(73).
Résumé: When confronted with a great piece of art or research, one often wonders about what made it possible, what method was used by its author, in part so one can try to emulate it in one's own activities. Upon the retirement of Garrison Sposito after a long and very distinguished career, we considered that, as former doctoral students of Gary's, we were in a privileged position to write, in our own words and from our perspective, an account of the various key ingredients of his very successful “method.” In the following, we identify and review six components of this method, respectively his thorough bibliographical coverage, extreme rigor in research, meticulous crafting of manuscripts, parallel focus on several disciplines, firm conviction that it is not necessary to go out of one's way to promote good ideas or competent people, and finally his reluctance to jump on bandwagons. We hope that this analysis of the pillars of Gary's method, at least as we see them, will not only help pay tribute to an outstanding thinker, but also inspire and provide a roadmap to all those who strive to better themselves as researchers.
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Chevalier, M. L., Leloup, P. H., Replumaz, A., Pan, J. W., Liu, D. L., Li, H. B., et al. (2016). Tectonic-geomorphology of the Litang fault system, SE Tibetan Plateau, and implication for regional seismic hazard. Tectonophysics, 682, 278–292.
Résumé: The Litang fault system (LTFS) in the eastern Tibetan Plateau has generated several large (7.5>M>7) historical earthquakes and has exhumed granitic peaks rising >1700 m above the mean elevation of the plateau, despite being located within a tectonic block surrounded by highly active faults. We study horizontally offset moraine crests from the Cuopu basin and a vertically offset alluvio-glacial fan from the eastern Maoya basin. We determine a left-lateral rate of 0.09 +/- 0.02 mm/yr along a slowly slipping secondary fault at Cuopu, while the main active fault at present is the normal range-front N Cuopu fault, along which we determined a left-lateral rate of 2.3 +/- 0.6 mm/yr since 173 ka. At Maoya fan, matching the vertical 12 +/- 1 m cumulative offset with the 21.7 +/- 4.2 ka fan age yields a vertical (normal) rate of 0.6 +/- 0.1 mm/yr. This rate is very similar to that recently determined at the same location using low-temperature thermochronology (0.59 +/- 0.03 mm/yr since 6.6 +/- 05 Ma). Left-lateral rates along the main faults of the LTFS range between 0.9 and 23 mm/yr at all time scales from a few years to similar to 6 Ma. The facts that the LTFS is highly segmented and that at present, the Cuopu, Maoya and South Jawa segments are mostly normal (while the Litang and Dewu segments are left-lateral/normal), could prevent the occurrence of M>7.5 destructive earthquakes along the LTFS, as is generally assumed. However, motion on the normal faults appears to be linked with motion on the strike-slip faults, potentially allowing for exceptional larger earthquakes, and implying that the area is not experiencing pure similar to NS extension but rather NW-SE left-lateral transtension. (C) 2016 Elsevier B.V. All rights reserved.
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Chien, Y. C., Burwell, A. K., Saeki, K., Fernandez-Martinez, A., Pugach, M. K., Nonomura, G., et al. (2016). Distinct decalcification process of dentin by different cariogenic organic acids: Kinetics, ultrastructure and mechanical properties. Archives Of Oral Biology, 63, 93–105.
Résumé: Objectives: We studied artificial dentin lesions in human teeth generated by lactate and acetate buffers (pH 5.0), the two most abundant acids in caries. The objective of this study was to determine differences in mechanical properties, mineral density profiles and ultrastructural variations of two different artificial lesions with the same approximate depth. Methods: 0.05 M (pH 5.0) acetate or lactate buffer was used to create 1) 180 μm-deep lesions in non-carious human dentin blocks (acetate 130 h; lactate 14days); (2) demineralized, similar to 180 μm-thick non-carious dentin discs (3 weeks). We performed nanoindentation to determine mechanical properties across the hydrated lesions, and micro X-ray computed tomography (MicroXCT) to determine mineral profiles. Ultrastructure in lesions was analyzed by TEM/selected area electron diffraction (SAED). Demineralized dentin discs were analyzed by small angle X-ray scattering (SAXS). Results: Diffusion-dominated demineralization was shown based on the linearity between lesion depths versus the square root of exposure time in either solution, with faster kinetics in acetate buffer. Nanoindentation revealed lactate induced a significantly sharper transition in reduced elastic modulus across the lesions. MicroXCT showed lactate demineralized lesions had swelling and more disorganized matrix structure, whereas acetate lesions had abrupt X-ray absorption near the margin. At the ultrastructural level, TEM showed lactate was more effective in removing minerals from the collagenous matrix, which was confirmed by SAXS analysis. Conclusions: These findings indicated the different acids yielded lesions with different characteristics that could influence lesion formation resulting in their distinct predominance in different caries activities, and these differences may impact strategies for dentin caries remineralization. (C) 2015 Elsevier Ltd. All rights reserved.
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Chiodini, G., Paonita, A., Aiuppa, A., Costa, A., Caliro, S., De Martino, P., et al. (2016). Magmas near the critical degassing pressure drive volcanic unrest towards a critical state. Nature Communications, 7.
Résumé: During the reawaking of a volcano, magmas migrating through the shallow crust have to pass through hydrothermal fluids and rocks. The resulting magma-hydrothermal interactions are still poorly understood, which impairs the ability to interpret volcano monitoring signals and perform hazard assessments. Here we use the results of physical and volatile saturation models to demonstrate that magmatic volatiles released by decompressing magmas at a critical degassing pressure (CDP) can drive volcanic unrest towards a critical state. We show that, at the CDP, the abrupt and voluminous release of H2O-rich magmatic gases can heat hydrothermal fluids and rocks, triggering an accelerating deformation that can ultimately culminate in rock failure and eruption. We propose that magma could be approaching the CDP at Campi Flegrei, a volcano in the metropolitan area of Naples, one of the most densely inhabited areas in the world, and where accelerating deformation and heating are currently being observed.
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Choblet, G., Amit, H., & Husson, L. (2016). Constraining mantle convection models with palaeomagnetic reversals record and numerical dynamos. Geophysical Journal International, 207(2), 1165–1184.
Résumé: We present numerical models of mantle dynamics forced by plate velocities history in the last 450 Ma. The lower-mantle rheology and the thickness of a dense basal layer are systematically varied and several initial procedures are considered for each case. For some cases, the dependence on the mantle convection vigour is also examined. The resulting evolution of the CMB heat flux is analysed in terms of criteria to promote or inhibit reversals inferred from numerical dynamos. Most models present a rather dynamic lower mantle with the emergence of two thermochemical piles towards present-day. Only a small minority of models present two stationary piles over the last 450 Myr. At present-day, the composition field obtained in our models is found to correlate better with tomography than the temperature field. In addition, the temperature field immediately at the CMB (and thus the heat flux pattern) slightly differs from the average temperature field over the 100-km thick mantle layer above it. The evolution of the mean CMB heat flux or of the amplitude of heterogeneity seldom presents the expected correlation with the evolution of the palaeomagnetic reversal frequency suggesting these effects cannot explain the observations. In contrast, our analysis favours 'inertial control' on the geodynamo associated with polar cooling and in some cases break of Taylor columns in the outer core as sources of increased reversal frequency. Overall, the most likely candidates among our mantle dynamics models involve a viscosity increase in the mantle equal or smaller than 30: models with a discontinuous viscosity increase at the transition zone tend to agree better at present-day with observations of seismic tomography, but models with a gradual viscosity increase agree better with some of the criteria proposed to affect reversal frequency.
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Colombi, A., Colquitt, D., Roux, P., Guenneau, S., & Craster, R. V. (2016). A seismic metamaterial: The resonant metawedge. Scientific Reports, 6.
Résumé: Critical concepts from three different fields, elasticity, plasmonics and metamaterials, are brought together to design a metasurface at the geophysical scale, the resonant metawedge, to control seismic Rayleigh waves. Made of spatially graded vertical subwavelength resonators on an elastic substrate, the metawedge can either mode convert incident surface Rayleigh waves into bulk elastic shear waves or reflect the Rayleigh waves creating a “seismic rainbow” effect analogous to the optical rainbow for electromagnetic metasurfaces. Time-domain spectral element simulations demonstrate the broadband efficacy of the metawedge in mode conversion while an analytical model is developed to accurately describe and predict the seismic rainbow effect; allowing the metawedge to be designed without the need for extensive parametric studies and simulations. The efficiency of the resonant metawedge shows that large-scale mechanical metamaterials are feasible, will have application, and that the time is ripe for considering many optical devices in the seismic and geophysical context.
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Colombi, A., Guenneau, S., Roux, P., & Craster, R. V. (2016). Transformation seismology: composite soil lenses for steering surface elastic Rayleigh waves. Scientific Reports, 6.
Résumé: Metamaterials are artificially structured media that exibit properties beyond those usually encountered in nature. Typically they are developed for electromagnetic waves at millimetric down to nanometric scales, or for acoustics, at centimeter scales. By applying ideas from transformation optics we can steer Rayleigh-surface waves that are solutions of the vector Navier equations of elastodynamics. As a paradigm of the conformal geophysics that we are creating, we design a square arrangement of Luneburg lenses to reroute Rayleigh waves around a building with the dual aim of protection and minimizing the effect on the wavefront (cloaking). To show that this is practically realisable we deliberately choose to use material parameters readily available and this metalens consists of a composite soil structured with buried pillars made of softer material. The regular lattice of inclusions is homogenized to give an effective material with a radially varying velocity profile and hence varying the refractive index of the lens. We develop the theory and then use full 3D numerical simulations to conclusively demonstrate, at frequencies of seismological relevance 3-10 Hz, and for low-speed sedimentary soil (v(s): 300-500 m/s), that the vibration of a structure is reduced by up to 6 dB at its resonance frequency.
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Colombi, A., Roux, P., Guenneau, S., Gueguen, P., & Craster, R. V. (2016). Forests as a natural seismic metamaterial: Rayleigh wave bandgaps induced by local resonances. Scientific Reports, 6.
Résumé: We explore the thesis that resonances in trees result in forests acting as locally resonant metamaterials for Rayleigh surface waves in the geophysics context. A geophysical experiment demonstrates that a Rayleigh wave, propagating in soft sedimentary soil at frequencies lower than 150 Hz, experiences strong attenuation, when interacting with a forest, over two separate large frequency bands. This experiment is interpreted using finite element simulations that demonstrate the observed attenuation is due to bandgaps when the trees are arranged at the sub-wavelength scale with respect to the incident Rayleigh wave. The repetitive bandgaps are generated by the coupling of the successive longitudinal resonances of trees with the vertical component of the Rayleigh wave. For wavelengths down to 5 meters, the resulting bandgaps are remarkably large and strongly attenuating when the acoustic impedance of the trees matches the impedance of the soil. Since longitudinal resonances of a vertical resonator are inversely proportional to its length, a man-made engineered array of resonators that attenuates Rayleigh waves at frequency <= 10 Hz could be designed starting from vertical pillars coupled to the ground with longitudinal resonance <= 10 Hz.
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Colon, C., Webb, A. A. G., Lasserre, C., Doin, M. P., Renard, F., Lohman, R., et al. (2016). The variety of subaerial active salt deformations in the Kuqa fold-thrust belt (China) constrained by InSAR. Earth And Planetary Science Letters, 450, 83–95.
Résumé: Surface salt bodies in the western Kuqa fold-thrust belt of northwestern China allow study of subaerial salt kinematics and its possible correlations with weather variations. Ephemeral subaerial salt exposure during the evolution of a salt structure can greatly impact the subsequent development and deformation of its tectonic setting. Here, we present a quantitative time-lapse survey of surface salt deformation measured from interferometric synthetic aperture radar (InSAR) using Envisat radar imagery acquired between 2003 and 2010. Time series analysis and inspection of individual interferograms confirm that the majority of the salt bodies in western Kuqa are active, with significant InSAR observable displacements at 3 of 4 structures studied in the region. Subaerial salt motion toward and away from the satellite at rates up to 5 mm/yr with respect to local references. Rainfall measurements from the Tropical Rainfall Measuring Mission (TRMM) and temperature from a local weather station are used to test the relationship between seasonality and surface salt motion. We observe decoupling between surface salt motion and seasonality and interpret these observations to indicate that regional and local structural regimes exert primary control on surface salt displacement rates. (C) 2016 Elsevier B.V. All rights reserved.
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Corbi, F., Rivalta, E., Pinel, V., Maccaferri, F., & Acocella, V. (2016). Understanding the link between circumferential dikes and eruptive fissures around calderas based on numerical and analog models. Geophysical Research Letters, 43(12), 6212–6219.
Résumé: Active calderas are seldom associated with circumferential eruptive fissures, but eroded magmatic complexes reveal widespread circumferential dikes. This suggests that, while the conditions to emplace circumferential dikes are easily met, mechanisms must prevent them from reaching the surface. We explain this discrepancy with experiments of air injection into gelatin shaped as a volcano with caldera. Analog dikes show variable deflection, depending on the competition between overpressure, P-e, and topographic unloading, P-l; when P-l/P-e = 4.8-5.3, the dikes propagate orthogonal to the least compressive stress. Due to the unloading, they become circumferential and stall below the caldera rim; buoyancy is fundamental for the further rise and circumferential fissure development. Numerical models quantitatively constrain the stress orientation within the gelatin, explaining the observed circumferential dikes. Our results explain how dikes propagate below the rim of felsic and mafic calderas, but only in the latter they are prone to feed circumferential fissures.
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Cordier, C., Chauvel, C., & Hemond, C. (2016). High-precision lead isotopes and stripy plumes: Revisiting the Society chain in French Polynesia. Geochimica Et Cosmochimica Acta, 189, 236–250.
Résumé: An increasing number of geochemical studies looked for spatial organization of the isotopic variations along Pacific volcanic island chains (e.g., Hawaii, Marquesas, Samoa and Society Islands) in order to discuss the possible zoning of the plume conduits. Here, we reexamine the occurrence of isotopic stripes in the Society archipelago in French Polynesia, using new Sr-Nd-Hf-Pb isotope ratios of sixty-six lavas from six islands (Mehetia, Moorea, Maupiti, Huahine, Raiatea, Bora-Bora). We demonstrate that the Pb isotope variability observed using literature data is an analytical artifact related to the poor control of mass fractionation during Pb measurements by conventional TIMS technique. New MC-ICP-MS Pb data demonstrate that the isotopic stripes as previously defined disappear. They rather show that individual islands cover a significant part of the entire isotopic range of the chain. We suggest, therefore, that the dominant characteristic of the Society plume is small-scale heterogeneities, evenly distributed within the plume conduit. At a global scale, we show that some ocean island chains with similar geochemical and isotopic characteristics, such as Samoa and Society Islands, define different arrays when variations of Nd with high-precision Pb isotopes are considered. We proposed that this puzzling observation might record differences in recycling age of the basalt + sediment mixture subducted into the mantle and sampled by mantle plume. (C) 2016 Elsevier Ltd. All rights reserved.
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Cordier, C., Sauzeat, L., Arndt, N. T., Boullier, A. M., Batanova, V., & Barou, F. (2016). The Geochemical Complexity of Kimberlite Rocks and their Olivine Populations: a Reply to the Comment on Cordier et al. (2015) by Andrea Giuliani & Stephen F. Foley. Journal Of Petrology, 57(5), 927–931.
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Cordonnier, G., Braun, J., Cani, M. P., Benes, B., Galin, E., Peytavie, A., et al. (2016). Large Scale Terrain Generation from Tectonic Uplift and Fluvial Erosion. Computer Graphics Forum, 35(2), 165–175.
Résumé: At large scale, landscapes result from the combination of two major processes: tectonics which generate the main relief through crust uplift, and weather which accounts for erosion. This paper presents the first method in computer graphics that combines uplift and hydraulic erosion to generate visually plausible terrains. Given a user-painted uplift map, we generate a stream graph over the entire domain embedding elevation information and stream flow. Our approach relies on the stream power equation introduced in geology for hydraulic erosion. By combining crust uplift and stream power erosion we generate large realistic terrains at a low computational cost. Finally, we convert this graph into a digital elevation model by blending landform feature kernels whose parameters are derived from the information in the graph. Our method gives high-level control over the large scale dendritic structures of the resulting river networks, watersheds, and mountains ridges.
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Courboulex, F., Vallee, M., Causse, M., & Chounet, A. (2016). Stress-Drop Variability of Shallow Earthquakes Extracted from a Global Database of Source Time Functions. Seismological Research Letters, 87(4), 912–918.
Résumé: We use the new global database of source time functions (STFs) and focal mechanisms proposed by Vallee (2013) using the automatic SCARDEC method (Vallee et al., 2011) to constrain earthquake rupture duration and variability. This database has the advantage of being very consistent since all the events with moment magnitudes M-w > 5.8 that have occurred during the last 20 years were reanalyzed with the same method and the same station configuration. We analyze 1754 shallow earthquakes (depth < 35 km) and use high-quality criteria for the STFs, which result in the selection of 660 events. Among these, 313 occurred on the subduction interface (SUB events) and 347 outside (NOT-SUB events). We obtain that for a given magnitude, STF duration is log normally distributed and that STFs are longer for SUB than NOT-SUB events. We then estimate the stress drop using a proxy for the rupture process duration obtained from the measurement of the maximum amplitude of the STF. The resulting stress drop is independent of magnitude and is about 2.5 times smaller for the subduction events compared with the other events. Assuming a constant rupture velocity and source model, the resulting standard deviation of the stress drop is 1.13 for the total dataset (natural log), and about 1 for separate datasets. These values are significantly lower than the ones generally obtained from corner-frequency analyses with global databases (similar to 1.5 for Allmann and Shearer, 2009) and are closer to the values inferred from strong-motion measurements (similar to 0.5 as reported by Cotton et al., 2013). This indicates that the epistemic variability is reduced by the use of STF properties, which allows us to better approach the natural variability of the source process, related to stress-drop variability and/or variation in the rupture velocity.
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Crouzet, C., Recham, N., Brunet, F., Findling, N., David, R., & Sougrati, M. T. (2016). A novel route for FePO4 olivine synthesis from sarcopside oxidation. Solid State Sciences, 62, 29–33.
Résumé: Heterosite FePO4 is synthesized for the first time by direct thermal oxidation of sarcopside Fe-3(PO4)(2). Both FePO4 and Fe-3(PO4)(2) have a pseudo olivine structure. Complete isostructural conversion of sarcopside into FePO4 is achieved at a temperature of 450 degrees C within 3 days according to the reaction Fe-3(PO4)(2) + 3/4 O-2 -> 2 FePO4 + 1/2 Fe2O3 which leads to the extraction of iron from the sarcopside structure. Appropriate heating ramp must be applied in order to avoid the crystallization of Fe-7(PO4)(6). Electrochemical performances of the oxidation product are consistent with those of olivine FePO4. (C) 2016 Elsevier Masson SAS. All rights reserved.
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Cruz-Atienza, V. M., Tago, J., Sanabria-Gomez, J. D., Chaljub, E., Etienne, V., Virieux, J., et al. (2016). Long Duration of Ground Motion in the Paradigmatic Valley of Mexico. Scientific Reports, 6.
Résumé: Built-up on top of ancient lake deposits, Mexico City experiences some of the largest seismic site effects worldwide. Besides the extreme amplification of seismic waves, duration of intense ground motion from large subduction earthquakes exceeds three minutes in the lake-bed zone of the basin, where hundreds of buildings collapsed or were seriously damaged during the magnitude 8.0 Michoacan earthquake in 1985. Different mechanisms contribute to the long lasting motions, such as the regional dispersion and multiple-scattering of the incoming wavefield from the coast, more than 300 km away the city. By means of high performance computational modeling we show that, despite the highly dissipative basin deposits, seismic energy can propagate long distances in the deep structure of the valley, promoting also a large elongation of motion. Our simulations reveal that the seismic response of the basin is dominated by surface-waves overtones, and that this mechanism increases the duration of ground motion by more than 170% and 290% of the incoming wavefield duration at 0.5 and 0.3 Hz, respectively, which are two frequencies with the largest observed amplification. This conclusion contradicts what has been previously stated from observational and modeling investigations, where the basin itself has been discarded as a preponderant factor promoting long and devastating shaking in Mexico City.
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D'Amato, J., Hantz, D., Guerin, A., Jaboyedoff, M., Baillet, L., & Mariscal, A. (2016). Influence of meteorological factors on rockfall occurrence in a middle mountain limestone cliff. Natural Hazards And Earth System Sciences, 16(3), 719–735.
Résumé: The influence of meteorological conditions on rockfall occurrence has been often highlighted, but knowledge of it is still not sufficient due to the lack of exhaustive and precise rockfall databases. In this study, rockfalls have been detected in a limestone cliff by annual terrestrial laser scanning, and dated by photographic survey over a period of 2.5 years. A near-continuous survey (one photo every 10 min) with a wide-angle lens has made it possible to date 214 rockfalls larger than 0.1 m(3), and a monthly survey with a telephoto lens has dated 854 rockfalls larger than 0.01 m(3). Analysis of the two databases shows that the rockfall frequency can be multiplied by a factor as high as 7 during freeze-thaw episodes and 26 when the mean rainfall intensity (since the beginning of the rainfall episode) is higher than 5 mm h(-1). Based on these results, a three-level scale has been proposed for predicting the temporal variations of rockfall frequency. The more precise database and freeze-thaw episode definition make it possible to distinguish different phases in freeze-thaw episodes: negative temperature cooling periods, negative temperature warming periods and thawing periods. It appears that rockfalls occur more frequently during warming and thawing periods than during cooling periods. It can be inferred that rockfalls are caused by thermal ice dilatation rather than by dilatation due to the phase transition. But they may occur only when the ice melts, because the cohesion of the ice-rock interface can be sufficient to hold the rock compartment which has been cut.
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Dai, C., Stack, A. G., Koish, A., Fernandez-Martinez, A., Lee, S. S., & Hu, Y. D. (2016). Heterogeneous Nucleation and Growth of Barium Sulfate at Organic-Water Interfaces: Interplay between Surface Hydrophobicity and Ba2+ Adsorption. Langmuir, 32(21), 5277–5284.
Résumé: Barium sulfate (BaSO4) is a common scale-forming mineral in natural and engineered systems, yet the rates and mechanisms of heterogeneous BaSO4 nucleation are not understood. To address these, we created idealized interfaces on which to study heterogeneous nucleation rates and mechanisms, which also are good models for organic-water interfaces: self-assembled thin films terminated with different functional groups (i.e., -COOH, -SH, or mixed -SH & COOH) coated on glass slides. BaSO4 precipitation on coatings from Barite-supersaturated solutions (saturation index, SI, = 1.1) was investigated using grazing-incidence small-angle X-ray scattering. After reaction for 1 h, a little amount of BaSO4 formed on hydrophilic bare and -COOH coated glasses. Meanwhile, BaSO4 nucleation was significantly promoted on hydrophobic-SH and mixed-SH & COOH coatings. This is because substrate hydrophobicity likely affected the interfacial energy and hence thermodynamic favorability of heterogeneous nucleation. The heterogeneous BaSO4 nucleation and growth kinetics were found to be affected by the amount of Ba2+ adsorption onto the substrate and incipient BaSO4 nuclei. The importance of Ba2+ adsorption was further corroborated by the finding that precipitation rate increased under [Ba2+]/[SO42-] concentration ratios >1. These observations suggest that thermodynamic favorability for nucleation is governed by substrate water interfacial energy, while given favorable thermodynamics, the rate is governed by ion attachment to substrates and incipient nuclei.
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Dansereau, V., Weiss, J., Saramito, P., & Lattes, P. (2016). A Maxwell elasto-brittle rheology for sea ice modelling. Cryosphere, 10(3), 1339–1359.
Résumé: A new rheological model is developed that builds on an elasto-brittle (EB) framework used for sea ice and rock mechanics, with the intent of representing both the small elastic deformations associated with fracturing processes and the larger deformations occurring along the faults/leads once the material is highly damaged and fragmented. A viscous-like relaxation term is added to the linear-elastic constitutive law together with an effective viscosity that evolves according to the local level of damage of the material, like its elastic modulus. The coupling between the level of damage and both mechanical parameters is such that within an undamaged ice cover the viscosity is infinitely large and deformations are strictly elastic, while along highly damaged zones the elastic modulus vanishes and most of the stress is dissipated through permanent deformations. A healing mechanism is also introduced, counterbalancing the effects of damaging over large timescales. In this new model, named Maxwell-EB after the Maxwell rheology, the irreversible and reversible deformations are solved for simultaneously; hence drift velocities are defined naturally. First idealized simulations without advection show that the model reproduces the main characteristics of sea ice mechanics and deformation: strain localization, anisotropy, intermittency and associated scaling laws.
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Daout, S., Barbot, S., Peltzer, G., Doin, M. P., Liu, Z., & Jolivet, R. (2016). Constraining the kinematics of metropolitan Los Angeles faults with a slip-partitioning model. Geophysical Research Letters, 43(21), 11192–11201.
Résumé: Due to the limited resolution at depth of geodetic and other geophysical data, the geometry and the loading rate of the ramp-decollement faults below the metropolitan Los Angeles are poorly understood. Here we complement these data by assuming conservation of motion across the Big Bend of the San Andreas Fault. Using a Bayesian approach, we constrain the geometry of the ramp-decollement system from the Mojave block to Los Angeles and propose a partitioning of the convergence with 25.5 +/- 0.5 mm/yr and 3.1 +/- 0.6 mm/yr of strike-slip motion along the San Andreas Fault and the Whittier Fault, with 2.7 +/- 0.9 mm/yr and 2.5 +/- 1.0 mm/yr of updip movement along the Sierra Madre and the Puente Hills thrusts. Incorporating conservation of motion in geodetic models of strain accumulation reduces the number of free parameters and constitutes a useful methodology to estimate the tectonic loading and seismic potential of buried fault networks.
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Daout, S., Jolivet, R., Lasserre, C., Doin, M. P., Barbot, S., Tapponnier, P., et al. (2016). Along-strike variations of the partitioning of convergence across the Haiyuan fault system detected by InSAR. Geophysical Journal International, 205(1), 536–547.
Résumé: Oblique convergence across Tibet leads to slip partitioning with the coexistence of strike-slip, normal and thrust motion on major fault systems. A key point is to understand and model how faults interact and accumulate strain at depth. Here, we extract ground deformation across the Haiyuan Fault restraining bend, at the northeastern boundary of the Tibetan plateau, from Envisat radar data spanning the 2001-2011 period. We show that the complexity of the surface displacement field can be explained by the partitioning of a uniform deep-seated convergence. Mountains and sand dunes in the study area make the radar data processing challenging and require the latest developments in processing procedures for Synthetic Aperture Radar interferometry. The processing strategy is based on a small baseline approach. Before unwrapping, we correct for atmospheric phase delays from global atmospheric models and digital elevation model errors. A series of filtering steps is applied to improve the signal-to-noise ratio across high ranges of the Tibetan plateau and the phase unwrapping capability across the fault, required for reliable estimate of fault movement. We then jointly invert our InSAR time-series together with published GPS displacements to test a proposed long-term slip-partitioning model between the Haiyuan and Gulang left-lateral Faults and the Qilian Shan thrusts. We explore the geometry of the fault system at depth and associated slip rates using a Bayesian approach and test the consistency of present-day geodetic surface displacements with a long-term tectonic model. We determine a uniform convergence rate of 10 [8.6-11.5] mm yr(-1) with an N89 [81-97]A degrees E across the whole fault system, with a variable partitioning west and east of a major extensional fault-jog (the Tianzhu pull-apart basin). Our 2-D model of two profiles perpendicular to the fault system gives a quantitative understanding of how crustal deformation is accommodated by the various branches of this thrust/strike-slip fault system and demonstrates how the geometry of the Haiyuan fault system controls the partitioning of the deep secular motion.
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de Arcangelis, L., Godano, C., Grasso, J. R., & Lippiello, E. (2016). Statistical physics approach to earthquake occurrence and forecasting. Physics Reports-Review Section Of Physics Letters, 628, 1–91.
Résumé: There is striking evidence that the dynamics of the Earth crust is controlled by a wide variety of mutually dependent mechanisms acting at different spatial and temporal scales. The interplay of these mechanisms produces instabilities in the stress field, leading to abrupt energy releases, i.e., earthquakes. As a consequence, the evolution towards instability before a single event is very difficult to monitor. On the other hand, collective behavior in stress transfer and relaxation within the Earth crust leads to emergent properties described by stable phenomenological laws for a population of many earthquakes in size, time and space domains. This observation has stimulated a statistical mechanics approach to earthquake occurrence, applying ideas and methods as scaling laws, universality, fractal dimension, renormalization group, to characterize the physics of earthquakes. In this review we first present a description of the phenomenological laws of earthquake occurrence which represent the frame of reference for a variety of statistical mechanical models, ranging from the spring-block to more complex fault models. Next, we discuss the problem of seismic forecasting in the general framework of stochastic processes, where seismic occurrence can be described as a branching process implementing space time-energy correlations between earthquakes. In this context we show how correlations originate from dynamical scaling relations between time and energy, able to account for universality and provide a unifying description for the phenomenological power laws. Then we discuss how branching models can be implemented to forecast the temporal evolution of the earthquake occurrence probability and allow to discriminate among different physical mechanisms responsible for earthquake triggering. In particular, the forecasting problem will be presented in a rigorous mathematical framework, discussing the relevance of the processes acting at different temporal scales for different levels of prediction. In this review we also briefly discuss how the statistical mechanics approach can be applied to non-tectonic earthquakes and to other natural stochastic processes, such as volcanic eruptions and solar flares. (C) 2016 Elsevier B.V. All rights reserved.
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de Cacqueray, B., Roux, P., & Campillo, M. (2016). Using slowness and azimuth fluctuations as new observables for four-dimensional reservoir seismic monitoring. Geophysical Prospecting, 64(6), 1537–1555.
Résumé: Four-dimensional imaging using geophysical data is of increasing interest in the oil and gas industries. While travel-time and amplitude variations are commonly used to monitor reservoir properties at depth, their interpretation can suffer from a lack of information to decipher the parts played by different parameters. In this context, this study focuses on the slowness and azimuth angle measured at the surface using source and receiver arrays as complementary observables. In the first step, array processing techniques are used to extract both azimuth and incidence angles at the source side (departure angles) and at the receiver side (arrival angles). In the second step, the slowness and angle variations are monitored in a laboratory environment. These new observables are compared with traditional arrival-time variations when the propagation medium is subject to temperature fluctuations. Finally, field data from a heavy-oil permanent reservoir monitoring system installed onshore and facing steam injection and temperature variations are investigated. The slowness variations are computed over a period of 152 days. In agreement with Fermat's principle, strong correlations between the slowness and arrival-time variations are highlighted, as well as good consistency with other techniques and field pressure measurements. Although the temporal variations of slowness and arrival time show the same features, there are still differences that can be considered for further characterization of the physical changes at depth.
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de Lepinay, M. M., Loncke, L., Basile, C., Roest, W. R., Patriat, M., Maillard, A., et al. (2016). Transform continental margins – Part 2: A worldwide review. Tectonophysics, 693, 96–115.
Résumé: We present a global inventory of transform continental margins, based on both a worldwide comparison of continent-ocean boundary identifications with oceanic fracture zones traces, and a compilation of published regional studies. This inventory increases the number of identified transform margins from 29 to 78. These margins represent 16% of continental margins in cumulative length and 31% of non-convergent margins. We include morphological data, published upper crustal sections, continent to ocean transition locations and published Moho shape data in the new database. This review confirms that continent to ocean transitions are sharper at transform margins than at divergent margins. It also emphasizes the structural diversity of transform margins. Associated with one third of transform margins, we define marginal plateaus as a new type of relief that corresponds to a flat but deep surface inside the continental slope, and that may be inherited from crustal thinning prior to transform faulting. Transform margin initiation appears to be favoured along propagating oceans and within cold and thick lithospheres. (C) 2016 Elsevier B.V. All rights reserved.
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de Oliveira, C. H. E., Jelinek, A. R., Chemale, F., & Bernet, M. (2016). Evidence of post-Gondwana breakup in Southern Brazilian Shield: Insights from apatite and zircon fission track thermochronology. Tectonophysics, 666, 173–187.
Résumé: Apatite and zircon fission track thermochronology studies are applied to basement and sedimentary rocks from the Sul-Rio-Grandense Shield to unravel the tectonic history of the onshore southernmost Brazilian margin. The Sul-Rio-Grandense Shield is a major geotectonic feature of southernmost Brazil that includes Paleoproterozoic basement areas and Neoproterozoic fold belts linked to the Brasiliano/Pan-African orogeny. Crustal reworking and juvenile accretion events related to this cycle were dated in the region between 900 and 500 Ma and were responsible for the assembly of southwestern Gondwana in southeastern South America. Apatite fission track (AFT) ages range from 340 +/- 33 to 77 +/- 6 Ma and zircon fission track (ZFT) ages range from ca. 386 to 210 Ma. Based on thermal history modeling, the most part of the samples record an early cooling event during the Carboniferous, which reflect the main tectonic activity of the final stages of the Gondwanides at the Pacific margin of West Gondwana. Subsequently, the Permo-Triassic cooling event is related to the last stages of the Gondwanides, with convergence along the southern border of Western Gondwana and consequent reactivation of N-S and NE-SW trending basement structures. The onset of initial breakup of southwestern Gondwana with opening of the South Atlantic Ocean is mostly recorded in the eastern terrain and ZFT ages show that the temperature during this period was high enough for total or at least partial resetting of fission tracks in zircon. The last cooling event of the Sul-Rio-Grandense Shield records the final breakup between South America and Africa, which began during the Late Cretaceous. However, the Cenozoic rapid cooling episode probably is a result of plate adjustment after breakup and neotectonic reactivation of faults associated with South Atlantic rift evolution. (C) 2015 Elsevier B.V. All rights reserved.
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de Oliveira, C. H. E., Jelinek, A. R., Chemale, F., & Bernet, M. (2016). Evidence of post-Gondwana breakup in Southern Brazilian Shield: Insights from apatite and zircon fission track thermochronology. Tectonophysics, 666, 173–187.
Résumé: Apatite and zircon fission track thermochronology studies are applied to basement and sedimentary rocks from the Sul-Rio-Grandense Shield to unravel the tectonic history of the onshore southernmost Brazilian margin. The Sul-Rio-Grandense Shield is a major geotectonic feature of southernmost Brazil that includes Paleoproterozoic basement areas and Neoproterozoic fold belts linked to the Brasiliano/Pan-African orogeny. Crustal reworking and juvenile accretion events related to this cycle were dated in the region between 900 and 500 Ma and were responsible for the assembly of southwestern Gondwana in southeastern South America. Apatite fission track (AFT) ages range from 340 +/- 33 to 77 +/- 6 Ma and zircon fission track (ZFT) ages range from ca. 386 to 210 Ma. Based on thermal history modeling, the most part of the samples record an early cooling event during the Carboniferous, which reflect the main tectonic activity of the final stages of the Gondwanides at the Pacific margin of West Gondwana. Subsequently, the Permo-Triassic cooling event is related to the last stages of the Gondwanides, with convergence along the southern border of Western Gondwana and consequent reactivation of N-S and NE-SW trending basement structures. The onset of initial breakup of southwestern Gondwana with opening of the South Atlantic Ocean is mostly recorded in the eastern terrain and ZFT ages show that the temperature during this period was high enough for total or at least partial resetting of fission tracks in zircon. The last cooling event of the Sul-Rio-Grandense Shield records the final breakup between South America and Africa, which began during the Late Cretaceous. However, the Cenozoic rapid cooling episode probably is a result of plate adjustment after breakup and neotectonic reactivation of faults associated with South Atlantic rift evolution. (C) 2015 Elsevier B.V. All rights reserved.
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de Ridder, S., Brenguier, F., Forghani, F., Galetti, E., Nakata, N., & Weemstra, C. (2016). Introduction to special section: Ambient noise. Interpretation-A Journal Of Subsurface Characterization, 4(3).
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Debret, B., Koga, K. T., Cattani, F., Nicollet, C., Van den Bleeken, G., & Schwartz, S. (2016). Volatile (Li, B, F and Cl) mobility during amphibole breakdown in subduction zones. Lithos, 244, 165–181.
Résumé: Amphiboles are ubiquitous minerals in the altered oceanic crust. During subduction, their breakdown is governed by continuous reactions up to eclogitic facies conditions. Amphiboles thus contribute to slab-derived fluid throughout prograde metamorphism and continuously record information about volatile exchanges occurring between the slab and the mantle wedge. However, the fate of volatile elements and especially halogens, such as F and Cl, in amphibole during subduction is poorly constrained. We studied metagabbros from three different localities in the Western Alps: the Chenaillet ophiolite, the Queyras Schistes Lustre's and the Monviso meta-ophiolitic complexes. These samples record different metamorphic conditions, from greenschist to eclogite facies, and have interacted with different lithologies (e.g. sedimentary rocks, serpentinites) from their formation at mid oceanic ridge, up to their devolatilization during subduction. In the oceanic crust, the initial halogen budget is mostly stored in magmatic amphibole (F = 300-7000 ppm; Cl = 20-1200 ppm) or in amphibole corona (F = 100-7000 ppm; Cl = 80-2000 ppm) and titanite (F = 200-1500 ppm; Cl < 200 ppm) formed during hydrothermal seafloor alteration. It is thus the fate of these phases that govern the halogen fluxes between the crust and the overlying mantle and/or the plate interface in subduction zones. Li and B are poorly stored in the oceanic crust (<5 ppm). In subduction zones, prograde metamorphism of metagabbros is first marked by the crystallization of glaucophane at the expense of magmatic and amphibole coronas. This episode is accompanied with a decrease of halogen concentrations in amphiboles (<200 ppm of F and Cl) suggesting that these elements can be transferred to the mantle wedge by fluids. In the Queyras Schistes Lustre's complex, the intense deformation and the abundant devolatilization of metasedimentary rocks produce large fluid flows that promote rock chemical hybridization (metasomatic mixing with hybrid composition between metasedimentary rock and metagabbro) at the metasedimentary rock/metagabbro contacts. Such fluid/rock interactions result in a strong addition of Li in glaucophane (up to 600 ppm) whereas halogen concentrations are unaffected. At eclogite fades conditions, metagabbros display low halogens concentrations (<200 ppm of F and < 100 ppm of Cl) relative to altered oceanic crust (F = 40-650 ppm; Cl = 40-1400 ppm) suggesting that these elements are continuously released by fluids during the first 30-80 km of subduction whatever the tectonic environment (e.g. slab, plate interface) and the considered fluid/rock interactions. (C) 2015 Elsevier B.V. All rights reserved.
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del Real, A. E. P., Garcia-Gonzalo, P., Gil-Diaz, M. M., Gonzalez-Rodriguez, A., Lobo, C., & Perez-Sanz, A. (2016). ECO-physiological response of S-vulgaris to CR(VI): Influence of concentration and genotype. International Journal Of Phytoremediation, 18(6), 567–574.
Résumé: The objective of this work is to study the response of Silene vulgaris to a range of environmentally relevant concentrations of Cr(VI) in order to evaluate its potential use in the phytomanagement of Cr polluted sites. Cuttings of six homogenous genotypes from Madrid (Spain) have been used as plant material. The eco-physiological response of S. vulgaris to Cr(VI) changed with the genotype. The yield dose-response curve was characterized by stimulation at low doses of Cr(VI). The effects of metal concentration were quantified on root dry weight, water content and chlorophyll content, determined by SPAD index. The response was not homogeneous for all studied genotypes. At high doses of Cr(VI), plants increased micronutrient concentration in dry tissues which suggested that nutrient balance could be implicated in the alleviation of Cr toxicity. This work highlights the importance of studying the eco-physiological response of metallophytes under a range of pollutant concentrations to determine the most favorable traits to be employed in the phytomanagement process.
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Delavault, H., Chauvel, C., Thomassot, E., Devey, C. W., & Dazas, B. (2016). Sulfur and lead isotopic evidence of relic Archean sediments in the Pitcairn mantle plume. Proceedings Of The National Academy Of Sciences Of The United States Of America, 113(46), 12952–12956.
Résumé: The isotopic diversity of oceanic island basalts (OIB) is usually attributed to the influence, in their sources, of ancient material recycled into the mantle, although the nature, age, and quantities of this material remain controversial. The unradiogenic Pb isotope signature of the enriched mantle I (EM I) source of basalts from, for example, Pitcairn or Walvis Ridge has been variously attributed to recycled pelagic sediments, lower continental crust, or recycled subcontinental lithosphere. Our study helps resolve this debate by showing that Pitcairn lavas contain sulfides whose sulfur isotopic compositions are affected by mass-independent fractionation (S-MIF down to Delta S-33 = -0.8), something which is thought to have occurred on Earth only before 2.45 Ga, constraining the youngest possible age of the EM I source component. With this independent age constraint and a Monte Carlo refinement modeling of lead isotopes, we place the likely Pitcairn source age at 2.5 Ga to 2.6 Ga. The Pb, Sr, Nd, and Hf isotopic mixing arrays show that the Archean EM I material was poor in trace elements, resembling Archean sediment. After subduction, this Archean sediment apparently remained stored in the deep Earth for billions of years before returning to the surface as Pitcairn's characteristic EM I signature. The presence of negative S-MIF in the deep mantle may also help resolve the problem of an apparent deficit of negative Delta S-33 anomalies so far found in surface reservoirs.
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Derras, B., Bard, P. Y., & Cotton, F. (2016). Site-Condition Proxies, Ground Motion Variability, and Data-Driven GMPEs: Insights from the NGA-West2 and RESORCE Data Sets. Earthquake Spectra, 32(4), 2027–2056.
Résumé: We compare the ability of various site-condition proxies (SCPs) to reduce the aleatory variability of ground motion prediction equations (GMPEs). Three SCPs (measured V-S30, inferred V-S30, local topographic slope) and two accelerometric databases (RESORCE and NGA-West2) are considered. An artificial neural network (ANN) approach including a random-effect procedure is used to derive GMPEs setting the relationship between peak ground acceleration (PGA), peak ground velocity (PGV), pseudo-spectral acceleration [PSA(T)], and explanatory variables (M-w, R-JB, and V-S30 or Slope). The analysis is performed using both discrete site classes and continuous proxy values. All “non-measured” SCPs exhibit a rather poor performance in reducing aleatory variability, compared to the better performance of measured V-S30. A new, fully data-driven GMPE based on the NGA-West2 is then derived, with an aleatory variability value depending on the quality of the SCP. It proves very consistent with previous GMPEs built on the same data set. Measuring V-S30 allows for benefit from an aleatory variability reduction up to 15%.
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Devoy, J., Gehin, A., Muller, S., Melczer, M., Remy, A., Antoine, G., et al. (2016). Evaluation of chromium in red blood cells as an indicator of exposure to hexavalent chromium: An in vitro study. Toxicology Letters, 255, 63–70.
Résumé: Chromium(VI) compounds are classified as carcinogenic to humans. Whereas chromium measurements in urine and whole blood (i.e., including plasma) are indicative of recent exposure, chromium in red blood cells (RBC) is attributable specifically to Cr(VI) exposure. Before recommending Cr in RBC as a biological indicator of Cr(VI) exposure, in-vitro studies must be undertaken to assess its reliability. The present study examines the relationship between the chromium added to a blood sample and that subsequently found in the RBC. After incubation of total blood with chromium, RBC were isolated, counted and their viability assessed. Direct analysis of chromium in RBC was conducted using Atomic Absorption Spectrometry. Hexavalent, but not trivalent Cr, was seen to accumulate in the RBC and we found a strong correlation between the Cr(VI) concentration added to a blood sample and the amount of Cr in RBC. This relationship appears to be independent of the chemical properties of the human blood samples (e.g., different blood donors or different reducing capacities). Even though in-vivo studies are still needed to integrate our understanding of Cr(VI) toxicokinetics, our findings reinforce the idea that a single determination of the chromium concentration in RBC would enable biomonitoring of critical cases of Cr(VI) exposure. (C) 2016 Elsevier Ireland Ltd. All rights reserved.
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Di Bartolomeo, M., Massi, F., Baillet, L., Culla, A., & Fregolent, A. (2016). Interplay Between Local Frictional Contact Dynamics and Global Dynamics of a Mechanical System (Vol. 1).
Résumé: Friction affects almost the entirety of the mechanical systems in relative motion. In spite of intense and long-time research activities many aspects of this phenomenon still lack of a meaningful interpretation. Some of them could be explained by not focusing only on the interface properties. In fact recent literature confirms the picture of a macroscopic frictional behaviour of a mechanical system as the outcome of a complex interaction between the local dynamics at the frictional interface (wave and rupture nucleation and propagation) and the global dynamics of the system. This paper presents the results of a 2D non-linear finite element analysis under large transformations of the onset and evolution of sliding between two isotropic elastic bodies separated by a frictional interface. The aim is to investigate the trigger of the dynamic rupture at the interface, which preludes and goes with the sliding and its interaction with the global dynamics to determine the observed macroscopic frictional behaviour (stick-slip, continuous sliding). The analysis is focused on the observed phenomena during the onset of the sliding (micro-slips, precursors, macro-slips), accounting for the frictional properties and the inertial and elastic properties of the system.
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Drignon, M. J., Bechon, T., Arbaret, L., Burgisser, A., Komorowski, J. C., Martel, C., et al. (2016). Preexplosive conduit conditions during the 2010 eruption of Merapi volcano (Java, Indonesia). Geophysical Research Letters, 43(22), 11595–11602.
Résumé: The 2010 eruption is the largest explosive event at Merapi volcano since 1872. The high energy of the initial 26 October explosions cannot be explained by simple gravitational collapse, and the paroxysmal explosions were preceded by the growth of a lava dome not large enough to ensure significant pressurization of the system. We sampled pumice from these explosive phases and determined the preexplosive depths of the pumices by combining textural analyses with glass water content measurements. Our results indicate that the magma expelled was tapped from depths of several kilometers. Such depths are much greater than those involved in the pre-2010 effusive activity. We propose that the water-rich magma liberated enough gas to sustain the explosivity. Our results imply that the explosive potential of volcanoes having dome-forming, effusive activity is linked to the depth from which fresh magma can be evacuated in a single explosion, regardless of the evacuated volume.
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Dujardin, A., Causse, M., Courboulex, F., & Traversa, P. (2016). Simulation of the Basin Effects in the Po Plain During the Emilia-Romagna Seismic Sequence (2012) Using Empirical Green's Functions. Pure And Applied Geophysics, 173(6), 1993–2010.
Résumé: The two main earthquakes that occurred in 2012 (May 20 and 29) in the Reggio-Emiliano region (Northern Italy) were relatively small (Mw 6.1 and Mw 5.9) but they generated unexpected damages in a large area around the epicenter. On some stations, the observed seismic levels exceeded design levels recommended by the EC8 seismic code for buildings and civil engineering works. The ground motions generated by the two mainshocks have specific characteristics: the waveforms are mainly controlled by surface waves generated by the deep sedimentary Po plain, by local site effects and also, on some stations, by non-linear behaviors. In this particular context, we test the ability of an empirical Green's function (EGF) simulation approach to reproduce the recorded seismograms in a large frequency band without any knowledge of the underground medium. We focus on the possibility to reproduce the strong surface waves generated by the basin at distances between 25 and 90 km. We choose to work on the second mainshock of the sequence (Mw 5.9), which occurred on May 29, 2012, because it is better recorded by the seismological networks than the May 20th first mainshock. We use a k-2 kinematic source model to generate a set of 100 slip distributions on the fault plane and choose the recordings of a close-by Mw 3.9 event as EGF. We then generate a set of broad-band seismograms (from 0.2 to 35 Hz) and compare them to the mainshock signals at 15 stations (Seismograms, Fourier spectra, PGA, PGV, duration, Stockwell Transforms) at epicentral distances from 5 to 160 km. We find that the main specific features of the signals are very well reproduced for all the stations within and beyond the basin. Nevertheless, at nearby stations, the PGA values are over-evaluated, which could be explained by the fact that non- linear effects are not taken into account in the simulation process. A better fit was found for a position of the nucleation point to the bottom west of the fault, that suggest a directivity effect of the rupture process of the May 29th event towards the North-East.
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Dumont, S., Socquet, A., Grandin, R., Doubre, C., & Klinger, Y. (2016). Surface displacements on faults triggered by slow magma transfers between dyke injections in the 2005-2010 rifting episode at Dabbahu-Manda-Hararo rift (Afar, Ethiopia). Geophysical Journal International, 204(1), 399–417.
Résumé: The rifting episode that occurred in Dabbahu-Manda-Hararo (Ethiopia) between 2005 and 2010 during which 14 dyke intrusions were emitted, was a unique opportunity to study interactions between tectonic deformation and magmatic processes. While magmatism has been shown to control primarily the spatial and temporal distribution of dyke intrusions during this accretion sequence, the role of faults in accommodating plate spreading in rift segments is poorly understood. During interdyking periods, transient ground deformation due to magma movement is generally observed. Investigating such a small-scale deformation and in particular the movement along faults during these periods will help understanding the factors that trigger fault movement in magmatic rifts. We analyse fault activity during three interdyking periods: 2006 December-June (d0-d1), 2007 January-July (d5-d6) and 2009 November-January (d10-d11). The time-space evolution of surface displacements along similar to 700 faults is derived from pairs of ascending and descending SAR interferograms. Surface slip distributions are then compared with codyking ground deformation fields. The results show that faults are mainly activated above the areas affected by magma emplacement during interdyking periods. A detailed analysis of brittle deformation during the six months following the 2005 September intrusion shows asymmetric deformation on the rift shoulders, with significant opening on faults located to the west of the dyke. We explain this feature by the activation of westward dipping pre-existing faults, with block rotations in between. In addition, we observe that the strip encompassing the activated faults narrows by 30 per cent from co- to interdyking period. This suggests that magma keeps migrating to shallower depths after the dyke intrusion. During a rifting episode, activation of faults in a pre-existing fracture network therefore seems to be mainly controlled by deep magma processes.
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Dupuy, B., Garambois, S., Asnaashari, A., Balhareth, H. M., Landro, M., Stovas, A., et al. (2016). Estimation of rock physics properties from seismic attributes – Part 2: Applications. Geophysics, 81(4), M55–M69.
Résumé: The estimation of quantitative rock physics properties is of great importance for reservoir characterization and monitoring in CO2 storage or enhanced oil recovery as an example. We have combined the high-resolution results of full-waveform inversion (FWI) methods with rock physics inversion. Because we consider a generic and dynamic rock physics model, our method is applicable to most kinds of rocks for a wide range of frequencies. The first step allows determination of viscoelastic effective properties, i.e., quantitative seismic attributes, whereas the rock physics inversion estimates rock physics properties (porosity, solid frame moduli, fluid phase properties, or saturation). This two-step workflow is applied to time-lapse synthetic and field cases. The sensitivity tests that we had previously carried out showed that it can be crucial to use multiparameter inputs to accurately recover fluid saturations and fluid properties. However, due to the limited data availability and difficulties in getting reliable multiparameter FWI results, we are limited to acoustic FWI results. The synthetic tests are conclusive even if they are favorable cases. For the first time-lapse fluid substitution synthetic case, we first characterize the rock frame parameters on the baseline model using P-wave velocity estimations obtained by acoustic FWI. Then, we obtain an accurate estimation of fluid bulk modulus from the time-lapse P-wave velocity. In the Marmousi synthetic case, the rock frame properties are accurately recovered for the baseline model, whereas the gas saturation change in the monitor model is not estimated correctly. On the field data example (time-lapse monitoring of an underground blowout in the North Sea), the estimation of rock frame properties gives results on a relatively narrow range, and we use this estimation as a starting model for the gas saturation inversion. We have found that the estimation of the gas saturation is not accurate enough, and the use of attenuation data is then required. However, the uncertainty on the estimation of baseline rock frame properties is not critical to monitor gas saturation changes.
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Dupuy, B., Garambois, S., & Virieux, J. (2016). Estimation of rock physics properties from seismic attributes – Part 1: Strategy and sensitivity analysis. Geophysics, 81(3), M35–M53.
Résumé: The quantitative estimation of rock physics properties is of great importance in any reservoir characterization. We have studied the sensitivity of such poroelastic rock physics properties to various seismic viscoelastic attributes (velocities, quality factors, and density). Because we considered a generalized dynamic poroelastic model, our analysis was applicable to most kinds of rocks over a wide range of frequencies. The viscoelastic attributes computed by poroelastic forward modeling were used as input to a semiglobal optimization inversion code to estimate poroelastic properties (porosity, solid frame moduli, fluid phase properties, and saturation). The sensitivity studies that we used showed that it was best to consider an inversion system with enough input data to obtain accurate estimates. However, simultaneous inversion for the whole set of poroelastic parameters was problematic due to the large number of parameters and their trade-off. Consequently, we restricted the sensitivity tests to the estimation of specific poroelastic parameters by making appropriate assumptions on the fluid content and/or solid phases. Realistic a priori assumptions were made by using well data or regional geology knowledge. We found that (1) the estimation of frame properties was accurate as long as sufficient input data were available, (2) the estimation of permeability or fluid saturation depended strongly on the use of attenuation data, and (3) the fluid bulk modulus can be accurately inverted, whereas other fluid properties have a low sensitivity. Introducing errors in a priori rock physics properties linearly shifted the estimations, but not dramatically. Finally, an uncertainty analysis on seismic input data determined that, even if the inversion was reliable, the addition of more input data may be required to obtain accurate estimations if input data were erroneous.
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El Goresy, A., Lin, Y., Miyahara, M., Gillet, P., Ohtani, E., Trieloff, M., et al. (2016). Metal Nodules In El3 And Eh3 Primitive Chondrites: Conglomerates Of Micro Pebble Metals With A Menagerie Of Sulfide Assemblages; Graphite Feathers And Various Sinoite Morphologies, Metal Clasts. No Evidence For Melting. Meteoritics & Planetary Science, 51, A245.
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Enescu, M., Nagy, K. L., & Manceau, A. (2016). Nucleation of mercury sulfide by dealkylation. Scientific Reports, 6, 39359.
Résumé: Metal sulfide minerals are assumed to form naturally at ambient conditions via reaction of a metallic element with (poly) sulfide ions, usually produced by microbes in oxygen-depleted environments. Recently, the formation of mercury sulfide (beta-HgS) directly from linear Hg(II)-thiolate complexes (Hg(SR)(2)) in natural organic matter and in cysteine solutions was demonstrated under aerated conditions. Here, a detailed description of this non-sulfidic reaction is provided by computations at a high level of molecular-orbital theory. The HgS stoichiometry is obtained through the cleavage of the S-C bond in one thiolate, transfer of the resulting alkyl group (R') to another thiolate, and subsequent elimination of a sulfur atom from the second thiolate as a thioether (RSR'). Repetition of this mechanism leads to the formation of RS-(HgS)(n)-R chains which may self-assemble in parallel arrays to form cinnabar (alpha-HgS), or more commonly, quickly condense to four-coordinate metacinnabar (beta-HgS). The mechanistic pathway is thermodynamically favorable and its predicted kinetics agrees with experiment. The results provide robust theoretical support for the abiotic natural formation of nanoparticulate HgS under oxic conditions and in the absence of a catalyst, and suggest a new route for the (bio) synthesis of HgS nanoparticles with improved technological properties.
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Fazio, A., D'Orazio, M., Cordier, C., & Folco, L. (2016). Target-projectile interaction during impact melting at Kamil Crater, Egypt. Geochimica Et Cosmochimica Acta, 180, 33–50.
Résumé: In small meteorite impacts, the projectile may survive through fragmentation; in addition, it may melt, and chemically and physically interact with both shocked and melted target rocks. However, the mixing/mingling between projectile and target melts is a process still not completely understood. Kamil Crater (45 m in diameter; Egypt), generated by the hypervelocity impact of the Gebel Kamil Ni-rich ataxite on sandstone target, allows to study the target-projectile interaction in a simple and fresh geological setting. We conducted a petrographic and geochemical study of macroscopic impact melt lapilli and bombs ejected from the crater, which were collected during our geophysical campaign in February 2010. Two types of glasses constitute the impact melt lapilli and bombs: a white glass and a dark glass. The white glass is mostly made of SiO2 and it is devoid of inclusions. Its negligible Ni and Co contents suggest derivation from the target rocks without interaction with the projectile (<0.1 wt% of projectile contamination). The dark glass is a silicate melt with variable contents of Al2O3 (0.84-18.7 wt%), FeOT (1.83-61.5 wt%), and NiO (< 0.01-10.2 wt%). The dark glass typically includes fragments (from few lm to several mm in size) of shocked sandstone, diaplectic glass, lechatelierite, and Ni-Fe metal blebs. The metal blebs are enriched in Ni compared to the Gebel Kamil meteorite. The dark glass is thus a mixture of target and projectile melts (11-12 wt% of projectile contamination). Based on recently proposed models for target-projectile interaction and for impact glass formation, we suggest a scenario for the glass formation at Kamil. During the transition from the contact and compression stage and the excavation stage, projectile and target liquids formed at their interface and chemically interact in a restricted zone. Projectile contamination affected only a shallow portion of the target rocks. The SiO2 melt that eventually solidified as white glass behaved as an immiscible liquid and did not interact with the projectile. During the excavation stage dark glass melt engulfed and coated the white glass melt, target fragments, and got stuck to iron meteorite shrapnel fragments. This model could also explain the common formation of white and dark glasses in small impact craters generated by iron bodies (e.g., Wabar). (C) 2016 Elsevier Ltd. All rights reserved.
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Fillon, C., Pedreira, D., van der Beek, P. A., Huismans, R. S., Barbero, L., & Pulgar, J. A. (2016). Alpine exhumation of the central Cantabrian Mountains, Northwest Spain. Tectonics, 35(2), 339–356.
Résumé: The Cantabrian Mountains extend along the Atlantic coast of northern Spain and are known to have experienced an Alpine phase of deformation, reactivating well-expressed Variscan structures. They form the westward continuation of the Pyrenean range and were similarly uplifted consequently to the convergence between the Iberian and European plates. Nevertheless, due to the scarcity of syntectonic sediments and structural markers in a large outcrop of Variscan basement, little is known about the precise timing and amount of the Alpine exhumation phase in the Cantabrian Mountains. We present a new low-temperature thermochronology data set, composed of nine apatite fission track (AFT) and six zircon (U-Th)/He (ZHe) ages, sampled along structurally well-constrained N-S profiles through the central part of the Cantabrian Mountains and complemented by 3-D thermokinematic modeling. The occurrence of Eocene-Oligocene AFT and ZHe ages in the center of the profiles allows us to frame the period of Alpine exhumation from 39 to 29Ma, at a rate of 0.24-0.3kmMyr(-1). Moreover, the reset ZHe ages imply significant burial of the samples, by up to 8-10km in the center of the range. Therefore, the Alpine exhumation phase was significant, and synchronous to the main phase of exhumation in the central Pyrenees, although exhumation rates were an order of magnitude lower. Three-dimensional thermokinematic modeling of the data confirms the timing of uplift of this area, but its resolution is limited by the relatively small number of reset ages over a large area.
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Finlay, C. C., Aubert, J., & Gillet, N. (2016). Gyre-driven decay of the Earth's magnetic dipole. Nature Communications, 7.
Résumé: Direct observations indicate that the magnitude of the Earth's magnetic axial dipole has decreased over the past 175 years; it is now 9% weaker than it was in 1840. Here we show how the rate of dipole decay may be controlled by a planetary-scale gyre in the liquid metal outer core. The gyre's meridional limbs on average transport normal polarity magnetic flux equatorward and reverse polarity flux poleward. Asymmetry in the geomagnetic field, due to the South Atlantic Anomaly, is essential to the proposed mechanism. We find that meridional flux advection accounts for the majority of the dipole decay since 1840, especially during times of rapid decline, with magnetic diffusion making an almost steady contribution generally of smaller magnitude. Based on the morphology of the present field, and the persistent nature of the gyre, the current episode of dipole decay looks set to continue, at least for the next few decades.
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Finlay, C. C., Olsen, N., Kotsiaros, S., Gillet, N., & Toffner-Clausen, L. (2016). Recent geomagnetic secular variation from Swarm and ground observatories as estimated in the CHAOS-6 geomagnetic field model. Earth Planets And Space, 68.
Résumé: We use more than 2 years of magnetic data from the Swarm mission, and monthly means from 160 ground observatories as available in March 2016, to update the CHAOS time-dependent geomagnetic field model. The new model, CHAOS-6, provides information on time variations of the core-generated part of the Earth's magnetic field between 1999.0 and 2016.5. We present details of the secular variation (SV) and secular acceleration (SA) from CHAOS-6 at Earth's surface and downward continued to the core surface. At Earth's surface, we find evidence for positive acceleration of the field intensity in 2015 over a broad area around longitude 90 degrees E that is also seen at ground observatories such as Novosibirsk. At the core surface, we are able to map the SV up to at least degree 16. The radial field SA at the core surface in 2015 is found to be largest at low latitudes under the India-South-East Asia region, under the region of northern South America, and at high northern latitudes under Alaska and Siberia. Surprisingly, there is also evidence for significant SA in the central Pacific region, for example near Hawaii where radial field SA is observed on either side of a jerk in 2014. On the other hand, little SV or SA has occurred over the past 17 years in the southern polar region. Inverting for a quasi-geostrophic core flow that accounts for this SV, we obtain a prominent planetary-scale, anticyclonic, gyre centred on the Atlantic hemisphere. We also find oscillations of non-axisymmetric, azimuthal, jets at low latitudes, for example close to 40 degrees W, that may be responsible for localized SA oscillations. In addition to scalar data from Orsted, CHAMP, SAC-C and Swarm, and vector data from Orsted, CHAMP and Swarm, CHAOS-6 benefits from the inclusion of along-track differences of scalar and vector field data from both CHAMP and the three Swarm satellites, as well as east-west differences between the lower pair of Swarm satellites, Alpha and Charlie. Moreover, ground observatory SV estimates are fit to a Huber-weighted rms level of 3.1 nT/year for the eastward components and 3.8 and 3.7 nT/year for the vertical and southward components. We also present an update of the CHAOS high-degree lithospheric field, making use of along-track differences of CHAMP scalar and vector field data to produce a new static field model that agrees well with the MF7 field model out to degree 110.
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Francois, C., de Sigoyer, J., Pubellier, M., Bailly, V., Cocherie, A., & Ringenbach, J. C. (2016). Short-lived subduction and exhumation in Western Papua (Wandamen peninsula): Co-existence of HP and HT metamorphic. rocks in a young geodynamic setting. Lithos, 266, 44–63.
Résumé: Understanding processes of formation of accretionary wedges requires studying young and well preserved examples. The Lengguru wedge (West Papua) is younger than 10 Myr and is a result of oblique and fast subduction (11 cm/yr) of the Bird's Head (a part of the Australian margin beneath the Melanesian Arc). Thus, the rapid formation of this wedge (actually a Fold and Thrust Belt) may be attributed to a single tectonic event. High pressure (HP) metabasic and metasedimentary rocks have been discovered in the core of the wedge in the Wandamen peninsula. Locally, these rocks are overprinted by migmatization during the decompression, Field relationships indicate that migmatites and anatectic leucogranite crosscut the HP metamorphic rocks. This paper reports characterization of petrology and thermobarometry of metasediments and metabasic samples, all included in a former melange-type rock association, as well as geochronology of metasediments. Pressure-Temperature (P-T) conditions highlight two stages of metamorphism within a small time bracket In metasediments, a first stage of relatively HP (similar to 13-17 kbar) is observed as attested by a first paragenesis of garnet-kyanite-phengite. Garnet, kyanite and phengite are then destabilized in favor of biotite during the decompression (5-12 kbar and >550 degrees C). Late fractures filled with chlorite and a second generation of white mica crosscut the foliation (<7 kbar and 500-600 degrees C). In metabasic rocks, the peak of pressure is reached from 17 to 23 kbar and from 700 to 800 degrees C. Geochronological study was conducted using U-Pb dating (LA-MC-ICPMS) on zircons from the metasedimentary and migmatitic rocks. Some zircon cores often present high Th/U ratio typical for magmatic origin, as confirmed by trace element signature of metasediments, and recorded ages older than 300 Ma, witness of the activity of a volcanic arc on the former margin of the Australian craton. Most other zircons present a low Th/U ratio attesting their metamorphic origin, confirmed by inclusions of kyanite. The metamorphic zircons are dated between 5.61 +/- 0.04 Ma and 8.1 +/- 1.1 Ma. These very young metamorphic ages attest for a rapid subduction and exhumation event (C) 2016 Elsevier B.V. All rights reserved.
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Frank, W. B., Shapiro, N. M., Husker, A. L., Kostoglodov, V., & Campillo, M. (2016). Repeating seismicity in the shallow crust modulated by transient stress perturbations. Tectonophysics, 687, 105–110.
Résumé: Recent studies have reported seismic phenomena that are modulated by small stress perturbations (similar to 10 kPa), revealing their critically stressed nature. Such observations have been principally limited to plate interfaces with their occurrence linked to high fluid pore-pressure. In this study, we report observations of nine repeating seismic sources in the shallow crust in Guerrero, Mexico that emit events at rates comparable to other seismic phenomena in low stress environments. Testing their susceptibility to small stress perturbations, we find that all nine sources appear to be modulated by mining activity, tides, and a large slow slip event (Mw 7.5). Our results suggest that the fault conditions necessary for low effective stress seismicity can occur away from plate interfaces. (C) 2016 Elsevier B.V. All rights reserved.
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Frank, W. B., Shapiro, N. M., Husker, A. L., Kostoglodov, V., Gusev, A. A., & Campillo, M. (2016). The evolving interaction of low-frequency earthquakes during transient slip. Science Advances, 2(4).
Résumé: Observed along the roots of seismogenic faults where the locked interface transitions to a stably sliding one, low-frequency earthquakes (LFEs) primarily occur as event bursts during slow slip. Using an event catalog from Guerrero, Mexico, we employ a statistical analysis to consider the sequence of LFEs at a single asperity as a point process, and deduce the level of time clustering from the shape of its autocorrelation function. We show that while the plate interface remains locked, LFEs behave as a simple Poisson process, whereas they become strongly clustered in time during even the smallest slow slip, consistent with interaction between different LFE sources. Our results demonstrate that bursts of LFEs can result from the collective behavior of asperities whose interaction depends on the state of the fault interface.
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Fritsch, E., Juillot, F., Dublet, G., Fonteneau, L., Fandeur, D., Martin, E., et al. (2016). An alternative model for the formation of hydrous Mg/Ni layer silicates ('deweylite'/'garnierite') in faulted peridotites of New Caledonia: I. Texture and mineralogy of a paragenetic succession of silicate infillings. European Journal Of Mineralogy, 28(2), 295–311.
Résumé: Detailed textural and mineralogical investigations carried out in mineralized veins of the New Caledonian peridotites reveal three major periods of infilling and alteration closely linked to post-obduction tectonic activity. The first two periods of infillings are related to the alteration of hydrothermal serpentines, mostly found in the thick serpentine network of the peridotites, into fine-grained serpentine-like residues and newly formed talc-like minerals of weak but variable swelling capacity. The alteration of serpentine into talc-like minerals is limited during the first period of infilling and almost completed during the second one. In some fault zones of the New Caledonian peridotites, talc-like minerals are replaced by sepiolite. Such alterations are reported in both the Ni-free and Ni-rich zones of the infillings (i.e. in the white 'deweylite' and greenish 'garnierite' of the fault zones, respectively). They led to the individualization of the hydrous Mg/Ni silicate ore, which is nowadays found in fractures of the saprock and saprolite units of thick lateritic profiles. The third and last period of infilling is assigned to the accumulation of silica and crystallization of quartz. This succession of clay minerals (serpentine-like and talc-like minerals, sepiolite) and quartz in the infillings is interpreted as the result of sequential exportation of Mg and redistribution of Ni along the reactivated faults, generating periods of increasing Si activity in solutions. In this paragenetic model, the meteoric water infiltrating repeatedly the permeable network created by post-obduction tectonic activity would have interacted with a low-temperature hydrothermal field following the exhumation and cooling of the ophiolite nappe. In the less permeable parts of the fault network, restricted leaching conditions would have generated greater alkalinity in solutions and therefore favored the crystallization of sepiolite instead of finely divided talc-like minerals.
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Gao, L., Brossier, R., & Virieux, J. (2016). Using time filtering to control the long-time instability in seismic wave simulation. Geophysical Journal International, 204(3), 1443–1461.
Résumé: Long-time instabilities have been observed in various scenarios of numerical simulation for seismic wave propagation. They appear as slowly magnifying spurious oscillations in the seismograms at the late stage of the simulation. Their magnifying speed is typically much slower than the magnifying speed observed when the Courant-Friedrichs-Lewy condition is violated. The simulations can therefore continue to proceed for a relatively long period without floating-point overflow. The impact of the long-time instabilities on the simulation accuracy at the early stage can be negligible in some cases. In existing literatures, spatial-filtering techniques that, in principle, average the solution within certain spatial range at the same time level are typically utilized to control the long-time instability. In this paper, we present an alternative time-filtering approach that, in principle, averages the solution at different time levels of the same spatial location to control the long-time instability. Comparing with the spatial filtering, the advantages of this time-filtering approach lie in its flexibility, particularly when boundaries or interfaces are involved, its simplicity and low additional arithmetic operations, at the expense of extra memory cost. When application of the time filtering is localized to regions where long-time instabilities are emitted from, for example, a boundary or an interface layer, the additional cost is negligible when compared with the cost of wave simulation. For linear wave equations, this time-filtering approach can be understood as the introduction of artificial diffusion. Its application has impact on the accuracy of the solution and the restriction of the time step size. We present an indicator-based approach to adjust the filtering parameters both spatially and temporally, in order to provide the best trade-off between accuracy and stability. The indicator is calculated heuristically by monitoring the spurious oscillation as the simulation evolves in time.
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Gao, L. F., Tan, X. S., & Chung, E. T. (2016). Application of the generalized multiscale finite element method in parameter-dependent PDE simulations with a variable-separation technique. Journal Of Computational And Applied Mathematics, 300, 183–191.
Résumé: In this paper, we combine the generalized multiscale finite element method (GMsFEM) with a variable-separation technique to tackle the parameter-dependent partial differential equations (PDEs). The solution is approximated via an expansion series, each term of which lives in the tensor product of the parametric space and the spatial space. Governing equations for each term are derived based on energy minimization. An iterative algorithm is presented to obtain the expansion series, which requires solving parameter independent PDEs repeatedly. We then present the procedure of GMsFEM and apply it to these parameter-independent PDEs. Numerical examples are presented to demonstrate the effectiveness of the expansion series and the computational efficiency brought by GMsFEM. (C) 2015 Elsevier B.V. All rights reserved.
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Garambois, S., Legchenko, A., Vincent, C., & Thibert, E. (2016). Ground-penetrating radar and surface nuclear magnetic resonance monitoring of an englacial water-filled cavity in the polythermal glacier of Tete Rousse. Geophysics, 81(1), WA131–WA146.
Résumé: In polythermal glaciers, specific climatic, topographic, and exposure conditions may lead to the formation of englacial lakes that can produce catastrophic effects downstream in the event of abrupt natural drainage. We have determined how a combination of ground-penetrating radar (GPR) and surface nuclear magnetic resonance (SNMR) surveys helped to locate and visualize the evolution of a water-filled cavity within the Tete Rousse glacier (French Alps). We have used GPR results to delineate the roof of the cavity and monitor the cavity deformation caused by artificial drainage. Because the glacier bed and cavity have complex 3D geometries, we needed dense acquisition lines and 3D GPR views to qualitatively identify out-of-plane reflections. This 3D approach made it possible to establish a precise map of the glacier bed topography, the accuracy of which was verified against borehole observations. Then, repetitive GPR measurements were used to obtain a quantitative estimate of the vertical deflection of the cavity's roof and changes in crevasse geometry observed in response to the decrease in the water pressure when 47; 800 m(3) of water was drained by pumping. We have used 3D SNMR imaging to locate water accumulation zones within the glacier and to estimate the volume of accumulated water. The SNMR monitoring revealed that in two years, the cavity lost approximately 73% of its initial volume, with 65% lost after the first drainage. Knowledge of the water contained in the ice provided a better understanding of GPR images and thus a more reliable interpretation of GPR data. However, SNMR imaging had a much lower resolution in comparison with GPR, and consequently GPR allowed a more accurate study of the evolution of cavity geometry caused by consecutive drainage and refilling. This study demonstrated the value of combining GPR data with SNMR data for the study of polythermal glaciers.
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Garenne, A., Beck, P., Montes-Hernandez, G., Brissaud, O., Schmitt, B., Quirico, E., et al. (2016). Bidirectional reflectance spectroscopy of carbonaceous chondrites: Implications for water quantification and primary composition. Icarus, 264, 172–183.
Résumé: In this study, we measured bidirectional reflectance spectra (0.5-4.0 μm) of 24 CMs, five CRs, one Cl, one CV, and one C2 carbonaceous chondrites. These meteorites are known to have experienced an important variability in their relative degrees of aqueous alteration degree (Rubin et al. [2007]. Geochim. Cosmochim. Acta 71, 2361-2382; Howard et al. [2009]. Geochim. Cosmochim. Acta 73, 4576-4589; Howard et al. [2011]. Geochim. Cosmochim. Acta 75, 2735-2751; Alexander et al. [2013]. Geochim. Cosmochim. Acta 123, 244-260). These measurements were performed on meteorite powders inside an environmental cell under a primary vacuum and heated at 60 degrees C in order to minimize adsorbed terrestrial water. This protocol allows controlling of atmospheric conditions (i.e. humidity) in order to avoid contamination by terrestrial water. We discuss various spectral metrics (e.g. reflectance, band depth, single-scattering albedo,...) in the light of recent bulk composition characterization (Howard et al. [2009]. Geochim. Cosmochim. Acta 73, 4576-4589; Howard et al. [2015]. Geochim. Cosmochim. Acta 149, 206-222; Alexander et al. [2012]. Science 337, 721; Beck et al. [2014]. Icarus 229, 263-277; Garenne et al. [2014]. Geochim. Cosmochim. Acta 137, 93-112). This study reveals variability of reflectance among meteorite groups. The reflectance is not correlated with carbon or hydrogen abundance neither with measured grain size distribution. We suggest that it is rather controlled by the nature of accreted components, in particular the initial matrix/chondrule proportion. Band depth, integrated band depth, mean optical path length, normalized optical path length, effective single-particle absorption thickness were calculated on the so called 3-mu m band for reflectance spectra and for single scattering albedo spectra. They were compared with hydrated phase proportions from previous study on the same meteorites by thermogravimetric analyses and infrared spectroscopy in transmission. We find that normalized optical path length (NOPL) is the most appropriate to quantify water abundance, with an absolute error of about 5 wt.%. These datasets also reveal a variability of the band shape between 2.8 and 2.9 μm, which is interpreted as reflecting variation in the chemical composition and structure of phyllosilicates. This chemical variation could also be used to quantify the aqueous alteration degree between meteorite groups. The combination of reflectance at 2 μm and the depth of 3-mu m band can be combined, to classify carbonaceous chondrites in reflectance in term of primary composition (e.g. matrix/chondrule ratio, carbon content) and secondary processes (e.g. aqueous alteration, thermal metamorphism). This could be used to decipher the nature of aqueous alteration in C-complex asteroids. (C) 2015 Elsevier Inc. All rights reserved.
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Garofalo, F., Foti, S., Hollender, F., Bard, P. Y., Cornou, C., Cox, B. R., et al. (2016). InterPACIFIC project: Comparison of invasive and non-invasive methods for seismic site characterization. Part II: Inter-comparison between surface-wave and borehole methods. Soil Dynamics And Earthquake Engineering, 82, 241–254.
Résumé: The InterPACIFIC project was aimed at assessing the reliability, resolution, and variability of geophysical methods in estimating the shear-wave velocity profile for seismic ground response analyses. Three different subsoil conditions, which can be broadly defined as soft-soil, stiff-soil, and hard-rock, were investigated. At each site, several participants performed and interpreted invasive measurements of shear wave velocity (Vs) and compression wave velocity (Vp) in the same boreholes. Additionally, participants in the project analysed a common surface-wave dataset using their preferred strategies for processing and inversion to obtain Vs profiles. The most significant difference between the invasive borehole methods and non-invasive surface wave methods is related to resolution of thin layers and abrupt contrasts, which is inherently better for invasive methods. However, similar variability is observed in the estimated invasive and non-invasive Vs profiles, underscoring the need to account for such uncertainty in site response studies. V-s,V-30 estimates are comparable between invasive and non-invasive methods, confirming that the higher resolution provided by invasive methods is quite irrelevant for computing this parameter. (C) 2015 Elsevier Ltd. All rights reserved.
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Gasc, J., Brunet, F., Brantut, N., Corvisier, J., Findling, N., Verlaguet, A., et al. (2016). Effect of Water Activity on Reaction Kinetics and Intergranular Transport: Insights from the Ca(OH)(2) + MgCO3 -> CaCO3 + Mg(OH)(2) Reaction at 1.8 GPa. Journal Of Petrology, 57(7), 1389–1407.
Résumé: The kinetics of the irreversible reaction Ca(OH)(2)+MgCO3 -> CaCO3+Mg(OH)(2) were investigated at high pressures and temperatures relevant to metamorphic petrology, using both in situ synchrotron X-ray diffraction and post-mortem analysis of reaction rim growth on recovered samples. Reaction kinetics are found to strongly depend on water content; comparable bulk-reaction kinetics are obtained under water-saturated (excess water, c. 10 wt %) and under intermediate (0.1-1wt % water) conditions when temperature is increased by c. 300 K. In contrast, similar reaction kinetics were observed at similar to 673 K and 823 K between intermediate and dry experiments, respectively, where dry refers to a set of experiments with water activity below 1.0 (no free water), as buffered by the CaO-Ca(OH)(2) assemblage. Given the activation energies at play, this gap-corresponding to the loss of no more than 1 wt % of water by the assemblage-leads to a difference of several orders of magnitude in reaction kinetics at a given temperature. Further analysis, at the microscopic scale, of the intermediate and dry condition samples, shows that intergranular transport of calcium controls the reaction progress. Grain boundary diffusivities could be retrieved from the classic treatment of reaction rim growth rate. In turn, once modeled, this rate was used to fit the bulk kinetic data derived from X-ray powder diffraction, offering an alternative means to derive calcium diffusivity data. Based on a comparison with effective grain boundary data for Ca and Mg from the literature, it is inferred that both dry and intermediate datasets are consistent with a water-saturated intergranular medium with different levels of connectivity. The very high diffusivity of Ca in the CaCO3+Mg(OH)(2) rims, in comparison with that of Mg in enstatite rims found by earlier workers, emphasizes the prominent role of the interactions between diffusing species and mineral surfaces in diffusion kinetics. Furthermore, we show that the addition of water is likely to change the relative diffusivity of Mg and Ca in carbonate aggregates. From a qualitative point of view, we confirm, in a carbonate-bearing system, that small water content variations within the 0-1wt % range have tremendous effects on both intergranular transport mechanisms and kinetics. We also propose that the water content dependent diffusivity of major species (Mg, Ca) in low-porosity metamorphic rocks is strongly dependent on the interaction between diffusing species and mineral surfaces. This parameter, which will vary from one rock-type to another, needs also to considered when extrapolating (P, T, t, xH(2)O) laboratory diffusion data to metamorphic processes.
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Gaudin, D., Beauducel, F., Coutant, O., Delacourt, C., Richon, P., de Chabalier, J. B., et al. (2016). Mass and heat flux balance of La Soufriere volcano (Guadeloupe) from aerial infrared thermal imaging. Journal Of Volcanology And Geothermal Research, 320, 107–116.
Résumé: La Soufriere of Guadeloupe is an active volcano of Lesser Antilles that is closely monitored due to a high eruptive hazard potential. Since 1992 it exhibits a medium-level but sustained background hydrothermal activity with low-energy and shallow seismicity, hot springs temperature increase and high flux acidic gas fumaroles at the summit. The problem of estimating the heat balance and quantifying the evolution of hydrothermal activity has become a key challenge for surveillance. This work is the first attempt of a global mapping and quantification of La Soufriere thermal activity performed in February 2010 using aerial thermal infrared imagery. After instrument calibration and data processing, we present a global map of thermal anomalies allowing to spot the main active sites: the summit area (including the fumaroles of Tarissan Pit and South Crater), the Ty Fault fumarolic zone, and the hot springs located at the vicinity of the dome. In a second step, we deduce the mass and the energy fluxes released by the volcano. In particular, we propose a simple model of energy balance to estimate the mass flux of the summit fumaroles from their brightness temperature and size. In February 2010, Tarissan Pit had a 22.8 +/- 8.1 kg s(-1) flux (1970 +/- 704 tons day(-1)), while South Crater vents had a total of 19.5 +/- 4.0 kg s(-1) (1687 +/- 348 tons day(-1)). Once converted into energy flux, summit fumaroles represent 98% of the 106 +/- 30 MW released by the volcano, the 2% remaining being split between the hot springs and the thermal anomalies at the summit and at the Ty Fault fumarolic zone. These values are in the high range of the previous estimations, highlighting the short-term variability of the expelled fluxes. Such a heat flux requires the cooling of 1500 m(3) of magma per day, in good agreement with previous geochemical studies. (C) 2016 Elsevier B.V. All rights reserved.
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Gavilan, L., Jager, C., Simionovici, A., Lemaire, J. L., Sabri, T., Foy, E., et al. (2016). Hard X-ray irradiation of cosmic silicate analogs: structural evolution and astrophysical implications. Astronomy & Astrophysics, 587.
Résumé: Context. Protoplanetary disks, interstellar clouds, and active galactic nuclei contain X-ray-dominated regions. X-rays interact with the dust and gas present in such environments. While a few laboratory X-ray irradiation experiments have been performed on ices, X-ray irradiation experiments on bare cosmic dust analogs have been scarce up to now. Aims. Our goal is to study the effects of hard X-rays on cosmic dust analogs via in situ X-ray diffraction. By using a hard X-ray synchrotron nanobeam, we seek to simulate cumulative X-ray exposure on dust grains during their lifetime in these astrophysical environments and provide an upper limit on the effect of hard X-rays on dust grain structure. Methods. We prepared enstatite (MgSiO3) nanograins, which are analogs to cosmic silicates, via the melting-quenching technique. These amorphous grains were then annealed to obtain polycrystalline grains. These were characterized via scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) before irradiation. Powder samples were prepared in X-ray transparent substrates and were irradiated with hard X-rays nanobeams (29.4 keV) provided by beamline ID16B of the European Synchrotron Radiation Facility (Grenoble). X-ray diffraction images were recorded in transmission mode, and the ensuing diffractograms were analyzed as a function of the total X-ray exposure time. Results. We detected the amorphization of polycrystalline silicates embedded in an organic matrix after an accumulated X-ray exposure of 6.4 x 10(27) eV cm(-2). Pure crystalline silicate grains (without resin) do not exhibit amorphization. None of the amorphous silicate samples (pure and embedded in resin) underwent crystallization. We analyze the evolution of the polycrystalline sample embedded in an organic matrix as a function of X-ray exposure. Conclusions. Loss of diffraction peak intensity, peak broadening, and the disappearance of discrete spots and arcs reveal the amorphization of the resin embedded (originally polycrystalline) silicate sample. We explore the astrophysical implications of this laboratory result as an upper limit to the effect of X-rays on the structure of cosmic silicates.
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Geremia-Nievinski, F., Silva, M. F. E., Boniface, K., & Monico, J. F. G. (2016). GPS Diffractive Reflectometry: Footprint of a Coherent Radio Reflection Inferred From the Sensitivity Kernel of Multipath SNR. Ieee Journal Of Selected Topics In Applied Earth Observations And Remote Sensing, 9(10), 4884–4891.
Résumé: The validation of remote sensing environmental estimates requires knowledge of their spatial extent and resolution. Here, we consider coherent radio reflections routinely observed in ground-based global positioning system (GPS) reflectometry. Their footprint is often conceptualized in terms of the specular point (SP) and the first Fresnel zone (FFZ). Such infinitesimal point and finite zone can be generalized into a spatially continuous sensitivity kernel (SK). The SK represents a diffraction pattern, as the importance of each surface portion depends on its scattered field contribution in power and phase. We measured the SK of a GPS radio reflection under bipath reception conditions. The SK exhibited oscillations along the plane of incidence. The envelope of oscillations peaked near the SP and persisted in its decay well beyond the FFZ. Within the FFZ, sensitivity was skewed toward the antenna. This experiment suggests the feasibility of overcoming the diffraction limit and resolving features smaller than the FFZ with the exploitation of GPS diffraction patterns.
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Gimbert, F., Geffard, A., Guedron, S., Dominik, J., & Ferrari, B. J. D. (2016). Mercury tissue residue approach in Chironomus riparius: Involvement of toxicokinetics and comparison of subcellular fractionation methods. Aquatic Toxicology, 171, 1–8.
Résumé: Along with the growing body of evidence that total internal concentration is not a good indicator of toxicity, the Critical Body Residue (CBR) approach recently evolved into the Tissue Residue Approach (TRA) which considers the biologically active portion of metal that is available to contribute to the toxicity at sites of toxic action. For that purpose, we examined total mercury (Hg) bioaccumulation and subcellular fractionation kinetics in fourth stage larvae of the midge Chironomus riparius during a four-day laboratory exposure to Hg-spiked sediments and water. The debris (including exoskeleton, gut contents and cellular debris), granule and organelle fractions accounted only for about 10% of the Hg taken up, whereas Hg concentrations in the entire cytosolic fraction rapidly increased to approach steady-state. Within this fraction, Hg compartmentalization to metallothionein-like proteins (MTLP) and heat-sensitive proteins (HSP), consisting mostly of enzymes, was assessed in a comparative manner by two methodologies based on heat-treatment and centrifugation (HT&C method) or size exclusion chromatography separation (SECS method). The low Hg recoveries obtained with the HT&C method prevented accurate analysis of the cytosolic Hg fractionation by this approach. According to the SECS methodology, the Hg-bound MTLP fraction increased linearly over the exposure duration and sequestered a third of the Hg flux entering the cytosol. In contrast, the HSP fraction progressively saturated leading to Hg excretion and physiological impairments. This work highlights several methodological and biological aspects to improve our understanding of Hg toxicological bioavailability in aquatic invertebrates. (C) 2015 Elsevier B.V. All rights reserved.
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Giraud, F., Mattioli, E., Lopez-Otalvaro, G. E., Lecuyer, C., Sucheras-Marx, B., Almeras, Y., et al. (2016). Deciphering processes controlling mid-Jurassic coccolith turnover. Marine Micropaleontology, 125, 36–50.
Résumé: The Middle Jurassic is characterized by major changes within the fossil coccolithophorid community, with a transition from Lotharingius-dominated to Watznaueria-dominated assemblages, concomitant with a significant increase in the pelagic carbonate production. The mechanisms that triggered this overturn remain poorly understood. Here, we present a compilation (new and previously published data) of Lotharingius and Watznaueria abundances through the Early -Middle Jurassic transition. Alongside this, trends in newly-acquired and literature-derived carbon and oxygen isotope data were used to represent paleoceanographic indicators, such as nutrient and temperature changes. The nannofossil data show a rapid (around 1.5 Myr) turnover around the Aalenian-Bajocian transition. Across the Aalenian/Bajocian boundary, assemblages dominated by Lotharingius spp. give way to assemblages dominated by Watznaueria spp., coinciding with a peak in a particular morphological group of Watznaueria (species with a cross in the central area). The proliferation of this morphogroup occurred during a time of oceanic opening and rearrangement of ocean circulation. This led on to the evolution of pioneering coccolithophorid taxa, but also to extinctions in several marine groups. In the Early Bajocian, the proliferation of two other morphogroups (Watznaueria without a central-area structure and Watznaueria with a bar) corresponds to the major diversification of Watznaueria, and the beginning of its Mesozoic dominance. The Watznaueria diversification and dominance are associated with radiation in other marine groups, and these biotic changes occurred during a time of putative enhanced oceanic fertility and relatively low temperatures. This study suggests that restructuring of fossil coccolithophorid communities may be favored during short turnover intervals related to major paleoceanographic change. (C) 2016 Elsevier B.V. All rights reserved.
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Graham, S., DeMets, C., Cabral-Cano, E., Kostoglodov, V., Rousset, B., Walpersdorf, A., et al. (2016). Slow Slip History for the MEXICO Subduction Zone: 2005 Through 2011. Pure And Applied Geophysics, 173(10-11), 3445–3465.
Résumé: To further our understanding of the seismically hazardous Mexico subduction zone, we estimate the first time-dependent slip distributions and Coulomb failure stress changes for the six major slow slip events (SSEs) that occurred below Mexico between late 2005 and mid-2011. Slip dist ributions are the first to be estimated from all continuous GPS data in central and southern Mexico, which better resolves slow slip in space and time than was previously possible in this region. Below Oaxaca, slip during previously un-modeled SSEs in 2008/9 and 2010/11 extended farther to the west than previous SSEs. This constitutes the first evidence that slow slip accounts for deep slip within a previously noted gap between the Oaxaca and Guerrero SSE source regions. The slip that we estimate for the two SSEs that originated below Guerrero between 2005 and 2011 agrees with slip estimated in previous, mostly static-offset SSE modeling studies; however, we show that both SSEs migrated eastward toward the Oaxaca SSE source region. In accord with previous work, we find that slow slip below Guerrero intrudes up-dip into the potentially seismogenic region, presumably accounting for some of the missing slip within the well-described Guerrero seismic gap. In contrast, slow slip below Oaxaca between 2005 and 2011 occurred mostly down-dip from the seismogenic regions defined by the rupture zones of large thrust earthquakes in 1968 and 1978 and released all of the slip deficit that accumulated in the down-dip region during this period.
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Grand'Homme, A., Janots, E., Bosse, V., Seydoux-Guillaume, A. M., & Guedes, R. D. (2016). Interpretation of U-Th-Pb in-situ ages of hydrothermal monazite-(Ce) and xenotime-(Y): evidence from a large-scale regional study in clefts from the western alps. Mineralogy And Petrology, 110(6), 787–807.
Résumé: In eleven Alpine clefts of the western Alps, in-situ dating of monazite-(Ce) and xenotime-(Y) has been attempted to gain insights on possible disturbances of the geochronological U-Th-Pb systems and age interpretations in hydrothermal conditions. In most clefts, monazite-(Ce) in-situ Pb-208/Th-232 dating using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) yields well-resolved ages (with errors typically < 0.3 Ma, quoted at the 2 sigma level), indicative of a short duration monazite-(Ce) growth. However, monazite-(Ce) dating demonstrates two successive episodes of growth separated by several million years within two single clefts. Only in one cleft, complex age mixture in a porous and complex zoned monazite-(Ce) suggests disturbance of the Pb-208/Th-232 ages due to replacement by dissolution-precipitation processes. While some U-Pb ages are coherent with the Pb-208/Th-232 ages, U-Pb ages are generally disturbed by significant Pb-206 excess in monazite-(Ce) with high Th/U ratio (> 100). Xenotime-(Y) has remarkably high Th/U ratios and U-Pb dating is also disturbed by Pb-206 excess, whereas Pb-208/Th-232 dating gave well-resolved ages (34.9 +/- A 0.5 Ma), close to but higher than the monazite-(Ce) age obtained in the same cleft (32.3 +/- A 0.3 Ma). Correlation of the monazite-(Ce) U-Th-Pb age dataset with other geochronological data suggests for monazite-(Ce) precipitation at periods of high tectonic activity. In the external massifs, monazite-(Ce) dating confirms a polyphased transpressive regime with activity periods around 13-11 Ma and 8-6 Ma. Older monazite-(Ce) ages in the Argentera massif (20.6 +/- A 0.3 Ma) are consistent with the regional diachronism in the western external Alps. In the 2 clefts of the internal massifs, monazite-(Ce) dating provides first ages of hydrothermal activity: the monazite-(Ce) age at 32.3 +/- A 0.3 Ma coincides with the exhumation along the Penninic front, but the monazite-(Ce) age at 23.3 +/- A 0.2 Ma is complex to attribute to a specific deformation stage.
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Grand'Homme, A., Janots, E., Seydoux-Guillaume, A. M., Guillaume, D., Bosse, V., & Magnin, V. (2016). Partial resetting of the U-Th-Pb systems in experimentally altered monazite: Nanoscale evidence of incomplete replacement. Geology, 44(6), 431–434.
Résumé: Alteration experiments on natural monazite crystals (Manangotry standard, Madagascar) under alkali conditions at 300, 400, 500 and 600 degrees C and 200 MPa were conducted to clarify mechanisms behind incomplete resetting of U-Th-Pb geochronological systems in monazite replaced by dissolution and precipitation processes. Above 400 degrees C, experimental products show typical replacement textures: a compositionally distinct monazite rim, referred as altered rim, surrounds the primary monazite (Mnz1). Isotopic and electron microprobe U-Th-Pb in situ dating of the altered rim yields intermediate ages between pristine monazite (555 Ma) and complete experimental resetting (0 Ma). Lead is systematically detected in altered rims, with concentration decreasing from 400 degrees C to 600 degrees C. The origin of incomplete resetting is elucidated with transmission electron microscope images that reveal an incomplete replacement of Mnz1 by a secondary monazite (Mnz2) within the altered rim. With increasing temperature, the size and volume of the Mnz2 within the altered rim become more important. Because no structural Pb or Pb nanoinclusions were observed, Pb in the altered rim is attributed to the Mnz1 component. Partial resetting of U-Th-Pb systems depends on the nanomixture of different Mnz1 proportions in the analyzed volume, and explains the higher rejuvenation at 600 degrees C than at lower temperatures. Although microanalytical techniques have the spatial resolution to date micrometer-sized rims, they are unable to resolve a nanoscale mixture of pristine and secondary monazite that could occur in altered rims formed by fluid-driven replacement, especially at low temperatures. Porosity and/or inclusions and complex age scattering in zoned monazite are significant markers that can indicate a possible nano-sized partial replacement.
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Gresse, M., Vandemeulebrouck, J., Byrdina, S., Chiodini, G., & Bruno, P. P. (2016). Changes in CO2 diffuse degassing induced by the passing of seismic waves. Journal Of Volcanology And Geothermal Research, 320, 12–18.
Résumé: Solfatara crater, located in the Campi Flegrei caldera, is a volcano with one of the highest degassing rates on Earth, more than 1500 t of CO2 released by diffusion or through vents. Here, we investigated how this gas release can be disrupted by the passage of seismic waves. We performed continuous soil CO2 flux measurements during the propagation of seismic vibrations in the range of 5 Hz to 200 Hz induced by a vibroseis truck. The CO2 flux was continuously recorded using the accumulation chamber method. The data show a temporary and drastic (up to two-fold) increase in CO2 flux exclusively during the vibrations, before returning to the initial flux values. These transient variations are interpreted as fluidization of the surficial granular layer that releases the stored gas. Similar degassing processes might occur at a larger scale during earthquakes, to cause temporary increases in the total gas outflow in volcanic or tectonic areas. Our findings are useful to better assess and monitor the potential hazard from sudden CO2 flux release during earthquakes as several cases of intoxication or death have already been related to volcanic degassing. (C) 2016 Elsevier B.V. All rights reserved.
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Guedron, S., Amouroux, D., Sabatier, P., Desplanquee, C., Develle, A. L., Barre, J., et al. (2016). A hundred year record of industrial and urban development in French Alps combining Hg accumulation rates and isotope composition in sediment archives from Lake Luitel. Chemical Geology, 431, 10–19.
Résumé: This study reconstructs the history of multiple industrial and urban mercury (Hg) emissions recorded in the sediment archive of Lake Luitel (France) from AD similar to 1860 to AD 2011. For this purpose, we provide a well constrained short-lived radionuclides continuous age-depth relationship of the sediment sequence (mean accumulation rate of 5.18 +/- 0.28 mm.yr(-1)) with Hg accumulation rates (Hg AR), Hg isotopic composition and extensive historical data. Hg AR were stable around 45 μg.m(-2).y(-1) from 1860 to WWI and rose to reach their maximum at the end of WWII (250 μg m(-2) y(-1)) followed by a gradual decreased to reach about 90 μg m(-2) y(-1) in the current period. Normalization to a terrigenous Hg proxy highlighted the dominance of atmospheric Hg inputs to the lake. The combination of Hg AR with isotopic signatures through the use of binary mixing (Delta Hg-199 vs 1/Hg AR) models and isotopic plots (and comparison to literature data) allowed us to identify the main industrial and urban historical inputs. The major outcome of this study is that the Hg mass independent fractionation (MIF) signature did not enable the identification of particular anthropogenic sources but reflected an integrated pool of industrial and urban emissions which tend to shift to less negative MIF values (mean: -0.15 +/- 0.04%) during their period of maximum emissions. Temporal MIF and Hg AR variations depict the rising Hg emissions from the industrial revolution (1860-1910) to the modern industrial and urban development period (1950-1980). Mass dependent fractionation (MDF) signatures enabled the identification of major contributors in relation to their relative intensities lying between two endmember pools: (i) the combustion activities (smelters, cement factories and urban heating) with more negative delta Hg-202 values, and (ii) the chemical and electrometallurgical activities (electrochemistry, chlor-alkali) with higher delta Hg-202 values. Unconformities of MIF and MDF signatures were observed during WWI, WWII and interwar period, and were attributed to drastic and rapid changes in regional industrial activities. Finally, recent laws regarding Hg emissions (1998-2011) prove their efficiency as Hg AR decreased with a return to more negative MIF and MDF signatures such as during the industrial revolution period. Our study highlights that the combination of Hg isotopic data with Hg AR in sediment archives is a useful tool for reconstructing the history of anthropogenic Hg emissions, and has the potential to identifiy their relative contributions. (C) 2016 Elsevier B.V. All rights reserved.
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Guédron, S., Devin, S., & Vignati, D. A. L. (2016). Total and methylmercury partitioning between colloids and true solution: From case studies in sediment overlying and porewaters to a generalized model. Environmental Toxicology And Chemistry, 35(2), 330–339.
Résumé: Tangential flow ultrafiltration was used to determine the partitioning of total mercury (THg) and monomethylmercury (MMHg) between colloids and true solution in sediment overlying and porewaters collected in Lake Geneva (Switzerland and France), Venice Lagoon (Italy), and Baihua Reservoir (China). Overlying water and porewater spanned different ranges of THg and MMHg concentrations, redox conditions, and salinity. Total Hg, MMHg, and dissolved organic carbon (DOC) concentrations were measured in filter-passing (<0.45m), colloidal (3 kDa-0.45m), and truly dissolved (<3kDa) fractions. The percentages of filterable Hg and MMHg associated with colloids (arithmetic means +/- 1 standard deviation [SD]) were 29 +/- 11% for THg (range, 4-60%) and 44 +/- 17% for MMHg (range, 15-65%). Ultrafiltration DOC mass balances were often not satisfactory. However, this was apparently without consequences on THg/MMHg fractionation, suggesting that only a part of total DOC controlled THg/MMHg partitioning in overlying water and porewater. Linear relationships existed between filter passing and truly dissolved concentrations of THg and MMHg, suggesting that mechanisms controlling their partitioning are, at least partly, similar across aquatic systems. These linear relationships could be extended to data from published studies and ultrafilterable concentrations often could be predicted, within a factor of 2, from the measurement of filter-passing ones. The possibility to easily model THg/MMHg partitioning across aquatic systems will facilitate its consideration in general biogeochemical THg/MMHg models. Environ Toxicol Chem 2016;35:330-339. (c) 2015 SETAC
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Gueguen, P. (2016). Predicting Nonlinear Site Response Using Spectral Acceleration Vs PGV/Vs30: A Case History Using the Volvi-Test Site. Pure And Applied Geophysics, 173(6), 2047–2063.
Résumé: In this study, we analyze the efficiency of the ratio between particle velocity and shear wave velocity as a strain proxy for evaluating the nonlinear seismic response of sediments. The in situ stress-strain relationships are derived from accelerometric vertical array recordings at the TST site in Volvi (Thessaloniki, Greece). First, the shear wave velocity between two successive sensors was computed by seismic interferometry and strain was computed as the velocity ratio or the relative displacement between sensors. The shear-wave velocity profile and in situ shear modulus degradation curve with strain were compared with previous studies performed at the TST site. Finally, the stress-strain relationships were derived from data recorded at the surface by extending the strain proxy and stress values to the ratio between peak ground velocity and the Vs30 parameter used for site classification, i.e. without requiring the accelerometric vertical array. Our model captures the in situ nonlinear response of the site, without consideration of azimuth or distance of the earthquakes. In conclusion, the acceleration (stress) values, based on the accelerometric response spectra instead of peak ground acceleration compared with the deformation (strain) proxy, provide an effective model of the in situ nonlinear response, providing information that can be integrated into ground motion prediction equations.
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Gueguen, P., & Colombi, A. (2016). Experimental and Numerical Evidence of the Clustering Effect of Structures on Their Response during an Earthquake: A Case Study of Three Identical Towers in the City of Grenoble, France. Bulletin Of The Seismological Society Of America, 106(6), 2855–2864.
Résumé: In this article, interpretation of an equivalent to a macroseismic intensity survey, performed in three identical stand-alone buildings located in Grenoble, France, after an M-L 4.1 earthquake, reveals a clustering effect, resulting in different levels of perception of seismic loading by inhabitants. The clustering effect is confirmed using numerical simulation; the variation of the seismic response of the building in the middle of the cluster depends on the azimuth of the seismic source relative to the building cluster. The major effect is the splitting of its resonance frequency, accompanied by a decrease in vibration amplitude. We conclude that clustering has an impact on urban effects, calling into question the validity of seismic design, which considers buildings in urban areas as stand-alone constructions, and the interpretation of macroseismic intensity surveys conducted in dense urban areas.
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Gueguen, P., Johnson, P., & Roux, P. (2016). Nonlinear dynamics induced in a structure by seismic and environmental loading. Journal Of The Acoustical Society Of America, 140(1), 582–590.
Résumé: In this study, it is shown that under very weak dynamic and quasi-static deformation that is orders of magnitude below the yield deformation of the equivalent stress-strain curve (around 10(-3)), the elastic parameters of a civil engineering structure (resonance frequency and damping) exhibit nonlinear softening and recovery. These observations bridge the gap between laboratory and seismic scales where elastic nonlinear behavior has been previously observed. Under weak seismic or atmospheric loading, modal frequencies are modified by around 1% and damping by more than 100% for strain levels between 10(-7) and 10(-4). These observations support the concept of universal behavior of nonlinear elastic behavior in diverse systems, including granular materials and damaged solids that scale from millimeter dimensions to the scale of structures to fault dimensions in the Earth. (C) 2016 Acoustical Society of America.
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Guervilly, C., & Cardin, P. (2016). Subcritical convection of liquid metals in a rotating sphere using a quasi-geostrophic model. Journal Of Fluid Mechanics, 808, 61–89.
Résumé: We study nonlinear convection in a rapidly rotating sphere with internal heating for values of the Prandtl number relevant for liquid metals (Pr is an element of[10(-2), 10(-1)]) We use a numerical model based on the quasi-geostrophic approximation, in which variations of the axial vorticity along the rotation axis are neglected, whereas the temperature field is fully three-dimensional. We identify two separate branches of convection close to onset: (i) a well-known weak branch for Ekman numbers greater than 10(-6) which is continuous at the onset (supercritical bifurcation) and consists of thermal Rosshy waves and (ii) a novel strong branch at lower Ekman numbers, which is discontinuous at the onset. The strong branch becomes subcritical for Ekman numbers of the order of 10(-8). On the strong branch, the Reynolds number of the flow is greater than 10(3), and a strong zonal flow with multiple jets develops, even close to the nonlinear onset of convection. We find that the subcriticality is amplified by decreasing the Prandtl number. The two branches can co-exist for intermediate Ekman numbers, leading to hysteresis (Ek = 10(-6), Pr = 10(-2)), Nonlinear oscillations are observed near the onset of convection for Ek = 10(-7) and Pr = 10(-1).
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Guillaume, B., Pochat, S., Monteux, J., Husson, L., & Choblet, G. (2016). Can eustatic charts go beyond first order? Insights from the Permian-Triassic. Lithosphere, 8(5), 505–518.
Résumé: First-order variations of eustatic charts (200-400 m.y.) are in agreement with our understanding of the geodynamic processes that control sea level. By extrapolation, second-order (10-100 m.y.) and third-order (1-10 m.y.) variations are also thought to follow the same rules. However, this assumption may be jeopardized by a closer examination of the Permian-Triassic example, for which climatic and tectonic eustasy fails to explain the variations of the eustatic charts. During this period, eustatic charts peak down to their lowermost Phanerozoic values and display second-order variations at rates of up to 3 m/m.y., which is inconsistent with the expected eustatic signal during the early fragmentation of the Pangean supercontinent and the late Paleozoic melting of ice sheets. Here, we review the possible mechanisms that could explain the apparent sea-level variations. Some of them do modify the eustatic sea level (ESL). In particular, dynamic deflections of Earth's surface above subduction zones and their locations with respect to continents appear to have been the primary controls of absolute sea level as the Pangean supercontinent formed and broke up. Other mechanisms instead only locally or regionally produced vertical ground motions, either uplifting continents or tilting the margins where the control points were located. We show that (1) the thermal uplift associated with supercontinent insulation and (2) the dynamic uplift associated with the emplacement of a superplume both give rates of sea-level change in the range of long-term changes of ESL. We also show that (3) the dynamic tilt of continental margins not only produces apparent sea-level changes, but it also modifies the absolute sea level, which in turn may end up in the paradoxical situation wherein fingerprints of ESL drop are found in the geological record during actual ESL rise. We conclude that second-order absolute sea-level changes may remain elusive for some time.
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Guillier, B., Chatelain, J. L., Perfettini, H., Oubaiche, E., Voisin, C., Bensalem, R., et al. (2016). Building frequency fluctuations from continuous monitoring of ambient vibrations and their relationship to temperature variations. Bulletin Of Earthquake Engineering, 14(8), 2213–2227.
Résumé: Building frequencies (fundamental and higher modes) are a critical parameter especially in the field of structural health monitoring mainly based on the stability of the structural dynamic parameters of individual building (frequencies, damping and modes shape). One of the most used methods to find out these parameters is based on the use on ambient vibration analysis. In this work, we study the fluctuations over a month period of the fundamental frequencies (transverse and longitudinal) of a 3.5-story RC-building made of 2 identical units connected by a structural joint. Time independent building frequencies is a strong assumption; as illustrated by our experiment showing that over an observation period of a month, building frequencies fluctuate of about 3.5 %. A clear correlation is found between the building frequency fluctuations and temperature variations, with a phase-shift interpreted as the characteristic time of heat diffusion within the walls. This allows: (1) determining the thermal diffusivity of the structure, (2) inferring its relative stiffness variations, and (3) showing that its Young modulus varies linearly with temperature.
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Hamdouni, A., Montes-Hernandez, G., Tlili, M., Findling, N., Renard, F., & Putnis, C. V. (2016). Removal of Fe(II) from groundwater via aqueous portlandite carbonation and calcite-solution interactions. Chemical Engineering Journal, 283, 404–411.
Résumé: Fresh groundwater is sometimes enriched with dissolved ferrous iron (Fe(II)) that restricts its consumption as potable water because it forms colloidal red matter (mainly ferric oxyhydroxides) under oxic conditions at near neutral pH (>6) conditions. As already demonstrated, natural or synthetic calcite material can be used to accelerate the iron oxidation process from Fe(II) to Fe(III), a process that then enhances its precipitation at the calcite-solution interface as confirmed by in situ atomic force microcopy (AFM) observations in this study. The present study mainly reports on a simplified water treatment method to remove ferrous iron (Fe(II)) from water via aqueous carbonation of calcium hydroxide (Ca(OH)(2)) at ambient temperature (approximate to 20 degrees C) and moderate CO2 pressure (10 bar) conditions. In practice, high concentrations of dissolved iron (up to 100 mg/L) can be successfully removed using only 4 g of Ca(OH)(2) per liter of Fe-rich solution (close to 100% of efficiency) and a short treatment time is required (<1 h). This method offers various advantages compared with other calcite-based water treatments. For example, other pre-existent dissolved toxic and eutrophic ions such as As, Cu, Cd, Se, P, S, N, etc. can be simultaneously removed from water during the precipitation of calcite and iron oxyhydroxide nanoparticles (<100 nm). Additionally, the dissolution of calcium hydroxide prior to the carbonation process increases the pH (12.4), a process that can act as a softening agent in the water being treated. Finally, the resultant red solid-residue containing mainly calcite and iron oxyhydroxide (FeOOH type) nanoparticles could be reused as pigment or mineral filler powder for industrial applications. This integrated method could be used successfully to remove toxic dissolved ions from water while generating solid residues with industrial uses. (C) 2015 Elsevier B.V. All rights reserved.
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He, J., Bardelli, F., Gehin, A., Silvester, E., & Charlet, L. (2016). Novel chitosan goethite bionanocomposite beads for arsenic remediation. Water Research, 101, 1–9.
Résumé: We report on the synthesis and As adsorption properties of a novel chitosan iron (oxyhydr)oxide composite material for the remediation of arsenic-contaminated water supplies. FE-SEM, Mossbauer spectroscopy, ICP-OES and synchrotron (Bulk XAS, μARE) techniques were applied to determine the composition of the new material and investigate the As uptake efficiency and mechanism. The iron (oxyhydr)oxide phase has been identified as a nano-sized goethite, well dispersed in the chitosan matrix, leading to the name 'chitosan goethite bionanocomposite' (CGB). The CGB material is prepared in the form of beads of high density and excellent compression strength; the embedding of the goethite nanoparticles in the chitosan matrix allows for the high adsorption capacity of nanoparticles to be realized. CGB beads remove both As(III) and As(V) efficiently from water, over the pH range 5-9, negating the need for pre-oxidation of As(III). Kinetic studies and μXRF analysis of CGB bead sections show that diffusion-adsorption of As(V) into CGB beads is faster than for As(III). Using CGB beads, synthetic high arsenic water (0.5 mg-As/L) could be purified to world drinking standard level (< 0.01 mg-As/L) using only 1.4 g/L CGB. When considered in combination with the advantages of the low-cost of raw materials required, and facile (green) synthesis route, CGB is a promising material for arsenic remediation, particularly in developing countries, which suffer a diversity of socio-economical-traditional constraints for water purification and sanitation. (C) 2016 Elsevier Ltd. All rights reserved.
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Hillers, G., & Campillo, M. (2016). Fault zone reverberations from cross-correlations of earthquake waveforms and seismic noise. Geophysical Journal International, 204(3), 1503–1517.
Résumé: Seismic wavefields interact with low-velocity fault damage zones. Waveforms of ballistic fault zone head waves, trapped waves, reflected waves and signatures of trapped noise can provide important information on structural and mechanical fault zone properties. Here we extend the class of observable fault zone waves and reconstruct in-fault reverberations or multiples in a strike-slip faulting environment. Manifestations of the reverberations are significant, consistent wave fronts in the coda of cross-correlation functions that are obtained from scattered earthquake waveforms and seismic noise recorded by a linear fault zone array. The physical reconstruction of Green's functions is evident from the high similarity between the signals obtained from the two different scattered wavefields. Modal partitioning of the reverberation wavefield can be tuned using different data normalization techniques. The results imply that fault zones create their own ambiance, and that the here reconstructed reverberations are a key seismic signature of wear zones. Using synthetic waveform modelling we show that reverberations can be used for the imaging of structural units by estimating the location, extend and magnitude of lateral velocity contrasts. The robust reconstruction of the reverberations from noise records suggests the possibility to resolve the response of the damage zone material to various external and internal loading mechanisms.
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Hobiger, M., Cornou, C., Bard, P. Y., Le Bihan, N., & Imperatori, W. (2016). Analysis of seismic waves crossing the Santa Clara Valley using the three-component MUSIQUE array algorithm. Geophysical Journal International, 207(1), 439–456.
Résumé: We introduce the MUSIQUE algorithm and apply it to seismic wavefield recordings in California. The algorithm is designed to analyse seismic signals recorded by arrays of three-component seismic sensors. It is based on the MUSIC and the quaternion-MUSIC algorithms. In a first step, the MUSIC algorithm is applied in order to estimate the backazimuth and velocity of incident seismic waves and to discriminate between Love and possible Rayleigh waves. In a second step, the polarization parameters of possible Rayleigh waves are analysed using quaternion-MUSIC, distinguishing retrograde and prograde Rayleigh waves and determining their ellipticity. In this study, we apply the MUSIQUE algorithm to seismic wavefield recordings of the San Jose Dense Seismic Array. This array has been installed in 1999 in the Evergreen Basin, a sedimentary basin in the Eastern Santa Clara Valley. The analysis includes 22 regional earthquakes with epicentres between 40 and 600 km distant from the array and covering different backazimuths with respect to the array. The azimuthal distribution and the energy partition of the different surface wave types are analysed. Love waves dominate the wavefield for the vast majority of the events. For close events in the north, the wavefield is dominated by the first harmonic mode of Love waves, for farther events, the fundamental mode dominates. The energy distribution is different for earthquakes occurring northwest and southeast of the array. In both cases, the waves crossing the array are mostly arriving from the respective hemicycle. However, scattered Love waves arriving from the south can be seen for all earthquakes. Combining the information of all events, it is possible to retrieve the Love wave dispersion curves of the fundamental and the first harmonic mode. The particle motion of the fundamental mode of Rayleigh waves is retrograde and for the first harmonic mode, it is prograde. For both modes, we can also retrieve dispersion and ellipticity curves. Wave motion simulations for two earthquakes are in good agreement with the real data results and confirm the identification of the wave scattering formations to the south of the array, which generate the scattered Love waves visible for all earthquakes.
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Kang, M. L., Bardelli, F., Ma, B., Charlet, L., Chen, F. R., & Yang, Y. Q. (2016). The influence of pH and reaction time on the formation of FeSe2 upon selenite reduction by nano-sized pyrite-greigite. Radiochimica Acta, 104(9), 649–656.
Résumé: The influence of pH and reaction time on the formation of FeSe2 by reductive precipitation of Se(IV) with nano-sized pyrite-greigite was investigated. Reductive precipitation is an effective method of attenuating the mobility of Se-79, which is foreseen to be a dangerous radioisotope for the geological disposal of high-level radioactive waste (HLW). The results indicated that Se(0) was formed at pH < 4.05, whereas, at pH > 6.07, considerable amount of FeSe2 was formed along with Se(0). These observations are in agreement with the thermodynamic predictions reported in this work. Furthermore, the formation of FeSe2 was found to continue by increasing the reaction time, indicating that the Se(0) formed in the early reaction stage is gradually transformed to FeSe2 upon the depletion of aqueous Se(IV). Since FeSe2 has a stronger reactivity than pyrite, it was proposed that greigite, rather than pyrite, was responsible for the formation of FeSe2. The findings in this study are of interest for key geochemical processes governing the mobility of toxic Se-79 in the environment in presence of iron sulfides.
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Kessar, M., Balarac, G., & Plunian, F. (2016). The effect of subgrid-scale models on grid-scale/subgrid-scale energy transfers in large-eddy simulation of incompressible magnetohydrodynamic turbulence. Physics Of Plasmas, 23(10).
Résumé: In this work, the accuracy of various models used in large-eddy simulations (LES) of incompressible magnetohydrodynamic (MHD) turbulence is evaluated. Particular attention is devoted to the capabilities of models to reproduce the transfers between resolved grid-and subgrid-scales. The exact global balance of MHD turbulent flows is first evaluated from direct numerical simulation (DNS) database. This balance is controlled by the transfers between scales and between kinetic and magnetic energies. Two cases of forced homogeneous isotropic MHD turbulent flows are considered, with and without injecting large scale helicity. The strong helical case leads to domination of the magnetic energy due to an inverse cascade [A. Brandenburg, Astrophys. J. 550(2), 824 (2001); N. E. Haugen et al., Phys. Rev. E 70(1), 016308 (2004)]. The energy transfers predicted by various models are then compared with the transfer extracted from DNS results. This allows to discriminate models classically used for LES of MHD turbulence. In the non-helical case, the Smagorinsky-like model [M. L. Theobald et al., Phys. Plasmas 1, 3016 (1994)] and a mixed model are able to perform stable LES, but the helical case is a more demanding test and all the models lead to unstable simulations. Published by AIP Publishing.
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Kouketsu, Y., Hattori, K., Guillot, S., & Rayner, N. (2016). Eocene to Oligocene retrogression and recrystallization of the Stak eclogite in northwest Himalaya. Lithos, 240, 155–166.
Résumé: Highly retrogressed eclogite is present in the Stak massif located on the northern edge of the Indian continental margin in northern Pakistan. Garnet in foliated samples contains omphacite inclusions (X-jd = 0.33-0.40) and quartz inclusions and latter retain Raman spectroscopic evidence for high residual pressures up to 0.52 GPa. These garnet grains do not show apparent compositional zoning. By contrast, one sample contains euhedral grains of garnet with quartz inclusions that show residual pressures as low as 0.25 GPa. These garnet grains do not contain omphacite inclusions, and show different compositional zoning compared to the omphacitebearing garnet The metamorphic condition of this sample was estimated to be 1.0-1.4 GPa/650-710 degrees C using residual pressure values of quartz inclusions in garnets and the garnet-clinopyroxene geothermometer. The U-Pb ages of zircon grains range from 158 to 28 Ma with a cluster between at ca. 32 Ma, which is younger than that of the peak ultrahigh-pressure metamorphic ages of eclogitic massifs in the northwestern Himalaya, e.g. Kaghan and Tso Morari. We suggest that the retrogressed eclogitic rocks in the Stak massif were heated by nearby Nanga Parbat Haramosh massif at ca. 32 Ma, subsequent to peak eclogite facies conditions. During this heating, part of the eclogite was largely recrystallized to form euhedral garnet grains. These results suggest that the Stak massif resided at a lower crustal depth while other ultrahigh-pressure massifs were exhumed in western Himalaya. (C) 2015 Elsevier B.V. All rights reserved.
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Lacroix, P. (2016). Landslides triggered by the Gorkha earthquake in the Langtang valley, volumes and initiation processes. Earth Planets And Space, 68.
Résumé: The Gorkha earthquake (Nepal, 2015, M-w 7.9) triggered many landslides. The most catastrophic mass movement was a debris avalanche that buried several villages in the Langtang valley. In this study, questions are raised about its volume and initiation. I investigate the possibility of high-resolution digital surface models computed from tri-stereo SPOT6/7 images to resolve this issue. This high-resolution dataset enables me to derive an inventory of 160 landslides triggered by this earthquake. I analyze the source of errors and estimate the uncertainties in the landslide volumes. The vegetation prevents to correctly estimate the volumes of landslides that occured in vegetated areas. However, I evaluate the volume and thickness of 73 landslides developing in vegetated-free areas, showing a power law between their surface areas and volumes with exponent of 1.20. Accumulations and depletion volumes are also well constrained for larger landslides, and I find that the main debris avalanches accumulated 6.95 x 10(6) m(3) of deposits in the valley with thicknesses reaching 60 m, and 9.66 x 10(6) m(3) in the glaciated part above 5000 m asl. The large amount of sediments is explained by an initiation of the debris avalanche due to serac falls and snow avalanches from five separate places between 6800 and 7200 m asl over 3 km length.
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Lafay, R., Montes-Hernandez, G., Janots, E., Munoz, M., Auzende, A. L., Gehin, A., et al. (2016). Experimental investigation of As, Sb and Cs behavior during olivine serpentinization in hydrothermal alkaline systems. Geochimica Et Cosmochimica Acta, 179, 177–202.
Résumé: While Fluid-Mobile Elements (FMEs) such as B, Sb, Li, As or Cs are particularly concentrated in serpentinites, data on FME fluid-serpentine partitioning, distribution, and sequestration mechanisms are missing. In the present experimental study, the behavior of Sb, As and Cs during San Carlos olivine serpentinization was investigated using accurate mineralogical, geochemical, and spectroscopic characterization. Static-batch experiments were conducted at 200 degrees C, under saturated vapor pressure (approximate to 1.6 MPa), for initial olivine grain sizes of <30 μm (As), 30-56 μm (As, Cs, Sb) and 56-150 μm (Cs) and for periods comprised between 3 and 90 days. High-hydroxyl-alkaline fluid enriched with 200 mg L-1 of a single FME was used and a fluid/solid weight ratio of 15. For these particular conditions, olivine is favorably replaced by a mixture of chrysotile, polygonal serpentine and brucite. Arsenic, Cs or Sb reaction product content was determined as a function of reaction advancement for the different initial olivine grain sizes investigated. The results confirm that serpentinization products have a high FME uptake capacity with the partitioning coefficient increasing such as D-Cs(p/fl) = 1.5-1.6 < D-As(p/fl) = 3.5-4.5 < D-Sb(p/fl) = 28 after complete reaction of the 30-56 μm grain-sized olivine. The sequestration pathways of the three elements are however substantially different. While the As partition coefficient remains constant throughout the serpentinization reaction, the Cs partition coefficient decreases abruptly in the first stages of the reaction to reach a constant value after the reaction is 40-60% complete. Both As and Cs partitioning appear to decrease with increasing initial olivine grain size, but there is no significant difference in the partitioning coefficient between the 30-56 and 56-150 μm grain size after complete serpentinization. X-ray absorption spectroscopy (XAS) measurements combined with X-ray chemical measurements reveal that the As(V) is mainly adsorbed onto the serpentinization products, especially brucite. In contrast, mineralogical characterization combined with XAS spectroscopy reveal redox sensitivity for Sb sequestration within serpentine products, depending on the progress of the reaction. When serpentinization is < 50%, initial Sb(III) is oxidized into Sb(V) and substantially adsorbed onto serpentine. For higher degrees of reaction, a decrease in Sb sequestration by serpentine products is observed and is attributed to a reduction of Sb(V) into Sb(III). This stage is characterized by the precipitation of Sb-Ni-rich phases and a lower bulk partitioning coefficient compared to that of the serpentine and brucite assemblage. Antimony reduction appears linked to water reduction accompanying the bulk iron oxidation, as half the initial Fe(II) is oxidized into Fe(III) and incorporated into the serpentine products once the reaction is over. The reduction of Sb implies a decrease of its solubility, but the type of secondary Sb-rich phases identified here might not be representative of natural systems where Sb concentrations are lower. These results bring new insights into the uptake of FME by sorption on serpentine products that may form in hydrothermal environments at low temperatures. FME sequestration here appears to be sensitive to various physicochemical parameters and more particularly to redox conditions that appear to play a preponderant role in the concentrations and mechanism of sequestration of redox-sensitive elements. (C) 2016 Elsevier Ltd. All rights reserved.
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Lafay, R., A. Fernandez-Martinez, G. Montes-Hernandez, A.-L. Auzende and A. Poulain. (2016). Dissolution-reprecipitation and self-assembly of proto-serpentine nanoparticles precedes the formation of chrysotile nanotubes : Insights into the structure of proto-serpentine.101, 2666–2676.
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Lannes, A., Manceau, A., Rovezzi, M., Glatzel, P., Joly, Y., & Gautier-Luneau, I. (2016). Intramolecular Hg center dot center dot center dot pi interactions of d-character with non-bridging atoms in mercury-aryl complexes. Dalton Transactions, 45(36), 14035–14038.
Résumé: Mercury 5d-orbitals are involved in intramolecular p-interactions with carbon and sulfur nearest and next-nearest neighbors in mercury-aryl complexes. This unexpected character of the electron cloud of mercury was revealed by high energy-resolution XANES spectroscopy readily interpreted in terms of a final-state local (l, m)-projected density of states (DOS).
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Larue, C., Castillo-Michel, H., Stein, R. J., Fayard, B., Pouyet, E., Villanova, J., et al. (2016). Innovative combination of spectroscopic techniques to reveal nanoparticle fate in a crop plant. Spectrochimica Acta Part B-Atomic Spectroscopy, 119, 17–24.
Résumé: Nanotechnology is the new industrial revolution of our century. Its development leads to an increasing use of nanoparticles and thus to their dissemination. Their fate in the environment is of great concern and especially their possible transfer in trophic chains might be an issue for food safety. However, so far our knowledge on this topic has been restricted by the lack of appropriate techniques to characterize their behavior in complex matrices. Here, we present in detail the use of cutting-edge beam-based techniques for nanoparticle in situ localization, quantification and speciation in a crop plant species (Lactuca saliva). Lettuce seedlings have been exposed to TiO2 and Ag nanoparticles and analyzed by inductively coupled plasma spectrometry, micro-particle induced X-ray emission coupled to Rutherford backscattering spectroscopy on nuclear microprobe, micro-X-ray fluorescence spectroscopy and X-ray absorption near edge structure spectroscopy. The benefits and drawbacks of each technique are discussed, and the types of information that can be drawn, for example on the translocation to edible parts, change of speciation within the plant, detoxification mechanisms, or impact on the plant ionome, are highlighted. Such type of coupled approach would be an asset for nanoparticle risk assessment. (C) 2016 Elsevier B.V. All rights reserved.
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Letort, J., Bollinger, L., Lyon-Caen, H., Guilhem, A., Cano, Y., Baillard, C., et al. (2016). Teleseismic depth estimation of the 2015 Gorkha-Nepal aftershocks. Geophysical Journal International, 207(3), 1584–1595.
Résumé: The depth of 61 aftershocks of the 2015 April 25 Gorkha, Nepal earthquake, that occurred within the first 20 d following the main shock, is constrained using time delays between teleseismic P phases and depth phases (pP and sP). The detection and identification of these phases are automatically processed using the cepstral method developed by Letort et al., and are validated with computed radiation patterns from the most probable focal mechanisms. The events are found to be relatively shallow (13.1 +/- 3.9 km). Because depth estimations could potentially be biased by the method, velocity model or selected data, we also evaluate the depth resolution of the events from local catalogues by extracting 138 events with assumed well-constrained depth estimations. Comparison between the teleseismic depths and the depths from local and regional catalogues helps decrease epistemic uncertainties, and shows that the seismicity is clustered in a narrow band between 10 and 15 km depth. Given the geometry and depth of the major tectonic structures, most aftershocks are probably located in the immediate vicinity of the Main Himalayan Thrust (MHT) shear zone. The mid-crustal ramp of the flat/ramp MHT system is not resolved indicating that its height is moderate (less than 5-10 km) in the trace of the sections that ruptured on April 25. However, the seismicity depth range widens and deepens through an adjacent section to the east, a region that failed on 2015 May 12 during an M-w 7.3 earthquake. This deeper seismicity could reflect a step-down of the basal detachment of the MHT, a lateral structural variation which probably acted as a barrier to the dynamic rupture propagation.
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Li, Y., Han, B., Metivier, L., & Brossier, R. (2016). Optimal fourth-order staggered-grid finite-difference scheme for 3D frequency-domain viscoelastic wave modeling. Journal Of Computational Physics, 321, 1055–1078.
Résumé: We investigate an optimal fourth-order staggered-grid finite-difference scheme for 3D frequency-domain viscoelastic wave modeling. An anti-lumped mass strategy is incorporated to minimize the numerical dispersion. The optimal finite-difference coefficients and the mass weighting coefficients are obtained by minimizing the misfit between the normalized phase velocities and the unity. An iterative damped least-squares method, the Levenberg-Marquardt algorithm, is utilized for the optimization. Dispersion analysis shows that the optimal fourth-order scheme presents less grid dispersion and anisotropy than the conventional fourth-order scheme with respect to different Poisson's ratios. Moreover, only 3.7 grid-points per minimum shear wavelength are required to keep the error of the group velocities below 1%. The memory cost is then greatly reduced due to a coarser sampling. A parallel iterative method named CARP-CG is used to solve the large ill-conditioned linear system for the frequency-domain modeling. Validations are conducted with respect to both the analytic viscoacoustic and viscoelastic solutions. Compared with the conventional fourth-order scheme, the optimal scheme generates wavefields having smaller error under the same discretization setups. Profiles of the wavefields are presented to confirm better agreement between the optimal results and the analytic solutions. (C) 2016 Elsevier Inc. All rights reserved.
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Lincot, A., Cardin, P., Deguen, R., & Merkel, S. (2016). Multiscale model of global inner-core anisotropy induced by hcp alloy plasticity. Geophysical Research Letters, 43(3), 1084–1091.
Résumé: The Earth's solid inner core exhibits a global seismic anisotropy of several percents. It results from a coherent alignment of anisotropic Fe alloy crystals through the inner-core history that can be sampled by present-day seismic observations. By combining self-consistent polycrystal plasticity, inner-core formation models, Monte-Carlo search for elastic moduli, and simulations of seismic measurements, we introduce a multiscale model that can reproduce a global seismic anisotropy of several percents aligned with the Earth's rotation axis. Conditions for a successful model are an hexagonal close packed structure for the inner-core Fe alloy, plastic deformation by pyramidal c + a slip, and large-scale flow induced by a low-degree inner-core formation model. For global anisotropies ranging between 1 and 3%, the elastic anisotropy in the single crystal ranges from 5 to 20% with larger velocities along the c axis.
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Llordes, A., Wang, Y., Fernandez-Martinez, A., Xiao, P., Lee, T., Poulain, A., et al. (2016). Linear topology in amorphous metal oxide electrochromic networks obtained via low-temperature solution processing. Nature Materials, 15(12), 1267–1273.
Résumé: Amorphous transition metal oxides are recognized as leading candidates for electrochromic window coatings that can dynamically modulate solar irradiation and improve building energy efficiency. However, their thin films are normally prepared by energy-intensive sputtering techniques or high-temperature solution methods, which increase manufacturing cost and complexity. Here, we report on a room-temperature solution process to fabricate electrochromic films of niobium oxide glass (NbOx) and 'nanocrystal-in-glass' composites (that is, tin-doped indium oxide (ITO) nanocrystals embedded in NbOx glass) via acid-catalysed condensation of polyniobate clusters. A combination of X-ray scattering and spectroscopic characterization with complementary simulations reveals that this strategy leads to a unique one-dimensional chain-like NbOx structure, which significantly enhances the electrochromic performance, compared to a typical three-dimensional NbOx network obtained from conventional high-temperature thermal processing. In addition, we show how self-assembled ITO-in-NbOx composite films can be successfully integrated into high-performance flexible electrochromic devices.
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Loury, C., Rolland, Y., Cenki-Tok, B., Lanari, P., & Guillot, S. (2016). Late Paleozoic evolution of the South Tien Shan: Insights from P-T estimates and allanite geochronology on retrogressed eclogites (Chatkal range, Kyrgyzstan). Journal Of Geodynamics, 96, 62–80.
Résumé: In the South Tien Shan range (Kyrgyzstan), the Late Paleozoic geodynamic evolution remains debated especially to the west of the Talas-Fergana fault (TFF) fault where suture-related high-pressure (HP) rocks are scarce. We provide new petrological and geochronological data on garnet amphibolites from the Chatkal range, to the west of the TFF, northwest of the South Tien Shan suture. These rocks are retrogressed eclogites. We used a micro-mapping approach combined with forward modeling and empirical thermobarometry to decipher the P-T path of these amphibolitized eclogites. The metamorphic peak conditions culminated at 490 +/- 50 degrees C and 18.5 +/- 2 kbar and were followed by higher temperature retrogression (similar to 560 degrees C at 11-7 kbar). In order to constrain the age of the HP stage, we dated allanite crystals texturally coeval to the HP mineral assemblage. Allanite grains dated in situ with a U-Pb LA-ICPMS methodology yield an age of 301 +/- 15 Ma. Compared with previously published data for the east of the TFF, these P-T constraints allow improving the understanding of the Late Paleozoic geodynamic evolution of the South Tien Shan. To the east of TFF, the Turkestan Ocean closed around 320 Ma with the collision of the Tarim Craton with the Kazakh microcontinent. To the west of TFF, the Turkestan Ocean closed around 300 Ma, when the Alai block collided with the Kazakh microcontinent. This later collision involved nappe-stacking and intense subvertical folding in the western South Tien Shan. This complex folding explains the S-shape of the suture to the west of the TFF that cannot be observed in the eastern part. These new data allow us to propose a distinct tectonic evolution of the two sides of the TFF, which suggests that this fault was a major transform fault before being a strike-slip intra-continental fault. (C) 2015 Elsevier Ltd. All rights reserved.
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Luzi, L., Puglia, R., Russo, E., D'Amico, M., Felicetta, C., Pacor, F., et al. (2016). The Engineering Strong-Motion Database: A Platform to Access Pan-European Accelerometric Data. Seismological Research Letters, 87(4), 987–997.
Résumé: This article describes the Engineering Strong-Motion Database (ESM), developed in the framework of the European project Network of European Research Infrastructures for Earthquake Risk Assessment and Mitigation (NERA, see Data and Resources). ESM is specifically designed to provide end users only with quality-checked, uniformly processed strong-motion data and relevant parameters and has done so since 1969 in the Euro-Mediterranean region. The database was designed for a large variety of stakeholders (expert seismologists, earthquake engineers, students, and professionals) with a user-friendly and straightforward web interface. Users can access earthquake and station information and download waveforms of events with magnitude >= 4.0 (unprocessed and processed acceleration, velocity, and displacement, and acceleration and displacement response spectra at 5% damping). Specific tools are also available to users to process strong-motion data and select ground-motion suites for code-based seismic structural analyses.
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Mahaney, W. C., & Schwartz, S. (2016). Paleoclimate of Antarctica reconstructed from clast weathering rind analysis. Palaeogeography Palaeoclimatology Palaeoecology, 446, 205–212.
Résumé: Previous analysis of extractable Fe/Al in paleosols near New Mountain, Antarctica, suggests a pre-Middle Miocene, possibly Late Oligocene-Early Miocene age for paleosol 831 emplaced during the alpine event prior to the growth of the Inland Ice Sheet. Recent analysis of weathering zones in clasts with encrusted Fe/salts from the pebble pavement overlying the 831 paleosol reveals a succession of three weathering zones in a sandstone clast that record a paleoclimate transitioning from warm/wet (temperate) to cold/dry (polar). The first zone corresponds to an association of quartz cemented with berthierine (smectite-serpentine) and illite clay minerals. The second zone transitional from weathered clast to Na-encrusted rind contains smaller amounts of berthierine and illite formed in grains of partially dissolved quartz with minor salt content. Zone three corresponds to an similar to 3 mm (3 x 10(6) nm) thick mass of porous nitrate and gypsum. The contact between zones 2 and 3 appears to be correlative with the transition from temperate to polar ice which is considered to have occurred prior to or coincident with the Middle Miocene Climatic Optimum. (C) 2016 Elsevier B.V. All rights reserved.
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Maierova, P., Schulmann, K., Lexa, O., Guillot, S., Stipska, P., Janousek, V., et al. (2016). European Variscan orogenic evolution as an analogue of Tibetan-Himalayan orogen: Insights from petrology and numerical modeling. Tectonics, 35(7), 1760–1780.
Résumé: The European Variscan orogeny can be compared to the Tibetan-Himalayan system for three main reasons: (1) The Variscan belt originated through progressive amalgamation of Gondwanan blocks that were subsequently squeezed between the Laurussia and Gondwana continents. Similarly, the Tibetan-Himalayan orogen results from amalgamated Gondwanan blocks squeezed between Asia and India. (2) The duration of the collisional period and the scale of the two orogens are comparable. (3) In both cases the collisional process resulted in formation of a thick crustal root and long lasting high-pressure granulite facies metamorphism. Recent petrological data allow a more detailed comparison pointing to similarities also in the midcrustal re-equilibration of the granulites and their association with specific (ultra) potassic magmatic rocks. In both orogens, the origin of the granulites was attributed to relamination and thermal maturation of lower crustal allochthon below upper plate crust. Subsequent evolution was explained by midcrustal flow eventually leading to extrusion of the high-grade rocks. We propose that the lower and middle crustal processes in hot orogens are connected by gravity overturns. Such laterally forced gravity-driven exchanges of material in the orogenic root were already documented in the Variscides, but the recent data from Tibet and Himalaya show that this process may have occurred also elsewhere. Using numerical models, we demonstrate that the exchange of the lower and middle crust can be efficient even for a minor density inversion and various characteristics of the crustal layers. The modeled pressure-temperature paths are compatible with two-stage metamorphism documented in Tibet and Himalaya.
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Manceau, A., Enescu, M., Simionovici, A., Lanson, M., Gonzalez-Rey, M., Rovezzi, M., et al. (2016). Chemical Forms of Mercury in Human Hair Reveal Sources of Exposure. Environmental Science & Technology, 50(19), 10721–10729.
Résumé: Humans are contaminated by mercury in different forms from different sources. In practice, contamination by methylmercury from fish consumption is assessed by measuring hair mercury concentration, whereas exposure to elemental and inorganic mercury from other sources is tested by analysis of,blood or urine. Here, we show that diverse sources of hair mercury at concentrations as low as 0.5 ppm can be individually identified by specific coordination to C, N, and S ligands with high energy-resolution X-ray absorption spectroscopy. Methylmercury from seafood, ethylmercury used as a bactericide, inorganic mercury from dental amalgams, and exogenously derived atmospheric mercury bind in distinctive intermolecular configurations to hair proteins, as supported:by molecular modeling. A mercury spike located by X-ray nanofluorescence on one hair strand could even be dated to removal of a single dental amalgam. Chemical forms of other known or putative toxic metals in human tissues could be identified by this approach with potential broader applications to forensic, energy; and materials science.
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Mancini, S., Forestier-Coste, L., Burgisser, A., James, F., & Castro, J. (2016). An expansion-coalescence model to track gas bubble populations in magmas. Journal Of Volcanology And Geothermal Research, 313, 44–58.
Résumé: We propose a kinetic model that statistically describes the growth by decompression, exsolution and coalescence of a polydisperse population of gas bubbles in a silicate melt. The model is homogeneous in space and its main variable is a distribution function representing the probability to find a bubble of volume v and mass mat time t. The volume and mass growth rates are described by a simplification of the classical monodisperse bubble growth model. This simplification, which shortens computational time, removes the coupling between mass evolution and an advection-diffusion equation describing the behavior of the volatile concentration in the melt. We formulate three coalescence mechanisms: thinning of the inter-bubble planar films, film deformation by differential bubble pressure, and buoyancy-driven collision. Numerical simulations based on a semi-implicit numerical scheme show a good agreement between the coalescence-free runs and the monodisperse runs. When coalescence is introduced, numerical results show that coalescence kernels based on different physical mechanisms yield distinct evolutions of the size distributions. A preliminary comparison between runs and experimental data suggests a qualitative match of two out of the three proposed kernels. This kinetic model is thus a powerful tool that can help in assessing how bubble growth and coalescence occur in magmas. (C) 2016 Elsevier B.V. All rights reserved.
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Mao, D., Revil, A., & Hinton, J. (2016). Induced polarization response of porous media with metallic particles – Part 4: Detection of metallic and nonmetallic targets in time-domain induced polarization tomography. Geophysics, 81(4), D359–D375.
Résumé: Time-domain induced polarization (TDIP) is a nonintrusive imaging technique of the subsurface that can be used to localize polarizable bodies including metallic objects and clay-rich materials. We first reviewed recent advances in the interpretation of induced polarization data. Then, we performed laboratory and sandbox experiments to determine the frequency-domain and TDIP signature of (1) a metal bar in sand, (2) dispersed semiconductors (e.g., pyrite) in sand, and (3) bentonite. In the case of the sandbox experiments, the three types of bodies were localized in the center of the sandbox, which was filled with water-saturated sand. We determined that chargeability was the best parameter to characterize metallic bodies (the metallic bar and the dispersed pyrite), whereas normalized chargeability was the best parameter to characterize the cation exchange capacity and therefore the clay content of the subsurface at a given clay mineralogy. For interpretation purposes, it was therefore important to display the right parameters in TDIP depending on the type of target we wanted to image for engineering applications.
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Mao, D. Q., & Revil, A. (2016). Induced polarization response of porous media with metallic particles – Part 3: A new approach to time-domain induced polarization tomography. Geophysics, 81(4), D345–D357.
Résumé: The secondary voltage associated with time-domain induced polarization data of disseminated metallic particles (such as pyrite and magnetite) in a porous material can be treated as a transient self-potential problem. This self-potential field is associated with the generation of a secondary-source current density. This source current density is proportional to the gradient of the chemical potentials of the p-and n-charge carriers in the metallic particles or ionic charge carriers in the pore water including in the electrical double layer coating the surface of the metallic grains. This new way to treat the secondary voltages offers two advantages with respect to the classical approach. The first is a gain in terms of acquisition time. Indeed, the target can be illuminated with a few primary current sources, all the other electrodes being used simultaneously to record the secondary voltage distribution. The second advantage is with respect to the inversion of the obtained data. Indeed, the secondary (source) current is linearly related to the secondary voltage. Therefore, the inverse problem of inverting the secondary voltages is linear with respect to the source current density, and the inversion can be done in a single iteration. Several iterations are, however, required to compact the source current density distribution, still obtaining a tomogram much faster than inverting the apparent chargeability data using the classical Gauss-Newton approach. We have performed a sandbox experiment with pyrite grains locally mixed to sand at a specific location in the sandbox to demonstrate these new concepts. A method initially developed for self-potential tomography is applied to the inversion of the secondary voltages in terms of source current distribution. The final result compares favorably with the classical inversion of the time-domain induced polarization data in terms of chargeability, but it is much faster to perform.
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Mao, D. Q., Lu, L., Revil, A., Zuo, Y., Hinton, J., & Ren, Z. J. (2016). Geophysical Monitoring of Hydrocarbon-Contaminated Soils Remediated with a Bioelectrochemical System. Environmental Science & Technology, 50(15), 8205–8213.
Résumé: Efficient noninvasive techniques are desired for monitoring the remediation process of contaminated soils. We applied the direct current resistivity technique to image conductivity changes in sandbox experiments where two sandy and clayey soils were initially contaminated with diesel hydrocarbon. The experiments were conducted over a 230 day period. The removal of hydrocarbon was enhanced by a bioelectrochemical system (BES) and the electrical potentials of the BES reactors were also monitored during the course of the experiment. We found that the variation in electrical conductivity shown in the tomograms correlate well with diesel removal from the sandy soil, but this is not the case with the clayey soil. The clayey soil is characterized by a larger specific surface area and therefore a larger surface conductivity. In sandy soil, the removal of the diesel and products from degradation leads to an increase in electrical conductivity during the first 69 days. This is expected since diesel is electrically insulating. For both soils, the activity of BES reactors is moderately imaged by the inverted conductivity tomogram of the reactor. An increase in current production by electrochemically active bacteria activity corresponds to an increase in conductivity of the reactor.
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Mares, R., Barnard, H. R., Mao, D. Q., Revil, A., & Singha, K. (2016). Determining the influence of transpiration on soil moisture movement using electrical resistivity imaging. Journal Of Hydrology, 536, 327–338.
Résumé: The feedbacks among forest transpiration, soil moisture, and subsurface flowpaths are poorly understood. We investigate how soil moisture is affected by daily transpiration using time-lapse electrical resistivity imaging (ERI) on a highly instrumented ponderosa pine and the surrounding soil throughout the growing season. By comparing sap flow measurements to the ERI data, we find that periods of high sap flow within the diel cycle are aligned with decreases in ground electrical conductivity and soil moisture due to drying of the soil during moisture uptake. As sap flow decreases during the night, the ground conductivity increases as the soil moisture is replenished. The mean and variance of the ground conductivity decreases into the summer dry season, indicating drier soil and smaller diel fluctuations in soil moisture as the summer progresses. Sap flow did not significantly decrease through the summer suggesting use of a water source deeper than 60 cm to maintain transpiration during times of shallow soil moisture depletion. ERI captured spatiotemporal variability of soil moisture on daily and seasonal timescales. ERI data on the tree showed a diel cycle of conductivity, interpreted as changes in water content due to transpiration, but changes in sap flow throughout the season could not be interpreted from ERI inversions alone due to daily temperature changes. (C) 2016 Elsevier B.V. All rights reserved.
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Margirier, A., Audin, L., Robert, X., Herman, F., Ganne, J., & Schwartz, S. (2016). Time and mode of exhumation of the Cordillera Blanca batholith (Peruvian Andes). Journal Of Geophysical Research-Solid Earth, 121(8), 6235–6249.
Résumé: The Cordillera Blanca batholith (12-5Myr) forms the highest Peruvian summits and builds the footwall of the Cordillera Blanca normal fault (CBNF). Even if several models have been proposed, the processes driving both the exhumation of the Cordillera Blanca and extensional deformation along the CBNF are still debated. Here we quantify the emplacement depth and exhumation of the batholith of the northern Peru arc from the late Miocene to present. Based on a compilation of crystallization ages and new thermobarometry data in the Cordillera Blanca batholith, we propose that the batholith was emplaced at a depth of similar to 3km in successive sills from 14 to 5Ma. By contrast, the younger rocks exposed at the surface were emplaced the deepest (i.e., similar to 6km) and are located close to the CBNF, suggesting post 5Ma tilting. Furthermore, a formal inversion of the thermochronologic data indicates an increase of the exhumation rates in the Cordillera Blanca during the Quaternary. The higher predicted exhumation rates correlate with areas of high relief, both in the northern and central part of the Cordillera Blanca, suggesting that Quaternary valley carving by glaciations have a significant impact on the latest stage of the Cordillera Blanca exhumation (2-0Ma).
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Martinod, J., Pouyaud, B., Carretier, S., Guillaume, B., & Herail, G. (2016). Geomorphic Records along the General Carrera (Chile)-Buenos Aires (Argentina) Glacial Lake (46 degrees-48 degrees S), Climate Inferences, and Glacial Rebound for the Past 7-9 ka: A Discussion. Journal Of Geology, 124(5), 631–635.
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Martinod, J., Regard, V., Letourmy, Y., Henry, H., Hassani, R., Baratchart, S., et al. (2016). How do subduction processes contribute to forearc Andean uplift? Insights from numerical models. Journal Of Geodynamics, 96, 6–18.
Résumé: We present numerical models to study how changes in the process of subduction may explain the observed Quaternary uplift of the Andean forearc region. Indeed, most segments of the South American Pacific coasts between 16 and 32 degrees S have been uplifting since the Lower Pleistocene, following a period of stability of the forearc region. Models confirm that local uplift is expected to occur above ridges, this phenomenon being predominant in central Peru where the Nazca Ridge is subducting. We investigate the effects of slab pull, interplate friction and convergence velocity on the vertical displacements of the overriding plate. We propose that the global tendency to coastal uplift is accompanying the deceleration of the Nazca-South America convergence that occurred in the Pleistocene. In contrast, forearc subsidence may accompany increasing convergence velocities, as suggested by the subsidence history of the South America active margin. (C) 2015 Elsevier Ltd. All rights reserved.
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Martinod, J., Regard, V., Riquelme, R., Aguilar, G., Guillaume, B., Carretier, S., et al. (2016). Pleistocene uplift, climate and morphological segmentation of the Northern Chile coasts (24 degrees S-32 degrees S): Insights from cosmogenic Be-10 dating of paleoshorelines. Geomorphology, 274, 78–91.
Résumé: We present new cosmogenic (Be-10) exposure ages obtained on Pleistocene marine abrasion shore terraces of Northern Chile between 24 degrees S and 32 degrees S in order to evaluate the temporal and spatial variability of uplift rates along the coastal forearc. Both the dispersion of cosmogenic concentrations in samples from the same terrace and data obtained in vertical profiles show that onshore erosion rates, following emergence of paleoshorelines, approached 1 m/Myr. Therefore, minimum ages calculated without considering onshore erosion may be largely underestimated for Middle Pleistocene terraces. The elevation of the last interglacial (MIS-5) paleoshoreline is generally between 25 and 45 m amsl, suggesting that the entire coast of the study area has been uplifting during the Upper Pleistocene at rates approaching 0.3 mm/yr. Available ages for Middle Pleistocene terraces suggest similar uplift rates, except in the Altos de Talinay area where uplift may have been accelerated by the activity of the Puerto Aldea Fault. The maximum elevation of Pleistocene paleoshorelines is generally close to 250 m and there is no higher older Neogene marine sediment, which implies that uplift accelerated during the Pleistocene following a period of coastal stability or subsidence. We observe that the coastal morphology largely depends on the latitudinal climatic variability. North of 26.75 degrees S, the coast is characterized by the presence of a high scarp associated with small and poorly preserved paleoshorelines at its foot. The existence of the coastal scarp in the northern part of the study area is permitted by the hyper-arid climate of the Atacama Desert. This particular morphology may explain why paleoshorelines evidencing coastal uplift are poorly preserved between 26.75 degrees S and 24 degrees S despite Upper Pleistocene uplift rates being comparable with those prevailing in the southern part of the study area. (C) 2016 Elsevier B.V. All rights reserved.
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Marusczak, N., Castelle, S., de Vogue, B., Knoery, J., & Cossa, D. (2016). Seasonal Variations of Total Gaseous Mercury at a French Coastal Mediterranean Site. Aerosol And Air Quality Research, 16(1), 46–60.
Résumé: Total gaseous mercury (TGM) was continuously measured in 2009 and 2012, at a coastal site on the Mediterranean Sea (La Seyne-sur-Mer, France). Air temperature, humidity, wind speed and direction, and chemical parameters (O-3, CO, NOx and PM10) were also measured as tracers of atmospheric pollution. Average TGM concentrations did not differ between the two years, 2.20 +/- 0.54 and 2.16 +/- 0.60 ng m(-3) for 2009 and 2012 respectively. Diurnal variations of TGM were observed for both years and linked to local industrial or urban activities. Furthermore, a clear seasonal trend was observed, with TGM minima in summer and maxima in winter. This seasonality is common to several air pollutants, like the result of the variation in the dispersion of pollutants in the boundary layer and higher photochemical activity in summer. The highest TGM concentrations (> 3 ng m(-3)) were associated with air masses originating over urban and industrial areas of the Rhone Valley and local/regional anthropogenic sources. The influence of polluted air masses from these local/regional sources was confirmed by the significantly positive correlations between TGM and CO, NOx and PM10. We demonstrate that polluted air masses from nearby urban and industrial regions are an important source of TGM to Mediterranean coastal areas, rather than volatilization from the sea surface.
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Mathey, C., Feau, C., Politopoulos, I., Clair, D., Baillet, L., & Fogli, M. (2016). Behavior of rigid blocks with geometrical defects under seismic motion: an experimental and numerical study. Earthquake Engineering & Structural Dynamics, 45(15), 2455–2474.
Résumé: The present work investigates the influence of small geometrical defects on the behavior of slender rigid blocks. A comprehensive experimental campaign was carried out on one of the shake tables of CEA/Saclay in France. The tested model was a massive steel block with standard manufacturing quality. Release, free oscillations tests as well as shake table tests revealed a non-negligible out-of-plane motion even in the case of apparently plane initial conditions or excitations. This motion exhibits a highly reproducible part for a short duration that was used to calibrate a numerical geometrically asymmetrical model. The stability of this model when subjected to 2000 artificial seismic horizontal bidirectional signals was compared with the stability of a symmetrical one. This study showed that the geometrical imperfections slightly increase the rocking and overturning probabilities for earthquake signals in a narrow range of peak ground acceleration. Copyright (c) 2016 John Wiley & Sons, Ltd.
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Matsui, H., Heien, E., Aubert, J., Aurnou, J. M., Avery, M., Brown, B., et al. (2016). Performance benchmarks for a next generation numerical dynamo model. Geochemistry Geophysics Geosystems, 17(5), 1586–1607.
Résumé: Numerical simulations of the geodynamo have successfully represented many observable characteristics of the geomagnetic field, yielding insight into the fundamental processes that generate magnetic fields in the Earth's core. Because of limited spatial resolution, however, the diffusivities in numerical dynamo models are much larger than those in the Earth's core, and consequently, questions remain about how realistic these models are. The typical strategy used to address this issue has been to continue to increase the resolution of these quasi-laminar models with increasing computational resources, thus pushing them toward more realistic parameter regimes. We assess which methods are most promising for the next generation of supercomputers, which will offer access to O(10(6)) processor cores for large problems. Here we report performance and accuracy benchmarks from 15 dynamo codes that employ a range of numerical and parallelization methods. Computational performance is assessed on the basis of weak and strong scaling behavior up to 16,384 processor cores. Extrapolations of our weak-scaling results indicate that dynamo codes that employ two-dimensional or three-dimensional domain decompositions can perform efficiently on up to approximate to 10(6) processor cores, paving the way for more realistic simulations in the next model generation.
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Maufroy, E., Chaljub, E., Hollender, F., Bard, P. Y., Kristek, J., Moczo, P., et al. (2016). 3D numerical simulation and ground motion prediction: Verification, validation and beyond Lessons from the E2VP project. Soil Dynamics And Earthquake Engineering, 91, 53–71.
Résumé: The Euroseistest Verification and Validation Project (E2VP) is part of a series of complementary benchmarking exercises launched to better assess the ability of numerical simulation to accurately predict seismic ground motion. E2VP targeted more specifically the current, most-advanced numerical methods applied to realistic 3D, linear models of sedimentary basins through a quantitative comparison of the recorded and numerically simulated ground motions. The target site, located within the Mygdonian basin near Thessaloniki, Greece, has been thoroughly investigated for two decades and a detailed, realistic 3D model has been derived from geological, geophysical and geotechnical investigations, while a dedicated instrumentation provided a significant number of surface and borehole recordings. Verification and validation tests up to a frequency of 4 Hz, much beyond the 0.4 Hz fundamental frequency of the deepest part of the graben, have been performed for a set of 19 local, small to moderate magnitude events. For careful and accurate enough computations, the model-to-model differences are smaller than the model-to-observations differences, the latter being controlled by uncertainties primarily in the crustal propagation model and source properties, and secondarily in the shallow structure. It is therefore recommended to prefer distant and/or deep events (R > 10-20 km, Z > 8-10 km) for validation exercises. Additional sensitivity tests illustrate the ability of carefully verified numerical simulation tools to provide an instructive insight at the structure of the so-called “aleatory” variability of ground motion, for both its within- and between-event components. The between-event variability is shown to be very sensitive to hypocenter location errors (even as low as +/- 2 km), and to uncertainty in magnitude estimates. It explains the increase of aleatory variability for small magnitude events and emphasizes the usefulness of dense seismological networks. The within event, single-site variability is shown to be associated to an “epistemic” dependence of the 3D site response on the event back-azimuth, distance and depth, and calls for caution when interpreting single station variabilities derived from a too small number of events.
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Maurice, S., Clegg, S. M., Wiens, R. C., Gasnault, O., Rapin, W., Forni, O., et al. (2016). ChemCam activities and discoveries during the nominal mission of the Mars Science Laboratory in Gale crater, Mars. Journal Of Analytical Atomic Spectrometry, 31(4), 863–889.
Résumé: At Gale crater, Mars, ChemCam acquired its first laser-induced breakdown spectroscopy (LIBS) target on Sol 13 of the landed portion of the mission (a Sol is a Mars day). Up to Sol 800, more than 188 000 LIBS spectra were acquired on more than 5800 points distributed over about 650 individual targets. We present a comprehensive review of ChemCam scientific accomplishments during that period, together with a focus on the lessons learned from the first use of LIBS in space. For data processing, we describe new tools that had to be developed to account for the uniqueness of Mars data. With regard to chemistry, we present a summary of the composition range measured on Mars for major-element oxides (SiO2, TiO2, Al2O3, FeOT, MgO, CaO, Na2O, K2O) based on various multivariate models, with associated precisions. ChemCam also observed H, and the non-metallic elements C, O, P, and S, which are usually difficult to quantify with LIBS. F and Cl are observed through their molecular lines. We discuss the most relevant LIBS lines for detection of minor and trace elements (Li, Rb, Sr, Ba, Cr, Mn, Ni, and Zn). These results were obtained thanks to comprehensive ground reference datasets, which are set to mimic the expected mineralogy and chemistry on Mars. With regard to the first use of LIBS in space, we analyze and quantify, often for the first time, each of the advantages of using stand-off LIBS in space: no sample preparation, analysis within its petrological context, dust removal, sub-millimeter scale investigation, multi-point analysis, the ability to carry out statistical surveys and whole-rock analyses, and rapid data acquisition. We conclude with a discussion of ChemCam performance to survey the geochemistry of Mars, and its valuable support of decisions about selecting where and whether to make observations with more time and resource-intensive tools in the rover's instrument suite. In the end, we present a bird's-eye view of the many scientific results: discovery of felsic Noachian crust, first observation of hydrated soil, discovery of manganese-rich coatings and fracture fills indicating strong oxidation potential in Mars' early atmosphere, characterization of soils by grain size, and wide scale mapping of sedimentary strata, conglomerates, and diagenetic materials.
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Meier, C., Voegelin, A., Pradas del Real, A., Sarret, G., Mueller, C. R., & Kaegi, R. (2016). Transformation of Silver Nanoparticles in Sewage Sludge during Incineration. Environmental Science & Technology, 50(7), 3503–3510.
Résumé: Silver nanoparticles (Ag-NP) discharged into the municipal sewer system largely accumulate in the sewage sludge. Incineration and agricultural use are currently the most important strategies for sewage sludge management. Thus, "the behavior of Ag-NP during sewage sludge incineration is essential for a comprehensive life cycle analysis and a more complete understanding of the fate of Ag-NP in the (urban) environment. To address the transformation of Ag-NP during sewage sludge incineration, we spiked metallic Ag-0-NP to a pilot wastewater treatment plant and digested the sludge anaerobically. The sludge was then incinerated on a bench-scale fluidized bed reactor in a series of experiments under variable conditions. Complementary results from X-ray absorption spectroscopy (XAS) and electron microscopy energy dispersive X-ray (EM EDX) analysis revealed that Ag-0-NP transformed into Ag2S-NP during the wastewater treatment, in agreement with previous studies. On the basis of a principal component analysis and subsequent target testing of the XAS spectra, Ag-0 was identified as a major Ag component in the ashes, and Ag2S was clearly absent. The reformation of Ag-0-NP was confirmed by EM EDX. The fraction of Ag of the total Ag in the ashes was quantified by linear combination fitting (LCF) of XAS spectra, and values as high as 0.8 were found for sewage sludge incinerated at 800 degrees C in a synthetic flue gas atmosphere. Low LCF totals (72% to 94%) indicated that at least one relevant reference spectrum was missing in the LCF analysis. The presence of spherical Ag-NP with.a diameter of <50 nm extending into the subnm range was revealed by electron microscopy analyses. The rapid formation of Ag-0-NP from Ag2S during sewage sludge incineration, as demonstrated in this study, needs to, be considered in the life cycle assessment of engineered Ag-NP.
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Merkulova, M., Munoz, M., Vidal, O., & Brunet, F. (2016). Role of iron content on serpentinite dehydration depth in subduction zones: Experiments and thermodynamic modeling. Lithos, 264, 441–452.
Résumé: A series of dehydration experiments in the piston-cylinder apparatus was carried out at 2 GPa and 550-850 degrees C on a natural antigorite sample mixed with 5 wt.% of magnetite. Chemical analyses of experimental products show a progressive decrease of the Mg# in antigorite and dinopyroxene between 550 and 675 degrees C, whereas the Mg# of olivine increases. The observed behavior of Mg# signifies Fe-Mg exchange between coexisting minerals. At higher temperatures, between 700 and 850 degrees C, compositions remain stable for all minerals in experimental assemblages. Thermodynamic parameters of the ferrous antigorite end-member were refined with the use of Holland and Powell (1998) data set and added to the antigorite solid solution. Good agreement between theoretical calculations performed for the studied bulk composition and experimental results confirms extrapolated thermodynamic data for Fe-antigorite. Constrained parameters allowed to calculate phase relationships for various serpentinite compositions. First, we assessed the effect of bulk iron content, from 0 to 10 wt.% FeO, on the stability field of antigorite. The results show significant decrease of the antigorite thermal stability with increasing bulk Fe content. Second, we demonstrated the influence of bulk iron content on dehydration reactions in subduction zones along typical thermal gradients. Dehydration observed in pure MSH (MgO-SiO2-H2O) systems comprised of antigorite appears as a univariant reaction, which happens at 710 degrees C/3.7 GPa and 640 degrees C/6 GPa in “hot” and “cold” subduction, respectively. In contrast, more complex in composition Fe-bearing serpentinites show spread dehydration profiles through divariant reactions from similar to 300 degrees C/0.8 GPa to 700 degrees C/3.6 GPa and from 450 degrees C/4 GPa to 650 degrees C/7.4 GPa for “hot” and “cold” thermal gradients respectively. A comparison between depths of “water-release events” and “earthquake occurrence” in the South Chile slab (“hot” subduction) highlights a clear correlation between each other, suggesting a possible contribution of the dehydration of Fe-bearing serpentinites to the occurrence of seismic events. In contrast, and based on the same comparison applied to the Kermadec slab, our results demonstrate that there is no correlation in depth between serpentinite dehydration and seismicity in “cold” subduction zones. (C) 2016 Elsevier B.V. All rights reserved.
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Metivier, L., & Brossier, R. (2016). The SEISCOPE optimization toolbox: A large-scale nonlinear optimization library based on reverse communication. Geophysics, 81(2), F1–F15.
Résumé: The SEISCOPE optimization toolbox is a set of FORTRAN 90 routines, which implement first-order methods (steepest-descent and nonlinear conjugate gradient) and second-order methods (l-BFGS and truncated Newton), for the solution of large-scale nonlinear optimization problems. An efficient line-search strategy ensures the robustness of these implementations. The routines are proposed as black boxes easy to interface with any computational code, where such large-scale minimization problems have to be solved. Traveltime tomography, least-squares migration, or full-waveform inversion are examples of such problems in the context of geophysics. Integrating the toolbox for solving this class of problems presents two advantages. First, it helps to separate the routines depending on the physics of the problem from the ones related to the minimization itself, thanks to the reverse communication protocol. This enhances flexibility in code development and maintenance. Second, it allows us to switch easily between different optimization algorithms. In particular, it reduces the complexity related to the implementation of second-order methods. Because the latter benefit from faster convergence rates compared to first-order methods, significant improvements in terms of computational efforts can be expected.
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Metivier, L., Brossier, R., Merigot, Q., Oudet, E., & Virieux, J. (2016). An optimal transport approach for seismic tomography: application to 3D full waveform inversion. Inverse Problems, 32(11).
Résumé: The use of optimal transport distance has recently yielded significant progress in image processing for pattern recognition, shape identification, and histograms matching. In this study, the use of this distance is investigated for a seismic tomography problem exploiting the complete waveform; the full waveform inversion. In its conventional formulation, this high resolution seismic imaging method is based on the minimization of the L-2 distance between predicted and observed data. Application of this method is generally hampered by the local minima of the associated L-2 misfit function, which correspond to velocity models matching the data up to one or several phase shifts. Conversely, the optimal transport distance appears as a more suitable tool to compare the misfit between oscillatory signals, for its ability to detect shifted patterns. However, its application to the full waveform inversion is not straightforward, as the mass conservation between the compared data cannot be guaranteed, a crucial assumption for optimal transport. In this study, the use of a distance based on the Kantorovich-Rubinstein norm is introduced to overcome this difficulty. Its mathematical link with the optimal transport distance is made clear. An efficient numerical strategy for its computation, based on a proximal splitting technique, is introduced. We demonstrate that each iteration of the corresponding algorithm requires solving the Poisson equation, for which fast solvers can be used, relying either on the fast Fourier transform or on multigrid techniques. The development of this numerical method make possible applications to industrial scale data, involving tenths of millions of discrete unknowns. The results we obtain on such large scale synthetic data illustrate the potentialities of the optimal transport for seismic imaging. Starting from crude initial velocity models, optimal transport based inversion yields significantly better velocity reconstructions than those based on the L-2 distance, in 2D and 3D contexts.
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Metivier, L., Brossier, R., Merigot, Q., Oudet, E., & Virieux, J. (2016). Measuring the misfit between seismograms using an optimal transport distance: application to full waveform inversion. Geophysical Journal International, 205(1), 345–377.
Résumé: Full waveform inversion using the conventional L-2 distance to measure the misfit between seismograms is known to suffer from cycle skipping. An alternative strategy is proposed in this study, based on a measure of the misfit computed with an optimal transport distance. This measure allows to account for the lateral coherency of events within the seismograms, instead of considering each seismic trace independently, as is done generally in full waveform inversion. The computation of this optimal transport distance relies on a particular mathematical formulation allowing for the non-conservation of the total energy between seismograms. The numerical solution of the optimal transport problem is performed using proximal splitting techniques. Three synthetic case studies are investigated using this strategy: the Marmousi 2 model, the BP 2004 salt model, and the Chevron 2014 benchmark data. The results emphasize interesting properties of the optimal transport distance. The associated misfit function is less prone to cycle skipping. A workflow is designed to reconstruct accurately the salt structures in the BP 2004 model, starting from an initial model containing no information about these structures. A high-resolution P-wave velocity estimation is built from the Chevron 2014 benchmark data, following a frequency continuation strategy. This estimation explains accurately the data. Using the same workflow, full waveform inversion based on the L-2 distance converges towards a local minimum. These results yield encouraging perspectives regarding the use of the optimal transport distance for full waveform inversion: the sensitivity to the accuracy of the initial model is reduced, the reconstruction of complex salt structure is made possible, the method is robust to noise, and the interpretation of seismic data dominated by reflections is enhanced.
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Métois, M., Vigny, C., & Socquet, A. (2016). Interseismic Coupling, Megathrust Earthquakes and Seismic Swarms Along the Chilean Subduction Zone (38A degrees-18A degrees S). Pure And Applied Geophysics, 173(5), 1431–1449.
Résumé: The recent expansion of dense GPS networks over plate boundaries allows for remarkably precise mapping of interseismic coupling along active faults. The interseismic coupling coefficient is related to the ratio between slipping velocity on the fault during the interseismic period and the long-term plates velocity, but the interpretation of coupling in terms of mechanical behavior of the fault is still unclear. Here, we investigate the link between coupling and seismicity over the Chilean subduction zone that ruptured three times in the last 5 years with major earthquakes (Maule Mw 8.8 in 2010, Iquique Mw 8.1 in 2014 and Illapel Mw 8.4 in 2015). We combine recent GPS data acquired over the margin (38A degrees-18A degrees S) with older data to get the first nearly continuous picture of the interseismic coupling variations on the subduction interface. Here, we show that at least six low coupling zones (LCZ), areas where coupling is low relatively to the neighboring highly coupled segments can be identified. We also find that for the three most recent Mw > 8 events, co-seismic asperities correlate well with highly coupled segments, while LCZs behaved as barriers and stopped the ruptures. The relation between coupling and background seismicity in the interseismic period before the events is less clear. However, we note that swarm sequences are prone to occur in intermediate coupling areas at the transition between LCZ and neighboring segments, and that the background seismicity tends to concentrate on the downdip part of the seismogenic locked zone. Thus, highly coupled segments usually exhibit low background seismicity. In this overall context, the Metropolitan segment that partly ruptured during the 2015 Illapel earthquake appears as an outlier since both coupling and background seismicity were high before the rupture, raising the issue of the remaining seismic hazard in this very densely populated area.
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Mezzacappa, A., Melikechi, N., Cousin, A., Wiens, R. C., Lasue, J., Clegg, S. M., et al. (2016). Application of distance correction to ChemCam laser-induced breakdown spectroscopy measurements. Spectrochimica Acta Part B-Atomic Spectroscopy, 120, 19–29.
Résumé: Laser-induced breakdown spectroscopy (LIBS) provides chemical information from atomic, ionic, and molecular emissions from which geochemical composition can be deciphered. Analysis of LIBS spectra in cases where targets are observed at different distances, as is the case for the ChemCam instrument on the Mars rover Curiosity, which performs analyses at distances between 2 and 7.4 m is not a simple task. In our previous work we showed that spectral distance correction based on a proxy spectroscopic standard created from first-shot dust observations on Mars targets ameliorates the distance bias in multivariate-based elemental-composition predictions of laboratory data. In this work, we correct an expanded set of neutral and ionic spectral emissions for distance bias in the ChemCam data set. By using and testing different selection criteria to generate multiple proxy standards, we find a correction that minimizes the difference in spectral intensity measured at two different distances and increases spectral reproducibility. When the quantitative performance of distance correction is assessed, there is improvement for SiO2, Al2O3, CaO, FeOT, Na2O, K2O, that is, for most of the major rock forming elements, and for the total major-element weight percent predicted. However, for MgO the method does not provide improvements while for TiO2, it yields inconsistent results. In addition, we have observed that many emission lines do not behave consistently with distance, evidenced from laboratory analogue measurements and ChemCam data. This limits the effectiveness of the method. (C) 2016 Elsevier B.V. All rights reserved.
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Michalak, M. J., Hall, S. R., Farber, D. L., Audin, L., & Hourigan, J. K. (2016). (U-Th)/He thermochronology records late Miocene accelerated cooling in the north-central Peruvian Andes. Lithosphere, 8(2), 103–115.
Résumé: The along-strike morphology of the South American Andes varies significantly, but it remains unclear if the timing and magnitude of rock exhumation are similarly varied. We used low-temperature (U-Th)/He thermochronology to constrain the exhumation history of the Eastern Cordillera in the north-central Peruvian Andes (7 degrees S-8.5 degrees S). Nine zircon (U-Th)/He mean ages range from 28 +/- 4.5 Ma to 281 +/- 60 Ma, and seven apatite (U-Th)/He mean ages yield tightly clustered late Miocene ages of 6.4 +/- 3.8 Ma to 10.7 +/- 1.8 Ma. These results document slow rock cooling followed by abrupt, accelerated cooling in the mid-late Miocene. Model time-temperature histories show slow cooling throughout the late Paleozoic to early Miocene, followed by an increase in cooling initiating between 14 and 10 Ma and continuing to the present. This rock cooling signal is regionally synchronous along the strike of the range and occurs at a time of a shift to a more humid and erosive climate in the eastern Andes. We suggest that a mid-late Miocene climate shift, following or synchronous with topographic growth, was responsible for the acceleration of rock exhumation in the north-central Peruvian Andes.
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Milliner, C. W. D., Dolan, J. F., Hollingsworth, J., Leprince, S., & Ayoub, F. (2016). Comparison of coseismic near-field and off-fault surface deformation patterns of the 1992 M-w 7.3 Landers and 1999 M-w 7.1 Hector Mine earthquakes: Implications for controls on the distribution of surface strain. Geophysical Research Letters, 43(19), 10115–10124.
Résumé: Subpixel correlation of preevent and postevent air photos reveal the complete near-field, horizontal surface deformation patterns of the 1992 M-w 7.3 Landers and 1999 M-w 7.1 Hector Mine ruptures. Total surface displacement values for both earthquakes are systematically larger than on-fault displacements from geologic field surveys, indicating significant distributed, inelastic deformation occurred along these ruptures. Comparison of these two data sets shows that 4610% and 3922% of the total surface deformation were distributed over fault zones averaging 154m and 121m in width for the Landers and Hector Mine events, respectively. Spatial variations of distributed deformation along both ruptures show correlations with the type of near-surface lithology and degree of fault complexity; larger amounts of distributed shear occur where the rupture propagated through loose unconsolidated sediments and areas of more complex fault structure. These results have basic implications for geologic-geodetic rate comparisons and probabilistic seismic hazard analysis.
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Milliner, C. W. D., Sammis, C., Allam, A. A., Dolan, J. F., Hollingsworth, J., Leprince, S., et al. (2016). Resolving Fine-Scale Heterogeneity of Co-seismic Slip and the Relation to Fault Structure. Scientific Reports, 6.
Résumé: Fault slip distributions provide important insight into the earthquake process. We analyze high-resolution along-strike co-seismic slip profiles of the 1992 M-w = 7.3 Landers and 1999 M-w = 7.1 Hector Mine earthquakes, finding a spatial correlation between fluctuations of the slip distribution and geometrical fault structure. Using a spectral analysis, we demonstrate that the observed variation of co-seismic slip is neither random nor artificial, but self-affine fractal and rougher for Landers. We show that the wavelength and amplitude of slip variability correlates to the spatial distribution of fault geometrical complexity, explaining why Hector Mine has a smoother slip distribution as it occurred on a geometrically simpler fault system. We propose as a physical explanation that fault complexity induces a heterogeneous stress state that in turn controls co-seismic slip. Our observations detail the fundamental relationship between fault structure and earthquake rupture behavior, allowing for modeling of realistic slip profiles for use in seismic hazard assessment and paleoseismology studies.
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Misra, S., Torres-Verdin, C., Revil, A., Rasmus, J., & Homan, D. (2016). Interfacial polarization of disseminated conductive minerals in absence of redox-active species – Part 1: Mechanistic model and validation. Geophysics, 81(2), E139–E157.
Résumé: Electrically conductive mineral inclusions are commonly present in organic-rich mudrock and source-rock formations such as veins, laminations, rods, grains, flakes, and beds. Laboratory and subsurface electromagnetic (EM) measurements performed on geomaterials containing electrically conductive inclusions generally exhibit frequency dispersion due to interfacial polarization phenomena at host-inclusion interfaces. In the absence of redox-active species, surfaces of electrically conductive mineral inclusions are impermeable to the transport of charge carriers, inhibit the exchange of charges and behave as perfectly polarized (PP) interfaces under the influence of an externally applied EM field. Interfacial polarization phenomena involving charge separation, migration, accumulation/depletion, and relaxation around PP interfaces is referred to as PP interfacial polarization; it influences the magnitude and direction of the electric field and charge carrier migration in the geomaterial. We have developed a mechanistic model to quantify the complex-valued electrical conductivity response of geomaterials containing electrically conductive mineral inclusions, such as pyrite and magnetite, uniformly distributed in a fluid-filled, porous matrix made of nonconductive grains possessing surface conductance, such as silica and clay grains. The model first uses a linear approximation of the Poisson-Nernst-Planck equations of dilute solution theory to determine the induced dipole moment of a single isolated conductive inclusion and that of a single isolated nonconductive grain surrounded by an electrolyte. A consistent effective-medium formulation was then implemented to determine the effective complex-valued electrical conductivity of the geomaterial. Model predictions were in good agreement with laboratory measurements of multifrequency complex-valued electrical conductivity, relaxation time, and chargeability of mixtures containing electrically conductive inclusions.
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Misra, S., Torres-Verdin, C., Revil, A., Rasmus, J., & Homan, D. (2016). Interfacial polarization of disseminated conductive minerals in absence of redox-active species – Part 2: Effective electrical conductivity and dielectric permittivity. Geophysics, 81(2), E159–E176.
Résumé: Hydrocarbon-bearing conventional formations, mudrock formations, and source-rock formations generally contain clays, pyrite, magnetite, graphitelike carbon, and/or other electrically conductive mineral inclusions. Under redox-inactive conditions, these inclusions give rise to perfectly polarized interfacial polarization (PPIP) when subjected to an external electric field. Effective electrical conductivity and dielectric permittivity of geomaterials containing such inclusions are frequency-dependent properties due to the electric-field-induced interfacial polarization and associated charge relaxation around host-inclusion interfaces. Existing resistivity interpretation techniques do not account for PPIP phenomena, and hence they can lead to inaccurate estimation of water saturation, total organic content, and conductivity of formation water based on subsurface galvanic resistivity, electromagnetic (EM) induction, and EM propagation measurements in the presence of conductive mineral inclusions. In the first paper of our two-part publication series, we derived a mechanistic electrochemical model, the PPIP model, and we validated a coupled model that integrates the PPIP model with a surface-conductance-assisted interfacial polarization (SCAIP) model to quantify the frequency-dependent electrical complex conductivity of geomaterials. We have used the PPIP-SCAIP model to evaluate the dependence of effective complex-valued conductivity of geologic mixtures on (1) frequency, (2) conductivity of the host medium, and (3) material, size, and the shape of inclusions. Notably, we have used the PPIP-SCAIP model to identify rock conditions that give rise to significant differences in effective conductivity and effective relative permittivity of conductive-inclusion-bearing mixtures from those of conductive-inclusion-free homogeneous media. For a mixture containing as low as a 5% volume fraction of disseminated conductive inclusions, the low-frequency effective conductivity of the mixture is in the range of -30% to +100% with respect to the host conductivity for frequencies between 100 Hz and 100 kHz. Further, the high-frequency effective relative permittivity of that mixture is in the range of -10% to +90% with respect to the host relative permittivity for frequencies between 100 kHz and 10 MHz.
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Montes-Hernandez, G., & Renard, F. (2016). Time-Resolved in Situ Raman Spectroscopy of the Nucleation and Growth of Siderite, Magnesite, and Calcite and Their Precursors. Crystal Growth & Design, 16(12), 7218–7230.
Résumé: The nucleation and growth processes of particles and crystals from aqueous systems are actively investigated and occasionally open to debate because multistep nucleation and prenucleation events often exist. This study demonstrates that time-resolved Raman spectroscopic measurements can provide complementary and useful information on the nucleation and growth of particles and crystals from homogeneous and heterogeneous systems at different pressure-temperature conditions. Three minerals were chosen for this study: siderite, magnesite, and calcite, three carbonate minerals that are widespread in geological environments and have numerous industrial and medical applications. As expected, siderite and calcite can rapidly form via an amor-phous precursor when using concentrated solutions of reactants directly mixed at ambient temperature (similar to 25 degrees C) and pressure (similar to 1 bar) (i.e., via spinodal decomposition or when energetic barrier is close to zero). In addition, calcium carbonate clusters and/or probably also amorphous calcium carbonate (ACC) were detected in the first 5 min prior to calcite nucleation in a Ca(OH)(2)-H2O-CO2 concentrated slurry at 25 degrees C and 50 bar. The calcite and siderite crystals, nucleated from their respective amorphous phases, grow by oriented aggregation of crystalline nanoparticles leading to porous spherical siderite-mesocrystals or nonporous rhombohedral calcite crystals after 24 h of reaction, as deduced from field emission scanning electron microscopy images and X-ray diffraction analyses. Moreover, the possibility of an Ostwald ripening mechanism contributing to crystal growth is not excluded. Conversely, magnesite formation was not detected by Raman spectroscopy at ambient room temperature; only nesquehonite (MgCO3 center dot 3H(2)O) and dypingite (Mg-5(CO3)(4)center dot(OH)(2)center dot 5H(2)O) were formed, depending on the reacting solution chemistry. These two minerals transform rapidly into hydromagnesite (Mgs(CO3)(4)-(OH)(2)center dot 4H(2)O) by a heat-aging step at 50 degrees C. In fact, magnesite formation (MgCO3: anhydrous Mg carbonate) was only measured under hydrothermal conditions (e.g., 90 degrees C and 50 bar of initial CO, pressure), and systematically a transient crystalline phase such as hydromagnesite was observed prior to magnesite nucleation and growth at the investigated conditions. This confirms that crystalline phases (not necessarily polymorphs) can also act as precursors during nucleation and growth of more stable phases. The fact that direct nucleation of magnesite from ionic solutions and slurries at ambient temperature is not observed is probably due to the high level of hydration of Mg ions in aqueous systems.
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Montes-Hernandez, G., Chiriac, R., Findling, N., Toche, F., & Renard, F. (2016). Synthesis of ceria (CeO2 and CeO2-X) nanoparticles via decarbonation and Ce(III) oxydation of synthetic bastnasite (CeCO3F). Materials Chemistry And Physics, 172, 202–210.
Résumé: Ceria (CeO2) crystalline compound is widely used as a catalyst or catalyst support and many other applications. However, the studies are continuing with a view to improving existing methods and/or developing innovative routes to obtain well -controlled shapes and sizes of ceria nanoparticles. In the present study, we report an original method to synthesize ceria nanoparticles (CeO2 and CeO2-X) by using two independent stages: (1) the precipitation of bastnasite-rich material under hydrothermal conditions (90 and 300 degrees C) and (2) the calcination of powdered basnasite-rich material at different temperatures (500, 1000 and 1600 degrees C) and under different atmospheres (air, Ar, N-2 and secondary vacuum). In addition, simultaneous thermal analyses (TGA/DSC) coupled with gas chromatography (mu GC/MS) were performed in order to investigate on the ceria formation during bastnasite de -carbonation and its thermal behavior at high temperature (until 1600 degrees C) under three different gas atmospheres (air, Ar and N-2). Herein, ceria was in -situ formed independently on the gas investigated atmosphere. This means that sufficient oxygen was also available in the so-called inert atmospheres (Ar and N-2) to oxidize the Ce(III) contained in Ce-carbonates to Ce(IV) constituting ceria cubic structure. Moreover, μGC/MS measurements confirm that in-situ formed ceria CeO2 at about 600 degrees C is then partially reduced to CeO2-x at high temperature after 1000 degrees C because an increase in oxygen was clearly detected in expelled gas during heating process. This fundamental experimental study provides the hydrothermal conditions to which Ce fluorocarbonates could be formed in natural environments. In addition, new experimental conditions to produce ceria with oxygen vacancies CeO2-X without reducing gas agent and at lower temperature are also provided in this study. (C) 2016 Elsevier B.V. All rights reserved.
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Montes-Hernandez, G., Findling, N., & Renard, F. (2016). Dissolution-precipitation reactions controlling fast formation of dolomite under hydrothermal conditions. Applied Geochemistry, 73, 169–177.
Résumé: In laboratory experiments, the precipitation of dolomite at ambient temperature is virtually impossible due to strong solvation shells of magnesium ions in aqueous media and probably also due to the existence of a more intrinsic crystallization barrier that prevents the formation of long-range ordered crystallographic structures at ambient surface conditions. Conversely, dolomite can easily form at high temperature (> 100 degrees C), but its precipitation and growth requires several days or weeks depending on experimental conditions. In the present study, experiments were performed to assess how a single heat-ageing step promotes the formation of dolomite under high-carbonate alkaline conditions via dissolution-precipitation reactions. This reaction pathway is relevant for the so-called hydrothermal dolomite frequently observed in carbonate platforms, but still ill-defined and understood. Our precipitation route is summarized by two main sequential reactions: (1) precipitation of Mg-calcite at low temperature (similar to 20 degrees C) by aqueous carbonation of synthetic portlandite (Ca(OH)(2)) in a highly alkaline medium (1 M of NaOH and 1 M of MgCl2), leading to precipitation of oriented nanoparticles of low-and high-Mg calcite (similar to 79 wt%) coexisting with aragonite (similar to 18 wt%) and brucite (similar to 3 wt%) after 24 h; (2) fast dolomitization process starting from 1 h of reaction by a single heat-ageing step from similar to 20 to 200, 250 and 300 degrees C. Here, the Mg-calcite acts as a precursor that lowers the overall kinetics barrier for dolomite formation. Moreover, it is an important component in some bio-minerals (e.g. corals and seashells). Quantitative Rietveld refinements of XRD patterns, FESEM observations and FTIR measurements on the sequentially collected samples suggest fast dolomite precipitation coupled with dissolution of transient mineral phases such as low-Mg calcite (Mg < 4 mol%), high-Mg calcite (Mg > 4 mol%), proto-dolomite (or disordered dolomite; Mg > 40 mol%) and Ca-magnesite. In this case, the dolomite formation rate and the time-dependent mineral composition strongly depend on reaction temperature. For example, high-urity dolomitic material (87 wt% of dolomite mixed with 13 wt% of magnesite) was obtained at 300 degrees C after 48 h of reaction. Conversely, a lower proportion of dolomite (37 wt%), mixed with proto-olomite (43 wt%), Ca-magnesite (16 wt%) and high-Mg calcite (4 wt%), was obtained at 200 degrees C after 72 h. The present experiments provide an additional mechanism for the massive dolomite formation in sedimentary environments (ex. deep sea organic-rich carbonate-sediments) if such sediments are subjected to significant temperature variations, for example by hot fluid circulations related to volcanic activity. In such systems, organic degradation increases the carbonate alkalinity (HCO3-) necessary to induce the dolomitization process at low and high temperature. (C) 2016 Elsevier Ltd. All rights reserved.
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Nakata, N., Boue, P., Brenguier, F., Roux, P., Ferrazzini, V., & Campillo, M. (2016). Body and surface wave reconstruction from seismic noise correlations between arrays at Piton de la Fournaise volcano. Geophysical Research Letters, 43(3), 1047–1054.
Résumé: Body wave reconstruction from ambient seismic noise correlations is an important step toward improving volcano imaging and monitoring. Here we extract body and surface waves that propagate in Piton de la Fournaise volcano on La Reunion island using ambient noise cross correlation and array-processing techniques. Ambient noise was continuously recorded at three dense arrays, each comprising 49 geophones. To identify and enhance the Green's function from the ambient noise correlation, we apply a double beamforming (DBF) technique between the array pairs. The DBF allows us to separate surface and body waves, direct and reflected waves, and multipathing waves. Based on their azimuths and slownesses, we successfully extract body waves between all the combinations of arrays, including the wave that propagates through the active magmatic system of the volcano. Additionally, we identify the effects of uneven noise source distribution and interpret the surface wave reflections.
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Nasser, F., Li, Z. Y., Gueguen, P., & Martin, N. (2016). Frequency and damping ratio assessment of high-rise buildings using an Automatic Model-Based Approach applied to real-world ambient vibration recordings. Mechanical Systems And Signal Processing, 75, 196–208.
Résumé: This paper deals with the application of the Automatic Model-Based Approach (AMBA) over actual buildings subjected to real-world ambient vibrations. In a previous paper, AMBA was developed with the aim of automating the estimation process of the modal parameters and minimizing the estimation error, especially that of the damping ratio. It is applicable over a single-channel record, has no parameters to be set, and no manual initialization phase. The results presented in this paper should be regarded as further documentation of the approach over real-world ambient vibration signals. (C) 2016 Elsevier Ltd. All rights reserved.
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Nasser, F., Li, Z. Y., Martin, N., & Gueguen, P. (2016). An automatic approach towards modal parameter estimation for high-rise buildings of multicomponent signals under ambient excitations via filter-free Random Decrement Technique. Mechanical Systems And Signal Processing, 70-71, 821–831.
Résumé: This paper proposes an automatic modal analysis approach for signals of high-rise buildings recorded under real-world ambient excitations. The fact of working over such type of signals is faced with several challenges: the time-domain convolution between the system impulse response and the seismic noise, the existence of several components, the presence of closely-spaced frequency modes, with high additive noises, and low, exponential and damped amplitudes. The proposed approach handles these challenges simultaneously without the need for a user intervention. It is based on a filter-free Random Decrement Technique to estimate the free-decay response, followed by a spectral-based method for a rough modal estimate and finalized by a Maximum-Likelihood Estimation process to refine the modal estimates. Each of these processes is responsible to tackle one or more of the aforementioned challenges in the aim to provide an automatic and moreover a reliable modal analysis of the studied signals. (C) 2015 Elsevier Ltd. All rights reserved.
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Nehme, C., Jaillet, S., Voisin, C., Hellstrom, J., Gerard-Adjizian, J., & Delannoy, J. J. (2016). Control of cave levels in Kanaan, Kassarat and Jeita karst systems (Central Mount Lebanon, Lebanon). Zeitschrift Fur Geomorphologie, 60(2), 95–117.
Résumé: Mount Lebanon is a mountainous Mediterranean karst ridge, consisting of high plateaus reaching 3,088 m altitude and entrenched by deep valleys. Fluvial drainage systems run on a steep gradient and reach the Mediterranean Sea coast in less than 30 km distance. In Central Mount Lebanon, the downstream parts of Antelias and Kalb valleys host the Kanaan cave (160 m), the Kassarat cave (4.6 km) and the Jeita cave (10.05 km), whose subterranean rivers are connected to the karst springs located close to the contact between the Cretaceous aquidude and the Jurassic karst aquifer. The area thus comprises a dammed Jurassic aquifer in which all the studied cave levels developed at certain altitudes. A geomorphological study performed by speleological and geomorphological surveys and completed by analyses of cave sediments allowed the formulation of a first evolutionary framework of the karst system. Several features suggest a long-term and multi-stage evolution of the karst in both Antelias and Kalb valleys. The horizontal caves develop between 60 and 160 m a.s.l. and constitute water table caves in a steeply dipping structure (Mount Lebanon's western fold). These cave levels are part of an ancient system that developed near the water table controlled by the position of the aquiclude and correspond to the base level of a past fluvial network. An important phase of base level cave development is documented in the relict passages above 90 m a.s.l. Speleogenetic features between 90 and 160 m developed in a phreatic environment where paragenesis or “per ascensum erosion” processes occurred during base level rise. Epiphreatic features were identified at 60-70 m in Kassarat and Jeita caves. Typical morphological features such as horizontal solution passages and solution notches suggest a phase of stillstand of the base-level. The evolution of the water table level from a paragenetic rise above 90 m to a continuous lowering below 90 m and with a temporary stillstand phase at 70-60 m, is related to the fluvial base-level evolution. Preliminar chronological constraints for the evolution of the karst system are discussed based on U/Th dating of speleothems and cave levels (90-160 and 60-70 m) and their relationship with the altitude of the low-gradient surfaces. The cave levels between 90 and 160 m are related to a water table rise that caused an alluviation process at the river's mouth probably during the Pliocene transgression phase of the Mediterranean Sea (PHS). Abandoning of the upper cave levels (90-160 and 60-70 m) is the result of a continuous lowering of the water table related to fluvial incision. The lowering of the water table level below 90 m is mainly related to the fluvial incision of the acquiclude in a high geodynamic context (Mount Lebanon uplift) during the Pleistocene.
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Niu Q., M. P., A. Revil, and M. Saidian. (2016). Textural control on the quadrature conductivity of porous media. Geophysics, 50, 8205−8213.
Résumé: nduced polarization (IP) has been broadly used for environmental and hydrogeological applications and in civil engineering. The IP response of a porous medium without metallic particles (described by its quadrature conductivity or its normalized chargeability) is controlled by the interfacial electrochemistry of the electrical double layer and the pore-space geometry. We use the specific surface per unit pore volume normalized by the formation factor (i.e.,Spor/F)) as the controlling textural parameter for the quadrature conductivity. This relationship is obtained by averaging the surface conductance over the pore volume. A database that contains 76 samples (including porous borosilicate glass, sandstones, and clayey sediments) is used to check the new scaling. In addition to these data, we have conducted new IP measurements on 13 samples from the Middle Bakken Formation corresponding to low-porosity clayey materials. Comparison between the experimental data and our model confirms that the ratio Spor/F is the dominant textural parameter describing the quadrature conductivity σ''of a broad range of porous media. The database was also used to test whether the quadrature conductivity depended either on Spor
or the specific surface area Sm, or the ratio Sm/(Fφ) (φ being the connected porosity). Although the quadrature conductivity scales with Spor
and Sm for high-porosity sandstones, these relationships are not appropriate for the low-porosity clayey materials presented in this study. However, experimental data support the dependence of the quadrature conductivity on Sm/(Fφ) a published relationship obtained through the volume averaging approach.
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Niu, Q. F., & Revil, A. (2016). Connecting complex conductivity spectra to mercury porosimetry of sedimentary rocks. Geophysics, 81(1), E17–E32.
Résumé: The measured spectral-induced polarization (SIP) response of highly porous granular materials can be modeled by upscaling the Nernst-Planck equation for a single grain and performing a convolution product with the particle size distribution. The distribution of relaxation times associated with the polarization of consolidated porous media seems, intuitively, to be controlled by the pore size distribution because of the radius of curvature of the interface between the solid and the pore water. We have explored a mechanistic model connecting the SIP response of consolidated media to mercury injection capillary porosimetry (MICP) data. First, we developed a mechanistic electric double layer (EDL) polarization model for porous media, which considered the polarization of the Stern layer, which was possibly enhanced by the polarization of the diffuse layer and the effect of the pore size distribution. The new model revealed that the relaxation time of porous media such as sandstones could be overestimated if the enhancement of the overall polarization by the diffuse layer was not considered. Second, we have developed an empirical method to obtain the pore size distribution from MICP data by assuming a linear relation between the pore size and the pore throat size using a pore aspect ratio. Then, we compared the measured quadrature conductivities of nine samples with the theoretical quadrature conductivity obtained by convoluting the pore size distribution with the Warburg model. The Warburg model is considered to represent the quadrature conductivity response of a consolidated porous material characterized by an infinitively narrow unimodal pore size distribution coated by an EDL. The position of the peak of the phase was well-reproduced from the MICP data. In addition, the calculated broadness of the phase spectra was usually well-reproduced by convolving the Warburg function with the pore size distribution.
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Niu, Q. F., Revil, A., & Saidian, M. (2016). Salinity dependence of the complex surface conductivity of the Portland sandstone. Geophysics, 81(2), D125–D140.
Résumé: Induced polarization can be used to estimate surface conductivity by assuming a universal linear relationship between the surface and quadrature conductivities of porous media. However, this assumption has not yet been justified for conditions covering a broad range of fluid conductivities. We have performed complex conductivity measurements on Portland sandstone, an illite-and kaolinite-rich sandstone, at 13 different water salinities (NaCl) over the frequency range of 0.1 Hz to 45 kHz. The conductivity of the pore water sigma(w) affected the complex surface conductivity mainly by changing the tortuosity of the conduction paths in the pore network from high to low salinities. As the fluid conductivity decreases, the magnitude of the surface conductivity and quadrature conductivity was observed to decrease. At relatively high salinities (sigma(w) < 0.01 Sm-1), the ratio between the surface conductivity and quadrature conductivity was roughly constant. At low salinities (sigma(w) < 0.01 Sm-1), the ratio decreased slightly with the decrease of the salinity. A Stern layer polarization model was combined with the differential effective medium (DEM) theory to describe this behavior. The tortuosity entering the complex surface conductivity was salinity dependent following the prediction of the DEM theory. At high salinity, it reached the value of the bulk tortuosity of the pore space given by the product of the intrinsic formation factor and the connected porosity. The relaxation time distributions were also obtained at different salinities by inverting the measured spectra using a Warburg decomposition. The mode of the relaxation time probability distribution found a small but clear dependence on the salinity. This salinity dependence can be explained by considering the ions exchange between Stern and diffuse layers during polarization of the former. The pore-size distribution obtained from the distribution of the relaxation time agreed with the pore-size distribution from nuclear magnetic resonance measurements.
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Nocquet, J. M., Sue, C., Walpersdorf, A., Tran, T., Lenotre, N., Vernant, P., et al. (2016). Present-day uplift of the western Alps. Scientific Reports, 6.
Résumé: Collisional mountain belts grow as a consequence of continental plate convergence and eventually disappear under the combined effects of gravitational collapse and erosion. Using a decade of GPS data, we show that the western Alps are currently characterized by zero horizontal velocity boundary conditions, offering the opportunity to investigate orogen evolution at the time of cessation of plate convergence. We find no significant horizontal motion within the belt, but GPS and levelling measurements independently show a regional pattern of uplift reaching similar to 2.5 mm/yr in the northwestern Alps. Unless a low viscosity crustal root under the northwestern Alps locally enhances the vertical response to surface unloading, the summed effects of isostatic responses to erosion and glaciation explain at most 60% of the observed uplift rates. Rock-uplift rates corrected from transient glacial isostatic adjustment contributions likely exceed erosion rates in the northwestern Alps. In the absence of active convergence, the observed surface uplift must result from deep-seated processes.
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Noury, M., Bernet, M., Schildgen, T. F., Simon-Labric, T., Philippon, M., & Sempere, T. (2016). Crustal-scale block tilting during Andean trench-parallel extension: Structural and geo-thermochronological insights. Tectonics, 35(9), 2052–2069.
Résumé: Despite a long history of plate convergence at the western margin of the South American plate that has been ongoing since at least the Early Paleozoic, the southern Peruvian fore-arc displays little to no evidence of shortening. In the light of this observation, we assess the deformation history of the southern Peruvian fore-arc and its geodynamic implications. To accomplish this, we present a new structural and geo-thermochronological data set (zircon U-Pb, mica Ar-40/Ar-39, apatite and zircon fission-track and zircon (U-Th)/He analyses) for samples collected along a 400km long transect parallel to the trench. Our results show that the Mesoproterozoic gneissic basement was mainly at temperatures 350 degrees C since the Neoproterozoic and was later intruded by Jurassic volcanic arc plutons. Along the coast, a peculiar apatite fission-track age pattern, coupled with field observations and a synthesis of available geological maps, allows us to identify crustal-scale tilted blocks that span the coastal Peruvian fore-arc. These blocks, bounded by normal faults that are orthogonal to the trench, suggest post-60Ma trench-parallel extension that potentially accommodated oroclinal bending in this region. Block tilting is consistent with the observed and previously described switch in the location of sedimentary sources in the fore-arc basin. Our data set allows us to estimate the cumulative slip on these faults to be less than 2km and questions the large amount of trench-parallel extension suggested to have accommodated this bending.
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Obermann, A., Planes, T., Hadziioannou, C., & Campillo, M. (2016). Lapse-time-dependent coda-wave depth sensitivity to local velocity perturbations in 3-D heterogeneous elastic media. Geophysical Journal International, 207(1), 59–66.
Résumé: In the context of seismic monitoring, recent studies made successful use of seismic coda waves to locate medium changes on the horizontal plane. Locating the depth of the changes, however, remains a challenge. In this paper, we use 3-D wavefield simulations to address two problems: first, we evaluate the contribution of surface-and body-wave sensitivity to a change at depth. We introduce a thin layer with a perturbed velocity at different depths and measure the apparent relative velocity changes due to this layer at different times in the coda and for different degrees of heterogeneity of the model. We show that the depth sensitivity can be modelled as a linear combination of body-and surface-wave sensitivity. The lapse-time-dependent sensitivity ratio of body waves and surface waves can be used to build 3-D sensitivity kernels for imaging purposes. Second, we compare the lapse-time behaviour in the presence of a perturbation in horizontal and vertical slabs to address, for instance, the origin of the velocity changes detected after large earthquakes.
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Ossa, F. O., Hofmann, A., Vidal, O., Kramers, J. D., Belyanin, G., & Cavalazzi, B. (2016). Unusual manganese enrichment in the Mesoarchean Mozaan Group, Pongola Supergroup, South Africa. Precambrian Research, 281, 414–433.
Résumé: An unusual sediment-hosted manganese deposit is described from the Mesoarchean Mozaan Group, Pongola Supergroup, South Africa. MnO contents up to 15 wt.% were observed in marine clastic and chemical sedimentary rocks. Mn enrichment is interpreted to have resulted from the hydrothermal alteration of manganiferous shale and BIF parent rocks, the primary MnO contents of which are as high as 8.5 wt.%. A detailed mineralogical and petrographic study shows that these parent rocks are characterized by manganoan siderite, ferroan rhodochrosite and other Mn-Fe-rich mineral phases, such as kutnohorite and Fe-Mn-chlorite. Their hypogene alteration gave rise to a diversification of mineral assemblages where ferroan tephroite, calcian rhodochrosite, rhodochrosite, pyrochroite, pyrophanite, cronstedtite, manganoan Fe-rich chlorite and manganoan phlogopite partially or totally replaced the previous mineral assemblage. Thermodynamic modeling performed on chlorite phases associated with the described mineral assemblages illustrates a decrease of average crystallization temperatures from ca. 310 degrees C during early metamorphic stages to ca. 250 degrees C during a hydrothermal stage. Mineral transformation processes were thus related to retrograde metamorphism and/or hydrothermal alteration post-dating metamorphism and gave rise to progressive Mn enrichment from unaltered parent to altered rocks. The timing of hypogene alteration was constrained by Ar-40/Ar-39 dating to between about 1500 and 1100 Ma ago, reflecting tectonic processes associated with the Namaqua-Natal orogeny along the southern Kaapvaal Craton margin. Manganiferous shale and BIF of the Mozaan Group may represent the oldest known examples of primary sedimentary Mn deposition, related to oxidation of dissolved Mn(II) by free oxygen in a shallow marine environment. Oxygenic photosynthesis would have acted as a first-order control during Mn precipitation. This hypothesis opens a new perspective for better constraining secular evolution of sediment-hosted mineral deposits linked to oxygen levels in the atmosphere-hydrosphere system during the Archean Eon. (C) 2016 Elsevier B.V. All rights reserved.
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Oubaiche, E., Chatelain, J. L., Hellel, M., Wathelet, M., Machane, D., Bensalem, R., et al. (2016). The Relationship between Ambient Vibration H/V and SH Transfer Function: Some Experimental Results. Seismological Research Letters, 87(5), 1112–1119.
Résumé: The horizontal-to-vertical spectral ratios (HVSRs) of ambient vibrations are commonly used to observe soil resonance frequencies, which are revealed by HVSR curve peaks. These resonances have been explained either in terms of S-wave transfer function or in terms of Rayleigh-wave ellipticity. In this study, ambient vibration recordings have been carried out next to nine boreholes in the eastern Mitidja basin (Algeria), all of which have been characterized by downhole geophysical surveys. Using velocity profiles obtained from the downhole surveys, we compare the frequency of the second HVSR peak (f(HV)) to frequencies obtained with (1) the time-averaged velocity (f(T)), (2) depth-averaged velocity (f(D)), (3) the SH transfer function (f(SH)), and (4) the fundamental-mode Rayleigh-wave ellipticity (f(E)). We find that f(SH), f(T), and f(D) fit well with f(HV), whereas this is not the case for f(E), implying that the HVSR peak frequency is better explained by the SH transfer function peak than by the Rayleigh-wave ellipticity.
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Ougier-Simonin, A., Renard, F., Boehm, C., & Vidal-Gilbert, S. (2016). Microfracturing and microporosity in shales. Earth-Science Reviews, 162, 198–226.
Résumé: Shales are ubiquitous rocks in sedimentary basins, where their low permeability makes them efficient seals for conventional oil and gas reservoirs and underground waste storage repositories (waste waters, CO2, nuclear fuels). Moreover, when they contain organic matter, they form source rocks for hydrocarbons that may escape towards a more porous reservoir during burial, a process referred to as primary migration. And when the hydrocarbons cannot escape, these rocks can be exploited as oil or shale gas reservoirs. While the presence of fractures at the outcrop scale has been described, the existence of fractures at smaller scales, their link with microporosity, the mechanisms that created them, their persistence over geological times, and their effect on the petrophysical properties of shales represent scientific challenges for which drillings in various sedimentary basins over the past decades may hold timely key data. Here, we review and synthetize the current knowledge on how microfractures and micropores in shales can be imaged and characterized and how they control their anisotropic mechanical properties and permeability. One question is whether such microfractures, when observed in outcrops or in drilled core samples extracted from boreholes, are related to decompaction and do not exist at depth. Another question is whether veins observed in shales represent microfractures that were open long enough to have acted as flow paths across the formation. The mechanisms of microfracture development are described. Some have an internal origin (fracturing by maturation of organic matter, dehydration of clays) while others are caused by external factors (tectonic loading). Importantly, the amount of microfracturing in shales is shown to depend strongly on the content in 1) organic matter, and 2) strong minerals. The nucleation of microfractures depends on the existence of mechanical heterogeneities down to the nanometer scale. Their propagation and linkage to create a percolating network will depend on the presence of heterogeneities at the meso-to macro-scales. Such percolating microfracture networks could control both the long-term sealing capabilities of cap rocks and the further propagation of hydraulic fracturing cracks. Finally, possible areas of research for describing the mechanism of microfracture formation in greater detail and how this impacts the transport and mechanical properties of shales are also discussed. (C) 2016 Elsevier B.V. All rights reserved.
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Pedrosa, E. T., Putnis, C. V., Renard, F., Burgos-Cara, A., Laurich, B., & Putnis, A. (2016). Porosity generated during the fluid-mediated replacement of calcite by fluorite. Crystengcomm, 18(36), 6867–6874.
Résumé: Mineral replacement reactions are common phenomena in natural and laboratory environments where solids have re-equilibrated with aqueous solutions and are characterized by the generation or destruction of porosity in the product phase(s). Here, the evolution of porosity during the replacement of calcite by fluorite is used as a model system to characterize the kinetics of volume variations. Non-porous single crystals of calcite were reacted with sodium fluoride solutions for different reaction times. The crystals were pseudomorphically replaced by highly porous fluorite. Complementary use of porosimetry techniques, high resolution imaging, and mass-balance calculations revealed the total, open, and closed porosity in the samples. The infiltration of aqueous fluids in the Earth depends on the evolution of porosity and hence porosity variations are important in various geological processes such as, rock weathering and soil formation, fluid-controlled metamorphism, mineral ore emplacement, or oil and gas reservoir compaction. Such mechanisms can also be used to develop geo-inspired materials designed for industrial and medical applications.
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Pico, T., Mitrovica, J. X., Ferrier, K. L., & Braun, J. (2016). Global ice volume during MIS 3 inferred from a sea-level analysis of sedimentary core records in the Yellow River Delta. Quaternary Science Reviews, 152, 72–79.
Résumé: Estimates of global ice volume during the glacial phase of the most recent ice age cycle are characterized by significant uncertainty, reflecting the relative paucity of geological constraints on sea level relevant to this time interval. For example, during the middle stages of Marine Isotope Stage 3, published estimates of peak global mean sea level (GMSL) relative to the present range from -25 m to -87 m. The large uncertainty in GMSL at MIS 3 has significant implications for estimates of the rate of ice growth in the period leading to the Last Glacial Maximum (similar to 26 ka). We refine estimates of global ice volume during MIS 3 by employing sediment cores in the Bohai and Yellow Sea that record a migration of the paleoshoreline at similar to 50-37 ka through a transition from marine to brackish conditions. In particular, we correct relative sea level at these sites for contamination due to glacial isostatic adjustment using a sea-level calculation that includes a gravitationally self-consistent treatment of sediment redistribution and compaction, and estimate a peak global mean sea level of -38 +/- 7 m during the interval 50-37 ka. With suitable sedimentary core records, the approach described herein can be extended to refine existing constraints on global ice volume across the entire glacial period. (C) 2016 Elsevier Ltd. All rights reserved.
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Poprawski, Y., Basile, C., Jaillard, E., Gaudin, M., & Lopez, M. (2016). Halokinetic sequences in carbonate systems: An example from the Middle Albian Bakio Breccias Formation (Basque Country, Spain). Sedimentary Geology, 334, 34–52.
Résumé: In diapir flanks, unconformity-bounded sedimentary packages associated with gravity-driven deposits, controlled by the ratio between the rates of sediment accumulation and diapir growth can be interpreted in the context of halokinetic sequences. The Bakio Breccias Formation (Basque Country, Spain) corresponds to redeposited carbonate deposit that developed in response to the Bakio diapir growth during the Middle Albian. These deposits provide on of the rare documented example of carbonate-dominated halokinetic sequences. The Bakio Breccias Formation consists of an alternation of clast- and matrix-supported breccias, calcirudite, calcarenite and marl, deposited along the flanks of the diapir. The description and the analysis of the Bakio Breccias Formation lead to a new model for carbonate-dominated halokinetic sequences. These sequences differ from their siliciclastic counterpart because sediment accumulation rate is controlled by carbonate platform growth on the topographic relief top of the diapirs, while sediments are preferentially deposited in the mini basins adjacent of the diapirs, in siliciclastic settings. During transgressive system tract, carbonate platform are able to keep up with the sea level rise and to aggrade on top of the diapirs, forming thick and resistant roof, which is assumed to limit the diapir growth and thus to favour the development of halokinetic sequences with low angle unconformities (wedge halokinetic sequences). During late highstand system tract deposition (and lowstand system tract if present), platform progradation results in high sediment accumulation in the adjacent depocenters, loading the autochthonous salt layer and promote diapir growth and creation of topographic relief. In addition, if the diapir roof reaches emersion, karstification of the carbonate platform top may also favour roof destruction and diapir growth. Depending on the thickness of the roof developed previously and the amplitude of the sea level fall, the halokinetic sequences with the emersion and the karstification of the carbonate platform may display high angle unconformities (hook halokinetic sequences). Furthermore, gravity-driven deposits are assumed to be more common in carbonate-dominated halokinetic sequences, compared to their siliciclastic counterparts, since carbonate platform aggradation creates steep slopes on the diapir margins, leading to the partial collapse of the margin, even when limited diapir growth occurs. The carbonate-dominated halokinetic sequence model proposed here is an important tool for the prediction of potential reservoir distribution, seal and hydrocarbon migration in flanks of salt diapirs where carbonate platform developed. (C) 2016 Elsevier B.V. All rights reserved.
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Poulin, B. A., Aiken, G. R., Nagy, K. L., Manceau, A., Krabbenhoft, D. P., & Ryan, J. N. (2016). Mercury transformation and release differs with depth and time in a contaminated riparian soil during simulated flooding. Geochimica Et Cosmochimica Acta, 176, 118–138.
Résumé: Riparian soils are an important environment in the transport of mercury in rivers and wetlands, but the biogeochemical factors controlling mercury dynamics under transient redox conditions in these soils are not well understood. Mercury release and transformations in the O-a and underlying A horizons of a contaminated riparian soil were characterized in microcosms and an intact soil core under saturation conditions. Pore water dynamics of total mercury (Hg-T), methylmercury (MeHg), and dissolved gaseous mercury (Hg-(aq)(0)) along with selected anions, major elements, and trace metals were characterized across redox transitions during 36 d of flooding in microcosms. Next, HgT dynamics were characterized over successive flooding (17 d), drying (28 d), and flooding (36 d) periods in the intact core. The observed mercury dynamics exhibit depth and temporal variability. At the onset of flooding in microcosms (1-3 d), mercury in the Oa horizon soil, present as a combination of ionic mercury (Hg(II)) bound to thiol groups in the soil organic matter (SOM) and nanoparticulate metacinnabar (beta-HgS), was mobilized with organic matter of high molecular weight. Subsequently, under anoxic conditions, pore water HgT declined coincident with sulfate (3-11 d) and the proportion of nanoparticulate beta-HgS in the Oa horizon soil increased slightly. Redox oscillations in the intact Oa horizon soil exhausted the mobile mercury pool associated with organic matter. In contrast, mercury in the A horizon soil, present predominantly as nanoparticulate beta-HgS, was mobilized primarily as Hg-(aq)(0) under strongly reducing conditions (5-18 d). The concentration of Hg-(aq)(0) under dark reducing conditions correlated positively with byproducts of dissimilatory metal reduction (Sigma(Fe,Mn)). Mercury dynamics in intact A horizon soil were consistent over two periods of flooding, indicating that nanoparticulate beta-HgS was an accessible pool of mobile mercury over recurrent reducing conditions. The concentration of MeHg increased with flooding time in both the Oa and A horizon pore waters. Temporal changes in pore water constituents (iron, manganese, sulfate, inorganic carbon, headspace methane) all implicate microbial control of redox transitions. The mobilization of mercury in multiple forms, including HgT associated with organic matter, MeHg, and Hg-(aq)(0), to pore waters during periodic soil flooding may contribute to mercury releases to adjacent surface waters and the recycling of the legacy mercury to the atmosphere. Published by Elsevier Ltd.
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Pousse-Beltran, L., Pathier, E., Jouanne, F., Vassallo, R., Reinoza, C., Audemard, F., et al. (2016). Spatial and temporal variations in creep rate along the El Pilar fault at the Caribbean-South American plate boundary (Venezuela), from InSAR. Journal Of Geophysical Research-Solid Earth, 121(11), 8276–8296.
Résumé: In eastern Venezuela, the Caribbean-South American plate boundary follows the El Pilar fault system. Previous studies based on three GPS campaigns (2003-2005-2013) demonstrated that the El Pilar fault accommodates the whole relative displacement between the two tectonic plates (20 mm/yr) and proposed that 50-60% of the slip is aseismic. In order to quantify the possible variations of the aseismic creep in time and space, we conducted an interferometric synthetic aperture radar (InSAR) time series analysis, using the (NSBAS) New Small BAseline Subset method, on 18 images from the Advanced Land Observing Satellite (ALOS-1) satellite spanning the 2007-2011 period. During this 3.5 year period, InSAR observations show that aseismic slip decreases eastward along the fault: the creep rate of the western segment reaches 25.3 +/- 9.4 mm/yr on average, compared to 13.4 +/- 6.9 mm/yr on average for the eastern segment. This is interpreted, through slip distribution models, as being related to coupled and uncoupled areas between the surface and similar to 20 km in depth. InSAR observations also show significant temporal creep rate variations (accelerations) during the considered time span along the western segment. The transient behavior of the creep is not consistent with typical postseismic afterslip following the 1997 M-s 6.8 earthquake. The creep is thus interpreted as persistent aseismic slip during an interseismic period, which has a pulse-or transient-like behavior.
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Pradas del Real, A. E., Castillo-Michel, H., Kaegi, R., Sinnet, B., Magnin, V., Findling, N., et al. (2016). Fate of Ag-NPs in Sewage Sludge after Application on Agricultural Soils. Environmental Science & Technology, 50(4), 1759–1768.
Résumé: The objective of this work was to investigate the fate of silver nanoparticles (Ag-NPs) in a sludge-amended soil cultivated with monocot (Wheat) and dicot (Rape) crop species. A pot experiment was performed with sludges produced in a pilot wastewater treatment plant containing realistic Ag concentrations (18 and 400 mg kg(-1), 14 mg kg(-1) for the control). Investigations focused on the highest dose treatment. X-ray absorption spectroscopy (XAS) showed that Ag2S was the main species in the sludge and amended soil before and after plant culture. The second most abundant species was an organic and/or amorphous Ag-S phase whose proportion slightly vaned (from 24% to 36%) depending on the conditions. Micro and nano X-ray fluorescence (XRF) showed that Ag was preferentially associated with S-rich particles, including organic fragments, of the sludge and amended soils. Ag was distributed as heteroaggregates with soil components (size ranging from <= 0.5 to 1-3 μm) and as diffused zones likely corresponding to sorbed/complexed Ag species. Nano-XRF evidenced the presence of mixed metallic sulfides. Ag was weakly exchangeable and labile. However, micronutrient mobilization by plant roots and organic matter turnover may induce Ag species interconversion eventually leading to Ag release on longer time scales. Together, these data provide valuable information for risk assessment of sewage sludge application on agricultural soils.
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Radiguet, M., Perfettini, H., Cotte, N., Gualandi, A., Valette, B., Kostoglodov, V., et al. (2016). Triggering of the 2014M(w)7.3 Papanoa earthquake by a slow slip event in Guerrero, Mexico. Nature Geoscience, 9(11), 829–+.
Résumé: Since their discovery two decades ago(1,2), slow slip events have been shown to play an important role in accommodating strain in subduction zones. However, the physical mechanisms that generate slow slip and the relationships with earthquakes are unclear. Slow slip events have been recorded in the Guerrero segment of the Cocos-North America subduction zone(2,3). Here we use inversion of position time series recorded by a continuous GPS network to reconstruct the evolution of aseismic slip on the subduction interface of the Guerrero segment. We find that a slow slip event began in February 2014, two months before the magnitude (M-w) 7.3 Papanoa earthquake on 18 April. The slow slip event initiated in a region adjacent to the earthquake hypocentre and extended into the vicinity of the seismogenic zone. This spatio-temporal proximity strongly suggests that the Papanoa earthquake was triggered by the ongoing slow slip event. We demonstrate that the triggering mechanism could be either static stress increases in the hypocentral region, as revealed by Coulomb stress modelling, or enhanced weakening of the earthquake hypocentral area by the slow slip. We also show that the plate interface in the Guerrero area is highly coupled between slow slip events, and that most of the accumulated strain is released aseismically during the slow slip episodes.
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Raimondi, F., Comon, P., Michel, O., Sahnoun, S., & Helmstetter, A. (2016). Tensor decomposition exploiting diversity of propagation velocities: Application to localization of icequake events. Signal Processing, 118, 75–88.
Résumé: The problem of direction of arrival (DoA) estimation of seismic plane waves impinging on an array of sensors is considered from a new deterministic perspective using tensor decomposition techniques. In addition to temporal and spatial sampling, further information is taken into account, based on the different propagation speed of body waves (P and S) through solid media. Performances are evaluated through simulated data in terms of the Cramer-Rao bounds and compared to other reference methods such as ESPRIT and MUSIC, in the presence of additive Gaussian circular noise. The proposed approach is then applied to real seismic data recorded at the Argentiere glacier, occurring at the interface between the ice mass and the underlying bedrock. MUSIC and ESPRIT rely on the estimation of the covariance matrix of received data, thus requiring a large number of time samples. Moreover, information about propagation speed diversity is not taken into account by existing models in array processing. The discovered advantage in terms of the average error in estimating the direction of arrival of body waves is noteworthy, especially for a low number of sensors, and in separating closely located sources. Additionally, an improvement of precision in processing real seismic data is observed. (C) 2015 Elsevier B.V. All rights reserved.
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Regnier, J., Bonilla, L. F., Bard, P. Y., Bertrand, E., Hollender, F., Kawase, H., et al. (2016). International Benchmark on Numerical Simulations for 1D, Nonlinear Site Response (PRENOLIN): Verification Phase Based on Canonical Cases. Bulletin Of The Seismological Society Of America, 106(5), 2112–2135.
Résumé: PREdiction of NOn-LINear soil behavior (PRENOLIN) is an international benchmark aiming to test multiple numerical simulation codes that are capable of predicting nonlinear seismic site response with various constitutive models. One of the objectives of this project is the assessment of the uncertainties associated with nonlinear simulation of 1D site effects. A first verification phase (i.e., comparison between numerical codes on simple idealistic cases) will be followed by a validation phase, comparing the predictions of such numerical estimations with actual strong-motion recordings obtained at well-known sites. The benchmark presently involves 21 teams and 23 different computational codes. We present here the main results of the verification phase dealing with simple cases. Three different idealized soil profiles were tested over a wide range of shear strains with different input motions and different boundary conditions at the sediment/bedrock interface. A first iteration focusing on the elastic and viscoelastic cases was proved to be useful to ensure a common understanding and to identify numerical issues before pursuing the nonlinear modeling. Besides minor mistakes in the implementation of input parameters and output units, the initial discrepancies between the numerical results can be attributed to (1) different understanding of the expression “input motion” in different communities, and (2) different implementations of material damping and possible numerical energy dissipation. The second round of computations thus allowed a convergence of all teams to the Haskell-Thomson analytical solution in elastic and viscoelastic cases. For nonlinear computations, we investigate the epistemic uncertainties related only to wave propagation modeling using different nonlinear constitutive models. Such epistemic uncertainties are shown to increase with the strain level and to reach values around 0.2 (log 10 scale) for a peak ground acceleration of 5 m/s(2) at the base of the soil column, which may be reduced by almost 50% when the various constitutive models used the same shear strength and damping implementation.
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Regnier, J., Cadet, H., & Bard, P. Y. (2016). Empirical Quantification of the Impact of Nonlinear Soil Behavior on Site Response. Bulletin Of The Seismological Society Of America, 106(4), 1710–1719.
Résumé: We present an extensive analysis of the quantitative impact of the nonlinear soil behavior on site response at 174 sites of the Japanese Kiban-Kyoshin (KiK-net) network. The nonlinear to linear site-response ratio (RSRNL-L) is calculated by comparing the surface/downhole Fourier spectral ratio for strong events and for weak events. Three thresholds of surface peak ground acceleration (PGA) are tested to characterize the strong events: 100, 200, and 300 cm/s(2), whereas weak events correspond to surface PGA in the 0: 1-25 cm/s(2) range. This ratio exhibits a typical shape; with a low-frequency part above 1 and a high-frequency part generally below 1, separated by a transition zone around a site-dependent frequency labeled f(NL) (characterized by RSRNL-L = 1). The average maximum amplitudes of RSRNL-L are 1.4, 1.5, and 1.6, and the minimums are 0.6, 0.5, and 0.5 for PGA thresholds 100, 200, and 300 cm/s(2), respectively, showing that nonlinear soil behavior results in significant site-response modifications even for moderate PGA values of 100 cm/s(2). The f(NL) value exhibits a satisfactory correlation with site classifications based on either V-S30 (travel-time averaged shear-wave velocity over the top 30 m) or f(0) (site fundamental frequency): f(NL) decreases when either V-S30 or f(0) decreases. In addition, the amount of the low-frequency amplification increase depends on V-S30 and reaches a maximum of 1.6 for high V-S30 soil classes associated with shallow thin soft-soil layer underlain by stiff substratum. The average high-frequency decrease is about 0.5 for all soil classes defined from either V-S30 or f(0); for a few sites, however, this decrease is replaced by an increase as reported in previous studies, in relation with water contents and pore-pressure issues. The increase of amplification below f(NL) is found to be a quasi-systematic consequence of nonlinear soil behavior, which should be emphasized, because it can reach up to 1.6 for high V-S30 sites.
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Remy, D., Perfettini, H., Cotte, N., Avouac, J. P., Chlieh, M., Bondoux, F., et al. (2016). Postseismic relocking of the subduction megathrust following the 2007 Pisco, Peru, earthquake. Journal Of Geophysical Research-Solid Earth, 121(5), 3978–3995.
Résumé: Characterizing the time evolution of slip over different phases of the seismic cycle is crucial to a better understanding of the factors controlling the occurrence of large earthquakes. In this study, we take advantage of interferometric synthetic aperture radar data and 3.5 years of continuous Global Positioning System (GPS) measurements to determine interseismic, coseismic, and postseismic slip distributions in the region of the 2007, M-w 8.0 Pisco, earthquake, Peru, using the same fault geometry and inversion method. Our interseismic model, based on pre-2007 campaign GPS data, suggests that the 2007 Pisco seismic slip occurred in a region strongly coupled before the earthquake while afterslip occurred in low coupled regions. Large afterslip occurred in the peripheral area of coseismic rupture in agreement with the notion that afterslip is mainly induced by coseismic stress changes. The temporal evolution of the region of maximum afterslip, characterized by a relaxation time of about 2.3 years, is located in the region where the Nazca ridge is subducting, consistent with rate-strengthening friction promoting aseismic slip. We estimate a return period for the Pisco earthquake of about 230 years with an estimated aseismic slip that might account for about 50% of the slip budget in this region over the 0-50 km seismogenic depth range. A major result of this study is that the main asperity that ruptured during the 2007 Pisco earthquake relocked soon after this event.
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Renard, F., Cordonnier, B., Dysthe, D. K., Boller, E., Tafforeau, P., & Rack, A. (2016). A deformation rig for synchrotron microtomography studies of geomaterials under conditions down to 10 km depth in the Earth. Journal Of Synchrotron Radiation, 23, 1030–1034.
Résumé: A hard X-ray transparent triaxial deformation apparatus, called HADES, has been developed by Sanchez Technologies and installed on the microtomography beamline ID19 at the European Radiation Synchrotron Facility (ESRF). This rig can be used for time-lapse microtomography studies of the deformation of porous solids (rocks, ceramics, metallic foams) at conditions of confining pressure to 100 MPa, axial stress to 200 MPa, temperature to 250 degrees C, and controlled aqueous fluid flow. It is transparent to high-energy X-rays above 60 keV and can be used for in situ studies of coupled processes that involve deformation and chemical reactions. The rig can be installed at synchrotron radiation sources able to deliver a high-flux polychromatic beam in the hard X-ray range to acquire tomographic data sets with a voxel size in the range 0.7-6.5 μm in less than two minutes.
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Replumaz, A., Funiciello, F., Reitano, R., Faccenna, C., & Balon, M. (2016). Asian collisional subduction: A key process driving formation of the Tibetan Plateau. Geology, 44(11), 943–946.
Résumé: Using silicone slabs as a model analogue for lithospheric plates subducting into a box of glucose syrup, as an analogue of the mantle, we explore the subduction of continental lithosphere in a context of intercontinental collision. The continental indenter pushed by a piston, reproducing the collision, attached to a dense oceanic plate, subducts to two-thirds of the depth of the mantle box. We show that, surprisingly, the continental plate attached to the back wall of the box subducts, even if not attached to a dense oceanic slab. The engine of this subduction is not the weight of the slab, because the slab is lighter than the mantle, but the motion of the piston, which generates horizontal tectonic forces. These are transmitted to the back wall plate through the indenter and the upper plate at the surface, and by the advancing indenter slab through the mantle at shallow depth. We define this process as collisional subduction occurring in a compressional context. The collisional subduction absorbs between 14% and 20% of the convergence, and represents an unexplored component of collisional mass balance. The transmission of tectonic forces far from the collision front favors the formation of a wide plateau. Our experiments reproduce adequately the amount and geometry of the Asian lithosphere subduction episodes inferred during the collision, leading us to conclude that it reproduces adequately the physics of such process.
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Reverso, T., Marsan, D., Helmstetter, A., & Enescu, B. (2016). Background seismicity in Boso Peninsula, Japan: Long-term acceleration, and relationship with slow slip events. Geophysical Research Letters, 43(11), 5671–5679.
Résumé: Slow slip events (SSEs) in subduction zones can trigger earthquake swarms, especially at shallow depth. The monitoring of seismicity rates has therefore the potential to help detect and characterize SSEs, and transient changes in coupling. However, the relationship between seismicity rate and slow slip rate during a SSE is unknown and made complicated by aftershock triggering within the swarm. Here we propose to complement geodetic methods with an objective measure of the seismicity rate that is directly associated with changes in slip rate. We show that this measure, applied to known occurrences of SSEs in the Boso area, Japan, yields an estimate, albeit indirect, of their seismic moment, hence their slip rate. We finally prove that the background rate in Boso has been accelerating since 1990; this explains previous observations of the shortening of the recurrence time between SSEs in Boso, that clearly predate the 2011 M(w)9.0 Tohoku-Oki earthquake.
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Revil, A. (2016). Comment on: “Feasibility of electromagnetic methods to detect and image steam-assisted gravity drainage steam chambers” (S. G. R. Devriese and D. W. Oldenburg). Geophysics, 6(81), 1–2.
Résumé: Devriese and Oldenburg (2016), abbreviated below as DO16, propose a synthetic case study aimed at demonstrating the advantages and limitations in using galvanometric- and induction-based resistivity methods to monitor the growth of steam-assisted gravity drainage steam chambers. They first simulate a simplistic case and then they apply their strategy to a more realistic geometry inspired from a case study operated by Imperial Oil. The geophysical work is based on a set of petrophysical relationships and classical regularization methods for the inverse problem. The petrophysical model used to connect the underlying physics of the problem to the geophysical observable is far from being correct, raising some questions regarding the validity of the input parameters, hence conclusions reached in the paper. The choices for the regularizers and inversion schemes are also problematic as discussed below.
I start first with the petrophysical model used in DO16. Despite the claims made in DO16, equation 11 is not Archie’s law for the resistivity formation factor and cannot be found in the seminal paper of Archie (1942). It is a mix of the first and second Archie’s law with a tortuosity added to the equation without any justification. Archie’s law is an equation connecting the intrinsic formation factor to the porosity through a power law relationship. The formation factor can also be defined as the ratio of the tortuosity by the connected porosity (Pride, 1994). In their equation 11, we have both factors used concomitantly, which is not correct (see the discussion in Appendix A of Revil, 2013).
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Revil, A., Meyer, C. D., & Niu, Q. (2016). A laboratory investigation of the thermoelectric effect. Geophysics, 81(4), E243–E257.
Résumé: One contribution to self-potential signals is the thermoelectric coupling associated with a temperature gradient in a porous material, which causes mobile ions to diffuse from hot to cold regions. We have developed 35 laboratory experiments to measure the value of the Seebeck coefficient in two clean (silica) sands and two clayey sandstones fully saturated by NaCl solutions to explore the influence of salinity upon the Seebeck coefficient over four orders of magnitude in salinity. The two sands are characterized by two distinct grain sizes (coarse and medium) and therefore two low values of surface conductivity. Portland sandstone, rich in illite and kaolinite, is characterized by a high surface conductivity, and the Berea sandstone is characterized by an inter-mediate surface conductivity. The Seebeck coefficient of the sands ranges from -0.4 (at intermediate salinities) to +0.5 mV degrees C-1 at very low salinities, for which surface conductivity, associated with electromigration and electrodiffusion in the electrical double layer, dominates. For the Portland sandstone, the Seebeck coefficient is positive in the range +0.8 to +1.5 mV degrees C-1 and decreases with the increase of the salinity. A similar trend is observed for the Berea sandstone with the Seebeck coefficient going from positive to negative values at high salinity. Our experimental data can be fairly reproduced by a simple model accounting for the effect of surface conductivity due to the electrical double layer coating the surface of the grains and the dependence on salinity of the partial entropies of the ions in the pore water.
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Riel, N., Mercier, J., & Weinberg, R. (2016). Convection in a partially molten metasedimentary crust? Insights from the El Oro complex (Ecuador). Geology, 44(1), 31–34.
Résumé: The El Oro complex, southwestern Ecuador, is a tilted section of the metasedimentary Ecuadorian forearc, which was partially molten during Triassic time due to gabbroic magma emplacement. Pressure and maximum temperature estimates show that the metamorphic gradient during anatexis was 45 degrees C/km in the upper crust and 10 degrees C/km in the 7-8 km garnet-bearing migmatitic lower crust, controlled by biotite-breakdown melting reactions. Our petrological and geochemical studies indicate that melts produced during biotite-breakdown (5-15 vol%) were trapped and pervasively distributed in the garnet-bearing migmatite. Based on these results we carried out one-dimensional thermal modeling to characterize the heat transfer processes that led to the establishment of such a low thermal gradient during partial melting. Our results show that neither diffusive nor upward melt transfer models account for the low metamorphic gradient in the garnet-bearing migmatite. We demonstrate that in the El Oro complex, convection of the garnet-bearing migmatitic layer is the most likely heat transfer process that explains all the petrological, geochemical, and metamorphic data.
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Rittgers, J. B., Revil, A., Mooney, M. A., Karaoulis, M., Wodajo, L., & Hickey, C. J. (2016). Time-lapse joint inversion of geophysical data with automatic joint constraints and dynamic attributes. Geophysical Journal International, 207(3), 1401–1419.
Résumé: Joint inversion and time-lapse inversion techniques of geophysical data are often implemented in an attempt to improve imaging of complex subsurface structures and dynamic processes by minimizing negative effects of random and uncorrelated spatial and temporal noise in the data. We focus on the structural cross-gradient (SCG) approach (enforcing recovered models to exhibit similar spatial structures) in combination with time-lapse inversion constraints applied to surface-based electrical resistivity and seismic traveltime refraction data. The combination of both techniques is justified by the underlying petrophysical models. We investigate the benefits and trade-offs of SCG and time-lapse constraints. Using a synthetic case study, we show that a combined joint time-lapse inversion approach provides an overall improvement in final recovered models. Additionally, we introduce a new approach to reweighting SCG constraints based on an iteratively updated normalized ratio of model sensitivity distributions at each time-step. We refer to the new technique as the Automatic Joint Constraints (AJC) approach. The relevance of the new joint time-lapse inversion process is demonstrated on the synthetic example. Then, these approaches are applied to real time-lapse monitoring field data collected during a quarter-scale earthen embankment induced-piping failure test. The use of time-lapse joint inversion is justified by the fact that a change of porosity drives concomitant changes in seismic velocities (through its effect on the bulk and shear moduli) and resistivities (through its influence upon the formation factor). Combined with the definition of attributes (i.e. specific characteristics) of the evolving target associated with piping, our approach allows localizing the position of the preferential flow path associated with internal erosion. This is not the case using other approaches.
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Rivard, C., Lanson, B., & Cotte, M. (2016). Phosphorus speciation and micro-scale spatial distribution in North-American temperate agricultural soils from micro X-ray fluorescence and X-ray absorption near-edge spectroscopy. Plant And Soil, 401(1-2), 7–22.
Résumé: Background and Aims Phosphorus (P) is an essential nutrient for plants but its low availability often necessitates amendments for agronomical issues. Objectives were to determine P spatial distribution and speciation that remain poorly understood in cultivated soils. Methods Aquic Argiudoll soil samples developed on a calcareous loam glacial till were collected from experimental plots submitted to contrasting crop rotations and amendments. Micro-X-ray fluorescence (mu-XRF) maps were collected on undisturbed samples. X-ray absorption near edge structure (XANES) spectra were collected on bulk samples and on fractions thereof, and on points of interests selected from mu-XRF maps. Results were compared with chemical analyses and extraction techniques results. Results Chemical analyses show variations in total and exchangeable P contents depending on the samples but no significant difference is observed in terms of P distribution and speciation. P distribution is dominated by a low-concentration diffuse background with a minor contribution from minute hot spots. P speciation is dominated by phosphate groups bound to clay-humic complexes. No modification of P distribution and speciation is observed close to roots. Conclusions This study evidenced minor effect of cropping and fertilizing practices on P speciation in cultivated soils. Despite analytical challenges, the combined use of mu-XRF and XANES provides relevant information on P speciation in heterogeneous soil media.
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Roeoesli, C., Helmstetter, A., Walter, F., & Kissling, E. (2016). Meltwater influences on deep stick-slip icequakes near the base of the Greenland Ice Sheet. Journal Of Geophysical Research-Earth Surface, 121(2), 223–240.
Résumé: We detected over 11,000 stick-slip icequakes near the base of the western margin of the Greenland Ice Sheet using a 17-seismometer array. These icequakes have negative (i.e., very small) moment magnitudes and, according to similarities in their waveforms, group into over 100 distinct clusters distributed beneath our 3 x 3km study area. Some clusters were active for several weeks, while others have burst-like episodes lasting 1-6days only. Some clusters correlate with subglacial water pressure measured within a nearby moulin. For these clusters, we observe high water pressure concurrent with many small yet numerous stick-slip icequakes and periods of lower water pressures with larger, less frequent icequakes. These patterns might change over time and are not common to all clusters. We explain these observations that the stick-slip icequakes are located at sticky spots at the interface of the ice sheet with the glacier bed that consists of basal till characterized by different connectivity to the subglacial drainage system. Because the till's frictional strength depends on its pore pressure, variations in subglacial water pressure can either weaken or strengthen the bed; this explains the variation in seismic moments and interevent times. Our results suggest that seismogenic stick-slip motion is an integral part of the flow mechanism in the ablation zone in western Greenland, which is highly sensitive to the configuration of the local subglacial drainage system. Stick-slip motion may therefore play a key role in the relationship between climate-induced changes of surface runoff and ice sheet dynamics.
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Rohmer, J., Pluymakers, A., & Renard, F. (2016). Mechano-chemical interactions in sedimentary rocks in the context of CO2 storage: Weak acid, weak effects? Earth-Science Reviews, 157, 86–110.
Résumé: Due to the corrosive nature of dissolved CO2, the potential short or long term alteration of rock properties, represents a major issue in several sites where natural CO2 circulation is observed, as well as in reservoirs targeted for storage of anthropogenic CO2. To date, this has been primarily studied from a transport-chemical perspective, with laboratory evidence of microstructural modifications together with the consequences for flow properties. Compared to the transport-chemical aspects, the mechanical-chemical aspects have been less investigated, though it is to be expected that mechanical properties (e.g. elastic properties, failure parameters, and time-dependent mechanical behaviour) could potentially be affected in a similar manner to hydraulic parameters. Yet, since CO2 is a weak acid, the pH drop is expected to be moderate with a likely lower limit close to 4.0. The buffeting of pH by calcite minerals present in most reservoirs targeted for storage may further limit the pH drop, as well as confining it to a localized rock volume around the injection well. This leads to the question of the magnitude and time/spatial scales of chemically-mediated mechanical processes during CO2 sequestration. The authors propose to address this issue by reviewing recent laboratory-based studies restricted to sedimentary rocks, namely: reservoir rocks (carbonate or sandstone), intact or fractured caprocks and fault rocks. Key findings include the following: 1. the short-term impact on the elastic and inelastic behaviour of intact caprocks remains limited; 2. shear strength weakening is likely to be respectively low and low-to-moderate for shale/clay-rich and anhydrite-rich faults, but without modifying slip stability in either case; 3. the largest impact is located within carbonate reservoirs, but with a broad range of reported responses depending on hydrodynamic conditions (closed or open) and on dissolution regime (uniform or channelling); and 4. creep experiments confirm that CO2-induced dissolution may enhance long-term compaction of carbonate reservoirs, but the magnitude of acceleration (varying from non-significant to 50 times) depends to a large extent on site-specific conditions (grain size, pH, temperature, effective stress state, etc.), which renders any direct extrapolation from laboratory to reservoir scale difficult Finally, some directions for future research studies are discussed. (C) 2016 Elsevier B.V. All rights reserved.
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Rolland, Y., & Rossi, M. (2016). Two-stage fluid flow and element transfers in shear zones during collision burial-exhumation cycle: Insights from the Mont Blanc Crystalline Massif (Western Alps). Journal Of Geodynamics, 101, 88–108.
Résumé: The Mont-Blanc Massif was intensely deformed during the Alpine orogenesis: in a first stage of prograde underthrusting at c. 30 Ma and in a second stage of uplift and exhumation at 22-11 Ma. Mid-crustal shear zones of 1 mm-50 m size, neighbouring episyenites (quartz-dissolved altered granite) and alpine veins, have localised intense fluid flow, which produced substantial changes in mineralogy and whole-rock geochemistry. Four main metamorphic zones are oriented parallel to the strike of the massif: (i) epidote, (ii) chlorite, (iii) actinolite-muscovite +/- biotite and (iv) muscovite +/- biotite. In addition, phlogopite-bearing shear zones occur in the chlorite zone, and calcite-bearing shear zones are locally found in the muscovite zone. The initial chemical composition of the granitic protolith is relatively constant at massif scale, which allows investigating compositional changes related to shear zone activity, and subsequent volume change and elements mobility. The variations of whole-rock composition and mineral chemistry in shear zones reflect variations in fluid/rock ratios and fluid's chemistry, which have produced specific mineral reactions. Estimated time-integrated fluid fluxes are of the order of 10(6) m(3)/m(2). The mineral assemblages that crystallised upon these fluid-P-T conditions are responsible for specific major and trace element enrichments. The X-Fe (Fe/Fe + Mg) pattern of shear zone phyllosilicates and the delta C-13 pattern of vein calcite both show a bell-type pattern across the massif with high values on the massif rims and low values in the centre of the massif. These low X-Fe and delta(13)Cvalues are explained by down temperature up-flow of a Fe-Mg-CO2-rich and silica-depleted fluid during stage 1, while the massif was underthrusting. These produced phlogopite, chlorite and actinolite precipitation and quartz hydrolysis, resulting in strong volume losses. In contrast, during stage 2 (uplift), substantial volume gains occurred on the massif rims due to the precipitation of quartz, epidote and muscovite from a local fluid hosted in the Helvetic cover. These two fluids advocate for the presence of an upper-crustal scaled fluid convection cell, with up-going fluids through the lower crust and likely down-going fluids in the 15 km upper crust. (C) 2016 Elsevier Ltd. All rights reserved.
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Rolland, Y., Bosch, D., Guillot, S., de Sigoyer, J., Martinod, J., Agard, P., et al. (2016). Subduction & orogeny: Introduction to the special volume. Journal Of Geodynamics, 96, 1–5.
Résumé: Subduction processes play a major role in plate tectonics and the subsequent geological evolution of Earth. This special issue focuses on ongoing research in subduction dynamics to a large extent (oceanic subduction, continental subduction, obduction...) for both past and active subduction zones and into mountain building processes and the early evolution of orogens. It puts together various approaches combining geophysics (imaging of subduction zones), petrology/geochemistry (metamorphic analysis of HP-UHP rocks, fluid geochemistry and magmatic signal, geochronology), seismology and geodesy (present-day evolution of subduction zones, active tectonics), structural geology (structure and evolution of mountain belts), and numerical modelling to provide a full spectrum of tools that can be used to constrain the nature and evolution of subduction processes and orogeny. Studies presented in this special issue range from the long-term (orogenic cycle,) to short-term (seismic cycle). (C) 2016 Published by Elsevier Ltd.
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Rosa, A. D., Merkulova, M., Garbarino, G., Svitlyk, V., Jacobs, J., Sahle, C. J., et al. (2016). Amorphous boron composite gaskets for in situ high-pressure and high-temperature studies. High Pressure Research, 36(4), 564–574.
Résumé: The diamond anvil cell (DAC) is a fundamental device used to explore the properties of materials under extreme pressure and temperature (P/T) conditions. In the past years, simultaneous high P/T DAC experiments using the resistively heated DAC (RH-DAC) techniques have been developed for studying materials properties in a wide P/T range. However, the mechanical instability of metallic gaskets used for sample confinement at high P/T conditions remains a limiting factor for exploiting the accessible P/T range of the RH-DAC. In this study, we present a new gasket configuration that overcomes these limitations. It is based on an amorphous boron-epoxy mixture inserted in a rhenium gasket. We show how these gasket inserts stabilize the sample chamber over a wide P/T range, allowing monitoring sample properties using X-ray diffraction and absorption spectroscopy up to 50GPa and 1620K.
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Rousset, B., Jolivet, R., Simons, M., Lasserre, C., Riel, B., Milillo, P., et al. (2016). An aseismic slip transient on the North Anatolian Fault. Geophysical Research Letters, 43(7), 3254–3262.
Résumé: Constellations of Synthetic Aperture Radar (SAR) satellites with short repeat time acquisitions allow exploration of active faults behavior with unprecedented temporal resolution. Along the North Anatolian Fault (NAF) in Turkey, an 80 km long section has been creeping at least since the 1944, M-w 7.3 earthquake near Ismetpasa, with a current Interferometric Synthetic Aperture Radar (InSAR)-derived average creep rate of 8 +/- 3 mm/yr (i.e., a third of the NAF long-term slip rate). We use a dense set of SAR images acquired by the COSMO-SkyMed constellation to quantify the spatial distribution and temporal evolution of creep over 1 year. We identify a major burst of aseismic slip spanning 31 days with a maximum slip of 2 cm, between the surface and 4 km depth. This result shows that fault creep along this section of the NAF does not occur at a steady rate as previously thought, highlighting a need to revise our understanding of the underlying fault mechanics.
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Rousset, B., Lasserre, C., Cubas, N., Graham, S., Radiguet, M., DeMets, C., et al. (2016). Lateral Variations of Interplate Coupling along the Mexican Subduction Interface: Relationships with Long-Term Morphology and Fault Zone Mechanical Properties. Pure And Applied Geophysics, 173(10-11), 3467–3486.
Résumé: Although patterns of interseismic strain accumulation above subduction zones are now routinely characterised using geodetic measurements, their physical origin, persistency through time, and relationships to seismic hazard and long-term deformation are still debated. Here, we use GPS and morphological observations from southern Mexico to explore potential mechanical links between variations in inter-SSE (in between slow slip events) coupling along the Mexico subduction zone and the long-term topography of the coastal regions from Guerrero to Oaxaca. Inter-SSE coupling solutions for two different geometries of the subduction interface are derived from an inversion of continuous GPS time series corrected from slow slip events. They reveal strong along-strike variations in the shallow coupling (i.e. at depths down to 25 km), with high-coupling zones (coupling > 0.7) alternating with low-coupling zones (coupling < 0.3). Coupling below the continent is typically strong (> 0.7) and transitions to uncoupled, steady slip at a relatively uniform 175-km inland from the trench. Along-strike variations in the coast-to-trench distances are strongly correlated with the GPS-derived forearc coupling variations. To explore a mechanical explanation for this correlation, we apply Coulomb wedge theory, constrained by local topographic, bathymetric, and subducting-slab slopes. Critical state areas, i.e. areas where the inner subduction wedge deforms, are spatially correlated with transitions at shallow depth between uncoupled and coupled areas of the subduction interface. Two end-member models are considered to explain the correlation between coast-to-trench distances and along-strike variations in the inter-SSE coupling. The first postulates that the inter-SSE elastic strain is partitioned between slip along the subduction interface and homogeneous plastic permanent deformation of the upper plate. In the second, permanent plastic deformation is postulated to depend on frictional transitions along the subduction plate interface. Based on the location and friction values of the critical state areas identified by our Coulomb wedge analysis, we parameterise frictional transitions in plastic-static models of deformation over several seismic cycles. This predicts strong shear dissipation above frictional transitions on the subduction interface. The comparison of modelled surface displacements over a critical zone at a frictional transition and over a stable area with no internal wedge deformation shows differences of long-term uplift consistent with the observed along-strike variations in the coast-to-trench distances. Our work favours a model in which frictional asperities partly control short-term inter-SSE coupling as measured by geodesy and in which those asperities persist through time.
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Roux, P., Moreau, L., Lecointre, A., Hillers, G., Campillo, M., Ben-Zion, Y., et al. (2016). A methodological approach towards high-resolution surface wave imaging of the San Jacinto Fault Zone using ambient-noise recordings at a spatially dense array. Geophysical Journal International, 206(2), 980–992.
Résumé: We present a new technique for deriving detailed information on seismic velocities of the subsurface material from continuous ambient noise recorded by spatially dense seismic arrays. This method uses iterative double beamforming between various subarrays to extract surface wave contributions from the ambient-noise data in complex environments with unfavourable noise-source distributions. The iterative double beamforming extraction makes it possible to retrieve large amounts of Rayleigh wave traveltime information in a wide frequency band. The method is applied to data recorded by a highly dense Nodal array with 1108 vertical geophones, centred on the damage zone of the Clark branch of the San Jacinto Fault Zone south of Anza, California. The array covers a region of similar to 650 x 700 m(2), with instrument spacing of 10-30 m, and continuous recording at 500 samples s(-1) over 30 d in 2014. Using this iterative double beamforming on subarrays of 25 sensors and cross-correlations between all of the station pairs, we separate surface waves from body waves that are abundant in the raw cross-correlation data. Focusing solely on surface waves, maps of traveltimes are obtained at different frequencies with unprecedented accuracy at each point of a 15-m-spacing grid. Group velocity inversions at 2-4 Hz reveal depth and lateral variations in the structural properties within and around the San Jacinto Fault Zone in the study area. This method can be used over wider frequency ranges and can be combined with other imaging techniques, such as eikonal tomography, to provide unprecedented detailed structural images of the subsurface material.
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Saint Blanquat, M. D., Bajolet, F., Grand'Homme, A., Proietti, A., Zanti, M., Boutin, A., et al. (2016). Cretaceous mantle exhumation in the central Pyrenees: New constraints from the peridotites in eastern Ariege (North Pyrenean zone, France). Comptes Rendus Geoscience, 348(3-4), 268–278.
Résumé: We provide new constraints on the modes of mantle exhumation and denudation in the preorogenic Pyrenees by investigating the poorly known peridotites located east of the Lherz body, in eastern Ariege (Vicdessos, Urs, Bestiac, Caussou and Prades main peridotitic bodies). We show that: (1) numerous peridotite bodies, not described so far, are constituted by decametric to sub-metric outcrops scattered between and around the main outcrops identified by Monchoux (1970); (2) most of the peridotites form blocks and lenses of various sizes, from millimetric monocrystalline grains to hectometric olistoliths, embedded in debris flows involving mainly Mesozoic metasediments; these peridotites can therefore be linked to the S-type peridotites of Lagabrielle et al. (2010), and share similarities with the peridotites of Lherz region (Clerc et al., 2012). All originated from tectono-sedimentary processes associated with mantle exhumation in relation with extreme thinning and breakoff of the continental basement; (3) the various petrographic characters of these peridotites and their heterogeneity in serpentinisation degree imply a peculiar mode of exhumation, which merges mantle fragments inherited from different structural levels; (4) the lack of tectonic structures such as faults and shear planes associated with the ultramafic-rich breccia formation and the presence of neoformation of metamorphic minerals within the matrix preclude their origin as cataclasites related to the Latest Cretaceous and Tertiary Pyrenean contractional deformation. The peridotites of eastern Arie` ge are indisputable witnesses of the presence of an inverted hyper-extended Cretaceous passive margin forming the current North Pyrenean zone. The geometry of the extensional system was complex and probably associated with strike-slip faults and transcurrent motion. (C) 2016 The Authors. Published by Elsevier Masson SAS on behalf of Academie des sciences.
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Salameh, C., Guillier, B., Harb, J., Cornou, C., Bard, P. Y., Voisin, C., et al. (2016). Seismic response of Beirut (Lebanon) buildings: instrumental results from ambient vibrations. Bulletin Of Earthquake Engineering, 14(10), 2705–2730.
Résumé: Resonance period is a key parameter in the seismic design of a structure, thus dynamic parameters of buildings in Beirut (Lebanon) were investigated based on ambient vibration method for risk and vulnerability assessment. Lebanon is facing high seismic hazard due to its major faults, combined to a high seismic risk caused by dense urbanization in addition to the lack of a seismic design code implementation. For this study, ambient vibration recordings have been performed on 330 RC buildings, period parameters extracted and statistically analyzed to identify correlations with physical building parameters (height, horizontal dimensions, age) and site characteristics (rock sites or soft sites). The study shows that (1) the building height or number of floors (N) is the primary statistically robust parameter for the estimation of the fundamental period T; (2) the correlation between T and N is linear and site dependent: T ae N/23 for rock sites and N/18 for soft sites; (3) the measured damping is inversely proportional to the period: the taller the building the lower is the damping; (4) a significant overestimation of the period exists in current building codes. However part of the large discrepancy with building code recommendations may be due to the very low level of loading.
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Samaniego, P., Rivera, M., Marino, J., Guillou, H., Liorzou, C., Zerathe, S., et al. (2016). The eruptive chronology of the Ampato-Sabancaya volcanic complex (Southern Peru). Journal Of Volcanology And Geothermal Research, 323, 110–128.
Résumé: We have reconstructed the eruptive chronology of the Ampato-Sabancaya volcanic complex (Southern Peru) on the basis of extensive fieldwork, and a large dataset of geochronological (K-40-Ar-40, C-14 and He-3) and geochemical (major and trace element) data. This volcanic complex is composed of two successive edifices that have experienced discontinuous volcanic activity from Middle Pleistocene to Holocene times. The Ampato compound volcano consists of a basal edifice constructed over at least two cone-building stages dated at 450-400 ka and 230-200 ka After a period of quiescence, the Ampato Upper edifice was constructed firstly during an effusive stage (80-70 ka), and then by the formation of three successive peaks: the Northern, Southern (40-20 ka) and Central cones (20-10 ka). The Southern peak, which is the biggest, experienced large explosive phases, resulting in deposits such as the Corinta plinian fallout. During the Holocene, eruptive activity migrated to the NE and constructed the mostly effusive Sabancaya edifice. This cone comprised many andesitic and dacitic blocky lava flows and a young terminal cone, mostly composed of pyroclastic material. Most samples from the Ampato-Sabancaya define a broad high-K magmatic trend composed of andesites and dacites with a mineral assemblage of plagio-clase, amphibole, biotite, ortho -and clino-pyroxene, and Fe-Ti oxides. A secondary trend also exists, corresponding to rare dacitic explosive eruptions (i.e. Corinta fallout and flow deposits). Both magmatic trends are derived by fractional crystallisation involving an amphibole-rich cumulate with variable amounts of upper crustal assimilation. A marked change in the overall eruptive rate has been identified between Ampato (similar to 0.1 km(3)/ka) and Sabancaya (0.6-1.7 km(3)/ka). This abrupt change demonstrates that eruptive rates have not been homogeneous throughout the volcano's history. Based on tephrochronologic studies, the Late Holocene Sabancaya activity is characterised by strong vulcanian events, although its erupted volume remained low and only produced a local impact through ash fallout. We have identified at least 6 eruptions during the last 4-5 ka, including the historical AD 1750-1784 and 1987-1998 events. On the basis of this recurrent low-to-moderate explosive activity, Sabancaya must be considered active and a potentially threatening volcano. (C) 2016 Elsevier B.V. All rights reserved.
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Savelieva, G. N., Batanova, V. G., & Sobolev, A. V. (2016). Pyroxene-Cr-spinel exsolution in mantle lherzolites of the Syum-Keu ophiolite massif (Arctic Urals). Russian Geology And Geophysics, 57(10), 1419–1436.
Résumé: We consider the composition and microstructures of pyroxene-Cr-spinel exsolution products from lherzolites of the deep mantle section of the Syum-Keu ophiolite massif in the Arctic Urals. Enstatite and diopside from the lherzolites contain lamellae and diverse micron segregations of Cr-spinel. We have first determined the composition of Cr-spinel lamellae and the composition trend of pyroxenes undergoing exsolution. The zonal inhomogeneity of their composition is expressed as a decrease in the contents of Cr2O3, Al2O3, and Na2O from the core of coarse grains free of exsolution structures to the sites with Cr-spinel segregations. The Cr/(Cr + Al) value in the Cr-spinel lamellae varies from 0.23 to 0.33, and the Mg/(Mg + Fe) value, from 0.61 to 0.67. The degree of iron oxidation in the formed Cr-spinel is low (0.10-0.19) and virtually does not depend on the Cr content in this mineral. We calculated the temperature and pressure of the beginning and completion of pyroxene-Cr-spinel exsolution for the equilibrium enstatite-diopside (of different generations) pairs and established the participation of H2O fluid in the exsolution. During the exsolution, the temperature decreases from 970 to 650-700 degrees C and the pressure grows from 0.9 to 1.3 GPa. The exsolution of pyroxene and migration of elements proceeded under high-temperature solid-plastic flow of mantle material, probably in the local zones where peridotites were subjected to strong shearing strains caused by the above high-velocity flow. The zone with these processes was located in the lithospheric mantle (mantle wedge) above the subduction zone. Migration of ore components from silicates and formation of new Cr-spinel grains contributed to the formation of chromite segregations. (C) 2016, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.
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Savelieva, G. N., Raznitsin, Y. N., & Merkulova, M. V. (2016). Metamorphism of Peritotites in the Mantle Wedge above the Subduction Zone: Hydration of the Lithospheric Mantle. Doklady Earth Sciences, 468(1), 438–440.
Résumé: Two areas with different types of hydration (serpentinization), which occurred in two settings distinct in temperatures, pressures, and stresses, are spatially individualized in the ophiolitic ultramafic massifs of the Polar Urals. The high-temperature hydration of ultramafic rocks occurred in the lithosphere of the mantle wedge directly above the subducted slab. The initial conditions of hydration are limited to 1.2-2 GPa and 650-700 degrees C; a stable assemblage of olivine + antigorite + magnetite. amphibole. talc. chlorite was formed at 0.9-1.2 GPa and 550-600 degrees C. The low-temperature mesh lizardite-chrysotile serpentinization occurred in the crustal, near-surface conditions. Both types of hydration were accompanied by release of hydrogen, which participates in abiogenic CH4 synthesis in the presence of CO2 dissolved in water.
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Schaeffer, N., & Jault, D. (2016). Electrical conductivity of the lowermost mantle explains absorption of core torsional waves at the equator. Geophysical Research Letters, 43(10), 4922–4928.
Résumé: Torsional Alfven waves propagating in the Earth's core have been inferred by inversion techniques applied to geomagnetic models. They appear to propagate across the core but vanish at the equator, exchanging angular momentum between core and mantle. Assuming axial symmetry, we find that an electrically conducting layer at the bottom of the mantle can lead to total absorption of torsional waves that reach the equator. We show that the reflection coefficient depends on G (B) over tilde (r), where (B) over tilde (r) is the strength of the radial magnetic field at the equator, and G the conductance of the lower mantle there. With (B) over tilde (r) = 7 x 10(-4) T, torsional waves are completely absorbed when they hit the equator if G similar or equal to 1.3 x 10(8) S. For larger or smaller G, reflection occurs. As G is increased above this critical value, there is less attenuation and more angular momentum exchange. Our finding dissociates efficient core-mantle coupling from strong ohmic dissipation in the mantle.
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Schaeffer, N., Silva, E. L., & Pais, M. A. (2016). Can core flows inferred from geomagnetic field models explain the Earth's dynamo? Geophysical Journal International, 204(2), 868–877.
Résumé: We test the ability of large-scale velocity fields inferred from geomagnetic secular variation data to produce the global magnetic field of the Earth. Our kinematic dynamo calculations use quasi-geostrophic (QG) flows inverted from geomagnetic field models which, as such, incorporate flow structures that are Earth-like and may be important for the geodynamo. Furthermore, the QG hypothesis allows straightforward prolongation of the flow from the core surface to the bulk. As expected from previous studies, we check that a simple QG flow is not able to sustain the magnetic field against ohmic decay. Additional complexity is then introduced in the flow, inspired by the action of the Lorentz force. Indeed, on centennial timescales, the Lorentz force can balance the Coriolis force and strict quasi-geostrophy may not be the best ansatz. When our columnar flow is modified to account for the action of the Lorentz force, magnetic field is generated for Elsasser numbers larger than 0.25 and magnetic Reynolds numbers larger than 100. This suggests that our large-scale flow captures the relevant features for the generation of the Earth's magnetic field and that the invisible small-scale flow may not be directly involved in this process. Near the threshold, the resulting magnetic field is dominated by an axial dipole, with some reversed flux patches. Time dependence is also considered, derived from principal component analysis applied to the inverted flows. We find that time periods from 120 to 50 yr do not affect the mean growth rate of the kinematic dynamos. Finally, we note that the footprint of the inner core in the magnetic field generated deep in the bulk of the shell, although we did not include one in our computations.
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Scheck, J., Wu, B. H., Drechsler, M., Rosenberg, R., Van Driessche, A. E. S., Stawski, T. M., et al. (2016). The Molecular Mechanism of Iron(III) Oxide Nucleation. Journal Of Physical Chemistry Letters, 7(16), 3123–3130.
Résumé: A molecular understanding of the formation of solid phases from solution would be beneficial for various scientific fields. However, nucleation pathways are still not fully understood, whereby the case of iron (oxyhydr)oxides poses a prime example. We show that in the prenucleation regime, thermodynamically stable solute species up to a few nanometers in size are observed, which meet the definition of prenucleation clusters. Nucleation then is not governed by a critical size, but rather by the dynamics of the clusters that are forming at the distinct nucleation stages, based on the chemistry of the linkages within the clusters. This resolves a longstanding debate in the field of iron oxide nucleation, and the results may generally apply to oxides forming via hydrolysis and condensation. The (molecular) understanding of the chemical basis of phase separation is paramount for, e.g., tailoring size, shape and structure of novel nanocrystalline materials.
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Schleicher, J. M., Bergantz, G. W., Breidenthal, R. E., & Burgisser, A. (2016). Time scales of crystal mixing in magma mushes. Geophysical Research Letters, 43(4), 1543–1550.
Résumé: Magma mixing is widely recognized as a means of producing compositional diversity and preconditioning magmas for eruption. However, the processes and associated time scales that produce the commonly observed expressions of magma mixing are poorly understood, especially under crystal-rich conditions. Here we introduce and exemplify a parameterized method to predict the characteristic mixing time of crystals in a crystal-rich magma mush that is subject to open-system reintrusion events. Our approach includes novel numerical simulations that resolve multiphase particle-fluid interactions. It also quantifies the crystal mixing by calculating both the local and system-wide progressive loss of the spatial correlation of individual crystals throughout the mixing region. Both inertial and viscous time scales for bulk mixing are introduced. Estimated mixing times are compared to natural examples and the time for basaltic mush systems to become well mixed can be on the order of 10 days.
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Schmittbuhl, J., Karabulut, H., Lengline, O., & Bouchon, M. (2016). Long-lasting seismic repeaters in the Central Basin of the Main Marmara Fault. Geophysical Research Letters, 43(18), 9527–9534.
Résumé: The Main Marmara Fault which crosses the whole Marmara Sea is a significant seismic gap along the North Anatolian Fault. Here we show that nine long-lasting strike-slip seismic repeaters exist below the Central Basin within the seismogenic zone, in a 10 km region where deep creep was previously suggested from the analysis of the local seismicity. The typical recurrence time was 8 months during the 2008-2015 period. The cumulative slip of the repeating sequence appears to be compatible with the regional geodetic slip rate if they are assumed to be part of a large single asperity (10 km). The repeaters also exhibit short-term crises and are possibly related to bursts of creep.
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Schmittbuhl, J., Karabulut, H., Lengline, O., & Bouchon, M. (2016). Seismicity distribution and locking depth along the Main Marmara Fault, Turkey. Geochemistry Geophysics Geosystems, 17(3), 954–965.
Résumé: The seismicity along the Main Marmara Fault (MMF) below the Marmara Sea is analyzed during the 2007-2012 period to provide insights on the recent evolution of this important regional seismic gap. High precision locations show that seismicity is strongly varying along strike and depth providing fine details of the fault behavior that are inaccessible from geodetic observations. The activity strongly clusters at the regions of transition between basins. The Central basin shows significant seismicity located below the shallow locking depth inferred from GPS measurements. Its b-value is low and the average seismic slip is high. All observations are consistent with a deep creep of this segment. On the contrary, the Kumburgaz basin at the center of the fault shows sparse seismicity with the hallmarks of a locked segment. In the eastern Marmara Sea, the seismicity distribution along the Princes Island segment in the Cinarcik basin, is consistent with the geodetic locking depth of 10 km and a low contribution to the regional seismic energy release. The assessment of the locked segment areas provide an estimate of the magnitude of the main forthcoming event to be about 7.3 assuming that the rupture will not enter significantly within creeping domains.
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Schreck, E., Sarret, G., Oliva, P., Calas, A., Sobanska, S., Guedron, S., et al. (2016). Is Tillandsia capillaris an efficient bioindicator of atmospheric metal and metalloid deposition? Insights from five months of monitoring in an urban mining area. Ecological Indicators, 67, 227–237.
Résumé: Atmospheric pollution in megacities has a major impact on human health and environmental quality. Air quality bioindicators may have some advantages over standard devices such as impactors or filters. In this study we evaluated the reliability of Tillandsia sp. versus passive filters for monitoring the atmospheric deposition of metal(loid)s in an area affected by anthropogenic activities. We aimed to gain insight into the composition and origin of atmospheric particles and their fate after deposition on the plant. Three zones with different contamination levels were monitored for five months in 2012. For the highly contaminated area, a linear increase in metalloid) accumulation was found in passive filters, whereas for transplanted Tillandsia capillaris the increase was almost linear for As, Cd, Hg, and Sn, but not for Ag, Pb, Sb, and Zn. For the moderately contaminated zone, the results showed that the exposure time was not sufficient for metal(loid) concentrations to increase in either the plants or filters. However, natural specimens provided some indications of the levels of metal contamination. Metal particles were observed on the plant surface and also in the central disc underneath tillandsia trichomes, suggesting that this is a possible pathway for metals to enter the plant. X-ray absorption spectroscopy demonstrated chemical transformation for Pb and As, both in filters and plants. For Pb, sorbed Pb and/or cell wall complexes were identified in the plants. No As-III-S species, indicative of As detoxification, were identified in the plant. Arsenic was oxidized from As-III to As-V in both plants and filters. Thus, in the present study, passive filters proved more reliable than T. capillaris transplants, although natural specimens provided some insights into local contamination. Particulate contaminants underwent chemical transformation after being trapped in the plant, but there was no clear evidence of internalization and detoxification. (C) 2016 Elsevier Ltd. All rights reserved.
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Schwan, L., Boutin, C., Padron, L. A., Dietz, M. S., Bard, P. Y., & Taylor, C. (2016). Site-city interaction: theoretical, numerical and experimental crossed-analysis. Geophysical Journal International, 205(2), 1006–1031.
Résumé: The collective excitation of city structures by a seismic wavefield and the subsequent multiple Structure-Soil-Structure Interactions (SSSIs) between the buildings are usually disregarded in conventional seismology and earthquake engineering practice. The objective here is to qualify and quantify these complex multiple SSSIs through the design of an elementary study case, which serves as a benchmark for theoretical, numerical and experimental crossed-analysis. The experimental specimen consists of an idealized site-city setup with up to 37 anisotropic resonant structures arranged at the top surface of an elastic layer and in co-resonance with it. The experimental data from shaking table measurements is compared with the theoretical and numerical results provided respectively by an equivalent city-impedance model derived analytically from homogenization in the long-wavelength approximation and a model based on boundary elements. The signatures of the site-city interactions are identified in the frequency, time and space domain, and in particular consist of a frequency-dependent free/rigid switch in the surface condition at the city resonance, beatings in the records and the depolarization of the wavefield. A parametric study on the city density shows that multiple SSSIs among the city structures (five are sufficient) can have significant effects on both the seismic response of its implantation site and that of the buildings. Key parameters are provided to assess site-city interactions in the low seismic frequency range: They involve the mass and rigidity of the city compared to those of the soil and the damping of the building.
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Serlenga, V., de Lorenzo, S., Russo, G., Amoroso, O., Garambois, S., Virieux, J., et al. (2016). A three-dimensional Q(p) imaging of the shallowest subsurface of Campi Flegrei offshore caldera, southern Italy. Geophysical Research Letters, 43(21), 11209–11218.
Résumé: To improve the knowledge of the shallowest subsurface of Campi Flegrei caldera, a 3-D P wave attenuation tomography of the area was performed. We analyzed about 18,000 active seismic traces, which provided a data set of 11,873 At* measurements, e.g., the differential travel times to quality factor ratios. These were inverted through an adapted tomographic inversion procedure. The 3-D tomographic images reveal an average Qp about 70, interpreted as water -saturated volcanic and marine sediments. An arc -like, low-Qp structure at 0.5-1 km depths was interpreted as a densely fractured, fluid -saturated rock volume, well matching the buried rim of Campi Flegrei caldera. The spatial distribution of high- and low-Qp bodies in the inner caldera is correlated with low-Vp values and may reflect either the differences in the percentage of fluid saturation of sediments or the presence of vapor state fluids beneath fumarole manifestations.
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Serra, M., Festa, G., Roux, P., Gresse, M., Vandemeulebrouck, J., & Zollo, A. (2016). A strongly heterogeneous hydrothermal area imaged by surface waves: the case of Solfatara, Campi Flegrei, Italy. Geophysical Journal International, 205(3), 1813–1822.
Résumé: We investigated the shallow structure of the Solfatara, a volcano within the Campi Flegrei caldera, southern Italy, using surface waves as a diagnostic tool. We analysed data collected during the RICEN campaign, where a 3-D active seismic experiment was performed on a dense regular grid of 90 m x 115 m using a Vibroseis as the seismic source. After removal of the source time function, we analysed the surface wave contribution to the Green's function. Here, a 1-D approximation can hold for subgrids of 40 m x 40 m. Moreover, we stacked all of the signals in the subgrid according to source-receiver distance bins, despite the absolute location of the source and the receiver, to reduce the small-scale variability in the data. We then analysed the resulting seismic sections in narrow frequency bands between 7 and 25 Hz. We obtained phase and group velocities from a grid search, and a cost function based on the spatial coherence of both the waveforms and their envelopes. We finally jointly inverted the dispersion curves of the phase and group velocities to retrieve a 1-D S-wave model local to the subgrid. Together, the models provided a 3-D description of the S-wave model in the area. We found that the maximum penetration depth is 15 m. In the first 4 m, we can associate the changes in the S-wave field to the temperature gradient, while at greater depths, the seismic images correlate with the resistivity maps, which indicate the water layer close to the Fangaia area and an abrupt variation moving towards the northeast.
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Seydoux, L., Shapiro, N. M., de Rosny, J., Brenguier, F., & Landes, M. (2016). Detecting seismic activity with a covariance matrix analysis of data recorded on seismic arrays. Geophysical Journal International, 204(3), 1430–1442.
Résumé: Modern seismic networks are recording the ground motion continuously at the Earth's surface, providing dense spatial samples of the seismic wavefield. The aim of our study is to analyse these records with statistical array-based approaches to identify coherent time-series as a function of time and frequency. Using ideas mainly brought from the random matrix theory, we analyse the spatial coherence of the seismic wavefield from the width of the covariance matrix eigenvalue distribution. We propose a robust detection method that could be used for the analysis of weak and emergent signals embedded in background noise, such as the volcanic or tectonic tremors and local microseismicity, without any prior knowledge about the studied wavefields. We apply our algorithm to the records of the seismic monitoring network of the Piton de la Fournaise volcano located at La R,union Island and composed of 21 receivers with an aperture of similar to 15 km. This array recorded many teleseismic earthquakes as well as seismovolcanic events during the year 2010. We show that the analysis of the wavefield at frequencies smaller than similar to 0.1 Hz results in detection of the majority of teleseismic events from the Global Centroid Moment Tensor database. The seismic activity related to the Piton de la Fournaise volcano is well detected at frequencies above 1 Hz.
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Shalev, E., Kurzon, I., Doan, M. L., & Lyakhovsky, V. (2016). Sustained water-level changes caused by damage and compaction induced by teleseismic earthquakes. Journal Of Geophysical Research-Solid Earth, 121(7), 4943–4954.
Résumé: Sustained water-level increase and decrease induced by distant earthquakes were observed in two wells, Gome 1 and Meizar 1 in Israel. The Gome 1 well is located within a damage zone of a major fault zone, and Meizar 1 is relatively far from a fault. The monitored pressure change in both wells shows significant water-level oscillations and sustained water-level changes in response to the passage of the seismic waves. The sustained water-level changes include short-term (minutes) undrained behavior and longer-period (hours and days) drained behavior associated with groundwater flow. We model the short-term undrained response of water pressure oscillations and sustained change to the distant 2013 M-w 7.7 Balochistan earthquake by nonlinear elastic behavior of damaged rocks, accounting for small wave-induced compaction and damage accumulation. We suggest that the rocks are close to failure in both locations and strain oscillations produced by the passing seismic waves periodically push the rock above the yield cap, creating compaction when volumetric strain increases and damage when shear strain increases. Compaction increases pore pressure, whereas damage accumulation decreases pore pressure by fracture dilation. The dominant process depends on the properties of the rock. For highly damaged rocks, dilatancy is dominant and a sustained pressure decrease is expected. For low-damage rocks, compaction is the dominant process creating sustained water-level increase. We calculate damage and porosity changes associated to the Balochistan earthquake in both wells and quantify damage accumulation and compaction during the passage of the seismic waves.
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Shalev, E., Kurzon, I., Doan, M. L., & Lyakhovsky, V. (2016). Water-level oscillations caused by volumetric and deviatoric dynamic strains. Geophysical Journal International, 204(2), 841–851.
Résumé: Travelling seismic waves and Earth tides are known to cause oscillations in well water levels due to the volumetric strain characteristics of the ground motion. Although the response of well water levels to S and Love waves has been reported, it has not yet been quantified. In this paper we describe and explain the behaviour of a closed artesian water well (Gome 1) in response to teleseismic earthquakes. This well is located within a major fault zone and screened at a highly damaged (cracked) sandstone layer. We adopt the original Skempton approach where both volumetric and deviatoric stresses (and strains) affect pore pressure. Skempton's coefficients B and A couple the volumetric and deviatoric stresses respectively with pore pressure and BKu and N are the equivalent coupling terms to volumetric and deviatoric strains. The water level in this well responds dramatically to volumetric strain (P and Rayleigh waves) as well as to deviatoric strain (S and Love waves). This response is explained by the nonlinear elastic behaviour of the highly damaged rocks. The water level response to deviatoric strain depends on the damage in the rock; deviatoric strain loading on damaged rock results in high water level amplitudes, and no response in undamaged rock. We find high values of N = 8.5 GPa that corresponds to -0.5 < A < -0.25 expected at highly damaged rocks. We propose that the Gome 1 well is located within fractured rocks, and therefore, dilatency is high, and the response of water pressure to deviatoric deformation is high. This analysis is supported by the agreement between the estimated compressibility of the aquifer, independently calculated from Earth tides, seismic response of the water pressure and other published data.
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Shen, T. Y., Wang, G. C., Leloup, P. H., van der Beek, P., Bernet, M., Cao, K., et al. (2016). Controls on Cenozoic exhumation of the Tethyan Himalaya from fission-track thermochronology and detrital zircon U-Pb geochronology in the Gyirong basin area, southern Tibet. Tectonics, 35(7), 1713–1734.
Résumé: The Gyirong basin, southern Tibet, contains the record of Miocene-Pliocene exhumation, drainage development, and sedimentation along the northern flank of the Himalaya. The tectonic controls on basin formation and their potential link to the South Tibetan Detachment System (STDS) are not well understood. We use detrital zircon (ZFT) and apatite (AFT) fission-track analysis, together with detrital zircon U-Pb dating to decipher the provenance of Gyirong basin sediments and the exhumation history of the source areas. Results are presented for nine detrital samples of Gyirong basin sediments (AFT, ZFT, and U-Pb), two modern river-sediment samples (ZFT and AFT), and six bedrock samples (ZFT) from transect across the Gyirong fault bounding the basin to the east. The combination of detrital zircon U-Pb and fission-track data demonstrates that the Gyirong basin sediments were sourced locally from the Tethyan Sedimentary Sequence. This provenance pattern indicates that deposition was controlled by the Gyirong fault, active since similar to 10 Ma, whose vertical throw was probably <similar to 5000 m, rather than being controlled by normal faults associated with the STDS. The detrital thermochronology data contain two prominent age groups at similar to 37-41 and 15-18 Ma, suggesting rapid exhumation at these times. A 15-18 Ma phase of rapid exhumation has been recorded widely in both southern Tibet and the Himalaya. A possible interpretation for such a major regional exhumation event might be detachment of the subducting Indian plate slab during the middle Miocene, inducing dynamic uplift of the Indian plate overriding its own slab.
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Smittarello, D., Grandin, R., De Chabalier, J. B., Doubre, C., Deprez, A., Masson, F., et al. (2016). Transient deformation in the Asal-Ghoubbet Rift (Djibouti) since the 1978 diking event: Is deformation controlled by magma supply rates? Journal Of Geophysical Research-Solid Earth, 121(8), 6030–6052.
Résumé: The Asal-Ghoubbet Rift (AG Rift) in Djibouti lies in the subaerial continuation of the Aden ridge system, thereby constituting a unique location to study rifting processes and mechanisms involved in continental breakup and oceanic spreading. Continually upgraded and expanded geodetic technology has been used to record the 1978 Asal rifting event and postdiking deformation. In light of recent results obtained for the Manda Hararo-Dabbahu rifting event (2005-2010), we propose that the horizontal and vertical geodetic data can be modeled with a double source, involving a dike-like inflation component aligned along the rift axis and a spherical pressure source located at midsegment below the Fieale caldera. By revisiting the codiking data, we propose that the reservoir below Fieale could have fed, at least partially, the 1978 injection and the contemporaneous Ardoukoba eruption and potentially induced local subsidence due to magma draining out of the central reservoir. As an alternative to previously proposed viscoelastic relaxation models, we reinterpret postdiking observations using a purely elastic rheology. We determine the relative contribution of a midsegment reservoir inflation and a dike-like opening component, together with their respective time evolutions. Our results suggest that interactions between steadily accumulating tectonic strain and temporal variations in melt supply to the shallow magma plumbing system below the AG Rift may entirely explain the geodetic observations and that viscoelastic deformation processes played a minor role in the 30 years following the 1978 rifting event.
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Sobolev, A. V., Asafov, E. V., Gurenko, A. A., Arndt, N. T., Batanova, V. G., Portnyagin, M. V., et al. (2016). Komatiites reveal a hydrous Archaean deep-mantle reservoir. Nature, 531(7596), 628–632.
Résumé: Archaean komatiites (ultramafic lavas) result from melting under extreme conditions of the Earth's mantle. Their chemical compositions evoke very high eruption temperatures, up to 1,600 degrees Celsius, which suggests even higher temperatures in their mantle source(1,2). This message is clouded, however, by uncertainty about the water content in komatiite magmas. One school of thought holds that komatiites were essentially dry and originated in mantle plumes(3-6) while another argues that these magmas contained several per cent water, which drastically reduced their eruption temperature and links them to subduction processes(7-9). Here we report measurements of the content of water and other volatile components, and of major and trace elements in melt inclusions in exceptionally magnesian olivine (up to 94.5 mole per cent forsterite). This information provides direct estimates of the composition and crystallization temperature of the parental melts of Archaean komatiites. We show that the parental melt for 2.7-billion-year-old komatiites from the Abitibi greenstone belt in Canada contained 30 per cent magnesium oxide and 0.6 per cent water by weight, and was depleted in highly incompatible elements. This melt began to crystallize at around 1,530 degrees Celsius at shallow depth and under reducing conditions, and it evolved via fractional crystallization of olivine, accompanied by minor crustal assimilation. As its major-and trace-element composition and low oxygen fugacities are inconsistent with a subduction setting, we propose that its high H2O/Ce ratio (over 6,000) resulted from entrainment into the komatiite source of hydrous material from the mantle transition zone(10). These results confirm a plume origin for komatiites and high Archaean mantle temperatures, and evoke a hydrous reservoir in the deep mantle early in Earth's history.
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Soueid Ahmed, A., Jardani, A., Revil, A., & Dupont, J. P. (2016). Joint inversion of hydraulic head and self-potential data associated with harmonic pumping tests. Water Resources Research, 52(9), 6769–6791.
Résumé: Harmonic pumping tests consist in stimulating an aquifer by the means of hydraulic stimulations at some discrete frequencies. The inverse problem consisting in retrieving the hydraulic properties is inherently ill posed and is usually underdetermined when considering the number of well head data available in field conditions. To better constrain this inverse problem, we add self-potential data recorded at the ground surface to the head data. The self-potential method is a passive geophysical method. Its signals are generated by the groundwater flow through an electrokinetic coupling. We showed using a 3-D saturated unconfined synthetic aquifer that the self-potential method significantly improves the results of the harmonic hydraulic tomography. The hydroelectric forward problem is obtained by solving first the Richards equation, describing the groundwater flow, and then using the result in an electrical Poisson equation describing the self-potential problem. The joint inversion problem is solved using a reduction model based on the principal component geostatistical approach. In this method, the large prior covariance matrix is truncated and replaced by its low-rank approximation, allowing thus for notable computational time and storage savings. Three test cases are studied, to assess the validity of our approach. In the first test, we show that when the number of harmonic stimulations is low, combining the harmonic hydraulic and self-potential data does not improve the inversion results. In the second test where enough harmonic stimulations are performed, a significant improvement of the hydraulic parameters is observed. In the last synthetic test, we show that the electrical conductivity field required to invert the self-potential data can be determined with enough accuracy using an electrical resistivity tomography survey using the same electrodes configuration as used for the self-potential investigation.
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Souied Ahmed, A., Jardani, A., Revil, A., & Dupont, J. P. (2016). Specific storage and hydraulic conductivity tomography through the joint inversion of hydraulic heads and self-potential data. Advances In Water Resources, 89, 80–90.
Résumé: Transient hydraulic tomography is used to image the heterogeneous hydraulic conductivity and specific storage fields of shallow aquifers using time series of hydraulic head data. Such ill-posed and non-unique inverse problem can be regularized using some spatial geostatistical characteristic of the two fields. In addition to hydraulic heads changes, the flow of water, during pumping tests, generates an electrical field of electrokinetic nature. These electrical field fluctuations can be passively recorded at the ground surface using a network of non-polarizing electrodes connected to a high impedance (> 10 MOhin) and sensitive (0.1 mV) voltmeter, a method known in geophysics as the self-potential method. We perform a joint inversion of the self-potential and hydraulic head data to image the hydraulic conductivity and specific storage fields. We work on a 3D synthetic confined aquifer and we use the adjoint state method to compute the sensitivities of the hydraulic parameters to the hydraulic head and self-potential data in both steady-state and transient conditions. The inverse problem is solved using the geostatistical quasi-linear algorithm framework of Kitanidis. When the number of piezometers is small, the record of the transient self-potential signals provides useful information to characterize the hydraulic conductivity and specific storage fields. These results show that the self-potential method reveals the heterogeneities of some areas of the aquifer, which could not been captured by the tomography based on the hydraulic heads alone. In our analysis, the improvement on the hydraulic conductivity and specific storage estimations were based on perfect knowledge of electrical resistivity field. This implies that electrical resistivity will need to be jointly inverted with the hydraulic parameters in future studies and the impact of its uncertainty assessed with respect to the final tomograms of the hydraulic parameters. (C) 2016 Elsevier Ltd. All rights reserved.
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Stawski, T. M., van Driessche, A. E. S., Ossorio, M., Rodriguez-Blanco, J. D., Besselink, R., & Benning, L. G. (2016). Formation of calcium sulfate through the aggregation of sub-3 nanometre primary species. Nature Communications, 7.
Résumé: The formation pathways of gypsum remain uncertain. Here, using truly in situ and fast time-resolved small-angle X-ray scattering, we quantify the four-stage solution-based nucleation and growth of gypsum (CaSO4 center dot 2H(2)O), an important mineral phase on Earth and Mars. The reaction starts through the fast formation of well-defined, primary species of <3 nm in length (stage I), followed in stage II by their arrangement into domains. The variations in volume fractions and electron densities suggest that these fast forming primary species contain Ca-SO4-cores that self-assemble in stage III into large aggregates. Within the aggregates these well-defined primary species start to grow (stage IV), and fully crystalize into gypsum through a structural rearrangement. Our results allow for a quantitative understanding of how natural calcium sulfate deposits may form on Earth and how a terrestrially unstable phase-like bassanite can persist at low-water activities currently dominating the surface of Mars.
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Sucheras-Marx, B., Giraud, F., Simionovici, A., Daniel, I., & Tucoulou, R. (2016). Perspectives on heterococcolith geochemical proxies based on high-resolution X-ray fluorescence mapping. Geobiology, 14(4), 390–403.
Résumé: Heterococcoliths are micron-scale calcite platelets produced by coccolithophores. They have been the most abundant and continuous fossil record over the last 215 million years (Myr), offering great potential for geochemical studies, although the heterococcolith fossil record remains underutilised in this domain. We have mapped heterococcoliths' composition using X-ray fluorescence (XRF) with a 100-nm resolution beam to decipher element distributions in heterococcoliths and to investigate the potential development of geochemical proxies for palaeoceanography. The study presents two Middle Jurassic Watznaueria britannica heterococcoliths from Cabo Mondego, Portugal. XRF analysis was performed with a 17 keV incident energy beam at the European Synchrotron Radiation Facility ID22NI beamline to study elements from Sr down to S. Ca, Sr and Mn are distributed following the heterococcolith crystalline arrangement. Cl, Br and S display an homogeneous distribution, whereas K, Fe, Cu, Zn and Rb are concentrated at the edges and in the central area of the heterococcoliths. Distributions of K, Fe, Ti, Fe, Cu, Zn, Rb and to a lesser extent V and Cr are highly influenced by clay contamination and peripheral diagenetic overgrowth. Mn is related to diagenetic Mn-rich CaCO3 overgrowth on top of or between heterococcoliths shields. Cl and Br are likely to be present in heterococcoliths inside interstitial nano-domains. We assume that the cytoplasm [Cl-] and [Br-] are mediated and constant during heterococcolithogenesis. Assuming a linear correlation between cytoplasm [Cl-] and sea water [Cl-], heterococcolith Cl may have potential as a salinity proxy. As S is incorporated into heterococcoliths by sulphated polysaccharides, our study suggests a role for such polysaccharides in heterococcolithogenesis for at least 170 Myr. The low Sr/Ca in the W. britannica specimens studied here may either highlight an unusual cellular physiology of Mesozoic coccolithophores or result from low growth rates in oligotrophic environments.
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Taira, T., & Brenguier, F. (2016). Response of hydrothermal system to stress transients at Lassen Volcanic Center, California, inferred from seismic interferometry with ambient noise. Earth Planets And Space, 68.
Résumé: Time-lapse monitoring of seismic velocity at volcanic areas can provide unique insight into the property of hydrothermal and magmatic fluids and their temporal variability. We established a quasi real-time velocity monitoring system by using seismic interferometry with ambient noise to explore the temporal evolution of velocity in the Lassen Volcanic Center, Northern California. Our monitoring system finds temporal variability of seismic velocity in response to stress changes imparted by an earthquake and by seasonal environmental changes. Dynamic stress changes from a magnitude 5.7 local earthquake induced a 0.1 % velocity reduction at a depth of about 1 km. The seismic velocity susceptibility defined as ratio of seismic velocity change to dynamic stress change is estimated to be about 0.006 MPa-1, which suggests the Lassen hydrothermal system is marked by high-pressurized hydrothermal fluid. By combining geodetic measurements, our observation shows that the long-term seismic velocity fluctuation closely tracks snow-induced vertical deformation without time delay, which is most consistent with an hydrological load model (either elastic or poroelastic response) in which surface loading drives hydrothermal fluid diffusion that leads to an increase of opening of cracks and subsequently reductions of seismic velocity. We infer that heated-hydrothermal fluid in a vapor-dominated zone at a depth of 2-4 km range is responsible for the long-term variation in seismic velocity
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Tallobre, C., Loncke, L., Bassetti, M. A., Giresse, P., Bayon, G., Buscail, R., et al. (2016). Description of a contourite depositional system on the Demerara Plateau: Results from geophysical data and sediment cores. Marine Geology, 378, 56–73.
Résumé: The Demerara Plateau, belonging to the passive transform margin of French Guiana, was investigated during the IGUANES cruise in 2013. The objectives of the cruise were to explore the poorly-known surficial sedimentary column overlying thick mass transport deposits as well as to understand the factors controlling recent sedimentation. The presence of numerous bedforms at the seafloor was observed thanks to newly acquired IGUANES bathymetric, high resolution seismic and chirp data, while sediment cores allowed the characterization of the deposits covering the mass transport deposits. Modern oceanographic conditions were determined in situ, using mooring monitoring over a 10-month period. Our data indicate the presence of a Contourite Depositional System along the Demerara Plateau, most likely related to bottom current activity of the North Atlantic Deep Water (NADW). However, at the regional scale, large longitudinal waves parallel the NADW flow. Their shape and orientation seem to be inherited from interactions between bottom currents and paleomorphologies expressed at the top of mass transport deposits. Their evolution is possibly driven by the intensity of bottom current activity that might have changed over time. Overall, this work presents an integrated approach combining seismic and sedimentological evidence to study the processes at the origin of contourite formation in the Demerara Plateau. Other regional factors, such as local slope values and slope instability, also control sedimentation. (C) 2016 Elsevier B.V. All rights reserved.
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Teng, F. Z., Hu, Y., & Chauvel, C. (2016). Magnesium isotope geochemistry in arc volcanism. Proceedings Of The National Academy Of Sciences Of The United States Of America, 113(26), 7082–7087.
Résumé: Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the delta Mg-26 of the Martinique Island lavas varies from -0.25 to -0.10, in contrast to the narrow range that characterizes the mantle (-0.25 +/- 0.04, 2 SD). These high delta Mg-26 values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid-mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration.
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Thouvenot, F., Jenatton, L., Scafidi, D., Turino, C., Potin, B., & Ferretti, G. (2016). Encore Ubaye: Earthquake Swarms, Foreshocks, and Aftershocks in the Southern French Alps. Bulletin Of The Seismological Society Of America, 106(5), 2244–2257.
Résumé: The earthquake swarm that took place in 2012-2015 in the Upper Ubaye Valley (the most active seismic zone in the French Alps) is peculiar for two reasons: (1) it occurred a few kilometers from a previous swarm (active in 2003-2004); (2) it was initiated by an M-L 4.3 shock and reactivated, more than two years later, by another M-L 4.8 shock with an identical epicenter but a deeper focus. We present here the corresponding data set of similar to 13,000 events, of which similar to 3000 were relocated using a double-difference algorithm. The swarm extends north-northwest-south-southeast (N165 degrees E) over a distance of 11 km, but daily snapshots along a 2.5 yr period allow us to identify transverse faults whose activity was often ephemeral. Focal mechanisms for 13 M-L >= 3 events confirm the complexity of the swarm geometry, although the fault plane for the two “mainshocks” is very consistent (N156 degrees E-N160 degrees E strike, 52 degrees-55 degrees SW dip), with clear normal faulting and a slight dextral strike-slip component. Most foci were located in the 4-11-km depth range, within the crystalline basement. Taking into account the source sizes for the two “mainshocks”, the hydraulic diffusivity of 0: 05 m(2) s(-1) found for the 2003-2004 swarm is shown to fit reasonably well the 2012 data, but not the 2014 reactivation sequence. Throughout the article, we discuss the difficult issue of the identification of “foreshocks” and “aftershocks” within such a sequence, even though a swarm, per se, makes this terminology inadequate. As previously suggested by other authors, between a foreshock-mainshock-aftershock sequence and an earthquake swarm also exists a whole gamut of seismic activity which makes this dichotomy much more complex than anticipated.
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Trevlopoulos, K., & Gueguen, P. (2016). Period elongation-based framework for operative assessment of the variation of seismic vulnerability of reinforced concrete buildings during aftershock sequences. Soil Dynamics And Earthquake Engineering, 84, 224–237.
Résumé: Safety assessment of structures and/or critical infrastructures is a key factor in post-seismic decision making. In this context we present a performance-based framework for modeling time-variant vulnerability of reinforced concrete buildings during aftershock sequences. Structural damage is associated with first eigenperiod elongation, a performance metric whose measurement can complement visual inspection and assessment of structural health as a post-seismic operative tool. The proposed framework is applied for a series of reinforced concrete building models and two aftershock sequences. Damage states are defined using thresholds of period elongation. Numerical models of the buildings in each damage state are considered and their fragility curves are computed. The time-variant vulnerability is modeled with Markov chain as a function of the characteristics of the aftershocks sequence. Finally, the probabilities of the damage states are computed as a function of time during two real aftershock sequences. (C) 2016 Elsevier Ltd. All rights reserved.
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Vacherat, A., Mouthereau, F., Pik, R., Bellahsen, N., Gautheron, C., Bernet, M., et al. (2016). Rift-to-collision transition recorded by tectonothermal evolution of the northern Pyrenees. Tectonics, 35(4), 907–933.
Résumé: The impact of rift-related processes on tectonic and thermal evolution of collisional orogens is poorly documented. Here, we study the northern Pyrenees, a region that has preserved a geological record of the transition from rifting to collision. Using modeling of new low-temperature thermochronological data, including fission track and (U-Th)/He on apatite and zircon, we propose a temporal reconstruction of the inversion of the European rifted margin. Our data confirm that rifting and related cooling started in the Late Paleozoic-Triassic. Throughout the Jurassic and Early Cretaceous the European margin recorded slow heating during postrift subdsidence. Modeling of thermochronological data allows distinguishing subsidence and denudation controlled by south dipping normal faults in granitic massifs that reflect a second episode of crustal thinning at 130-110Ma. Following onset of convergence at 83Ma, shortening accumulated into the weak and hot Albian-Cenomanian rift basins floored by both hyperextended continental crust and exhumed subcontinental mantle. The lack of cooling during this initial stage of convergence is explained by the persistence of a high geothermal gradient. The onset of exhumation-related cooling is recognized in the whole Pyrenean region at 50-35Ma. This timing reveals that the main phase of mountain building started when hyperextended rift basins closed and collision between proximal domains of the rifted margin occurred.
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Valla, P. G., Rahn, M., Shuster, D. L., & van der Beek, P. A. (2016). Multi-phase late-Neogene exhumation history of the Aar massif, Swiss central Alps. Terra Nova, 28(6), 383–393.
Résumé: The late-Neogene evolution of the European Alps was influenced by both tectonic and climatically driven erosion processes, which are difficult to disentangle. We use low-temperature thermochronometry data from surface and borehole samples in the Aar massif-Rhone valley (Swiss central Alps) to constrain the exhumation history of the region. Multiple exhumation events are distinguished and linked to regional-scale tectonic deformation (before 5Ma), short-lived climatically driven orogen contraction (between 4 and 3Ma), and glacial valley carving since c.1Ma. Compared with previous studies, we clearly show the existence of two separate exhumation phases in the Late Miocene-Pliocene and better constrain the onset of glacial valley carving. The hydrothermal activity and geothermal anomalies currently observed in the borehole have been local and short-lived, with only a minor influence on thermochronometric observations. We thus suggest that late-stage glacial valley carving may have triggered topography-driven fluid flow and transient hydrothermal circulation.
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Van Daele, M., Bertrand, S., Meyer, I., Moernaut, J., Vandoorne, W., Siani, G., et al. (2016). Late Quaternary evolution of Lago Castor (Chile, 45.6 degrees S): Timing of the deglaciation in northern Patagonia and evolution of the southern westerlies during the last 17 kyr. Quaternary Science Reviews, 133, 130–146.
Résumé: Even though Patagonia is ideally located to study climate of the southern mid-latitudes, many questions on the late Quaternary climate evolution remain unresolved. The timing of maximum glacier extent is still uncertain in vast areas, and the postglacial evolution of the Southern Westerly Wind Belt (SWWB) remains highly debated. Here, we study the sedimentary infill of a glacigenic lake (Lago Castor; 45.6 degrees S, 71.8 degrees W) located at the leeside of the Andes in Chilean Patagonia to i) reconstruct the deglacial evolution of the eastern flank of the Patagonian Ice Sheet (PIS), and ii) discuss postglacial changes in wind strength at a critical location where westerly wind records are critically lacking. A dense grid of high-resolution reflection-seismic data was used to reconstruct the large-scale infill history of the lake, and a radiocarbon dated sediment core penetrating all lacustrine seismic units, was retrieved. Results indicate that the deglaciation of the lake basin and its catchment occurred no later than similar to 28 cal kyr BP (i.e. an early LGM), but possibly even already after MIS 4. Afterwards, the Lago Castor area was covered by a large proglacial lake that drained possibly – through an outburst flood – when the PIS outlet glaciers retreated to a critical location. Subsequently, very dry conditions caused the lake to desiccate, as evidenced by an unconformity visible on the seismic profiles and in the sediment core. This dry period likely resulted from the increased orographic effect of the PIS-covered Andes, accompanied by weaker westerlies. From similar to 20 kyr BP onwards, the combination of a shrinking PIS and a southward shift of the SWWB resulted in increased precipitation, which caused the lake level to rise. After similar to 17 cal kyr BP, lake sedimentation was more directly influenced by the southern westerlies, with the formation of sediment drifts resulting from strong bottom current during periods of intense westerly winds. Our results suggest a progressive increase in wind strength at 46 degrees S from 11.2 to 4.5 cal kyr BP, which supports the hypothesis that the SWWB broadened during the early and middle Holocene. (C) 2015 Elsevier Ltd. All rights reserved.
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van der Beek, P., Litty, C., Baudin, M., Mercier, J., Robert, X., & Hardwick, E. (2016). Contrasting tectonically driven exhumation and incision patterns, western versus central Nepal Himalaya. Geology, 44(4), 327–330.
Résumé: Although the Himalayan range is classically presented as cylindrical along strike, segmentation of the range in terms of structure, topography, precipitation, and erosion patterns is becoming widely recognized. The potential climatic or tectonic controls on these lateral variations remain controversial. Thermokinematic models predict that the geometry of the main Himalayan detachment controls the kinematics, exhumation, and topography of the orogen: where the detachment includes a major crustal ramp, the topography shows a steep gradient that focuses orographic precipitation and exhumation, whereas the topography is gentler and exhumation less focused above a flatter detachment. We test this prediction by comparing the patterns of river incision (specific stream power) and long-term exhumation (from apatite fission track thermochronology) in central Nepal, where a major crustal ramp has been imaged by geophysical methods, with new exploratory data from the remote Karnali River transect in western Nepal, where a ramp is predicted to be absent or minor. Our results show that both exhumation rates and river incision capacity are significantly higher and focused on the crustal ramp in central Nepal, whereas they are lower and the pattern is more diffuse in western Nepal. These differences support a model in which lateral variations in topography and exhumation are controlled by variations in the geometry of the detachment, and imply that along-strike climatic variations in the Himalaya respond to tectonics rather than driving it.
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Van Driessche, A. E. S., Canals, A., Ossorio, M., Reyes, R. C., & Garcia-Ruiz, J. M. (2016). Unraveling the Sulfate Sources of (Giant) Gypsum Crystals Using Gypsum Isotope Fractionation Factors. Journal Of Geology, 124(2), 235–245.
Résumé: We combine newly determined isotope fractionation factors of gypsum precipitated in the laboratory with the isotopic compositions of natural anhydrite and gypsum to unravel the sulfate sources of the giant selenite crystals in the Naica mine (Chihuahua, Mexico). Gypsum was precipitated in the laboratory from CaSO4-NaCl-H2O solutions across a broad temperature range to establish the isotopic fractionation behavior of the sulfate molecule between the solid and dissolved phase. Oxygen isotopes show a significant fractionation dependence on temperature, with the solid phase more depleted in light isotopes with decreasing temperature. Sulfur isotopes display only a weak but similar dependence on temperature. At high salinity (4.5 M NaCl) no temperature dependence was found for the isotope composition. Based on this fractionation behavior, we attempt to elucidate the origin of the sulfate source(s) responsible for the formation of the (giant) gypsum crystals in the Naica mine. Detailed analysis of the isotopic composition of anhydrite, gypsum, and water samples strongly suggests that different types of anhydrite (of hypogenic and sedimentary origin) were dissolved to form these unique gypsum formations. The homogeneous isotopic composition of most gypsum crystals analyzed reveals an effective hydrodynamic mixing and a slow kinetics of precipitation fed by solutions of calcium sulfate from different anhydrite sources.
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Verlaguet, A., Brunet, F., Goffe, B., Menut, D., Findling, N., Poinssot, C., et al. (2016). Selective transfer of Li-Al-rich phyllosilicate to metamorphic veins (Western Alps): Laser Induced Breakdown Spectroscopy (LIBS) compositional profiles and microstructural characterization. Journal Of Geodynamics, 101, 51–72.
Résumé: In convergent settings, fluid-rock interactions generally result in quartz and calcite preferential transfer to metamorphic veins in classical metamarls, while phyllosilicates tend to remain in the host-rock. However, the mechanisms responsible for such a selective mass transfer are poorly discussed in the literature. Here, we study Alpine metabauxites in which phyllosilicates (Li-Al-rich chlorite called cookeite, followed by pyrophyllite) were preferentially transferred to veins at blueschist peak P-T conditions, by a dissolution-diffusion-precipitation process without any fluid infiltration or associated reaction. Cookeite fibrous en-echelon veins formed by extensional shear, and part of them evolved towards thicker fluid filled veins with euhedral cookeite crystallization. We performed chemical profiles across host-rocks between successive cookeite veins, using Laser Induced Breakdown Spectroscopy (LIBS), associated to a microstructural study. Flat LIBS Li profiles show that about half of the initial cookeite remains homogeneously distributed in host-rocks, which suggests a minimum diffusion distance of 2-4 cm for Li. The availability of an aqueous fluid during most of the metamorphic cycle is demonstrated here. A simple 10 reaction-diffusion model, assuming Li diffusion through a connected fluid-filled porosity network, is able to account for the observed lithium distribution assuming Li diffusion coefficients consistent with literature values in fluid-bearing systems. Chemical potential gradients that drove phyllosilicate transfer to veins can be either interfacial energy driven (i.e., Ostwald ripening), the anhedral phyllosilicate microsheets maintaining high supersaturation levels in the small host-rock pores compared to veins, or stress-induced: phyllosilicates present the highest solubility variations with pressure in the Vanoise bauxites (contrary to quartz-bearing rocks), which may account for their unusual selective transfer to veins. Therefore, mineral solubility variation with pressure seems to be the chief controlling parameter for pressure-solution creep. Cookeite (over pyrophyllite) transfer to veins was favoured by faster Li diffusion (compared to Si and Al). The shift from cookeite to pyrophyllite transfer, before host-rock cookeitedepletion, could reflect the onset of the retrograde P-T path, with pyrophyllite crystallization in response to P-T decrease. Lithium, which is a strategic element, was observed to preferentially migrate and segregate into veins during metamorphic processes, which may be of importance for exploration purposes. (C) 2016 Elsevier Ltd. All rights reserved.
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Vidal, O., Lanari, P., Munoz, M., Bourdelle, F., & De Andrade, V. (2016). Deciphering temperature, pressure and oxygen-activity conditions of chlorite formation. Clay Minerals, 51(4), 615–633.
Résumé: The advantages and limits of empirical, semi-empirical and thermodynamic methods devoted to the estimation of chlorite-formation temperature are discussed briefly. The results of semi-empirical and thermodynamic approaches with different assumptions regarding the redox state of iron in chlorite are compared for a large set of natural data covering a range of pressure conditions from a few hundred bars to 18 kbar and temperature from 100 to 500 degrees C. The T-XFe3+ evolution estimated using the thermodynamic approach of Vidal et al. (2005) shows a systematic increase in XFe3+ with decreasing temperature, which is compatible with the decrease in aO(2) buffered by magnetite-or hematite-chlorite equilibrium. This trend as well as the observed increase in vacancies in chlorite with decreasing temperature is interpreted as the incorporation of Fe3+-sudoite. The standard-state properties of this end-member have been derived to reproduce the observed T-aO(2)-XFe3+ evolutions. It can be used to estimate T-aO(2)-XFe3 values with a Chl-Qtz-H2O multi-equilibrium approach. When combining our results with those of other studies published recently, it appears that thermodynamic approaches and mapping techniques developed for metamorphic rocks can be used to discuss the conditions of formation of very low-grade rocks where kinetics is much more sluggish than in metamorphic rocks. This requires use of appropriate analytical tools and techniques with a spatial resolution of a few hundred nanometres.
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Virieux, J., Brossier, R., Metivier, L., Operto, S., & Ribodetti, A. (2016). Direct and indirect inversions. Journal Of Seismology, 20(4), 1107–1121.
Résumé: A bridge is highlighted between the direct inversion and the indirect inversion. They are based on fundamental different approaches: one is looking after a projection from the data space to the model space while the other one is reducing a misfit between observed data and synthetic data obtained from a given model. However, it is possible to obtain similar structures for model perturbation, and we shall focus on P-wave velocity reconstruction. This bridge is built up through the Born approximation linearizing the forward problem with respect to model perturbation and through asymptotic approximations of the Green functions of the wave propagation equation. We first describe the direct inversion and its ingredients and then we focus on a specific misfit function design leading to a indirect inversion. Finally, we shall compare this indirect inversion with more standard least-squares inversion as the FWI, enabling the focus on small weak velocity perturbations on one side and the speed-up of the velocity perturbation reconstruction on the other side. This bridge has been proposed by the group led by Raul Madariaga in the early nineties, emphasizing his leading role in efficient imaging workflows for seismic velocity reconstruction, a drastic requirement at that time.
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Voisin, C., Garambois, S., Massey, C., & Brossier, R. (2016). Seismic noise monitoring of the water table in a deep-seated, slow-moving landslide. Interpretation-A Journal Of Subsurface Characterization, 4(3), SJ67–SJ76.
Résumé: Daily correlations of ambient seismic noise on a large landslide at Utiku, New Zealand, reveal seismic velocity changes up to +/- 1.5% that follow a summer/winter cycle consistent with the pore-water pressures monitored at the basal slip surface in the landslide. The annual pattern of velocity changes is borne by a limited frequency band (6-8 Hz typically) that suggests a localized change in the medium. The Rayleigh waves that form the seismic signal within this frequency band have a maximum sensitivity at a depth of 2-3 m below the ground surface, consistent with the water table level. Fluid saturation changes in the landslide modeled using the Biot-Gassmann theory explain the limited frequency band and the amplitude of the seismic velocity change. This set of arguments suggests that seismic noise correlations are sensitive to water table oscillations through saturation changes and could be used as a nondestructive hydrologic monitoring tool.
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Weiss, J., V. Pellissier, D. Marsan, L. Arnaud and F. Renard. (2016). Cohesion versus friction in controlling the long-term strength of a self-healing experimental fault. J. Geophys. Res., 121(12), 8523–8547.
Résumé: The Coulomb's failure criterion, which postulates that failure occurs along a fault plane when the applied shear stress overcomes a resistance made of two parts of different nature, cohesion, and friction, remains the standard conceptual framework of faulting mechanics. More recently, rate-and-state friction laws became the main modeling tool of the seismic cycle. These laws implicitly assume that only frictional resistance sets the fault strength and its evolution. We therefore raise the question of the role of cohesion and related healing/sealing mechanisms on fault mechanics. We designed an original laboratory experiment based on a model material, an ice thin layer sitting on top of a water tank and mechanically deformed at various rates with a circular Couette-like geometry. This allowed sliding along the fault plane over arbitrarily large slip distances, and analyzing the competition between faulting and cohesion-healing rates, whereas frictional resistance, resulting from the fault roughness, is limited in magnitude. We show that cohesion-healing plays an essential role in the time evolution of the interface strength under constant loading rate. In particular, the magnitudes of shear stress fluctuations are observed to be temperature and velocity weakening. The present experiment shares several properties similar to that of active faults during seismic cycles, suggesting that cohesive healing could control some of these features: scale invariance properties, Gutenberg-Richter law of rupture event size distribution, Omori's law of energy dissipation, at least after major ruptures, time asymmetry in energy dissipation, and periods of creep under high shear stress alternating with major earthquake-like ruptures.
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Wilhelm, B., Nomade, J., Crouzet, C., Litty, C., Sabatier, P., Belle, S., et al. (2016). Quantified sensitivity of small lake sediments to record historic earthquakes: Implications for paleoseismology. Journal Of Geophysical Research-Earth Surface, 121(1), 2–16.
Résumé: Seismic hazard assessment is a critical but challenging issue for modern societies. A key parameter to be estimated is the recurrence interval of damaging earthquakes. This requires the establishment of earthquake records long enough to be relevant, i.e., far longer than historical observations. We study how lake sediments can be used for this purpose and explore conditions that enable lake sediments to record earthquakes. This was achieved (i) through the compilation of eight lake-sediment sequences from the European Alps to reconstruct chronicles of mass movement deposits and (ii) through the comparison of these chronicles with the well-documented earthquake history. This allowed 24 occurrences of mass movements to be identified, of which 21 were most probably triggered by an earthquake. However, the number of earthquake-induced deposits varies between lakes of a same region, suggesting variable thresholds of the lake sequences to record earthquake shaking. These thresholds have been quantified by linking the mass movement occurrences in a single lake to both intensity and distance of the triggering earthquakes. This method offers a quantitative approach to estimate locations and intensities of past earthquake epicenters. Finally, we explored which lake characteristics could explain the various sensitivities. Our results suggest that sedimentation rate should be larger than 0.5mmyr(-1) so that a given lake records earthquakes in moderately active seismotectonic regions. We also postulate that an increasing sedimentation rate may imply an increasing sensitivity to earthquake shaking. Hence, further paleoseismological studies should control carefully that no significant change in sedimentation rates occurs within a record, which could falsify the assessment of earthquake recurrence intervals.
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Wilhelm, B., Vogel, H., Crouzet, C., Etienne, D., & Anselmetti, F. S. (2016). Frequency and intensity of palaeofloods at the interface of Atlantic and Mediterranean climate domains. Climate Of The Past, 12(2), 299–316.
Résumé: The long-term response of the flood activity to both Atlantic and Mediterranean climatic influences was explored by studying a lake sequence (Lake Foreant) of the Western European Alps. High-resolution sedimentological and geochemical analysis revealed 171 event layers, 168 of which result from past flood events over the last millennium. The layer thickness was used as a proxy of intensity of past floods. Because the Foreant palaeoflood record is in agreement with the documented variability of historical floods resulting from local and mesoscale, summer-to-autumn convective events, it is assumed to highlight changes in flood frequency and intensity related to such events typical of both Atlantic (local events) and Mediterranean (mesoscale events) climatic influences. Comparing the Foreant record with other Atlantic-influenced and Mediterranean-influenced regional flood records highlights a common feature in all flood patterns that is a higher flood frequency during the cold period of the Little Ice Age (LIA, AD 1300-1900). In contrast, high-intensity flood events are apparent during both the cold LIA and the warm Medieval Climate Anomaly (MCA, AD 9501250). However, there is a tendency towards higher frequencies of high-intensity flood events during the warm MCA. The MCA extremes could mean that under the global warming scenario, we might see an increase in intensity (not in frequency). However, the flood frequency and intensity in the course of the 20th century warming trend did not change significantly. Uncertainties in future evolution of flood intensity lie in the interpretation of the lack of 20th century extremes (transition or stable?) and the different climate forcing factors between the two periods (greenhouse gases vs. solar and/or volcanic eruptions).
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Xie, F., Moreau, L., Zhang, Y. X., & Larose, E. (2016). A Bayesian approach for high resolution imaging of small changes in multiple scattering media. Ultrasonics, 64, 106–114.
Résumé: This paper introduces a Bayesian approach to achieve high-resolution imaging of sub-wavelength changes in the presence of multiple scattering. The approach is based on the minimization of a cost function defined by the decorrelations induced in the measured waveforms by the apparition of a local changes. Minimization is achieved via a Monte Carlo Markov Chain (MCMC) algorithm combined to an analytical model that computes the sensitivity kernel of the medium. In the inversion procedure, the parameters to infer represent the physics of the problem, such as the diffusivity in the medium and/or the geometrical features of the reflector (position and scattering cross-section). The method is successfully compared to the linear inversion approach initially proposed for the so-called Locadiff imaging method through several examples, both numerical and experimental. (C) 2015 Elsevier B.V. All rights reserved.
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Yang, P. L., Brossier, R., Metivier, L., & Virieux, J. (2016). A review on the systematic formulation of 3-D multiparameter full waveform inversion in viscoelastic medium. Geophysical Journal International, 207(1), 129–149.
Résumé: In this paper, we study 3-D multiparameter full waveform inversion (FWI) in viscoelastic media based on the generalized Maxwell/Zener body including arbitrary number of attenuation mechanisms. We present a frequency-domain energy analysis to establish the stability condition of a full anisotropic viscoelastic system, according to zero-valued boundary condition and the elastic-viscoelastic correspondence principle: the real-valued stiffness matrix becomes a complex-valued one in Fourier domain when seismic attenuation is taken into account. We develop a least-squares optimization approach to linearly relate the quality factor with the anelastic coefficients by estimating a set of constants which are independent of the spatial coordinates, which supplies an explicit incorporation of the parameter Q in the general viscoelastic wave equation. By introducing the Lagrangian multipliers into the matrix expression of the wave equation with implicit time integration, we build a systematic formulation of multiparameter FWI for full anisotropic viscoelastic wave equation, while the equivalent form of the state and adjoint equation with explicit time integration is available to be resolved efficiently. In particular, this formulation lays the foundation for the inversion of the parameter Q in the time domain with full anisotropic viscoelastic properties. In the 3-D isotropic viscoelastic settings, the anelastic coefficients and the quality factors using bulk and shear moduli parametrization can be related to the counterparts using P and S velocity. Gradients with respect to any other parameter of interest can be found by chain rule. Pioneering numerical validations as well as the real applications of this most generic framework will be carried out to disclose the potential of viscoelastic FWI when adequate high-performance computing resources and the field data are available.
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Yepes, H., Audin, L., Alvarado, A., Beauval, C., Aguilar, J., Font, Y., et al. (2016). A new view for the geodynamics of Ecuador: Implication in seismogenic source definition and seismic hazard assessment. Tectonics, 35(5), 1249–1279.
Résumé: A new view of Ecuador's complex geodynamics has been developed in the course of modeling seismic source zones for probabilistic seismic hazard analysis. This study focuses on two aspects of the plates' interaction at a continental scale: (a) age-related differences in rheology between Farallon and Nazca plates-marked by the Grijalva rifted margin and its inland projection-as they subduct underneath central Ecuador, and (b) the rapidly changing convergence obliquity resulting from the convex shape of the South American northwestern continental margin. Both conditions satisfactorily explain several characteristics of the observed seismicity and of the interseismic coupling. Intermediate-depth seismicity reveals a severe flexure in the Farallon slab as it dips and contorts at depth, originating the El Puyo seismic cluster. The two slabs position and geometry below continental Ecuador also correlate with surface expressions observable in the local and regional geology and tectonics. The interseismic coupling is weak and shallow south of the Grijalva rifted margin and increases northward, with a heterogeneous pattern locally associated to the Carnegie ridge subduction. High convergence obliquity is responsible for the North Andean Block northeastward movement along localized fault systems. The Cosanga and Pallatanga fault segments of the North Andean Block-South American boundary concentrate most of the seismic moment release in continental Ecuador. Other inner block faults located along the western border of the inter-Andean Depression also show a high rate of moderate-size earthquake production. Finally, a total of 19 seismic source zones were modeled in accordance with the proposed geodynamic and neotectonic scheme.
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Yoritomo, J. Y., Weaver, R. L., Roux, P., Rupin, M., & Williams, E. G. (2016). On band gap predictions for multiresonant metamaterials on plates (L). Journal Of The Acoustical Society Of America, 139(3), 1282–1284.
Résumé: Recently wide frequency band gaps were observed in an experimental realization of a multiresonant metamaterial for Lamb waves propagating in thin plates. The band gaps rose from hybridization between the flexural plate (A(0) Lamb waves) and longitudinal resonances in rods attached perpendicularly. Shortly thereafter a theory based on considering a one-dimensional periodic array of rods and the scattering matrix for a single rod successfully described the observations. This letter presents an alternative simpler theory, arguably accurate at high rod density, that treats the full two-dimensional array of rods and makes no assumption of periodicity. This theory also fits the measurements. (c) 2016 Acoustical Society of America.
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Zerathe, S., Lacroix, P., Jongmans, D., Marino, J., Taipe, E., Wathelet, M., et al. (2016). Morphology, structure and kinematics of a rainfall controlled slow-moving Andean landslide, Peru. Earth Surface Processes And Landforms, 41(11), 1477–1493.
Résumé: The large slow-moving landslide of Maca is located in the upper Colca valley (southern Peru), a region characterized by a well pronounced rainy period, and intense and recurrent sustained seismicity. The landslide, developed in deep lacustrine deposits, has recently accelerated, threatening the Maca village. This work aims at understanding the rupture mechanism and the causes of the recent landslide reactivation/acceleration. We present a multidisciplinary characterization of the Maca landslide that includes: (i) geological and morphological mapping in the field; (ii) remote sensing analysis using an historical aerial photograph of 1955 and the Pliades satellite images (2013); (iii) global positioning system (GPS) including time-series of surveys over 13 years, and continuous measurements over 14 months; (iv) a geophysical campaign with deep electrical resistivity tomography profiles acquired across the landslide mass. Our study shows that this 60 Mm(3) landslide, which can be classified as a clay/silt compound landslide, moved by 15m between 2001 and 2014 with a large inter-annual velocity variation (up to a factor of 500) depending on the rainfall intensity. We suggest that these dramatic changes in velocity are the result of the combination of a threshold mechanism and the short intense rainy season in Peru. This study reveals three main driving factors acting at different timescales: (i) over several decades, the river course has significantly changed, causing the Maca landslide reactivation in the 1980s due to the erosion of its toe; (ii) at the year scale, a minimum amount of rainfall is required to trigger the motion and this amount controls the landslide velocity; (iii) transient changes in slide velocity may occur anytime due to earthquakes. This study particularly highlights the non-linear behaviour of the motion with rainfall. Copyright (C) 2016 John Wiley & Sons, Ltd.
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Zhang, Y. X., Planes, T., Larose, E., Obermann, A., Rospars, C., & Moreau, G. (2016). Diffuse ultrasound monitoring of stress and damage development on a 15-ton concrete beam. Journal Of The Acoustical Society Of America, 139(4), 1691–1701.
Résumé: This paper describes the use of an ultrasonic imaging technique (Locadiff) for the Non-Destructive Testing & Evaluation of a concrete structure. By combining coda wave interferometry and a sensitivity kernel for diffuse waves, Locadiff can monitor the elastic and structural properties of a heterogeneous material with a high sensitivity, and can map changes of these properties over time when a perturbation occurs in the bulk of the material. The applicability of the technique to life-size concrete structures is demonstrated through the monitoring of a 15-ton reinforced concrete beam subject to a four-point bending test causing cracking. The experimental results show that Locadiff achieved to (1) detect and locate the cracking zones in the core of the concrete beam at an early stage by mapping the changes in the concrete's micro-structure; (2) monitor the internal stress level in both temporal and spatial domains by mapping the variation in velocity caused by the acoustoelastic effect. The mechanical behavior of the concrete structure is also studied using conventional techniques such as acoustic emission, vibrating wire extensometers, and digital image correlation. The performances of the Locadiff technique in the detection of early stage cracking are assessed and discussed. (C) 2016 Acoustical Society of America.
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Zhao, L., Paul, A., Malusà, M., Xu, X., Zheng, T., Solarino, S., Guillot, S., Schwartz, S., Dumont, T., Salimbeni, S., Aubert, C., Pondrelli, S., Wang, Q., Zhu, R. (2016). Continuity of the Alpine slab unraveled by high-resolution P-wave tomography. Journal of Geophysical Research, 121, 8720–8737.
Résumé: The question of lateral and/or vertical continuity of subducted slabs in active orogens is a hot topic partly due to poorly resolved tomographic data. The complex slab structure beneath the Alpine region is only partly resolved by available geophysical data, leaving many geological and geodynamical issues widely open. Based upon a finite-frequency kernel method, we present a new high-resolution tomography model using P wave data from 527 broadband seismic stations, both from permanent networks and temporary experiments. This model provides an improved image of the slab structure in the Alpine region and fundamental pinpoints for the analysis of Cenozoic magmatism, (U)HP metamorphism, and Alpine topography. Our results document the lateral continuity of the European slab from the Western Alps to the central Alps, and the downdip slab continuity beneath the central Alps, ruling out the hypothesis of slab break off to explain Cenozoic Alpine magmatism. A low-velocity anomaly is observed in the upper mantle beneath the core of the Western Alps, pointing to dynamic topography effects. A NE dipping Adriatic slab, consistent with Dinaric subduction, is possibly observed beneath the Eastern Alps, whereas the laterally continuous Adriatic slab of the Northern Apennines shows major gaps at the boundary with the Southern Apennines and becomes near vertical in the Alps-Apennines transition zone. Tear faults accommodating opposite-dipping subductions during Alpine convergence may represent reactivated lithospheric faults inherited from Tethyan extension. Our results suggest that the interpretations of previous tomography results that include successive slab break offs along the Alpine-Zagros-Himalaya orogenic belt might be proficiently reconsidered.
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Zhao, W. L., Amelung, F., Doin, M. P., Dixon, T. H., Wdowinski, S., & Lin, G. Q. (2016). InSAR observations of lake loading at Yangzhuoyong Lake, Tibet: Constraints on crustal elasticity. Earth And Planetary Science Letters, 449, 240–245.
Résumé: We use Envisat 2003-2010 InSAR imagery over Yangzhuoyong Lake in southeastern Tibet to study the elastic response of the Earth's crust to variations in lake level. The net lake level drop during our study period is similar to 3 m with seasonal variations of more than 1 m. The time-series close to the lake center shows a high correlation with the lake level history. Near the lake center the unit response with respect to lake level change is 2.5 minim in radar line-of-sight direction, or similar to 2.7 mm/yr in vertical direction, corresponding to a vertical response of similar to 4.3 mm/Gt load change. We show that the observations are most sensitive to the elastic properties of the crust in the 5-15 km depth range and explain them with a layered elastic half-space model with a Young's modulus of 50 +/- 9 GPa Young's modulus in the top 15 km of the crust and using moduli inferred from seismology at greater depth. The inferred Young's modulus is similar to 25% smaller than the seismic modulus, which we attribute to damaged rock and the presence of fluids. (C) 2016 Elsevier B.V. All rights reserved.
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Zhou, J. Y., Revil, A., & Jardani, A. (2016). Stochastic structure-constrained image-guided inversion of geophysical data. Geophysics, 81(2), E89–E101.
Résumé: Inverse modeling of geophysical data involves the recovery of a subsurface structural model and the distribution of petrophysical properties. Independent information regarding the subsurface structure is usually available, with some uncertainty, from the expertise of a geologist and possibly accounting for sedimentary and tectonic processes. We have used the available structural information to construct a model covariance matrix and to perform a structure-constrained inversion of the geophysical data to obtain a geophysical tomogramm. We have considered that the geologic models y were built from random variables and were described with a priori probability density function in the Bayesian framework. We have explored for the a posteriori probability density of the geologic models (i.e., the structure of the guiding image) with the Markov-chain Monte Carlo method, and we inverted at the same time, in a deterministic framework, the geophysical data. The sampling of the geologic models was performed in a stochastic framework, and each geologic model y was used to invert the geophysical model m using image-guided inversion. The adaptive metropolis algorithm was used to find the proposal distributions of y reproducing the geophysical data and the geophysical information. In other words, we have tried to find a compromise between the a priori geologic information and the geophysical data to get, as end products, an updated geologic model and a geophysical tomogram. To demonstrate our approach, we used here electrical resistivity tomography as a technique to identify a correct geologic model and its a posteriori probability density. The approach was tested using one synthetic example (with three horizontal layers displaced by a normal fault) and one field case corresponding to a sinkhole in a three-layer structure. In both cases, we were able to select the most plausible geologic models that agreed with a priori information and the geophysical data.
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Zhou, Y., Walker, R. T., Hollingsworth, J., Talebian, M., Song, X. G., & Parsons, B. (2016). Coseismic and postseismic displacements from the 1978 M-w 7.3 Tabas-e-Golshan earthquake in eastern Iran. Earth And Planetary Science Letters, 452, 185–196.
Résumé: We use optical image correlation of historical aerial photographs, and modern satellite images to investigate the 1978 M-w 7.3 Tabas-e-Golshan thrust earthquake in eastern Iran. Correlation of images between 1974 and 1991 reveals a near-surface shortening component of similar to 2.9 m across the margin of the Tabas fold, which is a combination of coseismic and postseismic deformation. Correlation of images between 1991 and 2013 shows a further similar to 0.3 m of postseismic shortening. Using six pre-earthquake aerial photographs acquired in 1956 and stereo SPOT-6 imagery from 2013, we also generate pre and post-earthquake digital elevation models (DEMs) for one of the main fold segments. Differencing of the two DEMs reveals a height change of similar to 4.7 m. Elastic dislocation modelling of the 1974-2013 displacement field requires 7 m slip on a 50 degrees dipping fault, extending from a depth of 0.1 km to 6 km at its base (the majority of slip, similar to 6.5 m, occurred prior to 1991). Our results, combined with previous InSAR observations, indicate time-decaying shallow postseismic afterslip. It is likely that most of the afterslip occurred prior to 1991. The slip appears to dissipate in the near surface, and is accommodated as a narrow band of flexural slip on bedding planes. Comparison of the fault slip model with terrace heights measured from the SPOT-6 DEM suggests that the Tabas fold system may exhibit characteristic slip behaviour. Such behaviour would require a magnitude M-w 7.3 earthquake every similar to 3500 years, based on the previously estimated shortening rate of similar to 1.0 mm/yr. This study highlights the usefulness of historical imagery in investigating past earthquakes, thus providing new information about historical faulting in continental regions. (C) 2016 Elsevier B.V. All rights reserved.
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