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Articles présents dans Web of Knowledge et...
**Articles présents dans Web of Knowledge et importés dans refbase
Dernière mise à jour : 12 février 2016, 254 articles
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Anderson R, Bridges JC, Williams A, Edgar L, Ollila A, Williams J, Nachon M, Mangold N, Fisk M, Schieber J, Gupta S, Dromart G, Wiens R, Le Mouelic S, Forni O, Lanza N, Mezzacappa A, Sautter V, Blaney D, Clark B, Clegg S, Gasnault O, Lasue J, Leveille R, Lewin E, Lewis KW, Maurice S, Newsom H, Schwenzer SP, Vaniman D (2015) ChemCam results from the Shaler outcrop in Gale crater, Mars. Icarus 249:2–21
Résumé: The ChemCam campaign at the fluvial sedimentary outcrop “Shaler” resulted in observations of 28 non-soil targets, 26 of which included active laser induced breakdown spectroscopy (LIBS), and all of which included Remote Micro-Imager (RMI) images. The Shaler outcrop can be divided into seven facies based on gain size, texture, color, resistance to erosion, and sedimentary structures. The ChemCam observations cover Facies 3 through 7. For all targets, the majority of the grains were below the limit of the RMI resolution, but many targets had a portion of resolvable grains coarser than similar to 0.5 mm. The Shaler facies show significant scatter in LIBS spectra and compositions from point to point, but several key compositional trends are apparent, most notably in the average K2O content of the observed facies. Facies 3 is lower in K2O than the other facies and is similar in composition to the “snake,” a clastic dike that occurs lower in the Yellowknife Bay stratigraphic section. Facies 7 is enriched in 1(20 relative to the other fades and shows some compositional and textural similarities to float rocks near Yellowknife Bay. The remaining facies (4, 5, and 6) are similar in composition to the Sheepbed and Gillespie Lake members, although the Shaler fades have slightly elevated K2O and FeOT. Several analysis points within Shaler suggest the presence of feldspars, though these points have excess FeOT which suggests the presence of Fe oxide cement or inclusions. The majority of LIBS analyses have compositions which indicate that they are mixtures of pyroxene and feldspar. The Shaler feldspathic compositions are more alkaline than typical feldspars from shergottites, suggesting an alkaline basaltic source region, particularly for the K2O enriched Facies 7. Apart from possible iron-oxide cement, there is little evidence for chemical alteration at Shaler, although calcium-sulfate veins comparable to those observed lower in the stratigraphic section are present. The differing compositions, and inferred provenances at Shaler, suggest compositionally heterogeneous terrain in the Gale crater rim and surroundings, and intermittent periods of deposition. Published by Elsevier Inc.
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Ansberque C, Godard V, Bellier O, De Sigoyer J, Jing Liu-Zeng, Xu X, Ren Z, Li Y (2015) Denudation pattern across the Longriba fault system and implications for the geomorphological evolution of the eastern Tibetan margin. Geomorphology 246:542–557
Résumé: Following the 2008 Wenchuan earthquake (Sichuan, China), the dextral strike-slip Longriba fault system (LFS) has been recognized as a main intracontinental structural boundary within the eastern Tibetan Plateau. While numerous studies have focused on the Longmen Shan frontal range to constrain the dynamics of the eastern Tibetan margin, little is known on the LFS, particularly on its eventual influence on the geomorphological evolution of the latter. Here, we provide a new data set of denudation rates derived from beryllium-10 concentrations in river sediments from 33 medium-sized catchments. Our sampling area covers the frontier between the dissected margin and the low relief interior plateau. Our results reveal a sharp increase of denudation across the LFS, from <0.1 mm/y in the Ruoergai basin to 0.3 mm/y toward the Longmen Shan range. Such denudation pattern indicates a major morphotectonic control of the fault system on the eastern Tibetan margin evolution. Additional topographic analysis confirms the role of the LFS as an important geomorphological boundary, restraining the westward propagation of river incision into the low-relief areas, thus partly preventing the dismantling of the eastern Tibetan Plateau. (C) 2015 Elsevier B.V. All rights reserved.
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Arzhannikova AV, Vassallo R, Arzhannikov SG, Jolivet M (2015) Morphotectonics and paleoseismology of the eastern end of the Bolnay fault (Mongolia). Russian Geology And Geophysics 56(10):1484–1490
Résumé: The Bolnay (Hangayn) fault is an active shear system which generated the M = 8.2-8.5 Bolnay earthquake of 23 July 1905, one of world's largest recorded intracontinental event. The fault follows the Mesozoic suture formed during the closure of the Mongolia-Okhotsk ocean. The Late Cenozoic faulting in the region was induced by propagation of strain from the India-Eurasia collision that had reached Mongolia at about 5 +/- 3 Ma. The left-lateral strike slip almost all over the fault length is compensated in its western end by Late Quaternary reverse motion. We estimated coseismic slip associated with the event of 1905 and the previous earthquakes in the eastern fault end and checked whether vertical offset compensates the strike slip in this part as well. The 1905 coseismic slip measured from a displaced dry stream bed and pebble bars in the Hasany-Gol river valley was 6.5-7.5 m. The 13 +/- 1 m left-lateral displacement of pebble bars in the same valley represents a cumulative slip of two events. Paleoseismological studies across the strike of surface ruptures reveal at least two generations of rupture in two events that postdated the deposition of sediments with a C-14 age of 4689 +/- 94 yr. Hypsometry of the alluvial surface in the zone of deformation shows gradual elevation increase toward the mountains, but without abrupt change across the fault. This means the absence of vertical offset and reactivation of the fault as a left-lateral strike slip. The horizontal slip in the eastern extension of the Bolnay fault is compensated rather by parallel fault-bounded pull-apart basins trending northeastward oblique to the principal fault strike. The age of their sedimentary fill suggests no older than middle Pleistocene normal faulting that compensated the Bolnay strike slip. (C) 2015, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.
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Asnaashari A, Brossier R, Garambois S, Audebert F, Thore P, Virieux J (2015) Time-lapse seismic imaging using regularized full-waveform inversion with a prior model: which strategy? Geophysical Prospecting 63(1):78–98
Résumé: Full-waveform inversion is an appealing technique for time-lapse imaging, especially when prior model information is included into the inversion workflow. Once the baseline reconstruction is achieved, several strategies can be used to assess the physical parameter changes, such as parallel difference (two separate inversions of baseline and monitor data sets), sequential difference (inversion of the monitor data set starting from the recovered baseline model) and double-difference (inversion of the difference data starting from the recovered baseline model) strategies. Using synthetic Marmousi data sets, we investigate which strategy should be adopted to obtain more robust and more accurate time-lapse velocity changes in noise-free and noisy environments. This synthetic application demonstrates that the double-difference strategy provides the more robust time-lapse result. In addition, we propose a target-oriented time-lapse imaging using regularized full-waveform inversion including a prior model and model weighting, if the prior information exists on the location of expected variations. This scheme applies strong prior model constraints outside of the expected areas of time-lapse changes and relatively less prior constraints in the time-lapse target zones. In application of this process to the Marmousi model data set, the local resolution analysis performed with spike tests shows that the target-oriented inversion prevents the occurrence of artefacts outside the target areas, which could contaminate and compromise the reconstruction of the effective time-lapse changes, especially when using the sequential difference strategy. In a strongly noisy case, the target-oriented prior model weighting ensures the same behaviour for both time-lapse strategies, the double-difference and the sequential difference strategies and leads to a more robust reconstruction of the weak time-lapse changes. The double-difference strategy can deliver more accurate time-lapse variation since it can focus to invert the difference data. However, the double-difference strategy requires a preprocessing step on data sets such as time-lapse binning to have a similar source/receiver location between two surveys, while the sequential difference needs less this requirement. If we have prior information about the area of changes, the target-oriented sequential difference strategy can be an alternative and can provide the same robust result as the double-difference strategy.
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Aucour A-M, Bedell J-P, Queyron M, Magnin V, Testemale D, Sarret G (2015) Dynamics of Zn in an urban wetland soil-plant system: Coupling isotopic and EXAFS approaches. Geochimica Et Cosmochimica Acta 160:55–69
Résumé: Plants play a key role in the stabilization of metals in contaminated environments. Studies have been performed on Zn uptake and storage mechanisms, mainly for Zn hyperaccumulating plants, though less is known about Zn stabilization in the rhizosphere of non-accumulating plants. This study was focused on the dynamics of Zn in a whole soil-litter-plant system and the processes controlling Zn mobilization and stabilization. The site studied was an infiltration basin receiving urban stormwater, in which Phalaris arundinacea (reed canary grass) developed spontaneously. A combination of chemical extractions (CaCl2, DTPA), EXAFS spectroscopy and Zn stable isotope measurements was applied for the water inlet, soil, plant organs and decaying biomass. Zn speciation changed from the water inlet to the soil. In the soil, Zn was present as Zn-layered double hydroxide (Zn-LDH), tetrahedral and octahedral sorbed Zn species. The formation of Zn-LDH participates in Zn stabilization. Tetrahedral Zn species, which were partly DTPA exchangeable, were enriched in heavy isotopes, whereas octahedral Zn (Zn-LDH and sorbed species) were enriched in light isotopes. Based on a linear model between delta Zn-66 and Zn speciation, delta Zn-66 for pure tetrahedral and octahedral end-members were estimated at ca. 0.33 parts per thousand and 0.04 parts per thousand, respectively. In the plant, a mixture of octahedral Zn (attributed to aqueous Zn-organic acid complexes present in the symplasm), and tetrahedral Zn (attributed to apoplasmic Zn-cell wall complexes) was observed in all organs. Large enrichment in light isotopes from the soil to the plant delta Zn-66 (of ca. -0.6 parts per thousand) was observed. The stem was enriched in light isotopes versus roots and, to a lesser extent, versus leaves. The results suggest that Zn was taken up via a low-affinity transport system and that Zn was sequestrated in the stem symplasm after transit through leaves. Finally, intense Zn exchanges were observed between the decaying biomass and the soil, with the sorption of heavy Zn from the soil to cell wall remains and release of light Zn to the soil. Overall, this study provides a complete overview of Zn cycling in an urban wetland soil-plant system, and describes several changes in Zn speciation with Zn isotopic fractionation processes in a complex system. (C) 2015 Elsevier Ltd. All rights reserved.
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Aurelio G, Curiale J, Bardelli F, Prado RJ, Hennet L, Cuello G, Campo J, Thiaudiere D (2015) Substitution site and effects on magnetism in Sr-for-Ca substituted CaBaCo4O7. Journal Of Applied Physics 118(13)
Résumé: Cationic substitutions in the novel magnetoelectric compound CaBaCo4O7 lead to profound changes in its magnetic and electric behaviors. In this work, we present a structural study of the isovalent substitution Sr-for-Ca in CaBaCo4O7. X-ray diffraction, as well as neutron powder diffraction experiments, are reported for a series of samples Ca1-xSrxBaCo4O7 with 0 <= x <= 0: 10. Special emphasis is given to the identification of the substitution site, as Sr has also been reported to substitute for Ba in this crystal structure. The solubility limit for Sr at the Ca site is shown to be at x similar or equal to 0.08. The variation of lattice constants with Sr-doping firmly supports the Sr-for-Ca substitution. Rietveld refinements of the Sr-substituted samples are presented, and used as starting point to analyse the local structure around Sr by means of X-ray absorption spectroscopy at the Sr K-edge. Both the near-edge absorption and the extended absorption fine-structure confirm the substitution of Sr for Ca, giving definite support to the proposed nominal formula. In addition, macroscopic magnetization measurements are presented which reveal the striking effects of Sr-substitution over the magnetic landscape of this puzzling compound. (C) 2015 AIP Publishing LLC.
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Auzende A-L, Escartin J, Walte NP, Guillot S, Hirth G, Frost DJ (2015) Deformation mechanisms of antigorite serpentinite at subduction zone conditions determined from experimentally and naturally deformed rocks. Earth And Planetary Science Letters 411:229–240
Résumé: We performed deformation-DIA experiments on antigorite serpentinite at pressures of 1-3.5 GPa and temperatures of between 400 and 650 degrees C, bracketing the stability of antigorite under subduction zone conditions. For each set of pressure-temperature (P-T) conditions, we conducted two runs at strain rates of 5 x 10(-5) and 1 x 10(-4) s(-1). We complemented our study with a sample deformed in a Griggs-type apparatus at 1 GPa and 400 degrees C (Chernak and Hirth, 2010), and with natural samples from Cuba and the Alps deformed under blueschist/eclogitic conditions. Optical and transmission electron microscopies were used for microstructural characterization and determination of deformation mechanisms. Our observations on experimentally deformed antigorite prior to breakdown show that deformation is dominated by cataclastic flow with observable but minor contribution of plastic deformation (microkinking and (001) gliding mainly expressed by stacking disorder mainly). In contrast, in naturally deformed samples, plastic deformation structures are dominant (stacking disorder, kinking, pressure solution), with minor but also perceptible contribution of brittle deformation. When dehydration occurs in experiments, plasticity increases and is coupled to local embrittlement that we attribute to antigorite dehydration. In dehydrating samples collected in the Alps, embrittlement is also observed suggesting that dehydration may contribute to intermediate-depth seismicity. Our results thus show that semibrittle deformation operates within and above the stability field of antigorite. However, the plastic deformation recorded by naturally deformed samples was likely acquired at low strain rates. We also document that the corrugated structure of antigorite controls the strain accommodation mechanisms under subduction conditions, with preferred inter- and intra-grain cracking along (001) and gliding along both a and b. We also show that antigorite rheology in subduction zones is partly controlled by the presence of fluids, which can percolate within the exhumation channel via deformation-induced interconnected porosity. (C) 2014 Elsevier B.V. All rights reserved.
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Bahniuk A, Mckenzie JA, Perri E, Bontognali TRR, Voegeli N, Rezende CE, Rangel TP, Vasconcelos C (2015) Characterization of environmental conditions during microbial Mg-carbonate precipitation and early diagenetic dolomite crust formation: Brejo do Espinho, Rio de Janeiro, Brazil. 243–259
Résumé: For many years, sedimentary dolomite rocks have been considered to be primarily a replacement product of the calcium carbonate components comprising the original limestone, a process known as secondary replacement dolomitization. Although numerous dolomite formations in the geological record are composed of fine-grained crystals of micritic dolomite, an alternative process, that is, direct precipitation, is often excluded because of the absence of visible or geochemical indicators supporting primary precipitation. In this research, we present a study of a modern coastal hypersaline lagoon, Brejo do Espinho, Rio de Janeiro State, Brazil, which is located in a special climatic regime where a well-defined seasonal cycle of wet and dry conditions occur. The direct precipitation of modern high-Mg calcite and Ca-dolomite mud from the lagoonal waters under low-temperature hypersaline conditions is associated with the activity of microbial organisms living in this restricted environment. The mud undergoes an early diagenetic transformation into a 100% dolomite crust on the margins of the lagoon. The biomineralization process, characterized by the variations of the physico-chemical conditions in this environment during the annual hydrological cycle, is integrated with isotopic analysis to define the early diagenetic processes responsible for the formation of both dolomitic mud and crust. The carbon isotope values indicate a contribution of respired organic carbon, which is greater for the crust (delta C-13 = -9.5 parts per thousand Vienna Pee Dee Belemnite (VPDB)) than mud (delta C-13 = -1.2 parts per thousand VPDB). The oxygen isotope values reflect a moderate degree of evaporation during mud formation (delta O-18 = 1.1 parts per thousand VPDB), whereas it is greatly enhanced during early diagenetic crust formation (delta O-18 = 4.2 parts per thousand VPDB). The clumped isotope formation temperature derived for the Brejo do Espinho mud is 34 degrees C, whereas it is 32 degrees C for the crust. These temperatures are consistent with the upper range of measured values during the dry season when the lagoon experiences the most hypersaline conditions.
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Baize S, Audin L, Winter T, Alvarado A, Pilatasig Moreno L, Taipe M, Reyes P, Kauffmann P, Yepes H (2015) Paleoseismology and tectonic geomorphology of the Pallatanga fault (Central Ecuador), a major structure of the South-American crust. Geomorphology 237:14–28
Résumé: The Pallatanga fault (PF) is a prominent NNE-SSW strike-slip fault crossing Central Ecuador. This structure is suspected to have hosted large earthquakes, including the 1797 Riobamba event which caused severe destructions to buildings and a heavy death toll (more than 12,000 people), as well as widespread secondary effects like landsliding, liquefaction and surface cracking. The scope of this study is to evaluate the seismic history of the fault through a paleoseismological approach. This work also aims at improving the seismotectonic map of this part of the Andes through a new mapping campaign and, finally, aims at improving the seismic hazard assessment. We show that the PF continues to the north of the previously mapped fault portion in the Western Cordillera (Rumipamba-Pallatanga portion) into the Inter-Andean Valley (Riobamba basin). Field evidences of faulting are numerous, ranging from a clear geomorphological signature to fault plane outcrops. Along the western side of the Riobamba basin, the strike-slip component seems predominant along several fault portions, with a typical landscape assemblage (dextral offsets of valleys, fluvial terrace risers and generation of linear pressure ridges). In the core of the inter-Andean valley, the main fault portion exhibits a vertical component along the c. 100 m-high cumulative scarp. The presence of such an active fault bounding the western suburbs of Riobamba drastically increases the seismic risk for this densely inhabited and vulnerable city. To the east (Peltetec Massif, Cordillera Real), the continuation of the Pallatanga fault is suspected, but not definitely proved yet. Based on the analysis of three trenches, we state that the Rumipamba-Pallatanga section of the PF experienced 4 (maybe 5) Holocene to Historical strong events (Mw > 7). The coseismic behavior of the fault is deduced from the occurrence of several colluvial wedges and layers associated with the fault activity and interbedded within the organic black soil sequence. According to a series of C-14 datings, we document that these events occurred during the last 6500 years. The clear deformation of the shallowest layer (14C: 1633 AD) is most likely associated with the 1797 Riobamba earthquake. After retrodeforming one of the 3 trenches, we estimate coseismic vertical throws (0.70 to 0.90 m). Because of bad outcrop conditions, we could not determine the horizontal component of slip and we used the slip vector determined in a previous work with a tectonic geomorphology study. Assuming this slip vector, we obtain total coseismic offsets between 3.5 and 4.5 m, indicative of earthquake magnitudes around c. Mw 7.5. The estimated recurrence time intervals range between 1300 and 3000 years, indicating an average slip rate of c. 2.5 mm/a for the Rumipamba-Pallatanga section of the fault. (C) 2014 Elsevier B.V. All rights reserved.
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Basile C (2015) Transform continental margins – part 1: Concepts and models. Tectonophysics 661:1–10
Résumé: This paper reviews the geodynamic concepts and models related to transform continental margins, and their implications on the structure of these margins. Simple kinematic models of transform faulting associated with continental rifting and oceanic accretion allow to define three successive stages of evolution, including intra-continental transform faulting, active transform margin, and passive transform margin. Each part of the transform margin experiences these three stages, but the evolution is diachronous along the margin. Both the duration of each stage and the cumulated strike-slip deformation increase from one extremity of the margin (inner corner) to the other (outer corner). Initiation of transform faulting is related to the obliquity between the trend of the lithospheric deformed zone and the relative displacement of the lithospheric plates involved in divergence. In this oblique setting, alternating transform and divergent plate boundaries correspond to spatial partitioning of the deformation. Both obliquity and the timing of partitioning influence the shape of transform margins. Oblique margin can be defined when oblique rifting is followed by oblique oceanic accretion. In this case, no transform margin should exist in the prolongation of the oceanic fracture zones. Vertical displacements along transform margins were mainly studied to explain the formation of marginal ridges. Numerous models were proposed, one of the most used is being based on thermal exchanges between the oceanic and the continental lithospheres across the transform fault But this model is compatible neither with numerical computation including flexural behavior of the lithosphere nor with timing of vertical displacements and the lack of heating related to the passing of the oceanic accretion axis as recorded by the Cote d'Ivoire-Ghana marginal ridge. Enhanced models are still needed. They should better take into account the erosion on the continental slope, and the level of coupling of the transform continental margin with the adjacent oceanic lithosphere. (C) 2015 Elsevier B.V. All rights reserved.
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Batanova VG, Sobolev AV, Kuzmin DV (2015) Trace element analysis of olivine: High precision analytical method for JEOL JXA-8230 electron probe microanalyser. Chemical Geology 419:149–157
Résumé: Olivine compositions provide critical information on the composition and origin of primary mantle-derived melts and their sources. The minor and trace elements (Ni, Mn, Ca, Al, Cr, Co, Ti, Zn, P, Na), which are present at concentrations over 10 ppm, are especially informative and can be determined by electron probe microanalysis (EPMA). Here we report a new analytical method to analyse these elements with unprecedented precision for an electron microprobe. The method was developed using the new JEOL JXA 8230 EPMA at ISTerre, UJF, Grenoble, France. The facility has a tungsten source gun and is equipped with five wavelength-dispersive spectrometers (WDS) and one silicon drift detector energy-dispersive spectrometer (SDD, EDS). It is placed in an environment with closely controlled temperature (+/-0.5 degrees C) and humidity (+/-4%). The analytical conditions are as follows: acceleration voltage 25 kV, 900 nA beamcurrent; WDS detection for trace elements (Ni, Mn, Ca, Al, Cr, Co, Ti, Zn, P, Na) and EDS detection for Si, Mg and Fe; total counting time 12 min; ZAF correction. The analysed volume is a half-sphere with a diameter of approximately 7 aem for most elements or a cylinder with a diameter of 7 μm and depth of approximately 2 μm for Al and Na. Instrumental drift during analytical sessions was monitored by repeated measurements of olivine standards. For trace elements, the method yields detection limits from 4 to 10 ppm and similar precision of individual analyses (2 standard errors). The detectable amount of an element is down to 2 * 10(-15) g and the precision for Fo in olivine is 200-300 ppm (2 standard errors). Comparison of data obtained using the EPMA with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for a large range of olivine compositions confirms the accuracy of the EPMA which is similar to the precision noted above. (C) 2015 Elsevier B.V. All rights reserved.
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Beck C, Campos C, Eris KK, Cagatay N, Mercier de Lepinay B, Jouanne F (2015) Estimation of successive coseismic vertical offsets using coeval sedimentary events – application to the southwestern limit of the Sea of Marmara's Central Basin (North Anatolian Fault). Nat. Hazards Earth Syst. Sci. 15(2):247–259
Résumé: In the deep part of the Sea of Marmara (Turkey), the sedimentation developing upon the North Anatolian Fault is strongly influenced by the associated seismic activity, through gravity reworking (fluidized landslides) and tsunamis. Specific layers (homogenites + turbidites, HmTu), representing individual sedimentary events, have been characterized along three giant piston cores retrieved from the Cinarcik and Central (or Orta) basins. Pre-Holocene, nonmarine sediments, were analyzed, representing the last 1217 kyr BP (before present). For a 2 kyr long interval, 11 events could be precisely correlated on both sides of the Central Basin's southwestern scarp. For each of them, based on the specific depositional process, the thickness difference between the two sites was considered as a direct estimation of the vertical component of a coeval coseismic offset. The homogenite (upper) component accounts for the major part of the thickness difference (ranging from 36 to 144 cm). These offsets were considered as likely representing dominantly vertical throws, along the transtensional southwestern boundary of the inner, pull-apart Central Basin. In terms of natural hazards, further investigations on this local behavior should rather be directed to tsunami genesis.
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Beck P, Pommerol A, Zanda B, Remusat L, Lorand JP, Goepel C, Hewins R, Pont S, Lewin E, Quirico E, Schmitt B, Montes-Hernandez G, Garenne A, Bonal L, Proux O, Hazemann JL, Chevrier VF (2015) A Noachian source region for the “Black Beauty” meteorite, and a source lithology for Mars surface hydrated dust? Earth And Planetary Science Letters 427:104–111
Résumé: The Martian surface is covered by a fine-layer of oxidized dust responsible for its red color in the visible spectral range (Bibring et al., 2006; Morris et al., 2006). In the near infrared, the strongest spectral feature is located between 2.6 and 3.6 μm and is ubiquitously observed on the planet (Jouglet et al., 2007; Milliken et al., 2007). Although this absorption has been studied for many decades, its exact attribution and its geological and climatic implications remain debated. We present new lines of evidence from laboratory experiments, orbital and landed missions data, and characterization of the unique Martian meteorite NWA 7533, all converging toward the prominent role of hydroxylated ferric minerals. Martian breccias (so-called “Black Beauty” meteorite NWA7034 and its paired stones NWA7533 and NWA 7455) are unique pieces of the Martian surface that display abundant evidence of aqueous alteration that occurred on their parent planet (Agee et al., 2013). These dark stones are also unique in the fact that they arose from a near surface level in the Noachian southern hemisphere (Humayun et al., 2013). We used IR spectroscopy, Fe-XANES and petrography to identify the mineral hosts of hydrogen in NWA 7533 and compare them with observations of the Martian surface and results of laboratory experiments. The spectrum of NWA 7533 does not show mafic mineral absorptions, making its definite identification difficult through NIR remote sensing mapping. However, its spectra are virtually consistent with a large fraction of the Martian highlands. Abundant NWA 7034/7533 (and paired samples) lithologies might abound on Mars and might play a role in the dust production mechanism. (C) 2015 Elsevier B.V. All rights reserved.
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Beckers A, Hubert-Ferrari A, Beck C, Bodeux S, Tripsanas E, Sakellariou D, De Batist M (2015) Active faulting at the western tip of the Gulf of Corinth, Greece, from high-resolution seismic data. Marine Geology 360:55–69
Résumé: The Gulf of Corinth is one of the fastest-spreading intra-continental rifts on Earth. GPS data indicate that the rift is currently opening in a NNE-SSW direction, with a rate of extension reaching up to 16mm yr(-1) in its westernmost part. Although the rest of the offshore rift has been well studied, the western tip of the rift is still poorly explored. We present an accurate map of submarine faults in this area based on two high-resolution seismic reflection surveys (single-channel sparker). In the eastern part of the studied area, the sedimentary infill is affected by the known North Eratini, South Eratini, and West Channel faults. Further to the west, the seafloor is mostly flat and is bounded to the north by the normal, south-dipping, Trizonia fault. To the north, the shallower part of the Gulf shows to the east a diffuse pattern of normal and strike-slip deformation, which is replaced to the west by a 7.5 km long SE striking strike-slip fault zone, called the Managouli fault zone. To the westernmost tip of the Gulf, in the Nafpaktos Basin, two fault sets with different strikes are encountered; the one with a NE-SW strike exhibits a clear strike-slip component. The western tip of the Gulf of Corinth is the only part of the Corinth Rift where convincing evidence for strike-slip movement has been found. This fault pattern is likely related to the complex deformation occurring at the diffuse junction at the western tip of the Rift between three crustal blocks: Continental Greece, Peloponnese, and the Ionian Island-Akarnania block. (C) 2015 Elsevier B.V. All rights reserved.
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Bellot N, Boyet M, Doucelance R, Pin C, Chauvel C, Auclair D (2015) Ce isotope systematics of island arc lavas from the Lesser Antilles. Geochimica Et Cosmochimica Acta 168:261–279
Résumé: The La-Ce systematics has one of the longest half-lifes (T-1/2 = 292.5 Ga) of radioactive decay systems used in isotope geochemistry. Variations of the Ce-138/Ce-142 ratio are expected to be small and the use of Ce as isotopic tracer requires a very precise measurement. Compared to Sm-Nd studies, the La-Ce decay system can provide additional information about the nature of sediments recycled in subduction zones, because unusually large Ce anomalies relative to the neighboring rare earth elements exist in marine sediments such as fish teeth or hydrothermal deposits. Here, we present a chemical purification technique for Ce, and mass spectrometric technique to perform accurate and reproducible analyses of Ce isotopes of natural samples. We report a large set of Ce isotope data including analysis of 2 Ce reference material solutions (AMES and JMC-304), 2 rock standards (BCR-2 and BHVO-2), 2 chondrites (the carbonaceous chondrite Allende and the enstatite chondrite Sahara 97072), 4 mid-ocean ridge basalts, 30 arc lavas from the Martinique Island and 5 oceanic sediments from DSDP-site 144 drilled on the Demerara rise. The long-term, external precision obtained on the AMES reference material is 80 ppm (2 s.d., Ce-138/Ce-142 = 0.0225732 +/- 18, n = 89). However, we note an evolution of isotopic ratios measured in static mode over the duration of this study (33 months). When the reproducibility is calculated from the AMES reference material measured during the same analytical session, it averages 40 ppm. All the Ce-138/Ce-142 ratios have been normalized to the AMES value of 0.0225746 (measured in session 7, 2 s.d. = 14 ppm, n = 8), a session during which the chondritic value has been defined and the peak tailing was negligible. The Ce-138/Ce-142 ratio measured for the JMC-Ce-304 reference reagent is 0.0225706 +/- 9 (2 s.d. = 38 ppm, n = 10). The analytical precision on natural samples is improved by a factor of about 4 in relation to previous studies on island arcs (Tanaka et al., 1987; Shimizu et al., 1992). The Ce-138/Ce-142 ratios of the two chondrites are identical within uncertainty and similar to previous determinations done on other meteorites; the average value is 0.0225654 +/- 7 (2 s.d. = 32 ppm). Martinique samples show a limited but significant range of variations for Ce-138/Ce-142 ratios (similar to 2 epsilon-units). The latter ratios correlate well with the Nd isotopes and define a binary mixing between a depleted mantle and subducted sediments that could be similar to those drilled at DSDP-site 144 (Leg 14). The Martinique lavas do not define a single curve in the epsilon Ce vs. epsilon Nd diagram, but a band. The apparent scattering can be explained by the involvement of sediments with different Ce isotope compositions and/or variations in the melting process itself such as the effect of melting on the light rare earth element ratios. The Ce isotopic signature of Martinique samples is dominated by the contribution of old terrigeneous sediments. However, according to our mixing models a low contribution of a few percent of marine sediment material in the source of the lavas is undetectable and therefore cannot be definitely excluded. Although the participation of marine sediments in this arc system is not demonstrated, our calculations show that the La-Ce system has a potential as geochemical tracer despite its very long half-life. (C) 2015 Elsevier Ltd. All rights reserved.
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Bendick R, Khan SF, Buergmann R, Jouanne F, Banerjee P, Khan MA, Bilham R (2015) Postseismic relaxation in Kashmir and lateral variations in crustal architecture and materials. Geophysical Research Letters 42(11):4375–4383
Résumé: Thirty horizontal displacement time series from GPS sites in the area around the 2005 Kashmir earthquake show lateral spatial variations in displacement magnitude and relaxation time for the postseismic interval from 2005 to 2012. The observed spatial pattern of surface displacements can only be reproduced by finite element models of postseismic deformation in elastic over viscoelastic crust that include lateral differences in both the thickness of the elastic layer and the viscosity of the viscoelastic layer. Solutions reproducing the sign of horizontal displacements everywhere in the epicentral region also require afterslip on the portion of the fault dislocation in the viscoelastic layer but not in the elastic lid. Although there are substantial tradeoffs among contributions to postseismic displacements of the surface, the observations preclude both crustal homogeneity and shallow afterslip. In the best family of solutions, the thickness of the elastic upper crust differs by a factor of 5 and the viscosity of the middle and lower crust by an order of magnitude between domains north and south of a suture zone containing the Main Boundary Thrust and Main Mantle Thrust.
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Benjelloun Y, de Sigoyer J, Carlut J, Hubert-Ferrari A, Dessales H, Pamir H, Karabacak V (2015) Characterization of building materials from the aqueduct of Antioch-on-the-Orontes (Turkey). Comptes Rendus Geoscience 347(4):170–180
Résumé: The Roman aqueduct of Antioch-on-the-Orontes (Turkey), a city located near the junction between the active Dead Sea fault and the East Anatolian fault, has been damaged several times due to historical earthquakes, as mentioned in ancient texts. The traces of repairs are studied in order to identify their potential seismic origin. The deformations of the structure were characterised thanks to a LIDAR scan. Several bricks were sampled on different parts of the city's aqueducts, on the original structure and on repaired parts. The bricks were characterized through a petrological approach. C-14 and archaeomagnetism were tested on the bricks in order to constrain the age of their production. The synthesis of all the data showed a local origin for the bricks, and led to the identification of several manufacturing techniques and several types of production, thus, confirming the potentiality of this approach to date and characterise post-seismic repairs. (C) 2015 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
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Bergantz GW, Schleicher JM, Burgisser A (2015) Open-system dynamics and mixing in magma mushes. Nature Geoscience 8(10):793–+
Résumé: Magma dominantly exists in a slowly cooling crystal-rich or mushy state(1-3). Yet, observations of complexly zoned crystals(4), some formed in just one to ten years(5-9), as well as time-transgressive crystal fabrics(10) imply that magmas mix and transition rapidly from a locked crystal mush to a mobile and eruptable fluid(5,6). Here we use a discrete-element numerical model that resolves crystal-scale granular interactions and fluid flow, to simulate the open-system dynamics of a magma mush. We find that when new magmais injected into a reservoir from below, the existing magma responds as a viscoplastic material: fault-like surfaces form around the edges of the new injection creating a central mixing bowl of magma that can be unlocked and become fluidized, allowing for complex mixing. We identify three distinct dynamic regimes that depend on the rate of magma injection. If the magma injection rate is slow, the intruded magma penetrates and spreads by porous media flow through the crystal mush. With increasing velocity, the intruded magma creates a stable cavity of fluidized magma that is isolated from the rest of the reservoir. At higher velocities still, the entire mixing bowl becomes fluidized. Circulation within the mixing bowl entrains crystals from the walls, bringing together crystals from different parts of the reservoir that may have experienced different physiochemical environments and leaving little melt unmixed. We conclude that both granular and fluid dynamics, when considered simultaneously, can explain observations of complex crystal fabrics and zoning observed in many magmatic systems.
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Bestani L, Espurt N, Lamarche J, Floquet M, Philip J, Bellier O, Hollender F (2015) Structural style and evolution of the Pyrenean-Provence thrust belt, SE France. Bulletin De La Societe Geologique De France 186(4-5):223–241
Résumé: The Pyrenean-Provence fold-thrust belt is characterized by a geological complexity arising from superimposed tectonic history and the propagation of the deformation through a heterogeneous mechanical substratum inherited from Paleozoic and Mesozoic times. The construction of a regional balanced cross section together with field data show that the thrust system of the southeastern Provence region is characterized by a mixed thick- and thin-skinned tectonic style related to the inversion of deep-seated late Paleozoic-Triassic extensional structures and the decollement of the Mesozoic-Cenozoic sedimentary cover above Triassic series. Earliest Cenomanian restoration state highlights the northward pinched-out of the Lower Cretaceous sedimentary series above the main long-wavelength Durance High uplift. Latest Santonian restoration state indicates a southward tilting of 2 of the basin attributed to the initial growth of the Pyrenean-Provence prism controlling the external flexure of the foreland. Thrusts propagation in the northern part of the Pyrenean-Provence fold-thrust belt was recorded to be synchronous during latest Cretaceous to Eocene time and produced a 7 southward basin tilting. This major tilting is attributed to the tectonic inversion and basement thrust stacking of the Cap Sicie-Sainte Baume units. Cross section balancing shows a total horizontal basement shortening of 40 km (similar to 35 %) across the Pyrenean-Provence foreland. The main part of this shortening (similar to 37 km) was accommodated by thick-skinned thrusts involving basement south of the Arc syncline. 5 km of shortening were accommodated northward by the Arc syncline and eastern Sainte-Victoire thin-skin structures, resulting from slip transferred from the deep thick-skinned intercutaneous thrust wedge. Finally we interpret salt tectonic structures of the southeastern Provence as passive diapirism growth during Jurassic to late Cretaceous time, and then reactivated during Pyrenean-Provence compression. Late normal faulting related to hypothetical reactive diapirism during the Oligocene extension episode was predominantly localized above inherited salt structures and probably controlled by inherited basement faults.
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Beyer HF, Gassner T, Trassinelli M, Hess R, Spillmann U, Banas D, Blumenhagen K-H, Bosch F, Brandau C, Chen W, Dimopoulou C, Foerster E, Grisenti RE, Gumberidze A, Hagmann S, Hillenbrand P-M, Indelicato P, Jagodzinski P, Kampfer T, Kozhuharov C, Lestinsky M, Liesen D, Litvinov YA, Loetzsch R, Manil B, Maertin R, Nolden F, Petridis N, Sanjari MS, Schulze KS, Schwemlein M, Simionovici A, Steck M, Stoehlker T, Szabo CI, Trotsenko S, Uschmann I, Weber G, Wehrhan O, Winckler N, Winters DFA, Winters N, Ziegler E (2015) Crystal optics for precision x-ray spectroscopy on highly charged ions-conception and proof. Journal Of Physics B-Atomic Molecular And Optical Physics 48(14)
Résumé: The experimental investigation of quantum-electrodydamic contributions to the binding energies of inner shells of highly charged heavy ions requires an accurate spectroscopy in the region of hard x-rays suitable at a limited source strength. For this purpose the focusing compensated asymmetric Laue crystal optics has been developed and a twin-spectrometer assembly has been built and commissioned at the experimental storage ring of the GSI Helmholtzzentrum Darmstadt. We characterize the crystal optics and demonstrate the usefulness of the instrumentation for accurate spectroscopy of both stationary and fast moving x-ray sources. The experimental procedures discussed here may also be applied for other spectroscopic studies where a transition from conventional germanium x-ray detectors to crystal spectrometers seems too demanding because of low source intensity.
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Binley A, Hubbard SS, Huisman JA, Revil A, Robinson DA, Singha K, Slater LD (2015) The emergence of hydrogeophysics for improved understanding of subsurface processes over multiple scales. Water Resources Research 51(6):3837–3866
Résumé: Geophysics provides a multidimensional suite of investigative methods that are transforming our ability to see into the very fabric of the subsurface environment, and monitor the dynamics of its fluids and the biogeochemical reactions that occur within it. Here we document how geophysical methods have emerged as valuable tools for investigating shallow subsurface processes over the past two decades and offer a vision for future developments relevant to hydrology and also ecosystem science. The field of hydrogeophysics arose in the late 1990s, prompted, in part, by the wealth of studies on stochastic subsurface hydrology that argued for better field-based investigative techniques. These new hydrogeophysical approaches benefited from the emergence of practical and robust data inversion techniques, in many cases with a view to quantify shallow subsurface heterogeneity and the associated dynamics of subsurface fluids. Furthermore, the need for quantitative characterization stimulated a wealth of new investigations into petrophysical relationships that link hydrologically relevant properties to measurable geophysical parameters. Development of time-lapse approaches provided a new suite of tools for hydrological investigation, enhanced further with the realization that some geophysical properties may be sensitive to biogeochemical transformations in the subsurface environment, thus opening up the new field of biogeophysics. Early hydrogeophysical studies often concentrated on relatively small plot-scale experiments. More recently, however, the translation to larger-scale characterization has been the focus of a number of studies. Geophysical technologies continue to develop, driven, in part, by the increasing need to understand and quantify key processes controlling sustainable water resources and ecosystem services.
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Blichert-Toft J, Arndt NT, Wilson A, Coetzee G (2015) Hf and Nd isotope systematics of early Archean komatiites from surface sampling and ICDP drilling in the Barberton Greenstone Belt, South Africa. American Mineralogist 100(11-12):2396–2411
Résumé: To constrain the origin of komatiites from the Barberton Green-stone Belt, South Africa, we measured Sm-147-Nd-143 and Lu-176-Hf-176 compositions for 18 komatiites from core obtained during the International Continental Drilling Program in the Komati Formation of the Barberton Belt, as well as 33 komatiites from surface outcrops of the Komati, Hooggenoeg, and Weltevreden Formations, these latter for purposes of comparison between core and surface samples. Magmatic clinopyroxene from surface samples near the drill site was also analyzed. For the Lu-Hf isotope system, the Komati Formation core and surface samples including the clinopyroxene define a linear array whose slope corresponds to an age of 3426 +/- 16 Ma (MSWD = 118; epsilon(Hf(T)) = +2.2), which is slightly younger than the accepted age of the rocks (3.48 Ga). The Sm-Nd isotope data for the same set of samples likewise fall along a linear array also yielding a younger age of 3339 12 Ma (MSWD = 42; epsilon(Nd(T)) = +2.8). The high MSWD for both isotope systems indicate substantial scatter at variance with normal magmatic processes, likely implying element mobility disturbing even these relatively robust isotopic systems shortly after eruption of the lavas. The average initial epsilon(Nd) and epsilon(Hf) of the core samples at 3.48 Ga are +0.45 and +1.4, respectively, in overall accordance with the positive errorchron intercepts and a depleted mantle source at 3.5 Ga. In contrast, the clinopyroxene and their host rocks have strongly positive epsilon(Hf(T)) of about +5 and negative epsilon(Nd(T)) of about -2. Given the overall scatter of the whole-rock data, the most robust constraint on the composition of the komatiite source comes from the clinopyroxene. Their positive slug) is in line with, though somewhat higher than other results from komatiites from the Komati Formation, but their negative epsilon(Nd(T)) is unexpected in that it indicates a source with long-term low Sm/Nd, which is at odds with its long-term high Lu/Hf. This signature is also found in the trace element compositions of some of the komatiites, such as moderately enriched LREE, negative Hf anomalies, and low Hf/Sm ratios. The origin of these features is uncertain but one possibility is that the discordance between the Hf and Nd isotope systems reflects the presence of deep-sea sediments in the source of some of the Barberton komatiites. The possible presence of a surface component in an ancient deep mantle source has wide-ranging implications for mantle-crust interaction and dynamics in the early Earth and for constraining a minimum age for the onset of plate tectonics.
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Bosson J-B, Deline P, Bodin X, Schoeneich P, Baron L, Gardent M, Lambiel C (2015) The influence of ground ice distribution on geomorphic dynamics since the Little Ice Age in proglacial areas of two cirque glacier systems. Earth Surface Processes And Landforms 40(5):666–680
Résumé: Holocene glaciers have contributed to an abundance of unstable sediments in mountainous environments. In permafrost environments, these sediments can contain ground ice and are subject to rapid geomorphic activity and evolution under condition of a warming climate. To understand the influence of ground ice distribution on this activity since the Little Ice Age (LIA), we have investigated the Pierre Ronde and Rognes proglacial areas, two cirque glacier systems located in the periglacial belt of the Mont Blanc massif. For the first time, electrical resistivity tomography, temperature data loggers and differential global positioning systems (dGPS) are combined with historical documents and glaciological data analysis to produce a complete study of evolution in time and space of these small landsystems since the LIA. This approach allows to explain spatial heterogeneity of current internal structure and dynamics. The studied sites are a complex assemblage of debris-covered glacier, ice-rich frozen debris and unfrozen debris. Ground ice distribution is related to former glacier thermal regime, isolating effect of debris cover, water supply to specific zones, and topography. In relation with this internal structure, present dynamics are dominated by rapid ice melt in the debris-covered upper slopes, slow creep processes in marginal glacigenic rock glaciers, and weak, superficial reworking in deglaciated moraines. Since the LIA, geomorphic activity is mainly spatially restricted within the proglacial areas. Sediment exportation has occurred in a limited part of the former Rognes Glacier and through water pocket outburst flood and debris flows in Pierre Ronde. Both sites contributed little sediment supply to the downslope geomorphic system, rather by episodic events than by constant supply. In that way, during Holocene and even in a paraglacial context as the recent deglaciation, proglacial areas of cirque glaciers act mostly as sediment sinks, when active geomorphic processes are unable to evacuate sediment downslope, especially because of the slope angle weakness. Copyright (c) 2014 John Wiley & Sons, Ltd.
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Bouchon M, Marsan D (2015) Reply to 'Artificial seismic acceleration'. Nature Geoscience 8(2):83
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Boue A, Lesage P, Cortes G, Valette B, Reyes-Davila G (2015) Real-time eruption forecasting using the material Failure Forecast Method with a Bayesian approach. Journal Of Geophysical Research-Solid Earth 120(4):2143–2161
Résumé: Many attempts for deterministic forecasting of eruptions and landslides have been performed using the material Failure Forecast Method (FFM). This method consists in adjusting an empirical power law on precursory patterns of seismicity or deformation. Until now, most of the studies have presented hindsight forecasts based on complete time series of precursors and do not evaluate the ability of the method for carrying out real-time forecasting with partial precursory sequences. In this study, we present a rigorous approach of the FFM designed for real-time applications on volcano-seismic precursors. We use a Bayesian approach based on the FFM theory and an automatic classification of seismic events. The probability distributions of the data deduced from the performance of this classification are used as input. As output, it provides the probability of the forecast time at each observation time before the eruption. The spread of the a posteriori probability density function of the prediction time and its stability with respect to the observation time are used as criteria to evaluate the reliability of the forecast. We test the method on precursory accelerations of long-period seismicity prior to vulcanian explosions at Volcan de Colima (Mexico). For explosions preceded by a single phase of seismic acceleration, we obtain accurate and reliable forecasts using approximately 80% of the whole precursory sequence. It is, however, more difficult to apply the method to multiple acceleration patterns.
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Bouvier J, Cebron D (2015) Protostellar spin-down: a planetary lift? Monthly Notices Of The Royal Astronomical Society 453(4):3720–3728
Résumé: When they first appear in the HR diagram, young stars rotate at a mere 10 per cent of their break-up velocity. They must have lost most of the angular momentum initially contained in the parental cloud, the so-called angular momentum problem. We investigate here a new mechanism by which large amounts of angular momentum might be shed from young stellar systems, thus yielding slowly rotating young stars. Assuming that planets promptly form in circumstellar discs and rapidly migrate close to the central star, we investigate how the tidal and magnetic interactions between the protostar, its close-in planet(s), and the inner circumstellar disc can efficiently remove angular momentum from the central object. We find that neither the tidal torque nor the variety of magnetic torques acting between the star and the embedded planet are able to counteract the spin-up torques due to accretion and contraction. Indeed, the former are orders of magnitude weaker than the latter beyond the corotation radius and are thus unable to prevent the young star from spinning up. We conclude that star-planet interaction in the early phases of stellar evolution does not appear as a viable alternative to magnetic star-disc coupling to understand the origin of the low angular momentum content of young stars.
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Braun J, Voisin C, Gourlan AT, Chauvel C (2015) Erosional response of an actively uplifting mountain belt to cyclic rainfall variations. Earth Surface Dynamics 3(1):1–14
Résumé: We present an approximate analytical solution to the stream power equation describing the erosion of bedrock in an actively uplifting mountain range subject to periodic variations in precipitation rate. It predicts a time lag between the climate forcing and the erosional response of the system that increases with the forcing period. The predicted variations in the sedimentary flux coming out of the mountain are also scaled with respect to the imposed rainfall variations in a direct proportion to the discharge exponent, m, in the stream power law expression. These findings are confirmed by 1-D and 2-D numerical solutions. We also show that the response of a river channel is independent of its length and thus the size of its catchment area, implying that all actively eroding streams in a mountain belt will constructively contribute to the integrated signal in the sedimentary record. We show that rainfall variability at Milankovitch periods should affect the erosional response of fast uplifting mountain belts such as the Himalayas, Taiwan or the South Island, New Zealand, and predict 1000 to 10 000-year offsets between forcing and response. We suggest that this theoretical prediction could be used to independently constrain the value of the poorly defined stream power law exponents, and provide an example of how this could be done, using geochemical proxy signals from an ODP borehole in the Bengal Fan.
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Bravo AG, Bouchet S, Guedron S, Amouroux D, Dominik J, Zopfi J (2015) High methylmercury production under ferruginous conditions in sediments impacted by sewage treatment plant discharges. Water Research 80:245–255
Résumé: Sewage treatment plants (STPs) are important point sources of mercury (Hg) to the environment. STPs are also significant sources of iron when hydrated ferric oxide (HFO) is used as a dephosphatation agent during water purification. In this study, we combined geochemical and microbiological characterization with Hg speciation and sediment amendments to evaluate the impact of STP's effluents on monomethylmercury (MMHg) production. The highest in-situ Hg methylation was found close to the discharge pipe in subsurface sediments enriched with Hg, organic matter, and iron. There, ferruginous conditions were prevailing with high concentrations of dissolved Fe2+ and virtually no free sulfide in the porewater. Sediment incubations demonstrated that the high MMHg production close to the discharge was controlled by low demethylation yields. Inhibition of dissimilatory sulfate reduction with molybdate led to increased iron reduction rates and Hg-methylation, suggesting that sulfate-reducing bacteria (SRB) may not have been the main Hg methylators under these conditions. However, Hg methylation in sediments amended with amorphous Fe(III)-oxides was only slightly higher than control conditions. Thus, in addition to iron-reducing bacteria, other non-SRB most likely contributed to Hg methylation. Overall, this study highlights that sediments impacted by STP discharges can become local hot-spots for Hg methylation due to the combined inputs of i) Hg, ii) organic matter, which fuels bacterial activities and iii) iron, which keeps porewater sulfide concentration low and hence Hg bioavailable. (C) 2015 Elsevier Ltd. All rights reserved.
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Brossier R, Operto S, Virieux J (2015) Velocity model building from seismic reflection data by full-waveform inversion. Geophysical Prospecting 63(2):354–367
Résumé: Full-waveform inversion is re-emerging as a powerful data-fitting procedure for quantitative seismic imaging of the subsurface from wide-azimuth seismic data. This method is suitable to build high-resolution velocity models provided that the targeted area is sampled by both diving waves and reflected waves. However, the conventional formulation of full-waveform inversion prevents the reconstruction of the small wavenumber components of the velocity model when the subsurface is sampled by reflected waves only. This typically occurs as the depth becomes significant with respect to the length of the receiver array. This study first aims to highlight the limits of the conventional form of full-waveform inversion when applied to seismic reflection data, through a simple canonical example of seismic imaging and to propose a new inversion workflow that overcomes these limitations. The governing idea is to decompose the subsurface model as a background part, which we seek to update and a singular part that corresponds to some prior knowledge of the reflectivity. Forcing this scale uncoupling in the full-waveform inversion formalism brings out the transmitted wavepaths that connect the sources and receivers to the reflectors in the sensitivity kernel of the full-waveform inversion, which is otherwise dominated by the migration impulse responses formed by the correlation of the downgoing direct wavefields coming from the shot and receiver positions. This transmission regime makes full-waveform inversion amenable to the update of the long-to-intermediate wavelengths of the background model from the wide scattering-angle information. However, we show that this prior knowledge of the reflectivity does not prevent the use of a suitable misfit measurement based on cross-correlation, to avoid cycle-skipping issues as well as a suitable inversion domain as the pseudo-depth domain that allows us to preserve the invariant property of the zero-offset time. This latter feature is useful to avoid updating the reflectivity information at each non-linear iteration of the full-waveform inversion, hence considerably reducing the computational cost of the entire workflow. Prior information of the reflectivity in the full-waveform inversion formalism, a robust misfit function that prevents cycle-skipping issues and a suitable inversion domain that preserves the seismic invariant are the three key ingredients that should ensure well-posedness and computational efficiency of full-waveform inversion algorithms for seismic reflection data.
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Burgisser A, Alletti M, Scaillet B (2015) Simulating the behavior of volatiles belonging to the C-O-H-S system in silicate melts under magmatic conditions with the software D-Compress. Computers & Geosciences 79:1–14
Résumé: Modeling magmatic degassing, or how the volatile distribution between gas and melt changes at pressure varies, is a complex task that involves a large number of thermodynamical relationships and that requires dedicated software. This article presents the software D-Compress, which computes the gas and melt volatile composition of five element sets in magmatic systems (O-H, S-O-H, C-S-O-H, C-S-O-H-Fe, and C-O-H). It has been calibrated so as to simulate the volatiles coexisting with three common types of silicate melts (basalt, phonolite, and rhyolite). Operational temperatures depend on melt composition and range from 790 to 1400 degrees C. A specificity of D-Compress is the calculation of volatile composition as pressure varies along a (de)compression path between atmospheric and 3000 bars. This software was prepared so as to maximize versatility by proposing different sets of input parameters. In particular, whenever new solubility laws on specific melt compositions are available, the model parameters can be easily tuned to run the code on that composition. Parameter gaps were minimized by including sets of chemical species for which calibration data were available over a wide range of pressure, temperature, and melt composition. A brief description of the model rationale is followed by the presentation of the software capabilities. Examples of use are then presented with outputs comparisons between D-Compress and other currently available thermodynamical models. The compiled software and the source code are available as electronic supplementary materials. (C) 2015 Published by Elsevier Ltd.
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C. Loury YR S. Guillot A. V. Mikolaichuk P. Lanari O. Bruguier and D. Bosch (2015) Crustal-scale structure of South Tien Shan: implications for subduction polarity and Cenozoic reactivation. Geological Society, London, Special Publications 427
Résumé: Based on new structural and petrological investigations, we present two crustal-scale cross-sections of the Kyrgyz South Tien Shan, and correlations of main faults and units between Kyrgyzstan and China. The overall structure corresponds to a doubly-vergent mountain belt. The Kyrgyz and Chinese areas exhibit identical structural and metamorphic histories. To the west, the Atbashi Range comprises high-pressure oceanic and continental units stacked by north-verging thrusts above a low metamorphic accretionary prism. High-pressure (HP) gneisses are bound to their south by a south-dipping detachment exhibiting mantle relicts. The high-pressure oceanic and continental units underwent similar pressure–temperature (P–T) paths with peak conditions of around 500 °C–20 kbar, followed by rapid exhumation. The overall south-dipping structure and kinematics indicate a south-dipping subduction of the Central Tien Shan Ocean at 320–310 Ma, ending with the docking of the Tarim block to the Kazakh continent. To the east, the Pobeda Massif shows a narrow push-up structure. A major north-vergent thrust exhumes deep-crustal-level granulites, constituting the highest summits, which were thrust towards the north onto low-grade Devonian–Carboniferous schists. The southern part of South Tien Shan is made up of a south-verging thrust stack that formed later during ongoing convergence, reactivated throughout post-30 Ma phases.
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Cao K, Wang G-C, Bernet M, van der Beek P, Zhang K-X (2015) Exhumation history of the West Kunlun Mountains, northwestern Tibet: Evidence for a long-lived, rejuvenated orogen. Earth And Planetary Science Letters 432:391–403
Résumé: How and when the northwestern Tibetan Plateau originated and developed upon pre-existing crustal and topographic features is not well understood. To address this question, we present an integrated analysis of detrital zircon U-Pb and fission-track double dating of Cenozoic synorogenic sediments from the Kekeya and Sanju sections in the southwestern Tarim Basin. These data help establishing a new chronostratigraphic framework for the Sanju section and confirm a recent revision of the chronostratigraphy at Kekeya. Detrital zircon fission-track ages present prominent Triassic-Early Jurassic (similar to 250-170 Ma) and Early Cretaceous (similar to 130-100 Ma) static age peaks, and Paleocene-Early Miocene (similar to 60-21 Ma) to Eocene-Late Miocene (similar to 39-7 Ma) moving age peaks, representing source exhumation. Triassic-Early Jurassic static peak ages document unroofing of the Kunlun terrane, probably related to the subduction of Paleotethys oceanic lithosphere. In combination with the occurrence of synorogenic sediments on both flanks of the Kunlun terrane, these data suggest that an ancient West Kunlun range had emerged above sea level by Triassic-Early Jurassic times. Early Cretaceous fission-track peak ages are interpreted to document exhumation related to thrusting along the Tam Karaul fault, kinematically correlated to the Main Pamir thrust further west. Widespread Middle-Late Mesozoic crustal shortening and thickening likely enhanced the Early Mesozoic topography. Paleocene-Early Eocene fission-track peak ages are presumably partially reset. Limited regional exhumation indicates that the Early Cenozoic topographic and crustal pattern of the West Kunlun may be largely preserved from the Middle-Late Mesozoic. The Main Pamir-Tam Karaul thrust belt could be a first-order tectonic feature bounding the northwestern margin of the Middle-Late Mesozoic to Early Cenozoic Tibetan Plateau. Toward the Tarim basin, Late Oligocene-Early Miocene steady exhumation at a rate of similar to 0.9 km/Myr is likely related to initial thrusting of the Tiklik fault and reactivation of the Tam Karaul thrust. Thrusting together with upper crustal shortening in the mountain front indicates basinward expansion of the West Kunlun orogen at this time. This episode of exhumation and uplift, associated with magmatism across western Tibet, is compatible with a double-sided lithospheric wedge model, primarily driven by breakoff of the Indian crustal slab. Accelerated exhumation of the mountain front at a rate of similar to 1.1 km/Myr since similar to 15 Ma supports active compressional deformation at the margins of the northwestern Tibetan Plateau. We thus propose that the West Kunlun Mountains are a long-lived topographic unit, dating back to Triassic-Early Jurassic times, and have experienced Middle-Late Mesozoic to Early Cenozoic rejuvenation and Late Oligocene-Miocene expansion. (C) 2015 Elsevier B.V. All rights reserved.
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Capitanio FA, Replumaz A, Riel N (2015) Reconciling subduction dynamics during Tethys closure with large-scale Asian tectonics: Insights from numerical modeling. Geochemistry Geophysics Geosystems 16(3):962–982
Résumé: We use three-dimensional numerical models to investigate the relation between subduction dynamics and large-scale tectonics of continent interiors. The models show how the balance between forces at the plate margins such as subduction, ridge push, and far-field forces, controls the coupled plate margins and interiors evolution. Removal of part of the slab by lithospheric break-off during subduction destabilizes the convergent margin, forcing migration of the subduction zone, whereas in the upper plate large-scale lateral extrusion, rotations, and back-arc stretching ensue. When external forces are modeled, such as ridge push and far-field forces, indentation increases, with large collisional margin advance and thickening in the upper plate. The balance between margin and external forces leads to similar convergent margin evolutions, whereas major differences occur in the upper plate interiors. Here, three strain regimes are found: large-scale extrusion, extrusion and thickening along the collisional margin, and thickening only, when negligible far-field forces, ridge push, and larger far-field forces, respectively, add to the subduction dynamics. The extrusion tectonics develops a strong asymmetry toward the oceanic margin driven by large-scale subduction, with no need of preexisting heterogeneities in the upper plate. Because the slab break-off perturbation is transient, the ensuing plate tectonics is time-dependent. The modeled deformation and its evolution are remarkably similar to the Cenozoic Asian tectonics, explaining large-scale lithospheric faulting and thickening, and coupling of indentation, extrusion and extension along the Asian convergent margin as a result of large-scale subduction process.
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Cardin P and O Peter (2015) Experiments on core dynamics. In: Schubert G.(ed.-in-chief) and Olson P. (ed). Elsevier, Oxford, pp 317–339
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Carrero S, Perez-Lopez R, Fernandez-Martinez A, Cruz-Hernandez P, Ayora C, Poulain A (2015) The potential role of aluminium hydroxysulphates in the removal of contaminants in acid mine drainage. Chemical Geology 417:414–423
Résumé: Sorption of trace elements onto poorly-crystalline Al-hydroxysulphate minerals from acid mine drainage (AMD) has received less attention compared to similar Fe(III)-phases because the former are less abundant in many mine drainage environments. In addition, Al-hydroxysulphates precipitate at a higher pH, so their sorption characteristics could be masked or less significant after sorption of trace elements to Fe minerals, which form at lower pH. In this study, oxidation and titration experiments were conducted with Fe(II)-rich AMD solutions under atmospheric and anoxic conditions to elucidate, individually, the sorption capacity of trace elements in solution by Fe and Al-hydroxysulphates. Under atmospheric conditions, precipitation of Fe(III) as schwertmannite, led to total removal of Fe, As, Cr and Pb in solution and 50% of Al. Subsequently, contaminant-depleted solution began to be controlled by precipitation of basaluminite, which acted as an effective sink for the remaining Al, Cu and Si. On the contrary, under anoxic conditions, neutralisation of Fe(II)-rich solutions led first to the basaluminite precipitation, keeping all Fe available in solution and unveiling a heretofore unknown affinity for As and Cr. Basaluminite retains 60% of As in solution compared to 100% removal of As by schwertmannite. However, the sorption capacity of basaluminite is even more significant than that of Fe-phases, considering that Al concentrations in solution were much lower than those of Fe. These findings give new insights into the processes controlling contaminant mobility in anoxic environments (e.g., the bottom of AMD-affected water reservoirs) and pose new opportunities for treatment strategies. (C) 2015 Elsevier B.V. All rights reserved.
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Carretier S, Regard V, Vassallo R, Aguilar G, Martinod J, Riquelme R, Christophoul F, Charrier R, Gayer E, Farias M, Audin L, Lagane C (2015) Differences in Be-10 concentrations between river sand, gravel and pebbles along the western side of the central Andes. Quaternary Geochronology 27:33–51
Résumé: Cosmogenic nuclides in river sediment have been used to quantify catchment-mean erosion rates. Nevertheless, variable differences in Be-10 concentrations according to grain size have been reported. We analyzed these differences in eleven catchments on the western side of the Andes, covering contrasting climates and slopes. The data include eight sand (0.5-1 mm) and gravel (1-3 cm) pairs and twelve sand (0.5-1 mm) and pebble (5-10 cm) pairs. The difference observed in three pairs can be explained by a difference in the provenance of the sand and coarser sediment. The other sand pebble pairs show a lower Be-10 concentration in the pebbles, except for one pair that shows similar concentrations. Two sand-gravel pairs show a lower Be-10 concentration in the gravel and the other five pairs show a higher Be-10 concentration in the gravel. Differences in climate do not reveal a particular influence on the Be-10 concentration between pairs. The analysis supports a model where pebbles and gravel are mainly derived from catchment areas that are eroding at a faster rate. The five gravel samples with high Be-10 concentrations probably contain gravel that were derived from the abrasion of cobbles exhumed at high elevations. In order to validate this model, further work should test if pebbles are preferentially exhumed from high erosion rate areas, and if the difference between pebbles with high Be-10 concentrations and sand decreases when the erosion rate tends to be homogeneous within a catchment. (C) 2014 Elsevier B.V. All rights reserved.
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Carretier S, Regard V, Vassallo R, Martinod J, Christophoul F, Gayer E, Audin L, Lagane C (2015) A note on Be-10-derived mean erosion rates in catchments with heterogeneous lithology: examples from the western Central Andes. Earth Surface Processes And Landforms 40(13):1719–1729
Résumé: Millennial catchment-mean erosion rates derived from terrestrial cosmogenic nuclides are generally based on the assumption that the lithologies of the parent rock each contain the same proportion of quartz. This is not always true for large catchments, in particular at the edge of mountainous plateaus where quartz-rich basement rocks may adjoin sedimentary or volcano-sedimentary rocks with low quartz content. The western Central Andes is an example of this type of situation. Different quartz contents may be taken into account by weighting the TCN production rates in the catchment. We recall the underlying theory and show that weighting the TCN production rate may also lead to bias in the case of a spatial correlation between erosion rate and lithology. We illustrate the difference between weighted and unweighted erosion rates for seven catchments (16 samples) in southern Peru and northern Chile and show variations up to a factor of 2 between both approaches. In this dataset, calculated erosion rates considering only granitoid outcrops are better correlated with catchment mean slopes than those obtained without taking into account the geological heterogeneity of the drained watershed. This dataset analysis demonstrates that weighting erosion rates by relative proportions of quartz is necessary to evaluate the uncertainties for calculated catchment-mean erosion rates and may reveal the correlation with geomorphic parameters. Copyright (c) 2015 John Wiley & Sons, Ltd.
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Carrier A, Got J-L, Peltier A, Ferrazzini V, Staudacher T, Kowalski P, Boissier P (2015) A damage model for volcanic edifices: Implications for edifice strength, magma pressure, and eruptive processes. Journal Of Geophysical Research-Solid Earth 120(1):567–583
Résumé: Monitoring of large basaltic volcanoes, such as Piton de la Fournaise (La Reunion Island, France), has revealed preeruptive accelerations in surface displacements and seismicity rate over a period of between 1h and several weeks before magma reaches the surface. Such eruptions are attributed to ruptures of pressurized magma reservoirs. Elastic models used to describe surface deformation would assume that accelerations in surface deformation are due to increases in reservoir pressure. This assumption requires changes in magma or pressure conditions at the base of the magma feeding system that are unrealistic over the observed timescale. Another possible cause for these accelerations is magma pressure in the reservoir weakening the volcanic edifice. In the present study, we modeled such weakening by progressive damage to an initially elastic edifice. We used an incremental damage model, with seismicity as a damage variable with daily increments. Elastic moduli decrease linearly with each damage increment. Applied to an initially elastic edifice with constant pressure at the base of the system, this damage model reproduces surface displacement accelerations quite well when damage is sufficient. Process dynamics is controlled by the damage parameter, taken as the ratio between the incremental rupture surface and the surface to be ruptured. In this case, edifice strength and magma reservoir pressure decrease with decreasing elastic moduli, whereas surface displacement accelerates. We discuss the consequences of pressure decreases in magma reservoirs.
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Castellanos C, Metivier L, Operto S, Brossier R, Virieux J (2015) Fast full waveform inversion with source encoding and second-order optimization methods. Geophysical Journal International 200(2):718–742
Résumé: Full waveform inversion (FWI) of 3-D data sets has recently been possible thanks to the development of high performance computing. However, FWI remains a computationally intensive task when high frequencies are injected in the inversion or more complex wave physics (viscoelastic) is accounted for. The highest computational cost results from the numerical solution of the wave equation for each seismic source. To reduce the computational burden, one well-known technique is to employ a random linear combination of the sources, rather that using each source independently. This technique, known as source encoding, has shown to successfully reduce the computational cost when applied to real data. Up to now, the inversion is normally carried out using gradient descent algorithms. With the idea of achieving a fast and robust frequency-domain FWI, we assess the performance of the random source encoding method when it is interfaced with second-order optimization methods (quasi-Newton l-BFGS, truncated Newton). Because of the additional seismic modelings required to compute the Newton descent direction, it is not clear beforehand if truncated Newton methods can indeed further reduce the computational cost compared to gradient algorithms. We design precise stopping criteria of iterations to fairly assess the computational cost and the speed-up provided by the source encoding method for each optimization method. We perform experiment on synthetic and real data sets. In both cases, we confirm that combining source encoding with second-order optimization methods reduces the computational cost compared to the case where source encoding is interfaced with gradient descent algorithms. For the synthetic data set, inspired from the geology of Gulf of Mexico, we show that the quasi-Newton l-BFGS algorithm requires the lowest computational cost. For the real data set application on the Valhall data, we show that the truncated Newton methods provide the most robust direction of descent.
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Causse M, Song SG (2015) Are stress drop and rupture velocity of earthquakes independent? Insight from observed ground motion variability. Geophysical Research Letters 42(18):7383–7389
Résumé: We demonstrate that the variability of the peak ground acceleration (PGA) generated by earthquakes can be simply related to the variability of stress drop (), rupture velocity (V-r) and their correlation. By compiling recent observations of variability of and V-r, we show that the hypothesis of independence between and V-r leads to an overestimation of the PGA variability. We suggest that and V-r must be anticorrelated so as to match recent observations of PGA variability.
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Cebron D (2015) Bistable flows in precessing spheroids. Fluid Dynamics Research 47(2)
Résumé: Precession driven flows are found in any rotating container filled with liquid, when the rotation axis itself rotates about a secondary axis that is fixed in an inertial frame of reference. Because of its relevance for planetary fluid layers, many works consider spheroidal containers, where the uniform vorticity component of the bulk flow is reliably given by the well-known equations obtained by Busse (1968 J. Fluid Mech. 33 739-51). So far however, no analytical result for the solutions is available. Moreover, the cases where multiple flows can coexist have not been investigated in detail since their discovery by Noir et al (2003 Geophys. J. Int. 154 407-16). In this work we aim at deriving analytical results for the solutions, aiming in particular at first estimating the ranges of parameters where multiple solutions exist, and second studying quantitatively their stability. Using the models recently proposed by Noir and Cebron (2013 J. Fluid Mech. 737 412-39), which are more generic in the inviscid limit than the equations of Busse, we analytically describe these solutions, their conditions of existence, and their stability in a systematic manner. We then successfully compare these analytical results with the theory of Busse (1968). Dynamical model equations are finally proposed to investigate the stability of the solutions, which describe the bifurcation of the unstable flow solution. We also report for the first time the possibility that time-dependent multiple flows can coexist in precessing triaxial ellipsoids. Numerical integrations of the algebraic and differential equations have been efficiently performed with the dedicated script FLIPPER (supplementary material).
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Chaljub E, Maufroy E, Moczo P, Kristek J, Hollender F, Bard P-Y, Priolo E, Klin P, de Martin F, Zhang Z, Zhang W, Chen X (2015) 3-D numerical simulations of earthquake ground motion in sedimentary basins: testing accuracy through stringent models. Geophysical Journal International 201(1):90–111
Résumé: Differences between 3-D numerical predictions of earthquake ground motion in the Mygdonian basin near Thessaloniki, Greece, led us to define four canonical stringent models derived from the complex realistic 3-D model of the Mygdonian basin. Sediments atop an elastic bedrock are modelled in the 1D-sharp and 1D-smooth models using three homogeneous layers and smooth velocity distribution, respectively. The 2D-sharp and 2D-smooth models are extensions of the 1-D models to an asymmetric sedimentary valley. In all cases, 3-D wavefields include strongly dispersive surface waves in the sediments. We compared simulations by the Fourier pseudo-spectral method (FPSM), the Legendre spectral-element method (SEM) and two formulations of the finite-difference method (FDM-S and FDM-C) up to 4 Hz. The accuracy of individual solutions and level of agreement between solutions vary with type of seismic waves and depend on the smoothness of the velocity model. The level of accuracy is high for the body waves in all solutions. However, it strongly depends on the discrete representation of the material interfaces (at which material parameters change discontinuously) for the surface waves in the sharp models. An improper discrete representation of the interfaces can cause inaccurate numerical modelling of surface waves. For all the numerical methods considered, except SEM with mesh of elements following the interfaces, a proper implementation of interfaces requires definition of an effective medium consistent with the interface boundary conditions. An orthorhombic effective medium is shown to significantly improve accuracy and preserve the computational efficiency of modelling. The conclusions drawn from the analysis of the results of the canonical cases greatly help to explain differences between numerical predictions of ground motion in realistic models of the Mygdonian basin. We recommend that any numerical method and code that is intended for numerical prediction of earthquake ground motion should be verified through stringent models that would make it possible to test the most important aspects of accuracy.
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Chandra J, Gueguen P, Steidl JH, Bonilla LF (2015) In Situ Assessment of the G-gamma Curve for Characterizing the Nonlinear Response of Soil: Application to the Garner Valley Downhole Array and the Wildlife Liquefaction Array. Bulletin Of The Seismological Society Of America 105(2a):993–1010
Résumé: We analyze the nonlinear and near-surface geological effects of two Network for Earthquake Engineering Simulation at University of California, Santa Barbara (NEES@UCSB) instrumented sites: the Garner Valley Downhole Array (GVDA) and the Wildlife Liquefaction Array (WLA). The seismic interferometry by deconvolution method is applied to earthquake data recorded by the multisensor vertical array between January 2005 and September 2013. Along the cross section, local shear-wave velocity is extracted by estimating travel time between sensors. The S-wave velocity profiles are constructed and compared with classical in situ geophysical surveys. We show that velocity values change according to the amplitude of the ground motion, and we find anisotropy between east-west and north-south directions at the GVDA site. The ratio between average peak particle velocity v* and local S-wave velocity V-S* between two boreholes is tested as a deformation proxy. Using average peak particle acceleration a*, the a* versus v*/V-S* curve is used to represent the stress-strain curve for observing the site's nonlinear responses under different levels of excitation. Nonlinearity is observed from quite low shear-strain levels (similar to 1 x 10(-5)) and a classic hyperbolic model is derived. v*/V-S* proves to be a good deformation proxy. Finally, the shear modulus degradation curves are constructed for each depth and test site, and they are similar to previous laboratory measurements or in situ geophysical surveys. A simple comparison regarding nonlinear behavior between GVDA and WLA is performed.
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Chevrot S, Sylvander M, Diaz J, Ruiz M, Paul A (2015) The Pyrenean architecture as revealed by teleseismic P-to-S converted waves recorded along two dense transects. Geophysical Journal International 200(2):1094–1105
Résumé: Between 2011 and 2013, two dense transects were deployed across the central and western Pyrenees to get better constraints on the deep lithospheric architecture and discriminate the competing models of the structure and formation of the Pyrenees. Each transect recorded the regional and global seismicity during a period of approximately 1 yr. Here, we exploit the records of teleseismic compressional waves and of their conversions to shear waves on internal discontinuities in order to map lithospheric interfaces beneath the two transects. The migrated sections, obtained by performing common conversion point stacks, are in remarkable agreement with the results of the ECORS-Pyrenees and ECORS-Arzacq deep seismic surveys. However, the migrations of converted waves reveal new details of the deep lithospheric architecture that could not be seen with the active source experiments. The new images provide clear and definite evidence for the subduction of a thinned Iberian crust down to at least similar to 70 km depth, a result that has important implications for the formation of the Pyrenees. The subduction of the Iberian lithosphere leads to reconsider the amount of convergence between Iberia and Europe during the Cenozoic. A recent regional P-wave tomography, relying on the data of the PYROPE and IBERARRAY temporary experiments, revealed the segmentation of lithospheric structures by inherited Hercynian NE-SW transfer faults that were reactivated during the Albian rifting. Our migration images are consistent with this model, and give further support to the idea that the Pyrenees were produced by the tectonic inversion of a segmented hyperextended rift that was buried by subduction beneath the European Plate.
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Chiodini G, Vandemeulebrouck J, Caliro S, D'Auria L, De Martino P, Mangiacapra A, Petrillo Z (2015) Evidence of thermal-driven processes triggering the 2005-2014 unrest at Campi Flegrei caldera. Earth And Planetary Science Letters 414:58–67
Résumé: An accelerating process of ground deformation that began 10 years ago is currently affecting the Campi Flegrei caldera. The deformation pattern is here explained with the overlapping of two processes: short time pulses that are caused by injection of magmatic fluids into the hydrothermal system; and a long time process of heating of the rock. The short pulses are highlighted by comparison of the residuals of ground deformation (fitted with an accelerating polynomial function) with the fumarolic CO2/CH4 and He/CH4 ratios (which are good geochemical indicators of the arrival of magmatic gases). The two independent datasets show the same sequence of five peaks, with a delay of similar to 200 days of the geochemical signal with respect to the geodetic signal. The heating of the hydrothermal system, which parallels the long-period accelerating curve, is inferred by temperature-pressure gas geoindicators. Referring to a recent interpretation that relates variations in the fumarolic inert gas species to open system magma degassing, we infer that the heating is caused by enrichment in water of the magmatic fluids and by an increment in their flux. Heating of the rock caused by magmatic fluids can be a central factor in triggering unrest at calderas. (C) 2015 Elsevier B.V. All rights reserved.
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Chirouze F, Huyghe P, Chauvel C, van der Beek P, Bernet M, Mugnier J-L (2015) Stable Drainage Pattern and Variable Exhumation in the Western Himalaya since the Middle Miocene. Journal Of Geology 123(1):1–20
Résumé: Sedimentary records in peripheral basins of mountain belts record changes in erosion dynamics and drainage-network reorganization, but it is often difficult to discriminate between these different controls. Geochemical provenance data on paleo-Indus deposits from the western Himalayan foreland provide constraints on the possible variation of the position of the drainage divide between the Indus and Ganges river systems. Here we present geochemical (trace element and Hf-Nd isotopic) and thermochronological (detrital zircon fission-track [DZFT]) analyses of modern Indus and Miocene Siwalik sediments from northern Pakistan and compare these with published data on the Indus Fan. Available bedrock isotopic data are used to define three end-member sediment sources (Himalaya, Karakorum, and the Kohistan-Ladakh arc) and to calculate the contribution of each of these sources to the foreland basin and Indus Fan. Our results indicate that since the Miocene the contribution of the Himalayan rivers reaching the Indus in the foreland remained constant, whereas the contributions of sediment sources of the upper Indus catchment changed: those of the Kohistan-Ladakh arc diminished strongly in favor of Karakorum and Himalayan sources. Analysis of the DZFT data from the Miocene foreland basin and sediments of the modern upper Indus reach suggests that the exhumation pattern changed due to an increase in exhumation rate of the Karakorum and Himalayan units of the syntaxis since Miocene times, whereas that in the Kohistan-Ladakh arc remained relatively stable. These results imply that the Indus sediments record changing relative erosion rates in the different source regions rather than widespread drainage rearrangement, as suggested previously.
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Colombi A, Roux P, Guenneau S, Rupin M (2015) Directional cloaking of flexural waves in a plate with a locally resonant metamaterial. Journal Of The Acoustical Society Of America 137(4):1783–1789
Résumé: This paper deals with the numerical design of a directional invisibility cloak for backward scattered elastic waves propagating in a thin plate (A(0) Lamb waves). The directional cloak is based on a set of resonating beams that are attached perpendicular to the plate and are arranged at a sub-wavelength scale in ten concentric rings. The exotic effective properties of this locally resonant metamaterial ensure coexistence of bandgaps and directional cloaking for certain beam configurations over a large frequency band. The best directional cloaking was obtained when the resonators' length decreases from the central to the outermost ring. In this case, flexural waves experience a vanishing index of refraction when they cross the outer layers, leading to a frequency bandgap that protects the central part of the cloak. Numerical simulation shows that there is no back-scattering in these configurations. These results might have applications in the design of seismic-wave protection devices. (C) 2015 Acoustical Society of America.
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Colon S, Audemard FA, Beck C, Avila J, Padron C, De Batist M, Paolini M, Leal AF, Van Welden A (2015) The 1900 Mw 7.6 earthquake offshore north-central Venezuela: Is La Tortuga or San Sebastian the source fault? Marine And Petroleum Geology 67:498–511
Résumé: A new high resolution shallow marine seismic survey provides further insights on the fault source of the October 29th, 1900 earthquake, which affected a large region of North-central Venezuela, both offshore islands and mainland. This Mw 7.6 to 7.7 seismic event has been indistinctly ascribed to either the La Tortuga or San Sebastian fault, which has installed a live debate among different authors. These two faults allegedly run roughly east-west offshore, along the Coastal range. The San Sebastian fault (SSF) bounds this range to the north, being responsible for its linearity and the steep slope of its northern flank, whereas the La Tortuga fault (LTF) would do about the same, but some 20-30 km farther north, based on acoustic surveys carried out in the late 70's and early 80's. We herein bring strong evidence to support that the SSF is the source fault of this major offshore earthquake, mainly based on the freshness of its submarine scarp and recent fault throw, preserved at the Chuspa bay (close to Cabo Codera, eastern end of the Coastal range in central Venezuela), as depicted by one of the profiles. In addition, it is shown that most of the previous extent ascribed to LTF is not so. The LTF, besides exhibiting mainly normal slip, is much shorter than originally proposed. This precludes that LTF may have the seismic potential for an earthquake as big as the 1900 event. Finally, available reflection seismic data reveal the existence of a major fault system bounding the La Guaira shelf on the north, which exhibits tectonic inversion of pre existing extensional faults, shortening and strong syn-tectonic deformation during the Plio-Quaternary deposition. Sedimentation in the Bonaire basin during the Plio-Quaternary time is strongly controlled by this system activity. (C) 2015 Elsevier Ltd. All rights reserved.
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Condie KC, Davaille A, Aster RC, Arndt N (2015) Upstairs-downstairs: supercontinents and large igneous provinces, are they related? International Geology Review 57(11-12):1341–1348
Résumé: There is a correlation of global large igneous province (LIP) events with zircon age peaks at 2700, 2500, 2100, 1900, 1750, 1100, and 600 and also probably at 3450, 3000, 2000, and 300Ma. Power spectral analyses of LIP event distributions suggest important periodicities at 250, 150, 100, 50, and 25million years with weaker periodicities at 70-80, 45, and 18-20Ma. The 25million year periodicity is important only in the last 300million years. Some LIP events are associated with granite-forming (zircon-producing) events and others are not, and LIP events at 1900 and 600Ma correlate with peaks in craton collision frequency. LIP age peaks are associated with supercontinent rifting or breakup, but not dispersal, at 2450-2400, 2200, 1380, 1280, 800-750, and <= 200Ma, and with supercontinent assembly at 1750 and 600Ma. LIP peaks at 2700 and 2500Ma and the valley between these peaks span the time of Neoarchaean supercraton assemblies. These observations are consistent with plume generation in the deep mantle operating independently of the supercontinent cycle and being controlled by lower-mantle and core-mantle boundary thermochemical dynamics. Two processes whereby plumes can impact continental assembly and breakup are (1) plumes may rise beneath supercontinents and initiate supercontinent breakup, and (2) plume ascent may increase the frequency of craton collisions and the rate of crustal growth by accelerating subduction.
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Corbi F, Rivalta E, Pinel V, Maccaferri F, Bagnardi M, Acocella V (2015) How caldera collapse shapes the shallow emplacement and transfer of magma in active volcanoes. Earth And Planetary Science Letters 431:287–293
Résumé: Calderas are topographic depressions formed by the collapse of a partly drained magma reservoir. At volcanic edifices with calderas, eruptive fissures can circumscribe the outer caldera rim, be oriented radially and/or align with the regional tectonic stress field. Constraining the mechanisms that govern this spatial arrangement is fundamental to understand the dynamics of shallow magma storage and transport and evaluate volcanic hazard. Here we show with numerical models that the previously unappreciated unloading effect of caldera formation may contribute significantly to the stress budget of a volcano. We first test this hypothesis against the ideal case of Fernandina, Galapagos, where previous models only partly explained the peculiar pattern of circumferential and radial eruptive fissures and the geometry of the intrusions determined by inverting the deformation data. We show that by taking into account the decompression due to the caldera formation, the modeled edifice stress field is consistent with all the observations. We then develop a general model for the stress state at volcanic edifices with calderas based on the competition of caldera decompression, magma buoyancy forces and tectonic stresses. These factors control: 1) the shallow accumulation of magma in stacked sills, consistently with observations; 2) the conditions for the development of circumferential and/or radial eruptive fissures, as observed on active volcanoes. This top-down control exerted by changes in the distribution of mass at the surface allows better understanding of how shallow magma is transferred at active calderas, contributing to forecasting the location and type of opening fissures. (C) 2015 Elsevier B.V. All rights reserved.
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Cordier C, Sauzeat L, Arndt NT, Boullier A-M, Batanova V, Barou F (2015) Metasomatism of the Lithospheric Mantle Immediately Precedes Kimberlite Eruption: New Evidence from Olivine Composition and Microstructures. Journal Of Petrology 56(9):1775–1795
Résumé: Most kimberlites contain abundant dunitic nodules. These are centimetre-sized, rounded and multi-grained assemblages of xenocrystic olivine with a wide range of compositions (Fo83 to Fo94). The absence of orthopyroxene and other mantle minerals and the range of olivine compositions have been attributed to reaction between mantle peridotite and (proto) kimberlitic fluid or melt, but the timing of the reaction is a subject of debate. In a kimberlite from the Kangamiut region of Greenland, nodule cores are surrounded by fine-grained outer margins with near-constant Fo contents (similar to Fo88) but highly variable minor element contents (e.g. 500-2500 ppm Ni). These margins crystallized from the kimberlite melt and we show that their compositions can be explained by crystallization of olivine alone, if a high partition coefficient for Ni between melt and olivine (D-Ni>20) is assumed. Orthopyroxene assimilation is not required, removing the constraint that its dissolution occurred during ascent of the kimberlite magma. Within some nodules, in addition to the usual core-to-margin gradients, we observe asymmetric compositional changes (variable Fo but near-constant minor element contents) across mobile grain boundaries. These changes document fluid percolation at the grain scale that occurred during dynamic recrystallization in the deforming lithospheric mantle. We note that chemical gradients associated with mobile grain boundaries are observed in olivines that cover the entire compositional range of the nodules, and propose that fluid-assisted dynamic recrystallization took place in dunite that was already compositionally heterogeneous. Reaction between peridotite and protokimberlitic melt or fluid and dissolution of orthopyroxene thus occurred within the lithospheric mantle, immediately (a few days) prior to the ascent of the kimberlite melt and the entrainment of the dunite nodules. We propose that the grain boundary zones probably mimic, at a fine scale, the fluid-peridotite interaction that caused, at a larger scale, orthopyroxene dissolution and formation of compositionally diverse olivine in kimberlites.
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Cortes-Aranda J, Gonzalez G, Remy D, Martinod J (2015) Normal upper plate fault reactivation in northern Chile and the subduction earthquake cycle: From geological observations and static Coulomb Failure Stress (CFS) change. Tectonophysics 639:118–131
Résumé: The northern Chile subduction zone constitutes a seismic gap where no great interplate earthquakes (Mw > 8.8) have nucleated since 1877. Active normal faulting occurs conspicuously in the Coastal Forearc at the southern end of this gap, between 22.7 degrees S and 24 degrees S. There, upper crustal extension is present right above a suggested subduction segment boundary of the Nazca-South America interplate contact. In this work, by using Coulomb Failure Stress Change (CFS) models, we explore the effects of coseismic and interseismic stages of the subduction earthquake cycle on the reactivation of pre-existing upper plate normal faults in this area. We attempt to unravel the first-order interplate conditions required to explain this extensional pattern, putting specific focus on the influence of the megathrust segmentation defined by the Mejillones Peninsula. It is suggested that the restricted occurrence of active normal faulting in the study area is tightly related to the structure of the interplate seismogenic zone. Positive CFS values are induced in the study area by the coseismic and interseismic stages of the subduction earthquake cycle, in a region characterized by lower coupling beneath the Mejillones Peninsula. We propose that fault reactivation in this zone is particularly favored during the coseismic stage by earthquakes occurring offshore of the Mejillones Peninsula and surrounding areas. In the adjacent subduction segments, coseismic and interseismic CFS values tend to counterbalance each other, resulting in no tensional conditions capable to cause normal fault reactivation. We suggest that the coupling variation in the seismogenic zone is long term controlled by the geological structure of the upper plate. (C) 2014 Elsevier B.V. All rights reserved.
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Coutant O, De Mengin M, Le Coarer E (2015) Fabry-Perot optical fiber strainmeter with an embeddable, low-power interrogation system. Optica 2(5):400–404
Résumé: Detection of earthquakes and tidal variations via measurement of strain in the Earth's crust requires compact and robust instrumentation with low power usage that can be deployed in the field. Here we demonstrate a stationary-wave integrated Fourier transform spectrometer (SWIFTS) and measure the variations induced by ground strain on an optical fiber Bragg grating sensor using two short (17 +/- 2 mm) Fabry-Perot (FP) cavities, one for the sensor, and one for temperature compensation. The SWIFTS delivers spatial interferograms that are then Fourier transformed to deduce the deformation from a cross-spectral analysis of the FP spectra. The full system is tested in field conditions to record crustal earth strain signals and successfully detect the earth tide and an earthquake signal. With this low-coherency interferometry technique, this system offers an excellent compromise between the resolution needed and the cost of a fully autonomous field instrument. (C) 2015 Optical Society of America
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Couture R-M, Charlet L, Markelova E, Made B, Parsons CT (2015) On-Off Mobilization of Contaminants in Soils during Redox Oscillations. Environmental Science & Technology 49(5):3015–3023
Résumé: Near-surface biogeochemical systems can oscillate between oxic and anoxic conditions. Under such periodic changes many redox-sensitive inorganic contaminants undergo speciation, mobility and toxicity changes. We investigated the changes to chromium (Cr), arsenic (As), selenium (Se), antimony (Sb) and uranium (U) mobility during a series of laboratory experiments where argillaceous substrates were subjected to successive cycles of oxidizing and reducing conditions. The E-H oscillated between -320 and +470 mV, induced via both abiotic and microbial forcings. Chemically induced cycles of oxidation and reduction were achieved via a combination of gas (N-2:CO2 vs compressed air) and carbon (ethanol) addition, to stimulate the metabolism of a natively present microbial community. The contaminants were added either alone or as contaminant mixtures. Results show clear on-off switch mobility behavior for both major elements such as carbon (C), iron (Fe) and manganese (Mn) and for contaminants. Mn, Fe, and As were mobilized under anoxic conditions, whereas Sb, Se, and U were mobilized under oxic conditions. While As, Sb, and U were reversibly sorbed, Se and Cr were irreversibly sequestered via reductive precipitation. When present in aqueous solutions at high concentrations, Cr-VI prevented the reduction of Mn and Fe, and inhibited the mobilization of elements with lower E-H(o). To improve remediation strategies for multiple contaminants in redox-dynamic environments, we propose a mixed kinetic-equilibrium biogeochemical model that can be forced by oscillating boundary conditions and that uses literature rates and constants to capture the key processes responsible for the mobilization of contaminants in soils.
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Cresson P, Bouchoucha M, Miralles F, Elleboode R, Mahe K, Marusczak N, Thebault H, Cossa D (2015) Are red mullet efficient as bio-indicators of mercury contamination? A case study from the French Mediterranean. Marine Pollution Bulletin 91(1):191–199
Résumé: Mercury (Hg) is one of the main chemicals currently altering Mediterranean ecosystems. Red mullet (Mullus barbatus and M. surmuletus) have been widely used as quantitative bio-indicators of chemical contamination. In this study, we reassess the ability of these species to be used as efficient bio-indicators of Hg contamination by monitoring during 18 months Hg concentrations in muscle tissue of mullet sampled from 5 French Mediterranean coastal areas. Mean concentrations ranged between 0.23 and 0.78 μg g(-1) dry mass for both species. Values were consistent with expected contamination patterns of all sites except Corsica. Results confirmed that red mullets are efficient bio-indicators of Hg contamination. Nevertheless, the observed variability in Hg concentrations calls for caution regarding the period and the sample size. Attention should be paid to environmental and biologic specificities of each studied site, as they can alter the bioaccumulation of Hg, and lead to inferences about environmental Hg concentrations. (C) 2014 Elsevier Ltd. All rights reserved.
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Cresson P, Bouchoucha M, Morat F, Miralles F, Chavanon F, Loizeau V, Cossa D (2015) A multitracer approach to assess the spatial contamination pattern of hake (Merluccius merluccius) in the French Mediterranean. Science Of The Total Environment 532:184–194
Résumé: Chemical contamination levels and stable isotope ratios provide integrated information about contaminant exposure, trophic position and also biological and environmental influences on marine organisms. By combining these approaches with otolith shape analyses, the aim of the present study was to document the spatial variability of Hg and PCB contamination of the European hake (Merluccius merluccius) in the French Mediterranean, hypothesizing that local contaminant sources, environmental conditions and biological specificities lead to site-specific contamination patterns. High Hg concentrations discriminated Corsica (average: 1.36 +/- 0.80 μg g(-1) dm) from the Gulf of Lions (average values < 0.5 μg g(-1) dm), where Rhone River input caused high PCB burdens. CB 153 average concentrations ranged between 4.00 +/- 0.64 and 18.39 +/- 12.38 ng g-1 dm in the Gulf of Lions, whatever the sex of the individuals, whereas the highest values in Corsica were 6.75 +/- 4.22 ng g(-1) dm. Otolith shape discriminated juveniles and adults, due to their different habitats. The use of combined ecotracers was revealed as a powerful tool to discriminate between fish populations at large and small spatial scale, and to enable understanding of the environmental and biological influences on contamination patterns. (C) 2015 Elsevier B.V. All rights reserved.
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Cubas N, Lapusta N, Avouac J-P, Perfettini H (2015) Numerical modeling of long-term earthquake sequences on the NE Japan megathrust: Comparison with observations and implications for fault friction. Earth And Planetary Science Letters 419:187–198
Résumé: We use numerical modeling to investigate fault properties that explain key features of the 2011 Mw 9.0 Tohoku-Oki earthquake as well as the overall regional behavior of the NE Japan megathrust In particular, we study the possibility that slip near the trench resulted from thermal pressurization on a shallow patch of the megathrust, and investigate whether low-velocity friction on that patch is rate-strengthening or rate-weakening. Our models also contain a deeper rate-weakening patch, not prone to efficient thermal pressurization, to account for the moderate-sized interplate seismicity. We produce earthquake sequences and aseismic slip in our models using 2D dynamic simulations that incorporate shear-induced temperature variations and the associated change in pore fluid pressure to capture thermal pressurization. We find that all our models can reproduce more frequent deeper moderate (Mw 7.5) events and less frequent larger events with substantial slip at shallow depth, as observed along the Fukushima-Miyagi segment of the Japan megathrust. However, only the scenario with a sufficiently rate-strengthening patch can match the thousand-year recurrence time of Tohoku-Oki-like earthquakes suggested by the historical and geological record, due to co-existence of seismic and aseismic slip at the shallow depths. This scenario also reproduces other characteristics of the Tohoku-Oki earthquake: the trenchward-skewed distribution of slip, the backward re-rupture of the deeper patch, as well as the weaker radiation at high frequency of the shallower portion of the rupture in spite of its larger slip. (C) 2015 Elsevier B.V. All rights reserved.
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D'Amato J, Guerin A, Hantz D, Rossetti J-P, Jaboyedoff M (2015) Investigating Rock Fall Frequency and Failure Configurations Using Terrestrial Laser Scanner. 1919–1923
Résumé: Terrestrial laser scanner has been used to detect rock falls greater than 0.01 m(3) which have occurred during some years in different rock walls consisting of massive to thin-bedded limestones of the Subalpine Chains and gneiss of the Massif de l'Oisans. For each rock wall, spatial-temporal rock fall frequencies have been determined and the volume-frequency relation has been fitted with a power law. The influence of the geological context on the power law parameters has been studied. These parameters can be used for quantitative assessment of diffuse hazard in rock walls having similar geological and morphodynamic contexts. The geometrical configurations prior to rock fall have also been studied in order to better identify the future rock fall locations. Prone to fall configurations depend on the rock mass internal structure and the wall surface geometry.
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Dazas B, Lanson B, Delville A, Robert J-L, Komarneni S, Michot LJ, Ferrage E (2015) Influence of Tetrahedral Layer Charge on the Organization of Inter layer Water and Ions in Synthetic Na-Saturated Smectites. Journal Of Physical Chemistry C 119(8):4158–4172
Résumé: Smectite hydration strongly influences dynamical properties of interlayer cations and thus the fate of H2O and pollutants in surficial systems where smectite-based materials are often used as a major barrier component. Smectite crystal chemistry is known to rule its hydration, although the influence of specific parameters such as the amount and location of layer charge deficit remains poorly understood. A set of tetrahedrally charged trioctahedral smectites, with a common structural formula (inter)[Na-x](oct)[Mg-6](tet)[Si(8.0-x)Alx(])O(20)(OH,F)(4) and a layer charge (x) varying from 0.8 to 3.0, were thus synthesized to assess the influence of layer charge on smectite hydration and interlayer structure. Both hydroxylated and fluorinated samples were synthesized because of the increasing use of the latter varieties in recent spectroscopic studies aiming at the determination of interlayer H2O dynamical properties. The distribution of charge-compensating cations and of associated H2O molecules was determined both experimentally from the modeling of X-ray diffraction patterns and numerically from Monte Carlo molecular simulations performed in the grand canonical ensemble. The consistency of both approaches for hydroxylated samples allowed gaining insights into the specific influence of smectite crystal chemistry. For a given hydration state, H2O content is about constant in hydroxylated saponites, independent of layer charge, whereas smectite layer-to-layer distance decreases with increasing layer charge because of the enhanced cation-layer electrostatic attraction. As a result, positional disorder of interlayer H2O molecules is reduced because of stronger steric constraints and of the increased density of electronegative sites at the surface of the clay layer. Fluorine-for-hydroxyl isomorphic substitutions likely increase further electronegativity of the clay layer surface leading to further reduction of the interlayer H2O content and to the formation of Na+ inner sphere complexes at the clay layer surface. When normalized to the number of interlayer cations, the number of interlayer H2O molecules decreases with increasing layer charge, and the proportion of these H2O molecules hydrating interlayer cations increases, thus increasing the stability of most hydrated states toward lower relative humidity conditions. Smectite hydration evolution appears as a steady process with no tendency to interlayer cation ordering at the smectite-to-vermiculite limit of similar to 1.3 charge per O-20(OH,F)(4).
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de La Taille C, Jouanne F, Crouzet C, Beck C, Jomard H, de Rycker K, Van Daele M (2015) Impact of active faulting on the post LGM infill of Le Bourget Lake (western Alps, France). Tectonophysics 664:31–49
Résumé: We have used high resolution seismic imaging to detect and characterize the recent deformation recorded by the Quaternary sediments of Le Bourget Lake. The last glacial episodes (MIS 6a and 2, i.e., Riss and Wiirm) scoured out an elongated over-deepened basin to more than 300 m below the present lake level and the basin accumulated 150 m of post-LGM to Holocene sediments. The well-stratified character of the infill is locally disturbed by tectonic deformations and gravity reworking. A northern fault zone, in continuation with the left-lateral strike slip Culoz Fault, is imaged within the Holocene and Late Glacial accumulations. A southern fault zone is also detected, which can be related to the sub-lacustrine continuation of a much smaller fault affecting the Jura alpine foreland: the Col du Chat left lateral strike slip fault. Different generations of fractures have been identified in the lake, allowing correlation and mapping. In pre-Quaternary substratum, the Culoz Fault has a N 160 degrees orientation. Within the post-LGM sediments, fractures related to the Culoz Fault have an orientation between N135 degrees and 95 degrees. A Cloos model (1932) is thus proposed to explain the observed pattern of lacustrine deformations. The calculated horizontal slip rate for Culoz Fault during Holocene is about 13 mm. yr(-1), and for the Col du Chat Fault is around 0.6 mm.yr(-1). (C) 2015 Elsevier B.V. All rights reserved.
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Debret B, Bolfan-Casanova N, Padron-Navarta JA, Martin-Hernandez F, Andreani M, Garrido CJ, Lopez Sanchez-Vizcaino V, Teresa Gomez-Pugnaire M, Munoz M, Trcera N (2015) Redox state of iron during high-pressure serpentinite dehydration. Contributions To Mineralogy And Petrology 169(4)
Résumé: The Cerro del Almirez massif (Spain) represents a unique fragment of serpentinized oceanic lithosphere that has been first equilibrated in the antigorite stability field (Atg-serpentinites) and then dehydrated into chlorite-olivine-orthopyroxene (Chl-harzburgites) at eclogite facies conditions during subduction. The massif preserves a dehydration front between Atg-serpentinites and Chl-harzburgites. It constitutes a suitable place to study redox changes in serpentinites and the nature of the released fluids during their dehydration. Relative to abyssal serpentinites, Atg-serpentinites display a low Fe3+/Fe-Total(BR) (=0.55) and magnetite modal content (=2.8-4.3 wt%). Micro-X-ray absorption near-edge structure (mu-XANES) spectroscopy measurements of serpentines at the Fe-K edge show that antigorite has a lower Fe3+/Fe-Total ratio (=0.48) than oceanic lizardite/chrysotile assemblages. The onset of Atg-serpentinites dehydration is marked by the crystallization of a Fe3+-rich antigorite (Fe3+/Fe-Total =0.6-0.75) in equilibrium with secondary olivine and by a decrease in magnetite amount (=1.6-2.2 wt%). This suggests a preferential partitioning of Fe3+ into serpentine rather than into olivine. The Atg-breakdown is marked by a decrease in Fe3+/Fe-Total(BR) (=0.34-0.41), the crystallization of Fe2+-rich phases and the quasi-disappearance of magnetite (=0.6-1.4 wt.%). The observation of Fe3+-rich hematite and ilmenite intergrowths suggests that the O-2 released by the crystallization of Fe(2+)rich phases could promote hematite crystallization and a subsequent increase in fo(2) inside the portion of the sub-ducted mantle. Serpentinite dehydration could thus produce highly oxidized fluids in subduction zones and contribute to the oxidization of the sub-arc mantle wedge.
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Del Gaudio S, Causse M, Festa G (2015) Broad-band strong motion simulations coupling k-square kinematic source models with empirical Green's functions: the 2009 L'Aquila earthquake. Geophysical Journal International 203(1):720–736
Résumé: The use of simulated accelerograms may improve the evaluation of the seismic hazard when an accurate modelling of both source and propagation is performed. In this paper, we performed broad-band simulations of the 2009, M 6.3 L'Aquila earthquake, coupling a k(-2) kinematic model for the seismic source with empirical Green's functions (EGFs) as propagators. We extracted 10 EGFs candidates from a database of aftershocks satisfying quality criteria based on signal-to-noise ratio, fault proximity, small magnitude, similar focal mechanism and stress drop. For comparison with real observations, we also derived a low-frequency kinematic model, based on inversion of ground displacement as integrated from strong motion data. Kinematic properties of the inverted model (rupture velocity, position of the rupture nucleation, low-frequency slip and roughness degree of slip heterogeneity) were used as constraints in the k(-2) model, to test the use of a single specific EGF against the use of the whole set of EGFs. Comparison to real observations based on spectral and peak ground acceleration shows that the use of all available EGFs improves the fit of simulations to real data. Moreover the epistemic variability related to the selection of a specific EGF is significantly larger (two to three times) than recent observations of between event variability, that is the variability associated with the randomness of the rupture process. We finally performed 'blind' simulations releasing all the information on source kinematics and only considering the fault geometry and the magnitude of the target event as known features. We computed peak ground acceleration, acceleration Fourier and response spectra. Simulations follow the same trend with distance as real observations. In most cases these latter fall within one sigma from predictions. Predictions with source parameters constrained at low frequency do not perform better than 'blind' simulations, showing that extrapolation of the low-frequency description of the rupture front as inferred by the kinematic inversion may introduce some bias in the final simulations.
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Delavault H, Chauvel C, Sobolev A, Batanova V (2015) Combined petrological, geochemical and isotopic modeling of a plume source: Example of Gambier Island, Pitcairn chain. Earth And Planetary Science Letters 426:23–35
Résumé: Mantle plumes have been increasingly studied in the past years, yet they remain not well understood. While geophysical approaches attempt to locate the depth of sources, petrological approaches characterize the nature of the materials that melt and geochemical approaches trace their history and origin. However, combined studies remain rare while they could provide strong constraints on the processes that give rise to mantle plumes. Here we present a new model that combines petrological and geochemical approaches to constrain the nature of source materials, their temperature of melting, their composition and their age. We focus on Gambier Island, Pitcairn chain in Polynesia because it has the advantage of combining two important features, (a) most lavas are tholeiites, a necessary feature to perform an accurate petrological modeling that can be compared to other plumes and (b) it belongs to the Pitcairn Chain, whose composition varies through time and samples today the extreme EM1-type source. We present geochemical analyses as well as Sr-Nd-Pb-Hf isotopes of lavas and high-precision olivine analyses. Using in situ olivine analyses and REE modeling, we constrain the composition of the mantle source (5% recycled oceanic crust – 95% peridotite), how both components melt (25-30% versus 0.5-1.5%) and we estimate the temperature of Gambier source at about 1400 degrees C, a rather low temperature compared to Hawaii for example. We also constrain both the age and the nature of the recycled material using the isotopic data. They require the presence of about 3% sediment associated to recycled basalt in the pyroxenitic component and its age is about 1.5 Gyr. We also attribute the marked Nb-Ta positive anomalies and the elevated Ce/Pb ratios to the presence of recycled basalt in the mantle source. These features resemble typical HIMU lavas but the younger age of the recycled material together with the presence of sediment in the plume source explains the lower Pb isotopic ratios. The clear isotopic change between Gambier and Pitcairn Islands suggests that the plume source changed radically within 5 Ma. More generally, our new data and model suggest that the FOZO composition as sampled by Gambier lavas does not necessarily represent a large and rather primitive mantle source. (C) 2015 Elsevier B.V. All rights reserved.
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Doin M-P, Twardzik C, Ducret G, Lasserre C, Guillaso S, Sun Jianbao (2015) InSAR measurement of the deformation around Siling Co Lake: Inferences on the lower crust viscosity in central Tibet. Journal Of Geophysical Research-Solid Earth 120(7):5290–5310
Résumé: The Siling Co Lake is the largest endorheic lake in Central Tibet. Altimetric measures, combined with lake contours, show that in 1972-1999 its water level remained stable, while it increased by about 1.0m/yr in the period 2000-2006. The increased rate gradually stepped down to 0.2m/yr in 2007-2011. The ground motion associated with the water load increase is studied by interferometric synthetic aperture radar (InSAR) using 107 ERS and Envisat SAR images during the period 1992-2011. The deformation amplitude closely follows the lake level temporal evolution, except that subsidence continues in 2008-2011, while the lake level stagnated. This temporal evolution suggests a non elastic relaxation process taking place at a decade timescale. Phase delay maps are used to constrain possible layered viscoelastic rheological models. An elastic model could partly explain the observed subsidence rate if elastic moduli are about twice lower than those extracted from V-P/V-S profiles. The surface deformation pattern is also extracted by projecting the phase delay maps against the best fit model temporal behavior. It shows that deep relaxation in the asthenosphere is negligible at the decade timescale and favors the existence of a ductile channel in the deep crust above a more rigid mantle. Overall, the best fit model includes a ductile lower crust, with a viscosity of 1-3 x 10(18)Pas between 25 and 35km and the Moho (at 65km), overlying a rigid mantle.
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Dumont T, Replumaz A, Roumejon S, Briais A, Rigo A, Bouillin J-P (2015) Microseismicity of the Bearn range: Reactivation of inversion and collision structures at the northern edge of the Iberian plate. Tectonics 34(5):934–950
Résumé: The Bearn range, located to the north of the Axial Zone in the Western Pyrenees, is affected by numerous small-magnitude seismic events. These events overlap an area characterized by specific geological structures which are interpreted to have resulted from multistage extensional and compressional deformation. An analysis of surface geology draped over digital elevation model, together with field investigations, allow identification of two main shortening episodes with differing direction of contraction: D1 represents the inversion of the North Pyrenean Basin, whose Mesozoic infill was detached from highly extended crust and transported southward over the necking zone and the northern margin of the Iberian plate; D2 corresponds to the collision stage and is characterized in the study area by backfolding and backthrusting deformation coeval with uplift in the axial part of the chain due to thickening of the Iberian plate. The microseismicity appears to concentrate along the basal part of the inverted basin units (D1) where this initially low angle thrust has been tilted and steepened during collision (D2). We propose that local steepening of this ancient inversion structure, which should not be named North Pyrenean Fault, provided the suitable dip for extensional solicitation in association with the present uplift of the Axial Zone, whatever the driving mechanism of this uplift could be.
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Edwards B, Ktenidou O-J, Cotton F, Abrahamson N, Van Houtte C, Faeh D (2015) Epistemic uncertainty and limitations of the kappa(0) model for near-surface attenuation at hard rock sites. Geophysical Journal International 202(3):1627–1645
Résumé: The determination of near-surface attenuation for hard rock sites is an important issue in a wide range of seismological applications, particularly seismic hazard analysis. In this article we choose six hard to very-hard rock sites (Vs(30) 1030-3000ms(-1)) and apply a range of analysis methods to measure the observed attenuation at distance based on a simple exponential decay model with whole-path attenuation operator kappa(r). The kappa(r) values are subsequently decoupled from path attenuation (Q) so as to obtain estimates of near-surface attenuation (kappa(0)). Five methods are employed to measure kappa(r) which can be split into two groups: broad-band methods and high-frequency methods. Each of the applied methods has advantages and disadvantages, which are explored and discussed through the comparison of results from common data sets. In our first step we examine the variability of the individual measured kappa(r) values. Some variation between methods is expected due to simplifications of source, path, and site effects. However, we find that significant differences arise between attenuation measured on individual recordings, depending on the method employed or the modelling decisions made during a particular approach. Some of the differences can be explained through site amplification effects: although usually weak at rock sites, amplification may still lead to bias of the measured kappa(r) due to the chosen fitting frequency bandwidth, which often varies between methods. At some sites the observed high-frequency spectral shape was clearly different to the typical kappa(r) attenuation model, with curved or bi-linear rather than linear decay at high frequencies. In addition to amplification effects this could be related to frequency-dependent attenuation effects [e.g. Q(f)]: since the kappa(r) model is implicitly frequency independent, kappa(r) will in this case be dependent on the selected analysis bandwidth. In our second step, using the whole-path kappa(r) data sets from the five approaches, we investigate the robustness of the near-surface attenuation parameter kappa(0) and the influence of constraints, such as assuming a value for the regional crustal attenuation (Q). We do this by using a variety of fitting methods: least squares, absolute amplitude and regressions with and without fixing Q to an a priori value. We find that the value to which we fix Q strongly influences the near-surface attenuation term kappa(0). Differences in Q derived from the data at the six sites under investigation could not be reconciled with the average values found previously over the wider Swiss region. This led to starkly different kappa(0) values, depending on whether we allowed for a data-driven Q, or whether we forced Q to be consistent with existing simulation models or ground motion prediction equations valid for the wider region. Considering all the possible approaches we found that the contribution to epistemic uncertainty for kappa(0) determination at the six hard-rock sites in Switzerland could be represented by a normal distribution with standard deviation sigma kappa(0) = 0.0083 +/- A 0.0014 s.
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Eiche E, Bardelli F, Nothstein AK, Charlet L, Goettlicher J, Steininger R, Dhillon KS, Sadana US (2015) Selenium distribution and speciation in plant parts of wheat (Triticum aestivum) and Indian mustard (Brassica juncea) from a seleniferous area of Punjab, India. Science Of The Total Environment 505:952–961
Résumé: The concentration, distribution, and speciation of selenium in different parts of wheat and Indian mustard, grown in a seleniferous area in Punjab, were investigated using synchrotron based (XAS) and classical acid digestion and extraction methods. The analyses revealed a high Se enrichment in all investigated plant parts, with Se levels in the range of 133 931 mg/kg (dry weight, dw). Such high Se enrichment is mainly due to the considerable amounts of easily available Se detected in the soil, which are renewed on a yearly basis to some extent via irrigation. Speciation analysis in soil and plants indicated selenate and organic Se as major Se species taken up by plants, with a minor presence of selenite. The analyses also revealed that the highest Se enrichment occurs in the upper plant parts, in agreement with the high uptake rate and mobility of selenate within plants. In both wheat and mustard, highest Se enrichments were found in leaves (387 mg/kg. dw in wheat and 931 mg/kg. dw in mustard). Organic species (dimethylselenide and methylselenocysteine) were found in different parts of both plants, indicating that an active detoxification response to the high Se uptake is taking place through methylation and/or volatilization. The high proportion of selenate in wheat and mustard leaves (47% and 70%, respectively) is the result of the inability of the plant metabolism to completely transform selenate to non-toxic organic forms, if oversupplied. Methylselenocysteine, a common Se species in accumulating plants, was detected in wheat, suggesting that, in the presence of high Se concentration, this plant develops similar response mechanisms to accumulator plants. (C) 2014 Elsevier B.V. All rights reserved.
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El Khoury P, Revil A, Sava P (2015) Seismoelectric beamforming imaging: a sensitivity analysis. Geophysical Journal International 201(3):1781–1800
Résumé: The electrical current density generated by the propagation of a seismic wave at the interface characterized by a drop in electrical, hydraulic or mechanical properties produces an electrical field of electrokinetic nature. This field can be measured remotely with a signal-to-noise ratio depending on the background noise and signal attenuation. The seismoelectric beamforming approach is an emerging imaging technique based on scanning a porous material using appropriately delayed seismic sources. The idea is to focus the hydromechanical energy on a regular spatial grid and measure the converted electric field remotely at each focus time. This method can be used to image heterogeneities with a high definition and to provide structural information to classical geophysical methods. A numerical experiment is performed to investigate the resolution of the seismoelectric beamforming approach with respect to the main wavelength of the seismic waves. The 2-D model consists of a fictitious water-filled bucket in which a cylindrical sandstone core sample is set up vertically. The hydrophones/seismic sources are located on a 50-cm diameter circle in the bucket and the seismic energy is focused on the grid points in order to scan the medium and determine the geometry of the porous plug using the output electric potential image. We observe that the resolution of the method is given by a density of eight scanning points per wavelength. Additional numerical tests were also performed to see the impact of a wrong velocity model upon the seismoelectric map displaying the heterogeneities of the material.
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Ellis AP, DeMets C, Briole P, Molina E, Flores O, Rivera J, Lasserre C, Lyon-Caen H, Lord N (2015) Geodetic slip solutions for the M-w=7.4 Champerico (Guatemala) earthquake of 2012 November 7 and its postseismic deformation. Geophysical Journal International 201(2):856–868
Résumé: As the first large subduction thrust earthquake off the coast of western Guatemala in the past several decades, the 2012 November 7 M-w = 7.4 earthquake offers the first opportunity to study coseismic and postseismic behaviour along a segment of the Middle America trench where frictional coupling makes a transition from weak coupling off the coast of El Salvador to strong coupling in southern Mexico. We use measurements at 19 continuous GPS sites in Guatemala, El Salvador and Mexico to estimate the coseismic slip and postseismic deformation of the November 2012 Champerico (Guatemala) earthquake. An inversion of the coseismic offsets, which range up to similar to 47mm at the surface near the epicentre, indicates that up to similar to 2 m of coseismic slip occurred on a similar to 30 x 30 km rupture area between similar to 10 and 30 km depth, which is near the global CMT centroid. The geodetic moment of 13 x 10(19) N m and corresponding magnitude of 7.4 both agree well with independent seismological estimates. Transient postseismic deformation that was recorded at 11 GPS sites is attributable to a combination of fault afterslip and viscoelastic flow in the lower crust and/or mantle. Modelling of the viscoelastic deformation suggests that it constituted no more than similar to 30 per cent of the short-term postseismic deformation. GPS observations that extend six months after the earthquake are well fit by a model in which most afterslip occurred at the same depth or directly downdip from the rupture zone and released energy equivalent to no more than similar to 20 per cent of the coseismic moment. An independent seismological slip solution that features more highly concentrated coseismic slip than our own fits the GPS offsets well if its slip centroid is translated similar to 50 km to the west to a position close to our slip centroid. The geodetic and seismologic slip solutions thus suggest bounds of 2-7 m for the peak slip along a region of the interface no larger than 30 x 30 km.
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Emoto K, Campillo M, Brenguier F, Briand X, Takeda T (2015) Asymmetry of coda cross-correlation function: dependence of the epicentre location. Geophysical Journal International 201(3):1313–1323
Résumé: We analyze the cross-correlation function (CCF) of coda of earthquakes, which is used to retrieve the Green's function between two stations as well as the CCF of ambient noise. We select 74 Hi-net stations located in eastern Japan and 66 earthquakes to calculate the CCF. For each earthquake, we calculate the CCFs between possible pairs for the frequency bands of 0.1-0.2 Hz, 0.2-0.4 Hz and 0.4-0.8 Hz. Then we stack the CCFs for different earthquakes at each pair to obtain the average CCF. Although the correlation coefficients between the average and each CCFs are lower than 0.5 for most of the earthquakes, we obtain the propagating Rayleigh wave trace from average CCFs. We focus on the ratio of the amplitude in the positive lag time of the CCF to that in the negative lag time. CCFs for different earthquakes show different ratios which depend on the angle between the path of two stations and the epicentre. The amplitude in the lag time corresponding to the signal travelling from the near source station to the far source station is larger than that in the opposite lag time. Therefore the energy flux is not isotropic even in the coda and the energy from the source side is dominant. We average the ratios of pairs whose absolute values of angles are less than 45A degrees. The average ratios are 0.5 at 0.1-0.2 Hz. For higher frequencies, the ratio is not clear because of the bad signal-to-noise ratio. According to the diffusion model, the ratio is predicted as 0.6. Therefore, the coda is represented as the diffusion state in 0.1-0.2 Hz with our observation setting.
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Erdos Z, Huismans RS, van der Beek P (2015) First-order control of syntectonic sedimentation on crustal-scale structure of mountain belts. Journal Of Geophysical Research-Solid Earth 120(7):5362–5377
Résumé: The first-order characteristics of collisional mountain belts and the potential feedback with surface processes are predicted by critical taper theory. While the feedback between erosion and mountain belt structure has been fairly extensively studied, less attention has been given to the potential role of synorogenic deposition. For thin-skinned fold-and-thrust belts, recent studies indicate a strong control of syntectonic deposition on structure, as sedimentation tends to stabilize the thin-skinned wedge. However, the factors controlling basement deformation below fold-and-thrust belts, as evident, for example, in the Zagros Mountains or in the Swiss Alps, remain largely unknown. Previous work has suggested that such variations in orogenic structure may be explained by the thermotectonic age of the deforming lithosphere and hence its rheology. Here we demonstrate that sediment loading of the foreland basin area provides an additional control and may explain the variable basement involvement in orogenic belts. When examining the role of sedimentation, we identify two end-members: (1) sediment-starved orogenic systems with thick-skinned basement deformation in an axial orogenic core and thin-skinned deformation in the bordering forelands and (2) sediment-loaded orogens with thick packages of synorogenic deposits, derived from the axial basement zone, deposited on the surrounding foreland fold-and-thrust belts, and characterized by basement deformation below the foreland. Using high-resolution thermomechanical models, we demonstrate a strong feedback between deposition and crustal-scale thick-skinned deformation. Our results show that the loading effects of syntectonic sediments lead to long crustal-scale thrust sheets beneath the orogenic foreland and explain the contrasting characteristics of sediment-starved and sediment-loaded orogens, showing for the first time how both thin- and thick-skinned crustal deformations are linked to sediment deposition in these orogenic systems. We show that the observed model behavior is consistent with observations from a number of natural orogenic systems.
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Fauquette S, Bernet M, Suc J-P, Grosjean A-S, Guillot S, van der Beek P, Jourdan S, Popescu S-M, Jimenez-Moreno G, Bertini A, Pittet B, Tricart P, Dumont T, Schwartz S, Zheng Z, Roche E, Pavia G, Gardien V (2015) Quantifying the Eocene to Pleistocene topographic evolution of the southwestern Alps, France and Italy. Earth And Planetary Science Letters 412:220–234
Résumé: We evaluate the topographic evolution of the southwestern Alps using Eocene to Pleistocene pollen data combined with existing sedimentological, petrographic and detrital geo- and thermochronological data. We report 32 new pollen analyses from 10 sites completed by an existing dataset of 83 samples from 14 localities situated across the southwestern Alps, including both the pro- and the retro-foreland basins. The presence of microthermic tree pollen (mainly Abies, Picea) indicates that this part of the mountain belt attained elevations over 1900 m as early as the Oligocene. Inferred rapid suface uplift during the mid-Oligocene coincided with a previously documented brief phase of rapid erosional exhumation, when maximum erosion rates may have reached values of up to 1.5-2 km/Myr. Slower long-term average exhumation rates of 03 km/Myr since the Late Oligocene helped maintaining the high Alpine topography of the southwestern Alps until today. The relative abundances of meso-microthermic tree pollen (Cathaya, Cedrus and Tsuga) and microthermic tree pollen (Abies, Picea) in the pro- and retro-foreland basin deposits, indicate that the present-day asymmetric topography, with a relatively gentle western flank and steeper eastern flank, was established early in the southwestern Alps, at least since the Early Miocene, and possibly since the Oligocene or Late Eocene. Therefore, the high topography and asymmetric morphology of this part of the Alps has been maintained throughout the past similar to 30 Ma. (C) 2014 Elsevier B.V. All rights reserved.
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Flament N, Gurnis M, Mueller RD, Bower DJ, Husson L (2015) Influence of subduction history on South American topography. Earth And Planetary Science Letters 430:9–18
Résumé: The Cenozoic evolution of South American topography is marked by episodes of large-scale uplift and subsidence not readily explained by lithospheric deformation. The drying up of the inland Pebas system, the drainage reversal of the Amazon river, the uplift of the Sierras Pampeanas and the uplift of Patagonia have all been linked to the evolution of mantle flow since the Miocene in separate studies. Here we investigate the evolution of long-wavelength South American topography as a function of subduction history in a time-dependent global geodynamic model. This model is shown to be consistent with these inferred changes, as well as with the migration of the Chaco foreland basin depocentre, that we partly attribute to the inboard migration of subduction resulting from Andean mountain building. We suggest that the history of subduction along South America has had an important influence on the evolution of the topography of the continent because time-dependent mantle flow models are consistent with the history of vertical motions as constrained by the geological record at four distant areas over a whole continent. Testing alternative subduction scenarios reveals flat slab segments are necessary to reconcile inferred Miocene shorelines with a simple model paleogeography. As recently suggested, we find that the flattening of a subduction zone results in dynamic uplift between the leading edge of the flat slab segment and the trench, and in a wave of dynamic subsidence associated with the inboard migration of the leading edge of flat subduction. For example, the flattening of the Peruvian subduction contributed to the demise of Pebas shallow-water sedimentation, while continental-scale tilting also contributed to the drainage reversal of the Amazon River. The best correlation to P-wave tomography models for the Peruvian flat slab segment is obtained for a case when the asthenosphere, here considered to be 150 km thick and 10 times less viscous than the upper mantle, is restricted to the oceanic domain. (C) 2015 Elsevier B.V. All rights reserved.
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Folco L, D'Orazio M, Fazio A, Cordier C, Zeoli A, van Ginneken M, El-Barkooky A (2015) Microscopic impactor debris in the soil around Kamil crater (Egypt): Inventory, distribution, total mass, and implications for the impact scenario. Meteoritics & Planetary Science 50(3):382–400
Résumé: We report on the microscopic impactor debris around Kamil crater (45m in diameter, Egypt) collected during our 2010 geophysical expedition. The hypervelocity impact of Gebel Kamil (Ni-rich ataxite) on a sandstone target produced a downrange ejecta curtain of microscopic impactor debris due SE-SW of the crater (extending similar to 300,000m(2), up to similar to 400m from the crater), in agreement with previous determination of the impactor trajectory. The microscopic impactor debris include vesicular masses, spherules, and coatings of dark impact melt glass which is a mixture of impactor and target materials (Si-, Fe-, and Al-rich glass), plus Fe-Ni oxide spherules and mini shrapnel, documenting that these products can be found in craters as small as few tens of meters in diameter. Theestimated mass of the microscopic impactor debris (<290kg) derived from Ni concentrations in the soil is a small fraction of the total impactor mass (similar to 10t) in the form of macroscopic shrapnel. That Kamil crater was generated by a relatively small impactor is consistent with literature estimates of its pre-atmospheric mass (>20t, likely 50-60t).
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Frank WB, Radiguet M, Rousset B, Shapiro NM, Husker AL, Kostoglodov V, Cotte N, Campillo M (2015) Uncovering the geodetic signature of silent slip through repeating earthquakes. Geophysical Research Letters 42(8):2774–2779
Résumé: Slow transient slip that releases stress along the deep roots of plate interfaces is most often observed on regional GPS networks installed at the surface. The detection of slow slip is not trivial if the dislocation along the fault at depth does not generate a geodetic signal greater than the observational noise level. Instead of the typical workflow of comparing independently gathered seismic and geodetic observations to study slow slip, we use repeating low-frequency earthquakes to reveal a previously unobserved slow slip event. By aligning GPS time series with episodes of low-frequency earthquake activity and stacking, we identify a repeating transient slip event that generates a displacement at the surface that is hidden under noise prior to stacking. Our results suggest that the geodetic investigation of transient slip guided by seismological information is essential in exploring the spectrum of fault slip.
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Frank WB, Shapiro NM, Husker AL, Kostoglodov V, Bhat HS, Carnpillo M (2015) Along-fault pore-pressure evolution during a slow-slip event in Guerrero, Mexico. Earth And Planetary Science Letters 413:135–143
Résumé: Slow earthquakes are important constituents of the seismic cycle and are involved in the stress transfer between the viscously slipping portion of the plate interface and the seismogenic zone. Their occurrence is likely associated with the near-lithostatic pore pressure in the slow earthquake source region, where fluids might modify fault friction and whose presence is indicated by high ratios of compressional (P)wave velocity to shear (S)-wave velocity observed at the interface between the subducting plate and the overlying crust. Here we compare two slow earthquake phenomena observed in the Guerrero region of the Mexican subduction zone: low-frequency earthquakes (LFEs) and a slow-slip event (SSE) recorded by GPS. We observe variations of the LFE occurrence rates over month-long time scales during a large SSE that we interpret as a manifestation of transient changes in the fault shear strength. We argue that these transient changes are caused by a pore pressure fluctuation that migrates updip along the subduction interface. This mechanism suggests that fluids do not only passively weaken the plate interface but also play an active role in slow earthquake source regions. (C) 2015 Elsevier B.V. All rights reserved.
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Frery E, Gratier J-P, Ellouz-Zimmerman N, Loiselet C, Braun J, Deschamps P, Blamart D, Hamelin B, Swennen R (2015) Evolution of fault permeability during episodic fluid circulation: Evidence for the effects of fluid-rock interactions from travertine studies (Utah-USA). Tectonophysics 651:121–137
Résumé: Faults are known to be important pathways for fluid circulation within the crust. The transfer properties along faults can evolve over time and space. The Little Grand Wash and Salt Wash normal faults, located on the Colorado Plateau, are well known examples of natural CO2 leakage systems from depth to surface. Previous studies dated and established a chronology of CO2-enriched fluid source migration along the fault traces and linked the aragonite veins observed close to Crystal Geyser to CO2-pulses. However, multiple circulation events recorded along a given fault segment deserve to be studied in minute detail in order to unravel the chronology of these events, precipitation processes and associated mechanisms. A combination of structural geology, petrography, U/Th dating, oxygen and carbon isotope analysis were used to study the fault related CO2-enriched paleocirculations in order to build a conceptual model of CO2-circulation along the faults. This study resulted in the precise descriptions of the features attesting CO2-enriched fluid circulation by a characterization of their relationship and architecture at the outcrop scale. These features are witnesses of a large range of circulation/sealing mechanisms, as well as changes in fluid chemistry and thermodynamic state of the system, providing evidence for (i) the evolution of the fluid through a pathway from depth to the surface and (ii) different cycles of fault opening and sealing. Large circulation events linked with fault opening/sealing are observed and calibrated in nature with Millennial circulation and sealing time-lapses. Numerical modelling indicates that such sealing time-scale can be explained by the introduction of a fault sealing factor that allows modifying permeability with time and that is calibrated by the natural observations. (C) 2015 Elsevier B.V. All rights reserved.
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Gainsforth Z, Butterworth AL, Stodolna J, Westphal AJ, Huss GR, Nagashima K, Ogliore R, Brownlee DE, Joswiak D, Tyliszczak T, Simionovici AS (2015) Constraints on the formation environment of two chondrule-like igneous particles from comet 81P/Wild 2. Meteoritics & Planetary Science 50(5):976–1004
Résumé: Using chemical and petrologic evidence and modeling, we deduce that two chondrule-like particles named Iris and Callie, from Stardust cometary track C2052,12,74, formed in an environment very similar to that seen for type II chondrules in meteorites. Iris was heated near liquidus, equilibrated, and cooled at <= 100 degrees C h(-1) and within approximate to 2 log units of the IW buffer with a high partial pressure of Na such as would be present with dust enrichments of approximate to 10(3). There was no detectable metamorphic, nebular, or aqueous alteration. In previous work, Ogliore et al. (2012) reported that Iris formed late, >3 Myr after CAIs, assuming Al-26 was homogenously distributed, and was rich in heavy oxygen. Iris may be similar to assemblages found only in interplanetary dust particles and Stardust cometary samples called Kool particles. Callie is chemically and isotopically very similar, but not identical to Iris.
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Gao L, Brossier R, Pajot B, Tago J, Virieux J (2015) An immersed free-surface boundary treatment for seismic wave simulation. Geophysics 80(5):T193–T209
Résumé: Finite-difference methods are popular for wave simulation within the seismic exploration community, thanks to their efficiency. However, difficulties arise when encountering complex topography due to the regular grid pattern of the finitedifference schemes. Despite alternatives that can handle the free surface with little effort, such as the spectral element or discontinuous Galerkin's methods, incorporating a free-surface boundary condition within the finite-difference framework is still appealing, even at the cost of extra algorithm complexity and stronger requirement of computational resources. We present a free-surface boundary treatment within the finite-difference framework, belonging to the family of the immersed-boundary methods. Inherently, the presented boundary treatment is separated from the rest of the wave simulation, which makes it easy to be integrated in existing finite-difference codes. Specifically, we construct an extrapolation operator for each grid point above the free surface, if requested by the finite-difference stencil, to estimate its fictitious wavefield value at each time step. These operators are constructed only once and remain unchanged for all the time steps and source locations. The memory requirement of these operators is significant. Fortunately, grouping together multiple simulations concerning different source locations makes it possible to dilute the memory burden to a negligible level. Additionally, applying these operators incurs numerical noise, which may lead to long time instabilities. In such a scenario, additional numerical procedures, for instance, introducing artificial diffusion, are necessary to control the instability and obtain sensible simulation results. Successful applications of the presented boundary treatment to elastic-wave equations on domains with nontrivial topographies, in 2D and 3D, are presented. Robust and efficient numerical techniques to control high-frequency numerical noise remain to be investigated.
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Gardonio B, Marsan D, Lengline O, Enescu B, Bouchon M, Got J-L (2015) Changes in seismicity and stress loading on subduction faults in the Kanto region, Japan, 2011-2014. Journal Of Geophysical Research-Solid Earth 120(4):2616–2626
Résumé: Seismic activity has increased in the Kanto region, Japan, following the 2011 M9.0 Tohoku earthquake. We here reassess this increase up to June 2014, to show that normal, Omori-like relaxation characterizes the activity on crustal faults as well as on the Philippine Sea plate, but not on the deeper Pacific plate. There repeating earthquakes display a twofold rate of occurrence (still ongoing in June 2014) as compared to the pre-Tohoku rate, suggesting enhanced creep. We compute the Coulomb stress changes on the upper locked portion of the Philippine Sea plate, which last ruptured in 1923. We find that this fault was little affected by either the coseismic, the postseismic, the accelerated creep, or the 2011 Boso silent slip event.
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Gerault M, Husson L, Miller MS, Humphreys ED (2015) Flat-slab subduction, topography, and mantle dynamics in southwestern Mexico. Tectonics 34(9):1892–1909
Résumé: Topography above subduction zones arises from the isostatic contribution of crustal and lithospheric buoyancy, as well as the dynamic contribution from slab-driven mantle flow. We evaluate those effects in southwestern Mexico, where a segment of the Cocos slab subducts horizontally. The eastern part of the volcanic arc-the Trans-Mexican Volcanic Belt-stands at an average elevation of 2.3 km, nearly 1.3 km above the fore-arc. Lateral changes in bulk crustal density are relatively small, and seismic imaging shows that there is little variation in crustal thickness between these two regions. Thus, the elevation difference between the arc and the fore-arc should arise from differences in mantle properties. We present finite element models of flat-slab subduction that provide a simultaneous match to topography, plate velocities, and stress state in the overriding plate. We find that the dynamic effects are primarily controlled by the amount of coupling at the subduction interface and in the mantle wedge, the lack of slab anchoring into the lower mantle, and the absence of continental mantle lithosphere. With a mantle wedge and a subduction interface that are, respectively, 2 and 4 orders of magnitude weaker than the asthenosphere, the flat slab exerts a downward pull that can explain most of the elevation difference between the fore-arc and the arc. We infer that lateral viscosity variations play a significant role in shaping dynamic topography in complex tectonic settings and that sublithospheric dynamics can influence the topography at wavelengths that are significantly shorter than previously recognized.
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Gillet N, Barrois O, Finlay CC (2015) Stochastic forecasting of the geomagnetic field from the COV-OBS.x1 geomagnetic field model, and candidate models for IGRF-12. Earth Planets And Space 67:1–14
Résumé: We present the geomagnetic field model COV-OBS.x1, covering 1840 to 2020, from which have been derived candidate models for the IGRF-12. Towards the most recent epochs, it is primarily constrained by first differences of observatory annual means and measurements from the Oersted, Champ, and Swarm satellite missions. Stochastic information derived from the temporal spectra of geomagnetic series is used to construct the a priori model covariance matrix that complements the constraint brought by the data. This approach makes it possible the use of a posteriori model errors, for instance, to measure the 'observations' uncertainties in data assimilation schemes for the study of the outer core dynamics. We also present and illustrate a stochastic algorithm designed to forecast the geomagnetic field. The radial field at the outer core surface is advected by core motions governed by an auto-regressive process of order 1. This particular choice is motivated by the slope observed for the power spectral density of geomagnetic series. Accounting for time-correlated model errors (subgrid processes associated with the unresolved magnetic field) is made possible thanks to the use of an augmented state ensemble Kalman filter algorithm. We show that the envelope of forecasts includes the observed secular variation of the geomagnetic field over 5-year intervals, even in the case of rapid changes. In a purpose of testing hypotheses about the core dynamics, this prototype method could be implemented to build the 'state zero' of the ability to forecast the geomagnetic field, by measuring what can be predicted when no deterministic physics is incorporated into the dynamical model.
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Gillet N, Jault D, Finlay CC (2015) Planetary gyre, time-dependent eddies, torsional waves, and equatorial jets at the Earth's core surface. Journal Of Geophysical Research-Solid Earth 120(6):3991–4013
Résumé: We report a calculation of time-dependent quasi-geostrophic core flows for 1940-2010. Inverting recursively for an ensemble of solutions, we evaluate the main source of uncertainties, namely, the model errors arising from interactions between unresolved core surface motions and magnetic fields. Temporal correlations of these uncertainties are accounted for. The covariance matrix for the flow coefficients is also obtained recursively from the dispersion of an ensemble of solutions. Maps of the flow at the core surface show, upon a planetary-scale gyre, time-dependent large-scale eddies at midlatitudes, and vigorous azimuthal jets in the equatorial belt. The stationary part of the flow predominates on all the spatial scales that we can resolve. We retrieve torsional waves that explain the length-of-day changes at 4 to 9.5years periods. These waves may be triggered by the nonlinear interaction between the magnetic field and subdecadal nonzonal motions within the fluid outer core. Both the zonal and the more energetic nonzonal interannual motions were particularly intense close to the equator (below 10 latitude) between 1995 and 2010. We revise down the amplitude of the decade fluctuations of the planetary-scale circulation and find that electromagnetic core-mantle coupling is not the main mechanism for angular momentum exchanges on decadal time scales if mantle conductance is 3 x 10(8)S or lower.
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Glotzbach C, Braun J, van der Beek P (2015) A Fourier approach for estimating and correcting the topographic perturbation of low-temperature thermochronological data. Tectonophysics 649:115–129
Résumé: Thermochronology is a unique tool to reconstruct the long-term exhumation history of outcropping rocks. Pronounced (palaeo-) topography can markedly perturb near-surface isotherms, which can result in erroneous exhumation histories derived from age-elevation relationships but also offers the possibility to reconstruct palaeo-topography. Here we use a synthetic dataset to illustrate the complex non-linear relationships between the degree of topographic perturbation of thermochronological ages on one hand, and exhumation rate, geothermal gradient, and topographic wavelength and relief on the other. The dataset reveals that, in theory, relief changes can be retrieved for wavelengths as low as 5 km, and wavelength changes are possible to detect for relief as low as 0.5 km. In addition, the data attest that even in regions characterised by very slow exhumation rates (e.g. 0.03 km/Ma), changes in palaeo-topography can be successfully retrieved. Coupling of this dataset with a Fast Fourier Transform (FFT) algorithm to decompose complex 2D topography into sinusoidal functions allows a rapid and accurate estimation of the topographic perturbation and resulting thermochronological ages assuming steady-state exhumation. This coupled method was successfully implemented to (i) predict most promising sample sites for the estimation of palaeo-topography and (ii) correct exhumation rates derived from non-vertical age-elevation profiles. (C) 2015 Elsevier B.V. All rights reserved.
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Gnos E, Janots E, Berger A, Whitehouse M, Walter F, Pettke T, Bergemann C (2015) Age of cleft monazites in the eastern Tauern Window: constraints on crystallization conditions of hydrothermal monazite. Swiss Journal Of Geosciences 108(1):55–74
Résumé: Monazite-bearing Alpine clefts located in the Sonnblick region of the eastern Tauern Window, Austria, are oriented perpendicular to the foliation and lineation. Ion probe (SIMS) Th-Pb and U-Pb dating of four cleft monazites yields crystallization ages of different growth domains and aggregate regions ranging from 18.99 +/- A 0.51 to 15.00 +/- A 0.51 Ma. The crystallization ages obtained are overlapping or slightly younger than zircon fission track ages but older than zircon (U-Th)/He cooling ages from the same area. This constrains cleft monazite crystallization in this area to similar to 300-200 A degrees C. LA-ICP-MS data of dated hydrothermal monazites indicate that in graphite-bearing, reduced host lithologies, cleft monazite is poor in As and has higher La/Yb values and U concentrations, whereas in oxidised host rocks opposite trends are observed. Monazites show negative Eu anomalies and variable La/Yb values ranging from 520 to 6050. The positive correlation between Ca and Sr concentration indicates dissolution of plagioclase or carbonates as the source of these elements. The data show that early exhumation and cleft formation in the Tauern is related to metamorphic dome formation caused by the collision of the Adriatic with the European plate and that monazite crystallization in the clefts occurred later. Our data also demonstrate that hydrothermal monazite ages offer great potential in helping to constrain the chronology of exhumation in collisional orogens.
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Grangeon S, Fernandez-Martinez A, Warmont F, Gloter A, Marty N, Poulain A, Lanson B (2015) Cryptomelane formation from nanocrystalline vernadite precursor: a high energy X-ray scattering and transmission electron microscopy perspective on reaction mechanisms. Geochemical Transactions 16
Résumé: Background: Vernadite is a nanocrystalline and turbostratic phyllomanganate which is ubiquitous in the environment. Its layers are built of (MnO6)(8-) octahedra connected through their edges and frequently contain vacancies and (or) isomorphic substitutions. Both create a layer charge deficit that can exceed 1 valence unit per layer octahedron and thus induces a strong chemical reactivity. In addition, vernadite has a high affinity for many trace elements (e.g., Co, Ni, and Zn) and possesses a redox potential that allows for the oxidation of redox-sensitive elements (e.g., As, Cr, Tl). As a result, vernadite acts as a sink for many trace metal elements. In the environment, vernadite is often found associated with tectomanganates (e.g., todorokite and cryptomelane) of which it is thought to be the precursor. The transformation mechanism is not yet fully understood however and the fate of metals initially contained in vernadite structure during this transformation is still debated. In the present work, the transformation of synthetic vernadite (delta-MnO2) to synthetic cryptomelane under conditions analogous to those prevailing in soils (dry state, room temperature and ambient pressure, in the dark) and over a time scale of similar to 10 years was monitored using high-energy X-ray scattering (with both Bragg-rod and pair distribution function formalisms) and transmission electron microscopy. Results: Migration of Mn3+ from layer to interlayer to release strains and their subsequent sorption above newly formed vacancy in a triple-corner sharing configuration initiate the reaction. Reaction proceeds with preferential growth to form needle-like crystals that subsequently aggregate. Finally, the resulting lath-shaped crystals stack, with n x 120 degrees (n = 1 or 2) rotations between crystals. Resulting cryptomelane crystal sizes are similar to 50-150 nm in the ab plane and similar to 10-50 nm along c*, that is a tenfold increase compared to fresh samples. Conclusion: The presently observed transformation mechanism is analogous to that observed in other studies that used higher temperatures and (or) pressure, and resulting tectomanganate crystals have a number of morphological characteristics similar to natural ones. This pleads for the relevance of the proposed mechanism to environmental conditions.
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Gratier J-P, Noiriel C, Renard F (2015) Experimental evidence for rock layering development by pressure solution. Geology 43(10):871–874
Résumé: Natural deformation of rocks is commonly associated with development of mineralogical layering, leading to irreversible transformations of their microstructure. The mechanisms of such chemical differentiation processes during diagenesis, tectonics, metamorphism, or fault differentiation remain poorly understood, as they are difficult to reproduce experimentally due to the very slow kinetics involved. This paper shows that development of differentiated layering, similar to that observed in natural deformation, is stress driven and can be obtained from indenter experiments. Samples of (1) gypsum plaster mixed with clay, and (2) natural diatomite loosely interbedded with volcanic ash, saturated with aqueous solutions in equilibrium, were subjected to loading for several months at 40 degrees C and 150 degrees C, respectively. X-ray microtomography and scanning electron microscopy observations show that layering develops by a self-organized pressure solution process. Stress-driven dissolution of the soluble minerals (either gypsum or silica) is initiated in the areas initially richer in insoluble species (clay or volcanic ash), as diffusive mass transfer along the interface between soluble and insoluble minerals is much faster than along the healed boundaries of the soluble minerals. The passive concentration of the insoluble minerals amplifies the dissolution along layers oriented perpendicularly to the maximum compressive stress. Conversely, in areas with an initial low content of insoluble minerals and clustered soluble minerals, dissolution is slower. Consequently, these areas are less deformed; they host the re-deposition of the soluble species and act as rigid objects that concentrate both stress and dissolution near their boundaries, thus amplifying the differentiation and the development of layered microstructures.
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Guilhem A, Walter F (2015) Full, constrained and stochastic source inversions support evidence for volumetric changes during the Basel earthquake sequence. Swiss Journal Of Geosciences 108(2-3):361–377
Résumé: Co-seismic volumetric changes are often interpreted as tensile fracturing in response to fluid injection during geothermal reservoir stimulation. Such volumetric changes manifest themselves as isotropic moment tensor components, which may thus constitute a measure for hydraulic stimulation efficiency. Recent analyses found significant isotropic moments of M2+ earthquakes during the 2006 hydraulic stimulation of a geothermal reservoir in Basel, Switzerland. The results contradicted first-motion focal mechanisms, which are in close agreement with shear sources without volumetric changes. Here we revisit the magnitude 1.7+ Basel events with full and stochastic moment tensor inversions in order to provide additional and/or supporting evidences for the occurrence of volumetric sources, if any. We furthermore apply purely deviatoric, and superimposed tensile and shear fault mechanisms, which we believe are meaningful constraints for fluid-induced earthquakes. As a result, we only find a single earthquake with statistically significant volumetric faulting. Spatial and temporal patterns of fluid-induced sources therefore have to be taken as indicative only, even though they suggest a clear relationship between fluid injections and fault mechanisms. On the other hand, we confirm that most inverted moment tensors (including the statistically significant one) show some inconsistencies with first motion focal mechanisms. We suggest that this is a manifestation of a more complicated fault geometry, which none of our moment tensor constraints can describe.
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Guillon H, Mugnier J-L, Buoncristiani J-F, Carcaillet J, Godon C, Prud'homme C, van der Beek P, Vassallo R (2015) Improved discrimination of subglacial and periglacial erosion using Be-10 concentration measurements in subglacial and supraglacial sediment load of the Bossons glacier (Mont Blanc massif, France). Earth Surface Processes And Landforms 40(9):1202–1215
Résumé: Deciphering the complex interplays between climate, uplift and erosion is not straightforward and estimating present-day erosion rates can provide useful insights. Glaciers are thought to be powerful erosional agents, but most published glacial' erosion rates combine periglacial, subglacial and proglacial erosion processes. Within a glaciated catchment, sediments found in subglacial streams originate either from glacial erosion of substratum or from the rock walls above the glacier that contribute to the supraglacial load. Terrestrial cosmogenic nuclides (TCN) are produced by interactions between cosmic ray particles and element targets at the surface of the Earth, but their concentration becomes negligible under 15 m of ice. Measuring TCN concentrations in quartz sand sampled in subglacial streams and in supraglacial channels is statistically compliant with stochastic processes (e.g. rockfalls) and may be used to discriminate subglacial and periglacial erosion. Results for two subglacial streams of the Bossons glacier (Mont Blanc massif, France) show that the proportion of sediments originating from glacially eroded bedrock is not constant: it varies from 50% to 90% (n = 6). The difference between the two streams is probably linked to the presence or absence of supraglacial channels and sinkholes, which are common features of alpine glaciers. Therefore, most of the published mean catchment glacial erosion rates should not be directly interpreted as subglacial erosion rates. In the case of catchments with efficient periglacial erosion and particularly rockfalls, the proportion of sediments in the subglacial stream originating from the supraglacial load could be considerable and the subglacial erosion rate overestimated. Here, we estimate warm-based subglacial and periglacial erosion rates to be of the same order of magnitude: 0.39 +/- 0.33 and 0.29 +/- 0.17 mm a(-1), respectively. Copyright (c) 2015John Wiley & Sons, Ltd.
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Guillot S, Garcon M, Weinman B, Gajurel A, Tisserand D, France-Lanord C, van Geen A, Chakraborty S, Huyghe P, Upreti BN, Charlet L (2015) Origin of arsenic in Late Pleistocene to Holocene sediments in the Nawalparasi district (Terai, Nepal). Environmental Earth Sciences 74(3):2571–2593
Résumé: A sedimentological and geochemical study was carried out to explore the origin of arsenic contamination in sediments in Nawalparasi district, in the western Terai of Nepal. The investigation tools include major, trace and rare earth element analyses of core sediments, as well as C-14 datings, and O, C isotopic analyses on mollusk shells. The results show that black schists from the Lesser Himalaya highly contributed to the detrital input in Parasi during the Pleistocene-Holocene transition because of focused erosion related to rapid uplift and high rainfall along the Main Central Thrust zone. In addition, aquifer silts, sands, and most of the brown clays underwent a certain degree of chemical weathering and physical reworking, and show possible inputs from the Siwaliks during the Late Holocene. A possible correlation between late Quaternary climate regimes and the concentration of arsenic in sediments is suspected, with arsenic preferentially concentrated during the drier periods of the last 25 kyr BP. The process of arsenic eluviations in sandy and silty sediments can explain the lower arsenic concentrations in sediments during humid periods. During the drier periods, seasonal precipitation was smaller and temperature was lower, leading to wet (less evaporative) soils in swampy environments. This environment favoured the development of aquatic plants and bacteria growing within in the moist land areas, enhancing the strong weathering of initially suspended load particles (micas and clays), which were preferentially deposited in quiet hydraulic environments. These sorting and weathering processes presumably allowed the arsenic to be concentrated in the finest sediment fraction.
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Guillot S, Schwartz S, Reynard B, Agard P, Prigent C (2015) Tectonic significance of serpentinites. Tectonophysics 646:1–19
Résumé: At plate boundaries, where deformation is localized along centimetre-to kilometre-scale shear zones, the influence of serpentinite on tectonic processes is linked to its unique rheological properties. In this paper we review the physical properties of serpentinites and their role in tectonic processes. At the ocean-continent transition, serpentinization weakens the upper mantle layer, promoting strain localization and allowing the normal faults in the distal margin to root at low angle. Similarly, at slow to ultra-slow spreading ridges, serpentinite is potentially very abundant at the seafloor and locally associated with domal structures. Extensional deformation is localized in a similar to 100 m thick shear zone at the footwall of detachment zones dominated by serpentine derived minerals. Within subduction zone, the depth of decoupling between the mantle wedge and the subducting slab corresponds to the stability depth of serpentine weak mineral. Dehydration of serpentine has also been hypothesized to play an important role in the origin of double seismic zones, however the exact mechanism through which dehydration promotes seismicity remains a matter of debate. During exhumation of high-pressure or ultrahigh-pressure rocks, the opposite trajectories of exhumation and subduction require a decoupling zone within the subducting slab. A serpentinized layer has the potential to become a decoupling zone between the oceanic crust and underlying lithosphere. The buoyancy of serpentinite also likely contributes to eclogite exhumation. Finally, along major strike-slip faults, serpentinites have been associated with fault creep, as well as low fault strength. The presence of serpentinite blocks along creeping segments of active faults worldwide is therefore likely to originate from fluids deriving from the progressive dehydration of the mantle wedge that move such bodies upward. (C) 2015 Elsevier B.V. All rights reserved.
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Gurioli L, Andronico D, Bachelery P, Balcone-Boissard H, Battaglia J, Boudon G, Burgisser A, Burton MR, Cashman K, Cichy S, Cioni R, Di Muro A, Dominguez L, D'Oriano C, Druitt T, Harris AJL, Hort M, Kelfoun K, Komorowski JC, Kueppers U, Le Pennec L, Menand T, Paris R, Pioli L, Pistolesi M, Polacci M, Pompilio M, Ripepe M, Roche O, Rose-Koga E, Rust A, Schiavi F, Scharff L, Sulpizio R, Taddeucci J, Thordarson T (2015) MeMoVolc consensual document: a review of cross-disciplinary approaches to characterizing small explosive magmatic eruptions. Bulletin Of Volcanology 77(6)
Résumé: A workshop entitled “Tracking and understanding volcanic emissions through cross-disciplinary integration: a textural working group” was held at the Universite Blaise Pascal (Clermont-Ferrand, France) on the 6-7 November 2012. This workshop was supported by the European Science Foundation (ESF). The main objective of the workshop was to establish an initial advisory group to begin to define measurements, methods, formats and standards to be applied in the integration of geophysical, physical and textural data collected during volcanic eruptions. This would homogenize procedures to be applied and integrated during both past and ongoing events. The workshop comprised a total of 35 scientists from six countries (France, Italy, Great Britain, Germany, Switzerland and Iceland). The four main aims were to discuss and define: standards, precision and measurement protocols for textural analysis; identification of textural, field deposit, chemistry and geophysical parameters that can best be measured and combined; the best delivery formats so that data can be shared between and easily used by different groups; and multi-disciplinary sampling and measurement routines currently used and measurement standards applied, by each community. The group agreed that community-wide, cross-disciplinary integration, centred on defining those measurements and formats that can be best combined, is an attainable and key global focus. Consequently, we prepared this paper to present our initial conclusions and recommendations, along with a review of the current state of the art in this field that supported our discussions.
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Gurioli L, Andronico D, Bachelery P, Balcone-Boissard H, Battaglia J, Boudon G, Burgisser A, Burton MR, Cashman K, Cichy S, Cioni R, Di Muro A, Dominguez L, D'Oriano C, Druitt T, Harris AJL, Hort M, Kelfoun K, Komorowski JC, Kueppers U, Le Pennec L, Menand T, Paris R, Pioli L, Pistolesi M, Polacci M, Pompilio M, Ripepe M, Roche O, Rose-Koga E, Rust A, Schiavi F, Scharff L, Sulpizio R, Taddeucci J, Thordarson T (2015) MeMoVolc consensual document: a review of cross-disciplinary approaches to characterizing small explosive magmatic eruptions. Bulletin Of Volcanology 77(6)
Résumé: A workshop entitled “Tracking and understanding volcanic emissions through cross-disciplinary integration: a textural working group” was held at the Universite Blaise Pascal (Clermont-Ferrand, France) on the 6-7 November 2012. This workshop was supported by the European Science Foundation (ESF). The main objective of the workshop was to establish an initial advisory group to begin to define measurements, methods, formats and standards to be applied in the integration of geophysical, physical and textural data collected during volcanic eruptions. This would homogenize procedures to be applied and integrated during both past and ongoing events. The workshop comprised a total of 35 scientists from six countries (France, Italy, Great Britain, Germany, Switzerland and Iceland). The four main aims were to discuss and define: standards, precision and measurement protocols for textural analysis; identification of textural, field deposit, chemistry and geophysical parameters that can best be measured and combined; the best delivery formats so that data can be shared between and easily used by different groups; and multi-disciplinary sampling and measurement routines currently used and measurement standards applied, by each community. The group agreed that community-wide, cross-disciplinary integration, centred on defining those measurements and formats that can be best combined, is an attainable and key global focus. Consequently, we prepared this paper to present our initial conclusions and recommendations, along with a review of the current state of the art in this field that supported our discussions.
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Guyonnet-Benaize C, Lamarche J, Hollender F, Viseur S, Muench P, Borgomano J (2015) Three-dimensional structural modeling of an active fault zone based on complex outcrop and subsurface data: The Middle Durance Fault Zone inherited from polyphase Meso-Cenozoic tectonics (southeastern France). Tectonics 34(2):265–289
Résumé: The objective of this study was to realize a three-dimensional (3-D) geological model of the deep basin structure of the Middle Durance region (of folds and faults) by integration of geological and geophysical data, and to evaluate its fault geometry and tectonic history. All of the available geophysical and geological data were compiled in three dimensions using the gOcad geomodeler. The geological and geophysical data were used to build a 3-D geological model of the Middle Durance region. The data on the 3-D geometry of fault surfaces and stratigraphic horizons and the thickness maps of the main stratigraphic units are supported by the 3-D geological model. We show that the Middle Durance Fault cannot be interpreted as a single fault plane that affected the entire Meso-Cenozoic sedimentary layers and the Paleozoic basement but as a listric segmented faulting system in sedimentary layers, rooted in Triassic evaporites and a normal block faulting system in the basement. This decoupling level in the Triassic layers reveals thin-skin deformation, formed by strong mechanical decoupling between the Mesozoic sedimentary cover and the Paleozoic basement. This study also confirms that the Provence geological structure has resulted mainly from Pyrenean deformation, which was partly reactivated by Alpine deformation. We demonstrate that the Middle Durance Fault Zone is a transfer fault that accommodates deformation of the sedimentary filling of the South-East Basin through modified fold geometry over a zone of 7km to 8km around the main segment of the fault zone.
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Heimbuerger L-E, Sonke JE, Cossa D, Point D, Lagane C, Laffont L, Galfond BT, Nicolaus M, Rabe B, van der Loeff MR (2015) Shallow methylmercury production in the marginal sea ice zone of the central Arctic Ocean. Scientific Reports 5
Résumé: Methylmercury (MeHg) is a neurotoxic compound that threatens wildlife and human health across the Arctic region. Though much is known about the source and dynamics of its inorganic mercury (Hg) precursor, the exact origin of the high MeHg concentrations in Arctic biota remains uncertain. Arctic coastal sediments, coastal marine waters and surface snow are known sites for MeHg production. Observations on marine Hg dynamics, however, have been restricted to the Canadian Archipelago and the Beaufort Sea (<79 degrees N). Here we present the first central Arctic Ocean (79-90 degrees N) profiles for total mercury (tHg) and MeHg. We find elevated tHg and MeHg concentrations in the marginal sea ice zone (81-85 degrees N). Similar to other open ocean basins, Arctic MeHg concentration maxima also occur in the pycnocline waters, but at much shallower depths (150-200 m). The shallow MeHg maxima just below the productive surface layer possibly result in enhanced biological uptake at the base of the Arctic marine food web and may explain the elevated MeHg concentrations in Arctic biota. We suggest that Arctic warming, through thinning sea ice, extension of the seasonal sea ice zone, intensified surface ocean stratification and shifts in plankton ecodynamics, will likely lead to higher marine MeHg production.
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Hellmann R, Cotte S, Cadel E, Malladi S, Karlsson LS, Lozano-Perez S, Cabie M, Seyeux A (2015) Nanometre-scale evidence for interfacial dissolution-reprecipitation control of silicate glass corrosion. Nature Materials 14(3):307–311
Résumé: Silicate glasses are durable solids, and yet they are chemically unstable in contact with aqueous fluids-this has important implications for numerous industrial applications related to the corrosion resistance of glasses(1), or the biogeochemical weathering of volcanic glasses in seawater(2). The aqueous dissolution of synthetic and natural glasses results in the formation of a hydrated, cation-depleted near-surface alteration zone(1,3-8) and, depending on alteration conditions, secondary crystalline phases on the surface(1,2,4-7). The long-standing accepted model of glass corrosion is based on diffusion-coupled hydration and selective cation release, producing a surface-altered zone(2,5-8). However, using a combination of advanced atomic-resolution analytical techniques, our data for the first time reveal that the structural and chemical interface between the pristine glass and altered zone is always extremely sharp, with gradients in the nanometre to sub-nanometre range. These findings support a new corrosion mechanism, interfacial dissolution-reprecipitation. Moreover, they also highlight the importance of using analytical methods with very high spatial and mass resolution for deciphering the nanometre-scale processes controlling corrosion. Our findings provide evidence that interfacial dissolution-reprecipitation may be a universal reaction mechanism that controls both silicate glass corrosion and mineral weathering(9-13).
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Helmstetter A, Moreau L, Nicolas B, Comon P, Gay M (2015) Intermediate-depth icequakes and harmonic tremor in an Alpine glacier (Glacier d'Argentiere, France): Evidence for hydraulic fracturing? Journal Of Geophysical Research-Earth Surface 120(3):402–416
Résumé: We detected several thousand deep englacial icequakes on Glacier d'Argentiere (Mont-Blanc massif) between 30 March and 3 May 2012. These events have been classified in eight clusters. Inside each cluster, the waveforms are similar for P waves and S waves, although the time delay between the P waves and the S waves vary by up to 0.03 s, indicating an extended source area. Although these events were recorded by a single accelerometer, they were roughly located using a polarization analysis. The deepest events were located at a depth of 130 m, 60 m above the ice/bed interface. The clusters are separated in space. The largest cluster extends over about 100 m. For this cluster, the strike of the rupture plane is nearly parallel to the direction of the open crevasses, and the dip angle is 56 degrees. Deep icequakes occur in bursts of activity that last for a few hours and are separated by quiet periods. Many events occurred on 28 and 29 April 2012, during the warmest days, when snowmelting was likely important. The distributions of interevent times and peak amplitudes obey power laws as also observed for earthquakes, but with larger exponents. The polarity of the P waves for all of the events is consistent with tensile faulting. Finally, between 25 April and 3 May, we observed a gliding harmonic tremor with a fundamental resonance frequency that varied between 30 Hz and 38 Hz, with additional higher-frequency harmonics. During this time we also observed shallow hybrid events with high-frequency onsets and a monochromatic coda. These events might be produced by the propagation of fractures and the subsequent flow of water into the fracture. The strongest resonance was observed just after a strong burst of deep icequakes and during an unusually warm period when the snow height decreased by 60 cm in 1 week. The resonance frequency shows a succession of several sharp decreases and phases of progressive increases. One of the strongest negative steps of the resonance frequency on 28 April coincides with a burst of deep icequakes. These events appear to be associated with the propagation of fractures, which can explain the decrease in the resonance frequency. Finally, we observed an acceleration of glacier flow on 29 April, suggesting that meltwater had reached the ice/bed interface. These observations suggest that deep icequakes are due to hydraulic fracturing and that they can be used to track fluid flow inside glaciers.
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Helmstetter A, Nicolas B, Comon P, Gay M (2015) Basal icequakes recorded beneath an Alpine glacier (Glacier d'Argentiere, Mont Blanc, France): Evidence for stick-slip motion? Journal Of Geophysical Research-Earth Surface 120(3):379–401
Résumé: While basal icequakes associated with glacier motion have been detected under Antarctica for several decades, there remains very little evidence of stick-slip motion for Alpine glaciers. Here we analyzed 2357 basal icequakes that were recorded at Glacier d'Argentiere (Mont-Blanc Massif) between February and November of 2012 and that are likely to be associated with basal sliding. These events have been classified into 18 multiplets, based on their waveforms. The strong similarity of the waveforms within each multiplet suggests an isolated repeating source. Despite this similarity, the peak amplitude within each multiplet varies gradually in time, by up to a factor of 18. The distribution of these events in time is relatively complex. For long time scales, we observe progressive variations in the amplitudes of events within each multiplet. For intermediate time scales (hours), the events occur regularly in time, with typical return times of several minutes up to several hours. For short time scales (from 0.01 to 100s), the largest multiplet shows clustering in time, with a power law distribution of the interevent times. The location of these events and their focal mechanisms are not well constrained, because most of these events were detected by a single seismometer. Nevertheless, the locations can be estimated with an accuracy of a few tens of meters using a polarization analysis. The estimated average depth of the basal events is 179m, which is in good agreement with the estimated glacier thickness. The relative changes in distance between the source and the sensor can be measured accurately by correlating separately the P wave and S wave parts of the seismograms of each event with the template waveforms, which are obtained by averaging the signals within each multiplet. We observed small variations in the times between the P wave and the S wave of up to 0.6ms over 50days. These variations cannot be explained by displacement of the sensor with respect to the glacier but might be due to small changes in the seismic wave velocities with time. Finally, we found using numerical simulations that the observed signals are better explained by a horizontal shear fault with slip parallel to the glacier flow than by a tensile fault. These results suggest that the basal events are associated with stick-slip motion of the glacier over rough bedrock. The rupture length and the slip are difficult to estimate. Nonetheless, the rupture length is likely to be of the order of meters, and the total seismic slip accumulated over one day might be as large as the glacier motion during the most active bursts.
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Hibert C, Mangeney A, Polacci M, Di Muro A, Vergniolle S, Ferrazzini V, Peltier A, Taisne B, Burton M, Dewez T, Grandjean G, Dupont A, Staudacher T, Brenguier F, Kowalski P, Boissier P, Catherine P, Lauret F (2015) Toward continuous quantification of lava extrusion rate: Results from the multidisciplinary analysis of the 2 January 2010 eruption of Piton de la Fournaise volcano, La Reunion. Journal Of Geophysical Research-Solid Earth 120(5):3026–3047
Résumé: The dynamics of the 2-12 January 2010 effusive eruption at Piton de la Fournaise volcano were examined through seismic and infrasound records, time-lapse photography, SO2 flux measurements, deformation data, and direct observations. Digital elevation models were constructed for four periods of the eruption, thus providing an assessment of the temporal evolution of the morphology, the volume and the extrusion rate of the lava flow. These data were compared to the continuous recording of the seismic and infrasonic waves, and a linear relationship was found between the seismic energy of the tremor and the lava extrusion rate. This relationship is supported by data from three other summit eruptions of Piton de la Fournaise and gives total volume and average lava extrusion rate in good agreement with previous studies. We can therefore provide an estimate of the lava extrusion rate for the January 2010 eruption with a very high temporal resolution. We found an average lava extrusion rate of 2.4m(3)s(-1) with a peak of 106.6m(3)s(-1) during the initial lava fountaining phase. We use the inferred average lava extrusion rate during the lava fountaining phase (30.23m(3)s(-1)) to estimate the value of the initial overpressure in the magma reservoir, which we found to range from 3.7x10(6)Pa to 5.9x10(6)Pa. Finally, based on the estimated initial overpressure, the volume of magma expelled during the lava fountaining phase and geodetic data, we inferred the volume of the magma reservoir using a simple Mogi model, between 0.25 km(3) and 0.54 km(3), which is in good agreement with previous studies.
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Hillers G, Ben-Zion Y, Campillo M, Zigone D (2015) Seasonal variations of seismic velocities in the San Jacinto fault area observed with ambient seismic noise. Geophysical Journal International 202(2):920–932
Résumé: We observe seasonal seismic wave speed changes (dv/v) in the San Jacinto fault area and investigate several likely source mechanisms. Velocity variations are obtained from analysis of 6 yr data of vertical component seismic noise recorded by 10 surface and six borehole stations. We study the interrelation between dv/v records, frequency-dependent seismic noise properties, and nearby environmental data of wind speed, rain, ground water level, barometric pressure and atmospheric temperature. The results indicate peak-to-peak seasonal velocity variations of similar to 0.2 per cent in the 0.5-2 Hz frequency range, likely associated with genuine changes of rock properties rather than changes in the noise field. Phase measurements between dv/v and the various environmental data imply that the dominant source mechanism in the arid study area is thermoelastic strain induced by atmospheric temperature variations. The other considered environmental effects produce secondary variations that are superimposed on the thermal-based changes. More detailed work with longer data on the response of rocks to various known external loadings can help tracking the evolving stress and effective rheology at depth.
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Hillers G, Husen S, Obermann A, Planes T, Larose E, Campillo M (2015) Noise-based monitoring and imaging of aseismic transient deformation induced by the 2006 Basel reservoir stimulation. Geophysics 80(4):KS51–KS68
Résumé: We have analyzed the time-dependent properties of the ambient seismic wavefield between 0.1 and 8 Hz to detect, resolve, monitor, and image the deformation induced by the water injection associated with the stimulation of the 2006 Deep Heat Mining Project in the city of Basel, Switzerland. The application of passive methods allowed the detection of an aseismic transient of approximately 35 days' duration that began with the onset of the reservoir stimulation. Peak deformation was reached some 15 days after the bleed-off and after the induced seismicity ceased. We resolved a significant increase in seismic velocities and a simultaneous decorrelation of the noise correlation coda waveforms. The wavefield properties implied that the material response was monitored mainly in the sedimentary layer (<2.5 km) above the stimulated volume that was approximately 4.5 km deep. We inverted the velocity-change and decorrelation data to estimate the spatial distribution of the medium changes. The resulting images showed that the strong velocity variations and medium perturbations were generally colocated with the lateral distribution of the induced seismicity. Positive velocity changes and damage around the injection site indicated subsidence, settling, and compaction of the material overlying the stimulated volume. Our results demonstrate that noise-based analysis tools can provide important observables that are complementary to results obtained with standard microseismicity tools. Passive monitoring and imaging have the potential to mature into routinely applied observation techniques that support reservoir management in a variety of geotechnical contexts, such as for mining, fluid injection, hydraulic fracturing, nuclear waste management, and CO2 storage.
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Hillers G, Retailleau L, Campillo M, Inbal A, Ampuero J-P, Nishimura T (2015) In situ observations of velocity changes in response to tidal deformation from analysis of the high-frequency ambient wavefield. Journal Of Geophysical Research-Solid Earth 120(1):210–225
Résumé: We report systematic seismic velocity variations in response to tidal deformation. Measurements are made on correlation functions of the ambient seismic wavefield at 2-8 Hz recorded by a dense array at the site of the Pinon Flat Observatory, Southern California. The key observation is the dependence of the response on the component of wave motion and coda lapse time . Measurements on the vertical correlation component indicate reduced wave speeds during periods of volumetric compression, whereas data from horizontal components show the opposite behavior, compatible with previous observations. These effects are amplified by the directional sensitivities of the different surface wave types constituting the early coda of vertical and horizontal correlation components to the anisotropic behavior of the compliant layer. The decrease of the velocity (volumetric) strain sensitivity S with indicates that this response is constrained to shallow depths. The observed velocity dependence on strain implies nonlinear behavior, but conclusions regarding elasticity are more ambiguous. The anisotropic response is possibly associated with inelastic dilatancy of the unconsolidated, low-velocity material above the granitic basement. However, equal polarity of vertical component velocity changes and deformation in the vertical direction indicate that a nonlinear Poisson effect is similarly compatible with the observed response pattern. Peak relative velocity changes at small are 0.03%, which translates into an absolute velocity strain sensitivity of S approximate to 5 x 10(3) and a stress sensitivity of 0.5 MPa-1. The potentially evolving velocity strain sensitivity of crustal and fault zone materials can be studied with the method introduced here.
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Hort RD, Revil A, Munakata-Marr J, Mao D (2015) Evaluating the potential for quantitative monitoring of in situ chemical oxidation of aqueous-phase TCE using in-phase and quadrature electrical conductivity. Water Resources Research 51(7):5239–5259
Résumé: Electrical resistivity measurements can potentially be used to remotely monitor fate and transport of ionic oxidants such as permanganate (MnO4-) during in situ chemical oxidation (ISCO) of contaminants like trichloroethene (TCE). Time-lapse two-dimensional bulk conductivity and induced polarization surveys conducted during a sand tank ISCO simulation demonstrated that MnO4- plume movement could be monitored in a qualitative manner using bulk conductivity tomograms, although chargeability was below sensitivity limits. We also examined changes to in-phase and quadrature electrical conductivity resulting from ion injection, MnO2 and Cl- production, and pH change during TCE and humate oxidation by MnO4- in homogeneous aqueous solutions and saturated porous media samples. Data from the homogeneous samples demonstrated that inversion of the sand tank resistivity data using a common Tikhonov regularization approach was insufficient to recover an accurate conductivity distribution within the tank. While changes to in-phase conductivity could be successfully modeled, quadrature conductivity values could not be directly related to TCE oxidation product or MnO4- concentrations at frequencies consistent with field induced polarization surveys, limiting the utility of quadrature conductivity for monitoring ISCO.
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Huguet S, Isaure M-P, Bert V, Laboudigue A, Proux O, Flank A-M, Vantelon D, Sarret G (2015) Fate of cadmium in the rhizosphere of Arabidopsis halleri grown in a contaminated dredged sediment. Science Of The Total Environment 536:468–480
Résumé: In regions impacted by mining and smelting activities, dredged sediments are often contaminated with metals. Phytotechnologies could be used for their management, but more knowledge on the speciation of metals in the sediment and on their fate after colonization by plant roots is needed. This work was focused on a dredged sediment from the Scarpe river (North of France), contaminated with Zn and Cd. Zn, Cd hyperaccumulating plants Arabidopsis halleri from metallicolous and non-metallicolous origin were grown on the sediment for five months in a pot experiment. The nature and extent of the modifications in Cd speciation with or without plant were determined by electron microscopy, micro X-ray fluorescence and bulk and micro X-ray absorption spectroscopy. In addition, changes in Cd exchangeable and bioavailable pools were evaluated, and Cd content in leachates was measured. Finally, Cd plant uptake and plant growth parameters were monitored. In the original sediment, Cd was present as a mixed Zn, Cd, Fe sulfide. After five months, although pots still contained reduced sulfur, Cd-bearing sulfides were totally oxidized in vegetated pots, whereas a minor fraction (8%) was still present in non-vegetated ones. Secondary species included Cd bound to O-containing groups of organic matter and Cd phosphates. Cd exchangeability and bioavailability were relatively low and did not increase during changes in Cd speciation, suggesting that Cd released by sulfide oxidation was readily taken up with strong interactions with organic matter and phosphate ligands. Thus, the composition of the sediment, the oxic conditions and the rhizospheric activity (regardless of the plant origin) created favorable conditions for Cd stabilization. However, it should be kept in mind that returning to anoxic conditions may change Cd speciation, so the species formed cannot be considered as stable on the long term. (C) 2015 Elsevier B.V. All rights reserved.
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Humphreys MCS, Brooker RA, Fraser DG, Burgisser A, Mangan MT, McCammon C (2015) Coupled Interactions between Volatile Activity and Fe Oxidation State during Arc Crustal Processes. Journal Of Petrology 56(4):795–814
Résumé: Arc magmas erupted at the Earth's surface are commonly more oxidized than those produced at mid-ocean ridges. Possible explanations for this high oxidation state are that the transfer of fluids during the subduction process results in direct oxidation of the sub-arc mantle wedge, or that oxidation is caused by the effect of later crustal processes, including protracted fractionation and degassing of volatile-rich magmas. This study sets out to investigate the effect of disequilibrium crustal processes that may involve coupled changes in H2O content and Fe oxidation state, by examining the degassing and hydration of sulphur-free rhyolites. We show that experimentally hydrated melts record strong increases in Fe3+/Sigma Fe with increasing H2O concentration as a result of changes in water activity. This is relevant for the passage of H2O-undersaturated melts from the deep crust towards shallow crustal storage regions, and raises the possibility that vertical variations in fO(2) might develop within arc crust. Conversely, degassing experiments produce an increase in Fe3+/Sigma Fe with decreasing H2O concentration. In this case the oxidation is explained by loss of H-2 as well as H2O into bubbles during decompression, consistent with thermodynamic modelling, and is relevant for magmas undergoing shallow degassing en route to the surface. We discuss these results in the context of the possible controls on fO(2) during the generation, storage and ascent of magmas in arc settings, in particular considering the timescales of equilibration relative to observation as this affects the quality of the petrological record of magmatic fO(2).
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Husson L, Yamato P, Bezos A (2015) Ultraslow, slow, or fast spreading ridges: Arm wrestling between mantle convection and far-field tectonics. Earth And Planetary Science Letters 429:205–215
Résumé: Oceanic spreading rates are highly variable, and these variations are known to correlate to a variety of surface observables, like magmatic production, heat flow or bathymetry. This correlation lead to classify ridges into fast and slow spreading ridges, but also into the more peculiar ultraslow spreading regime. Here we explore the dynamic relationships between spreading ridges, plate tectonics and mantle flow. We first focus on the thermal signature of the mantle, that we infer from the global S-wave seismic tomography model of Debayle and Ricard (2012). We show that the thermal structure of ridges gradually departs from the half-space cooling model for slow, and above all ultraslow spreading ridges. We also infer that the sublithospheric mantle temperature decreases by more than 150 degrees C from fast to ultraslow spreading regimes. Both observations overall indicate that the mantle convection pattern is increasingly chaotic underneath slow and ultraslow spreading ridges. We suggest that this is due to far-field tectonics at the other ends of lithospheric plates: not only it modulates the spreading rates but it also alters the convection regime by obstructing the circulation of plates, which in turn modifies the surface kinematic conditions for the convecting mantle. We test this hypothesis using a thermo-mechanical model that represents a convection cell carrying a continental lithosphere atop. The continent gradually drifts away from the spreading ridge, from which the oceanic lithosphere grows and cools while the continent eventually collides at the opposite side. In turn, this event drastically modifies the upper kinematic condition for the convecting mantle that evolves from a mobile lid regime to an almost stagnant lid regime. Implications on spreading ridges are prominent: heat advection decreases with respect to thermal conduction, which causes the oceanic lithosphere to thicken faster; the oceanic plates get compressed and destabilized by a growing number of small scale transient plumes, which disrupt the structure of the oceanic lithospheres, lower the heat flow and may even starve ultraslow ridges from partial melting. It follows that the spreading rate of a modern ridge mirrors its status in the global plate tectonics framework within a unique breakup, drift, collision scenario, within the transition from mobile to stagnant lid, and that it is the same mechanism that build mountains at converging boundaries and control spreading rates. Oceanic ridges thus can be regarded as a sensor of the resisting rather than driving forces. Both the model and the seismic structure of the mantle underneath ridges reveal that the temperature variations are largest at shallow depths in the upper mantle, i.e. at the critical depth where the melt supply to the above ridges can be modulated, thereby also explaining why slow and ultraslow ridges are almost exclusively associated to cold mantle. It follows that the chemistry of oceanic ridge basalts may not strictly reveal the mantle potential temperature, but the variations in the sublithospheric temperature field. (C) 2015 Elsevier B.V. All rights
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Ikard SJ, Rittgers J, Revil A, Mooney MA (2015) Geophysical Investigation of Seepage Beneath an Earthen Dam. Groundwater 53(2):238–250
Résumé: A hydrogeophysical survey is performed at small earthen dam that overlies a confined aquifer. The structure of the dam has not shown evidence of anomalous seepage internally or through the foundation prior to the survey. However, the surface topography is mounded in a localized zone 150 m downstream, and groundwater discharges from this zone periodically when the reservoir storage is maximum. We use self-potential and electrical resistivity tomography surveys with seismic refraction tomography to (1) determine what underlying hydrogeologic factors, if any, have contributed to the successful long-term operation of the dam without apparent indicators of anomalous seepage through its core and foundation; and (2) investigate the hydraulic connection between the reservoir and the seepage zone to determine whether there exists a potential for this success to be undermined. Geophysical data are informed by hydraulic and geotechnical borehole data. Seismic refraction tomography is performed to determine the geometry of the phreatic surface. The hydro-stratigraphy is mapped with the resistivity data and groundwater flow patterns are determined with self-potential data. A self-potential model is constructed to represent a perpendicular profile extending out from the maximum cross-section of the dam, and self-potential data are inverted to recover the groundwater velocity field. The groundwater flow pattern through the aquifer is controlled by the bedrock topography and a preferential flow pathway exists beneath the dam. It corresponds to a sandy-gravel layer connecting the reservoir to the downstream seepage zone.
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Ilanko T, Oppenheimer C, Burgisser A, Kyle P (2015) Cyclic degassing of Erebus volcano, Antarctica. Bulletin Of Volcanology 77(6)
Résumé: Field observations have previously identified rapid cyclic changes in the behaviour of the lava lake of Erebus volcano. In order to understand more fully the nature and origins of these cycles, we present here a wavelet-based frequency analysis of time series measurements of gas emissions from the lava lake, obtained by open-path Fourier transform infrared spectroscopy. This reveals (i) a cyclic change in total gas column amount, a likely proxy for gas flux, with a period of about 10 min, and (ii) a similarly phased cyclic change in proportions of volcanic gases, which can be explained in terms of chemical equilibria and pressure-dependent solubilities. Notably, the wavelet analysis shows a persistent periodicity in the CO2/CO ratio and strong periodicity in H2O and SO2 degassing. The 'peaks' of the cycles, defined by maxima in H2O and SO2 column amounts, coincide with high CO2/CO ratios and proportionally smaller increases in column amounts of CO2, CO, and OCS. We interpret the cycles to arise from recharge of the lake by intermittent pulses of magma from shallow depths, which degas H2O at low pressure, combined with a background gas flux that is decoupled from this very shallow magma degassing.
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Imtiaz A, Causse M, Chaljub E, Cotton F (2015) Is Ground-Motion Variability Distance Dependent? Insight from Finite-Source Rupture Simulations. Bulletin Of The Seismological Society Of America 105(2a):950–962
Résumé: The ground-motion variability sigma is a fundamental component in probabilistic seismic-hazard assessment because it controls the hazard level at very low probabilities of exceedance. So far, most of the analyses based on empirical ground-motion prediction equations do not consider any distance dependency of sigma. This study aims to analyze the potential distance dependency of ground-motion variability, especially in the near-field region, where the variability is poorly constrained due to the lack of available records. We, therefore, investigate the distance dependency of sigma by performing numerical simulations of ground motion for some strike-slip events. Synthetic velocity seismograms (up to 3 Hz) have been generated from a suite of finite-source rupture models of past earthquakes. Green's functions were calculated for a 1D velocity structure using a discrete wavenumber technique (Bouchon, 1981). The within-event component of the ground-motion variability was then evaluated from the synthetic data as a function of distance. The simulations reveal that the within-event component of the ground motion shows a distance dependency, subject to the rupture type. For bilateral ruptures, the variability tends to increase with distance. On the contrary, in case of unilateral events, the variability decreases with distance.
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Isaure M-P, Huguet S, Meyer C-L, Castillo-Michel H, Testemale D, Vantelon D, Saumitou-Laprade P, Verbruggen N, Sarret G (2015) Evidence of various mechanisms of Cd sequestration in the hyperaccumulator Arabidopsis halleri, the non-accumulator Arabidopsis lyrata, and their progenies by combined synchrotron-based techniques. Journal Of Experimental Botany 66(11):3201–3214
Résumé: Arabidopsis halleri is a model plant for Zn and Cd hyperaccumulation. The objective of this study was to determine the relationship between the chemical forms of Cd, its distribution in leaves, and Cd accumulation and tolerance. An interspecific cross was carried out between A. halleri and the non-tolerant and non-hyperaccumulating relative A. lyrata providing progenies segregating for Cd tolerance and accumulation. Cd speciation and distribution were investigated using X-ray absorption spectroscopy and microfocused X-ray fluorescence. In A. lyrata and non-tolerant progenies, Cd was coordinated by S atoms only or with a small contribution of O groups. Interestingly, the proportion of O ligands increased in A. halleri and tolerant progenies, and they were predominant in most of them, while S ligands were still present. Therefore, the binding of Cd with O ligands was associated with Cd tolerance. In A. halleri, Cd was mainly located in the xylem, phloem, and mesophyll tissue, suggesting a reallocation process for Cd within the plant. The distribution of the metal at the cell level was further discussed. In A. lyrata, the vascular bundles were also Cd enriched, but the epidermis was richer in Cd as compared with the mesophyll. Cd was identified in trichomes of both species. This work demonstrated that both Cd speciation and localization were related to the tolerance character of the plant.
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Janots E, Bernier F, Brunet F, Munoz M, Trcera N, Berger A, Lanson M (2015) Ce(III) and Ce(IV) (re)distribution and fractionation in a laterite profile from Madagascar: Insights from in situ XANES spectroscopy at the Ce L-III-edge. Geochimica Et Cosmochimica Acta 153:134–148
Résumé: The distribution of trivalent and tetravalent cerium, Ce(III) and Ce(IV) respectively, in a lateritic profile from Madagascar, has been characterized by X-ray-absorption near-edge structure (XANES) spectroscopy at the Ce L-III-edge on the LUCIA beamline (SOLEIL synchrotron, France). XANES spectra were acquired on bulk-rock samples as well as on specific lateritic minerals or polymineral zones (in-situ measurements) of the tonalite bedrock and the three overlying weathered horizons (C-, B-and A-horizons). Geochemically, the bedrock, and the A-and C-horizons show similar rare earth element content (REE = 363-405 mg/kg). They also display the same positive Ce-anomaly (Ce-CN/Ce* = 1.12-1.45), which is therefore likely to be inherited from the bedrock. In the B-horizon, the higher REE content (REE = 2194 mg/kg) and the larger Ce-anomaly (Ce-CN/Ce* = 4.26) are consistent with an accumulation zone caused by the evaporation of groundwater during the dry season. There is a good agreement between the Ce(III)/Ce-total ratio (X-Ce(III)) deduced from the positive Ce-anomaly (bulk-rock geochemical data) and that derived from XANES spectroscopy on the same bulk-rock samples (BR-X-Ce(III)-XANES) in the bedrock, and the C-and B-horizons. In the A-horizon, XANES measurements on bulk rock and minerals revealed a higher BR-X-Ce(III)-XANES (up to 100%) compared to the X-Ce(III) deduced from geochemical data (X-Ce(III) = 79%). The preservation of a positive Ce-anomaly in the A-horizon suggests that the Ce mobilization and redistribution during weathering occurred with no significant Ce fractionation from other trivalent REE. Remarkably, the only investigated sample where cerianite is observed belongs to the B-horizon. Within this horizon, Ce oxidation state varies depending on the microstructural position (porosity, cracks, clay-rich groundmass). The highest Ce(IV) concentrations are measured in cerianite (and alumino-phosphates) localized in pores at the vicinity of Mn-rich domains (X-Ce(III)-XANES = 30-51%). Therefore, Ce fractionation from other REE is attributed to a Ce oxidation and precipitation potentially assisted by oxyhydroxide scavenging. In the C-horizon, Ce(III) and Ce(IV) are mainly distributed in REE-minerals of the rhabdophane group found in pores and cracks. The similarity between the Ce(III) proportion of rhabdophane grains (X-Ce(III)-XANES = 74-89%) with that of the bedrock (BR-X-Ce(III)-XANES = 79%) suggests no significant fractionation of Ce(III) and Ce(IV) between solution and mineral during the successive stages of primary REE-mineral alteration, transport in solution and secondary precipitation in the incipient stages of weathering. Overall, our novel spectroscopic approach shows that Ce is not necessarily oxidized nor fractionated from other REE during weathering in lateritic conditions. This implies that like Ce(III), Ce(IV) can be mobilized in aqueous fluids during weathering, possibly thanks to complexation with organic molecules, and can precipitate together with Ce(III) in secondary REE-bearing minerals. The corollary is that (paleo) redox reconstructions in soils and/or sediments based on Ceanomaly in weathered rocks or minerals must be interpreted with caution. (C) 2015 Elsevier Ltd. All rights reserved.
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Jardani A, Revil A (2015) Seismoelectric couplings in a poroelastic material containing two immiscible fluid phases. Geophysical Journal International 202(2):850–870
Résumé: A new approach of seismoelectric imaging has been recently proposed to detect saturation fronts in which seismic waves are focused in the subsurface to scan its heterogeneous nature and determine saturation fronts. Such type of imaging requires however a complete modelling of the seismoelectric properties of porous media saturated by two immiscible fluid phases, one being usually electrically insulating (for instance water and oil). We combine an extension of Biot dynamic theory, valid for porous media containing two immiscible Newtonian fluids, with an extension of the electrokinetic theory based on the notion of effective volumetric charge densities dragged by the flow of each fluid phase. These effective charge densities can be related directly to the permeability and saturation of each fluid phase. The coupled partial differential equations are solved with the finite element method. We also derive analytically the transfer function connecting the macroscopic electrical field to the acceleration of the fast P wave (coseismic electrical field) and we study the influence of the water content on this coupling. We observe that the amplitude of the co-seismic electrical disturbance is very sensitive to the water content with an increase in amplitude with water saturation. We also investigate the seismoelectric conversions (interface effect) occurring at the water table. We show that the conversion response at the water table can be identifiable only when the saturation contrasts between the vadose and saturated zones are sharp enough. A relatively dry vadose zone represents the best condition to identify the water table through seismoelectric measurements. Indeed, in this case, the coseismic electrical disturbances are vanishingly small compared to the seismoelectric interface response.
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Jault D (2015) Illuminating the electrical conductivity of the lowermost mantle from below. Geophysical Journal International 202(1):482–496
Résumé: The magnetic field that originates in the earth's core is transformed across the electrically conducting mantle before being observed, at the earth's surface or above. Assuming that the conductivity depends only on radius, it has been customary to treat the mantle as a linear time-invariant filter for the core magnetic field, with properties (as a function of the frequency.) specified by the transfer function Gamma (omega). An high-frequency approximation to Gamma (omega), which is derived from a three terms WKBJ expansion with omega(-1/2) as small parameter, is found here to reproduce adequately, for low harmonic degrees and/or thin conducting layers, the exact solution, which is evaluated numerically. It is contrasted with the low-frequency estimation of Gamma, which consists in a perturbation procedure and in writing Gamma (omega) as a series in powers of omega (omega -> 0). The low-frequency theory is applied to the magnetic variations produced by the geostrophic core flows with about 6 yr period as the phase of these flows is independently determined from their effect on the length of the day. Apart from that, the low-frequency approximation overestimates the screening by the mantle of high-frequency signals, especially the low harmonic degree ones. In practice, the attenuating factor defined from the O(omega(2)) term in the expansion of Gamma as omega -> 0 cannot be retrieved from analyses of geomagnetic time-series. Application of the mantle filter theory hinges on our knowledge about the time spectrum of the magnetic field at the core surface. The low-frequency theory had been previously applied to observatory series on the assumption that geomagnetic jerks occurring in the core are rare and isolated events. Rather than following up these earlier studies, I note that the spectral density function for the second time derivative of the main magnetic field coefficients is approximately independent of. in a frequency range for which the mantle has undoubtedly negligible influence. In the absence of any other information, this scaling law is extrapolated to higher frequencies.
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Jault D and F Christopher (2015) Waves in the core and mechanical core-mantle interactions. 8, Core Dynamics(2nd Edition):225–244
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Jolivet R, Candela T, Lasserre C, Renard F, Klinger Y, Doin M-P (2015) The Burst-Like Behavior of Aseismic Slip on a Rough Fault: The Creeping Section of the Haiyuan Fault, China. Bulletin Of The Seismological Society Of America 105(1):480–488
Résumé: Recent observations suggesting the influence of creep on earthquakes nucleation and arrest are strong incentives to investigate the physical mechanisms controlling how active faults slip. We focus here on deriving generic characteristics of shallow creep along the Haiyuan fault, a major strike-slip fault in China, by investigating the relationship between fault slip and geometry. We use optical images and time series of Synthetic Aperture Radar data to map the surface fault trace and the spatiotemporal distribution of surface slip along the creeping section of the Haiyuan fault. The fault trace roughness shows a power-law behavior similar to that of the aseismic slip distribution, with a 0.8 roughness exponent, typical of a self-affine regime. One possible interpretation is that fault geometry controls to some extent the distribution of aseismic slip, as it has been shown previously for coseismic slip along active faults. Creep is characterized by local fluctuations in rates that we define as creep bursts. The potency of creep bursts follows a power-law behavior similar to the Gutenberg-Richter earthquake distribution, whereas the distribution of bursts velocity is non-Gaussian, suggesting an avalanche-like behavior of these slip events. Such similarities with earthquakes and lab experiments lead us to interpret the rich dynamics of creep bursts observed along the Haiyuan fault as resulting from long-range elastic interactions within the heterogeneous Earth's crust.
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Jongmans D, Baillet L, Larose E, Bottelin P, Mainsant G, Chambon G, Jaboyedoff M (2015) Application of Ambient Vibration Techniques for Monitoring the Triggering of Rapid Landslides. 371–374
Résumé: Ambient vibration techniques are increasingly used for monitoring landslides. Two types of rapid landslides are considered in this study: mudslides in clayey sediments and rockfalls of intermediate size (10(3)-10(5) m(3)) in rigid rocks. The change of ambient vibration properties with time allows variations of internal mass characteristics to be obtained. This information is complementary to the surface motion measurements derived from air or ground based techniques and could be included in a monitoring system for landslides exhibiting a rapid mass movement.
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Kessar M, Plunian F, Stepanov R, Balarac G (2015) Non-Kolmogorov cascade of helicity-driven turbulence. Physical Review E 92(3)
Résumé: We solve the Navier-Stokes equations with two simultaneous forcings. One forcing is applied at a given large scale and it injects energy. The other forcing is applied at all scales belonging to the inertial range and it injects helicity. In this way we can vary the degree of turbulence helicity from nonhelical to maximally helical. We find that increasing the rate of helicity injection does not change the energy flux. On the other hand, the level of total energy is strongly increased and the energy spectrum gets steeper. The energy spectrum spans from a Kolmogorov scaling law k(-5/3) for a nonhelical turbulence, to a non-Kolmogorov scaling law k(-7/3) for a maximally helical turbulence. In the latter case we find that the characteristic time of the turbulence is not the turnover time but a time based on the helicity injection rate. We also analyze the results in terms of helical modes decomposition. For a maximally helical turbulence one type of helical mode is found to be much more energetic than the other one, by several orders of magnitude. The energy cascade of the most energetic type of helical mode results from the sum of two fluxes. One flux is negative and can be understood in terms of a decimated model. This negative flux, however, is not sufficient to lead an inverse energy cascade. Indeed, the other flux involving the least energetic type of helical mode is positive and the largest. The least energetic type of helical mode is then essential and cannot be neglected.
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Koufoudi E, Ktenidou O-J, Cotton F, Dufour F, Grange S (2015) Empirical ground-motion models adapted to the intensity measure ASA(40). Bulletin Of Earthquake Engineering 13(12):3625–3643
Résumé: Relative average-spectral-acceleration (ASA(40)), a recently developed intensity measure, is defined as the average spectral pseudo-acceleration on the probable interval of evolution of the fundamental frequency of a structure. This article presents two ground motion prediction equations (GMPEs) appropriate for the prediction of ASA(40), using a pan-European strong motion database. Taking advantage of the strong correlation between the new intensity measure ASA(40) and the spectral pseudo-acceleration (SA), existing GMPEs predicting SA can be adapted to predict ASA(40). The first GMPE used in this study is the modified version of a new generation ground motion model, ASB13. In order to decrease the high aleatory uncertainty (sigma) that accompanies predictions when using this modified model, a new model is developed for the prediction of ASA(40). Its range of applicability is for magnitudes M-w from 5.5 to 7.6 and distances out to 200 km, it includes site amplification and it is applicable for a range of periods between 0.01 and 4 s. The proposed model decreases the aleatory uncertainty by almost 15 % with respect to the uncertainty of the modified ground motion model.
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Labbe F, Jault D, Gillet N (2015) On magnetostrophic inertia-less waves in quasi-geostrophic models of planetary cores. Geophysical And Astrophysical Fluid Dynamics 109(6):587–610
Résumé: We investigate quasi-geostrophic waves in a rotating spherical shell permeated by an imposed magnetic field (B) over bar. A projection of the momentum equation onto a well chosen class of velocity fields results in a quasi-geostrophic reduced model where, in contrast with previous such models, the evolution of the velocity is not prescribed by an equation for the axial vorticity. We consider fields (B) over bar that may be longitudinally dependent. Increasing the angular rotation frequency, we find that the non-axisymmetric Alfven waves that are present at low rotation morph into inertial waves, torsional Alfven waves and low frequency magnetostrophic waves that satisfy Taylor's constraint (i.e. vanishing acceleration of the geostrophic cylinders by the magnetic forces).
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Lacroix P, Berthier E, Taipe Maquerhua E (2015) Earthquake-driven acceleration of slow-moving landslides in the Colca valley, Peru, detected from Pleiades images. Remote Sensing Of Environment 165:148–158
Résumé: Major earthquakes in mountainous areas often trigger rapid landslides. Some observations also suggest that earthquakes can damage landslide prone areas or cause slow-moving landslides to accelerate, with a risk of evolution to rapid landslides in the following months after the earthquake. Here, we use optical images from the Pleiades satellites to detect slow-moving landslides and quantify the effect of earthquakes on the landslide motion. We process multi-temporal Pleiades images acquired in March, April, and July 2013 over an area of 210 km(2) in the Colca valley (South Peru), to obtain two Digital Elevation Models (DEM) and three displacement fields of the area. The processed DEMs have an uncertainty of 0.6 m (1 sigma), an order of magnitude better than two global and freely available DEMs (GDEM-v2 and SRTM), whereas the displacement fields have an uncertainty of between 0.11 and 0.18 m (1 alpha) in both horizontal directions. Using these data, we detect 9 slow-moving landslides and compare their velocities during the March-April and April-July periods. We find that landslide velocities are highest during the wet season, which suggests a strong groundwater control, and we also highlight a landslide acceleration caused by a regional Mw 6.0 earthquake. The major parameters controlling the acceleration of the slow-moving landslides are the rock type and the distance to the source, suggesting that friction at the basal interface in the weeks after the earthquake is dependent on the shaking intensity. (C) 2015 Elsevier Inc. All rights reserved.
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Lancieri M, Renault M, Berge-Thierry C, Gueguen P, Baumont D, Perrault M (2015) Strategy for the selection of input ground motion for inelastic structural response analysis based on naive Bayesian classifier. Bulletin Of Earthquake Engineering 13(9):2517–2546
Résumé: An application of the naive Bayesian classifier for selecting strong motion data in terms of the deformation probably induced on a given structural system is presented. The main differences between the proposed method and the “standard” procedure based on the inference of a polynomial relationship between a single intensity measure and the engineering demand parameter are: the discrete description of the engineering demand parameter; the use of an array of intensity measures; the combination of the information issued from the training phase via a Bayesian formulation. Six non-linear structural systems with initial fundamental frequency of 1, 2 and 5 Hz and with different strength reduction factors are modelled. Their behaviour is described using the Takeda hysteretic model and the engineering demand parameter is expressed as the relative drift. A database of 6,373 strong motion records is built from worldwide catalogues and is described by a set of “classical” intensity measures; it constitutes the “training dataset” used to feed the Bayesian classifier. The structural system response is reduced to a description of three possible classes: elastic, if the induced drift is lower than the yield displacement; plastic, if the drift ranges between the yield and the ultimate drift values; fragile if the drift reaches the ultimate drift. The goal is to evaluate the conditional probability of observing a given status of the system as a function of the intensity measure array. To validate the presented methodology and evaluate its prediction capability, a blind test on a second dataset, completely disjointed from the training one, composed of 7,000 waveforms recorded in Japan, is performed. The Japanese data are classed using the probability distribution functions derived on the first data set. It is shown that, by combining several intensity measures through the likelihood product, a stable result is obtained whereby most of the data (75 %) are well classed. The degree of correlation between the intensity measure and the engineering demand parameter controls the reliability of the probability curves associated to each intensity measure.
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Lanson B, Ferrage E, Hubert F, Pret D, Mareschal L, Turpault M-P, Ranger J (2015) Experimental aluminization of vermiculite interlayers: An X-ray diffraction perspective on crystal chemistry and structural mechanisms. Geoderma 249:28–39
Résumé: Natural aluminization of swelling clay minerals is ubiquitous in acidic soils leading to the formation of hydroxy-interlayered (HI) minerals. This process has drawn special attention over the last 4-5 decades owing to the negative impact on soil fertility of the induced reduction of cation exchange capacity. Combination of chemical analyses and of X-ray diffraction profile modeling on a series of experimentally self-aluminized samples aimed at an improved description of HI minerals and more especially of their interlayer crystal chemistry. Both exchangeable alkali cations and hydroxy (Al, Fe) cations coexist within HI vermiculite interlayers. The latter form discontinuous gibbsite-like interlayer sheets with similar to 15% completeness, despite layer-to-layer distances similar to that of chlorite. From charge compensation considerations, the isolated hydroxy (Al, Fe) cation clusters bear similar to 1.5 positive charges per cation. Analysis of X-ray diffraction data indicates that aluminization of initially swelling interlayers is a layer-by-layer process leading to mixed layers composed of randomly interstratified swelling and aluminized layers, all aluminized layers likely hosting a similar number of hydroxy (Al, Fe) cations along the aluminization process. This model contradicts the widely accepted description of HI minerals as a solid solution between expandable 2:1 clay and aluminous chlorite end-members. As a consequence, the proportion of HI layers in the mixed layer is a robust estimate of aluminization progress and both the amount of extractible (Al, Fe) and the extent of CEC decrease are positively correlated to this essential parameter. (C) 2015 Elsevier B.V. All rights reserved.
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Larose E, Carriere S, Voisin C, Bottelin P, Baillet L, Gueguen P, Walter F, Jongmans D, Guillier B, Garambois S, Gimbert F, Massey C (2015) Environmental seismology: What can we learn on earth surface processes with ambient noise? Journal Of Applied Geophysics 116:62–74
Résumé: Environmental seismology consists in studying the mechanical vibrations that originate from, or that have been affected by external causes, that is to say causes outside the solid Earth. This includes for instance the coupling between the solid Earth and the cryosphere, or the hydrosphere, the anthroposphere and the specific sources of vibration developing there. Environmental seismology also addresses the modifications of the wave propagation due to environmental forcing such as temperature and hydrology. Recent developments in data processing, together with increasing computational power and sensor concentration have led to original observations that allow for the development of this new field of seismology. In this article, we will particularly review how we can track and interpret tiny changes in the subsurface of the Earth related to external changes from modifications of the seismic wave propagation, with application to geomechanics, hydrology, and natural hazard. We will particularly demonstrate that, using ambient noise, we can track 1) thermal variations in the subsoil, in buildings or in rock columns; 2) the temporal and spatial evolution of a water table; 3) the evolution of the rigidity of the soil constituting a landslide, and especially the drop of rigidity preceding a failure event. (C) 2015 Elsevier B.V. All rights reserved.
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Larose E, Obermann A, Digulescu A, Planes T, Chaix J-F, Mazerolle F, Moreau G (2015) Locating and characterizing a crack in concrete with diffuse ultrasound: A four-point bending test. Journal Of The Acoustical Society Of America 138(1):232–241
Résumé: This paper describes an original imaging technique, named Locadiff, that benefits from the diffuse effect of ultrasound waves in concrete to detect and locate mechanical changes associated with the opening of pre-existing cracks, and/or to the development of diffuse damage at the tip of the crack. After giving a brief overview of the theoretical model to describe the decorrelation of diffuse waveforms induced by a local change, the article introduces the inversion procedure that produces the three dimensional maps of density of changes. These maps are interpreted in terms of mechanical changes, fracture opening, and damage development. In addition, each fracture is characterized by its effective scattering cross section. (C) 2015 Acoustical Society of America.
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Lasbleis M, Deguen R, Cardin P, Labrosse S (2015) Earth's inner core dynamics induced by the Lorentz force. Geophysical Journal International 202(1):548–563
Résumé: Seismic studies indicate that the Earth's inner core has a complex structure and exhibits a strong elastic anisotropy with a cylindrical symmetry. Among the various models which have been proposed to explain this anisotropy, one class of models considers the effect of the Lorentz force associated with the magnetic field diffused within the inner core. In this paper, we extend previous studies and use analytical calculations and numerical simulations to predict the geometry and strength of the flow induced by the poloidal component of the Lorentz force in a neutrally or stably stratified growing inner core, exploring also the effect of different types of boundary conditions at the inner core boundary (ICB). Unlike previous studies, we show that the boundary condition that is most likely to produce a significant deformation and seismic anisotropy is impermeable, with negligible radial flow through the boundary. Exact analytical solutions are found in the case of a negligible effect of buoyancy forces in the inner core (neutral stratification), while numerical simulations are used to investigate the case of stable stratification. In this situation, the flow induced by the Lorentz force is found to be localized in a shear layer below the ICB, whose thickness depends on the strength of the stratification, but not on the magnetic field strength. We obtain scaling laws for the thickness of this layer, as well as for the flow velocity and strain rate in this shear layer as a function of the control parameters, which include the magnitude of the magnetic field, the strength of the density stratification, the viscosity of the inner core and the growth rate of the inner core. We find that the resulting strain rate is probably too small to produce significant texturing unless the inner core viscosity is smaller than about 10(12) Pa s.
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Lattanzi P, Aquilanti G, Bardelli F, Iadecola A, Rosellini I, Tassi E, Pezzarossa B, Petruzzelli G (2015) Spectroscopic evidence of Cr(VI) reduction in a contaminated soil by in situ treatment with whey. Agrochimica 59(3):218–230
Résumé: A soil in southern Italy contaminated by hexavalent chromium [Cr(VI)] was treated in situ with whey in order to reduce it to the much less toxic trivalent form [Cr(III)]. A site assessment was carried out by sampling soil at 1m depth before and after the addition of whey to continuously evaluate the efficiency of the treatment. A quantitative evaluation by best-fit linear combination analysis of the XANES portion of X-ray absorption spectra revealed that the treatment had only a moderate success, and suggests that additional studies are required before this technique can be considered as viable for the remediation of Cr(VI)-contaminated soils.
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Lavoue F, Brossier R, Metivier L, Garambois S, Virieux J (2015) Frequency-domain modelling and inversion of electromagnetic data for 2D permittivity and conductivity imaging: An application to the Institut Fresnel experimental dataset. Near Surface Geophysics 13(3)
Résumé: The need for quantitative imaging of the near subsurface leads to the development of inversion algorithms to infer ground properties from recorded data. The aim of this study is to validate an inversion method recently developed for the simultaneous imaging of dielectric permittivity and electrical conductivity from 2D ground-penetrating radar measurements. The validation is performed using electromagnetic data collected in a well-controlled laboratory environment. In this experiment, the knowledge of the targets enables a quality control of the inversion results. In addition, the free space environment and the measurement of the incident field simplify the choice of a starting model for the inversion, as well as the calibration of the data with respect to the source signature and to the geometrical spread. To perform accurate and efficient forward simulations, we use a frequency-domain finite-difference scheme whose stencil coefficients can be optimized for each simulated frequency. As the objects of interest are locally concentrated at the centre of the acquisition array, it is possible to restrict the computation domain to a small region enclosing the targets using an integral representation of the analytical incident field coming from the sources and of the scattered field that we analytically propagate towards the receivers. An analysis of the numerical errors done on synthetic data shows that this strategy provides an error level that is low enough not to perturb the inversion, while dramatically decreasing the computational cost compared to a full-domain simulation. The monoparameter reconstruction of a purely dielectric target recovers permittivity values in very good agreement with the expected ones, as well as a very satisfying data fit. We also validate our strategy for multiparameter inversion on targets involving both a purely dielectric cylinder and a purely metallic copper tube, although the optimization cannot recover the exact conductivity of copper.
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Le Bars M, Cebron D, Le Gal P (2015) Flows Driven by Libration, Precession, and Tides. 163–193
Résumé: Because of gravitational interactions with their companions, the rotational dynamics of planets and stars involve periodic perturbations of their shape, the direction of their rotational vector, and their rotation rate. These perturbations correspond in planetary terms to tides, precession, and longitudinal libration. We review here the flows driven by those mechanical forcings on rotating spheres and ellipsoids. Special focus is placed on the associated instabilities and on the various routes toward turbulence recently studied. The key point is that mechanical forcings do not provide the energy to the excited flows: They convey part of the available rotational energy and generate intense fluid motions through the excitation of localized jets, shear layers, and resonant inertial modes. Hence, even very small forcings may have large-scale consequences. Mechanically driven flows thus play a fundamental role in planets and stars, significantly influencing their shape, their rotational dynamics, and their magnetic field.
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Ledevin M, Arndt N, Davaille A, Ledevin R, Simionovici A (2015) The rheological behaviour of fracture-filling cherts: example of Barite Valley dikes, Barberton Greenstone Belt, South Africa. Solid Earth 6(1):253–269
Résumé: In the Barberton Greenstone Belt, South Africa, a 100-250 m thick complex of carbonaceous chert dikes marks the transition from the Mendon Formation to the Mapepe Formation (3260 Ma). The sub-vertical- to vertical position of the fractures, the abundance of highly shattered zones with poorly rotated angular fragments and common jigsaw fit, radial structures, and multiple injection features point to repetitive hydraulic fracturing that released overpressured fluids trapped within the shallow crust. The chemical and isotopic compositions of the chert favour a model whereby seawater-derived fluids circulated at low temperature (< 100-150 A degrees C) within the shallow crust. From the microscopic structure of the chert, the injected material was a slurry of abundant clay-sized, rounded particles of silica, carbonaceous matter and minor clay minerals, all suspended in a siliceous colloidal solution. The dike geometry and characteristics of the slurry concur on that the chert was viscoelastic, and most probably thixotropic at the time of injection: the penetration of black chert into extremely fine fractures is evidence for low viscosity at the time of injection and the suspension of large country rock fragments in the chert matrix provides evidence of high viscosity soon thereafter. We explain the rheology by the particulate and colloidal structure of the slurry, and by the characteristic of silica suspensions to form cohesive 3-D networks through gelation. Our results provide valuable information about the compositions, physical characteristics and rheological properties of the fluids that circulated through Archean volcano-sedimentary sequences, which is an additional step to understand conditions on the floor of Archean oceans, the habitat of early life.
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Lehoucq R, Weiss J, Dubrulle B, Amon A, Le Bouil A, Crassous J, Amitrano D, Graner F (2015) Analysis of image vs. position, scale and direction reveals pattern texture anisotropy. Front. Physics 2:15 pp
Résumé: Pattern heterogeneities and anisotropies often carry significant physical information. We provide a toolbox which: (i) cumulates analysis in terms of position, direction and scale; (ii) is as general as possible; (iii) is simple and fast to understand, implement, execute and exploit. It consists in dividing the image into analysis boxes at a chosen scale; in each box an ellipse (the inertia tensor) is fitted to the signal and thus determines the direction in which the signal is more present. This tensor can be averaged in position and/or be used to study the dependence with scale. This choice is formally linked with Leray transforms and anisotropic wavelet analysis. Such protocol is intuitively interpreted and consistent with what the eye detects: relevant scales, local variations in space, privileged directions. It is fast and parallelizable. Its several variants are adaptable to the users' data and needs. It is useful to statistically characterize anisotropies of 2D or 3D patterns in which individual objects are not easily distinguished, with only minimal pre-processing of the raw image, and more generally applies to data in higher dimensions. It is less sensitive to edge effects, and thus better adapted for a multiscale analysis down to small scale boxes, than pair correlation function or Fourier transform. Easy to understand and implement, it complements more sophisticated methods such as Hough transform or diffusion tensor imaging. We use it on various fracture patterns (sea ice cover, thin sections of granite, granular materials), to pinpoint the maximal anisotropy scales. The results are robust to noise and to users choices. This toolbox could turn also useful for granular materials, hard condensed matter, geophysics, thin films, statistical mechanics, characterization of networks, fluctuating amorphous systems, inhomogeneous and disordered systems, or medical imaging, among others.
Mots-Clés: patterns; multi-scale; image analysis; anisotropy; fracture; heterogeneous materials
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Letort J, Guilbert J, Cotton F, Bondar I, Cano Y, Vergoz J (2015) A new, improved and fully automatic method for teleseismic depth estimation of moderate earthquakes (4.5 < M < 5.5): application to the Guerrero subduction zone (Mexico). Geophysical Journal International 201(3):1834–1848
Résumé: The depth of an earthquake is difficult to estimate because of the trade-off between depth and origin time estimations, and because it can be biased by lateral Earth heterogeneities. To face this challenge, we have developed a new, blind and fully automatic teleseismic depth analysis. The results of this new method do not depend on epistemic uncertainties due to depth-phase picking and identification. The method consists of a modification of the cepstral analysis from Letort et al. and Bonner et al., which aims to detect surface reflected (pP, sP) waves in a signal at teleseismic distances (30A degrees-90A degrees) through the study of the spectral holes in the shape of the signal spectrum. The ability of our automatic method to improve depth estimations is shown by relocation of the recent moderate seismicity of the Guerrero subduction area (Mexico). We have therefore estimated the depth of 152 events using teleseismic data from the IRIS stations and arrays. One advantage of this method is that it can be applied for single stations (from IRIS) as well as for classical arrays. In the Guerrero area, our new cepstral analysis efficiently clusters event locations and provides an improved view of the geometry of the subduction. Moreover, we have also validated our method through relocation of the same events using the new International Seismological Centre (ISC)-locator algorithm, as well as comparing our cepstral depths with the available Harvard-Centroid Moment Tensor (CMT) solutions and the three available ground thrust (GT5) events (where lateral localization is assumed to be well constrained with uncertainty < 5 km) for this area. These comparisons indicate an overestimation of focal depths in the ISC catalogue for deeper parts of the subduction, and they show a systematic bias between the estimated cepstral depths and the ISC-locator depths. Using information from the CMT catalogue relating to the predominant focal mechanism for this area, this bias can be explained as a misidentification of sP phases by pP phases, which shows the greater interest for the use of this new automatic cepstral analysis, as it is less sensitive to phase identification.
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Li C, Arndt NT, Tang Q, Ripley EM (2015) Trace element indiscrimination diagrams. Lithos 232:76–83
Résumé: We tested the accuracy of trace element discrimination diagrams for basalts using new datasets from two petrological databases, PetDB and GEOROC Both binary and ternary diagrams using Zr, Ti, V, Y, Th, Hf, Nb, Ta, Sm, and Sc do a poor job of discriminating between basalts generated in various tectonic environments (continental flood basalt, mid-ocean ridge basalt, ocean island basalt, oceanic plateau basalt, back-arc basin basalt, and various types of arc basalt). The overlaps between the different types of basalt are too large for the confident application of such diagrams when used in the absence of geological and petrological constraints. None of the diagrams we tested can dearly discriminate between back-arc basin basalt and mid-ocean ridge basalt, between continental flood basalt and oceanic plateau basalt, and between different types of arc basalt (intra-oceanic, island and continental arcs). Only ocean island basalt and some mid-ocean ridge basalt are generally distinguishable in the diagrams, and even in this case, mantle-normalized trace element patterns offer a better solution for discriminating between the two types of basalt. (C) 2015 Elsevier B.V. All rights reserved.
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Li Y, Metivier L, Brossier R, Han B, Virieux J (2015) 2D and 3D frequency-domain elastic wave modeling in complex media with a parallel iterative solver. Geophysics 80(3):T101–T118
Résumé: Full-waveform inversion and reverse time migration rely on an efficient forward-modeling approach. Current 3D large-scale frequency-domain implementations of these techniques mostly extract the desired frequency component from the time-domain wavefields through discrete Fourier transform. However, instead of conducting the time-marching steps for each seismic source, in which the time step is limited by the stability condition, performing the wave modeling directly in the frequency domain using an iterative linear solver may reduce the entire computational complexity. For 2D and 3D frequency-domain elastic wave modeling, a parallel iterative solver based on a conjugate gradient acceleration of the symmetric Kaczmarz row-projection method, named the conjugate-gradient-accelerated component-averaged row projections (CARP-CG) method, shows interesting convergence properties. The parallelization is realized through row-block division and component averaging operations. Convergence is achieved systematically even when different physical factors such as the space-dependent Poisson's ratio, free-surface condition, and seismic attenuation are incorporated in the wave modeling. We determined that the scalability of CARP-CG was satisfactory, especially for large-scale applications, using up to several hundred computational cores. We found a potential improvement in computational complexity compared to time-domain modeling through numerical experiments. Finally, we achieved a convergence at 5 Hz in a 3D heterogeneous model, involving fast-slow-fast layers resembling waveguide geometries, with up to several hundred million unknowns, in fewer than 10 h on fewer than 200 cores. All of these results make CARP-CG a potential candidate of the forward modeling engine for seismic imaging on challenging models.
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Li Y, Metivier L, Brossier R, Han B, Virieux J (2015) 2D and 3D frequency-domain elastic wave modeling in complex media with a parallel iterative solver. Geophysics 80(3):T101–T118
Résumé: Full-waveform inversion and reverse time migration rely on an efficient forward-modeling approach. Current 3D large-scale frequency-domain implementations of these techniques mostly extract the desired frequency component from the time-domain wavefields through discrete Fourier transform. However, instead of conducting the time-marching steps for each seismic source, in which the time step is limited by the stability condition, performing the wave modeling directly in the frequency domain using an iterative linear solver may reduce the entire computational complexity. For 2D and 3D frequency-domain elastic wave modeling, a parallel iterative solver based on a conjugate gradient acceleration of the symmetric Kaczmarz row-projection method, named the conjugate-gradient-accelerated component-averaged row projections (CARP-CG) method, shows interesting convergence properties. The parallelization is realized through row-block division and component averaging operations. Convergence is achieved systematically even when different physical factors such as the space-dependent Poisson's ratio, free-surface condition, and seismic attenuation are incorporated in the wave modeling. We determined that the scalability of CARP-CG was satisfactory, especially for large-scale applications, using up to several hundred computational cores. We found a potential improvement in computational complexity compared to time-domain modeling through numerical experiments. Finally, we achieved a convergence at 5 Hz in a 3D heterogeneous model, involving fast-slow-fast layers resembling waveguide geometries, with up to several hundred million unknowns, in fewer than 10 h on fewer than 200 cores. All of these results make CARP-CG a potential candidate of the forward modeling engine for seismic imaging on challenging models.
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Lincot A, Merkel S, Cardin P (2015) Is inner core seismic anisotropy a marker for plastic flow of cubic iron? Geophysical Research Letters 42(5):1326–1333
Résumé: This paper investigates whether observations of seismic anisotropy are compatible with a cubic structure of the inner core Fe alloy. We assume that anisotropy is the result of plastic deformation within a large-scale flow induced by preferred growth at the inner core equator. Based on elastic moduli from the literature, body-centered cubic or face-centered cubic Fe produces seismic anisotropy well below seismic observations (<0.4%). A Monte Carlo approach allows us to generalize this result to any form of elastic anisotropy in a cubic system. Within our model, inner core global anisotropy is not compatible with a cubic structure of Fe alloy. Hence, if the inner core material is indeed cubic, large-scale coherent anisotropic structures, incompatible with plastic deformation induced by large-scale flow, must be present.
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Lounis GC, Chatelain JL, Mimouni O, Machane D (2015) Assessment of Flood Risk in Kniss Wadi Catchment in Urbain Area Algiers-Algeria. 459–462
Résumé: The Kniss Wadi catchment, highly urbanized in its northern part, is located in the center of Algiers. Along this wadi, anarchical buildings are developing and a road network is constructed. An exceptional flood may weaken these zones. Flood hazard determination needs a statistic analysis of daily maximum rainfalls, which adjustments to the Gumbel law allows to determinate the maximum rainfall for different return periods. The calculation of maximum discharges linked to different return periods allows the evaluation of overflowing on cross section along the The Kniss Wadi. Hazard maps, obtained show evidence zones that are potentially threatened by flooding. Such maps should be considered and used as main tools to reduce the risk.
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Mainsant G, Chambon G, Jongmans D, Larose E, Baillet L (2015) Shear-wave-velocity drop prior to clayey mass movement in laboratory flume experiments. Engineering Geology 192:26–32
Résumé: Clay slopes are susceptible to suddenly liquefy into rapidly accelerating landslides, thereby threatening people and facilities in mountainous areas. Because the shear-wave velocity (V-s) characterizes the medium stiffness, this parameter can potentially be used to investigate the rheological behavior of clay materials before and during the solid-to-fluid transition associated to such landslide failures. Previous rheometrical studies performed on clay samples coming from Trieves landslides (French Alps) have established that this material behaves as a yield stress fluid with a marked viscosity bifurcation. When the applied stress reaches a critical level, the viscosity decreases abruptly, along with V-s which tends to zero in the fully fluidized material. Here, we monitor the Rayleigh wave velocity (V-R) variations in a saturated clay layer placed in a flume and progressively brought to failure by tilting the device. Experiments performed on clay samples with different water contents show a significant relative drop in V-R values (and hence in V-s) before the onset of the mass movement. Additional rheometrical analyses point out that this precursory drop in V-s is presumably due to a complex transient rheological response of the clay. These new results confirm that V-s variations constitute a good indicator for monitoring clay slope stability. (C) 2015 Elsevier B.V. All rights reserved.
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Manceau A, Nagy KL (2015) Comment on “Molecular controls on Cu and Zn isotopic fractionation in Fe-Mn crusts” by Little et al. Earth And Planetary Science Letters 411:310–312
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Manceau A, Lemouchi C, Enescu M, Gaillot A-C, Lanson M, Magnin V, Glatzel P, Poulin BA, Ryan JN, Aiken GR, Gautier-Luneau I, Nagy KL (2015) Formation of Mercury Sulfide from Hg(II)-Thiolate Complexes in Natural Organic Matter. Environmental Science & Technology 49(16):9787–9796
Résumé: Methylmercury is the environmental form of neurotoxic mercury that is biomagnified in the food chain. Methylation rates are reduced when the metal is sequestered in crystalline mercury sulfides or bound to thiol groups in macromolecular natural organic matter. Mercury sulfide minerals are known to nucleate in anoxic zones, by reaction of the thiol-bound mercury with biogenic sulfide, but not in oxic environments. We present experimental evidence that mercury sulfide forms from thiolbound mercury alone in aqueous dark systems in contact with air. The maximum amount of nanoparticulate mercury sulfide relative to thiolbound mercury obtained by reacting dissolved mercury and soil organic matter matches that detected in the organic horizon of a contaminated soil situated downstream from Oak Ridge, TN, in the United States. The nearly identical ratios of the two forms of mercury in field and experimental systems suggest a common reaction mechanism for nucleating the mineral. We identified a chemical reaction mechanism that is thermodynamically favorable in which thiol-bound mercury polymerizes to mercury sulfur clusters. The clusters form by elimination of sulfur from the thiol complexes via breaking of mercury sulfur bonds as in an alkylation reaction. Addition of sulfide is not required. This nucleation mechanism provides one explanation for how mercury may be immobilized, and eventually sequestered, in oxygenated surface environments.
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Manceau A, Lemouchi C, Rovezzi M, Lanson M, Gatzel P, Nagy KL, Gautier-Luneau I, Joly Y, Enescu M (2015) Structure, Bonding, and Stability of Mercury Complexes with Thiolate and Thioether Ligands from High-Resolution XANES Spectroscopy and First-Principles Calculations. Inorganic Chemistry 54(24):11776–11791
Résumé: We present results obtained from high energy-resolution L3-edge XANES spectroscopy and first-principles calculations for the structure, bonding, and stability of mercury(II) complexes with thiolate and thioether ligands in crystalline compounds, aqueous solution, and macromolecular natural organic matter (NOM). Core-to-valence XANES features that vary in intensity differentiate with unprecedented sensitivity the number and identity of Hg ligands and the geometry of the ligand environment. Post-Hartree-Fock XANES calculations, coupled with natural population analysis, performed on MP2-optimized Hg[(SR)(2)center dot center dot center dot(RSR)(n)] complexes show that the shape, position, and number of electronic transitions observed at high energy-resolution are directly correlated to the Hg and S (l,m)-projected empty densities of states and occupations of the hybridized Hg 6s and 5d valence orbitals. Linear two-coordination, the most common coordination geometry in mercury chemistry, yields a sharp 2p to 6s + 5d electronic transition. This transition varies in intensity for Hg bonded to thiol groups in macromolecular NOM. The intensity variation is explained by contributions from next-nearest, low-charge, thioether-type RSR ligands at 3.0-3.3 angstrom from Hg. Thus, Hg in NOM has two strong bonds to thiol S and k additional weak Hg center dot center dot center dot S contacts, or 2 + k coordination. The calculated stabilization energy is -5 kcal/mol per RSR ligand. Detection of distant ligands beyond the first coordination shell requires precise measurement of, and comparison to, spectra of reference compounds as well as accurate calculation of spectra for representative molecular models. The combined experimental and theoretical approaches described here for Hg can be applied to other closed-shell atoms, such as AgI and AuI. To facilitate further calculation of XANES spectra, experimental data, a new crystallographic structure of a key mercury thioether complex, Cartesian coordinates of the computed models, and examples of input files are provided as Supporting Information.
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Mangold N, Forni O, Dromart G, Stack K, Wiens RC, Gasnault O, Sumner DY, Nachon M, Meslin P-Y, Anderson RB, Barraclough B, Bell JF III, Berger G, Blaney DL, Bridges JC, Calef F, Clark B, Clegg SM, Cousin A, Edgar L, Edgett K, Ehlmann B, Fabre C, Fisk M, Grotzinger J, Gupta S, Herkenhoff KE, Hurowitz J, Johnson JR, Kah LC, Lanza N, Lasue J, Le Mouelic S, Leveille R, Lewin E, Malin M, McLennan S, Maurice S, Melikechi N, Mezzacappa A, Milliken R, Newsom H, Ollila A, Rowland SK, Sautter V, Schmidt M, Schroeder S, d'Uston C, Vaniman D, Williams R (2015) Chemical variations in Yellowknife Bay formation sedimentary rocks analyzed by ChemCam on board the Curiosity rover on Mars. Journal Of Geophysical Research-Planets 120(3):452–482
Résumé: The Yellowknife Bay formation represents a similar to 5m thick stratigraphic section of lithified fluvial and lacustrine sediments analyzed by the Curiosity rover in Gale crater, Mars. Previous works have mainly focused on the mudstones that were drilled by the rover at two locations. The present study focuses on the sedimentary rocks stratigraphically above the mudstones by studying their chemical variations in parallel with rock textures. Results show that differences in composition correlate with textures and both manifest subtle but significant variations through the stratigraphic column. Though the chemistry of the sediments does not vary much in the lower part of the stratigraphy, the variations in alkali elements indicate variations in the source material and/or physical sorting, as shown by the identification of alkali feldspars. The sandstones contain similar relative proportions of hydrogen to the mudstones below, suggesting the presence of hydrous minerals that may have contributed to their cementation. Slight variations in magnesium correlate with changes in textures suggesting that diagenesis through cementation and dissolution modified the initial rock composition and texture simultaneously. The upper part of the stratigraphy (similar to 1m thick) displays rocks with different compositions suggesting a strong change in the depositional system. The presence of float rocks with similar compositions found along the rover traverse suggests that some of these outcrops extend further away in the nearby hummocky plains.
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Manighetti I, Perrin C, Dominguez S, Garambois S, Gaudemer Y, Malavieille J, Matteo L, Delor E, Vitard C, Beaupretre S (2015) Recovering paleoearthquake slip record in a highly dynamic alluvial and tectonic region (Hope Fault, New Zealand) from airborne lidar. Journal Of Geophysical Research-Solid Earth 120(6):4484–4509
Résumé: Knowing the slip amplitudes that large earthquakes produced in prehistorical times is one key to anticipate the magnitude of large forthcoming events. It is long known that the morphology is preserving remnants of paleoearthquake slips in the form of fault-offset landforms. However, the measured offsets that can be attributed to the most recent paleoearthquakes are generally few along a fault, so that they rarely allow recovering the slip distributions and largest slips of these earthquakes. We acquired similar to 1m resolution airborne lidar data on a 30km stretch of a fast-slipping strike-slip fault (eastern Hope Fault, New Zealand) located in a region of high alluvial dynamics where landforms are rapidly evolving. Data analysis reveals >200 offset landforms; only 30% allow a good to moderate quality offset measurement. From these good to moderate quality measures, we recover the slip-length distributions and largest slips of the four most recent large paleoearthquakes and find evidence of 4-6 prior events. The record suggests that large earthquake slip recurred in multiples of about 4m along the 30km stretch. Although they have larger uncertainties, the more numerous lower-quality offsets that we also measured reveal a similar earthquake slip record. This shows that, although offset landforms are partly degraded in dynamically active landscapes, they store valuable information on paleoearthquake slips. This information might be recovered provided that the morphology is analyzed at high resolution and continuously over a significant fault length. Remote lidar data are powerful to perform such analyses.
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Mao D, Revil A, Hort RD, Munakata-Marr J, Atekwana EA, Kulessa B (2015) Resistivity and self-potential tomography applied to groundwater remediation and contaminant plumes: Sandbox and field experiments. Journal Of Hydrology 530:1–14
Résumé: Geophysical methods can be used to remotely characterize contaminated sites and monitor in situ enhanced remediation processes. We have conducted one sandbox experiment and one contaminated field investigation to show the robustness of electrical resistivity tomography and self-potential (SP) tomography for these applications. In the sandbox experiment, we injected permanganate in a trichloroethylene (TCE)-contaminated environment under a constant hydraulic gradient. Inverted resistivity tomograms are able to track the evolution of the permanganate plume in agreement with visual observations made on the side of the tank. Self-potential measurements were also performed at the surface of the sandbox using non-polarizing Ag-AgCl electrodes. These data were inverted to obtain the source density distribution with and without the resistivity information. A compact horizontal dipole source located at the front of the plume was obtained from the inversion of these self-potential data. This current dipole may be related to the redox reaction occurring between TCE and permanganate and the strong concentration gradient at the front of the plume. We demonstrate that time-lapse self-potential signals can be used to track the kinetics of an advecting oxidizer plume with acceptable accuracy and, if needed, in real time, but are unable to completely resolve the shape of the plume. In the field investigation, a 3D resistivity tomography is used to characterize an organic contaminant plume (resistive domain) and an overlying zone of solid waste materials (conductive domain). After removing the influence of the streaming potential, the identified source current density had a magnitude of 0.5 A m(-2). The strong source current density may be attributed to charge movement between the neighboring zones that encourage abiotic and microbially enhanced reduction and oxidation reactions. In both cases, the self-potential source current density is located in the area of strong resistivity gradient (C) 2015 Elsevier B.V. All rights reserved.
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Margirier A, Audin L, Carcaillet J, Schwartz S, Benavente C (2015) Tectonic and climatic controls on the Chuquibamba landslide (western Andes, southern Peru). Earth Surface Dynamics 3(2):281–289
Résumé: The contribution of landslides to the Quaternary evolution of relief is poorly documented in arid contexts. In southernPeru and northern Chile, several massive landslides disrupt the arid western Andean front. The Chuquibamba landslide, located in southern Peru, belongs to this set of large landslides. In this area, the Incapuquio fault system captures the intermittent drainage network and localizes rotational landslides. Seismic activity is significant in this region with recurrent M-w 9 subduction earthquakes; however, none of the latest seismic events have triggered a major landslide. New terrestrial cosmogenic dating of the Chuquibamba landslide provides evidence that the last major gravitational mobilization of these rotational landslide deposits occurred at similar to 102 ka, during the Ouki wet climatic event identified on the Altiplano between 120 and 98 ka. Our results suggest that wet events in the arid and fractured context of the Andean forearc induced these giant debris flows. Finally, our study highlights the role of tectonics and climate on (i) the localization of large Andean landslides in the Western Cordillera and on (ii) the long-term mass transfer to the trench along the arid Andean front.
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Margirier A, Robert X, Audin L, Gautheron C, Bernet M, Hall S, Simon-Labric T (2015) Slab flattening, magmatism, and surface uplift in the Cordillera Occidental (northern Peru). Geology 43(11):1031–1034
Résumé: The impact of subduction processes on surface uplift and relief building in the Andes is not well understood. In northern Peru, we have access to a modern flat subduction zone (3 degrees-15 degrees S) where both the geometry and timing of the flattening of the slab are well constrained. Some of the highest Andean peaks, the Cordillera Blanca (6768 m) and the Cordillera Negra (5187 m), are located just above the Peruvian flat slab. This is a perfect target to explore the impact of slab flattening and associated magmatism on Andean topography and uplift. We present new apatite (U-Th)/He and fission-track data from three vertical profiles in the Cordillera Blanca and the Cordillera Negra. Time-temperature inverse modeling of the thermochronological data suggests that regional exhumation in the Cordillera Occidental started at ca. 15 Ma, synchronous with the onset of subduction of the Nazca Ridge and eastward movement of regional magmatism. We propose that ridge subduction at 15 Ma and onset of slab flattening drove regional surface uplift, with an important contribution of magmatism to relief building in the Cordillera Occidental.
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Mathon O, Beteva A, Borrel J, Bugnazet D, Gatla S, Hino R, Kantor I, Mairs T, Munoz M, Pasternak S, Perrin F, Pascarelli S (2015) The time-resolved and extreme conditions XAS (TEXAS) facility at the European Synchrotron Radiation Facility: the general-purpose EXAFS bending-magnet beamline BM23. Journal Of Synchrotron Radiation 22:1548–1554
Résumé: BM23 is the general-purpose EXAFS bending-magnet beamline at the ESRF, replacing the former BM29 beamline in the framework of the ESRF upgrade. Its mission is to serve the whole XAS user community by providing access to a basic service in addition to the many specialized instruments available at the ESRF. BM23 offers high signal-to-noise ratio EXAFS in a large energy range (5-75 keV), continuous energy scanning for quick-EXAFS on the second timescale and a micro-XAS station delivering a spot size of 4 μm x 4 μm FWHM. It is a user-friendly facility featuring a high degree of automation, online EXAFS data reduction and a flexible sample environment.
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Maufroy E, Chaljub E, Hollender F, Kristek J, Moczo P, Klin P, Priolo E, Iwaki A, Iwata T, Etienne V, De Martin F, Theodoulidis NP, Manakou M, Guyonnet-Benaize C, Pitilakis K, Bard P-Y (2015) Earthquake Ground Motion in the Mygdonian Basin, Greece: The E2VP Verification and Validation of 3D Numerical Simulation up to 4 Hz. Bulletin Of The Seismological Society Of America 105(3):1398–1418
Résumé: In a low-seismicity context, the use of numerical simulations becomes essential due to the lack of representative earthquakes for empirical approaches. The goals of the EUROSEISTEST Verification and Validation Project (E2VP) are to provide (1) a quantitative analysis of accuracy of the current, most advanced numerical methods applied to realistic 3D models of sedimentary basins (verification) and (2) a quantitative comparison of the recorded ground motions with their numerical predictions (validation). The target is the EUROSEISTEST site located within the Mygdonian basin, Greece. The site is instrumented with surface and borehole accelerometers, and a 3D model of the medium is available. The simulations are performed up to 4 Hz, beyond the 0.7 Hz fundamental frequency, thus covering a frequency range at which ground motion undergoes significant amplification. The discrete representation of material heterogeneities, the attenuation model, the approximation of the free surface, and nonreflecting boundaries are identified as the main sources of differences among the numerical predictions. The predictions well reproduce some, but not all, features of the actual site effect. The differences between real and predicted ground motions have multiple origins: the accuracy of source parameters (location, hypocentral depth, and focal mechanism), the uncertainties in the description of the geological medium (damping, internal sediment layering structure, and shape of the sediment-basement interface). Overall, the agreement reached among synthetics up to 4 Hz despite the complexity of the basin model, with code-to-code differences much smaller than predictions-to-observations differences, makes it possible to include the numerical simulations in site-specific analysis in the 3D linear case and low-to-intermediate frequency range.
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Maufroy E, Cruz-Atienza VM, Cotton F, Gaffet S (2015) Frequency-Scaled Curvature as a Proxy for Topographic Site-Effect Amplification and Ground-Motion Variability. Bulletin Of The Seismological Society Of America 105(1):354–367
Résumé: We introduce a new methodology to predict the topographic site-effect amplification. Ground motions obtained from a large database of 3D earthquake simulations show that the curvature of the Earth's surface, defined as the second spatial derivative of the elevation map, is correlated with the topographic site amplification. The highest correlation between the frequency-dependent topographic amplification and the topographic curvature is reached when the curvature is smoothed over a characteristic length equal to the S wavelength divided by two (i.e., frequency-scaled curvature [FSC]). This implies the amplification is caused by topographic features for which horizontal dimensions are similar to half of the S wavelength. The largest ground-motion variabilities are found at sites located on slopes and on the largest summits, whereas intermediate variabilities occur over narrow ridges and a stable behavior in the bottom valleys. The FSC proxy allows the identification of topographic features with similar characteristic dimensions and probabilistic estimates of amplification values accounting on the variability of ground motions due to source-site interactions. Amplification estimates using the FSC proxy are robust and easily computed from digital elevation maps provided that reasonable values of S-wave velocities are available in the area of interest.
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Mercer CN, Hofstra AH, Todorov TI, Roberge J, Burgisser A, Adams DT, Cosca M (2015) Pre-Eruptive Conditions of the Hideaway Park Topaz Rhyolite: Insights into Metal Source and Evolution of Magma Parental to the Henderson Porphyry Molybdenum Deposit, Colorado. Journal Of Petrology 56(4):645–679
Résumé: The Hideaway Park tuff is the only preserved extrusive volcanic unit related to the Red Mountain intrusive complex, which produced the world-class Henderson porphyry Mo deposit. Located within the Colorado Mineral Belt, USA, Henderson is the second largest Climax-type Mo deposit in the world, and is therefore an excellent location to investigate magmatic processes leading to Climax-type Mo mineralization. We combine an extensive dataset of major element, volatile, and trace element abundances in quartz-hosted melt inclusions and pumice matrix glass with major element geochemistry from phenocrysts to reconstruct the pre-eruptive conditions and the source and evolution of metals within the magma. Melt inclusions are slightly peraluminous topaz rhyolitic in composition and are volatile-charged (<= 6 wt % H2O, <= 600 ppm CO2, similar to 0.3-1.0 wt % F, similar to 2300-3500 ppm Cl) and metal-rich (similar to 7-24 ppm Mo, similar to 4-14 ppm W, similar to 21-52 ppm Pb, similar to 28-2700 ppm Zn, <0.1-29 ppm Cu, similar to 0.3-1.8 ppm Bi, similar to 40-760 ppb Ag, similar to 690-1400 ppm Mn). Melt inclusion and pumice matrix glass chemistry reveal that the Hideaway Park magma evolved by large degrees of fractional crystallization (<= 60-70%) during quartz crystallization and melt inclusion entrapment at pressures of <= 300 MPa (<= 8km depth), with little to no crystallization upon shallow ascent and eruption. Filter pressing, crystal settling, magma recharge and mixing of less evolved rhyolite melt, and volatile exsolution were important processes during magma evolution; the low estimated viscosities (similar to 10(5)-10(10) Pa s) of these H2O- and F-rich melts probably enhanced these processes. A noteworthy discrepancy between the metal contents in the pumice matrix glass and in the melt inclusions suggests that after quartz crystallization ceased upon shallow magma ascent and eruption, the Hideaway Park magma exsolved an aqueous fluid into which Mo, Bi, Ag, Zn, Mn, Cs, and Y strongly partitioned. Given that the Henderson deposit contains anomalous abundances of not only Mo, but also W, Pb, Zn, Cu, Bi, Ag, and Mn, we suggest that these metals were sourced from similar fluids exsolved from unerupted portions of the same magmatic system. Trace element ratios imply that Mo was sourced deep, from either the lower crust or metasomatized mantle. The origin of sulfur remains unresolved; however, given the extremely low S solubility of rhyolite melts in the shallow crust we favor the possibility that another source of S might supplement or account for that present in the ore deposit, probably the comagmatic, mantle-derived lamprophyres that occur in minor quantities with the voluminous topaz rhyolites in the area. To account for the 437 Mt of MoS2 (similar to 1.0 x 10(6) t Mo) present in the Henderson ore deposit, a volume of similar to 45 km(3) of Hideaway Park rhyolite magma would have been necessary to supply the Mo (a cylindrical pluton measuring 3.1 km x 6.0 km) along with sparging of similar to 6.8 x 10(5) t of S from similar to 0.05 km(3) of lamprophyre magma. Based on a weighted mean Ar-40/Ar-39 age of 27.58 +/- 0.24 Ma, similar melt geochemistry, and characteristically F-rich biotite phenocrysts, we conclude that the Hideaway Park tuff was cogenetic with the intrusions at Red Mountain that formed the Henderson deposit.
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Metivier L, Brossier R, Virieux J (2015) Combining asymptotic linearized inversion and full waveform inversion. Geophysical Journal International 201(3):1682–1703
Résumé: A method for combining the asymptotic operator designed by Beylkin (Born migration operator) for the solution of linearized inverse problems with full waveform inversion is presented. This operator is used to modify the standard L-2 norm that measures the distance between synthetic and observed data. The modified misfit function measures the discrepancy of the synthetic and observed data after they have been migrated using the Beylkin operator. The gradient of this new misfit function is equal to the cross-correlation of the single scattering data with migrated/demigrated residuals. The modified misfit function possesses a Hessian operator that tends asymptotically towards the identity operator. The trade-offs between discrete parameters are thus reduced in this inversion scheme. Results on 2-D synthetic case studies demonstrate the fast convergence of this inversion method in a migration regime. From an accurate estimation of the initial velocity, three and five iterations only are required to generate high-resolution P-wave velocity estimation models on the Marmousi 2 and synthetic Valhall case studies.
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Milesi V, Guyot F, Brunet F, Richard L, Recham N, Benedetti M, Dairou J, Prinzhofer A (2015) Formation of CO2, H-2 and condensed carbon from siderite dissolution in the 200-300 degrees C range and at 50 MPa. Geochimica Et Cosmochimica Acta 154:201–211
Résumé: Laboratory experiments were conducted to investigate the chemical processes governing the carbon speciation associated to hydrothermal decomposition of siderite. Experiments were carried out in sealed gold capsules using synthetic siderite and deionised water. The samples were reacted at 200 and 300 degrees C, under a pressure of 50 MPa. Siderite dissolved to reach the 3FeCO(3) + H2O = Fe3O4 + 3CO(2) + H-2 equilibrium and magnetite, Fe3O4, was produced accordingly. The gas phase was dominated by CO2, H-2 and CH4, the latter being in strong thermodynamic disequilibrium with CO2. Contrary to the other gas products, H-2 concentration was found to decrease with run duration. TEM observations showed the occurrence of condensed carbon phases at the surfaces of magnetite and residual siderite grains. Thermodynamic calculations predict the formation of condensed carbon in the experiments according to the reaction: CO2 + 2H(2) -> C + 2H(2)O, which accounted for the observed H-2 concentration decrease up to the point where H-2 and CO2 activities were buffered by the graphite-siderite-magnetite assemblage. The well-organized structure of the carbon coating around magnetite emphasizes the high catalytic potential of magnetite surface for carbon reduction and polymerization. The formation of such C-rich phases may represent a potential source of CH4 by hydrogenation. On the other hand, the catalysis of Fischer-Tropsch type reactions may be poisoned by the presence of carbon coating on mineral surfaces. In any case, this study also demonstrates that abiotic H-2 generation by water reduction, widely studied in recent years in ultrabasic contexts, can also occur in sedimentary contexts where siderite is present. We show that, in the latter case, natural H-2 concentration will be buffered by a condensed carbon phase associated with magnetite. (C) 2015 Elsevier Ltd. All rights reserved.
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Minsley BJ, Wellman TP, Walvoord MA, Revil A (2015) Sensitivity of airborne geophysical data to sublacustrine and near-surface permafrost thaw. Cryosphere 9(2):781–794
Résumé: A coupled hydrogeophysical forward and inverse modeling approach is developed to illustrate the ability of frequency-domain airborne electromagnetic (AEM) data to characterize subsurface physical properties associated with sublacustrine permafrost thaw during lake-talik formation. Numerical modeling scenarios are evaluated that consider non-isothermal hydrologic responses to variable forcing from different lake depths and for different hydrologic gradients. A novel physical property relationship connects the dynamic distribution of electrical resistivity to ice saturation and temperature outputs from the SUTRA groundwater simulator with freeze-thaw physics. The influence of lithology on electrical resistivity is controlled by a surface conduction term in the physical property relationship. Resistivity models, which reflect changes in subsurface conditions, are used as inputs to simulate AEM data in order to explore the sensitivity of geophysical observations to permafrost thaw. Simulations of sublacustrine talik formation over a 1000-year period are modeled after conditions found in the Yukon Flats, Alaska. Synthetic AEM data are analyzed with a Bayesian Markov chain Monte Carlo algorithm that quantifies geophysical parameter uncertainty and resolution. Major lithological and permafrost features are well resolved by AEM data in the examples considered. The subtle geometry of partial ice saturation beneath lakes during talik formation cannot be resolved using AEM data, but the gross characteristics of sub-lake resistivity models reflect bulk changes in ice content and can identify the presence of a talik. A final synthetic example compares AEM and ground-based electro-magnetic responses for their ability to resolve shallow permafrost and thaw features in the upper 1-2m below ground outside the lake margin.
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Molina I, Burgisser A, Oppenheimer C (2015) A model of the geochemical and physical fluctuations of the lava lake at Erebus volcano, Antarctica. Journal Of Volcanology And Geothermal Research 308:142–157
Résumé: Erebus volcano, Antarctica, exhibits periodical surface fluctuations of both geochemical and physical nature. Modeling the physics driving the lake oscillation is a challenge, even with a relatively simple theoretical framework. We present a quantitative analysis that aims to reconcile both lake level and gas geochemical cycles. Our model is based on the assumption that the periodicity is caused by the regular release of magma batches and/or core annular flow that have a fixed volume of melt and ascend and degas in equilibrium. Results suggest that cycles are not caused by the mixing between magma residing in the lake and a deep magma but by two distinct deep sources that rise separately. These sources of bubbly magma come from at most 2-3 km depth and rise buoyantly. Individual batches detach from the rising magmas at depths of 20-250 m. The two batch types can coexist in a single conduit up to a depth of similar to 30 m, above which they rise alternately to release respectively 19 and 23 kg/s of gas at the lake surface every 10 min. The temperature of the descending flow is between 890 and 950 degrees C, which is roughly 100 degrees C colder than the ascending currents. Batch pairs have shapes likely constrained by the conduit width. Regardless of their shapes, the pairs reach very high porosities near the surface and have diameters of 4-14 m that are consistent with video observations showing spreading waves at the lake surface. The alternating arrival of these large batches suggests a lava lake mostly filled with gas-rich magma. (C) 2015 Elsevier B.V. All rights reserved.
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Mondelli C, Bardelli F, Vitillo JG, Didier M, Brendle J, Cavicchia DR, Robinet J-C, Charlet L (2015) Hydrogen adsorption and diffusion in synthetic Na-montmorillonites at high pressures and temperature. International Journal Of Hydrogen Energy 40(6):2698–2709
Résumé: Sodium montmorillonite (Na-Mt) was synthesized with the aim to investigate the adsorption and diffusion of hydrogen gas in a model smectite at high pressures (up to 90 bar) and non-cryogenic temperature (363 K). Na-Mt samples were synthesized from hydrogels in mild conditions (493 K and autogenous pressure). Two further Na-Mt samples with different levels of structural iron were prepared to investigate the effect of iron on the textural and hydrogen adsorption properties. Structural and elemental analyses confirmed that well crystalline smectite samples were obtained according to the nominal chemical formulae. Nitrogen adsorption-desorption isotherms revealed that the synthesized materials have specific areas in the range 90-120 m(2)/g and are mainly mesoporous. High pressure volumetric measurements showed that hydrogen absorption at 363 K saturated between 40 and 60 bar, reaching 0.2 +/- 0.02 wt% (i.e. similar to 1.0 mmol/g) at the plateau. Quasielastic neutron scattering revealed ' that hydrogen diffuses inside the clay porous network according to the Fick's law (continuous diffusion), while jump diffusion cannot be excluded at distances lower than 6.3 angstrom, i.e. less than the one between two Na+ exchangeable ions. The hydrogen self-diffusion coefficients in the temperature range 25-300 K were determined to fall in the interval 0.1-1.0 10(-7) m(2) s(-1). The results are compared with H-2(g) adsorption and diffusion in other systems. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
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Montes-Hernandez G, Renard F, Findling N, Auzende A-L (2015) Formation of porous calcite mesocrystals from CO2-H2O-Ca(OH)(2) slurry in the presence of common domestic drinks. Crystengcomm 17(30):5725–5733
Résumé: This study reports a simple, innovative and fast method to synthesize porous calcite mesocrystals with high specific surface area from Ca(OH)(2)-water-CO2 slurry in the presence of common domestic drinks ( soluble coffee, orange juice, carrot juice, white wine, sugar-water and milk). As already reported in previous studies, calcite nanoparticles (<100 nm) can be obtained at low temperature (<= 30 degrees C) in the absence of additives. We demonstrate herein that the use of common domestic drinks as additives can induce the formation of calcite mesocrystals with a peanut-like morphology, i.e. the formation of a nanostructured material in which the constituent calcite nanoparticles (10 < size < 50 nm) are aligned and/or oriented, forming regular micrometric (<3 μm) 3D porous aggregates. We note that the additives used in the system did not induce polymorphism because only calcite was measured/observed in the solid products using XRD, FESEM and TEM or in collected-time suspensions using Raman spectroscopy. This innovative method for synthesizing porous calcite mesocrystals has significant relevance because only a few hours (6 h < time < 24 h) were required and synthesis was possible using a dispersed triphasic gas-liquid-solid system under high non-constant CO2 pressure (anisobaric conditions), contrary to available methods requiring days or weeks, in which reactant diffusion is typically imposed since these systems were initially designed to mimic biomineralization processes. Moreover, this new synthesis method could easily be scaled to industrial processes to produce calcite mesocrystals with high specific surface area (up to 30 m(2) g(-1)). The nanostructured state, the mesoporosity and the high specific surface area for these synthesized calcite mesocrystals could improve the typical industrial and medical uses for synthetic calcite.
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Monteux J, Amit H, Choblet G, Langlais B, Tobie G (2015) Giant impacts, heterogeneous mantle heating and a past hemispheric dynamo on Mars. Physics Of The Earth And Planetary Interiors 240:114–124
Résumé: The martian surface exhibits a strong dichotomy in elevation, crustal thickness and magnetization between the southern and northern hemispheres. A giant impact has been proposed as an explanation for the formation of the Northern Lowlands on Mars. Such an impact probably led to strong and deep mantle heating which may have had implications on the magnetic evolution of the planet. We model the effects of such an impact on the martian magnetic field by imposing an impact induced thermal heterogeneity, and the subsequent heat flux heterogeneity, on the martian core-mantle boundary (CMB). The CMB heat flux lateral variations as well as the reduction in the mean CMB heat flux are determined by the size and geographic location of the impactor. A polar impactor leads to a north-south hemispheric magnetic dichotomy that is stronger than an east-west dichotomy created by an equatorial impactor. The amplitude of the hemispheric magnetic dichotomy is mostly controlled by the horizontal Rayleigh number Ra-h which represents the vigor of the convection driven by the lateral variations of the CMB heat flux. We show that, for a given Rah, an impact induced CMB heat flux heterogeneity is more efficient than a synthetic degree-1 CMB heat flux heterogeneity in generating strong hemispheric magnetic dichotomies. Large Rah values are needed to get a dichotomy as strong as the observed one, favoring a reversing paleo-dynamo for Mars. Our results imply that an impactor radius of 1000 km could have recorded the magnetic dichotomy observed in the martian crustal field only if very rapid post-impact magma cooling took place. (C) 2014 Elsevier B.V. All rights reserved.
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Montinaro A Strauss H. Mason P.R.D. Roerdink D. Münker C. Schwarz-Schampera U. Arndt N.T. Farquhar J. Beukes N. Gutzmer J. Peters M (2015) Paleoarchean sulfur cycling: multiple sulfur isotope constraints from the Barberton Greenstone Belt, South Africa. Precambrian Research 267:311–322
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Morel L, Pottiaux E, Durand F, Fund F, Boniface K, de Oliveira Junior PS, Van Baelen J (2015) Validity and behaviour of tropospheric gradients estimated by GPS in Corsica. Advances In Space Research 55(1):135–149
Résumé: Estimation of tropospheric gradients in GNSS data processing is a well-known technique to improve positioning (e.g. Bar-Sever et al., 1998; Chen and Herring, 1997). More recently, several authors also focused on the estimation of such parameters for meteorological studies and demonstrated their potential benefits (e.g. Champollion et al., 2004). Today, they are routinely estimated by several global and regional GNSS analysis centres but they are still not yet used for operational meteorology. This paper discusses the physical meaning of tropospheric gradients estimated from GPS observations recorded in 2011 by 13 permanent stations located in Corsica Island (a French Island in the western part of Italy). Corsica Island is a particularly interesting location for such study as it presents a significant environmental contrast between the continent and the sea, as well as a steep topography. Therefore, we estimated Zenith Total Delay (ZTD) and tropospheric gradients using two software: GAMIT/GLOBK (GAMIT version 10.5) and GIPSY-OASIS II version 6.1. Our results are then compared to radiosonde observations and to the IGS final troposphere products. For all stations we found a good agreement between the ZWD estimated by the two software (the mean of the ZWD differences is 1 mm with a standard deviation of 6 mm) but the tropospheric gradients are in less good agreement (the mean of the gradient differences is 0.1 mm with a standard deviation of 0.7 mm), despite the differences in the processing strategy (double-differences for GAMIT/GLOBK versus zero-difference for GIPSY-OASIS). We also observe that gradient amplitudes are correlated with the seasonal behaviour of the humidity. Like ZWD estimates, they are larger in summer than in winter. Their directions are stable over the time but not correlated with the IWV anomaly observed by ERA-Interim. Tropospheric gradients observed at many sites always point to inland throughout the year. These preferred directions are almost opposite to the largest slope of the local topography as derived from the world Digital Elevation Model ASTER GDEM v2. These first results give a physical meaning to gradients but the origin of such directions need further investigations. (C) 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.
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Mousavi Z, Pathier E, Walker RT, Walpersdorf A, Tavakoli F, Nankali H, Sedighi M, Doin M-P (2015) Interseismic deformation of the Shahroud fault system (NE Iran) from space-borne radar interferometry measurements. Geophysical Research Letters 42(14):5753–5761
Résumé: The Shahroud fault system is a major active structure in the Alborz range of NE Iran whose slip rate is not well constrained despite its potential high seismic hazard. In order to constrain the slip rate of the eastern Shahroud fault zone, we use space-borne synthetic aperture radar interferometry with both ascending and descending Envisat data to determine the rate of interseismic strain accumulation across the system. We invert the slip rate from surface velocity measurements using a half-space elastic dislocation model. The modeling results are consistent with a left-lateral slip rate of 4.750.8mm/yr on the Abr and Jajarm, strands of the Shahroud fault, with a 104km locking depth. This is in good agreement with the 4-6mm/yr of left-lateral displacement rate accumulated across the total Shahroud fault system obtained from GPS measurements.
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Moussallam Y, Oppenheimer C, Scaillet B, Buisman I, Kimball C, Dunbar N, Burgisser A, Schipper CI, Andujar J, Kyle P (2015) Megacrystals track magma convection between reservoir and surface. Earth And Planetary Science Letters 413:1–12
Résumé: Active volcanoes are typically fed by magmatic reservoirs situated within the upper crust. The development of thermal and/or compositional gradients in such magma chambers may lead to vigorous convection as inferred from theoretical models and evidence for magma mixing recorded in volcanic rocks. Bi-directional flow is also inferred to prevail in the conduits of numerous persistently-active volcanoes based on observed gas and thermal emissions at the surface, as well as experiments with analogue models. However, more direct evidence for such exchange flows has hitherto been lacking. Here, we analyse the remarkable oscillatory zoning of anorthoclase feldspar megacrystals erupted from the lava lake of Erebus volcano, Antarctica. A comprehensive approach, combining phase equilibria, solubility experiments and melt inclusion and textural analyses shows that the chemical profiles are best explained as a result of multiple episodes of magma transport between a deeper reservoir and the lava lake at the surface. Individual crystals have repeatedly travelled up-and-down the plumbing system, over distances of up to several kilometers, presumably as a consequence of entrainment in the bulk magma flow. Our findings thus corroborate the model of bi-directional flow in magmatic conduits. They also imply contrasting flow regimes in reservoir and conduit, with vigorous convection in the former (regular convective cycles of similar to 150 days at a speed of similar to 0.5 mm s(-1)) and more complex cycles of exchange flow and re-entrainment in the latter. We estimate that typical, 1-cm-wide crystals should be at least 14 years old, and can record several (from 1 to 3) complete cycles between the reservoir and the lava lake via the conduit. This persistent recycling of phonolitic magma is likely sustained by CO2 fluxing, suggesting that accumulation of mafic magma in the lower crust is volumetrically more significant than that of evolved magma within the edifice. (C) 2015 The Authors. Published by Elsevier B.V.
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Nataf H-C and S Nathanael (2015) Turbulence in the core. 8, Core Dynamics(2nd Edition):161–181
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Naylor M, Sinclair HD, Bernet M, van der Beek P, Kirstein LA (2015) Bias in detrital fission track grain-age populations: Implications for reconstructing changing erosion rates. Earth And Planetary Science Letters 422:94–104
Résumé: The sedimentary record is our principal archive of mass transfer across the Earth's surface in response to tectonic and climatic changes in the geologic past. The thermochronology of individual sediment grains (detrital thermochronology) has emerged as a critical tool to infer erosion rates and track mountain belt evolution. Such inferences are reliant upon the statistical inversion of detrital grain ages to unbiasedly approximate the cooling history of the source areas from which the sediment originated. However, it is challenging to critique the reliability and consistency of modelled ages. These arise both from fundamental measurement uncertainties and the assumptions we employ in inverting the data. For detrital fission track modelling of young detrital samples, this problem is particularly acute since the uncertainty on the track counts produces uncertainty in the age estimates. We apply Monte-Carlo modelling to generate synthetic detrital data conditioned on known closure age models, and then invert the grain data to assess the reliability of different inversion schemes. The results clearly demonstrate that existing practice can be subject to large uncertainty, to systematic bias and to non-uniqueness of interpretation. We then show how to map such regions of systematic bias in the population modelling as a function of the true closure ages, and how this bias propagates through into the lag-time modelling. Applying the method to real data from the Siwalik group sediments in western Nepal, we find no evidence for a change in the underlying climate or tectonic processes, since the apparent change in lag coincides with a thresholded change in the resolution of the population modelling. This paper shows how to map regions of systematic bias in the population modelling as a function of the true closure ages, and how this bias propagates through into the lag-time modelling and can be applied retrospectively to existing studies. However, it is equally applicable to other age inversion schemes such as minimum age modelling. The application of these methods will enhance current practice and facilitate more robust interpretation of grain ages, in particular in discriminating between stationary and non-stationary geological and climatic processes. Crown Copyright (C) 2015 Published by Elsevier BAT. All rights reserved.
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Nexer M, Authemayou C, Schildgen T, Hantoro WS, Molliex S, Delcaillau B, Pedoja K, Husson L, Regard V (2015) Evaluation of morphometric proxies for uplift on sequences of coral reef terraces: A case study from Sumba Island (Indonesia). Geomorphology 241:145–159
Résumé: Sequences of coral reef terraces characterized by staircase morphologies and a homogeneous lithology make them appropriate to isolate the influence of uplift on drainage morphology. Along the northern coast of Sumba Island, Indonesia, we investigated the correlations between landscape morphology and uplift rates, which range from 0.02 to 0.6 mm.yr(-1). We studied eight morphometric indices at two scales: whole island (similar to 11,000 km(2)) and within sequences of reefal terraces (similar to 3000 km(2)). At the latter scale, we extracted morphometric indices for 15 individual catchments draining mostly the reefal terraces and for 30 areas undergoing specific ranges of uplift rates draining only the reefal terraces. Indices extracted from digital elevation models include residual relief, incision, stream gradient indices (SL and k(sn)), the hypsometric integral, drainage area, mean relief, and the shape factor. We find that SL, the hypsometric integral, mean relief and the shape factor of catchments positively correlate with uplift rates, whereas incision, residual relief, and k(sn) do not. More precisely, we find that only the areas that are uplifting at a rate faster than 03 mm.yr(-1) can yield the extreme values for these indices, implying that these extreme values are indicative of fast uplifting areas. However, the relationship is not bivalent because any uplift rate can be associated with low values of the same indices. For all indices, the transient conditions of the drainage influence the correlation with Pleistocene mean uplift rates, illustrating the necessity to extract morphometric indices with an appropriate choice of catchment scale. This type of analysis helps to identify the morphometric indices that are most useful for tectonic analysis in areas of unknown uplift, allowing for easy identification of short spatial variations of uplift rate and detection of areas with relatively fast uplift rates in unstudied coastal zones. (C) 2015 Elsevier B.V. All rights reserved.
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Niane B, Guedron S, Moritz R, Cosio C, Ngom PM, Deverajan N, Pfeifer HR, Pote J (2015) Human exposure to mercury in artisanal small-scale gold mining areas of Kedougou region, Senegal, as a function of occupational activity and fish consumption. Environmental Science And Pollution Research 22(9):7101–7111
Résumé: We investigated mercury (Hg) exposure of food web and humans in the region of Kedougou, Senegal, where Hg is used for gold amalgamation in artisanal small-scale gold mining (ASGM). For this purpose, total mercury (THg) concentration was determined in eight fish species and two shellfish species from Gambia River and in human hair from 111 volunteers of different age and sex, living in urban locations (Kedougou and Samekouta) or in ASGM areas (Tinkoto and Bantako). THg concentrations in fish samples range from 0.03 to 0.51 mg kg(-1) wet weight (ww) and 0.5 to 1.05 mg kg(-1) ww for shellfish. THg concentrations in fish are below the WHO guideline of 0.5 mg kg(-1) ww, whereas 100 % of shellfish are above this safety guideline. In the entire set of fish and shellfish samples, we documented a decrease of THg concentrations with increasing selenium to mercury (Se:Hg) ratio suggesting a protection of Se against Hg. However, local population consuming fish from the Gambia River in the two ASGM areas have higher THg concentrations (median = 1.45 and 1.5 mg kg(-1) at Bantako and Tinkoto) in hair than those from others localities (median = 0.42 and 0.32 mg kg(-1) at Kedougou town and Samekouta) who have diverse diets. At ASGM sites, about 30 % of the local population present Hg concentrations in hair exceeding 1 mg kg(-1), defined as the reference concentration of Hg in hair. We also evidence a higher exposure of women to Hg in the Tinkoto ASGM site due to the traditional distribution of daily tasks where women are more involved in the burning of amalgams. The discrepancy between the calculated moderate exposure through fish consumption and the high Hg concentrations measured in hair suggest that fish consumption is not the only source of Hg exposure and that further studies should focus on direct exposure to elemental Hg of population living at ASGM sites.
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Noel V, Morin G, Juillot F, Marchand C, Brest J, Bargar JR, Munoz M, Marakovic G, Ardo S, Brown GE Jr. (2015) Ni cycling in mangrove sediments from New Caledonia. Geochimica Et Cosmochimica Acta 169:82–98
Résumé: Covering more than 70% of tropical and subtropical coastlines, mangrove intertidal forests are well known to accumulate potentially toxic trace metals in their sediments, and thus are generally considered to play a protective role in marine and lagoon ecosystems. However, the chemical forms of these trace metals in mangrove sediments are still not well known, even though their molecular-level speciation controls their long-term behavior. Here we report the vertical and lateral changes in the chemical forms of nickel, which accumulates massively in mangrove sediments downstream from lateritized ultramafic deposits from New Caledonia, where one of nature's largest accumulations of nickel occurs. To accomplish this we used Ni K-edge Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy data in combination with microscale chemical analyses using Scanning Electron Microscopy coupled with Energy-Dispersive X-ray Spectroscopy (SEM-EDXS). After Principal Component and Target Transform analyses (PCA-TT), the EXAFS data of the mangrove sediments were reliably least-squares fitted by linear combination of 3-components chosen from a large model compound spectral database including synthetic and natural Ni-bearing sulfides, clay minerals, oxyhydroxides, and organic complexes. Our results show that in the inland salt flat Ni is hosted in minerals inherited from the eroded lateritic materials, i.e. Ni-poor serpentine (44-58%), Ni-rich talc (20-31%), and Ni-goethite (18-24%). In contrast, in the hydromorphic sediments beneath the vegetated Avicennia and Rhizophora stands, a large fraction of Ni is partly redistributed into a neoformed smectite pool (20-69% of Ni-montmorillonite), and Ni speciation significantly changes with depth in the sediment. Indeed, Ni-rich talc (25-56%) and Ni-goethite (15-23%) disappear below similar to 15 cm depth in the sediment and are replaced by Ni-sorbed pyrite (23-52%) in redox-active intermediate depth layers and by pyrite (34-55%) in the deepest sediment layers. Ni-incorporation in pyrite is especially observed beneath an inland Avicennia stand where anoxic conditions are dominant. In contrast, beneath a Rhizophora stand closer to the ocean, where the redox cycle is intensified due to the tide cycle, partial re-oxidation of Ni-bearing pyrites favors nickel mobility, as confirmed by Ni-mass balance estimates and by higher Ni concentration in the pore waters. These findings have important environmental implications for better evaluating the protective role of mangroves against trace metal dispersion into marine ecosystems. They may also help in predicting the response of mangrove ecosystems to increasing anthropogenic pressure on coastal areas. (C) 2015 Elsevier Ltd. All rights reserved.
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Obermann A, Kraft T, Larose E, Wiemer S (2015) Potential of ambient seismic noise techniques to monitor the St. Gallen geothermal site (Switzerland). Journal Of Geophysical Research-Solid Earth 120(6):4301–4316
Résumé: The failures of two recent deep geothermal energy projects in Switzerland (Basel, 2006; St. Gallen, 2013) have again highlighted that one of the key challenges for the successful development and operation of deep underground heat exchangers is to control the risk of inducing potentially hazardous seismic events. In St. Gallen, after an injection test and two acid injections that were accompanied by a small number of micro-earthquakes (M-L<0.2), operators were surprised by an uncontrolled gas release from the formation (gas kick). The killing procedures that had to be initiated following standard drilling procedures led to a M(L)3.5 earthquake. With ambient seismic noise cross correlations from nine stations, we observe a significant loss of waveform coherence that we can horizontally and vertically constrain to the injection location of the fluid. The loss of waveform coherence starts with the onset of the fluid injections 4days prior to the gas kick. We interpret the loss of coherence as a local perturbation of the medium. We show how ambient seismic noise analysis can be used to assess the aseismic response of the subsurface to geomechanical well operations and how this method could have helped to recognize the unexpected reservoir dynamics at an earlier stage than the microseismic response alone, allowed.
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Olivier G, Brenguier F, Campillo M, Lynch R, Roux P (2015) Body-wave reconstruction from ambient seismic noise correlations in an underground mine. Geophysics 80(3):KS11–KS25
Résumé: The reconstruction of seismic Green's functions from correlations of ambient seismic noise has recently developed as a promising approach for exploring the earth's interiors without the requirement of costly active seismic sources. This approach is widely used for imaging the crust at a kilometer scale. However, few studies report noise-based Green's function reconstruction at smaller scales in industrial environments. We have investigated the possibility of constructing seismic Green's functions between sensors in an active underground mine (Garpenberg, Sweden) by crosscorrelating seismic noise generated by mining activities. We have determined with realistic numerical simulations that the mining excavations in an underground mine lead to a regime of strong scattering, which is favorable for constructing seismic Green's functions by crosscorrelating seismic noise. One month of continuous data was recorded by 18 seismic sensors located more than 1 km below surface. A variety of broadband (10-3000 Hz) seismic sources were present, but the seismic wave-fields are directional and often monochromatic, so that the conditions for constructing Green's functions by crosscorrelating ambient seismic noise were not ideal (isotropic illumination and spectrally white). We developed a stacking scheme that dismissed data during periods when the seismic noise was dominated by monochromatic signals or when noise sources were not in stationary phase locations. Estimates of the seismic Green's functions were retrieved for a broad frequency range (20-400 Hz) for almost all of the correlation pairs when we used the selective stacking scheme. We used the direct body waves present at low frequencies (less than 100 Hz) in the reconstructed seismic Green's functions to invert for the 3D S-wave velocity structure of the mine. Our results revealed the existence of a high-velocity zone and a low-velocity zone that corresponded with known ore bodies.
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Olivier G, Brenguier F, Campillo M, Roux P, Shapiro NM, Lynch R (2015) Investigation of coseismic and postseismic processes using in situ measurements of seismic velocity variations in an underground mine. Geophysical Research Letters 42(21):9261–9269
Résumé: The in situ mechanical response of a rock mass to a sudden dynamic and static stress change is still poorly known. To tackle this question, we conducted an experiment in an underground mine to examine (1) the influence of dynamic and static stress perturbations on seismic velocities, (2) elastic static stress changes, and (3) induced earthquake activity associated with the blast and removal of a portion of hard rock. We accurately (0.01%) measured seismic velocity variations with ambient seismic noise correlations, located aftershock activity, and performed elastic static stress modeling. Overall, we observe that the blast induced a sudden decrease in seismic velocities over the entire studied area, which we interpreted as the damage due to the passing of strong seismic waves. This sudden process is followed by a slow relaxation lasting up to 5 days, while seismic activity returns to its background level after 2 days. In some locations, after the short-term effects of the blast have subsided, the seismic velocities converge to new baseline levels and permanent changes in seismic velocity become visible. After comparing the spatial pattern of permanent seismic velocity changes with elastic static stress modeling, we infer that the permanent seismic velocity changes are due to the change in the static volumetric stress induced by the removal of a solid portion of rock by the blast. To our knowledge, this is the first observation of noise-based permanent seismic velocity changes associated with static stress changes.
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Operto S, Miniussi A, Brossier R, Combe L, Metivier L, Monteiller V, Ribodetti A, Virieux J (2015) Efficient 3-D frequency-domain mono-parameter full-waveform inversion of ocean-bottom cable data: application to Valhall in the visco-acoustic vertical transverse isotropic approximation. Geophysical Journal International 202(2):1362–1391
Résumé: Computationally efficient 3-D frequency-domain full waveform inversion (FWI) is applied to ocean-bottom cable data from the Valhall oil field in the visco-acoustic vertical transverse isotropic (VTI) approximation. Frequency-domain seismic modelling is performed with a parallel sparse direct solver on a limited number of computer nodes. A multiscale imaging is performed by successive inversions of single frequencies in the 3.5-10 Hz frequency band. The vertical wave speed is updated during FWI while density, quality factor Q(P) and anisotropic Thomsen's parameters delta and epsilon are kept fixed to their initial values. The final FWI model shows the resolution improvement that was achieved compared to the initial model that was built by reflection traveltime tomography. This FWI model shows a glacial channel system at 175 m depth, the footprint of drifting icebergs on the palaeo-seafloor at 500 m depth, a detailed view of a gas cloud at 1 km depth and the base cretaceous reflector at 3.5 km depth. The relevance of the FWI model is assessed by frequency-domain and time-domain seismic modelling and source wavelet estimation. The agreement between the modelled and recorded data in the frequency domain is excellent up to 10 Hz although amplitudes of modelled wavefields propagating across the gas cloud are overestimated. This might highlight the footprint of attenuation, whose absorption effects are underestimated by the homogeneous background Q(P) model (Q(P) = 200). The match between recorded and modelled time-domain seismograms suggests that the inversion was not significantly hampered by cycle skipping. However, late arrivals in the synthetic seismograms, computed without attenuation and with a source wavelet estimated from short-offset early arrivals, arrive 40ms earlier than the recorded seismograms. This might result from dispersion effects related to attenuation. The repeatability of the source wavelets inferred from data that are weighted by a linear gain with offset is dramatically improved when they are estimated in the FWI model rather than in the smooth initial model. The two source wavelets, estimated in the FWI model from data with and without offset gain, show a 40ms time-shift, which is consistent with the previous analysis of the time-domain seismograms. The computational efficiency of our frequency-domain approach is assessed against a recent time-domain FWI case study performed in a similar geological environment. This analysis highlights the efficiency of the frequency-domain approach to process a large number of sources and receivers with limited computational resources, thanks to the efficiency of the substitution step performed by the direct solver. This efficiency can be further improved by using a block-low rank version of the multifrontal solver and by exploiting the sparsity of the source vectors during the substitution step. Future work will aim to update attenuation and density at the same time of the vertical wave speed.
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Ou J, Gillet N, Du A (2015) Geomagnetic observatory monthly series, 1930 to 2010: empirical analysis and unmodeled signal estimation. Earth Planets And Space 67
Résumé: Ground-based magnetic observatory series are the main source of information for constructing time-dependent spherical harmonic geomagnetic field models from sub-annual to pluri-decadal time scales. Assessing the reliability of such models requires accurate estimation of the data errors. We propose an analysis of observatory monthly means over the period 1930 to 2010, where we sequentially isolate (i) a stochastic regression for the main field at every site, performed in the framework of Gaussian processes, (ii) a local fit to annual and semiannual signals, (iii) a month by month estimate of global, large length-scale external and induced fields. We then estimate the unmodeled signal level (UMSL, which refers to the instrumental noise plus extra signals not captured by the above data treatment) from the standard deviation of the residuals to the sequential analysis. This may be used to estimate data error covariances in future field modeling studies. Mainly a function of the geomagnetic latitude, the UMSL is larger towards auroral regions and carries the temporal signature of solar activity. While the UMSL shows rather similar magnitudes in all three components in recent epochs (typically a few nT), a significant decrease is found in the downward component of the field around 1960, which correlates with the introduction of proton magnetometers. We detail the geographic distribution of the periodic signals and confirm the variation of their amplitude at pluri-decadal time scales. From the spherical harmonic description of horizontal and vertical fields, we isolate the main patterns of the inducing field in Z. These are dominated by a zonal structure of degree 1 (and to a lesser extent, of degree 3) in dipole coordinates. We nevertheless isolate secondary, non-zonal sources that are most active during the 1960s and around 1990, periods of particularly large solar activity, denoting an unusual morphology of the inducing field.
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Pais MA, Morozova AL, Schaeffer N (2015) Variability modes in core flows inverted from geomagnetic field models. Geophysical Journal International 200(1):402–420
Résumé: The flow of liquid metal inside the Earth's core produces the geomagnetic field and its time variations. Understanding the variability of those deep currents is crucial to improve the forecast of geomagnetic field variations and may provide relevant information on the core dynamics. The main goal of this study is to extract and characterize the leading variability modes of core flows over centennial periods, and to assess their statistical robustness. To this end, we use flows that we invert from two geomagnetic fieldmodels ('gufm1' and 'COV-OBS'), and apply principal component analysis and singular value decomposition of coupled fields. The quasi-geostrophic (QG) flows inverted from both geomagnetic field models show similar features. However, 'COV-OBS' flows have a less energetic mean and larger time variability. The statistical significance of flow components is tested from analyses performed on subareas of the whole domain. Bootstrapping methods are also used to extract significant flow features required by both 'gufm1' and 'COV-OBS'. Three main empirical circulation modes emerge, simultaneously constrained by both geomagnetic field models and expected to be robust against the particular a priori used to build them (large-scale QG dynamics). Mode 1 exhibits three large vortices at medium/high latitudes, with opposite circulation under the Atlantic and the Pacific hemispheres. Mode 2 interestingly accounts for most of the variations of the Earth's core angular momentum. In this mode, the regions close to the tangent cylinder and to the equator are correlated, and oscillate with a period between 80 and 90 yr. Each of these two modes is energetic enough to alter the mean flow, sometimes reinforcing the eccentric gyre, and other times breaking it up into smaller circulations. The three main circulation modes added to the mean flow account for about 70 per cent of the flows variability, 90 per cent of the rms total velocities, and 95 per cent of the secular variation induced by the total flows. Direct physical interpretation of the computed modes is not straightforward. Nonetheless, similarities found between the two first modes and time/spatial features identified in different studies of core dynamics, suggest that our approach can help to pinpoint the relevant physical processes inside the core on centennial timescales.
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Pattier F, Loncke L, Imbert P, Gaullier V, Basile C, Maillard A, Roest WR, Patriat M, Vendeville BC, Marsset T, Bayon G, Cathalot C, Caprais JC, Bermell S, Sotin C, Hebert B, de Lepinay MM, Lebrun JF, Marcaillou B, Heuret A, Droz L, Graindorge D, Poetisi E, Berrenstein H (2015) Origin of an enigmatic regional Mio-Pliocene unconformity on the Demerara plateau. Marine Geology 365:21–35
Résumé: The Demerara plateau, located offshore French Guiana and Suriname, is part of a passive transform continental margin particularly prone to develop slope instabilities, probably in relation to the presence of a free distal border along its steep continental slope. Slope failure occurred at different periods (Cretaceous to Neogene) and shows an overall retrogressive evolution through time. Upslope these failure headscarp, an enigmatic regional MioPliocene unconformity has been discovered through the interpretation of new academic and industrial datasets. The aim of this work is to describe and understand the origin of this surface. Our analysis shows that this unconformity is made of a series of valleys that cross-cut sedimentary strata. Each one of these valleys has a short lateral extent and is closed along two perpendicular directions, which suggests that it could correspond to a highly meandering system, or to some sub-circular depressions. The infill of these features is equivalent to the regional stratigraphic strata found outside the structures, but in a subdued position. This seems to imply that the structures have originated by a local loss of sediments at their base or by sliding processes. Furthermore, these depressions intersect each other through time, while migrating progressively downslope. We discuss a series of hypotheses that try to explain the onset and evolution of these depressions forming the Mio-Pliocene unconformity (Canyons? Slope failures? Contourite moats? Hydrate pockmarks?). Having established that these structures are depressions formed by collapse, and have many similarities with structures recently described in the literature as pockmarks associated with gas hydrate dissolution, we favor this hypothesis. We propose that these hydrate pockmarks form with a mass failure that was triggered by fluid-overpressure development at the base of the hydrate stability zone. (C) 2015 Elsevier B.V. All rights reserved.
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Pedersen HA, Boue P, Poli P, Colombi A (2015) Arrival angle anomalies of Rayleigh waves observed at a broadband array: a systematic study based on earthquake data, full waveform simulations and noise correlations. Geophysical Journal International 203(3):1626–1641
Résumé: Deviation of seismic surface waves from the great-circle between source and receiver is illustrated by the anomalies in the arrival angle, that is the difference between the observed backazimuth of the incident waves and the great-circle. Such arrival angle anomalies have been known for decades, but observations remain scattered. We present a systematic study of arrival angle anomalies of fundamental mode Rayleigh waves (20-100 s period interval) from 289 earthquakes and recorded by a broadband network LAPNET, located in northern Finland. These observations are compared with those of full waveform synthetic seismograms for the same events, calculated in a 3-D Earth and also compared with those of seismograms obtained by ambient noise correlation. The arrival angle anomalies for individual events are complex, and have significant variations with period. On average, the mean absolute deviation decreases from similar to 9 degrees. at 20 s period to similar to 3 degrees. at 100 s period. The synthetic seismograms show the same evolution, albeit with somewhat smaller deviations. While the arrival angle anomalies are fairly well simulated at long periods, the deviations at short periods are very poorly modelled, demonstrating the importance of the continuous improvement of global crustal models. At 20-30 s period, both event data and numerical simulations have strong multipathing, and relative amplitude changes between different waves will induced differences in deviations between very closely located events. The source mechanism has only limited influence on the deviations, demonstrating that they are directly linked to propagation effects, including near-field effects in the source area. This observation is confirmed by the comparison with seismic noise correlation records, that is where the surface waves correspond to those emitted by a point source at the surface, as the two types of observations are remarkably similar in the cases where earthquakes are located close to seismic stations. This agreement additionally confirms that the noise correlations capture the complex surface wave propagation.
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Peltier A, Got J-L, Villeneuve N, Boissier P, Staudacher T, Ferrazzini V, Walpersdorf A (2015) Long-term mass transfer at Piton de la Fournaise volcano evidenced by strain distribution derived from GNSS network. Journal Of Geophysical Research-Solid Earth 120(3):1874–1889
Résumé: Basaltic volcanoes are among the largest volcanic edifices on the Earth. These huge volcanoes exhibit rift zones and mobile flanks, revealing specific stress field conditions. In this paper, we present new deformation data issued from the Global Navigation Satellite Systems (GNSS) network installed on Piton de la Fournaise. Density of the GNSS stations allowed us to reach a sufficient resolution to perform a spatially significant analysis of strain at the scale of the active part of the volcano. Since 2007, summit inflation during preeruptive/eruptive sequences (summit extension/cone flanks contraction) alternates with summit deflation during posteruptive/rest periods (summit contraction/cone flanks extension) and generates a pulsation of the volcano. This volcano pulsation increases rock fracturing and damage, decreases the rock stiffness, and increases the medium permeability. The deformation regime of the mobile eastern flank evidences mass transfer in depth from the summit to the east. During the long-term summit deflation recorded between 2011 and 2014, the upper eastern flank extended steadily eastward whereas the lower eastern flank contracted. Simultaneous extension and eastward displacement of the upper eastern flank and eastward contraction of the middle and lower eastern flank contributes to build the Grandes Pentes relief, steeping the topographic slope. We relate the eastern flank topographic slope spatial variations to rock or basal friction angle changes. The lower flank contraction process is an evidence of its progressive loading by the upper eastern flank, which brings this flank closer to an eventual instability.
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Perrault M, Gueguen P (2015) Correlation between Ground Motion And Building Response Using California Earthquake Records. Earthquake Spectra 31(4):2027–2046
Résumé: Using data from the California Strong Motion Instrumentation Program, we studied the relationship between building response and parameters describing the noxiousness of ground motion. According to vulnerability methods that use structural drift as damage criteria, we estimated the building response on the basis of the normalized relative roof displacement (NRRD), considered as damage criteria. The relationships between the NRRD and the intensity measures of the ground motion are developed using simulated annealing method. Grouping buildings by typology (defined according to their main construction material and height) reduces the variability of the building response. Furthermore, by combining IMs, the NRRD can be predicted more accurately by a building damage prediction equation. A functional form is thus proposed to estimate the NRRD for several building typologies, calibrated on the building responses recorded in California. This functional form can be used to obtain a fast and overall damage forecast after an earthquake.
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Perrouty S, Moussirou B, Martinod J, Bonvalot S, Carretier S, Gabalda G, Monod B, Herail G, Regard V, Remy D (2015) Geometry of two glacial valleys in the northern Pyrenees estimated using gravity data. Comptes Rendus Geoscience 347(1):13–23
Résumé: We estimate using gravity data the thickness of post-glacial unconsolidated sediment filling two major glacial valleys in northern Pyrenees: the Gave de Pau valley between Pierrefitte-Nestalas and Lourdes, and the Garonne valley between Saint-Beat and Barbazan. One hundred and eighty-four new gravity data complete 74 measurements obtained from the International Gravimetric Bureau database. Negative residual anomalies resulting from the presence of small-density unconsolidated sediment approach 4 mgal in both the Gave de Pau and the Garonne valleys. Estimating the sediment thickness requires knowing the density contrast between Quaternary sediments and the underlying bedrock. Supposing this density contrast is 600 kg/m(3), the maximum estimated thickness of post-glacial sediment is similar to 230 and 300 meters, and the volume of sediment is 2.1 and 3.2 km(3) in the Gave de Pau and Garonne valleys, respectively. In both valleys, the depth of Quaternary sediment suddenly increases at the confluence between two major glacial valleys (Gave de Pau – Gave de Cauterets, and Garonne – Pique confluences). Overdeepened basins are less deep downstream when approaching terminal moraines (Lourdes and Barbazan area), illustrating that the efficiency of glacial erosion depends on the ice flux flowing through valleys. (C) 2015 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
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Planes T, Larose E, Rossetto V, Margerin L (2015) Imaging multiple local changes in heterogeneous media with diffuse waves. Journal Of The Acoustical Society Of America 137(2):660–667
Résumé: This study focuses on imaging local changes in heterogeneous media. The method employed is demonstrated and validated using numerical experiments of acoustic wave propagation in a multiple scattering medium. Changes are simulated by adding new scatterers of different sizes at various positions in the medium, and the induced decorrelation of the diffuse (coda) waveforms is measured for different pairs of sensors. The spatial and temporal dependences of the decorrelation are modeled through a diffuse sensitivity kernel, based on the intensity transport in the medium. The inverse problem is then solved with a linear least square algorithm, which leads to a map of scattering cross section density of the changes. (C) 2015 Acoustical Society of America.
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Poli P, Thomas C, Campillo M, Pedersen HA (2015) Imaging the D '' reflector with noise correlations. Geophysical Research Letters 42(1):60–65
Résumé: The lowermost mantle of the Earth is characterized by seismic structures that range from a few tens to thousands of kilometers. At present, it is difficult to test hypotheses put forward to explain seismic observations due to poor seismic coverage, as particular earthquake-station geometries are needed. We demonstrate here that seismic noise correlations can be used to robustly image deep-mantle reflections with larger stacked amplitudes of reflected waves compared with earthquake data. In a comparison between noise and earthquake data, we find that the arrival times and the slowness of reflected waves, both sampling a region beneath Siberia, agree with those for a reflector at 2530km depth, and the small amplitude reflections are sufficiently clear in the noise correlations to compare them reliably with synthetic data. Our data open exciting prospects for illuminating new target zones in the deep mantle to further constrain the dynamics and mineralogy of the deep Earth.
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Pradhan GK, Fiquet G, Siebert J, Auzende A-L, Morard G, Antonangeli D, Garbarino G (2015) Melting of MORB at core-mantle boundary. Earth And Planetary Science Letters 431:247–255
Résumé: We investigated the melting properties of natural mid-ocean ridge basalt (MORB) up to core-mantle boundary (CMB) pressures using laser-heated diamond anvil cell. Textural and chemical characterizations of quenched samples were performed by analytical transmission electron microscopy. We used in situ X-ray diffraction primarily for phase identification whereas our melting criterion based on laser power versus temperature plateau combined with textural analysis of recovered solidus and subsolidus samples is accurate and unambiguous. At CMB pressure (135 GPa), the MORB solidus temperature is 3970 (+/- 150) K. Quenched melt textures observed in recovered samples indicate that CaSiO3 perovskite (CaPv) is the liquidus phase in the entire pressure range up to CMB. The partial melt composition derived from the central melt pool is enriched in FeO, which suggests that such melt pockets may be gravitationally stable at the core mantle boundary. (C) 2015 Elsevier B.V. All rights reserved.
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Qiu L, Yan D-P, Tang S-L, Arndt NT, Fan L-T, Guo Q-Y, Cui J-Y (2015) Cooling and exhumation of the oldest Sanqiliu uranium ore system in Motianling district, South China Block. Terra Nova 27(6):449–457
Résumé: The Sanqiliu uranium deposit belongs to a uranium ore system in Motianling district. It is the oldest uranium deposit in South China. Primary uranium mineralization occurred almost simultaneously with the emplacement of the host granites and subsequent dykes, and it has a relatively high grade of uranium (0.421%). We clarify the age of mineralization and investigate the cooling history through new pitchblende U-Pb and apatite fission-track thermochronology. The pitchblende U-Pb results indicate that uranium mineralization occurred at similar to 801-759 Ma. Fractionation of uranium and lead at similar to 374-295 Ma is interpreted as remobilization and resetting of the original uranium. The Motianling area has apatite fission-track ages of 57 to 18 Ma. By combining our results with previous work, we conclude that the deposit cooled slowly and was exposed at the surface during the Cenozoic. The timing and depth of exhumation helped to preserve and avoid erosion of the uranium deposit, and highlight the potential for regional uranium exploration.
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Rabatel M, Labbe S, Weiss J (2015) Dynamics of an assembly of rigid ice floes. Journal Of Geophysical Research-Oceans 120(9):5887–5909
Résumé: In this paper, we present a model describing the dynamics of a population of ice floes with arbitrary shapes and sizes, which are exposed to atmospheric and oceanic skin drag. The granular model presented is based on simplified momentum equations for ice floe motion between collisions and on the resolution of linear complementarity problems to deal with ice floe collisions. Between collisions, the motion of an individual ice floe satisfies the linear and angular momentum conservation equations, with classical formula applied to account for atmospheric and oceanic skin drag. To deal with collisions, before they lead to interpenetration, we included a linear complementarity problem based on the Signorini condition and Coulombs law. The nature of the contact is described through a constant coefficient of friction , as well as a coefficient of restitution (0 epsilon 1) describing the loss of kinetic energy during the collision. In the present version of our model, this coefficient is fixed. The model was validated using data obtained from the motion of interacting artificial wood floes in a test basin. The results of simulations comprising few hundreds of ice floes of various shapes and sizes, exposed to different forcing scenarios, and under different configurations, are also discussed. They show that the progressive clustering of ice floes as the result of kinetic energy dissipation during collisions is well captured, and suggest a collisional regimes of floe dispersion at small scales, different from a large-scale regime essentially driven by wind forcing.
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Ramos Riesco M, Martinez-Casado FJ, Rodriguez Cheda JA, Redondo Yelamos MI, Fernandez-Martinez A, Lopez-Andres S (2015) Study of the Polymorphism in Copper(II) Decanoate through Its Phase Diagram with Decanoic Acid, and Texture of the Columnar Thermotropic Liquid Crystal Developable Domains in This and Similar Systems. Crystal Growth & Design 15(1):497–509
Résumé: A new third polymorph of copper(II) decanoate has been found by two methods: from the crystallization of the saltacid solution and from a specific thermal treatment of the polymorph obtained in n-heptane. The new polymorph, whose crystal structure has been solved for the first time, is the most stable from the thermodynamic point of view. It presents a bilayer structure, but with two different types of paddle-wheels catenae with opposite orientations. This polymorphism as well as the temperature vs composition phase diagram of the system, [(1 – x) C9H21CO2H + (x) (C9H21CO2)(2)Cu], were solved by differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction, pair distribution function, and optical microscopy. The singularities of the phase diagram are (a) a Krafft-like process of molecular association of the copper(II) decanoate into the acid solution, at about T = 361.5 K and x = 0.022 (forming salt-acid adducts of 1:1 stoichiometry); (b) a fusion transition as an invariant (T = 379.1 K) of the solid salt in excess from the copper(II) decanoate crystal phase to the discotic liquid crystal, forming homeotropic developable domains (seen for the first time in these systems) of the pure salt into the saturated acid solution. These domains are seen not only in the copper(II) decanoate but also in other members of the series, at high salt concentration in the corresponding acid solution, and allow identification of the hexagonal columnar discotic structure of the mesophase (with the exception of the copper(II) butanoate, where the tetragonal domains with tilted disks, paddle-wheels, were seen in the same salt-acid region).
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Reinoza C, Jouanne F, Audemard FA, Schmitz M, Beck C (2015) Geodetic exploration of strain along the El Pilar Fault in northeastern Venezuela. Journal Of Geophysical Research-Solid Earth 120(3):1993–2013
Résumé: We use Global Navigation Satellite Systems observations in northeastern Venezuela to constrain the El Pilar Fault (EPF) kinematics and to explore the effects of the variable elastic properties of the surrounding medium and of the fault geometry on inferred slip rates and locking depth. The velocity field exhibits an asymmetric velocity gradient on either side of the EPF. We use five different approaches to explore possible models to explain this asymmetry. First, we infer a 1.6km locking depth using a classic elastic half-space dislocation model. Second, we infer a 1.5km locking depth and a 0.33 asymmetry coefficient using a heterogeneous asymmetric model, including contrasting material properties on either side of a vertical fault, suggesting that the igneous-metamorphic terranes on the northern side are similar to 2times more rigid than the sedimentary southern side. Third, we use a three-dimensional elastostatic model to evaluate the presence of a compliant zone, suggesting a 30% reduction of rigidity in the upper 3km at the depth of a 1 to 5km wide fault zone. Fourth, we evaluate the distribution of fault slip, revealing a widespread partial creep pattern in the eastern upper segment, while the upper western segment exhibits a partially locked area, which coincides with the rupture surface of the 1797 and 1929 earthquakes. To supplement these models, we upgrade the previously published displacement simulation method using nonvertical dislocations with data acquired between 2003 and 2013. The localized aseismic displacement pattern associated with creeping or partially creeping fault segments could explain the low level of historic seismicity.
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Renard F, Putnis CV, Montes-Hernandez G, Ruiz-Agudo E, Hovelmann J, Sarret G (2015) Interactions of arsenic with calcite surfaces revealed by in situ nanoscale imaging. Geochimica Et Cosmochimica Acta 159:61–79
Résumé: Arsenic dissolved in water represents a key environmental and health challenge because several million people are under the threat of contamination. In calcareous environments calcite may play an important role in arsenic solubility and transfer in water. Arsenic-calcite interactions remain controversial, especially for As-(III) which was proposed to be either incorporated as such, or as As-(V) after oxidation. Here, we provide the first time-lapse in situ study of the evolution of the (10-14) calcite cleavage surface morphology during dissolution and growth in the presence of solutions with various amounts of As-(III) or As-(V) at room temperature and pH range 6-11 using a flow-through cell connected to an atomic force microscope (AFM). Reaction products were then characterized by Raman spectroscopy. In parallel, co-precipitation experiments with either As-(III) or As-(V) were performed in batch reactors, and the speciation of arsenic in the resulting solids was studied by X-ray absorption spectroscopy (XAS). For As-(V), AFM results showed that it interacts strongly with the calcite surface, and XAS results showed that As-(V) was mostly incorporated in the calcite structure. For As-(III), AFM results showed much less impact on calcite growth and dissolution and less incorporation was observed. This was confirmed by XAS results that indicate that As-(III) was partly oxidized into As-(V) before being incorporated into calcite and the resulting calcite contained 36% As-(III) and 64% As-(V). All these experimental results confirm that As-(V) has a much stronger interaction with calcite than As-(III) and that calcite may represent an important reservoir for arsenic in various geological environments. (C) 2015 Elsevier Ltd. All rights reserved.
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Reverso T, Marsan D, Helmstetter A (2015) Detection and characterization of transient forcing episodes affecting earthquake activity in the Aleutian Arc system. Earth And Planetary Science Letters 412:25–34
Résumé: Crustal, slow deformation transients can be caused by fluid or magmatic intrusions, and by slow slip on faults. They can affect earthquake dynamics, if they occur close to or within seismically active zones. We here further develop, and test, a statistical method for detecting and characterizing seismicity anomalies that is only based on earthquake occurrence times and locations. We make use of this method to analyze the 2004-2013 seismicity at m(c) = 3.5 in the Aleutian subduction system, to find six statistically significant anomalies, with typical 1 day duration and 30 to 50 km size, that are likely related to slow deformation transients. They tend to be located in zones characterized by intermediate seismic coupling, and to mark the termination of past large to mega-thrust earthquakes. These anomalies account for a non-negligible (9%) part of the total activity, proving that non-stationary aseismic loading plays an important role in the dynamics of crustal deformation. (C) 2014 Elsevier B.V. All rights reserved.
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Revil A, Aal GZA, Atekwana EA, Mao D, Florsch N (2015) Induced polarization response of porous media with metallic particles – Part 2: Comparison with a broad database of experimental data. Geophysics 80(5):D539–D552
Résumé: We have derived a set of new relationships describing polarization parameters in porous materials with disseminated particles made of a semiconductor, such as pyrite or magnetite. We have compared various predictions of this model to a broad set of experimental data. The chargeability was found to be controlled only by the volume fraction of metallic particles in agreement with the experimental data. The relaxation time, defined from the peak frequency of the phase, was observed to be proportional to the square of the size of the metallic particles and was independent of the salinity of the pore water solution. The relationship between the peak frequency and the grain size could be used to determine the diffusion coefficient of the n- and p-charge carriers in the semiconductor. This diffusion coefficient was consistent with the mobility of the charge carriers derived from theoretical considerations or electric-conductivity measurements. The resistivity of a mixture of a porous matrix characterized by a low-chargeability and dispersed semiconductors does not depend on the content of metallic grains, as long as the grains are below a percolation threshold (<22 vol.%). Various experiments were performed using magnetite and pyrite at different grain sizes, weight fractions, and with/without porous materials (i.e., suspended in agar gel). These data were used to test some additional aspects of the model. We found excellent agreement between the model predictions and these experimental data.
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Revil A, Binley A, Mejus L, Kessouri P (2015) Predicting permeability from the characteristic relaxation time and intrinsic formation factor of complex conductivity spectra. Water Resources Research 51(8):6672–6700
Résumé: Low-frequency quadrature conductivity spectra of siliclastic materials exhibit typically a characteristic relaxation time, which either corresponds to the peak frequency of the phase or the quadrature conductivity or a typical corner frequency, at which the quadrature conductivity starts to decrease rapidly toward lower frequencies. This characteristic relaxation time can be combined with the (intrinsic) formation factor and a diffusion coefficient to predict the permeability to flow of porous materials at saturation. The intrinsic formation factor can either be determined at several salinities using an electrical conductivity model or at a single salinity using a relationship between the surface and quadrature conductivities. The diffusion coefficient entering into the relationship between the permeability, the characteristic relaxation time, and the formation factor takes only two distinct values for isothermal conditions. For pure silica, the diffusion coefficient of cations, like sodium or potassium, in the Stern layer is equal to the diffusion coefficient of these ions in the bulk pore water, indicating weak sorption of these couterions. For clayey materials and clean sands and sandstones whose surface have been exposed to alumina (possibly iron), the diffusion coefficient of the cations in the Stern layer appears to be 350 times smaller than the diffusion coefficient of the same cations in the pore water. These values are consistent with the values of the ionic mobilities used to determine the amplitude of the low and high-frequency quadrature conductivities and surface conductivity. The database used to test the model comprises a total of 202 samples. Our analysis reveals that permeability prediction with the proposed model is usually within an order of magnitude from the measured value above 0.1 mD. We also discuss the relationship between the different time constants that have been considered in previous works as characteristic relaxation time, including the mean relaxation time obtained from a Debye decomposition of the spectra and the Cole-Cole time constant.
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Revil A, Cuttler S, Karaoulis M, Zhou J, Raynolds B, Batzle M (2015) The plumbing system of the Pagosa thermal Springs, Colorado: Application of geologically constrained geophysical inversion and data fusion. Journal Of Volcanology And Geothermal Research 299:1–18
Résumé: Fault and fracture networks usually provide the plumbing for movement of hydrothermal fluids in geothermal fields. The Big Springs of Pagosa Springs in Colorado is known as the deepest geothermal hot springs in the world. However, little is known about the plumbing system of this hot spring, especially regarding the position of the reservoir (if any) or the position of the major tectonic faults controlling the flow of the thermal water in this area. The Mancos shale, a Cretaceous shale, dominates many of the surface expressions around the springs and impede an easy recognition of the fault network. We use three geophysical methods (DC resistivity, self-potential, and seismic) to image the faults in this area, most of which are not recognized in the geologic fault map of the region. Results from these surveys indicate that the hot Springs (the Big Spring and a warm spring located 1.8 km further south) are located at the intersection of the Victoire Fault, a major normal crustal fault, and two north-northeast trending faults (Fault A and B). Self-potential and DC resistivity tomographies can be combined and a set of joint attributes defined to determine the localization of the flow of hot water associated with the Eight Miles Mesa Fault, a second major tectonic feature responsible for the occurrence of warm springs further West and South from the Big Springs of Pagosa Springs. (C) 2015 Elsevier B.V. All rights reserved.
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Revil A, Mao D, Haas AK, Karaoulis M, Frash L (2015) Passive electrical monitoring and localization of fluid leakages from wells. Journal Of Hydrology 521:286–301
Résumé: Electrokinetic phenomena are a class of cross-coupling phenomena involving the relative displacement between the pore water (together with the electrical diffuse layer) with respect to the solid phase of a porous material. We demonstrate that electrical fields of electrokinetic nature can be associated with fluid leakages from wells. These leakages can be remotely monitored and the resulting signals used to localize their causative source distribution both in the laboratory and in field conditions. The first laboratory experiment (Experiment #1) shows how these electrical fields can be recorded at the surface of a cement block during the leakage of a brine from a well. The measurements were performed with a research-grade medical electroencephalograph and were inverted using a genetic algorithm to localize the causative source of electrical current and therefore, localize the leak in the block. Two snapshots of electrical signals were used to show how the leak evolved over time. The second experiment (Experiment #2) was performed to see if we could localize a pulse water injection from a shallow well in field conditions in the case of a heterogeneous subsurface. We used the same equipment as in Experiment #1 and processed the data with a trend removal algorithm, picking the amplitude from 24 receiver channels just after the water injection. The amplitude of the electric signals changed from the background level indicating that a volume of water was indeed flowing inside the well into the surrounding soil and then along the well. We used a least-square inversion algorithm to invert a snapshot of the electrical potential data at the injection time to localize the source of the self-potential signals. The inversion results show positive potential anomalies in the vicinity of the well. For both experiments, forward numerical simulations of the problem using a finite element package were performed in order to assess the underlying physics of the causative source of the observed electrical potential anomalies and how they are related to the flow of the water phase. (C) 2014 Elsevier B.V. All rights reserved.
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Richard J, Doan M-L, Gratier J-P, Renard F (2015) Microstructures Induced in Porous Limestone by Dynamic Loading, and Fracture Healing: An Experimental Approach. Pure And Applied Geophysics 172(5):1269–1290
Résumé: Fracturing and healing are crucial processes inducing changes in the permeability and mechanical behavior of fault zones. Fracturing increases the permeability of fault rocks, creating flow-channels for fluid circulation and enhancing the kinetics of such fluid-rock processes as pressure solution or metamorphism. Conversely, healing processes reduce permeability by closing the fractures and lead to rock strengthening. Consequently, the timescales of these two processes are important in determining the strength of fault zones and their ability to rupture during earthquakes. This article reports observations of the microstructure of porous limestone samples subjected to rapid dynamic loading, and long-term healing as a result of fluid percolation. Dynamic loading was performed by impacting the samples with steel bars inside a split Hopkinson pressure bar apparatus. Healing was performed by leaving the samples for three months within a triaxial machine with percolation of supersaturated fluids for five weeks. Two kinds of fracture network were observed in samples damaged at high strain rate: a series of radial and circular macrofractures and an incipient pulverization zone at the center of the sample loaded at the highest strain rate. Fracture density determined microscopically from X-ray images correlates with dissipated energy computed from macro-mechanical data. X-ray images enable good quantification of the damaged state of the samples. Percolation experiments under stress with high-solubility fluid at room temperature show that the main healing processes promoting closure of the fractures in the sample are a combination of mechanical and chemical compaction. Microfracturing networks were found to heal faster than the largest fractures, leading to heterogeneous strengthening of the rock. This feature affects the processes of earthquake nucleation and rupture propagation.
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Riedel I, Gueguen P, Dalla Mura M, Pathier E, Leduc T, Chanussot J (2015) Seismic vulnerability assessment of urban environments in moderate-to-low seismic hazard regions using association rule learning and support vector machine methods. Natural Hazards 76(2):1111–1141
Résumé: The estimation of the seismic vulnerability of buildings at an urban scale, a crucial element in any risk assessment, is an expensive, time-consuming, and complicated task, especially in moderate-to-low seismic hazard regions, where the mobilization of resources for the seismic evaluation is reduced, even if the hazard is not negligible. In this paper, we propose a way to perform a quick estimation using convenient, reliable building data that are readily available regionally instead of the information usually required by traditional methods. Using a dataset of existing buildings in Grenoble (France) with an EMS98 vulnerability classification and by means of two different data mining techniques-association rule learning and support vector machine-we developed seismic vulnerability proxies. These were applied to the whole France using basic information from national databases (census information) and data derived from the processing of satellite images and aerial photographs to produce a nationwide vulnerability map. This macroscale method to assess vulnerability is easily applicable in case of a paucity of information regarding the structural characteristics and constructional details of the building stock. The approach was validated with data acquired for the city of Nice, by comparison with the RiskUE method. Finally, damage estimations were compared with historic earthquakes that caused moderate-to-strong damage in France. We show that due to the evolution of vulnerability in cities, the number of seriously damaged buildings can be expected to double or triple if these historic earthquakes were to occur today.
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Ring U, Bernet M, Tulloch A (2015) Kinematic, finite strain and vorticity analysis of the Sisters Shear Zone, Stewart Island, New Zealand. Journal Of Structural Geology 73:114–129
Résumé: The Sisters Shear Zone (SSZ) on Stewart Island, New Zealand, is a greenschist-facies extensional shear zone active prior to and possibly during the development of the Pacific Antarctica spreading ridge at similar to 76 Ma. We report quantitative kinematic and rotation data as well as apatite fission-track (AFT) ages from the SSZ. Early kinematic indicators associated with the NNE-trending stretching lineation formed under upper greenschist-facies metamorphism and show alternating top-to-the-NNW and top-to-the-SSE senses of shear. During progressive exhumation lowermost greenschist-facies and brittle-ductile kinematic indicators depict a more uniform top-to-the-SSE sense of shear in the topmost SSZ just below the detachment plane. Deformed metagranites in the SSZ allow the reconstruction of deformation and flow parameters. The mean kinematic vorticity number (W-m) ranges from 0.10 to 0.89; smaller numbers prevail in the deeper parts of the shear zone with a higher degree of simple shear deformation in the upper parts of the shear zone (deeper and upper parts relate to present geometry). High finite strain intensity correlates with low Wm and high Wm numbers near the detachment correlate with relatively weak strain intensity. Finite strain shows oblate geometries. Overall, our data indicate vertical and possibly temporal variations in deformation of the SSZ. Most AFT ages cluster around 85-75 Ma. We interpret the AFT ages to reflect the final stages of continental break-up just before and possibly during the initiation of sea-floor spreading between New Zealand and Antarctica. (C) 2015 Elsevier Ltd. All rights reserved.
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Rittgers JB, Revil A, Planes T, Mooney MA, Koelewijn AR (2015) 4-D imaging of seepage in earthen embankments with time-lapse inversion of self-potential data constrained by acoustic emissions localization. Geophysical Journal International 200(2):756–770
Résumé: New methods are required to combine the information contained in the passive electrical and seismic signals to detect, localize and monitor hydromechanical disturbances in porous media. We propose a field experiment showing how passive seismic and electrical data can be combined together to detect a preferential flow path associated with internal erosion in a Earth dam. Continuous passive seismic and electrical (self-potential) monitoring data were recorded during a 7-d full-scale levee (earthen embankment) failure test, conducted in Booneschans, Netherlands in 2012. Spatially coherent acoustic emissions events and the development of a self-potential anomaly, associated with induced concentrated seepage and internal erosion phenomena, were identified and imaged near the downstream toe of the embankment, in an area that subsequently developed a series of concentrated water flows and sand boils, and where liquefaction of the embankment toe eventually developed. We present a new 4-D grid-search algorithm for acoustic emissions localization in both time and space, and the application of the localization results to add spatially varying constraints to time-lapse 3-D modelling of self-potential data in the terms of source current localization. Seismic signal localization results are utilized to build a set of time-invariant yet spatially varying model weights used for the inversion of the self-potential data. Results from the combination of these two passive techniques show results that are more consistent in terms of focused ground water flow with respect to visual observation on the embankment. This approach to geophysical monitoring of earthen embankments provides an improved approach for early detection and imaging of the development of embankment defects associated with concentrated seepage and internal erosion phenomena. The same approach can be used to detect various types of hydromechanical disturbances at larger scales.
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Rivet D, Brenguier F, Cappa F (2015) Improved detection of preeruptive seismic velocity drops at the Piton de La Fournaise volcano. Geophysical Research Letters 42(15):6332–6339
Résumé: The unexpected 2014 and 2015 Ontake (Japan) and Calbuco (Chile) eruptions proved that improving volcanic eruption prediction is still a great challenge. Decreases of seismic velocities of the Piton de la Fournaise volcano inferred from seismic noise correlations have been shown to precede eruptions. However, seismic velocities are strongly influenced by rainfall and subsequent pore pressure perturbations. Here we increase the detection of precursory seismic velocity changes to an eruption by removing the effects of pore pressure changes. During 2011-2013, the volcano exhibits a low eruptive activity during which we observe seismic velocity variations well correlated with rainfall episodes. We estimated the transfer function between fluid pressure and seismic velocity changes. We use these results to correct seismic velocity change time series for pore pressure changes, due to rainfall and found a preeruptive velocity drop (0.15%) associated with the 21 June 2014 eruption that was undetected before correction.
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Rivet D, Campillo M, Sanchez-Sesma F, Shapiro NM, Singh K (2015) Identification of surface wave higher modes using a methodology based on seismic noise and coda waves. Geophysical Journal International 203(2):856–868
Résumé: Dispersion analysis of Rayleigh waves is performed to assess the velocity of complex structures such as sedimentary basins. At short periods several modes of the Rayleigh waves are often exited. To perform a reliable inversion of the velocity structure an identification of these modes is thus required. We propose a novel method to identify the modes of surface waves. We use the spectral ratio of the ground velocity for the horizontal components over the vertical component (H/V) measured on seismic coda. We then compare the observed values with the theoretical H/V ratio for velocity models deduced from surface wave dispersion when assuming a particular mode. We first invert the Rayleigh wave measurements retrieved from ambient noise cross-correlation with the assumptions that (1) the fundamental mode and (2) the first overtone are excited. Then we use these different velocity models to predict theoretical spectral ratios of the ground velocity for the horizontal components over the vertical component (H/V). These H/V ratios are computed under the hypothesis of equipartition of a diffuse field in a layered medium. Finally we discriminate between fundamental and higher modes by comparing the theoretical H/V ratio with the H/V ratio measured on seismic coda. In an application, we reconstruct Rayleigh waves from cross-correlations of ambient seismic noise recorded at seven broad-band stations in the Valley of Mexico. For paths within the soft quaternary sediments basin, the maximum energy is observed at velocities higher than expected for the fundamental mode. We identify that the dominant mode is the first higher mode, which suggests the importance of higher modes as the main vectors of energy in such complex structures.
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Rupin M, Catheline S, Roux P (2015) Super-resolution experiments on Lamb waves using a single emitter. Applied Physics Letters 106(2)
Résumé: In this letter, we present super-resolution experiments from a single emission channel located in the far-field of an elastic metamaterial for Lamb waves. The experiment is performed in the kHz regime, with centimetric waves that are refocused numerically through cross-correlation computations. The originality of this approach lies in the direct link established between super-resolution results and the wavefield dispersion induced by a metamaterial made of long rods that are attached to a plate, and that behave as sub-wavelength resonators. We believe that such a clear origin of a far-field super-resolution experiment is of major interest for the design of a meta-lens for waves in plates. (C) 2015 AIP Publishing LLC.
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Rupin M, Roux P, Lerosey G, Lemoult F (2015) Symmetry issues in the hybridization of multi-mode waves with resonators: an example with Lamb waves metamaterial. Scientific Reports 5
Résumé: Locally resonant metamaterials derive their effective properties from hybridization between their resonant unit cells and the incoming wave. This phenomenon is well understood in the case of plane waves that propagate in media where the unit cell respects the symmetry of the incident field. However, in many systems, several modes with orthogonal symmetries can coexist at a given frequency, while the resonant unit cells themselves can have asymmetric scattering cross-sections. In this paper we are interested in the influence of symmetry breaking on the hybridization of a wave field that includes multiple propagative modes. The A(o) and S-o Lamb waves that propagate in a thin plate are good candidates for this study, as they are either anti-symmetric or symmetric. First we designed an experimental setup with an asymmetric metamaterial made of long rods glued to one side of a metallic plate. We show that the flexural resonances of the rods induce a break of the orthogonality between the A(o)/S-o modes of the free-plate. Finally, based on numerical simulations we show that the orthogonality is preserved in the case of a symmetric metamaterial leading to the presence of two independent polariton curves in the dispersion relation.
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Saade M, Montagner JP, Roux P, Cupillard P, Durand S, Brenguier F (2015) Influence of seismic anisotropy on the cross correlation tensor: numerical investigations. Geophysical Journal International 201(2):595–604
Résumé: Temporal changes in seismic anisotropy can be interpreted as variations in the orientation of cracks in seismogenic zones, and thus as variations in the stress field. Such temporal changes have been observed in seismogenic zones before and after earthquakes, although they are still not well understood. In this study, we investigate the azimuthal polarization of surface waves in anisotropic media with respect to the orientation of anisotropy, from a numerical point of view. This technique is based on the observation of the signature of anisotropy on the nine-component cross-correlation tensor (CCT) computed from seismic ambient noise recorded on pairs of three-component sensors. If noise sources are spatially distributed in a homogeneous medium, the CCT allows the reconstruction of the surface wave Green's tensor between the station pairs. In homogeneous, isotropic medium, four off-diagonal terms of the surface wave Green's tensor are null, but not in anisotropic medium. This technique is applied to three-component synthetic seismograms computed in a transversely isotropic medium with a horizontal symmetry axis, using a spectral element code. The CCT is computed between each pair of stations and then rotated, to approximate the surface wave Green's tensor by minimizing the off-diagonal components. This procedure allows the calculation of the azimuthal variation of quasi-Rayleigh and quasi-Love waves. In an anisotropic medium, in some cases, the azimuth of seismic anisotropy can induce a large variation in the horizontal polarization of surface waves. This variation depends on the relative angle between a pair of stations and the direction of anisotropy, the amplitude of the anisotropy, the frequency band of the signal and the depth of the anisotropic layer.
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Sauret A, Boulogne F, Cebron D, Dressaire E, Stone HA (2015) Wetting morphologies on an array of fibers of different radii. Soft Matter 11(20):4034–4040
Résumé: We investigate the equilibrium morphology of a finite volume of liquid placed on two parallel rigid fibers of different radii. As observed for identical radii fibers, the liquid is either in a column morphology or adopts a drop shape depending on the inter-fiber distance. However the cross-sectional area and the critical inter-fiber distance at which the transition occurs are both modified by the polydispersity of the fibers. Using energy considerations, we analytically predict the critical inter-fiber distance corresponding to the transition between the column and the drop morphologies. This distance depends both on the radii of the fibers and on the contact angle of the liquid. We perform experiments using a perfectly wetting liquid on two parallel nylon fibers: the results are in good agreement with our analytical model. The morphology of the capillary bridges between fibers of different radii is relevant to the modeling of large arrays of polydisperse fibers.
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Sauzeat L, Rudnick RL, Chauvel C, Garcon M, Tang M (2015) New perspectives on the Li isotopic composition of the upper continental crust and its weathering signature. Earth And Planetary Science Letters 428:181–192
Résumé: Lithium isotopes are increasingly used to trace both present-day and past weathering processes at the surface of the Earth, and could potentially be used to evaluate the average degree of past weathering recorded by the upper continental crust (UCC). Yet the previous estimate of average delta Li-7 of the UCC has a rather large uncertainty, hindering the use of Li isotopes for this purpose. New delta Li-7 for desert and periglacial loess deposits (windblown dust) from several parts of the world (Europe, Argentina, China and Tajikistan) demonstrate that the former are more homogeneous than the latter, and may therefore serve as excellent proxies of the average composition of large tracts of the UCC. The Li isotopic compositions and concentrations of desert loess samples are controlled by eolian sorting that can be quantified by a binary mixing between a weathered, fine-grained end-member, dominated by phyllosilicates and having low delta Li-7, and an unweathered, coarse-grained end-member, that is a mixture of quartz and plagioclase having higher delta Li-7. We use correlations between insoluble elements (REE, Nd/Hf and Fe2O3/SiO2), Li concentrations (henceforth referred as [Li]), and delta Li-7 to estimate a new, more precise, average Li isotopic composition and concentration for the UCC: [Li] = 30.5 +/- 3.6(2 sigma) ppm, and delta Li-7 = +0.6 +/- 0.6(2 sigma). The delta Li-7 for desert loess deposits is anti-correlated with the chemical index of alteration (CIA). Using this relationship, along with our average delta Li-7 we infer that (1) the present-day CIA of the average UCC is 61(-2)(+4)(2 sigma), higher than the common reference value of 53, and (2) the average proportion of chemically weathered components is as high as 37(-10)(+17)(2 sigma)% at the surface of the Earth. (c) 2015 Elsevier B.V. All rights reserved.
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Savage MK, Ferrazzini V, Peltier A, Rivemale E, Mayor J, Schmid A, Brenguier F, Massin F, Got J-L, Battaglia J, DiMuro A, Staudacher T, Rivet D, Taisne B, Shelley A (2015) Seismic anisotropy and its precursory change before eruptions at Piton de la Fournaise volcano, La Reunion. Journal Of Geophysical Research-Solid Earth 120(5):3430–3458
Résumé: The Piton de la Fournaise volcano exhibits frequent eruptions preceded by seismic swarms and is a good target to test hypotheses about magmatically induced variations in seismic wave properties. We use a permanent station network and a portable broadband network to compare seismic anisotropy measured via shear wave splitting with geodetic displacements, ratios of compressional to shear velocity (Vp/Vs), earthquake focal mechanisms, and ambient noise correlation analysis of surface wave velocities and to examine velocity and stress changes from 2000 through 2012. Fast directions align radially to the central cone and parallel to surface cracks and fissures, suggesting stress-controlled cracks. High Vp/Vs ratios under the summit compared with low ratios under the flank suggest spatial variations in the proportion of fluid-filled versus gas-filled cracks. Secular variations of fast directions () and delay times (dt) between split shear waves are interpreted to sense changing crack densities and pressure. Delay times tend to increase while surface wave velocity decreases before eruptions. Rotations of may be caused by changes in either stress direction or fluid pressure. These changes usually correlate with GPS baseline changes. Changes in shear wave splitting measurements made on multiplets yield several populations with characteristic delay times, measured incoming polarizations, and fast directions, which change their proportion as a function of time. An eruption sequence on 14 October 2010 yielded over 2000 shear wave splitting measurements in a 14h period, allowing high time resolution measurements to characterize the sequence. Stress directions from a propagating dike model qualitatively fit the temporal change in splitting.
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Savelieva GN, Batanova VG, Kuz'min DV, Sobolev AV (2015) Composition of Minerals in Mantle Peridotites as Proxy of Ore-Forming Processes in the Mantle: Evidence from Ophiolites in the Voykar-Synya and Kempirsai Massifs. Lithology And Mineral Resources 50(1):80–91
Résumé: It is shown that ortho- and clinopyroxenes in mantle peridotites, which host different-scale chromite deposits, are marked by significant differences in the structure of rocks, composition of olivine and chromian spinel, and, primarily, content and distribution of the major ore-forming oxides therein. Enstatites and diopsides in peridotites from the southern Kempirsai Massif are notably depleted in the major oxides as compared to minerals in harzburgites from the Voykar-Synya Massif. The central portion of some large enstatite grains in peridotites from the Kempirsai Massif is marked by high contents of chromium oxide and alumina. Correlation of the prominent strain-mediated zonation in large relict pyroxene grains with decrease in Cr2O3 and Al2O3 at their rims suggests an initially high content of these components in pyroxenes. Extremely narrow variation range of the composition of high-Mg olivine in harzburgites from the Kempirsai Massif and its relatively small grain size as compared to harzburgites from the Voykar Massif were also provoked by the high-temperature recrystallization of mantle rocks accompanied by the transition of Cr and Al from silicates (pyroxene) into ore mineral (chromian spinel). Redistribution of components and recrystallization of peridotites were likely caused by the emplacement of harzburgites by a large volume of fluid/melt, which reacted with the host rocks, and by the high rate of mantle deformation (contraction of olivine grains) during this process. Components (Cr, Al, Fe) needed for the formation of chromium ores were extracted from both rock-forming silicates and migrating melts.
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Shervais JW, Arndt N, Goodenough KM (2015) Drilling the solid earth: global geodynamic cycles and earth evolution. International Journal Of Earth Sciences 104(6):1573–1587
Résumé: The physical and chemical evolution of the Earth is driven by geodynamic cycles that are global in scale, operating over 4.57 Ga of Earth's history. Some processes are truly cyclic, e.g., the Wilson Cycle, while others are irreversible (e.g., core formation). Heat and mass transfer between the lowermost mantle (e.g., core-mantle boundary) and the surface drives these global geodynamic processes. Subduction of lithospheric plates transfers cool fractionated material into the lower mantle and leads indirectly to the formation of new oceanic lithosphere, while the rise of thermochemical plumes recycles the remnants of these plates back to the surface, driven by heat transfer across the core-mantle boundary. These global geodynamic cycles are responsible for hotspot volcanism, the formation of continental crust, collisional orogenies, continental rifting, subduction zone processes (arcs, accretionary prisms), and ore deposits. Each of these presents opportunities for investigation by continental scientific drilling. In addition, these cycles affect other processes that are targets of continental scientific drilling: the origin and evolution of life and an oxygenated atmosphere, the impact of large volcanic eruptions on climate, and geological hazards such as earthquakes and volcanic eruptions. In this paper, we present the scientific rationale for continental scientific drilling to study global geodynamic processes, review past successes in this realm that were sponsored in part by ICDP, and suggest potential new targets for drilling campaigns that focus on solid earth evolution. This paper builds on discussions at the 2013 ICDP Science Meeting on the future of continental scientific drilling, held in Potsdam in November 2013.
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Simionovici AS, David G, Lemelle L, Boyet M, Gillet P, Rivard C, El Goresy A (2015) Dual energy nano-XRF quantification in EL-3 fragments of the Almahata Sitta TC3 asteroid. Meteoritics & Planetary Science 50
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Smulders S, Larue C, Sarret G, Castillo-Michel H, Vanoirbeek J, Hoet PHM (2015) Lung distribution, quantification, co-localization and speciation of silver nanoparticles after lung exposure in mice. Toxicology Letters 238(1):1–6
Résumé: Large knowledge gaps still exist on the toxicological mechanisms of silver (Ag) engineered nanoparticles (ENPs); a comprehensive understanding of the sources, biodistribution, toxicity and transformation of Ag ENPs along their life cycle and after transfer in living organisms is needed. In a previous study, mice were pulmonary exposed to Ag ENPs and local (lung) and systemic toxic effects together with biodistribution to organs including heart, liver, spleen and kidney were investigated. Here, Ag lung distribution, local concentration, co-localization with other elements such as Fe, Cu and S, and speciation were determined after lung exposure to Ag ENPs using micro X-ray fluorescence (mu XRF), micro X-ray absorption near edge structure spectroscopy (mu XANES) and micro proton-induced X-ray emission (mu PIXE) techniques. We found that approximately a quarter of all macrophages in the lumen of the airways contained ENPs. High local concentrations of Ag were also detected in the lung tissue, probably phagocytized by macrophages. The largest part of the ENPs was dissolved and complexed to thiol-containing molecules. Increased concentrations of Fe and Cu observed in the Ag-rich spots suggest that these molecules are metallothioneins (MTs). These results give more insights on the behavior of Ag ENPs in the lung in vivo and will help in the understanding of the toxicological mechanisms of Ag ENPs. (C) 2015 Elsevier Ireland Ltd. All rights reserved.
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Sobolev NV, Sobolev AV, Tomilenko AA, Batanova VG, Tolstov AV, Logvinova AM, Kuz'min DV (2015) Unique compositional peculiarities of olivine phenocrysts from the post flood basalt diamondiferous Malokuonapskaya kimberlite pipe, Yakutia. Doklady Earth Sciences 463(2):828–832
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Sobolev NV, Sobolev AV, Tomilenko AA, Kovyazin SV, Batanova VG, Kuz'min DV (2015) Paragenesis and complex zoning of olivine macrocrysts from unaltered kimberlite of the Udachnaya-East pipe, Yakutia: relationship with the kimberlite formation conditions and evolution. Russian Geology And Geophysics 56(1-2):260–279
Résumé: Unaltered Mg-olivine (Fo = 85-94) is a predominant mineral of the kimberlite block (serpentine-free) of the Udachnaya-East pipe, and it prevails in peridotite xenoliths and as inclusions in diamonds. The kimberlite of this pipe, like a series of hypabyssal kimberlites in other regions, contains two main types of olivine macrocrysts according to their size and morphology: those rounded or irregularly shaped (olivine I) and euhedral phenocrysts (olivine II), which are usually no larger than 0.5 mm and very seldom reach 1 mm in size. This study was focused on several thousand olivine samples assigned both to olivines I and to olivines II, with a gradual transition between them. Particular attention was paid to the search for mineral inclusions in olivine and for phenocrysts with a clear zoning. In the phenocryst cores of homogeneous composition, we have revealed orthopyroxene inclusions as well as clinopyroxene (chrome-diopside and chrome-omphacite) inclusions with wide variations in the Na2O and Cr2O3 contents, significantly higher than the previously established ones: up to 6.00 wt.% Na2O and 4.23 wt.% Cr2O3. Convincing evidence for the high-pressure origin of the olivine macrocryst cores is the presence of pyrope inclusions with 1.41-9.14 wt.% Cr2O3, 4.64-6.61 wt.% CaO, and Mg# = 75.6-83.7 in six samples, which testifies to the high-pressure lherzolite paragenesis of the phenocrysts cores. The cores of the studied olivine phenocrysts are identical in the contents of Ni, Co, Ca, Cr, and Mn to olivines from diamonds and peridotite xenoliths. However, they differ significantly in the steady elevated Ti content, equal to 100-300 ppm for the majority of the phenocrysts, including those containing pyroxene and pyrope inclusions. (C) 2015, V. S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.
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Solikhin A, Pine V, Vandemeulebrouck J, Thouret J-C, Hendrasto M (2015) Mapping the 2010 Merapi pyroclastic deposits using dual-polarization Synthetic Aperture Radar (SAR) data. Remote Sensing Of Environment 158:180–192
Résumé: L-band ALOS-PALSAR images acquired before, during and after the 2010 Merapi eruption have been used to classify and map the pyroclastic deposits emplaced during this VEI-4 event. We characterize the deposits using direct-polarized and cross-polarized L-band SAR data and by combining the information of amplitude evolution with temporal decorrelation. Changes in amplitude of the radar signal enable us to map the pyroclastic density currents (PDCs) and tephra-fall deposits. Radar amplitudes in direct (HH) and cross (HV) polarizations decrease where the valley-confined and overbank block-and-ash flow (BAF) deposits (D1) are emplaced. Rainfall- and runoff-reworked PDC deposits (D2) are characterized by an increase in ground backscattering for HH polarization and a decrease for HV polarization. Ground backscattering transiently increases in both polarizations after pyrodastic surge (D3) and tephra fall (D4) deposition. We use a supervised classification method based on maximum likelihood to map the deposits D1-D4. The temporal decorrelation of the radar signal and the amplitude evolution improve the quality of classification results. Classification derived from ALOS-PALSAR images using the maximum likelihood classification provides a result with 70% classification accuracy for deposits overall. The estimated areas of valley-confined and overbank PDC deposits (either primary or reworked by rainfall and runoff) are consistent with the areas measured by other studies, while the large discrepancy in area estimated for pyroclastic-surge deposits can be partly explained by the strong erosion due to intense rainfall that removed a large part of these thin deposits. (C) 2014 Elsevier Inc. All rights reserved.
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Soueid Ahmed A, Jardani A, Revil A, Dupont JP (2015) HT2DINV: A 2D forward and inverse code for steady-state and transient hydraulic tomography problems. Computers & Geosciences 85:36–44
Résumé: Hydraulic tomography is a technique used to characterize the spatial heterogeneities of storativity and transmissivity fields. The responses of an aquifer to a source of hydraulic stimulations are used to recover the features of the estimated fields using inverse techniques. We developed a 2D free source Matlab package for performing hydraulic tomography analysis in steady state and transient regimes. The package uses the finite elements method to solve the ground water flow equation for simple or complex geometries accounting for the anisotropy of the material properties. The inverse problem is based on implementing the geostatistical quasi-linear approach of Kitanidis combined with the adjoint-state method to compute the required sensitivity matrices. For undetermined inverse problems, the adjoint-state method provides a faster and more accurate approach for the evaluation of sensitivity matrices compared with the finite differences method. Our methodology is organized in a way that permits the end-user to activate parallel computing in order to reduce the computational burden. Three case studies are investigated demonstrating the robustness and efficiency of our approach for inverting hydraulic parameters. (C) 2015 Elsevier Ltd. All rights reserved.
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Soueid Ahmed A, Zhou J, Jardani A, Revil A, Dupont JP (2015) Image-guided inversion in steady-state hydraulic tomography. Advances In Water Resources 82:83–97
Résumé: In steady-state hydraulic tomography, the head data recorded during a series of pumping or/and injection tests can be inverted to determine the transmissivity distributions of an aquifer. This inverse problem is usually under-determined and ill-posed. We propose to use structural information inferred from a guiding image to constrain the inversion process. The guiding image can be drawn from soft data sets such as seismic and ground penetrating radar sections or from geological cross-sections inferred from the wells and some geological expertise. The structural information is extracted from the guiding image through some digital image analysis techniques. Then, it is introduced into the inversion process of the head data as a weighted four direction smoothing matrix used in the regularizer. Such smoothing matrix allows applying the smoothing along the structural features. This helps preserving eventual drops in the hydraulic properties. In addition, we apply a procedure called image-guided interpolation. This technique starts with the tomogram obtained from the image-guided inversion and focus this tomogram. These new approaches are applied on four synthetic toy problems. The hydraulic distributions estimated from the image-guided inversion are closer to the true transmissivity model and have higher resolution than those computed from a classical Gauss-Newton method with uniform isotropic smoothing. (C) 2015 Elsevier Ltd. All rights reserved.
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Stehly L, Froment B, Campillo M, Liu QY, Chen JH (2015) Monitoring seismic wave velocity changes associated with the Mw 7.9 Wenchuan earthquake: increasing the temporal resolution using curvelet filters. Geophysical Journal International 201(3):1939–1949
Résumé: The aim of this study is to improve the temporal resolution of seismic wave velocity variations measured using ambient noise correlations. We first reproduce the result obtained by Chen et al. using a network of 21 broad-band stations ideally located around the fault system activated during the Wenchuan earthquake.We measure a velocity drop of 0.07 per cent that was associated with the main shock, with a temporal resolution of 30 days. To determine whether this velocity drop is co-seismic or post-seismic, we attempt to increase the temporal resolution of our observations. By taking advantage of the properties of the curvelet transform, we increase the signal-to-noise ratio of the daily correlations computed between each station pair. It is then possible to measure the velocity drop associated with the Wenchuan earthquake with a temporal resolution of 1 day. This shows that the velocity drop started on 2008 May 12, which was the day of the earthquake, and the velocity reached its lowest value 2 days after the main shock. Moreover, there was a second velocity drop on 2008 May 27, which might relate to strong aftershocks.
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Stelzer Z, Cebron D, Miralles S, Vantieghem S, Noir J, Scarfe P, Jackson A (2015) Experimental and numerical study of electrically driven magnetohydrodynamic flow in a modified cylindrical annulus. I. Base flow. Physics Of Fluids 27(7)
Résumé: Shear layers in confined liquid metal magnetohydrodynamic (MHD) flow play an important role in geo- and astrophysical bodies as well as in engineering applications. We present an experimental and numerical study of liquid metal MHD flow in a modified cylindrical annulus that is driven by an azimuthal Lorentz force resulting from a forced electric current under an imposed axial magnetic field. Hartmann and Reynolds numbers reach M-max approximate to 2000 and Re-max approximate to 1.3 x 10(4), respectively, in the steady regime. The peculiarity of our model geometry is the protruding inner disk electrode which gives rise to a free Shercliff layer at its edge. The flow of liquid GaInSn in the experimental device ZUCCHINI (ZUrich Cylindrical CHannel INstability Investigation) is probed with ultrasound Doppler velocimetry. We establish the base flow in ZUCCHINI and study the scaling of velocities and the free Shercliff layer in both experiment and finite element simulations. Experiment and numerics agree well on the mean azimuthal velocity u(phi)(r) following the prediction of a large-M theoretical model. The large-M limit, which is equivalent to neglecting inertial effects, appears to be reached for M greater than or similar to 30 in our study. In the numerics, we recover the theoretical scaling of the free Shercliff layer delta(S) similar to M-1/2 whereas dS appears to be largely independent of M in the experiment. (C) 2015 AIP Publishing LLC.
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Stelzer Z, Miralles S, Cebron D, Noir J, Vantieghem S, Jackson A (2015) Experimental and numerical study of electrically driven magnetohydrodynamic flow in a modified cylindrical annulus. 11. Instabilities. Physics Of Fluids 27(8)
Résumé: We present an investigation of the stability of liquid metal flow under the influence of an imposed magnetic field by means of a laboratory experiment as well as a linear stability analysis of the setup using the finite element method. The experimental device ZUrich Cylindrical CHannel INstability Investigation is a modified cylindrical annulus with electrically driven flow of liquid GaInSn operating at Hartmann and Reynolds numbers up to M = 2022 and Re = 2.6. 10(5), respectively. The magnetic field gives rise to a free shear layer at the prominent inner electrode. We identify several flow regimes characterized by the nature of the instabilities. Above a critical current I-c = 0(0.1 A), the steady flow is destabilized by a Kelvin-Helmholtz mechanism at the free shear layer. The instability consists of countenotating vortices traveling with the mean flow. For low forcing, the vortices are restricted to the free shear layer. Their azimuthal wave number m grows with M and decreases with Re. At Re/M approximate to 25, the instability becomes container-filling and energetically significant. It enhances the radial momentum transport which manifests itself in a broadening of the free shear layer width delta(s). We propose that this transition may be related to an unstable Hartmann layer. At Re/M-2 = 0(1), an abrupt change is observed in the mean azimuthal velocity (tTb) and the friction factor F, which we interpret as the transition between an inertialess and an inertial regime. (C) 2015 AIP Publishing LLC.
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Strasser FO, Albini P, Flint NS, Beauval C (2015) Twentieth century seismicity of the Koffiefontein region (Free State, South Africa): consistent determination of earthquake catalogue parameters from mixed data types. Journal Of Seismology 19(4):915–934
Résumé: The preparation of earthquake catalogues for seismic hazard analysis requires the use of uniform parameters, in particular for magnitudes, although the original data include a variety of formats, such as macroseismic intensities and various instrumental magnitude scales. In regions of low seismicity, such as South Africa, data are generally sparse and not always sufficient to develop locally calibrated conversion relations. They can nevertheless be used to test the applicability of imported conversion relations, as well as their consistency. The Koffiefontein region of South Africa provides a good test case in view of its somewhat higher level of seismicity, and central geographic location within the country. This paper reviews determinations of location and magnitude parameters for a suite of moderate-to-large earthquakes that have occurred in this region between 1903 and 1985.
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Sucheras-Marx B, Mattioli E, Giraud F, Escarguel G (2015) Paleoenvironmental and paleobiological origins of coccolithophorid genus Watznaueria emergence during the late Aalenian-early Bajocian. Paleobiology 41(3):415–435
Résumé: The latest Aalenian-early Bajocian time interval (ca. 171-169 Ma) is marked by a global reorganization of oceanic plates with the Central Atlantic opening and the formation of the Pacific plate. This time interval is also marked by a global geochemical perturbation of delta C-13 with a negative excursion at the Aalenian/Bajocian boundary and a positive excursion during the early Bajocian. Evolutionary diversifications of marine invertebrate taxa, namely ammonites, radiolarians, and coccolithophorids, are recorded at that time. Concerning coccolithophorids, this interval witnesses the diversification and expansion of the most successful Mesozoic genus: Watznaueria. In this study, we explore the potential environmental, ecological, and biological forcing at the origin of Watznaueria diversification and its effect on the coccolith assemblages through quantification of the absolute and relative abundances of calcareous nannofossils in two Middle Jurassic key sections: Cabo Mondego (Portugal) and Chaudon-Norante (France). In both sections, we find an increase in nannofossil absolute abundance and flux at the beginning of the lower Bajocian, coeval with an increase in absolute and relative abundances of Watznaueria spp., followed by a plateau in the middle and upper part of the lower Bajocian. The increase of Watznaueria spp. is synchronous with a decrease in relative abundance of other major coccolith taxa, whereas the absolute abundance of these species did not decrease. During the climatically driven early Bajocian eutrophication event, Watznaueria spp. integrated into the calcareous nannoplankton community in two successive evolutionary steps involving first W. contracta and W. colaccicchii, and second W. britannica and W. aff. manivitiae. Step 1 was driven by an increase in niche carrying capacities linked to the early Bajocian eutrophication. Step 2 was driven by specific adaptation of the newly evolved Watznaueria species to bloom in nutrient-rich environments not exploited before. These evolutionary events have initiated the 100-Myr reign of Watznaueria over the calcareous nannoplankton community.
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Tahir M, Grasso JR (2015) Faulting Style Controls for the Space-Time Aftershock Patterns. Bulletin Of The Seismological Society Of America 105(5):2480–2497
Résumé: To understand the complexity and thus to predict earthquake occurrence in size, time, and space, seismicity patterns are characterized by two robust empirical laws: the exponential distribution of magnitude and the power law decrease of aftershock rate over time. These laws are known as the Gutenberg-Richter law and the Omori law, respectively. Using global earthquake catalogs, we resolve that on average the K (aftershock productivity) and the p-value (exponent of the power law decrease of aftershock rate over time) are dependent on the mainshock faulting style. Strike-slip events have a lower aftershock rate (N) and K-values and a larger p-value than thrust and normal events, respectively. Within the epidemic-type aftershock sequence model, strong K, N values are driven by a high-branching ratio value (n). Within the same framework, a relatively higher n value for the thrust events also predicts the lower p-value we observe for thrust events as compared to strike-slip and normal-faulting events, respectively. Furthermore, we observed that earthquake interactions through time and space are a function of the faulting style when measured by mu(t), the exponent of the power law decrease of earthquake density over space. The mu(t) values of thrust events for different time windows always remain smaller than those of the strike-slip events. When changes in faulting styles are driven by stress pattern, the Anderson faulting theory predicts thrust faulting that requires somewhat larger stresses, in absolute magnitude, than do normal and strike-slip faulting. Within the framework of rate-and-state friction law, changes in the stress heterogeneity patterns reproduce the p-value changes we observe. Our results suggest that only stress perturbations associated with mainshock rupture affect the productivity and decay rate over time of aftershocks.
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Taira T'aki, Brenguier F, Kong Q (2015) Ambient noise-based monitoring of seismic velocity changes associated with the 2014 M-w 6.0 South Napa earthquake. Geophysical Research Letters 42(17):6997–7004
Résumé: We perform an ambient noise-based monitoring to explore temporal variations of crustal seismic velocities before, during, and after the 24 August 2014 M-w 6.0 South Napa earthquake. A velocity drop of about 0.08% is observed immediately after the South Napa earthquake. Spatial variability of the velocity reduction is most correlated with the pattern of the peak ground velocity of the South Napa mainshock, which suggests that fracture damage in rocks induced by the dynamic strain is likely responsible for the coseismic velocity change. About 50% of the velocity reduction is recovered at the first 50 days following the South Napa mainshock. This postseismic velocity recovery may suggest a healing process of damaged rocks.
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Thebault E, Finlay CC, Beggan CD, Alken P, Aubert J, Barrois O, Bertrand F, Bondar T, Boness A, Brocco L, Canet E, Chambodut A, Chulliat A, Coisson P, Civet F, Du A, Fournier A, Fratter I, Gillet N, Hamilton B, Hamoudi M, Hulot G, Jager T, Korte M, Kuang W, Lalanne X, Langlais B, Leger J-M, Lesur V, Lowes FJ, Macmillan S, Mandea M, Manoj C, Maus S, Olsen N, Petrov V, Ridley V, Rother M, Sabaka TJ, Saturnino D, Schachtschneider R, Sirol O, Tangborn A, Thomson A, Toffner-Clausen L, Vigneron P, Wardinski I, Zvereva T (2015) International Geomagnetic Reference Field: the 12th generation. Earth Planets And Space 67
Résumé: The 12th generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2014 by the Working Group V-MOD appointed by the International Association of Geomagnetism and Aeronomy (IAGA). It updates the previous IGRF generation with a definitive main field model for epoch 2010.0, a main field model for epoch 2015.0, and a linear annual predictive secular variation model for 2015.0-2020.0. Here, we present the equations defining the IGRF model, provide the spherical harmonic coefficients, and provide maps of the magnetic declination, inclination, and total intensity for epoch 2015.0 and their predicted rates of change for 2015.0-2020.0. We also update the magnetic pole positions and discuss briefly the latest changes and possible future trends of the Earth's magnetic field.
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Theule JI, Liebault F, Laigle D, Loye A, Jaboyedoff M (2015) Channel scour and fill by debris flows and bedload transport. Geomorphology 243:92–105
Résumé: In steep channels, debris flows are known to dramatically increase in volume under the effect of channel erosion. However, the critical factors controlling channel erosion by debris flows are not well documented by field studies. This is particularly true for the effect of slope on the depth at which erodible beds are scoured during debris flows and during bedload transport. This topic has been addressed by intensive cross section resurveys (54 cross sections) of debris flows (n = 5) and flow events (n = 9) that occurred in two torrents of the French Prealps, the Manival and Real torrents, between 2009 and 2012. This study provided evidence that debris-flow scouring increases with slope, whereas this is not the case for bedload transport (no slope effect detected during floods). A functional relationship defined from a piecewise regression model is proposed as an empirical fit for the prediction of channel erosion by debris flows with a critical slope threshold at 0.19 (95% confidence interval: 0.17-0.21). This slope threshold is interpreted as the transition between the transport-limited and supply-limited regimes, associated with the upstream decreasing erodible bed thickness. The erodible bed was also characterized by quantifying erosion, deposition, and surface roughness with multidate terrestrial laser scans (TLSs) in a short reach of high sensitivity of the Manival torrent. Debris-flow erosion occurred preferentially on smooth surfaces corresponding to the unconsolidated gravel deposits from bedload transport. A 20-cm resolution roughness profile from an airborne laser scan (ALS) and a slope profile of the whole channel were used to detect the unconsolidated sediment deposits that can potentially feed future debris flows. (C) 2015 Elsevier B.V. All rights reserved.
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Thu Trang Le, Atto AM, Trouve E, Solikhin A, Pinel V (2015) Change detection matrix for multitemporal filtering and change analysis of SAR and PolSAR image time series. Isprs Journal Of Photogrammetry And Remote Sensing 107:64–76
Résumé: This paper presents a method for analyzing Synthetic Aperture Radar (SAR) and polarimetric SAR (PolSAR) image time series based on change detection matrices (CDM) containing information on changed and unchanged pixels. These matrices are constructed for each spatial position over the time series by implementing similarity cross tests. The proposed matrix is then exploited for adaptive temporal filtering, analysis of change dynamics and multitemporal change detection. The proposed approach is illustrated on the three following data sets: 25 ascending TerraSAR-X images and 7 descending RADARSAT 2 full polarization images over Chamonix-MontBlanc, France, where the seasonal evolution of glaciers and mountains can be observed, and a time series of 11 ascending ALOS-PALSAR dual polarization images over Merapi volcano, Indonesia during a period including the 2010 eruption. Published by Elsevier B.V. on behalf of International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS).
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Tonazzi D, Massi F, Baillet L, Culla A, Di Bartolomeo M, Berthier Y (2015) Experimental and numerical analysis of frictional contact scenarios: from macro stick-slip to continuous sliding. Meccanica 50(3):649–664
Résumé: This work is an in-depth analysis of frictional phenomena including macroscopic stick-slip and mode coupling instabilities, which can occur at different scales ranging from earthquakes to vibrational issues in machining processes. The paper presents a comparison between experimental observations of frictional macroscopic behaviours reproduced in a dedicated laboratory set-up and numerical simulations, obtained by transient finite element simulations able to reproduce the contact dynamics. The explicit finite element code PLASTD has been used to perform numerical transient analysis of two elastic bodies in frictional contact. On the other hand an experimental set-up has been used to investigate the macroscopic response of two blocks of polycarbonate in relative motion, highlighting how the contact frictional behaviour is affected by the imposed boundary conditions. Time evolution of global contact forces has been investigated; macroscopic stick-slip, modal instability behaviours and the transition to continuous sliding as a function of the system parameters have been observed. The frequency and time analysis of experimental phenomena exhibits a good agreement with numerical results obtained through transient contact simulations. The numerical analysis allows for explaining the interaction between local contact behaviour and system dynamics, which is at the origin of the different frictional scenarios. Maps of the instability scenarios are drawn as a function of boundary conditions or system parameters.
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Trincal V, Lanari P, Buatier M, Lacroix B, Charpentier D, Labaume P, Munoz M (2015) Temperature micro-mapping in oscillatory-zoned chlorite: Application to study of a green-schist facies fault zone in the Pyrenean Axial Zone (Spain). American Mineralogist 100(11-12):2468–2483
Résumé: Oscillatory compositional zoning in minerals has been observed in hydrothermal, magmatic, and metamorphic environments and is commonly attributed to chemical or physical cyclical changes during crystal growth. Chemical zoning is a common feature of solid solutions, which has been rarely reported in phyllosilicates. In this study, oscillatory zoning in chlorite is described in samples from the Pic-de-Port-Vieux thrust, a minor thrust fault associated to the major Gavarnie thrust fault zone (Central Pyrenees, Spain). The Pic-de-Port-Vieux thrust sheet comprises a 1-20 m thick layer of Triassic red pelite and sandstone thrust over mylonitized Cretaceous dolomitic limestone. The thrust fault zone deformation comprises secondary faults and cleavage affecting the Triassic pelite and sandstone. An important feature responsible to this deformation is a set of veins filled by quartz and chlorite. Chlorite is present in crack-seal extension veins and in shear veins; both structures opened under the same stress conditions. In some shear veins, chlorite occurs as pseudo-uniaxial plates arranged in rosette-shaped aggregates. These aggregates appear to have developed as a result of radial growth of the chlorite platelets. Oscillatory zoning has been imaged by backscattered scanning electron microscopy and by X-ray quantitative micro-mapping. These oscillations correspond to chemical zoning with alternating iron-rich and magnesium-rich bands. The chlorite composition ranges from a Fe-rich pole to a Mg-rich pole. Fe3+/Sigma Fe values were measured in chlorite using mu-XANES spot analyses and vary from 0.23 to 0.44. The highest values are in the Ferich area. Temperature maps, built from standardized microprobe X-ray images and redox state using the program XMapTools, indicate oscillatory variations from about 310 to 400 +/- 50 degrees C during chlorite crystallization. These temperature variations are correlated with a Fe3+/Sigma Fe variation by Al3+Fe-13+ and ditrioctahedral substitutions highlighted by Mg and Fe-Tot contents (Fe-Mg zoning). Chemical variations could be then explained by alternation of cooling times and cyclical pulses of a fluid hotter than the host rock. It is however not excluded that kinetic effects influence the incorporation of Mg or Fe during chlorite crystallization.
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Tudisco E, Roux P, Hall SA, Viggiani GMB, Viggiani G (2015) Timelapse ultrasonic tomography for measuring damage localization in geomechanics laboratory tests. Journal Of The Acoustical Society Of America 137(3):1389–1400
Résumé: Variation of mechanical properties in materials can be detected non-destructively using ultrasonic measurements. In particular, changes in elastic wave velocity can occur due to damage, i.e., microcracking and particles debonding. Here the challenge of characterizing damage in geomaterials, i.e., rocks and soils, is addressed. Geomaterials are naturally heterogeneous media in which the deformation can localize, so that few measurements of acoustic velocity across the sample are not sufficient to capture the heterogeneities. Therefore, an ultrasonic tomography procedure has been implemented to map the spatial and temporal variations in propagation velocity, which provides information on the damage process. Moreover, double beamforming has been successfully applied to identify and isolate multiple arrivals that are caused by strong heterogeneities (natural or induced by the deformation process). The applicability of the developed experimental technique to laboratory geomechanics testing is illustrated using data acquired on a sample of natural rock before and after being deformed under triaxial compression. The approach is then validated and extended to time-lapse monitoring using data acquired during plane strain compression of a sample including a well defined layer with different mechanical properties than the matrix. (C) 2015 Acoustical Society of America.
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Valla M, Gueguen P, Augere B, Goular D, Perrault M (2015) Remote Modal Study of Reinforced Concrete Buildings Using a Multipath Lidar Vibrometer. Journal Of Structural Engineering 141(1)
Résumé: Over recent years there has been growing interest in building frequency analysis using ambient vibrations in the fields of structural engineering with application to earthquakes, health monitoring, or operative testing. The direct applications are (1) to define the modal characteristics of existing buildings for modeling their seismic response, (2) to monitor the long-term variations in their structural health, and (3) to detect and localize changes in the structure such as those produced by earthquake damage. Simultaneously, velocity measurements with laser remote sensing techniques have gained interest for several applications. For example, coherent lidar systems enable accurate measurement of the vibration velocity of remote targets. This allows operative modal analysis (OMA) of potentially damaged buildings, for their diagnosis from a safe distance after a seismic event. This paper compares the frequency analyses obtained using sensitive velocimeter sensors and coherent lidar sensors, applied to a number of existing reinforced concrete (RC) buildings. Ambient vibrations recorded by velocimeters are processed using the frequency domain decomposition method for defining building frequency and mode shape, while the laser remote sensing approach uses the coherent lidar method to measure velocity, frequency, and mode shape. The results of a real-scale trial on five buildings in Grenoble, France, are presented. The reliability of this technique for remote structural diagnosis is discussed and the modal parameters, as measured by lidar at a range of 200 m and by in situ velocimeters, are compared. The results from the two instruments were in good agreement, which leads us to conclude on the ability of the coherent lidar approach to assess the modal frequencies and mode shapes of existing buildings at long range and without any retroreflectors on the structure for structural and earthquake engineering purposes. (C) 2014 American Society of Civil Engineers.
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Vantieghem S, Cebron D, Noir J (2015) Latitudinal libration driven flows in triaxial ellipsoids. Journal Of Fluid Mechanics 771
Résumé: Motivated by understanding the liquid core dynamics of tidally deformed planets and moons, we present a study of incompressible flow driven by latitudinal libration within rigid triaxial ellipsoids. We first derive a laminar solution for the inviscid equations of motion under the assumption of uniform vorticity flow. This solution exhibits a resonance if the libration frequency matches the frequency of the spin-over inertial mode. Furthermore, we extend our model by introducing a reduced model of the effect of viscous Ekman layers in the limit of low Ekman number (Noir & Cebron, J. Fluid Mech., vol. 737, 2013, pp. 412-439). This theoretical approach is consistent with the results of Chan et al. (Phys. Earth Planet. Inter., vol. 187, 2011, pp. 404-415) and Zhang et al. (J. Fluid Mech., vol. 692, 2012, pp. 420-445) for spheroidal geometries. Our results are validated against systematic three-dimensional numerical simulations. In the second part of the paper, we present the first linear stability analysis of this uniform vorticity flow. To this end, we adopt different methods (Lifschitz & Hameiri, Phys. Fluids A, vol. 3, 1991, p. 2644; Gledzer & Ponomarev, Acad. Sci., USSR, Izv., Atmos. Ocean. Phys., vol. 13, 1977, pp. 565-569) that allow us to deduce upper and lower bounds for the growth rate of an instability. Our analysis shows that the uniform vorticity base flow is prone to inertial instabilities caused by a parametric resonance mechanism. This is confirmed by a set of direct numerical simulations. Applying our results to planetary settings, we find that neither a spin-over resonance nor an inertial instability can exist within the liquid core of the Moon, Io and Mercury.
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Vassallo R, Mugnier J-L, Vignon V, Malik MA, Jayangondaperumal R, Srivastava P, Jouanne F, Carcaillet J (2015) Distribution of the Late-Quaternary deformation in Northwestern Himalaya. Earth And Planetary Science Letters 411:241–252
Résumé: Three main Cenozoic thrusts at the front of Northwestern Himalaya have accommodated most of the India-Eurasia convergence across the belt over the last million years and produced the present relief. Their recent tectonic activity is poorly known because of the long period of inaccessibility of the Jammu and Kashmir state, and because the latest and only large earthquake recorded in the region occurred in 1555 AD. We show where the deformation is localized during the Late-Quaternary, and determine shortening rates across the structures by analyzing the geometry and chronology of geomorphic markers. The Main Boundary Thrust in this region ceased moving at least similar to 30 ka ago. On the contrary, the more external Medlicott-Wadia Thrust and Main Frontal Thrust, both merging at depth on the sub-flat detachment of the Main Himalayan Thrust, exhibit hectometric-scale deformations accumulated during the last thousands of years. The total shortening rate absorbed by these faults over the last 14-24 ka is between 13.2 and 27.2 mm/yr (11.2 +/- 3.8 and 9.0 +/- 3.2 mm/yr, respectively). Part of this deformation may be associated to the geometry of the Chenab reentrant, which could generate an extra oblique component. However, the lower bound of our shortening rates is consistent with previously determined geodetic rates. Active deformation on these structures follows an in-sequence/out-of-sequence pattern, with breaking of both ramps being possible for earthquakes triggered on the main detachment. (C) 2014 Elsevier B.V. All rights reserved.
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Vidal J, Schaeffer N (2015) Quasi-geostrophic modes in the Earth's fluid core with an outer stably stratified layer. Geophysical Journal International 202(3):2182–2193
Résumé: Seismic waves sensitive to the outermost part of the Earth's liquid core seem to be affected by a stably stratified layer at the core-mantle boundary. Such a layer could have an observable signature in both long-term and short-term variations of the magnetic field of the Earth, which are used to probe the flow at the top of the core. Indeed, with the recent SWARM mission, it seems reasonable to be able to identify waves propagating in the core with period of several months, which may play an important role in the large-scale dynamics. In this paper, we characterize the influence of a stratified layer at the top of the core on deep quasi-geostrophic (Rossby) waves. We compute numerically the quasi-geostrophic eigenmodes of a rapidly rotating spherical shell, with a stably stratified layer near the outer boundary. Two simple models of stratification are taken into account, which are scaled with commonly adopted values of the Brunt-Vaisala frequency in the Earth's core. In the absence of magnetic field, we find that both azimuthal wavelength and frequency of the eigenmodes control their penetration into the stratified layer: the higher the phase speed, the higher the permeability of the stratified layer to the wave motion. We also show that the theory developed by Takehiro & Lister for thermal convection extends to the whole family of Rossby waves in the core. Adding a magnetic field, the penetrative behaviour of the quasi-geostrophic modes (the so-called fast branch) is insensitive to the imposed magnetic field and only weakly sensitive to the precise shape of the stratification. Based on these results, the large-scale and high-frequency modes (1-2 month periods) may be detectable in the geomagnetic data measured at the Earth's surface, especially in the equatorial area where the modes can be trapped.
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Villacorta S, Ubeda J, Tatard L, Diez A (2015) Proposal for Climate Change Impact Research in Western Central Andes of Peru. 13–16
Résumé: In this paper an initiative of the Peruvian Geological Survey, INGEMMET, is shown to promote the research on geomorphology and climate change in Peru. The plan is to elaborate geomorphological maps of the Lima Metropolitan Area and its watershed headers (Chillon, Rimac and Lurin rivers), in order to generate analytical instruments to achieve the following objectives: (1) Decode the record of climatic changes in landforms. (2) Delimit water reserves stored as ice masses (cryosphere). (3) Recognize the relationship between the geomorphology and the geological hazards which may affect people and their economic activities. (4) Design a methodology that can be extrapolated to others Peruvian regions. To reach this objective, geomorphological mapping will be integrated into a GIS, so the morphoclimatic units and the related genetic processes will be identified. Also, their relative chronologies will be proposed. Then, the absolute dating of key units will be established, to confirm or correct the relative chronologies. The information will be compiled into databases, to be contrasted with other evidences and paleoclimatic proxies. This is intended to produce models of climate evolution, to contribute to the assessment of geological hazards, and the knowledge of current state of cryosphere, including recent trends and future forecasts.
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Vincent C, Thibert E, Gagliardini O, Legchenko A, Gilbert A, Garambois S, Condom T, Baltassat JM, Girard JF (2015) Mechanisms of subglacial cavity filling in Glacier de Tete Rousse, French Alps. Journal Of Glaciology 61(228):609–623
Résumé: The deadliest outburst flood from an englacial cavity occurred on Glacier de Tete Rousse in the Mont Blanc area, French Alps, in 1892. A subglacial reservoir was discovered in the same glacier in 2010 and drained artificially in 2010, 2011 and 2012 to protect the 3000 inhabitants downstream. The mechanism leading to the spontaneous refilling of the cavity following these pumping operations has been analyzed. For this purpose, the subglacial water volume changes between 2010 and 2013 were reconstructed. The size of the cavity following the pumping was found to have decreased from 53 500 m(3) in 2010 to 12 750 m(3) in 2013. Creep and the partial collapse of the cavity roof explain a large part of the volume loss. Analysis of cavity filling showed a strong relationship between measured surface melting and the filling rate, with a time delay of 4-6 hours. A permanent input of 15 m(3) d(-1), not depending on surface melt, was also found. The meltwater and rain from the surface is conveyed to bedrock through crevasses and probably through a permeable layer of rock debris at the glacier bed. The drainage pathway permeability was estimated at 0.054 m s(-1) from water discharge measurements and dye-tracing experiments.
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Vincent C, Thibert E, Gagliardini O, Legchenko A, Gilbert A, Garambois S, Condom T, Baltassat JM, Girard JF (2015) Mechanisms of subglacial cavity filling in Glacier de Tete Rousse, French Alps. Journal Of Glaciology 61(228):609–623
Résumé: The deadliest outburst flood from an englacial cavity occurred on Glacier de Tete Rousse in the Mont Blanc area, French Alps, in 1892. A subglacial reservoir was discovered in the same glacier in 2010 and drained artificially in 2010, 2011 and 2012 to protect the 3000 inhabitants downstream. The mechanism leading to the spontaneous refilling of the cavity following these pumping operations has been analyzed. For this purpose, the subglacial water volume changes between 2010 and 2013 were reconstructed. The size of the cavity following the pumping was found to have decreased from 53 500 m(3) in 2010 to 12 750 m(3) in 2013. Creep and the partial collapse of the cavity roof explain a large part of the volume loss. Analysis of cavity filling showed a strong relationship between measured surface melting and the filling rate, with a time delay of 4-6 hours. A permanent input of 15 m(3) d(-1), not depending on surface melt, was also found. The meltwater and rain from the surface is conveyed to bedrock through crevasses and probably through a permeable layer of rock debris at the glacier bed. The drainage pathway permeability was estimated at 0.054 m s(-1) from water discharge measurements and dye-tracing experiments.
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Walpersdorf A, Sue C, Baize S, Cotte N, Bascou P, Beauval C, Collard P, Daniel G, Dyer H, Grasso J-R, Hautecoeur O, Helmstetter A, Hok S, Langlais M, Menard G, Mousavi Z, Ponton F, Rizza M, Rolland L, Souami D, Thirard L, Vaudey P, Voisin C, Martinod J (2015) Coherence between geodetic and seismic deformation in a context of slow tectonic activity (SW Alps, France). Journal Of Geodynamics 85:58–65
Résumé: A dense, local network of 30 geodetic markers covering a 50 x 60 km(2) area in the southwestern European Alps (Briancon region) has been temporarily surveyed in 1996, 2006 and 2011 by GPS. The aim is to measure the current deformation in this seismically active area. The study zone is characterized by a majority of extensional and dextral focal mechanisms, along north-south to N160 oriented faults. The combined analysis of the three measurement campaigns over 15 years and up to 16 years of permanent GPS data from the French RENAG network now enables to assess horizontal velocities below 1 mm/year within the local network. The long observation interval and the redundancy of the dense campaign network measurement help to constrain a significant local deformation pattern in the Briancon region, yielding an average E-W extension of 16 +/- 11 nanostrain/year. We compare the geodetic deformation field to the seismic deformation rate cumulated over 37 years, and obtain good coherencies both in amplitude and direction. Moreover, the horizontal deformation localized in the Briancon region represents a major part of the Adriatic-European relative plate motion. However, the average uplift of the network in an extensional setting needs the presence of buoyancy forces in addition to plate tectonics. (C) 2015 Elsevier Ltd. All rights reserved.
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Walter F, Roux P, Roeoesli C, Lecointre A, Kilb D, Roux P-F (2015) Using glacier seismicity for phase velocity measurements and Green's function retrieval. Geophysical Journal International 201(3):1722–1737
Résumé: High-melt areas of glaciers and ice sheets foster a rich spectrum of ambient seismicity. These signals not only shed light on source mechanisms (e.g. englacial fracturing, water flow, iceberg detachment, basal motion) but also carry information about seismic wave propagation within glacier ice. Here, we present two approaches to measure and potentially monitor phase velocities of high-frequency seismic waves (a parts per thousand yen1 Hz) using naturally occurring glacier seismicity. These two approaches were developed for data recorded by on-ice seasonal seismic networks on the Greenland Ice Sheet and a Swiss Alpine glacier. The Greenland data set consists of continuous seismograms, dominated by long-term tremor-like signals of englacial water flow, whereas the Alpine data were collected in triggered mode producing 1-2 s long records that include fracture events within the ice ('icequakes'). We use a matched-field processing technique to retrieve frequency-dependent phase velocity measurements for the Greenland data. In principle, this phase dispersion relationship can be inverted for ice sheet thickness and bed properties. For these Greenland data, inversion of the dispersion curve yields a bedrock depth of 541 m, which may be too small by as much as 35 per cent. We suggest that the discrepancy is due to lateral changes in ice sheet depth and bed properties beneath the network, which may cause unaccounted mixing of surface wave modes in the dispersion curve. The Swiss Alpine icequake records, on the other hand, allow for reconstruction of the impulse response between two seismometers. The direct and scattered wave fields from the vast numbers of icequake records (tens of thousands per month) can be used to measure small changes in englacial velocities and thus monitor structural changes within the ice.
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Weiss J, Ben Rhouma W, Richeton T, Dechanel S, Louchet F, Truskinovsky L (2015) From Mild to Wild Fluctuations in Crystal Plasticity. Physical Review Letters 114(10)
Résumé: Macroscopic crystal plasticity is classically viewed as an outcome of uncorrelated dislocation motions producing Gaussian fluctuations. An apparently conflicting picture emerged in recent years emphasizing highly correlated dislocation dynamics characterized by power-law distributed fluctuations. We use acoustic emission measurements in crystals with different symmetries to show that intermittent and continuous visions of plastic flow are not incompatible. We demonstrate the existence of crossover regimes where strongly intermittent events coexist with a Gaussian quasiequilibrium background and propose a simple theoretical framework compatible with these observations.
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Westall F, Campbell KA, Breheret JG, Foucher F, Gautret P, Hubert A, Sorieul S, Grassineau N, Guido DM (2015) Archean (3.33 Ga) microbe-sediment systems were diverse and flourished in a hydrothermal context. Geology 43(7):615–618
Résumé: Interacting, diverse microbe-sediment systems exist in natural environments today but have not yet been recognized in the oldest records of life on Earth (older than 3.3 Ga) because of lack of distinctive biomarker molecules and patchy preservation of microbial paleocommunities. In an in-situ outcrop-to microbial-scale study, we have differentiated probable phototrophic, chemolithotrophic, and chemo-organotrophic fossil microbial signatures in a nearshore volcanogenic sedimentary setting in 3.33 Ga rocks of the Josefsdal Chert, Barberton greenstone belt, South Africa, while demonstrating the importance of contemporaneous hydrothermal activity. Hydrothermal fluids, as a nutrient source, strongly controlled the development and distribution of the microbial communities and, as a silicifying agent, contributed to their rapid fossilization. We thus show that intricate microbe-sediment systems are deep-rooted in time and that at least some early life may indeed have been thermophilic.
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Wibowo SB, Lavigne F, Mourot P, Metaxian J-P, Zeghdoudi M, Virmoux C, Sukatja CB, Hadmoko DS, Mutaqin BW (2015) Coupling between Video and Seismic Data Analysis for the Study of Lahar Dynamics at Merapi Volcano, Indonesia. Geomorphologie-Relief Processus Environnement 21(3):251–265
Résumé: Lahar flow dynamics is still poorly understood due to the difficulty of data acquisition in the field. The eruption of the Merapi volcano (Indonesia) in October-November 2010 allowed us to collect new information in the frame of the SEDIMER research program (Sediment-related Disasters following the 2010 eruption of Merapi Volcano, Java, Indonesia, 2012-2015). Lahar dynamics are studied based on the coupling between video images and seismic data. We installed a seismic station at Gendol river (1090 meters asl, 4.6 km south from the summit) consisting of two geophones placed 76 meters apart parallel to the river, a high definition camera on the edge of the river and two raingauges at east and west side of the river. We also used a walkie-talkie to receive seismic signal from the seismometers belonging to the Merapi Observatory (BPPTKG) and to communicated with local commnuities. This article focuses on the debris-flow-type lahar which was recorded on February 28, 2014. The results of the video and the seismic analysis show that the behavior of this lahar changed continuously during the event. The lahar front moved at an average speed of 4.1 m/s at the observation site. Its maximum velocity reached 14.5 m/s with a peak discharge of 473 m(3)/s. The maximus depth of the flow reached 7 m. Almost 600 blocks of more than 1 m main axis were identified on the surface of the lahar during 36 minutes, which represent an average block discharge of 17 blocks per minute. The interpretation of amplitude and frequency of the seismic signals were improved by video analysis data, especially for the contrast between debris flow and hyperconcentrated flow during lahar occurrence.
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Wiersberg T, Schleicher AM, Horiguchi K, Mai-Linh Doan, Eguchi N, Erzinger J (2015) Origin and in situ concentrations of hydrocarbons in the Kumano forearc basin from drilling mud gas monitoring during IODP NanTroSEIZE Exp. 319. Applied Geochemistry 61:206–216
Résumé: NanTroSEIZE Exp. 319 of the Integrated Ocean Drilling Program (IODP) was the first cruise in the history of scientific ocean drilling with drilling mud circulation through a riser. Drilling mud was pumped through the drill string and returned to the drill ship through the riser pipe during drilling of hole C0009A from 703 to 1604 mbsf (meter below sea floor) and hole enlargement from 703 to 1569 mbsf. During riser drilling, gas from returning drilling mud was continuously extracted, sampled and analyzed in real time to reveal information on the gas composition and gas concentrations at depth. Hydrocarbons were the only formation-derived gases identified in drilling mud and reached up to 14 vol.% of methane and 48 ppmv of ethane. The chemical and isotopic compositions of hydrocarbons exhibit a microbial origin. Hydrocarbons released from drilling mud and cuttings correlate with visible allochthonous material (wood, lignite) in drilling cuttings. At greater depth, addition of small but increasing amounts of hydrocarbons probably from low-temperature thermal degradation of organic matter is indicated. The methane content is also tightly correlated with several intervals of low Poisson's ratio from Vp/Vs observed in sonic velocity logs, suggesting that the gas is situated in the pore space of the rock as free gas. The gas concentrations in the formation, determined from drilling mud gas monitoring, reaching up to 24 L-gas/L-sediment for methane in hole C0009A, in line with gas concentrations from interpreted down-hole sonic logs. (C) 2015 Elsevier Ltd. All rights reserved.
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Wilkinson PB, Uhlemann S, Meldrum PI, Chambers JE, Carriere S, Oxby LS, Loke MH (2015) Adaptive time-lapse optimized survey design for electrical resistivity tomography monitoring. Geophysical Journal International 203(1):755–766
Résumé: Adaptive optimal experimental design methods use previous data and results to guide the choice and design of future experiments. This paper describes the formulation of an adaptive survey design technique to produce optimal resistivity imaging surveys for time-lapse geoelectrical monitoring experiments. These survey designs are time-dependent and, compared to dipole-dipole or static optimized surveys that do not change over time, focus a greater degree of the image resolution on regions of the subsurface that are actively changing. The adaptive optimization method is validated using a controlled laboratory monitoring experiment comprising a well-defined cylindrical target moving along a trajectory that changes its depth and lateral position. The algorithm is implemented on a standard PC in conjunction with a modified automated multichannel resistivity imaging system. Data acquisition using the adaptive survey designs requires no more time or power than with comparable standard surveys, and the algorithm processing takes place while the system batteries recharge. The results show that adaptively designed optimal surveys yield a quantitative increase in image quality over and above that produced by using standard dipole-dipole or static (time-independent) optimized surveys.
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Williams EG, Roux P, Rupin M, Kuperman WA (2015) Theory of multiresonant metamaterials for A(0) Lamb waves. Physical Review B 91(10)
Résumé: We develop an analytical wave approach to describe the physics properties of multiresonant metamaterials for Lamb waves propagating in plates. The metamaterial that we characterize consists of a 10 by 10 uniform, periodic array of long rods attached to the surface of the plate that forms the substrate in which antisymmetric A(0) Lamb waves are excited. We show that the A(0) Lamb wave propagation through the metamaterial can be accurately modeled using a simplified theory that replaces the two-dimensional array with a one-dimensional beam with a linear array of 10 rods. The wave propagation problem is solved rigorously for this one-dimensional system using the scattering matrix for a single rod. The exact eigenvalues of the system are approximated in a long wavelength expansion to determine a simple expression for the effective wave number and dispersion of the metamaterial. The modeled dispersion is compared with an experimental measurement of the dispersion inside the metamaterial with excellent agreement. The multiresonant rods, restricted to longitudinal vibration consistent with A(0) Lamb waves excited in the plate, produce two wide stop bands in the frequency domain from 0 to 10 kHz where the stop or passband boundaries align with the minima and maxima of the rod's impedance. We show that a negative effective density is obtained in the stop band. With the simple yet highly accurate relations given in this paper we have a tool to develop more complex metamaterials with rods and plates of different properties.
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Woodruff WF, Revil A, Prasad M, Torres-Verdin C (2015) Measurements of elastic and electrical properties of an unconventional organic shale under differential loading. Geophysics 80(4):D363–D383
Résumé: We have developed an experimental approach to simultaneously measure the stress dependence of ultrasonic wave velocities at 1 MHz, and therefore the components of the undrained elastic stiffness tensor, as well as the components of the complex conductivity tensor in the frequency range from 100 mHz to 10 Hz. We performed the experiments on a cylindrical core sample from the Haynesville Formation (porosity of approximately 0.08, bound water excluded, and clay content, mostly illite, approximately 30-40 wt%). We performed experiments under controlled confining and pore fluid pressures, achieving differential pressure states representative of autochthonous reservoir conditions. Directional measurements were made using independent acquisition arrays (piezoelectric crystals and nonpolarizing electrodes) distributed azimuthally on the core sample external surface, the bedding plane being along the axis of the cylindrical core sample. Ultrasonic waveforms were recorded on a high-resolution oscilloscope, and complex impedance spectra were recorded with a four-electrode acquisition system using an impedance meter with precision of 0.1 mrad. Experiments were repeated under drained and undrained conditions, over loading and unloading sequences for fully water-saturated conditions. Measurements show strong stress dependence on ultrasonic and complex conductivity measurements, which can be ascribed to the opening and closing of cracks within the samples. The data were used to estimate the anisotropic electrical and elastic effective pressure coefficients of the core sample, resulting in effective stress coefficients smaller than one for both elastic and electrical properties. These effective stress coefficients were also smaller for the electrical and acoustic properties once the cracks have closed. The anisotropy ratio for the components of the complex conductivity tensor was on the order of 30, whereas it was only 2 for the compressional components of the stiffness tensor (C-11/C-33)
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Zhang J, Revil A (2015) 2D joint inversion of geophysical data using petrophysical clustering and facies deformation. Geophysics 80(5):M69–M88
Résumé: Geologic expertise and petrophysical relationships can be brought together to provide prior information while inverting multiple geophysical data sets. The merging of such information can result in more realistic solution in the distribution of the model parameters. We have evaluated the geophysical inverse problem in terms of Gaussian random fields with mean functions controlled by petrophysical relationships and covariance functions controlled by a prior geologic cross section, including the definition of spatial boundaries for the geologic facies. The petrophysical relationship problem is formulated as a regression problem upon each facies. The inversion of the geophysical data is performed in a Bayesian framework. We have developed the usefulness of this strategy using a first synthetic case for which we have performed a joint inversion of gravity and ground surface. The joint inversion was used to recover the density and resistivity distributions of the subsurface. In a second step, we considered the possibility that the facies boundaries were deformable and their shapes were inverted as well. We used the level-set approach to perform such deformation preserving a priori topological properties of the facies throughout the inversion. With the help of a priori facies petrophysical relationships and the topological characteristics of each facies, we made a posteriori inference about multiple geophysical tomograms based on their corresponding geophysical data misfits. We have applied this method to a second synthetic case showing that we can recover the heterogeneities inside the facies, the mean values for the petrophysical properties, and, to some extent, the facies boundaries using the 2D joint inversion of gravity and galvanometric resistivity data.
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Zhang J, Revil A (2015) Cross-well 4-D resistivity tomography localizes the oil-water encroachment front during water flooding. Geophysical Journal International 201(1):343–354
Résumé: The early detection of the oil-water encroachment front is of prime interest during the water flooding of an oil reservoir to maximize the production of oil and to avoid the oil-water encroachment front to come too close to production wells. We propose a new 4-D inversion approach based on the Gauss-Newton approach to invert cross-well resistance data. The goal of this study is to image the position of the oil-water encroachment front in a heterogeneous clayey sand reservoir. This approach is based on explicitly connecting the change of resistivity to the petrophysical properties controlling the position of the front (porosity and permeability) and to the saturation of the water phase through a petrophysical resistivity model accounting for bulk and surface conductivity contributions and saturation. The distributions of the permeability and porosity are also inverted using the time-lapse resistivity data in order to better reconstruct the position of the oil water encroachment front. In our synthetic test case, we get a better position of the front with the by-products of porosity and permeability inferences near the flow trajectory and close to the wells. The numerical simulations show that the position of the front is recovered well but the distribution of the recovered porosity and permeability is only fair. A comparison with a commercial code based on a classical Gauss-Newton approach with no information provided by the two-phase flow model fails to recover the position of the front. The new approach could be used for the time-lapse monitoring of various processes in both geothermal fields and oil and gas reservoirs using a combination of geophysical methods.
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Zhang Y-Z, Replumaz A, Wang G-C, Leloup PH, Gautheron C, Bernet M, van der Beek P, Paquette JL, Wang A, Zhang K-X, Chevalier M-L, Li H-B (2015) Timing and rate of exhumation along the Litang fault system, implication for fault reorganization in Southeast Tibet. Tectonics 34(6):1219–1243
Résumé: The Litang fault system that crosses the Litang Plateau, a low relief surface at high elevation (similar to 4200-4800m above sea level) that is not affected by regional incision, provides the opportunity to study exhumation related to tectonics in the SE Tibetan Plateau independently of regional erosion. Combining apatite and zircon fission track with apatite (U-Th)/He thermochronologic data, we constrain the cooling history of the Litang fault system footwall along two transects. Apatite fission track ages range from 4 to 16Ma, AHe ages from 2 to 6Ma, and one zircon fission track age is similar to 99Ma. These data imply a tectonic quiet period sustained since at least 100Ma with a slow denudation rate of similar to 0.03km/Ma, interrupted at 7 to 5Ma by exhumation at a rate between 0.59 and 0.99km/Ma. We relate that faster exhumation to the onset of motion along the left-lateral/normal Litang fault system. That onset is linked to a Lower Miocene important kinematic reorganization between the Xianshuihe and the Red River faults, with the eastward propagation of the Xianshuihe fault along the Xiaojiang fault system and the formation of the Zhongdian fault. Such strike-slip faults allow the sliding to the east of a wide continental block, with the Litang fault system accommodating differential motion between rigid blocks. The regional evolution appears to be guided by the strike-slip faults, with different phases of deformation, which appears more in agreement with an hidden plate-tectonic model rather than with a lower channel flow model.
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Zhao L, Paul A, Guillot S, Solarino S, Malusa MG, Zheng T, Aubert C, Salimbeni S, Dumont T, Schwartz S, Zhu R, Wang Q (2015) First seismic evidence for continental subduction beneath the Western Alps. Geology 43(9):815–818
Résumé: The first discovery of ultrahigh-pressure coesite in the European Alps 30 years ago led to the inference that a positively buoyant continental crust can be subducted to mantle depth; this had been considered impossible since the advent of the plate tectonics concepts. Although continental subduction is now widely accepted, there remains debate because there is little direct (geophysical) evidence of a link between exhumed coesite at the surface and subducted continental crust at depth. Here we provide the first seismic evidence for continental crust at 75 km depth that is clearly connected with the European crust exactly along the transect where coesite was found at the surface. Our data also provide evidence for a thick suture zone with downward-decreasing seismic velocities, demonstrating that the European lower crust underthrusts the Adriatic mantle. These findings, from one of the best-preserved and long-studied ultrahigh-pressure orogens worldwide, shed decisive new light on geodynamic processes along convergent continental margins.
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Zhou W, Brossier R, Operto S, Virieux J (2015) Full waveform inversion of diving & reflected waves for velocity model building with impedance inversion based on scale separation. Geophysical Journal International 202(3):1535–1554
Résumé: Full waveform inversion (FWI) aims to reconstruct high-resolution subsurface models from the full wavefield, which includes diving waves, post-critical reflections and short-spread reflections. Most successful applications of FWI are driven by the information carried by diving waves and post-critical reflections to build the long-to-intermediate wavelengths of the velocity structure. Alternative approaches, referred to as reflection waveform inversion (RWI), have been recently revisited to retrieve these long-to-intermediate wavelengths from short-spread reflections by using some prior knowledge of the reflectivity and a scale separation between the velocity macromodel and the reflectivity. This study presents a unified formalism of FWI, named as Joint FWI, whose aim is to efficiently combine the diving and reflected waves for velocity model building. The two key ingredients of Joint FWI are, on the data side, the explicit separation between the short-spread reflections and the wide-angle arrivals and, on the model side, the scale separation between the velocity macromodel and the short-scale impedance model. The velocity model and the impedance model are updated in an alternate way by Joint FWI and waveform inversion of the reflection data (least-squares migration), respectively. Starting from a crude velocity model, Joint FWI is applied to the streamer seismic data computed in the synthetic Valhall model. While the conventional FWI is stuck into a local minimum due to cycle skipping, Joint FWI succeeds in building a reliable velocity macromodel. Compared with RWI, the use of diving waves in Joint FWI improves the reconstruction of shallow velocities, which translates into an improved imaging at deeper depths. The smooth velocity model built by Joint FWI can be subsequently used as a reliable initial model for conventional FWI to increase the high-wavenumber content of the velocity model.
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Zhuang G, Najman Y, Guillot S, Roddaz M, Antoine P-O, Metais G, Carter A, Marivaux L, Solangi SH (2015) Constraints on the collision and the pre-collision tectonic configuration between India and Asia from detrital geochronology, thermochronology, and geochemistry studies in the lower Indus basin, Pakistan. Earth And Planetary Science Letters 432:363–373
Résumé: Knowledge of the timing of India-Asia collision is a fundamental prerequisite for understanding the evolution of the Himalayan-Tibetan orogen and its role in global climate, oceanic chemistry, and ecological evolution. Despite much active research, the basic pre-collision tectonic configuration and the timing of terminal India-Asia suturing remain debated. For example, debates regarding when and how the intervening Kohistan-Ladakh arc was sutured with India and Asia still remain elusive; some models propose the arc collided with Asia at about 100 Ma, with India-sia collision at ca. 55 Ma, whilst a newer model proposed the arc's collision with India at 50 Ma and subsequently with Asia at 40 Ma. Another example is the recent proposition that an oceanic Greater India Basin separated the Tethyan Himalaya microcontinent from the remaining Indian plate until 20-25 Ma with the consumption of this oceanic basin marking the final collision at this time. These controversies relate to whether the commonly documented 50 Ma contact represents the terminal India-Asia suturing or the amalgamation between various arcs or microcontinents with India or Asia. Here we present an integrated provenance study of geochronology, thermochronology, and geochemistry on the late Cretaceous-Pleistocene sediments from the lower Indus basin on the Indian plate. The detrital zircon U-Pb and fission track data show a reversal in sediment source from a pure Indian signature to increasing inputs from the suture zone and the Asian plate between the middle Paleocene and early Oligocene. The Nd and Sr isotopes narrow down this change to 50 Ma by revealing input of Asian detritus and the establishment of a Nd & Sr isotopic pattern similar to the present-day Indus Fan by 50 Ma, with no significant variations up section, contrary to what might be expected if later major collisions had occurred. Our isotopic data indicate that Greater India was occupied by a fluvial-deltaic system, analogous to the present-day Indus and named as the Paleo-Indus, which has been transporting Asian detritus southward across the suture zone and Kohistan-Ladakh arc since 50 Ma, suggesting no other ocean basins intervened between India and Asia after this time in this region. Our data require that in the west the India-Asia collision were accomplished by similar to 50 Ma. (C) 2015 Elsevier B.V. All rights reserved.
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Zigone D, Ben-Zion Y, Campillo M (2015) Modelling non-volcanic tremor, slow slip events and large earthquakes in the Guerrero subduction zone (Mexico) with space-variable frictional weakening and creep. Geophysical Journal International 202(1):653–669
Résumé: We explore with numerical simulations basic physical conditions leading to key observed features of non-volcanic tremor (NVT) in relation to slow slip events (SSEs) and earthquakes along the Guerrero segment of the Mexican subduction zone. To study the interactions between different modes of slip, and examine possible variations over timescales larger than the 15 year observational interval, we use a model with a planar interface governed by space-varying static/kinetic friction and dislocation creep in a 3-D elastic solid. A fault section with zero weakening during frictional slip fails in a mode corresponding to a 'critical depinning transition' that produces generically many observed features of NVT. A patch with elevated creep coefficients represents a section with SSE. Simulations with small added stress oscillations are used to examine triggering of NVT by large remote earthquakes. The results reproduce well the basic observed properties of NVT and SSE in the Guerrero area, while pointing to complex interactions between large earthquake cycles, quasi-period SSE and scale-invariant NVT behaviour. The model simulations provide additional information on expected frequency-magnitude statistics, slip distributions and space-time properties of the different event types that may be tested with accumulation of future data. Some earthquake and NVT events near the opposite sides of the SSE patch have significant separation between their hypocentres and centroids. The rates of these events are correlated with the creep evolution in the SSE section. The results also suggest that aseismic deformation in the area may have transients on timescales larger than the observational period.
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Zigone D, Ben-Zion Y, Campillo M, Roux P (2015) Seismic Tomography of the Southern California Plate Boundary Region from Noise-Based Rayleigh and Love Waves. Pure And Applied Geophysics 172(5):1007–1032
Résumé: We use cross-correlations of ambient seismic noise between pairs of 158 broadband and short-period sensors to investigate velocity structure over the top 5-10 km of the crust in the Southern California plate boundary region around the San Jacinto Fault Zone (SJFZ). From the 9-component correlation tensors associated with all station pairs we derive dispersion curves of Rayleigh and Love wave group velocities. The dispersion results are inverted first for Rayleigh and Love waves group velocity maps on a 1.5 x 1.5 km(2) grid that includes portions of the SJFZ, the San Andreas Fault (SAF), and the Elsinore fault. We then invert these maps to 3D shear wave velocities in the top similar to 7 km of the crust. The distributions of the Rayleigh and Love group velocities exhibit 2 theta azimuthal anisotropy with fast directions parallel to the main faults and rotations in complex areas. The reconstructed 3D shear velocity model reveals complex shallow structures correlated with the main geological units, and strong velocity contrasts across various fault sections along with low-velocity damage zones and basins. The SJFZ is marked by a clear velocity contrast with higher V (s) values on the NE block for the section SE of the San Jacinto basin and a reversed contrast across the section between the San Jacinto basin and the SAF. Velocity contrasts are also observed along the southern parts on the SAF and the Elsinore fault, with a faster southwest block in both cases. The region around the Salton Trough is associated with a significant low-velocity zone. Strong velocity reductions following flower-shape with depth are observed extensively around both the SJFZ and the SAF, and are especially prominent in areas of geometrical complexity. In particular, the area between the SJFZ and the SAF is associated with an extensive low-velocity zone correlated with diffuse seismicity at depth, and a similar pattern including correlation with deep diffuse seismicity is observed on a smaller scale in the trifurcation area of the SJFZ. These results augment local earthquake tomography images that have low resolution in the top few km of the crust, and provide important constraints for studies concerned with behavior of earthquake ruptures, generation of rock damage, and seismic shaking hazard in the region.
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Zyserman FI, Jouniaux L, Warden S, Garambois S (2015) Borehole seismoelectric logging using a shear-wave source: Possible application to CO2 disposal? International Journal Of Greenhouse Gas Control 33:89–102
Résumé: The behaviour of CO2 deposition sites and their surroundings during and after carbon dioxide injection has been matter of study for several years, and several geophysical prospection techniques like surface and crosshole seismics, geoelectrics, controlled source electromagnetics among others, have been applied to characterize the behaviour of the gas in the reservoirs. Until now, Seismolectromagnetic wave conversions occurring in poroelastic media via electrokinetic coupling have not been tested for this purpose. In this work, by means of numerical experiments using Pride's equations extended to deal with partial saturations we show that the seismoelectric and seismomagnetic interface responses (IR) generated at boundaries of a layer containing carbon dioxide are sensitive to its CO2 content. Further, modeling shear wave sources in surface to borehole seismoelectric layouts and employing two different models for the saturation dependence of the electrokinetic coefficient, we observe that the IR are sensitive to CO2 saturations ranging between 10% and 90%, and that the CO2 saturation at which the IR maxima are reached depends on the aforementioned models. Moreover, the IR are still sensitive to different CO2 saturations for a sealed CO2 reservoir covered by a clay layer. These results, which should be complemented by the analysis of the IR absolute amplitude, could lead, once confirmed on the field, to a new monitoring tool complementing existing ones. (C) 2014 Elsevier Ltd. All rights reserved.
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**Publications non-ACL (non référencées dans ISI)
– Arndt, N.T. Ganino, C and Kesler. (2015) Ressources minérales : origine et exploitation. 2nd edition Dunod, Paris, 190pp (in French).
– Arndt, N.T., Kesler, S. and Ganino, C. (2015) “Metals and Society : an introduction to economic geology 2nd edition” Springer, Heidelburg, 207 p.
– Bajard M., Sabatier P., David F., Develle A.L., Reyss J.-L., Fanget B., Malet E., Arnaud D., Augustin L., Crouzet C., Poulenard J. et Arnaud F. (2015) : Reconstitution de l’évolution du paysage du lac de La Thuile (874 m, Massif des Bauges) durant l’Holocène : mise en évidence d’une domination des processus érosifs liés à l’homme à l’étage montagnard. Collection EDYTEM, 18, 41-56 ; numéro spécial « Sols et matières organiques : Mémoires et héritages ».
– Bouffette, J., J. Nomade, E. Robert, "Promenade géologique à Grenoble", Biotope Editions, 42 p., 2015, Ballades géologiques, Patrick de Wever, 978-2-36662-146-4
– Cardin, P. and P. Olson, 8.13 – Experiments on Core Dynamics, Treatise on Geophysics (Second Edition), 317-339, doi:10.1016/B978-0-444-53802-4.00147-0, 2015.
– Evans, P. L., Strollo, A., Clark, A., Ahern, T., Newman, R. Clinton, J. F., Pedersen, H. and Pequegnat, C., 2015. Why seismic networks need digital object identifiers, Eos,
96, doi:10.1029/2015EO036971.
– Folco L. and Cordier C. (2015) Micrometeorites. In Notes in Mineralogy : Planetary Mineralogy, ed. M. Lee, European Mineralogical Union, 15, pp. 253-297.
– France-Lanord, C., Spiess, V., Klaus, A., Schwenk, T., and the Expedition 354 Scientists, 2015. Proceedings of the International Ocean Discovery Program Volume 354 publications.iodp.orgdoi:10.14379/iodp.proc.354.104.2016
– Gavilan, L., Jäger, C., Simionovici, A., Lemaire, J. L., Sabri, T., Foy, E., et al. (2015) Hard X-ray irradiation of cosmic silicate analogs : structural evolution and astrophysical implications, Astronomy& Astrophysics, arXiv.org>astro-ph>arXiv:1601.05464:1.
– Hantz D. (2015) Mouvements de pente. In : Les risques naturels en montagne, F. Naaim-Bouvet, D. Richard, Editions Quae, chapitre 5, ISBN 978-2-7592-2386-2.
– Jault, D. and C.C. Finlay, 8.09 - Waves in the Core and Mechanical Core–Mantle Interactions, Treatise on Geophysics (Second Edition), 225-244, doi:10.1016/B978-0-444-53802-4.00150-0, 2015.
– Karaoulis, M., D.D. Werkema, and A. Revil, 2D time-lapse seismic tomography using an active time constraint (ATC) approach, The Leading Edge, 2, 206-212, doi : 10.1190/tle34020206.1, 2015.
– Loury C., Rolland, Y., Guillot S., Alexeiev D., Mikolaichuk A.V., Bruguier O., Bosch D. (2014) Crustal-scale structures of South Tianshan : implications for subduction polarity and Cenozoic reactivation. Geological Special Publication of London. 427, SP427. 4.
– Maufroy, E. Chaljub, F. Hollender, P.-Y. Bard, J. Kristek, P. Moczo, F. De Martin, N. Theodoulidis, M. Manakou, C. Guyonnet-Benaize, K. Pitilakis and N. Hollard, 2014. Validating the numerical simulation approach for ground motion predic-tion : General framework and latest lessons from the E2VP project. Invited theme lecture, 6ICEGE (6th IInternational Conference on Earthquake Geotechnical Engineering) Christchurch, New-Zealand, November 1-4, 2015.
– Nataf, H.-C. and N. Schaeffer, 8.06 - Turbulence in the Core, Treatise on Geophysics (Second Edition), 161–181, doi:10.1016/B978-0-444-53802-4.00142-1, 2015.
– Pavlov V., Fluteau F., Veselovskiy R., Fetisova A., Latyshev A., Elkins-Tanton L.T., Sobolev A.V. and N.A. Krivolutskaya (2015). Volcanic pulses in the Siberian Traps as inferred from Permo-Triassic geomagnetic secular variations. Chapter 5 in “Volcanism And Global Environmental Change”, A. Schmidt, K.E. Fristad and L. Elkins-Tanton ed., Cambridge University Press, pp. 63-78.
– Revil A., P. Fernandez, D. Mao, H.K. French, E. Bloem, and A. Binley, Self-potential monitoring of the enhanced biodegradation of an organic contaminant using a bioelectrochemical cell, The Leading Edge, 2, 198-202, doi : 10.1190/tle34020198.1, 2015.
– Schwan, L., C. Boutin, M. Dietz, L. Padron, P.-Y. Bard, E. Ibraim, O. Maeso, J.J. Aznarez & C. Taylor (2015). Multi-Building Interactions and Site-City Effect : An Idealized Experimental Model. In Experimental Research in Earthquake Engineering (pp. 459-476). Springer International Publishing.
– Sguerso D., Labbouz L., Walpersdorf A., 14 years of GPS tropospheric delays in the French-Italian border region : comparisons and first application in a case study, Applied Geomatics, 10.1007/s12518-015-0158-z, 2015.
– Sobolev A.V., Arndt N.T., Krivolutskaya N.A., Kuzmin D.V. and S.V. Sobolev (2015). The origin of gases that caused the Permian-Triassic extinction. Chapter 10 in “Volcanism And Global Environmental Change”, A. Schmidt, K.E. Fristad and L. Elkins-Tanton ed., Cambridge University Press, pp. 147-163.
– van der Beek, P.A., Exhumation (Thermochronology), in : Encyclopedia of Scientific Dating Methods, W.J. Rink, J.W. Thompson, A.J.T. Jull, J.B. Paces, and L. Heaman (Eds.), Springer Earth Science Series, pp. 261-264, doi : 10.1007/978-94-007-6304-3_249, 2015.