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Andreani, M., Munoz, M., Marcaillou, C., & Delacour, A. (2013). mu XANES study of iron redox state in serpentine during oceanic serpentinization. LITHOS, 178, 70–83.
Résumé: Serpentinization of ultramafic rocks at mid-ocean ridges generates significant amounts of H-2, CH4, and supports specific biological communities. The abiotic H-2 production is attributed to the reduction of H2O during serpentinization, which balances oxidation of ferrous iron contained in primary minerals (mainly olivines and pyroxenes) to ferric iron contained in secondary minerals (mainly serpentines and magnetite). Magnetite has thus far been considered as the sole Fe3+-carrier for estimating bulk H-2 production, notably because the valence of iron in serpentine minerals and its relationship with both magnetite abundance and serpentinization degree are usually not determined. We show that the serpentine contribution to the Fe and Fe3+ budget has a significant effect on H-2 production. We performed mu-XANES analysis at the Fe K-edge on thin sections of peridotites with various degrees of serpentinization from ODP Leg 153 (MARK region, 23 degrees N). Fe3+/Fe-Tot in oceanic serpentines is highly variable (from similar to 0.2 to 1) at the thin section scale, and it is related non-linearly to the local degree of serpentinization. A typical value of 0.7 is observed above 60% serpentinization. The highest values of Fe3+/Fe-Tot observed within or close to late veins suggest that the Fe3+/Fe-Tot in serpentine record the local water-rock (W/R) ratio, as previously proposed from thermodynamic modeling. We estimate that the (W/R) ratio increased from similar to 0.6 to 25 during serpentinization at MARK, and locally reached similar to 100 in veins. Mass balance calculations combining all mineral and bulk rock analyses provide the distribution of Fe and Fe3+ as serpentinization progresses. Serpentine dominates the Fe3+ budget of the rock over magnetite during the first 75% of serpentinization, contributing up to 80% of the total Fe3+. At later stages, serpentine contribution to the Fe3+ budget decreases down to similar to 20%, while magnetite formation exponentially increases. Iron transfer from serpentine to magnetite balances the bulk Fe3+ content of the rock that increases almost linearly with the advance of the reaction. Formation of serpentine accounts for the majority of Fe3+ and H-2 production at early stages of serpentinization at a depth >2 km at MARK where the concentration of H-2 can reach more than 100 mM according to the low W/R. H-2 production values and depths can vary from one site to another, depending on the evolution of the temperature, W/R ratio, inlet fluid composition, and favored formation of serpentine vs. magnetite. At MARK, Fe3+ in serpentine represents 15-27% of the total Fe contained in a rock serpentinized to more than 80%, and accounts for 25% of the total H-2 production that is estimated at 325-335 mmol/kg of rock. The absence of magnetite does not necessarily mean a negligible H-2 production, even at low T conditions (<150-200 degrees C) under which the Fe- and Fe3+-richest serpentines have been observed. Serpentine minerals are important Fe3+-carrier in the altered ocean lithosphere, and may affect mantle redox state while dehydrating at depth in subduction zones. 2013 Elsevier B.V. All rights reserved.
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Aristilde, L., Lanson, B., & Charlet, L. (2013). Interstratification Patterns from the pH-Dependent Intercalation of a Tetracycline Antibiotic within Montmorillonite Layers. LANGMUIR, 29(14), 4492–4501.
Résumé: Little is known about the distribution of the intercalated molecules within the interstratified layers resulting from the pH-dependent interlayer adsorption of ionizable organic molecules, including antibiotics, within smectite-type clay minerals. Here we employed experimental and simulated X-ray diffraction (XRD) to characterize interstratification (or mixed layering) from the intercalation of oxytetracycline (OTC), a commonly used tetracycline antibiotic, within Na-montmorillonite layers at pHs 4, 5, 6, and 8. Our XRD data reveal that OTC is distributed nonrandomly in the interlayers such that Na- and OTC-saturated interlayers coexist. The profile of the full width at half-maximum intensity (fwhm), monitored as a function of increasing layer-to-layer distance (40, resulting from an increasing amount of intercalated OTC, reflects such mixed-layer crystals under the acidic pH conditions. A minimum in fwhm occurs at a d spacing of about 1.8 nm, which is to be the optimal d(001) for OTC-saturated layers, in agreement with molecular modeling results. Using the coordinates of the thermodynamically favorable configuration of the adsorptives in a model montmorillonite interlayer, we simulated XRD profiles to unravel the different patterns of interstratification from the experimental data. At both pHs 4 and 5, Na- and OTC-interlayers are randomly interstratified, whereas at pH 6, these layers are clustered, as characterized by a segregated interstratification pattern. The theoretical layer stacking sequences of the simulated XRD illustrate, as pH increases, the clustering of similar layer types with the exclusion of OTC intercalation from clay populations enriched in Na. At pH 8, both fwhm and 401 indicate OTC adsorption primarily on external surface sites, not within interlayers. Our findings imply that, in addition to chemical speciation, a pH-dependent formation of montmorillonite crystallites with unexfoliated layers may be responsible both for the decreased OTC intercalation and for the increased binding on external sites, thus resulting in the different patterns of interstratification as a function of increasing pH.
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Arndt, N. (2013). The Lithospheric Mantle Plays No Active Role in the Formation of Orthomagmatic Ore Deposits. ECONOMIC GEOLOGY, 108(8), 1953–1970.
Résumé: The hypothesis that the metals in certain orthomagmatic ore deposits come from a source in the subcontinental lithospheric mantle is evaluated in this paper. According to this hypothesis, parts of the mantle beneath the continents are metasomatically enriched in metals like Ni, Cu, and the platinum group elements (PGE). It is proposed that under some circumstances, these metals are transported into the crust where they become concentrated in orebodies. An examination of the compositions of xenoliths from the lithospheric mantle reveals little evidence, however, of components that could represent the source of metal-enriched magmas. In addition, the mechanism whereby metals are brought from the source to the surface is very unclear. The lithosphere is the coldest part of the mantle and it only melts under special circumstances. The normal product is a low-degree melt, an alkaline, Si-undersaturated magma of the type that only rarely contains ore deposits. Major magmatic orebodies normally form from high-volume, high-flux magmas that are produced by high-degree melting in deeper, hotter parts of the mantle in the asthenosphere or a mantle plume. For melting to occur in the lithosphere, rather than in the hotter parts of the mantle, the melting point of the source must be drastically reduced by the presence of volatiles. On the other hand, there is ample evidence that the host magmas of ore deposits were abnormally rich in water or CO2 as would have been the case if they came from a volatile-rich metasomatized source. Magmas from sublithospheric sources could have interacted with the lithospheric mantle as they ascended toward the surface and they could have picked up some metals through this interaction. This process could have contributed to the formation of some ores, a notable example being the PGE deposits in Bushveld Complex. There is ample geological and geochemical evidence, however, that the majority of magmatic deposits form when magmas from sublithosphere sources assimilate material from the continental crust and that the latter process is instrumental in the formation of the deposits.
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Arndt, N., & Davaille, A. (2013). Episodic Earth evolution. TECTONOPHYSICS, 609, 661–674.
Résumé: U-Pb ages of zircons from Precambrian granitoids and major rivers are grouped into a series of major peaks at about 2.7, 2.5, 2.1, 1.9 and 1.1 Ga. Recently these peaks have been interpreted as times of enhanced preservation of the continental crust associated with the assembly of supercontinents. An older interpretation, which we support, is that they correspond instead to periods of accelerated crustal growth related to episodic convection of the mantle. In this paper we use fluid mechanics experiments to develop a new model of mantle convection and crustal growth. A dense layer at the base of the mantle persists until 2.7 Ga when it destabilizes and generates large domes that rise into the upper mantle. There they cause a large increase in the rate of subduction which leads to enhanced granite magmatism at convergent margins and thus to a pulse of crustal growth. The domes heat the upper mantle which partially melts at mid-ocean ridges to produce thick oceanic crust that resists subduction. The subsequent period of subdued plate motion is broken by the next generation of mantle domes. Before and after the Archean-Proterozoic period of episodic crustal growth, plate tectonics operated quasi-continuously. (C) 2013 Elsevier B.V. All rights reserved.
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Arndt, N., Sobolev, S., Barnes, S., & Robertson, J. (2013). Magma dynamics and the formation of magmatic sulfide deposits.
Résumé: Magmatic Ni-Cu sulfide deposits form when immiscible sulfide liquid separates from a mafic or ultramafic magma. The trigger is commonly assimilation of wall rocks, which adds sulfur and/or decreases sulfide solubility. When the segregated sulfide interacts with large volumes of magma, it scavenges chalcophile elements (Ni, Cu and PGE) to produce high-tenor ores. Such processes should operate in most or all magmatic systems, but ore deposits are found only in restricted parts of certain magmatic provinces. The restricted distribution might be explained by the craton-margin model, according to which deposits form when a mantle plume ascends at the sloping contact of cratonic lithosphere. The hypothesis that ore metals are derived from metasonnatically enriched portions of the sub-continental lithospheric mantle (SCLM) receives little support when the compositions of ore-bearing magmas and samples from the SCLM are examined. A better understanding of the controls on ore formation will come from modelling of flowage of mixtures of silicate and sulfide liquid and solid phases (crystals and rock fragments) in the complex magmatic conduits that constitute contain the ore deposits.
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Arndt, N. T. (2013). THE FORMATION AND EVOLUTION OF THE CONTINENTAL CRUST. GEOCHEMICAL PERSPECTIVES, 2(3), 405–533.
Résumé: In the Archean, like now, the granitoids that constitute the core of the continental crust formed in subduction zones. Hydrous basaltic magmas from the mantle wedge rose to the base of the crust where they fractionally crystallised or remelted underplated rocks to yield more evolved granitic magmas. Alternative models to explain Archean granitoids, which call on melting in intraplate settings such as the bases of oceanic plateaus, are implausible because such settings lack the water that is essential to form voluminous granitic melt. From the end of the Archean to the late Proterozoic, the continental crust grew in a series of major pulses, each triggered by accelerated mantle convection. The arrival of large mantle plumes displaced material from the upper mantle, accelerating the rate of subduction and causing a pulse of crustal growth. The Hadean crust was mafic and it underwent internal partial melting to produce the granitic melts that crystallised the Jack Hills zircons. This crust was disrupted by the Late Heavy Bombardment and from then on, since about 3.9 Ga, plate tectonics has operated.
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Arzhannikova, A. V., Jolivet, M., Arzhannikov, S. G., Vassallo, R., & Chauvet, A. (2013). The time of the formation and destruction of the Meso-Cenozoic peneplanation surface in East Sayan. RUSSIAN GEOLOGY AND GEOPHYSICS, 54(7), 685–694.
Résumé: The history of the peneplain in East Sayan was studied using apatite fission-track analysis (AFTA). This method is suitable for determining the formation time of the erosional surface and estimating its denudation rate. The largest known relic of the peneplanation surface in this area is the Oka Plateau, separated from the Kropotldn Ridge by the Oka-Zhombolok fault. The AFTA shows that the peneplain on the Oka Plateau formed in the Late Jurassic Early Cretaceous. This peneplain is much younger than the erosional surfaces that persist today in the Tien Shan, Gobi Altai, and Mongolian Altai (Early Jurassic). However, it is older than the peneplain on the Chulyshman Plateau, Altai (Late Cretaceous), suggesting asynchronous formation of the ancient peneplain in Central Asia. The similar exhumation histories of samples from the Oka Plateau and Kropotkin Ridge indicate that these morphotectonic structures developed from Jurassic to late Miocene as a single block, which underwent continuous slow denudation at an average rate of 0.0175 mm/yr. Active tectonic processes in the Late Miocene caused the destruction of the peneplanation surface and its partial uplifting to different altitudes. The rate of Pliocene-Quaternary vertical movements along the Oka-Zhombolok fault is roughly estimated at 0.046-0.080 mm/yr, which is several times higher than the denudation rate in this area. During the Pliocene-Quaternary, the Oka Plateau has not undergone any significant morphologic changes owing to its intermediate position between the summit plain and datum surface of East Sayan and to its partial shielding by basaltic lavas. (C) 2013, 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. (2013). Regularized seismic full waveform inversion with prior model information. GEOPHYSICS, 78(2), R25–R36.
Résumé: Full waveform inversion (FWI) delivers high-resolution quantitative images and is a promising technique to obtain macroscale physical property model of the subsurface. In most geophysical applications, prior information, such as that collected in wells, is available and should be used to increase the image reliability. For this, we propose to introduce three terms in the definition of the FWI misfit function: the data misfit itself, the first-order Tikhonov regularization term acting as a smoothing operator, and a prior model norm term. This last term is the way to smoothly introduce prior information into the FWI workflow. On a selected target of the Marmousi synthetic example, significant improvement was obtained when using the prior model term for noise-free and noisy synthetic data. The prior model term may significantly reduce the inversion sensitivity to incorrect initial conditions. The limited range of spatial wavenumber sampling by the acquisition may be compensated with the prior model information, for multiple-free and multiple-contaminated data. Prior and initial models play different roles in the inversion scheme. The starting model is used for wave propagation and therefore drives the data-misfit gradient, whereas the prior model is never explicitly used for solving the wave equation and only drives the optimization step as an additional constraint to minimize the total objective function. Thus, the prior model is not required to follow kinematic properties as precisely as the initial model, except in zones of poor illumination. In addition, we investigate the influence of a simple dynamic decreasing weighting of the prior model term. Once the cycle-skipping problem has been solved, the impact of the prior model term is gradually reduced within the misfit function to be driven by seismic-data only.
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Audin, L., & et al. (2013). Comment to “Open-source archive of active faults for northwest South America†by Gabriel Veloza, Richard Styron, Michael Taylor, and Andres. GSA Today,, 23(10).
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Aulanier, F., Nicolas, B., Mars, J. I., Roux, P., & Brossier, R. (2013). Shallow-water acoustic tomography from angle measurements instead of travel-time measurements. JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, 134(4), EL373–EL379.
Résumé: For shallow-water waveguides and mid-frequency broadband acoustic signals, ocean acoustic tomography (OAT) is based on the multi-path aspect of wave propagation. Using arrays in emission and reception and advanced array processing, every acoustic arrival can be isolated and matched to an eigenray that is defined not only by its travel time but also by its launch and reception angles. Classically, OAT uses travel-time variations to retrieve sound-speed perturbations; this assumes very accurate source-to-receiver clock synchronization. This letter uses numerical simulations to demonstrate that launch-and-reception-angle tomography gives similar results to travel-time tomography without the same requirement for high-precision synchronization. (C) 2013 Acoustical Society of America
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Aulanier, F., Nicolas, B., Roux, P., & Mars, J. I. (2013). Time-angle sensitivity kernels for sound-speed perturbations in a shallow ocean. JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, 134(1), 88–96.
Résumé: Acoustic waves traveling in a shallow-water waveguide produce a set of multiple paths that can be characterized as a geometric approximation by their travel time (TT), direction of arrival (DOA), and direction of departure (DOD). This study introduces the use of the DOA and DOD as additional observables that can be combined to the classical TT to track sound-speed perturbations in an oceanic waveguide. To model the TT, DOA, and DOD variations induced by sound-speed perturbations, the three following steps are used: (1) In the first-order Born approximation, the Frechet kernel provides a linear link between the signal fluctuations and the sound-speed perturbations; (2) a double-beamforming algorithm is used to transform the signal fluctuations received on two source-receiver arrays in the time, receiver-depth, and source-depth domain into the eigenray equivalent measured in the time, reception-angle and launch angle domain; and finally (3) the TT, DOA, and DOD variations are extracted from the double-beamformed signal variations through a first-order Taylor development. As a result, time-angle sensitivity kernels are defined and used to build a linear relationship between the observable variations and the sound-speed perturbations. This approach is validated with parabolic-equation simulations in a shallow-water ocean context. (C) 2013 Acoustical Society of America.
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Aurelio, G., Bardelli, F., Prado, R. J., Sanchez, R. D., Saleta, M. E., & Garbarino, G. (2013). On the Location of Host Ca Atoms Responsible for Ferrimagnetism in the Layered Cobaltites YBaCo2O5.5. CHEMISTRY OF MATERIALS, 25(16), 3307–3314.
Résumé: Recent studies have shown that the addition of Ca as host ion in the layered compounds RBaCo2O5+delta (with R a rare earth or yttrium) produces a dramatic effect on their magnetic properties, as well as on their Seebeck coefficient and resistivity. Studies performed so far have opened up the possibility that the substitution site for Ca atoms might not be obvious, having been reported at the Y site, at the Ba site, or regarded as not decisive to the ferromagnetism enhancement. In this work, we present a comparative study of Ca-doped cobaltite samples synthesized with two different nominal substitution sites, namely, Ca replacing Ba, and Ca replacing Y. X-ray absorption spectroscopy performed at the Ca, Ba, and Co edges to study the local environment around these elements allowed to unequivocally determine that the substitutional site of Ca is the Y site. This important result helps to clarify the mixed valence state of cobalt as Co3+ and Co4+, which would be responsible for the ferromagnetic interactions, and explains the antiferromagnetic to ferrimagnetic switch occurring already at 10% Ca doping level.
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Avril, C., Malavergne, V., Caracas, R., Zanda, B., Reynard, B., Charon, E., et al. (2013). Raman spectroscopic properties and Raman identification of CaS-MgS-MnS-FeS-Cr2FeS4 sulfides in meteorites and reduced sulfur-rich systems. METEORITICS & PLANETARY SCIENCE, 48(8), 1415–1426.
Résumé: Raman spectra were acquired on a series of natural and synthetic sulfide minerals, commonly found in enstatite meteorites: oldhamite (CaS), niningerite or keilite ((Mg,Fe)S), alabandite (MnS), troilite (FeS), and daubreelite (Cr2FeS4). Natural samples come from three enstatite chondrites, three aubrites, and one anomalous ungrouped enstatite meteorite. Synthetic samples range from pure endmembers (CaS, FeS, MgS) to complex solid solutions (Fe, Mg, Ca)S. The main Raman peaks are localized at 225, 285, 360, and 470cm-1 for the Mg-rich sulfides; at 185, 205, and 285cm-1 for the Ca-rich sulfides; at 250, 370, and 580cm-1 for the Mn-rich sulfides; at 255, 290, and 365cm-1 for the Cr-rich sulfides; and at 290 and 335cm-1 for troilite with, occasionally, an extra peak at 240cm-1. A peak at 160cm-1 is present in all Raman spectra and cannot be used to discriminate between the different sulfide compositions. According to group theory, none of the cubic monosulfides oldhamite, niningerite, or alabandite should present first-order Raman spectra because of their ideal rocksalt structure. The occurrence of broad Raman peaks is tentatively explained by local breaking of symmetry rules. Measurements compare well with the infrared frequencies calculated from first-principles calculations. Raman spectra arise from activation of certain vibrational modes due to clustering in the solid solutions or to coupling with electronic transitions in semiconductor sulfides.
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Bajolet, F., Replumaz, A., & Laine, R. (2013). Orocline and syntaxes formation during subduction and collision. TECTONICS, 32(5), 1529–1546.
Résumé: The present work investigates the formation of curved ranges and syntaxes with scaled laboratory experiments. We simulated subduction and collision processes comparable to India-Asia configuration involving a continental upper plate and a subducting plate composed of an oceanic lithosphere and a continental indenter. The experiments reveal that the shape of the mountain range (concave, straight, or convex) and the development of syntaxes are controlled by the subduction interface, the buoyancy number (F-b) of the upper plate (i.e., thickness and viscosity), and the boundary conditions. Four end-members regimes of indentation can be defined depending on the range shape and dynamics of the upper plate. The curvature of the range is convex toward the subducting plate with syntaxes for a weak subduction fault and concave without syntaxes for a strong subduction fault. Convex curvature and syntaxes form by overthrusting of upper plate material on the subducting plate, which is faster at the center than at the extremities. They are associated with a rather flat slab (underthrusting) during continental collision. Low-F-b experiments show less pronounced curvatures associated to thickening comparable to the early stages of the India-Asia collision. In contrast, a thick and weak upper plate (high F-b) leads to gravity collapse that increases the amplitude of the curvature and lateral escape, similar to the late evolution of the Himalaya-Tibet system. Important lateral decoupling on the sides of the indenter enhances the indentation and produces sharper syntaxes.
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Basile, C., Maillard, A., Patriat, M., Gaullier, V., Loncke, L., Roest, W., et al. (2013). Structure and evolution of the Demerara Plateau, offshore French Guiana: Rifting, tectonic inversion and post-rift tilting at transform-divergent margins intersection. TECTONOPHYSICS, 591, 16–29.
Résumé: We present the structure and evolution of the eastern part of the Demerara plateau, offshore French Guiana, from the analysis of geophysical data collected during GUYAPLAC cruise. This area is located at the intersection of a transform segment and a divergent segment of a continental margin related to the Early Cretaceous opening of the Equatorial Atlantic. The main structures are NNE-SSW to NNW-SSE trending normal faults on the eastern edge of the plateau, and WNW-ESE to NW-SE trending acoustic basement ridges on its northern edge. When replaced in their Albian position, these structures appear to be parallel to the coeval oceanic accretion axis and transform faults, respectively. The most striking structures are related to a post-rift but syn-transform tectonic inversion, producing E-W to WNW-ESE trending folds, sealed by a regional unconformity. This shortening cannot be related to ridge push, but is probably related to a plate kinematic change 105 My ago, that modified the deformation in the vicinity of the transform fault. late post-rift evolution also includes a significant Tertiary oceanward tilt of the edge of the Demerara plateau. The driving mechanism of this late tilt is unclear, but may be related to a lithospheric flexure resulting from the loading of the abyssal plain by the Orinoco and Amazon deep-sea fans. (C) 2012 Elsevier B.V. All rights reserved.
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Beaupretre, S., Manighetti, I., Garambois, S., Malavieille, J., & Dominguez, S. (2013). Stratigraphic architecture and fault offsets of alluvial terraces at Te Marua, Wellington fault, New Zealand, revealed by pseudo-3D GPR investigation. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 118(8), 4564–4585.
Résumé: Past earthquake slips on faults are commonly determined by measuring morphological offsets at current ground surface. Because those offsets might not always be well preserved, we examine whether the first 10m below ground surface contains relevant information to complement them. We focus on the Te Marua site, New Zealand, where 11 alluvial terraces have been dextrally offset by the Wellington fault. We investigated the site using pseudo-3D Ground Penetrating Radar and also produced a high-resolution digital elevation model (DEM) of the zone to constrain the surface slip record. The GPR data reveal additional information: (1) they image the 3D stratigraphic architecture of the seven youngest terraces and show that they are strath terraces carved into graywacke bedrock. Each strath surface is overlain by 3-5m of horizontally bedded gravel sheets, including two pronounced and traceable reflectors; (2) thanks to the multilayer architecture, terrace risers and channels are imaged at three depths and their lateral offsets can be measured three to four times, constraining respective offsets and their uncertainties more reliably; and (3) the offsets are better preserved in the subsurface than at the ground surface, likely due to subsequent erosion-deposition on the latter. From surface and subsurface data, we infer that Te Marua has recorded six cumulative offsets of 2.9, 7.6, 18, 23.2, 26, and 31m ( 1-2m). Large earthquakes on southern Wellington fault might produce 3-5m of slip, slightly less than previously proposed. Pseudo-3D GPR thus provides a novel paleoseismological tool to complement and refine surface investigations.
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Beauval, C., Yepes, H., Palacios, P., Segovia, M., Alvarado, A., Font, Y., et al. (2013). An Earthquake Catalog for Seismic Hazard Assessment in Ecuador. BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA, 103(2A), 773–786.
Résumé: Building a unified and homogeneous earthquake catalog is a preliminary step for estimating probabilistic seismic hazard in a country. Ecuador, a territory of similar to 600 km x 500 km, is characterized by an active seismicity, both in the shallow crust and in the subduction zone. Several international and local earthquake catalogs are available, covering different time and spatial windows, characterized by different magnitude types and uncertainties. After a careful analysis of each catalog, in particular for completeness and uncertainty levels, we propose a priority scheme for merging the instrumental catalogs. Moreover, several historical earthquakes are analyzed to estimate epicentral location and magnitude, completing the solutions obtained in a previous publication. Once the historical earthquakes are appended to the instrumental catalog, the resulting catalog covers five centuries in the Cordillera region. Next, homogenization of magnitudes and removal of aftershocks is performed; different options are studied and the impact on the recurrence curve is evaluated. For the Cordillera region within -2.5 degrees and 1 degrees latitude, the average occurrence of an earthquake with M-w >= 6.0 is 10-20 years based on the historical catalog.
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Bejar-Pizarro, M., Socquet, A., Armijo, R., Carrizo, D., Genrich, J., & Simons, M. (2013). Andean structural control on interseismic coupling in the North Chile subduction zone. Nature Geoscience, 6(6), 462–467.
Résumé: Segmentation can influence the extent of earthquake rupture and event magnitude(1): large megathrust earthquakes result from total rupture of relatively continuous segments of the subduction interface(2-5). Segmentation is attributed to variations in the frictional properties of the seismogenic zone or to topographic features on the down-going plate(6-9). Structures in the overriding plate may also influence segmentation(10-13), but their importance has been dismissed. Here, we investigate the links between interface segmentation at the North Chile seismic gap(14) and a crustal-scale fault structure in the overriding plate that forms a coastal scarp of about 1 km in height(10,15). We use satellite interferometric synthetic aperture radar (InSAR) and Global Positioning System (GPS) data to measure interseismic surface deformation between 2003 and 2009 and compare the deformation with rupture extent during well-documented earthquakes(5,16-18). From these data we infer the degree of coupling and segmentation at depth. We find that along a 500-km-long segment, the base of the strongly coupled seismogenic zone correlates with the line of the surface coastal scarp and follows the outline of the Mejillones Peninsula. This correlation implies that large-scale structures in the overriding plate can influence the frictional properties of the seismogenic zone at depth. We therefore suggest that the occurrence of megathrust earthquakes in northern Chile is controlled by the surface structures that build Andean topography.
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Ben-Naim, E., Daub, E. G., & Johnson, P. A. (2013). Recurrence statistics of great earthquakes. GEOPHYSICAL RESEARCH LETTERS, 40(12), 3021–3025.
Résumé: We investigate the sequence of great earthquakes over the past century. To examine whether the earthquake record includes temporal clustering, we identify aftershocks and remove those from the record. We focus on the recurrence time, defined as the time between two consecutive earthquakes. We study the variance in the recurrence time and the maximal recurrence time. Using these quantities, we compare the earthquake record with sequences of random events, generated by numerical simulations, while systematically varying the minimal earthquake magnitude M-min. Our analysis shows that the earthquake record is consistent with a random process for magnitude thresholds 7.0M(min)8.3, where the number of events is larger. Interestingly, the earthquake record deviates from a random process at magnitude threshold 8.4M(min)8.5, where the number of events is smaller; however, this deviation is not strong enough to conclude that great earthquakes are clustered. Overall, the findings are robust both qualitatively and quantitatively as statistics of extreme values and moment analysis yield remarkably similar results.
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Berger, A., Gnos, E., Janots, E., Whitehouse, M., Soom, M., Frei, R., et al. (2013). Dating brittle tectonic movements with cleft monazite: Fluid-rock interaction and formation of REE minerals. TECTONICS, 32(5), 1176–1189.
Résumé: Two millimeter-sized hydrothermal monazites from an open fissure (cleft) that developed late during a dextral transpressional deformation event in the Aar Massif, Switzerland, have been investigated using electron microprobe and ion probe. The monazites are characterized by high Th/U ratios typical of other hydrothermal monazites. Deformation events in the area have been subdivided into three phases: (D-1) main thrusting including formation of a new schistosity, (D-2) dextral transpression, and (D-3) local crenulation including development of a new schistosity. The two younger deformational structures are related to a subvertically oriented intermediate stress axis, which is characteristic for strike slip deformation. The inferred stress environment is consistent with observed kinematics and the opening of such clefts. Therefore, the investigated monazite-bearing cleft formed at the end of D-2 and/or D-3, and during dextral movements along NNW dipping planes. Interaction of cleft-filling hydrothermal fluid with wall rock results in rare earth element (REE) mineral formation and alteration of the wall rock. The main newly formed REE minerals are Y-Si, Y-Nb-Ti minerals, and monazite. Despite these mineralogical changes, the bulk chemistry of the system remains constant and thus these mineralogical changes require redistribution of elements via a fluid over short distances (centimeter). Low-grade alteration enables local redistribution of REE, related to the stability of the accessory phases. This allows high precision isotope dating of cleft monazite. Th-232/Pb-208 ages are not affected by excess Pb and yield growth domain ages between 8.030.22 and 6.250.60Ma. Monazite crystallization in brittle structures is coeval or younger than 8Ma zircon fission track data and hence occurred below 280 degrees C.
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Bermudez, M. A., van der Beek, P. A., & Bernet, M. (2013). Strong tectonic and weak climatic control on exhumation rates in the Venezuelan Andes. LITHOSPHERE, 5(1), 3–16.
Résumé: We studied the relationships among present-day relief, precipitation, stream power, seismic energy, seismic strain rate, and long-term exhumation rates for the Venezuelan Andes. Average long-term exhumation rates were determined for seven large catchments in the Venezuelan Andes from fission-track analysis of detrital apatite. A quantitative comparison between eight new detrital apatite fission-track (AFT) age distributions presented here and previously published bedrock AFT age patterns shows that detrital AFT ages can be used for predicting exhumation patterns across the mountain belt. Catchment-averaged exhumation rates estimated from the raw data range from 0.48 +/- 0.02 km m.y.(-1) to 0.80 +/- 0.26 km m.y.(-1) Accounting for variable sediment yield and assuming that short-term sediment production rates scale with long-term exhumation rates, these rates vary from 0.33 +/- 0.07 km m.y.(-1) to 0.48 +/- 0.08 km m.y.(-1) No variation in rates is observed between the northwestern and southeastern flanks of the mountain belt, despite a threefold increase in precipitation from the northwest to the southeast. Long-term exhumation rates are strongly correlated with relief in the different catchments, weak or negative correlations exist with precipitation data or present-day erosion indexes, while the correlation with seismic energy released by earthquakes is weak to moderate. This lack of correlation may be caused by the insufficient temporal range of the available precipitation and seismicity data, and the different time scales involved in the comparison. Long-term exhumation rates are, however, strongly correlated with seismic strain rates (which take the temporal earthquake magnitude-frequency scaling into account), suggesting that the moderate correlation with seismic energy is indeed related to the different time scales and that tectonic control on exhumation is significant. In contrast, given that precipitation patterns in the Venezuelan Andes should have been installed during Miocene times, we suggest that decoupling of relief and exhumation from present-day climate explains the lack of correlation between exhumation and precipitation. LITHOSPHERE; v. 5; no. 1; p. 3-16; GSA Data Repository Item 2012271. vertical bar Published online 5 September 2012 doi: 10.1130/L212.1
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Blanco, J. A., Fak, B., Jensen, J., Rotter, M., Hiess, A., Schmitt, D., et al. (2013). Phasons, amplitude modes, and spin waves in the amplitude-modulated magnetic phase of PrNi2Si2. PHYSICAL REVIEW B, 87(10).
Résumé: The magnetic excitations in the low-temperature amplitude-modulated magnetic structure of PrNi2Si2 have been investigated by inelastic neutron scattering. The dispersions and intensities of both longitudinal and transverse excitations are measured along the high-symmetry directions. The modulated magnitude of the ordered moments implies that the longitudinally polarized magnetic excitations are more intense and dispersive than the usual transverse spin waves. Several well-defined longitudinal amplitude modes are observed to coexist with the longitudinal phason mode. The experimental results are in good overall agreement with predictions from the random-phase approximation, using parameters already established from the macroscopic properties and the paramagnetic excitations. At low energies in the neighborhood of the magnetic zone center, the magnetic phason appears to hybridize with an unidentified dispersionless mode. DOI: 10.1103/PhysRevB.87.104411
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Borisova, A. Y., Martel, C., Gouy, S., Pratomo, I., Sumarti, S., Toutain, J. P., et al. (2013). Highly explosive 2010 Merapi eruption: Evidence for shallow-level crustal assimilation and hybrid fluid. JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, 261, 193–208.
Résumé: The processes responsible for the highly explosive events at Merapi, Central Java, Indonesia have been investigated through a petrological, mineralogical and geochemical study of the first-stage tephra and pyroclastic flows sampled in October and November 2010, and second-stage ash sampled shortly after the 5-6th November 2010 paroxysmal subplinian eruption. Several chemical and physical parameters suggest that the magma assimilated calc-silicate xenoliths derived from the surrounding carbonate-bearing crust (Javanese limestone). The bulk volcanic samples have highly radiogenic Sr-87/Sr-86 (0.70571-0.70598) ratios that approach the compositional field of material similar to the calc-silicate xenoliths. The 2010 plagioclase phenocrysts from the pyroclastic flow and tephra reveal anorthite cores (up to An(94-97)) with low FeO contents (<= 0.8 wt.%), and O-18 enrichment (6.5 parts per thousand delta O-18). The major and trace elements of the silicic glasses and phenocrysts (plagioclase, low-Al augite and titanomagnetite), the Sr-isotopic compositions of the bulk samples and plagioclases erupted in 2010 can be explained by complete digestion of the 1998 and 2006 calc-silicate xenoliths. The bulk assimilation proceeded through binary mixing between a calcic melt (representing Crustal Assimilant, CaO up to 10.5 wt.% and CaO/Al2O3 up to 1.2) and the deep source hydrous K-rich melt Similarly to the 1998 and 2006 calc-silicate xenolith composition, the 2010 Crustal Assimilant is enriched in Mn (MnO up to 0.5 wt.%), Zn, V, and Sc contents. In contrast, the hydrous K-rich melt is enriched in volatiles (Cl up to 0.37 wt.% and bulk H2O + CO2 up to 5 1 wt.%), Al2O3, TiO2 and REE contents, consistent with its derivation from deep source. This hydrous K-rich melt may have been saturated with an aqueous Cl-rich fluid at about 200 MPa, a pressure consistent with the level of the crustal assimilation. We estimated that the pre-eruptive basaltic andesite magma assimilated from 15 to 40 wt.% of the calc-silicate crustal material, corresponding to introduction of additional 0.19 to 2.1 Mt of CO2 to the magma. Experimental leaching of the ash samples documents the release of an aqueous fluid enriched in Cl, Na, Ca, Cd, Sb and Zn during the paroxysmal subplinian eruption. The paroxysmal eruption may have been produced by saturation of the pre-eruptive basaltic andesite magma with hybrid aqueous carbonic NaCl-HCl-rich fluid due to bulk assimilation creating elevated partial pressure of CO2 at shallow crustal conditions of about 200 MPa. In contrast, mildly explosive block-and-ash flows (typical Merapi-type) may result from selective assimilation of the carbonate-bearing xenoliths and lower CO2 partial pressure that may not lead to explosive degassing. (C) 2012 Elsevier B.V. All rights reserved.
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Bottelin, P., Jongmans, D., Baillet, L., Lebourg, T., Hantz, D., Levy, C., et al. (2013). Spectral Analysis of Prone-to-fall Rock Compartments using Ambient Vibrations. JOURNAL OF ENVIRONMENTAL AND ENGINEERING GEOPHYSICS, 18(4), 205–217.
Résumé: The dynamic response of four unstable rock compartments in the Alps has been studied using the ambient vibration technique, with the aim of identifying precursors to rockfalls. The test sites present various geological settings (limestone, argillite, and shale-sandstone series), failure mechanisms and volumes. The ambient vibration spectra measured on the unstable compartments systematically showed clear energy peaks at specific frequencies, in contrast with records made on the adjacent stable rock masses. These predominant frequencies were interpreted as resonant frequencies of the unstable compartments, in agreement with 2-D modal analysis. In the horizontal plane, ground motion at the fundamental frequency was found to be systematically parallel to the line of maximum slope gradient, and perpendicular to the main bounding fracture observed at most of the sites. The fundamental frequency of each prone-to-fall compartment shows reversible variations related to temperature fluctuations at different timescales, with a significant contrast in magnitude and phase shift between sites. At the more fractured site, resonance seems to result from a contrast in internal rigidity between the compartment and adjacent rock mass, rather than from decoupling along a rear fracture, which is the mechanism observed at the three other sites. No change in fundamental frequency resulting from damage was observed over the period of study.
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Bottelin, P., Levy, C., Baillet, L., Jongmans, D., & Gueguen, P. (2013). Modal and thermal analysis of Les Arches unstable rock column (Vercors massif, French Alps). GEOPHYSICAL JOURNAL INTERNATIONAL, 194(2), 849–858.
Résumé: A potentially unstable limestone column (similar to 1000 m(3), Vercors, French Alps) delineated by an open rear fracture was continuously instrumented with two three-component seismic sensors from mid-May 2009 to mid-October 2011. Spectral analysis of seismic noise allowed several resonance frequencies to be determined, ranging from 6 to 21 Hz. The frequency domain decomposition (FDD) technique was applied to the ambient vibrations recorded on the top of the rock column. Three vibration modes were identified at 6, 7.5 and 9 Hz, describing the upper part of corresponding modal shapes. Finite element numerical modelling of the column dynamic response confirmed that the first two modes are bending modes perpendicular and parallel to the fracture, respectively, while the third one corresponds to torsion. Seismic noise monitoring also pointed out that resonance frequencies fluctuate with time, under thermomechanical control. For seasonal cycles, changes in frequency are due to the variations of the bulk elastic properties with temperature. At daily scale, increase in fundamental frequency with temperature has been interpreted as resulting from the rock expansion inducing a closure of the rear fracture rock bridges, hence stiffening the contact between the column and the rock mass. Conversely, the rock contraction induces a fracture opening and a decrease in resonance frequency. In winter, when the temperature drops below 0 degrees C, a dramatic increase in fundamental frequency is observed from 6 Hz to more than 25 Hz, resulting from ice formation in the fracture. During spring, the resonance frequency gradually diminishes with ice melting to reach the value measured before winter.
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Bouchon, M., Durand, V., Marsan, D., Karabulut, H., & Schmittbuhl, J. (2013). The long precursory phase of most large interplate earthquakes. NATURE GEOSCIENCE, 6(4), 299–302.
Résumé: Many earthquakes are preceded by foreshocks(1,2). However, the mechanisms that generate foreshocks and the reason why they occur before some earthquakes and not others are unknown(3-8). Here we use seismic catalogues from the best instrumented areas of the North Pacific to analyse the foreshock sequences preceding all earthquakes there between 1999 and 2011, of magnitude larger than 6.5 and at depths shallower than 50 km. The data set comprises 31 earthquakes at plate boundaries, and 31 in plate interiors. We find that there is a remarkable contrast between the foreshock sequences of interplate compared with intraplate earthquakes. Most large earthquakes at plate interfaces in the North Pacific were preceded by accelerating seismic activity in the months to days leading up to the mainshock. In contrast, foreshocks are much less frequent in intraplate settings. We suggest that at plate boundaries, the interface between the two plates begins to slowly slip before the interface ruptures in a large earthquake. This relatively long precursory phase could help mitigate earthquake risk at plate boundaries.
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Boue, P., Poli, P., Campillo, M., Pedersen, H., Briand, X., & Roux, P. (2013). Teleseismic correlations of ambient seismic noise for deep global imaging of the Earth. GEOPHYSICAL JOURNAL INTERNATIONAL, 194(2), 844–848.
Résumé: We present here a global analysis showing that wave paths probing the deepest part of the Earth can be obtained from ambient noise records. Correlations of seismic noise recorded at sensors located various distances apart provide new virtual seismograms for paths that are not present in earthquake data. The main arrivals already known for earthquake data are also present in teleseismic correlations sections, including waves that have propagated through the Earth's core. We present examples of applications of such teleseismic correlations to lithospheric imaging, study of the core mantle boundary or of the anisotropy of the inner core.
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Boue, P., Roux, P., Campillo, M., & de Cacqueray, B. (2013). Double beamforming processing in a seismic prospecting context. GEOPHYSICS, 78(3), V101–V108.
Résumé: The use of larger numbers of sensors is becoming more common at the large, continental scale for deep-structure imaging in seismology, and at a smaller scale with exploration geophysics objectives. Seismic arrays require array processing from which new types of observables contribute to a better understanding of the wave propagation complexity. From among these array processing techniques, this study focuses on a way to select and identify different phases between two source-receiver arrays based on the double beamforming (DBF) method. At the exploration geophysics scale, the goal is to identify and separate low-amplitude body waves from high-amplitude dispersive surface waves. A synthetic data set from a finite-difference time-domain simulation is first used to validate the array processing method. From directional information obtained with DBF, and due to the double-plane wave projection, it is demonstrated that surface and body waves can be extracted with a higher efficacy compared to classical beamforming even at short offset. A seismic prospecting data set in a laterally heterogeneous medium is then investigated. This data set is a high-resolution survey which provides a perfect control on source and receiver arrays geometry. The separation between the direct surface and body waves is observed after DBF and ray bending is discussed from the additional azimuthal information.
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Bourdelle, F., Parra, T., Beyssac, O., Chopin, C., & Vidal, O. (2013). Clay minerals as geo-thermometer: A comparative study based on high spatial resolution analyses of illite and chlorite in Gulf Coast sandstones (Texas, USA). AMERICAN MINERALOGIST, 98(5-6), 914–926.
Résumé: Phyllosilicates are among the most important stable minerals within the Earth's crust. Their use as geo-thermometer bears great potential for application to the thermal history of rocks within the stability range of layered silicates and was tested here. A high-resolution analytical technique combining focused ion beam (FIB) milling and analytical electron microscopy (AEM) analysis has been applied to a series of sandstone core samples from the Gulf Coast (Texas, U.S.A.). The nanoscale compositional variations of K-deficient mica and chlorite flakes show that rim compositions are the most likely to approach equilibrium compositions, whereas core compositions may be relict, especially for illite-like phases. These rim analyses were used to test existing empirical or thermodynamically formulated thermo(baro)meters against maximum temperatures, which are perfectly constrained for the selected samples as they were measured in situ during drilling (100-230 degrees C and 300-1200 bars). The results show that most of the empirical models overestimate the temperature, while thermodynamic models yields reasonable estimates for diagenetic to anchizonal conditions, especially if the Fe3+ content is taken into account. This study clearly shows that phyllosilicates thermometry is reliable when combined with an analytical technique giving access to the fine-scale compositional variations that may represent local equilibration, whereas using micrometric compositional analysis precludes trustworthy application of such thermometers.
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Braun, J., & Willett, S. D. (2013). A very efficient O(n), implicit and parallel method to solve the stream power equation governing fluvial incision and landscape evolution. GEOMORPHOLOGY, 180, 170–179.
Résumé: We present a new algorithm to solve the basic stream power equation, which governs channel incision and landscape evolution in many geomorphic settings. The algorithm is highly efficient because computation time increases linearly with the number of points used to discretize the landscape and is ideally suited to parallelization. It is also unconditionally stable because it uses an implicit scheme for the time integration of the landscape evolution equation, which means that large time steps can be used without sacrificing accuracy. In this paper we describe the algorithm and present results that demonstrate its efficiency and accuracy. (C) 2012 Elsevier B.V. All rights reserved.
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Braun, J., Deschamps, F., Rouby, D., & Dauteuil, O. (2013). Flexure of the lithosphere and the geodynamical evolution of non-cylindrical rifted passive margins: Results from a numerical model incorporating variable elastic thickness, surface processes and 3D thermal subsidence. TECTONOPHYSICS, 604, 72–82.
Résumé: We present a new numerical model to calculate the surface deflection of a two-dimensional, yet variable thickness, thin elastic plate. The model is based on a multi-grid, finite difference solution of the fourth-order differential equation that incorporates the terms arising from the non-uniform thickness assumption. The model has been developed to calculate the flexural response of the continental lithosphere subjected to an arbitrary, instantaneous stretching. The flexural model is coupled to (a) a finite element, three dimensional thermal model incorporating the conduction, advection and production terms that allows the computation of the thermal subsidence resulting from the stretching-induced perturbation of the isotherms, assuming that the effective elastic thickness is controlled by the depth to a given isotherm; and (b) a finite difference surface process model that assumes that transport is linearly proportional to slope leading to a second-order, diffusion-type partial differential equation. The model also incorporates the effect of sediment compaction. We present a series of simple benchmarks that demonstrate the accuracy of the model. We also present results of simple 2D and 3D stretching experiments highlighting the importance of 3D flexural effects and the assumed variable elastic thickness on the development of a passive margin and its thermal evolution. Finally, we perform a numerical experiment based on a stretching geometry derived from the present-day geometry of the Western AfricaTransform Margin to predict sediment accumulation patterns and a stratigraphic architecture which we can compare to observations. (C) 2012 Elsevier B.V. All rights reserved.
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Braun, J., Robert, X., & Simon-Labric, T. (2013). Eroding dynamic topography. GEOPHYSICAL RESEARCH LETTERS, 40(8), 1494–1499.
Résumé: Geological observations of mantle flow-driven dynamic topography are numerous, especially in the stratigraphy of sedimentary basins; on the contrary, when it leads to subaerial exposure of rocks, dynamic topography must be substantially eroded to leave a noticeable trace in the geological record. Here, we demonstrate that despite its low amplitude and long wavelength and thus very low slopes, dynamic topography is efficiently eroded by fluvial erosion, providing that drainage is strongly perturbed by the mantle flow driven surface uplift. Using simple scaling arguments, as well as a very efficient surface processes model, we show that dynamic topography erodes in direct proportion to its wavelength. We demonstrate that the recent deep erosion experienced in the Colorado Plateau and in central Patagonia is likely to be related to the passage of a wave of dynamic topography generated by mantle upwelling.
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Bretaudeau, F., Brossier, R., Leparoux, D., Abraham, O., & Virieux, J. (2013). 2D elastic full-waveform imaging of the near-surface: application to synthetic and physical modelling data sets. NEAR SURFACE GEOPHYSICS, 11(3), 307–316.
Résumé: Standard seismic methods are generally not well adapted to provide sharp quantitative images of the first few metres of underground. A two-dimensional full-waveform inversion of land seismic data, based on frequency-domain viscoelastic modelling, offers a promising approach to take advantage of the full complexity of seismograms and to simultaneously build 2D images of V-p and V-s parameters. In order to understand the behaviour of this method in a near-surface context and anticipate the corresponding field applications, we perform this investigation by applying waveform inversion on a simple layered medium. We first use synthetic data obtained from numerical modelling and then we employ laboratory data obtained by small-scale physical modelling. We demonstrate that such a near-surface 2D model can be quantitatively determined even in a realistic situation where the data are dominated by high-amplitude surface waves. A comparison of results derived for the same medium from ideal synthetic data and noisy experimental data allows detecting anomalies in the reconstruction of velocity models due to the experimental nature of the data used.
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Bruna, P. O., Guglielmi, Y., Lamarche, J., Floquet, M., Fournier, F., Sizun, J. P., et al. (2013). Porosity gain and loss in unconventional reservoirs: Example of rock typing in Lower Cretaceous hemipelagic limestones, SE France (Provence). MARINE AND PETROLEUM GEOLOGY, 48, 186–205.
Résumé: We characterize porosity evolution in hemipelagic limestones of the Lower Cretaceous Vocontian Basin (Northern Provence, SE France), which are surface analogs for deep unconventional reservoirs. Firstly, a structural and sedimentologic analysis was conducted on outcrops and on borehole cores of Berriasian to Lower Valanginian rocks. Secondly, 330 plugs were analyzed for fades, pore typing, porosity and acoustic Vp velocity measurements. This petrophysical dataset was compared to the burial-uplift history of the host rock. Hemipelagic carbonates include four sedimentary formations comprising nine facies splitted into mud- and grain-dominated formations which display 0-8% porosity range depending on the initial grain to mud ratio of the sediments and on basin stress regime evolution during burial-uplift history. Initial porosity was better preserved in grain dominated formations where early micritic cements built bridges between grains, generating a solid skeleton that prevented/inhibited the burial compaction effects. In mud dominated facies, micrite was initially diffuse within the rock matrix but was progressively rearranged under burial stress, while the generation of an extensive amount of stylolites occurred. The differential response of compacted grain and mud dominated facies to a late regional 1 km uplift resulted in large porosity generation (should range from 15 to 35%) localized in the mud dominated facies through the dilatancy of stylolite and pressure-solution seams. This study highlights how important is the combination of classical approaches including facies, pore type and diagenesis characterization with the structural analyses. One key result applicable to several types of unconventional reservoirs is the effective porosity generated by reactivation of compaction structures. (c) 2013 Elsevier Ltd. All rights reserved.
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Budi-Santoso, A., Lesage, P., Dwiyono, S., Sumarti, S., Subandriyo, Surono, et al. (2013). Analysis of the seismic activity associated with the 2010 eruption of Merapi Volcano, Java. JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, 261, 153–170.
Résumé: The 2010 eruption of Merapi is the first large explosive eruption of the volcano that has been instrumentally observed. The main characteristics of the seismic activity during the pre-eruptive period and the crisis are presented and interpreted in this paper. The first seismic precursors were a series of four shallow swarms during the period between 12 and 4 months before the eruption. These swarms are interpreted as the result of perturbations of the hydrothermal system by increasing heat flow. Shorter-term and more continuous precursory seismic activity started about 6 weeks before the initial explosion on 26 October 2010. During this period, the rate of seismicity increased almost constantly yielding a cumulative seismic energy release for volcano-tectonic (VT) and multiphase events (MP) of 7.5 x 10(10) J. This value is 3 times the maximum energy release preceding previous effusive eruptions of Merapi. The high level reached and the accelerated behavior of both the deformation of the summit and the seismic activity are distinct features of the 2010 eruption. The hypocenters of VT events in 2010 occur in two clusters at of 2.5 to 5 km and less than 1.5 km depths below the summit. An aseismic zone was detected at 1.5-2.5 km depth, consistent with studies of previous eruptions, and indicating that this is a robust feature of Merapi's subsurface structure. Our analysis suggests that the aseismic zone is a poorly consolidated layer of altered material within the volcano. Deep VT events occurred mainly before 17 October 2010; subsequent to that time shallow activity strongly increased. The deep seismic activity is interpreted as associated with the enlargement of a narrow conduit by an unusually large volume of rapidly ascending magma. The shallow seismicity is interpreted as recording the final magma ascent and the rupture of a summit-dome plug, which triggered the eruption on 26 October 2010. Hindsight forecasting of the occurrence time of the eruption is performed by applying the Material Failure Forecast Method (FFM) using cumulative Real-time Seismic Amplitude (RSAM) calculated both from raw records and on signals classified according to their dominant frequency. Stable estimates of eruption time with errors as small as +/- 4 h are obtained within a 6 day lapse time before the eruption. This approach could therefore be useful to support decision making in the case of future large explosive episodes at Merapi. (C) 2013 Elsevier B.V. All rights reserved.
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Byrdina, S., Ramos, D., Vandemeulebrouck, J., Masias, P., Revil, A., Finizola, A., et al. (2013). Influence of the regional topography on the remote emplacement of hydrothermal systems with examples of Ticsani and Ubinas volcanoes, Southern Peru. EARTH AND PLANETARY SCIENCE LETTERS, 365, 152–164.
Résumé: Present work studies the influence of the regional topography on the hydrothermal fluid flow pattern in the subsurface of a volcanic complex. We discuss how the advective transfer of heat from a magmatic source is controlled by the regional topography for different values of the averaged permeability. For this purpose, we use a 2-D numerical model of coupled mass and heat transport and new data sets acquired at Ticsani and Ubinas, two andesitic volcanoes in Southern Peru which have typical topography, justifying this approach. A remarkable feature of these hydrothermal systems is their remote position not centered on the top of the edifice. It is evidenced by numerous hot springs located in more than 10 km distance from the top of each edifice. Upwelling of thermal water is also inferred from a positive self-potential anomaly at the summit of the both volcanoes, and by ground temperatures up to 37 degrees C observed at Ticsani. Our model results suggest that the regional topographic gradient is able to significantly divert the thermal water flow and can lead to an asymmetric emplacement of the hydrothermal system even considering a homogeneous permeability of the edifice. Inside the thermal flow, the hydraulic conductivity increases with the decrease of temperature-related viscosity, focusing the flow towards the surface and creating a hydrothermal zone at a large lateral distance from the heat source. The location and temperature of the hot springs together with the water table position given by self-potential data can be used to constrain the average permeability of the edifice, a key parameter influencing fluid flow and associated advective heat transfer in the direction opposite to the regional topographic gradient. Our study allows to explain the emplacement of the hydrothermal systems at volcanoes with asymmetric edifices or even the absence of a shallow hydrothermal system. These results can be generalized to the study of non-volcanic hydrothermal systems. (C) 2013 Elsevier B.V. All rights reserved.
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Campos, C., Beck, C., Crouzet, C., Carrillo, E., Van Welden, A., & Tripsanas, E. (2013). Late Quaternary paleoseismic sedimentary archive from deep central Gulf of Corinth: time distribution of inferred earthquake-induced layers. Annals of Geophysics, 56(6), S0670.
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Campos, C., Beck, C., Crouzet, C., Demory, F., Van Welden, A., & Eris, K. (2013). Deciphering hemipelagites from homogenites through anisotropy of magnetic susceptibility. Paleoseismic implications (Sea of Marmara and Gulf of Corinth). SEDIMENTARY GEOLOGY, 292, 1–14.
Résumé: In closed marine basins and large lakes, gravity re-depositional processes often result in specific turbidites with two abruptly separated layers: a coarse graded lower term and an upper homogenous fine-grained term. An additional mixed term generally occurs in between, indicating to and from particle displacements. The later ones are related to oscillating bottom currents responsible for a high increase of the fine fraction segregation, within the reworked wasted mass. The whole sedimentary event is the association “homogenite + turbidite” (HmTu), which specific a settling condition area here characterized through Anisotropy of Magnetic Susceptibility (AMS). Homogenites's magnetic foliation appears anomalously high with respect to their expected state of compaction, and strikingly higher than hemipelagites's values. We applied this approach to Late Pleistocene/Holocene sediments from the Sea of Marmara and from the Gulf of Corinth. Grain-size and other magnetic parameters related to mineralogy are added to better assess the granular array influence on AMS. As HmTu is considered as often related to earthquake-triggering and tsunami/seiche effects, AMS appears as a useful tool for subaqueous paleoseismic investigations. First, it may evidence the signature of paleo-earthquakes; second, it permits to decipher hemipelagic intervals which are inferred to represent the time elapsed between two successive reworking events. (C) 2013 Elsevier B.V. All rights reserved.
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Cao, K., Bernet, M., Wang, G. C., van der Beek, P., Wang, A., Zhang, K. X., et al. (2013). Focused Pliocene-Quaternary exhumation of the Eastern Pamir domes, western China. EARTH AND PLANETARY SCIENCE LETTERS, 363, 16–26.
Résumé: The Kongur Shan and Muztagata domes are the most prominent topographic features in the Eastern Pamir indenter corner. In spite of several previous bedrock thermochronology studies, the extent, processes and mechanisms of dome exhumation remain unclear. We present 1158 detrital zircon fission-track (DZFT) ages from modern glacier and river sediments along the domes to better constrain the spatial distribution of exhumation. Our thermochronologic dataset from the Chakragil massif shows a sharp increase in the proportion of DZFT ages > 10 Ma from basins that drain the peak region to those further to the north, which suggests that the Kalagile fault forms the northern boundary of the rapidly exhuming dome structure. A cluster of Middle Miocene DZFT ages in these samples documents pre-doming cooling, possibly associated with motion on the Main Pamir thrust and/or Oytag fault. Large fractions of DZFT grain ages < 10 Ma in samples from catchments east of the divide likely originate from the Chakragil, Kongur Shan and Muztagata massifs, implying focused exhumation consistent with DZFT age distributions in samples from catchments draining the western flank of the range and bedrock geo- and thermochronologic data from the core of the domes. Furthermore, the majority of the samples contain two distinct DZFT age groups at similar to 6-4 Ma and similar to 3-1 Ma respectively. These ages are synchronous with major fluvial sedimentation phases at the outlets of the rivers draining northeastward into the Tarim Basin and suggest rapid Pliocene-Quaternary exhumation of the domes. We interpret the similar to 6-4 Ma age group to record the onset of extension along the entire Kongur Shan fault; its timing with respect to compressional deformation supports a model of gravitational collapse of over-thickened crust. The fraction of similar to 3-1 Ma DZFT ages is larger than what would be inferred from the bedrock data alone. We interpret this to reflect recent focused denudation in response to glaciation and fluvial incision of the domes and their possible feedback with extensional faulting. (c) 2012 Elsevier B.V. All rights reserved.
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Cao, K., Wang, G. C., van der Beek, P., Bernet, M., & Zhang, K. X. (2013). Cenozoic thermo-tectonic evolution of the northeastern Pamir revealed by zircon and apatite fission-track thermochronology. TECTONOPHYSICS, 589, 17–32.
Résumé: The northeastern Pamir is a key location to explore Asian intracontinental tectonic processes during the Cenozoic. New zircon fission-track (ZFT) data show a 20- to 50-km-wide region of partially reset ages on the northeastern margin of the Pamir salient, interpreted as an exhumed and tilted partial annealing zone (PAZ). Widespread ZFT age peaks at similar to 50 Ma within the ZFT PAZ likely date early motion of the Kashgar-Yecheng transfer system (KYTS), but suggest this fault system was narrower in the Early Cenozoic than it is today. Apatite fission-track (AFT) ages of similar to 10-6 Ma, combined with field observations across the KYTS, hint at an episode of strong thrusting-related exhumational cooling, which indicates that the modern fault system probably formed at this time. To the southwest of the KYTS, the combination of new fission-track and existing thermochronology data allows establishing temperature-time trajectories that present diachronous rapid cooling from similar to 450 to 120 degrees C in the Sares (> 13-10 Ma), Muztagata (similar to 10-7 Ma) and Kongur Shan (similar to 3-1 Ma) domes. Rapid cooling in the eastern Sares and southern Muztagata massifs is driven by doming, as supported by kinematic analyses of the Shen-ti fault. Successive rapid cooling of these massifs confirms eastward propagation of doming processes, shortly postdating magma emplacement at similar to 11 Ma. We propose that the synchronicity of regional tectonism, magmatism and metamorphism implies that strong crustal thickening and contraction occurred beneath the northeastern Pamir during the Middle-Late Miocene, possibly associated with initial collision between the Pamir and Tian Shan. (c) 2013 Elsevier B.V. All rights reserved.
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Capitanio, F. A., & Replumaz, A. (2013). Subduction and slab breakoff controls on Asian indentation tectonics and Himalayan western syntaxis formation. GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, 14(9), 3515–3531.
Résumé: We test the link between large-scale Asian continent deformations and Indian slab subduction and breakoff during convergence by means of three-dimensional numerical models of the subducting-upper plates system. We find that the subduction of the buoyant continent results in the reduction of convergence velocity comparable to that observed in the Indian motions, yet the upper plate deformation remains accommodated in a narrow belt along a straight margin. Comparable rates are measured when the subducting slab breakoff is modeled, although the convergent margin deforms and curves markedly, with large underplating contiguous to ongoing subduction, similar to what observed along the Himalayan range. The models support the interpretation of the Himalayan Western Syntaxis evolution, the progressive curvature of the Indian margin and the underthrusting as a consequence of the Indian slab breakoff. The modeled slab detachment is followed by short-lived large stresses in the upper plate interiors, propagating at large distance from the margin with a trend similar to several major Asian lithospheric faults. Such localized stress has likely provided the conditions for the formation of the Central Asian intracontinental faulting, the Bangong-Red River and the Altyn Tagh faults, that followed successive Indian slab breakoff episodes. Continent subduction and breakoff during India-Asia convergence offer an explanation for the different deformation mechanisms as the long-lived understhrusting and the episodic lithospheric faulting in the Asian continent and their link to deep processes.
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Carcaillet, J., Angel, I., Carrillo, E., Audemard, F. A., & Beck, C. (2013). Timing of the last deglaciation in the Sierra Nevada of the Merida Andes, Venezuela. QUATERNARY RESEARCH, 80(3), 482–494.
Résumé: In the tropical Merida Andes (northwestern Venezuela), glacial landforms were found at altitudes between 2600 and 5000 m, corresponding to 600 km(2) of ice cover during the maximum glacial extension. However, the lack of sufficient absolute age data prevents detailed reconstruction of the timing of the last deglaciation. On the northwestern flank of the Mucunuque Massif, successive moraines and striated eroded basement surfaces were sampled for cosmogenic Be-10 investigation. Their compilation with published data allows the establishment of a detailed chronology of the post-LGM glacier history. The oldest moraines (18.1 and 16.8 ka) correspond to the Oldest Dryas. Successive moraine ridges indicate stops in the overall retreat between the LGM and the Younger Dryas. The cold and short Older Diyas stadial has been identified. Results indicate that most of the ice withdrew during the Pleistocene. The dataset supports an intensification of the vertical retreat rate from similar to 25 m/ka during the late Pleistocene to similar to 310 m/ka during the Pleistocene/Holocene. Afterwards, the glacier was confined and located in the higher altitude zones. The altitude difference of the Younger Diyas moraines in the Mucubajl, La Victoria and Los Zerpa valleys indicates a strong effect of valley orientation on the altitude of moraine development. (C) 2013 University of Washington. Published by Elsevier Inc. All rights reserved.
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Carpentier, M., Weis, D., & Chauvel, C. (2013). Large U loss during weathering of upper continental crust: The sedimentary record. CHEMICAL GEOLOGY, 340, 91–104.
Résumé: Oceanic sediments deposited at high rate close to continents are dominated by terrigenous material. Aside from dilution by biogenic components, their chemical compositions reflect those of nearby continental masses. This study focuses on oceanic sediments coming from the juvenile Canadian Cordillera and highlights systematic differences between detritus deriving from juvenile crust and detritus from old and mature crust. We report major and trace element concentrations for 68 sediments from the northernmost part of the Cascade forearc, drilled at ODP Sites 888 and 1027. The calculated weighted averages for each site can then be used in the future to quantify the contribution of subducted sediments to Cascades volcanism. The two sites have similar compositions but Site 888, located closer to the continent, has higher sandy turbidite contents and displays higher bulk SiO2/Al2O3 with lower bulk Nb/Zr, attributed to the presence of zircons in the coarse sands. Comparison with published data for other oceanic sedimentary piles demonstrates the existence of systematic differences between modern sediments deriving from juvenile terranes (juvenile sediments) and modem sediments derived from mature continental areas (cratonic sediments). The most striking systematic difference is for Th/Nb, Th/U, Nb/U and Th/Rb ratios: juvenile sediments have much lower ratios than cratonic sediments. The small enrichment of Th over Nb in cratonic sediments may be explained by intracrustal magmatic and metamorphic differentiation processes. In contrast, their elevated Th/U and Nb/U ratios (average values of 6.87 and 7.95, respectively) in comparison to juvenile sediments (Th/U similar to 3.09, Nb/U similar to 5.15) suggest extensive U and Rb losses on old cratons. Uranium and Rb losses are attributed to long-term leaching by rain and river water during exposure of the continental crust at the surface. Over geological times, the weathering effects create a slow but systematic increase of Th/U with exposure time. (c) 2013 Elsevier B.V. All rights reserved.
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Carretier, S., Regard, V., Vassallo, R., Aguilar, G., Martinod, J., Riquelme, R., et al. (2013). Slope and climate variability control of erosion in the Andes of central Chile. GEOLOGY, 41(2), 195–198.
Résumé: Climate and topography control millennial-scale mountain erosion, but their relative impacts remain matters of debate. Conflicting results may be explained by the influence of the erosion threshold and daily variability of runoff on long-term erosion. However, there is a lack of data documenting these erosion factors. Here we report suspended-load measurements, derived decennial erosion rates, and Be-10-derived millennial erosion rates along an exceptional climatic gradient in the Andes of central Chile. Both erosion rates (decennial and millenial) follow the same latitudinal trend, and peak where the climate is temperate (mean runoff similar to 500 mm yr(-1)). Both decennial and millennial erosion rates increase nonlinearly with slope toward a threshold of similar to 0.55 m/m. The comparison of these erosion rates shows that the contribution of rare and strong erosive events to millennial erosion increases from 0% in the humid zone to more than 90% in the arid zone. Our data confirm the primary role of slope as erosion control even under contrasting climates and support the view that the influence of runoff variability on millennial erosion rates increases with aridity.
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Catheline, S., Souchon, R., Rupin, M., Brum, J., Dinh, A. H., & Chapelon, J. Y. (2013). Tomography from diffuse waves: Passive shear wave imaging using low frame rate scanners. APPLIED PHYSICS LETTERS, 103(1).
Résumé: We present an approach to extract from the local measurement of a complex field a wavelength tomography. In contrast with noise correlation techniques developed in recent years in seismology or ultrasound, field measurement is under-sampled which opens applications to slow imaging devices. Through simulations and experiments, it is demonstrated that the loss of time and/or spatial coherence of the field measurement is not an obstacle for tomography reconstruction. We present an application in shear wave imaging: a conventional ultrasonic scanner working at 25 Hz is tested in a medical phantom and in the thyroid of a healthy volunteer. (C) 2013 AIP Publishing LLC.
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Causse, B., Spadini, L., Martins, J. F., Lenoir, T., Heyraud, A., & Delolme, C. (2013). Xanthan exopolysaccharide: Acid-base reactivity related to structure and conformation. A model for understanding the reactivity of degraded and colloidal soil organic matter. CHEMICAL GEOLOGY, 359, 150–158.
Résumé: Bacterial cells and bacterial exopolysaccharides differ strongly in their respective colloidal and polymeric habits. This suggests different reactivities toward metals and protons, although recent studies point to the similarity of such substrates in terms of site density and metal complexation strength. The aim of this paper is to investigate the causes of this surprising uniqueness by studying the reactivity of a model exopolysaccharide, xanthan. NMR and molecular analysis were used to unambiguously determine the total density of reactive carboxylic sites of the xanthan molecule (1.65 mmol/g xanthan dry weight dw). This allowed the independent determination of the average protonation constant of xanthan (Xan), which is more acidic than its constitutive reactive ligands, glucuronic and pyruvic acids (Glc + Pyr) at high (0.5) and medium (0.1), but not at low (0.01) ionic strength. This shows that xanthan is intrinsically more acidic than its constitutive reactive ligands, and that electrostatic effects developed at low ionic strength can limit the relative lability of xanthan's protons. A cylindrical electrostatic model based on the molecular structure of xanthan identified a single intrinsic constant (pK(I = 0) = 1.95 +/- 0.1) as the only adjustable parameter needed to fit our experimental data. The density of xanthan reactive sites (1.65 mmol/g dw) is comparable to that of whole bacterial cells and with known highly reactive biopolymers such as humic substances, nucleic acids, proteins, and polysaccharides (similar to 1 to 5 mmol/g dw). The surprising similarity in site densities of these substrates is explained by the constitutive reactive site versus carbon concentration ratio, which is 1/23 in xanthan (one out of 23 carbons bears an acid-base reactive functional group), which is about the same in bacteria, and which increases to 1/6 in fulvic acids. These high ratios suggest the physical limits of stability for these polymers, and thus their high and similar site densities. (C) 2013 Elsevier B. V. All rights reserved.
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Cavalie, O., Pathier, E., Radiguet, M., Vergnolle, M., Cotte, N., Walpersdorf, A., et al. (2013). Slow slip event in the Mexican subduction zone: Evidence of shallower slip in the Guerrero seismic gap for the 2006 event revealed by the joint inversion of InSAR and GPS data. EARTH AND PLANETARY SCIENCE LETTERS, 367, 52–60.
Résumé: Slow slip events (SSEs) in subduction zones have been observed in the last decade with continuous GPS stations. Some of them could be related to the lateral segmentation of subduction interface that seems to be a critical parameter for the propagation of large subduction earthquakes. In 2006, one of the largest SSEs recorded so far was captured by a dozen continuous GPS stations, in the Guerrero area (Mexico) along the Mexican subduction zone. Previous studies based on these data suggested a lateral variation of the updip depth of the SEE at the Guerrero seismic gap, but suffered from a lack of resolution east of the gap. Here, we show the ability of InSAR technique to capture a part of the 2006 SSE cumulative displacement east of the Guerrero gap by a stacking approach. We processed long strip Envisat interferograms corrected for orbital errors and interseismic signal using GPS data. We first use a forward modelling approach to test InSAR sensitivity to the amount of slip, depth and width of the slipping area on the subduction interface. Due to its high spatial resolution, InSAR allows one to comprehensively sample the North-South spatial wavelength of the SSE deformation, complementing the sparse GPS network. InSAR locates the maximum of uplift and subsidence caused by the SSE more precisely than the GPS data, giving better constraints on the updip slip limit of the SSE. We then inverted the InSAR and GPS data separately to understand how each inversion resolves the slip at depth. Finally, we performed a joint inversion of InSAR and GPS data, which constrained the SSE slip and its location on the plate interface over the entire Guerrero area. The joint inversion shows significant lateral variation of the SSE slip distribution along the trench with a shallower updip edge in the Guerrero seismic gap, west of Acapulco, and a deeper slip edge further east. (C) 2013 Elsevier B.V. All rights reserved.
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Charlet, L., Markelova, E., Parsons, C., Couture, R. M., & Made, B. (2013). Redox oscillation impact on natural and engineered biogeochemical systems: chemical resilience and implications for contaminant mobility (Vol. 7).
Résumé: Many geochemical systems fluctuate regularly from oxic to anoxic conditions (flooded soils and nuclear waste surface repositories, for instance). In these conditions many inorganic contaminants including Sb, Se, Cr, As, and U are highly sensitive to changes in redox conditions. These oscillations may result in changes to their speciation, toxicity, and mobility. We demonstrate through the combination of redox-stat batch-reactor experiments that periodic and cumulative changes to matrix mineralogy, contaminant speciation, and mineral surface properties occur following periodic cycles of reduction and oxidation. These changes result in both short-term (intra-cycle) and long-term (inter-cycle) changes to K-d values for a range of redox sensitive contaminants. These results demonstrate that naturally occurring redox oscillations may result in long-term immobilization of contaminants in the solid phase in addition to short-term variations in mobility. (C) 2013 The Authors. Published by Elsevier B.V.
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Chatelain, J. L., & Guillier, B. (2013). Reliable Fundamental Frequencies of Soils and Buildings Down to 0.1 Hz Obtained from Ambient Vibration Recordings with a 4.5-Hz Sensor. SEISMOLOGICAL RESEARCH LETTERS, 84(2), 199–209.
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Chirouze, F., Huyghe, P., van der Beek, P., Chauvel, C., Chakraborty, T., Dupont-Nivet, G., et al. (2013). Tectonics, exhumation, and drainage evolution of the eastern Himalaya since 13 Ma from detrital geochemistry and thermochronology, Kameng River Section, Arunachal Pradesh. GEOLOGICAL SOCIETY OF AMERICA BULLETIN, 125(3-4), 523–538.
Résumé: The exhumation history of the central Himalaya is well documented, but lateral variations in exhumation remain poorly constrained. In this study, we identify sediment source areas and examine the late Neogene exhumation history of the eastern Himalaya from the synorogenic sedimentary record of its foreland basin. We present Nd and Hf isotopic data as well as apatite and zircon fission-track analyses from the Miocene-Pliocene Siwalik Group along the recently dated Kameng River section in Arunachal Pradesh, northeastern India. Our isotopic data show that Siwalik Group sediments deposited between 13-7 and <2.6 Ma in Arunachal Pradesh were mainly derived from Higher Himalayan source rocks. In contrast, sediments deposited between ca. 7 and 3 Ma have far less negative epsilon(Nd) and epsilon(Hf) values that require involvement of the Gangdese Batholith and Yarlung suture zone source areas via the Brahmaputra River system. Consequently, these sediments should also record incision of the Namche Barwa massif by this river. Source-area exhumation rates of Himalayan-derived sediments, determined from detrital zircon fission-track data, were on the order of 1.8 km/m.y. in the fastest-exhuming areas. These rates are very similar to those calculated for the central Himalaya and have been relatively constant since ca. 13 Ma. Our results do not support the hypothesis of a major change in exhumation rate linked to either local or regional climate change or to Shillong Plateau uplift during the Miocene, as reported elsewhere. The zircon fission-track data further suggest that exhumation of the Namche Barwa massif between 7 and 3 Ma was much slower than the similar to 10 km/m.y. rate recorded in the recent past. Detrital apatite fission-track data indicate deformation of the Siwaliks due to forward propagation of the frontal thrust since around 1 Ma.
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Clarke, D., Brenguier, F., Froger, J. L., Shapiro, N. M., Peltier, A., & Staudacher, T. (2013). Timing of a large volcanic flank movement at Piton de la Fournaise Volcano using noise-based seismic monitoring and ground deformation measurements. GEOPHYSICAL JOURNAL INTERNATIONAL, 195(2), 1132–1140.
Résumé: In volcanic domains, magma transport and pressure build-up induce high stress-strain perturbations in the surrounding volcanic edifice that may lead to volcanic flank movements and possible instability. In this study, we focus on the 2007 March-April episode of volcanic activity at Piton de la Fournaise (PdF) Volcano, La Reunion Island. This episode was associated with a large volume of emitted lava (240 x 10(6) m(3)) and a 340-m caldera collapse. We present observations of continuous seismic velocity changes measured using cross-correlations of ambient seismic noise over 10 yr at PdF. Overall, we observe a large velocity reduction starting a few days prior to the major 2007 April 2 eruption. Comparison of seismic velocity change measurements with observations of deformation from InSAR and GPS shows that the seismic velocity reduction coincided with a widespread flank movement starting at the time of injection of magma to feed an initial eruption, a few days before the 2007 April 2 eruption. We emphasize the potential of noise-based seismic velocity change measurements, together with geodetic observations, to detect and monitor possibly hazardous slope instabilities.
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Costagliola, P., Bardelli, F., Benvenuti, M., Di Benedetto, F., Lattanzi, P., Romanelli, M., et al. (2013). Arsenic-Bearing Calcite in Natural Travertines: Evidence from Sequential Extraction, μXAS, and μXRF. Environmental Science & Technology, 47(12), 6231–6238.
Résumé: Recent studies demonstrated that synthetic calcite may host considerable amounts of arsenic (As). In this paper, the concentration of As in natural calcite was determined using two novel, specifically designed, sequential extraction procedures. In addition, the oxidation state of As and its distribution between calcite and coexisting Fe-oxyhydroxides was unravelled by μXRF elemental mapping and As K-edge μXAS spectroscopy. Our results conclusively demonstrate that arsenic can be found in natural calcite up to 2 orders of magnitude over the normal crustal As abundances. Because of the large diffusion of calcite in the environment, this phase may exert an important control on As geochemistry, mobility, and bioavailability.
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Cotton, F., Archuleta, R., & Causse, M. (2013). What is Sigma of the Stress Drop? SEISMOLOGICAL RESEARCH LETTERS, 84(1), 42–48.
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Courboulex, F., Dujardin, A., Vallee, M., Delouis, B., Sira, C., Deschamps, A., et al. (2013). High-Frequency Directivity Effect for an M-w 4.1 Earthquake, Widely Felt by the Population in Southeastern France. BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA, 103(6), 3347–3353.
Résumé: We document a moderate earthquake in the French Alps (26 February 2012 M-w 4.1) that has been much more distinctly felt south of the event than north of it. This discrepancy was especially clear in the two large cities of Nice and Grenoble, both situated at 100 km from the epicenter. This observation was confirmed by ground-motion measurements that were eight times larger in one city than in the other one, for the same site conditions. Using a time-domain deconvolution between the broadband recordings of the mainshock and an aftershock used as empirical Green's functions, we show that the rupture process of this event had a strong directivity effect toward a direction of N155 degrees +/- 5 on an similar to 2 km long fault, detectable only at frequencies higher than 1 Hz. The fault size and direction are in good accordance with the location of the aftershocks. Despite the various possible contributions leading to high-frequency amplification, we show here that this simple directivity effect controlled the intensity felt by the population and the acceleration measured in the cities.
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Croize, D., Renard, F., & Gratier, J. P. (2013). Compaction and Porosity Reduction in Carbonates: A Review of Observations, Theory, and Experiments (Vol. 54).
Résumé: Carbonates are major sedimentary materials found in many upper layers of the Earth's crust. Understanding their compaction behavior is important for porosity prediction in sedimentary basins and to improve the knowledge about sealing of active faults at shallow depths, where the faults cross-cut limestone formations. In carbonates, as opposed to siliciclastic sediments, diagenesis starts at shallow depths (<1 km) and can contribute to the formation of a mechanically stable solid framework. Vertical stress, grain size, and clay content are the main parameters influencing mechanical compaction. Mechanical compaction of unconsolidated carbonate sands in laboratory occurs mostly at low stress and is mainly controlled by mineralogy and initial packing of grains. It can explain porosity reduction down to about 30%. Conversely, very little porosity loss (<1%) is obtained by mechanical compaction of cemented rocks under laboratory conditions. In sedimentary basins, however, much lower porosity values are usually encountered, down to zero. Given that mechanical compaction does not explain satisfactorily porosity-depth trends observed in sedimentary basins, the effect of chemical compaction on porosity must be considered. Among chemical mechanisms, pressure solution creep involves local mass transfer by dissolution, diffusion, and precipitation processes at the grain scale. Subcritical crack growth is also a fluid-assisted process contributing to grain fragmentation and compaction by rearrangement of particles. Pressure solution creep strain rate depends on grain size, porosity, applied stress, fluid chemistry, and temperature. Chemical compaction by pressure solution creep becomes an effective process of porosity reduction from less than 1 km of depth, as soon as fluids are present. The main parameters controlling porosity loss then become vertical stress, temperature, diffusive flow, and pore fluid chemistry. Both mechanical and chemical compaction can lead to either pervasive compaction or localized deformation. The effect of different parameters cannot easily be differentiated in observations of natural samples, as various deformation processes occur and interact simultaneously. However, control parameters may be separated in specifically designed theoretical studies and laboratory experiments. So far, few experimental studies have been performed on pressure solution creep and subcritical crack growth in carbonates. Creep experiments on calcite powder and indenters experiments have shown that time-dependent compaction requires the presence of water. Even though the different controlling parameters were tested, no clear consensus exists on the rate limiting step of deformation and, consequently, on the creep law. Individual processes leading to porosity loss in carbonates are rather well identified. However, their respective importance during burial is still debated. Even at shallow burial (<1 km) chemical compaction is needed to explain the gap between porosity loss obtained during experimental mechanical compaction and porosity-depth curves from sedimentary basins. The present study reviews various processes at work during carbonate compaction and synthesizes the current understanding on the respective importance of thermodynamic and petrophysical parameters at different stages of carbonate compaction.
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Dauteuil, O., Deschamps, F., Bourgeois, O., Mocquet, A., & Guillocheau, F. (2013). Post-breakup evolution and palaeotopography of the North Namibian Margin during the Meso-Cenozoic. TECTONOPHYSICS, 589, 103–115.
Résumé: Passive margins display various structural and morphological patterns resulting in a complex coupling between local effects. We performed an integrated analysis from the ocean to the continent at the crustal scale of the post-breakup evolution of the northern Namibian margin in terms of vertical displacements and palaeotopography. A main topographic scarp that disappears where the Palaeo-Proterozoic Damara belt crosses the coast separates the Namibian margin and the South African plateau. We analysed this transition using a synthetic crustal cross-section based on a compilation of published data as well as new field data. The thinned margin displays two domains separated by a deep sedimentary trough. This trough separates a proximal part with landward tilted blocks from the distal part with seaward tilted blocks. This structural pattern reveals a complex flowing pattern of the ductile crust controlled by magmatism. Onshore, the basalts and Cenozoic conglomerates recorded a progressive seaward tilting of the coastal zone. Post-breakup vertical motions were estimated with subsidence curves in the offshore domain and from isostatic adjustments induced by the variations of cover thickness (depth of magmatic intrusions and Apatite Fission Tracks) in onshore domain. Three domains are recognised: a subsiding offshore domain, a uplifting continental domain and a transitional domain, located on both sides of the current shoreline with successive phases of uplift and subsidence. The offshore subsidence displays variations along the margin controlled by the thinning crust generated by the continental breakup. The onshore palaeotopogaphy is approximately assessed since the end of rifting by integrating the isostatic adjustment induced by denudation: the mean elevation of the plateau has remained above 1000 m since continental breakup. No significant additional uplift was pointed out during the late Cretaceous or late Neogene. Therefore, we conclude that the South African plateau has been present in northern Namibia since 130 Ma, at least. (c) 2013 Elsevier B.V. All rights reserved.
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Dauteuil, O., Rouby, D., Braun, J., Guillocheau, F., & Deschamps, F. (2013). Post-breakup evolution of the Namibian margin: Constraints from numerical modeling. TECTONOPHYSICS, 604, 122–138.
Résumé: The Namibian margin evolution started 130 Myr ago after the breakup between South America and southern Africa. Today, it shows specific features: (i) an elevation and a bathymetry about 1000 m higher than the surrounding areas, (ii) a significant sediment supply during the Late Cretaceous following the first sedimentary peak that occurred during rifting and just afterwards, and (iii) a long-term progradation since the Mid-Cretaceous. This present configuration results in couplings between several processes and the inherited structure. We constrained this evolution using a numerical simulation applied both onshore and offshore integrating different couplings: i) a thermal adjustment of a lithosphere driven by conductivity, ii) a flexural isostasy, and iii) the loading/unloading effects of surface matter transfer. Three processes were investigated: rock-uplift, a change in the erosion efficiency and a sea-level fall. The results were compared to some pertinent observations made on the Namibian margin such as the vertical displacements, the sediment transfers, the denudation and the stratigraphic architecture in the marginal basin. In each simulation, rift-related reliefs were rapidly relaxed resulting in an exponentially decreasing denudation and sediment accumulation. Sixty Myr after the breakup, we simulated an additional uplift, an increase in the transfer efficiency of the sediment and a sea-level fall. The subsidence increased by loading, inducing a new progradational trend. Nonetheless, the three types of events differed in the duration of this progradation trend. The larger the additional uplift, the longer the progradation. The transfer efficiency increase and sea-level fall only resulted in a transient progradation trend. From these results, we suggest that the post-rift evolution of the Namibian margin was associated, during the Upper Cretaceous, to the rejuvenation of its continental relief triggered by a climate change during the Turonian and by a slow long-term rock-uplift during the Cenozoic. (C) 2013 Elsevier B.V. All right reserved.
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Daval, D., Hellmann, R., Martinez, I., Gangloff, S., & Guyot, F. (2013). Lizardite serpentine dissolution kinetics as a function of pH and temperature, including effects of elevated pCO(2). CHEMICAL GEOLOGY, 351, 245–256.
Résumé: Measurements of the dissolution rate of lizardite (r) were carried out as a function of pH (2.5 <= pH <= 6.7) and temperature (27 degrees C <= T <= 90 degrees C) in continuously stirred flow-through systems, either in liquid-filled reactors or in aqueous solutions equilibrated with a headspace of gaseous CO2 (4 MPa <= pCO(2) <= 6 MPa). For the whole dataset, the stoichiometty of the reaction was highly correlated with the extent of Mg release, and congruent reactions were observed for the whole pH range only at T = 90 degrees C. Far from equilibrium, dissolution rates in dilute HCl solutions based on Si release and normalized to BET surface area can be described by: r = k(0) exp(-E-a/RT)a(H+)(n) with k(0) = 10(-2.27 +/- 0.56) mol.m(-2).s(-1); E-a = 42.0 +/- 1.5 kJ.mol(-1); R is the gas constant, n = 0.53 +/- 0.08. Moreover, in the pH range 3.2-6.2, the concentration of protons at the lizardite surface is proportional to a(H+)(0.47), which suggests that the dissolution rate has a first-order dependence on the surface concentration of protons. When the reaction was initiated in solutions equilibrated with elevated pCO(2), a slight increase of the dissolution rate (up to a 5-fold factor at pH = 5.0) was observed with respect to CO2-free solutions at the same pH. This may be attributed to the rate enhancing effect of HCO3- ligands. For any single pH-T condition investigated in the present study, lizardite dissolution rates are orders of magnitude lower than those of other anhydrous basic silicates, such as olivine or pyroxenes. The sluggishness of the dissolution reaction probably explains the slow carbonation rates that have been measured in previous studies. Crown Copyright (c) 2013 Published by Elsevier B.V. All rights reserved.
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Daval, D., Hellmann, R., Saldi, G. D., Wirth, R., & Knauss, K. G. (2013). Linking nm-scale measurements of the anisotropy of silicate surface reactivity to macroscopic dissolution rate laws: New insights based on diopside. GEOCHIMICA ET COSMOCHIMICA ACTA, 107, 121–134.
Résumé: The interfacial zone between a bulk fluid and a mineral surface is where all exchange of matter and energy occurs during chemical weathering. However, our knowledge is still limited with respect to understanding where and how the rate-determining dissolution reactions take place. A complicating factor is the commonplace formation of amorphous Si-rich surface layers (ASSLs), which may hinder contact between the fluid and the mineral surface. To address the role of ASSL, we investigated the dissolution of a common silicate (diopside), and related the bulk dissolution rate with the nanoscale dissolution rate and surface chemistry of its individual prevalent faces. While ASSL were evidenced on all of the investigated faces, only those formed on (110) and (1 (1) over bar0) were passivating, thereby controlling the reactivity of the underlying faces. The (110) and (1 (1) over bar0) faces intersect the highest density of Mg-O-Si and Fe-O-Si bonds, and this specificity may explain the passivating behavior of the corresponding ASSL. Moreover, we evidenced an inverse relation between aqueous silica concentration and the bulk dissolution rate of crushed diopside grains, which suggest that the (110) and (1 (1) over bar0) faces are predominant in a powder. By considering ASSL as a separate phase that can control silicate dissolution rates, extrapolated laboratory-based rates at conditions relevant to the field can be lowered by up to several orders of magnitude, thereby decreasing the large gap between laboratory and natural rates. This has important implications for more accurately modeling chemical weathering reactions, so important today for the C cycle and CO2 sequestration. (C) 2013 Elsevier Ltd. All rights reserved.
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Dazas, B., Lanson, B., Breu, J., Robert, J. L., Pelletier, M., & Ferrage, E. (2013). Smectite fluorination and its impact on interlayer water content and structure: A way to fine tune the hydrophilicity of clay surfaces? MICROPOROUS AND MESOPOROUS MATERIALS, 181, 233–247.
Résumé: In addition to isomorphic cation substitutions, smectite layers may present anionic substitutions with fluorine replacing the structural hydroxyl groups and inducing a reduced number of H2O molecules hydrating interlayer cations. The resulting additional versatility of smectite layers could be used to fine-tune the hydrophilicity of pure or intercalated smectite pending a detailed understanding of interlayer water organization. The present article thus reports on the hydration of (fluoro-)hectorite samples exhibiting similar charge density (structural formulae: [Na(0.8 center dot)nH(2)O](inter)[Mg5.2Li0.8](oct)[Si-8.0]O-tet(20)(OH,F)(4)). Water sorption isotherms and PIGE/PIXE analyses allowed constraining the water content over the probed range of relative humidity and the bulk chemistry, respectively. Modeling of X-ray diffraction (XRD) profiles obtained along water vapor desorption isotherms allowed gaining additional insights in the distribution of interlayer H2O molecules. Compared to hydroxylated smectites of similar charge, fluorinated hectorites contain similar to 30% less interlayer H2O molecules although transitions between discrete hydration states are observed for similar values of relative humidity. These molecules (3-4 and 6-8 H2O molecules per cation in the mono- and bi-hydrated states, respectively) predominantly belong to the hydration sphere of interlayer cations, although additional H2O molecules are present in the bi-hydrated state. As a consequence, the positional disorder of interlayer H2O molecules is much reduced in fluorinated samples, thus increasing the minimum distance from an interlayer H2O molecule to the smectite layer, most likely owing to the hydrophobicity of fluorinated layers. Finally, the distribution of layers with a given hydration state is more heterogeneous within smectite crystals for fluorinated smectites, compared to hydroxylated ones, possibly as the result of the improved crystallinity. (c) 2013 Elsevier Inc. All rights reserved.
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De Barros, L., Bean, C. J., Zecevic, M., Brenguier, F., & Peltier, A. (2013). Eruptive fracture location forecasts from high-frequency events on Piton de la Fournaise Volcano. GEOPHYSICAL RESEARCH LETTERS, 40(17), 4599–4603.
Résumé: Piton de la Fournaise (La Reunion island) is a very active basaltic volcano, with five eruptions between Nov 2009 and Dec 2010. Pre-eruptive seismic crises usually last for a few hours and mainly consist of a volcano-tectonic swarm. During the quiescent period between the volcano-tectonic swarm and the eruptive tremor, we identify another swarm of events with a very high frequency content. These events are shallow and are located close to the future eruption site. They seem associated with the opening of the path for the magma propagating laterally at shallow depth. As these events start to occur while the magma is still in a vertical propagation phase, this seismicity seems to be related with the generic response of the volcano to the stress perturbation and not directly induced by the magma pressure. This new observation brings new insights to short-term forecasting of the eruption location.
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de Cacqueray, B., Roux, P., Campillo, M., & Catheline, S. (2013). Tracking of velocity variations at depth in the presence of surface velocity fluctuations. GEOPHYSICS, 78(1), U1–U8.
Résumé: We tested a small-scale experiment that is dedicated to the study of the wave separation algorithm and to the velocity variations monitoring problem itself. It handles the case in which velocity variations at depth are hidden by near-surface velocity fluctuations. Using an acquisition system that combines an array of sources and an array of receivers, coupled with controlled velocity variations, we tested the ability of beam-forming techniques to track velocity variations separately for body waves and surface waves. After wave separation through double beam forming, the arrival time variations of the different waves were measured through the phase difference between the extracted wavelets. Finally, a method was tested to estimate near-surface velocity variations using surface waves or shallow reflection and compute a correction to isolate target velocity variations at depth.
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De Yoreo, J. J., Waychunas, G. A., Jun, Y. S., & Fernandez-Martinez, A. (2013). In situ Investigations of Carbonate Nucleation on Mineral and Organic Surfaces (Vol. 77).
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Debret, B., Andreani, M., Godard, M., Nicollet, C., Schwartz, S., & Lafay, R. (2013). Trace element behavior during serpentinization/de-serpentinization of an eclogitized oceanic lithosphere: A LA-ICPMS study of the Lanzo ultramafic massif (Western Alps). CHEMICAL GEOLOGY, 357, 117–133.
Résumé: Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its oceanic structure and recorded different steps of serpentinization/de-serpentinization from oceanic lizardite to prograde antigorite in subduction context, up to its dehydration and secondary olivine crystallization, and finally retrograde antigorite during massif exhumation. It constitutes a suitable place to study trace element behavior during serpentinization/de-serpentinization processes and associated chemical transfers between the different envelopes of the oceanic lithosphere and the mantle wedge. Geochemical analyses of serpentine and associated minerals show that the serpentinization/de-serpentinization of the Lanzo massif took place in a relatively closed system without significant trace element transfer between the different parts of the oceanic lithosphere. In the deeper part of the lithosphere, from the slightly serpentinized mantle peridotites (SSP, <20% serpentinization) to the paleo-Moho, composed of massive serpentinites (MS, 80% serpentinization), the trace elements mobility is reduced. The chemical composition of lizardite and antigorite is homogenized with the local degree of serpentinization: in SSP, serpentine veins composition is inherited from the host mineral while, in MS, their composition is homogenous between destabilized phases at the scale of the outcrop (similar to 5 m). In the shallowest part of the oceanic lithosphere, from the paleo-Moho to the oceanic paleo-seafloor, the serpentinites are foliated (FS, >90% serpentinization). In that zone, the alpine deformation enhances the mobility of trace elements and permits their redistribution and the homogenization of antigorite composition at massif scale. Locally, in the SSP and MS, the crystallization of metamorphic veins of similar to 1-2 m corresponds to channelized fluid flows that allowed fluid transfers – and thereby trace elements – to longer distance. The successive crystallizations of antigorite and then olivine are accompanied by a diminution of some FME (B, Li, As, Sb, Ba, Rb) and Eu contents attesting that these elements are removed from slab to mantle wedge during subduction. (C) 2013 Elsevier B. V. All rights reserved.
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Debret, B., Nicollet, C., Andreani, M., Schwartz, S., & Godard, M. (2013). Three steps of serpentinization in an eclogitized oceanic serpentinization front (Lanzo Massif – Western Alps). JOURNAL OF METAMORPHIC GEOLOGY, 31(2), 165–186.
Résumé: The Lanzo peridotite massif is a fragment of oceanic lithosphere generated in an oceancontinent transition context and eclogitized during alpine collision. Despite the subduction history, the massif has preserved its sedimentary oceanic cover, suggesting that it may have preserved its oceanic structure. It is an exceptional case for studying the evolution of a fragment of the lithosphere from its oceanization to its subduction and then exhumation. We present a field and petrological study retracing the different serpentinization episodes and their impact on the massif structure. The Lanzo massif is composed of slightly serpentinized peridotites (<20% serpentinization) surrounded by an envelope of foliated serpentinites (100% serpentinization) bordered by oceanic metabasalts and metasedimentary rocks. The limit between peridotites and serpentinites defines the front of serpentinization. This limit is sharp: it is marked by the presence of massive serpentinites (80% serpentinization) and, locally, by dykes of metagabbros and mylonitic gabbros. The deformation of these gabbros is contemporaneous with the emplacement of the magma. The presence of early lizardite in the peridotites testifies that serpentinization began during the oceanization, which is confirmed by the presence of meta-ophicarbonates bordering the foliated serpentinite envelope. Two additional generations of serpentine occur in the ultramafic rocks. The first is a prograde antigorite that partially replaced the lizardite and the relict primary minerals of the peridotite during subduction, indicating that serpentinization is an active process at the ridge and in the subduction zone. Locally, this episode is followed by the deserpentinization of antigorite at peak PT (estimated in eclogitized metagabbros at 22.5GPa and 550620 degrees C): it is marked by the crystallization of secondary olivine associated with chlorite and/or antigorite and of clinopyroxene, amphibole and chlorite assemblages. A second antigorite formed during exhumation partially to completely obliterating previous textures in the massive and foliated serpentinites. Serpentinites are an important component of the oceanic lithosphere generated in slow to ultraslow spreading settings, and in these settings, there is a serpentinization gradient with depth in the upper mantle. The seismic Moho limit could correspond to a serpentinization front affecting the mantle. This partially serpentinized zone constitutes a less competent level where, during subduction and exhumation, deformation and fluid circulation are localized. In this zone, the reaction kinetics are increased and the later steps of serpentinization obliterate the evidence of this progressive zone of serpentinization. In the Lanzo massif, this zone fully recrystallized into serpentinite during alpine subduction and collision. Thus, the serpentinite envelope represents the oceanic crust as defined by geophysicists, and the sharp front of serpentinization corresponds to an eclogitized seismic palaeo-Moho.
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Deguen, R., Alboussiere, T., & Cardin, P. (2013). Thermal convection in Earth's inner core with phase change at its boundary. GEOPHYSICAL JOURNAL INTERNATIONAL, 194(3), 1310–1334.
Résumé: Inner core translation, with solidification on one hemisphere and melting on the other, provides a promising basis for understanding the hemispherical dichotomy of the inner core, as well as the anomalous stable layer observed at the base of the outer core-the so-called F-layer which might be sustained by continuous melting of inner core material. In this paper, we study in details the dynamics of inner core thermal convection when dynamically induced melting and freezing of the inner core boundary (ICB) are taken into account. If the inner core is unstably stratified, linear stability analysis and numerical simulations consistently show that the translation mode dominates only if the viscosity eta is large enough, with a critical viscosity value, of order similar to 3 x 10(18) Pa s, depending on the ability of outer core convection to supply or remove the latent heat of melting or solidification. If eta is smaller, the dynamic effect of melting and freezing is small. Convection takes a more classical form, with a one-cell axisymmetric mode at the onset and chaotic plume convection at large Rayleigh number. eta being poorly known, either mode seems equally possible. We derive analytical expressions for the rates of translation and melting for the translation mode, and a scaling theory for high Rayleigh number plume convection. Coupling our dynamic models with a model of inner core thermal evolution, we predict the convection mode and melting rate as functions of inner core age, thermal conductivity, and viscosity. If the inner core is indeed in the translation regime, the predicted melting rate is high enough, according to Alboussiere et al.'s experiments, to allow the formation of a stratified layer above the ICB. In the plume convection regime, the melting rate, although smaller than in the translation regime, can still be significant if eta is not too small. Thermal convection requires that a superadiabatic temperature profile is maintained in the inner core, which depends on a competition between extraction of the inner core internal heat by conduction and cooling at the ICB. Inner core thermal convection appears very likely with the low thermal conductivity value proposed by Stacey & Loper, but nearly impossible with the much higher thermal conductivity recently put forward by Sha & Cohen, de Koker et al. and Pozzo et al. We argue however that the formation of an iron-rich layer above the ICB may have a positive feedback on inner core convection: it implies that the inner core crystallized from an increasingly iron-rich liquid, resulting in an unstable compositional stratification which could drive inner core convection, perhaps even if the inner core is subadiabatic.
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Deschamps, F., Godard, M., Guillot, S., & Hattori, K. (2013). Geochemistry of subduction zone serpentinites: A review. LITHOS, 178, 96–127.
Résumé: Over the last decades, numerous studies have emphasized the role of serpentinites in the subduction zone geodynamics. Their presence and role in subduction environments are recognized through geophysical, geochemical and field observations of modern and ancient subduction zones and large amounts of geochemical database of serpentinites have been created. Here, we present a review of the geochemistry of serpentinites, based on the compilation of similar to 900 geochemical data of abyssal, mantle wedge and exhumed serpentinites after subduction. The aim was to better understand the geochemical evolution of these rocks during their subduction as well as their impact in the global geochemical cycle. When studying serpentinites, it is essential to determine their protoliths and their geological history before serpentinization. The geochemical data of serpentinites shows little mobility of compatible and rare earth elements (REE) at the scale of hand-specimen during their serpentinization. Thus, REE abundance can be used to identify the protolith for serpentinites, as well as magmatic processes such as melt/rock interactions before serpentinization. In the case of subducted serpentinites, the interpretation of trace element data is difficult due to the enrichments of light REE, independent of the nature of the protolith. We propose that enrichments are probably not related to serpentinization itself, but mostly due to (sedimentary-derived) fluid/rock interactions within the subduction channel after the serpentinization. It is also possible that the enrichment reflects the geochemical signature of the mantle protolith itself which could derive from the less refractory continental lithosphere exhumed at the ocean-continent transition. Additionally, during the last ten years, numerous analyses have been carried out, notably using in situ approaches, to better constrain the behavior of fluid-mobile elements (FME; e.g. B, Li, Cl, As, Sb, U, Th, Sr) incorporated in serpentine phases. The abundance of these elements provides information related to the fluid/rock interactions during serpentinization and the behavior of FME, from their incorporation to their gradual release during subduction. Serpentinites are considered as a reservoir of the FME in subduction zones and their role, notably on arc magma composition, is underestimated presently in the global geochemical cycle. (C) 2013 Elsevier B.V. All rights reserved.
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Deshayes, J., Treguier, A. M., Barnier, B., Lecointre, A., Le Sommer, J., Molines, J. M., et al. (2013). Oceanic hindcast simulations at high resolution suggest that the Atlantic MOC is bistable. GEOPHYSICAL RESEARCH LETTERS, 40(12), 3069–3073.
Résumé: [1] All climate models predict a freshening of the North Atlantic at high latitude that may induce an abrupt change of the Atlantic Meridional Overturning Circulation (hereafter AMOC) if it resides in the bistable regime, where both a strong and a weak state coexist. The latter remains uncertain as there is no consensus among observations and ocean reanalyses, where the AMOC is bistable, versus most climate models that reproduce a mono-stable strong AMOC. A series of four hindcast simulations of the global ocean at 1/12 degrees resolution, which is presently unique, are used to diagnose freshwater transport by the AMOC in the South Atlantic, an indicator of AMOC bistability. In all simulations, the AMOC resides in the bistable regime: it exports freshwater southward in the South Atlantic, implying a positive salt advection feedback that would act to amplify a decreasing trend in subarctic deep water formation as projected in climate scenarios.
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Durand, V., Bouchon, M., Karabulut, H., Marsan, D., & Schmittbuhl, J. (2013). Link between Coulomb stress changes and seismic activation in the eastern Marmara sea after the 1999, Izmit (Turkey), earthquake. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 118(2), 681–688.
Résumé: We investigate the effect of dynamic and static stress changes produced by the 1999 Izmit earthquake, on four preexisting seismic clusters located in the eastern Marmara sea, beyond the western termination of the earthquake rupture. These four clusters show long-lasting modifications in their seismicity rate. We observe that these seismic activity variations are related to stress changes. Dynamic stress pulses activate strike-slip faulting instantaneously, but in the absence of a concomitant static Coulomb stress increase, this activation is short lived. Indeed, a large dynamic stress combined with a negative static Coulomb stress may result in an immediate activation followed by the occurrence of a seismicity shadow. In contrast, the activation of extensional clusters begins slowly and takes a few days to fully develop. It is also remarkably long lasting and does not follow a classical Omori decay. More than 10 years after the earthquake, the extensional clusters located near the termination of the rupture, where static stress and pressure changes were high, are still activated. Citation: Durand, V., M. Bouchon, H. Karabulut, D. Marsan, and J. Schmittbuhl (2013), Link between Coulomb stress changes and seismic activation in the eastern Marmara sea after the 1999, Izmit (Turkey), earthquake, J. Geophys. Res. Solid Earth, 118, 681-688, doi:10.1002/jgrb.50077.
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El Atrassi, F., Brunet, F., Chazot, G., Bouybaouene, M., & Chopin, C. (2013). Metamorphic and magmatic overprint of garnet pyroxenites from the Beni Bousera massif (northern Morocco) : Petrography, mineral chemistry and thermobarometry. LITHOS, 179, 231–248.
Résumé: A detailed mineralogical and textural study of two pyroxenites from the Beni Bousera massif, a garnet clinopyroxenite (GP) and a garnet clinopyroxenite containing graphite pseudomorphs after diamond (GGP), indicates a strong metamorphic overprint associated with the massif exhumation. In both pyroxenites, the primary assemblage [Cpx(I) + Gt(I) +/- Opx] originally stable with diamond, records temperatures in excess of 1200 C. Along the exhumation path, Cpx(I) has decomposed according to the reaction: Cpx(I) = 0.55-0.60 Cpx(II) + 0.30-0.35 Opx(II) + 0.03-0.05 Gt(II) + 0.03-0.5 PI. This breakdown reaction occurred under sub-solidus conditions in at least two stages, which first led to Cpx and Opx exsolution lamellae and second to garnet crystallization at the expense of the newly formed Cpx lamellae. Successive garnet generations, Gt(II), can be distinguished by their REE content; primary garnets Gt(I) have the highest HREE content. Secondary garnets, Gt(II), have grown in the 850-950 degrees C temperature range. We show that these conditions are below the blocking temperature of Mg-Fe exchange between garnet and pyroxene (ca. 1050 degrees C) and above the blocking temperature of Mg-Fe interdiffusion in garnet. Consequently, the original composition of the secondary garnet has not been modified upon further cooling; equilibrium with the appropriate pyroxene can be used to retrieve meaningful P-T conditions. This is however not the case for pairs of pyroxene inclusion and their porphyroclastic garnet host, formed earlier in the Beni Bousera history (i.e. at higher grade) and for which decoupling between Al diffusion and (Mg, Fe) interdiffusion (in pyroxene) has occurred. In that particular case of decoupling, conventional thermometry which yield apparent conditions around 2 GPa and 1000-1100 degrees C based on Al-content in pyroxene on one hand and Mg-Fe partitioning between the pyroxenite silicates on the other, will intrinsically fail at providing reliable P and T estimates. Detailed chemical inspection of Gt-Cpx-Opx inclusions in the graphite pseudomorphs indicates that (1) these silicates are genetically related to the same minerals in the bulk rocks and (2) they were chemically isolated from the bulk rock (included in diamond and/or graphite). Finally, the pyroxenite samples from Beni Bousera have recorded two major events pertaining to the late evolution of this massif: (1) the increase of the water activity in GP as shown by the crystallization of pargasitic amphibole which suggests the proximity to crustal units, and (2) a temperature increase up to ca. 1050 degrees C, which led to water-present partial melting of both GP and GGP. (C) 2013 Elsevier B.V. All rights reserved.
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Emoto, K., Sato, H., & Nishimura, T. (2013). Envelope synthesis of a cylindrical outgoing wavelet in layered random elastic media based on the Markov approximation. GEOPHYSICAL JOURNAL INTERNATIONAL, 194(2), 899–910.
Résumé: In the heterogeneous earth medium, short period seismograms of an earthquake are well characterized by their smooth envelopes with random phases. The Markov approximation has often been used for the practical synthesis of their envelopes for a given frequency band. It is a stochastic extension of the phase screen method to synthesize wave envelopes in media with random fluctuations under the condition that the wavelength is shorter than the correlation distance of the fluctuation. We propose an extension of the Markov approximation for the envelope synthesis to the case that an isotropically outgoing wavelet is radiated from a point source in horizontal layered random elastic media, where different layers have different randomness and different background velocities. In each layer, we solve the master equation for the two frequency mutual coherence function (TFMCF) which contains the information of the intensity in the frequency domain. Just below each layer boundary, we calculate the angular spectrum which is the expression of the TFMCF in the transverse wavenumber domain for up-going wavelets. The angular spectrum shows the ray angle distribution of intensities of scattered waves. Multiplying it by the square of transmission coefficients calculated from the background velocity contrast at the boundary, we evaluate the angular spectrum just above it. We neglect P to S (S to P) conversion scattering inside of each layer; however, we take into account the mode conversion at the layer boundary. Different from the vertical incidence of a plane wavelet, the wavefront expands with time and its curvature is modified at the layer boundary due to the Snell's law. Approximating the wavefront in the second layer by a circle for a small incidence angle, we may shift the real origin to the pseudo-origin of the wavefront circle, which leads to the change in geometrical spreading factor. Finally, we calculate the mean square envelope from the TFMCF by using an FFT. By multiplying the angular spectrum by conversion or reflection coefficients and calculate the TFMCF for the converted or reflected wavelets at layer boundaries, we can calculate any phase generated due to velocity discontinuities. For the reflected wavelets, we solve the master equation of the TFMCF downward. To confirm the validity of the method, we directly synthesize mean square envelopes in 2-D two-layered random elastic media and compare them with the averaged envelopes calculated by finite difference (FD) simulations of the wave propagation in random elastic media. We find that the Markov envelopes well agree with the FD envelopes not only for a transmitted wavelet but also for a P to S converted wavelet and a reflected wavelet at a layer boundary.
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Fernandez-Martinez, A., Hu, Y. D., Lee, B., Jun, Y. S., & Waychunas, G. A. (2013). In Situ Determination of Interfacial Energies between Heterogeneously Nucleated CaCO3 and Quartz Substrates: Thermodynamics of CO2 Mineral Trapping. ENVIRONMENTAL SCIENCE & TECHNOLOGY, 47(1), 102–109.
Résumé: The precipitation of carbonate minerals-mineral trapping-is considered one of the safest sequestration mechanisms ensuring long-term geologic storage of CO2. However, little is known about the thermodynamic factors controlling the extent of heterogeneous nucleation at mineral surfaces exposed to the fluids in porous reservoirs. The goal of this study is to determine the thermodynamic factors controlling heterogeneous nucleation of carbonate minerals on pristine quartz (100) surfaces, which are assumed representative of sandstone reservoirs. To probe CaCO3 nucleation on quartz (100) in solution and with nanoscale resolution, an in situ grazing incidence small-angle X-ray scattering technique has been utilized. With this method, a value of alpha' = 36 +/- 5 mJ/m(2) for the effective interfacial free energy governing heterogeneous nucleation of CaCO3 has been obtained by measuring nucleation rates at different solution supersaturations. This value is lower than the interfacial energy governing calcite homogeneous nucleation (alpha approximate to 120 mJ/m(2)), suggesting that heterogeneous nucleation of calcium carbonate is favored on quartz (100) at ambient pressure and temperature conditions, with nucleation barriers between 2.5% and 15% lower than those expected for homogeneous nucleation. These observations yield important quantitative parameters readily usable in reactive transport models of nucleation at the reservoir scale.
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Fernandez-Martinez, A., Kalkan, B., Clark, S. M., & Waychunas, G. A. (2013). Pressure-Induced Polyamorphism and Formation of 'Aragonitic' Amorphous Calcium Carbonate. ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 52(32), 8354–8357.
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Figueroa, A., Schaeffer, N., Nataf, H. C., & Schmitt, D. (2013). Modes and instabilities in magnetized spherical Couette flow. JOURNAL OF FLUID MECHANICS, 716, 445–469.
Résumé: Several teams have reported peculiar frequency spectra for flows in a spherical shell. To address their origin, we perform numerical simulations of the spherical Couette flow in a dipolar magnetic field, in the configuration of the DTS experiment. The frequency spectra computed from time-series of the induced magnetic field display similar bumpy spectra, where each bump corresponds to a given azimuthal mode number m. The bumps appear at moderate Reynolds number (similar or equal to 2600) if the time-series are long enough (>300 rotations of the inner sphere). We present a new method that permits retrieval of the dominant frequencies for individual mode numbers m, and extraction of the modal structure of the full nonlinear flow. The maps of the energy of the fluctuations and the spatio-temporal evolution of the velocity field suggest that fluctuations originate in the outer boundary layer. The threshold of instability is found at Re-c = 1860. The fluctuations result from two coupled instabilities: high-latitude Bodewadt-type boundary layer instability, and secondary non-axisymmetric instability of a centripetal jet forming at the equator of the outer sphere. We explore the variation of the magnetic and kinetic energies with the input parameters, and show that a modified Elsasser number controls their evolution. We can thus compare with experimental determinations of these energies and find a good agreement. Because of the dipolar nature of the imposed magnetic field, the energy of magnetic fluctuations is much larger near the inner sphere, but their origin lies in velocity fluctuations that are initiated in the outer boundary layer.
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Fillon, C., Gautheron, C., & van der Beek, P. (2013). Oligocene-Miocene burial and exhumation of the Southern Pyrenean foreland quantified by low-temperature thermochronology. JOURNAL OF THE GEOLOGICAL SOCIETY, 170(1), 67–77.
Résumé: The central Pyrenees experienced an episode of rapid exhumation in Late Eocene-Early Oligocene times. Erosional products shed from the range during this time were deposited in large palaeovalleys of the southern flank of the Axial Zone, leading to significant sediment accumulation. A recent numerical modelling study of the post-orogenic exhumation and relief history of the central Axial Zone allowed us to constrain this valley-filling episode in terms of timing and thickness of conglomeratic deposits. This paper aims to test these results for the southern fold-and-thrust belt using apatite fission-track and (U-Th)/He analysis on detrital samples from the Tremp-Graus and Ager basins. inverse thermal-history modelling of the low-temperature thermochronology data indicates that the fold-and-thrust belt was covered during the Late Eocene to Miocene by 0.7-1.6 km of sediments and confirms the timing of re-excavation of the valleys during the Miocene. A detailed analysis of the apatite (U-Th)/He results shows that the significant scatter in grain ages can be explained by the influence of alpha-recoil damage with varying effective uranium content together with distinct pre-depositional thermal histories; the age scatter is consistent with initial exhumation of the sediment sources during the Triassic and Early Cretaceous.
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Fillon, C., Huismans, R. S., & van der Beek, P. (2013). Syntectonic sedimentation effects on the growth of fold-and-thrust belts. GEOLOGY, 41(1), 83–86.
Résumé: We use two-dimensional mechanical models to investigate the effects of syntectonic sedimentation on fold-and-thrust belt development, testing variable syntectonic (wedge-top and foredeep) sediment thicknesses and flexural rigidities. Model results indicate a first-order control of syntectonic sedimentation on thrust-sheet length and thrust spacing. Thrust sheets are longer when syntectonic sediment thickness and/or flexural rigidity increase. Comparison with observations from several fold-and-thrust belts confirms this first-order control of syntectonic sedimentation.
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Fillon, C., Huismans, R. S., van der Beek, P., & Munoz, J. A. (2013). Syntectonic sedimentation controls on the evolution of the southern Pyrenean fold-and-thrust belt: Inferences from coupled tectonic-surface processes models. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 118(10), 5665–5680.
Résumé: Numerous studies in the Central Pyrenees have provided evidence for a rapid phase of exhumation of this mountain belt during the Late Eocene (37-30Ma). Simultaneously, the closure of the Ebro foreland basin allowed the accumulation of sediments at the southern Piedmont, which partially covered the fold-and-thrust belt from Late Eocene (e.g., when it was still actively deforming) to Miocene times. We aim here at understanding the consequences of such syntectonic sedimentation on the Southern Pyrenean fold-and-thrust belt by using a 2-D numerical model that reproduces the development of a thin-skinned wedge subject to different modes of sedimentation and erosion. The results show contrasting fold-and-thrust belt behavior when applying aggrading or prograding sedimentation, which we link to the critical state of the wedge. When the sediments are sourced from the hinterland (progradation), the thrusting propagates toward the foreland; whereas when the sediments aggrade from the basin, the thrusting sequence migrates backward. This latter mode shows patterns of deformation that compare favorably to the Pyrenean thrusting sequence observed during Eocene-Miocene times.
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Frank, W. B., Shapiro, N. M., Kostoglodov, V., Husker, A. L., Campillo, M., Payero, J. S., et al. (2013). Low-frequency earthquakes in the Mexican Sweet Spot. GEOPHYSICAL RESEARCH LETTERS, 40(11), 2661–2666.
Résumé: We use visually-identified templates to perform a network waveform correlation search that produced similar to 17,000 robustly detected LFEs that form 15 distinct families. Stacking an LFE family's corresponding detections results in seismograms with high signal-to-noise ratios and clear P and S wave arrivals; we use these travel times to locate the sources. The resulting locations superpose a previously identified region of permanent non-volcanic tremor (NVT) activity. Husker et al. (2012) called this region a Sweet Spot, suggesting that the local conditions are adequate to continuously generate NVT. The LFE hypocenters have been located at a depth of 40-45km in an area that is surrounding the upper slab-plate interface. We characterize their focal mechanisms by comparing their stacked seismograms to synthetic seismograms. This analysis reveals a common low-dipping focal mechanism.
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Fritz, B., Clement, A., Montes-Hernandez, G., & Noguera, C. (2013). Calcite formation by hydrothermal carbonation of portlandite: complementary insights from experiment and simulation. CRYSTENGCOMM, 15(17), 3392–3401.
Résumé: The present study complements experimental results of calcite nanoparticle formation by hydrothermal carbonation of calcium hydroxide by a simulation strategy, in which both the chemical evolution of the aqueous solution and the solid phases – dissolution of portlandite and nucleation and growth of secondary calcite particles – are considered. The simulation is performed with the help of the NANOKIN code. It includes a full treatment of speciation processes in the aqueous solution, a rate equation for the dissolution of primary minerals, and a full account of nucleation and growth processes during the formation of new particles. This strategy has allowed us to decipher the various steps in the mineral transformation and solution evolution. The comparison between experiment and simulation puts strong constraints on simulation parameters, while modeling can give information on in situ conditions, currently not often available experimentally.
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Froment, B., Campillo, M., Chen, J. H., & Liu, Q. Y. (2013). Deformation at depth associated with the 12 May 2008 MW 7.9 Wenchuan earthquake from seismic ambient noise monitoring. GEOPHYSICAL RESEARCH LETTERS, 40(1), 78–82.
Résumé: We track the temporal evolution of seismic wave speed to detect changes in material properties at depth, driven by deformation associated with the 2008 Mw 7.9 Wenchuan earthquake. We analyze ambient noise correlation functions to monitor seismic wave speed variations. The data were continuously recorded during 2 years by 114 broadband stations in a region that covers the southern two thirds of the ruptured fault. We perform the analysis in the 12-to-20-s period band. By comparison with measurements in the band 1-to-3 s, we show that the seismic velocity changes cannot be explained by a shallow perturbation but are related to deformation at depth in the crust. The spatial and temporal characteristics of these variations can thus be viewed as reflecting the middle crust behavior. In particular, the results suggest that the deformation in the middle crust is different beneath Tibet and the Sichuan basin. Citation: Froment B., M. Campillo, J. H. Chen, and Q. Y. Liu, (2013), Deformation at depth associated with the 12 May 2008 MW 7.9 Wenchuan earthquake from seismic ambient noise monitoring, Geophys. Res. Lett., 40, 78-82, doi: 10.1029/2012GL053995.
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Galvez, M. E., Beyssac, O., Martinez, I., Benzerara, K., Chaduteau, C., Malvoisin, B., et al. (2013). Graphite formation by carbonate reduction during subduction. NATURE GEOSCIENCE, 6(6), 473–477.
Résumé: Carbon is transported from Earth's surface into its interior at subduction zones. Carbonates in sediments overlying hydrothermally altered rocks (including serpentinites) within the subducted slab are the main carriers of this carbon(1). Part of the carbon is recycled back to the surface by volcanism, but some is transferred to the deep Earth(1,2). Redox transformations during shallow subduction control the transfer and long-term fate of carbon, but are poorly explored(1,3). Here we use carbon stable isotopes and Raman spectroscopy to analyse the reduction of carbonate in an exhumed serpentinite-sediment contact in Alpine Corsica, France. We find that highly crystalline graphite was formed during subduction metamorphism and was concentrated in the sediment, within a reaction zone in direct contact with the serpentinite. The graphite in this reaction zone has a carbon isotopic signature (delta C-13) of up to 0.8 +/- 0.1 parts per thousand, similar to that of the original calcite that composed the sediments, and is texturally associated with the calcium-bearing mineral wollastonite that is also formed in the process. We use mass-balance calculations to show that about 9% of the total carbonaceous matter in the sedimentary unit results from complete calcite reduction in the reaction zone. We conclude that graphite formation, under reducing and low-temperature conditions, provides a mechanism to retain carbon in a subducting slab, aiding transport of carbon into the deeper Earth.
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Ganino, C., N. T. Arndt, C. Chauvel, A. Jean, & C. Athurion. (2013). Melting of carbonate wall rocks and formation of the heterogeneous aureole of the Panzhihua intrusion, China. Geoscience Frontiers, 4(5), 535–546.
Résumé: The Panzhihua gabbroic intrusion, part of the plumbing system of the Emeishan large igneous province, intruded late-Proterozoic dolomites and marls about ∼263 Ma ago. The dolomites in the contact aureole were converted to brucite marbles and a diverse suite of forsterite, diopside and garnet skarns. The variation in mineralogy is explained in part by differences in the composition of the protolith, particularly the proportion of silica minerals and clay, and in part by transfer of elements from intruding magmas. The trace element compositions of most marbles and skarns are very similar to those of unmetamorphosed dolomites and marls, but some contain high Si, Ti, and Fe contents that are interpreted to have come from a magmatic source. Three brucite marbles sampled ∼10 m from the contact of the intrusion and named “enriched brucite marble†have trace element compositions very different from their dolomitic protolith: their rare earth elements are strongly enriched whereas levels of Nb-Ta, Zr-Hf and Ti are very low. These characteristics resemble those of carbonate liquid in equilibrium with silicate liquid or more probably with silicate minerals in the case of Panzhihua, a similarity we take to indicate that the sample underwent partial melting. Samples taken up to 300 m from the contact contain brucite indicating that high temperatures persisted well into the country rocks. However, other samples collected only tens of metres from the contact are only slightly recrystallized indicating that conditions in the aureole were highly variable. We suggest that temperatures within the aureole were controlled by conduction of heat from the main intrusion and by supply of additional heat from abundant small dykes within the aureole. Circulation of fluids derived from deeper levels in the aureole flushed the carbon dioxide from the dolomite, lowering temperature needed to partially melt carbonate to the temperatures attained near the intrusion. Irregular but extensive heating destabilized the carbonates of the aureole and decarbonation reactions associated with carbonate breakdown and melting emitted a large volume of CO2, with potential impact on global climate.
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Garcon, M., Chauvel, C., France-Lanord, C., Huyghe, P., & Lave, J. (2013). Continental sedimentary processes decouple Nd and Hf isotopes. GEOCHIMICA ET COSMOCHIMICA ACTA, 121, 177–195.
Résumé: The neodymium and hafnium isotopic compositions of most crustal and mantle rocks correlate to form the “Terrestrial Array”. However, it is now well established that whereas coarse detrital sediments follow this trend, fine-grained oceanic sediments have high Hf ratios relative to their Nd isotopic ratios. It remains uncertain whether this “decoupling” of the two isotopic systems only occurs in the oceanic environment or if it is induced by sedimentary processes in continental settings. In this study, the hafnium and neodymium isotopic compositions of sediments in large rivers is expressly used to constrain the behavior of the two isotopic systems during erosion and sediment transport from continent to ocean. We report major and trace element concentrations together with Nd and Hf isotopic compositions of bedloads, suspended loads and river banks from the Ganges River and its tributaries draining the Himalayan Range i.e. the Karnali, the Narayani, the Kosi and the Marsyandi Rivers. The sample set includes sediments sampled within the Himalayan Range in Nepal, at the Himalayan mountain front, and also downstream on the floodplain and at the outflow of the Ganges in Bangladesh. Results show that hydrodynamic sorting of minerals explains the entire Hf isotopic range, i.e. more than 10 epsilon(Hf) units, observed in the river sediments but does not affect the Nd isotopic composition. Bedloads and bank sediments have systematically lower epsilon(Hf) values than suspended loads sampled at the same location. Coarse-grained sediments lie below or on the Terrestrial Array in an epsilon(Hf) vs. epsilon(Nd) diagram. In contrast, fine-grained sediments, including most of the suspended loads, deviate from the Terrestrial Array toward higher epsilon(Hf) relative to their epsilon(Nd), as is the case for oceanic terrigenous clays. The observed Nd-Hf decoupling is explained by mineralogical sorting processes that enrich bottom sediments in coarse and dense minerals, including unradiogenic zircons, while surface sediments are enriched in fine material with radiogenic Hf signatures. The data also show that Nd-Hf isotopic decoupling increases with sediment transport in the floodplain to reach its maximum at the river mouth. This implies that the Nd-Hf isotopic decoupling observed in worldwide oceanic clays and river sediments is likely to have the same origin. Finally, we estimated the Nd-Hf isotopic composition of the present-day mantle if oceanic sediments had never been subducted and conclude that the addition of oceanic sediments with their anomalous Nd-Hf isotopic compositions has slowly shifted the composition of the Earth's mantle towards more radiogenic Hf values through time. (c) 2013 Elsevier Ltd. All rights reserved.
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Garcon, M., Chauvel, C., France-Lanord, C., Limonta, M., & Garzanti, E. (2013). Removing the “heavy mineral effect” to obtain a new Pb isotopic value for the upper crust. GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, 14(9), 3324–3333.
Résumé: Based on the concept that sedimentary processes average large areas of exposed crust, sediment data have been widely used to estimate the average Pb isotopic composition of the upper continental crust. However, the possible effects of mineral sorting processes on sediment Pb isotopes have never been fully investigated. Here, we report Pb isotopic compositions of Himalayan river sediments as well as those of several grain-size fractions and mineral separates. We demonstrate that Pb isotopes of both bed loads and suspended loads are biased toward more radiogenic values than their source rocks due to a heavy mineral effect caused by mineral sorting during fluvial transport on continents. The sparse zircons, monazites and allanites present in all samples (<1 wt%), including suspended loads, generate a Pb isotopic variability as large as that observed in the Earth's mantle. After correction of this effect, we propose an average value for the composition of the upper Himalayan crust together with a new Pb isotopic value for the Earth's upper continental crust. We conclude that mineralogical effects must be evaluated carefully before using Pb isotopes of sediments as provenance and anthropogenic tracers.
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Garenne, A., Beck, P., Montes-Hernandez, G., Chiriac, R., Toche, F., Brissaud, O., et al. (2013). Aqueous alteration of carbonaceous chondrites determined by thermogravimetric analysis and infrared spectroscopy. Implications for interpreting V-NIR asteroidal observation. METEORITICS & PLANETARY SCIENCE, 48, A140.
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Garenne, A., Montes-Hernandez, G., Beck, P., Schmitt, B., Brissaud, O., & Pommerol, A. (2013). Gas-solid carbonation as a possible source of carbonates in cold planetary environments. PLANETARY AND SPACE SCIENCE, 76, 28–41.
Résumé: Carbonates are abundant sedimentary minerals at the surface and sub-surface of the Earth and they have been proposed as tracers of liquid water in extraterrestrial environments. Their formation mechanism is since generally associated with aqueous alteration processes. Recently, carbonate minerals have been discovered on Mars' surface by different orbitals or rover missions. In particular, the phoenix mission has measured from 1% to 5% of calcium carbonate (calcite type) within the soil (Smith et al., 2009). These occurrences have been reported in area where the relative humidity is significantly high (Boynton et al., 2009). The small concentration of carbonates suggests an alternative process on mineral grain surfaces (as suggested by Shaheen et al., 2010) than carbonation in aqueous conditions. Such an observation could rather point toward a possible formation mechanism by dust-gas reaction under current Martian conditions. To understand the mechanism of carbonate formation under conditions relevant to current Martian atmosphere and surface, we designed an experimental setup consisting of an infrared microscope coupled to a cryogenic reaction cell (IR-CryoCell setup). Three different mineral precursors of carbonates (Ca and Mg hydroxides, and a hydrated Ca silicate formed from Ca2SiO4), low temperature (from -10 to +30 degrees C), and reduced CO2 pressure (from 100 to 2000 mbar) were utilized to investigate the mechanism of gas-solid carbonation at mineral surfaces. These mineral materials are crucial precursors to form Ca and Mg carbonates in humid environments (0% < relative humidity <100%) at dust-CO2 or dust-water ice-CO2 interfaces. Our results reveal a significant and fast carbonation process for Ca hydroxide and hydrated Ca silicate. Conversely, only a moderate carbonation is observed for the Mg hydroxide. These results suggest that gas-solid carbonation process or carbonate formation at the dust-water ice-CO2 interfaces could be a currently active Mars' surface process. To the best of our knowledge, we report for the first time that calcium carbonate can be formed at a negative temperature (10 degrees C) via gas-solid carbonation of Ca hydroxide. We note that the carbonation process at low temperature (<0 degrees C) described in the present study could also have important implications on the dust-water ice-CO2 interactions in cold terrestrial environments (e.g. Antarctic). (C) 2012 Elsevier Ltd. All rights reserved.
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Gaullier, V., Basile, C., Roure, F., & Scheck-Wenderoth, M. (2013). An introduction to the Tectonophysics Special Issue “Basin Dynamics”. TECTONOPHYSICS, 591, 1–2.
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Gautheron, C., Barbarand, J., Ketcham, R. A., Tassan-Got, L., van der Beek, P., Pagel, M., et al. (2013). Chemical influence on alpha-recoil damage annealing in apatite: Implications for (U-Th)/He dating. CHEMICAL GEOLOGY, 351, 257–267.
Résumé: Apatite (U-Th)/He (AHe) ages reflect the influence of several parameters such as grain size, thermal history and diffusion kinetics. Previous work has suggested that recoil damage produced by the U-Th decay chains can have a significant effect on He diffusion kinetics. Models taking into account damage production and annealing via a parameterization similar to that for apatite fission tracks (AFT) have been proposed. Complementary to these models, in this work we demonstrate that grain chemistry influences the annealing rate of diffusivity-altering damage in the same manner as for AFT, and thus is not constant across all apatites. The key parameter of the annealing law (r(mro)) is examined and its theoretical impact on AHe age is tested. In certain situations, the AHe age can be significantly affected by changes in the damage-annealing rate. For samples having undergone a long stay in the AHe partial retention zone (50-80 degrees C), AHe ages can diverge by more than 15% over a reasonable range of annealing rates. In addition, this hypothesis is tested on a geological case: well samples of Triassic sandstones at 67.5 +/- 1.5 degrees C at depth in the Paris Basin, France. AFT data and AHe ages have been measured on detrital apatite in addition to chemical analysis of the grains dated for AFT. Ages for both thermochronometers present similar histogram distributions, with younger ages for AHe (AFT: similar to 14-208 Ma; N = 117; AHe: similar to 4-76 Ma and one grain at 120 Ma; N = 36). The apatite grains are characterized by D-par values from 1.2 μm to 2.9 μm and Cl content ranging from 0.05 to 0.9 wt.%. Using a thermal history reconstruction based on AFT data and geological evidence, it is shown that the non-correlation observed between AHe age and eU content can be simply explained by changing the r(mro) value. We conclude that to fully access the AHe age meaning in terms of temperature sensitivity, the parameters of the annealing law stemming from the grain chemistry need to be considered. (c) 2013 Elsevier B.V. All rights reserved.
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Gholami, Y., Brossier, R., Operto, S., Prieux, V., Ribodetti, A., & Virieux, J. (2013). Which parameterization is suitable for acoustic vertical transverse isotropic full waveform inversion? Part 2: Synthetic and real data case studies from Valhall. GEOPHYSICS, 78(2), R107–R124.
Résumé: It is necessary to account for anisotropy in full waveform inversion (FWI) of wide-azimuth and wide-aperture seismic data in most geologic environments, for correct depth positioning of reflectors, and for reliable estimations of wave speeds as a function of the direction of propagation. In this framework, choosing a suitable anisotropic subsurface parameterization is a central issue in monoparameter and multiparameter FWI. This is because this parameterization defines the influence of each physical parameter class on the data as a function of the scattering angle, and hence the resolution of the parameter reconstruction, and on the potential trade-off between different parameter classes. We apply monoparameter and multiparameter frequency-domain acoustic vertical transverse isotropic FWI to synthetic and real wide-aperture data, representative of the Valhall oil field. We first show that reliable monoparameter FWI can be performed to build a high-resolution velocity model (for the vertical, the horizontal, or normal move-out velocity), provided that the background models of two Thomsen parameters describe the long wavelengths of the subsurface sufficiently accurately. Alternatively, we show the feasibility of the joint reconstruction of two wave speeds (e. g., the vertical and horizontal wave speeds) with limited trade-off effects, while Thomsen parameter delta is kept fixed during the inversion. The influence of the wave speeds on the data for a limited range of scattering angles when combined each other can, however, significantly hamper the resolution with which the two wave speeds are imaged. These conclusions inferred from the application to the real data are fully consistent with those inferred from the theoretical parameterization analysis of acoustic vertical transverse isotropic FWI performed in the companion report.
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Gholami, Y., Brossier, R., Operto, S., Ribodetti, A., & Virieux, J. (2013). Which parameterization is suitable for acoustic vertical transverse isotropic full waveform inversion? Part 1: Sensitivity and trade-off analysis. GEOPHYSICS, 78(2), R81–R105.
Résumé: In most geologic environments, accounting for anisotropy is necessary to perform acoustic full waveform inversion (FWI) of wide-azimuth and wide-aperture seismic data because of the potential dependence of wave speeds on the direction of the wave propagation. In the framework of multiparameter FWI, the subsurface parameterization controls the influence of the different parameter classes on the modeled seismic data as a function of the scattering angle and hence the resolution with which the parameters can be reconstructed and the potential trade-off between different parameters. We have evaluated a numerical procedure based on computation of the scattering patterns of the different parameters to assess the sensitivity of the seismic data to different parameterizations of vertical transverse isotropic media in the acoustic approximation. Among the different categories we have tested, a monoparametric FWI was found for imaging one wave speed with a broad wavenumber content, keeping the Thomsen parameters fixed, which have a small influence on the data relative to the wave speed. This raises the question of the initial information required in the background models of the Thomsen parameters to perform reliable monoparameter FWI. Alternatively, simultaneously inverting the horizontal and vertical wave speeds introduces limited trade-off effects because these wave speeds have significant influence on the data for distinct ranges of scattering angles, while the influence of the Thomsen parameter delta remains weak. With such parameterization, the short-to-intermediate wavelengths of the vertical velocity are updated from the short-to-intermediate scattering angles, while the long-to-intermediate wavelengths of the horizontal velocity are updated from the wide-to-intermediate scattering angles. We concluded that the choice of the subsurface parameterization can be driven by the acquisition geometry, which controls the scattering-angle coverage and hence the resolving power of FWI, and by the accuracy of the available initial FWI models.
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Gillet, N., Jault, D., Finlay, C. C., & Olsen, N. (2013). Stochastic modeling of the Earth's magnetic field: Inversion for covariances over the observatory era. GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, 14(4), 766–786.
Résumé: Inferring the core dynamics responsible for the observed geomagnetic secular variation requires knowledge of the magnetic field at the core-mantle boundary together with its associated model covariances. However, most currently available field models have been built using regularization conditions, which force the expansions in the spatial and time domains to converge but also hinder the calculation of reliable second-order statistics. To tackle this issue, we propose a stochastic approach that integrates, through time covariance functions, some prior information on the time evolution of the geomagnetic field. We consider the time series of spherical harmonic coefficients as realizations of a continuous and differentiable stochastic process. Our specific choice of process, such that it is not twice differentiable, mainly relies on two properties of magnetic observatory records (time spectra, existence of geomagnetic jerks). In addition, the required characteristic times for the low degree coefficients are obtained from available models of the magnetic field and its secular variation based on satellite data. We construct the new family COV-OBS of field models spanning the observatory and satellite era of 18402010. These models include the external dipole and permit sharper time changes of the internal field compared to previous regularized reconstructions. The a posteriori covariance matrix displays correlations in both space and time, which should be accounted for through the secular variation error model in core flow inversions and geomagnetic data assimilation studies.
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Gimbert, F., Amitrano, D., & Weiss, J. (2013). Crossover from quasi-static to dense flow regime in compressed frictional granular media. EPL, 104(4).
Résumé: Being ubiquitous in a large variety of geomaterials, granular assemblies play a crucial role in the mechanical stability of engineering and geophysical structures. For these applications, an accurate knowledge of the processes at the origin of shear localization, i.e. faulting, in frictional granular assemblies submitted to compressive loading is needed. Here we tackle this problem by performing discrete-element numerical simulations. A thorough analysis of the evolution of multi-scale mechanical properties as approaching sample macroscopic instability is performed. Spatial correlations operating within the shear stress and strain fields are analyzed by means of a coarse-graining analysis. The divergence of correlation lengths is reported on both shear stress and strain fields as approaching the transition to sample instability. We thus show that the crossover from a quasi-static regime where the sample deforms infinitely slowly to a dense flow regime, where inertial forces play a significant role, can be interpreted as a critical phase transition. At this transition, no shear band of characteristic thickness can be defined. Copyright (C) EPLA, 2013
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Giraud, F., Reboulet, S., Deconinck, J. F., Martinez, M., Carpentier, A., & Breziat, C. (2013). The Mid-Cenomanian Event in southeastern France: Evidence from palaeontological and clay mineralogical data. CRETACEOUS RESEARCH, 46, 43–58.
Résumé: Reconstruction of main palaeoenvironmental conditions across the Mid-Cenomanian Event (MCE I) in the hemipelagic Tethyan section of Blieux (Southeast France, Vocontian Basin) is proposed. Quantitative analyses of calcareous nannofossil, ammonoid and clay mineral assemblages have been made and compared with respect to sea level changes and the carbon cycle perturbations. The nannofossil primary productivity, as recorded by nannofossil fluxes and relative abundances of meso-eutrophic taxa, is low just below and during the MCE la, then slightly increases in the interval including the MCE Ib. The clay assemblages mainly consist of illite/smectite mixed-layers with a smaller proportion of kaolinite. The percentage of kaolinite strongly decreases in the interval including the MCE Ia and slightly increases in the interval including the MCE Ib. The clay assemblages are mainly detrital in origin and reflect environmental changes including differential settling processes, climate, intensity of runoff and detrital sources. The ammonoid assemblages are characterised by a significant change during the MCE I: planispirals (mainly Schloenbachia) are dominant until the MCE Ia, whereas heteromorphs (mainly Sciponoceras) become dominant from the MCE Ib onwards. Strongly oligotrophic levels in sea surfaces are recorded during the MCE Ia and are related both to arid climatic conditions and major sea level fall (both 3rd order and medium scale lowstand deposits). A decrease in bathymetry could partly explain the decrease in the relative abundance of Schloenbachia. The first occurrence of Sciponoceras took place during the MCE Ib; this second positive increase in delta C-13 is not associated with enhanced nannofossil primary productivity. No clear relations can be established between, the occurrence of Sciponoceras and trophic resources. (C) 2013 Elsevier Ltd. All rights reserved.
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Glotzbach, C., van der Beek, P., Carcaillet, J., & Delunel, R. (2013). Deciphering the driving forces of erosion rates on millennial to million-year timescales in glacially impacted landscapes: An example from the Western Alps. JOURNAL OF GEOPHYSICAL RESEARCH-EARTH SURFACE, 118(3), 1491–1515.
Résumé: In many regions, tectonic uplift is the main driver of erosion over million-year (Myr) timescales, but climate changes can markedly affect the link between tectonics and erosion, causing transient variations in erosion rates. Here we study the driving forces of millennial to Myr-scale erosion rates in the French Western Alps, as estimated from in situ produced cosmogenic Be-10 and a newly developed approach integrating detrital and bedrock apatite fission-track thermochronology. Millennial erosion rates from Be-10 analyses vary between similar to 0.27 and similar to 1.33m/kyr, similar to rates measured in adjacent areas of the Alps. Significant positive correlations of millennial erosion rates with geomorphic measures, in particular with the LGM ice thickness, reveal a strong transient morphological and erosional perturbation caused by repeated Quaternary glaciations. The perturbation appears independent of Myr-scale uplift and erosion gradients, with the effect that millennial erosion rates exceed Myr-scale erosion rates only in the internal Alps where the latter are low (<0.4km/Myr). These areas, moreover, exhibit channels that clearly plot above a general linear positive relation between Myr-scale erosion rates and normalized steepness index. Glacial erosion acts irrespective of rock uplift and thus not only leads to an overall increase in erosion rates but also regulates landscape morphology and erosion rates in regions with considerable spatial gradients in Myr-scale tectonic uplift. Our study demonstrates that climate change, e.g., through occurrence of major glaciations, can markedly perturb landscape morphology and related millennial erosion rate patterns, even in regions where Myr-scale erosion rates are dominantly controlled by tectonics.
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Godon, C., Mugnier, J. L., Fallourd, R., Paquette, J. L., Pohl, A., & Buoncristiani, J. F. (2013). The Bossons glacier protects Europe's summit from erosion. EARTH AND PLANETARY SCIENCE LETTERS, 375, 135–147.
Résumé: The contrasting efficiency of erosion beneath cold glacier ice, beneath temperate glacier ice, and on ice-free mountain slopes is one of the key parameters in the development of relief during glacial periods. Detrital geochronology has been applied to the subglacial streams of the north face of the Mont-Blanc massif in order to estimate the efficiency of erosional processes there. Litho logically this area is composed of granite intruded at similar to 303 Ma within an older polymetamorphic complex. We use macroscopic features (on similar to 10,000 clasts) and U-Pb dating of zircon (similar to 500 grains) to establish the provenance of the sediment transported by the glacier and its subglacial streams. The lithology of sediment collected from the surface and the base of the glacier is compared with the distribution of bedrock sources. The analysis of this distribution takes into account the glacier's surface flow lines, the surface areas beneath temperate and cold ice above and below the Equilibrium Line Altitude (ELA), and the extent of the watersheds of the three subglacial meltwater stream outlets located at altitudes of 2300 m, 1760 m and 1450 m. Comparison of the proportions of granite and metamorphics in these samples indicates that (1) glacial transport does not mix the clasts derived from subglacial erosion with the clasts derived from supraglacial deposition, except in the lower part of the ice tongue where supraglacial streams and moulins transfer the supraglacial load to the base of the glacier; (2) the glacial erosion rate beneath the tongue is lower than the erosion rate in adjacent non-glaciated areas; and (3) glacial erosion beneath cold ice is at least 16 times less efficient than erosion beneath temperate ice. The low rates of subglacial erosion on the north face of the Mont-Blanc massif mean that its glaciers are protecting “the roof of Europe” from erosion. A long-term effect of this might be a rise in the maximum altitude of the Alps. (c) 2013 Elsevier B.V. All rights reserved.
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Got, J. L., Peltier, A., Staudacher, T., Kowalski, P., & Boissier, P. (2013). Edifice strength and magma transfer modulation at Piton de la Fournaise volcano. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 118(9), 5040–5057.
Résumé: From 2003 to 2007, eruptive activity at Piton de la Fournaise was shown to follow cycles, comprising many summit/proximal eruptions and finishing by a distal eruption. GPS measurements evidenced striking asymmetric deformation between its western and eastern flanks. Horizontal displacements recorded during interdistal periods showed a characteristic amplitude at the top of the eastern flank. Displacements recorded at the base of the summit cone showed a bimodal distribution, with low amplitudes during interdistal periods and large ones during distal eruptions. To account for displacement asymmetry, characteristic amplitude, and large flank displacement, we modeled the volcanic edifice using a Drucker-Prager elastoplastic rheology. Friction angles of 15 degrees and >30 degrees were needed to model the displacements respectively during distal eruptions and interdistal periods; this change shows that strain weakening occurred during distal events. Large plastic displacement that occurred in the eastern flank during distal eruptions relaxed the horizontal elastic stress accumulated during interdistal periods; it triggered summit deflation, horizontal magma transfer, and distal flank eruption and reset the eruptive cycle. Our elastoplastic models also show that simple source geometries may induce large eastern flank displacements that would be explained by a complex geometry in a linear elastic edifice. Magma supply is often thought to control volcano's eruptive activity, with surface deformation reflecting changes in magma supply rate, the volcano's response being linear. Our results bring some evidences that on Piton de la Fournaise time-space discretization of magma transfer may be the result of the edifice's nonlinear response, rather than changes in magma supply.
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Grangeon, S., Claret, F., Lerouge, C., Warmont, F., Sato, T., Anraku, S., et al. (2013). On the nature of structural disorder in calcium silicate hydrates with a calcium/silicon ratio similar to tobermorite. CEMENT AND CONCRETE RESEARCH, 52, 31–37.
Résumé: Four calcium silicate hydrates (C-S-H) with structural calcium/silicon (Ca/Si) ratios ranging from 0.82 +/- 0.02 to 0.87 +/- 0.02 were synthesized at room temperature, 50, 80, and 110 degrees C. Their structure was elucidated by collating information from electron probe micro-analysis, transmission electron microscopy, extended X-ray absorption fine structure spectroscopy, and powder X-ray diffraction (XRD). A modeling approach specific to defective minerals was used because sample turbostratism prevented analysis using usual XRD refinement techniques (e.g. Rietveld analysis). It is shown that C-S-H with Ca/Si ratio of similar to 0.8 are structurally similar to nano-crystalline turbostratic tobermorite, a naturally occurring mineral. Their structure thus consists of sheets of calcium atoms in 7-fold coordination, covered by ribbons of silicon tetrahedra with a dreierketten (wollastonite-like) organization. In these silicate ribbons, 0.42 Si per bridging tetrahedron are missing. Random stacking faults occur systematically between successive layers (turbostratic stacking). Layer-to-layer distance is equal to 11.34 angstrom. Crystallites have a mean size of 10 nm in the a-b plane, and a mean number of 2.6-2.9 layers stacked coherently along the c* axis. (C) 2013 Elsevier Ltd. All rights reserved.
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Gratier, J. P., Dysthe, D. K., & Renard, F. (2013). The Role of Pressure Solution Creep in the Ductility of the Earth's Upper Crust (Vol. 54).
Résumé: The aim of this review is to characterize the role of pressure solution creep in the ductility of the Earth's upper crust and to describe how this creep mechanism competes and interacts with other deformation mechanisms. Pressure solution creep is a major mechanism of ductile deformation of the upper crust, accommodating basin compaction, folding, shear zone development, and fault creep and interseismic healing. However, its kinetics is strongly dependent on the composition of the rocks (mainly the presence of phyllosilicates minerals that activate pressure solution) and on its interaction with fracturing and healing processes (that activate and slow down pressure solution, respectively). The present review combines three approaches: natural observations, theoretical developments, and laboratory experiments. Natural observations can be used to identify the pressure solution markers necessary to evaluate creep law parameters, such as the nature of the material, the temperature and stress conditions, or the geometry of mass transfer domains. Theoretical developments help to investigate the thermodynamics and kinetics of the processes and to build theoretical creep laws. Laboratory experiments are implemented in order to test the models and to measure creep law parameters such as driving forces and kinetic coefficients. Finally, applications are discussed for the modeling of sedimentary basin compaction and fault creep. The sensitivity of the models to time is given particular attention: viscous versus plastic rheology during sediment compaction; steady state versus non-steady state behavior of fault and shear zones. The conclusions discuss recent advances for modeling pressure solution creep and the main questions that remain to be solved.
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Gratier, J. P., Thouvenot, F., Jenatton, L., Tourette, A., Doan, M. L., & Renard, F. (2013). Geological control of the partitioning between seismic and aseismic sliding behaviours in active faults: Evidence from the Western, Alps, France. TECTONOPHYSICS, 600, 226–242.
Résumé: Given that active faults can slide either continuously by aseismic creep or episodically during earthquakes, and that the same fault zone may evolve laterally from seismic to aseismic deformation, an important issue is to know whether seismic to aseismic transition can be geologically controlled. This article presents examples of contrasted mechanical behaviour along active faults that cross cut limestone and marl units within the sedimentary cover of the French Alps. By matching seismic events along strike-slip and normal faults with the nature and structure of the rocks, it is demonstrated that the partition between seismic and aseismic sliding at depth is geologically controlled: earthquakes nucleate in the strongest rocks, mainly limestones, whereas marls accommodate at least part of the tectonic loading by aseismic creep. By looking at exhumed rocks deformed in the same context it is possible to identify the mechanism of creep, which is shown to be pressure solution creep either as a permanent or post-seismic creep. As earthquakes slip are seen to propagate through the whole upper crust, creep processes do not necessarily prevent an earthquake rupture from propagating through creeping units. However, creep relaxes stress and consequently reduces the available elastic potential energy at the origin of earthquakes in such creeping zones. The key parameters of pressure solution creep laws are presented and discussed. Using these laws, it is possible to infer why marl may creep more easily than limestone or why highly fractured limestone may creep more easily than intact rock. This approach also identifies other rocks that could creep by pressure solution in subduction zones and indicates how creeping zones may act as barriers for earthquake rupture propagation. Finally, the criteria possibly, revealing geological control of the transition between seismic and aseismic sliding at depth are discussed with respect to subduction zones. (C) 2013 Elsevier B.V. All rights reserved.
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Guedron, S., Grangeon, S., Jouravel, G., Charlet, L., & Sarret, G. (2013). Atmospheric mercury incorporation in soils of an area impacted by a chlor-alkali plant (Grenoble, France): Contribution of canopy uptake. SCIENCE OF THE TOTAL ENVIRONMENT, 445, 356–364.
Résumé: This study focused on the fluxes of mercury (Hg) and mechanisms of incorporation into soils surrounding a chlor-alkali plant suspected to have emitted up to similar to 600 kg Hg year(-1) for decades into the atmosphere. Comparison of vertical Hg soil profiles with As, Cu, Ni and Zn (which were not emitted by the plant) support Hg enrichment in surface horizons due to atmospheric Hg inputs from the chlor-alkali plant. Based on chemical extractions and elemental correlations, Hg was found to be weakly leachable and bio-available for plants, and most probably strongly bound to organic matter. In contrast, other trace elements were probably associated with phyllosilicates, iron oxides or with primary minerals. Hg stocks in the surface horizon of a forested soil (1255 mg Hg m(-3)) were two-fold higher than in an agricultural soil (636 mg Hg m(-3)) at a similar distance to the plant. The difference was attributed to the interception of atmospheric Hg by the canopy (most likely gaseous elemental Hg and reactive gaseous Hg) and subsequent litterfall incorporation. Some differences in the ability to trap atmospheric Hg were observed between tree species. The characterization of the litter showed an increasing Hg concentration in the plant material proportional to their degradation stage. In agricultural soils, very low Hg concentrations found in corn leaves and grains suggested a limited uptake via both the foliar and root pathways. Thus, the short-term risk of Hg transfer to agricultural crops and higher levels of the trophic chain appeared limited. A possible risk which remains to be evaluated is the possible transfer of Hg-rich particles from the forest topsoil to downstream aquatic ecosystems during rain and snowmelt events. (C) 2013 Elsevier B.V. All rights reserved.
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Guillaume, B., Gautheron, C., Simon-Labric, T., Martinod, J., Roddaz, M., & Douville, E. (2013). Dynamic topography control on Patagonian relief evolution as inferred from low temperature thermochronology. EARTH AND PLANETARY SCIENCE LETTERS, 364, 157–167.
Résumé: We combine low-temperature thermochronology apatite (U-Th)/He data and semi-analytical modeling of dynamic topography to investigate the role of slab window and climate on cooling/heating history and relief evolution of the Patagonian Cordillera. In particular, we discuss a new thermochronological dataset consisting in 22 samples divided into four elevation transects. Sampling sites were chosen at the same distance from the trench (250-300 km), on the leeward eastern side of the orogen, for latitudes ranging between 45 degrees S and 48 degrees S to detect a potential northward migration of the thermal signal associated with the northward migration of the slab window. We show that history of heating and cooling for this region of the southern Andes compares well with the northward migration history of slab window. In particular, a phase of heating is recorded at 15-10 Ma to the south and at <= 5 Ma to the north, preceding by similar to 5 Ma the opening of the slab window beneath Patagonia, followed by a phase of rapid cooling and denudation to the south, with values as high as 650 m/Myr between 5 and 3 Ma. We also show that present-day latitudinal topographic variations require a support by dynamic topography associated with slab window. (C) 2013 Elsevier B.V. All rights reserved.
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Guillot, S., & Hattori, K. (2013). Serpentinites: Essential Roles in Geodynamics, Arc Volcanism, Sustainable Development, and the Origin of Life. ELEMENTS, 9(2), 95–98.
Résumé: Serpentinites are rocks consisting mostly of the serpentine-group minerals chrysotile, lizardite and antigorite. They are formed by the hydration of olivine-rich ultramafic rocks and they contain up to similar to 13 wt% H2O. They have long been used by many cultures as building and carving stones. Serpentinites play essential roles in numerous geological settings. They act as a lubricant along plate boundaries during aseismic creep and contribute to the geochemical cycle of subduction zones. In the mantle, they are a reservoir of water and fluid-mobile elements. Serpentinites can produce nickel ore where weathered, and they can sequester CO2 where carbonated. They may have provided an environment for the abiotic generation of amino acids on the early Earth and other planets, potentially leading to the development of life.
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Guillot, S., & Replumaz, A. (2013). Importance of continental subductions for the growth of the Tibetan plateau. BULLETIN DE LA SOCIETE GEOLOGIQUE DE FRANCE, 184(3), 199–223.
Résumé: How and when the Tibetan plateau developed has long been a puzzling question with implications for the current understanding of the behaviour of the continental lithosphere in convergent zones. We present and discuss recent data acquired in geology and geophysics and through igneous and metamorphic petrology and palaeo-altitude estimates. It appears from this research that Tibet initially resulted from the accretion of the Gondwana continental blocks to the southern Asian margin during the Palaeozoic and Mesozoic eras. These successive accretions have potentially favoured the creation of local landforms, particularly in southern Tibet, but no evidence exists in favour of the existence of a proto-Tibetan plateau prior to the Cenozoic. Moreover, before the India-Asia collision, the Tibetan crust had to be sufficiently cold and rigid to transfer the horizontal forces from India to northern Tibet and localize the deformation along the major strike-slip faults. However, these successive accretions associated with subductions have metasomatized the Tibetan lithospheric mantle and largely explain the potassium- and sodium-rich Cenozoic magmatism. Another consequence of this contamination by fluids is the softening of the Tibetan lithosphere, which favoured intra-continental subductions. The timing and the geochemical signatures of the magmatism and the palaeo-altitudes suggest the early growth of the Tibetan plateau. By the Eocene, the southern plateau and the northern portion of Himalaya would be at an altitude of approximately 4000 meters, while the central and northern Tibetan plateau was at altitudes of approximately 2000 to 3000 meters at the Eocene-Oligocene transition. From all of these data, we propose a model of the formation of the Tibetan plateau coupled with the formation of Himalaya, which accounts for more than 2500 km of convergence accommodated by the deformation of the Continental lithospheres. During the early Eocene (55-45 Ma), the continental subduction of the high-strength Indian continental lithosphere dominates, ending with the detachment of the Indian slab. Between 45 and 35 Ma, the continental collision is established, resulting in the thickening of the internal Himalayan region and southern Tibet and the initiation of intra-tibetan subductions. By 35 Ma, the southward subduction of the intra-tibetan Songpan-Ganze terrane ends in slab break-off and is relayed by the oblique subduction of the Tarim the Athyn Tagh propagated northeastward beneath the Qilina Shan. Southward, the dextral Red River fault accommodated the southeastward extrusion of the Indochina block. During the Miocene, specifically, between 25 and 15 Ma, the Indian slab undergoes a second break-off, while the central part of Tibet is extruded eastward. Northward, the continental subduction beneath the Qilian Shan continues. Discontinuous periods of magmatic activity associated with slab detachments play a fundamental role in the convergence process. These periods lead locally to a softening of the mid-crust by magma heat transfer and to the granulitisation of the lower crust, which becomes more resistant. We propose that due to these alternating periods of softening and hardening of the Tibetan crust, the rheological behaviour of the convergence system evolves in space and time, promoting homogeneous thickening periods alternating with periods of localised crustal or lithospheric deformations.
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Gurenko, A. A., Geldmacher, J., Hoernle, K. A., & Sobolev, A. V. (2013). A composite, isotopically-depleted peridotite and enriched pyroxenite source for Madeira magmas: Insights from olivine. LITHOS, 170, 224–238.
Résumé: The Madeira and Canary island/seamount chains represent two adjacent hotspot tracks in the eastern North Atlantic, which were derived from mixed peridotite-pyroxenite mantle sources. They possess systematically different Sr-Nd-Pb, Os and Hf isotope signatures, implying mixing of DMM-, HIMU- and EM-type components from different mantle lithologies. The lithological nature of these postulated mantle endmembers (e.g., if formed by peridotite, pyroxenite and/or eclogite) is still a subject of debate. We studied the chemical composition of olivine phenocrysts (focusing on their Ni, Mn and Ca concentrations) from the lavas covering the entire volcanic history of the Madeira Archipelago (similar to 0-5 Ma). We demonstrate that Ni x FeO/MgO and Mn/FeO ratios and Ca-concentrations of olivine correlate with Sr, Nd and Pb isotopic compositions of their host lavas. The amounts of peridotite- and pyroxenite-derived melt fractions in the parental Madeira magmas were inferred from olivine compositions and independently confirmed by modeling of two-component source melting using trace elements. Our calculations demonstrate that the amount of recycled crust (=eclogite) in the Madeira magma source varies but does not exceed similar to 10%. Strong linear relationships between chemical composition of olivine and radiogenic isotopes of the host lavas allow us to determine the isotopic composition of peridotite and pyroxenite endmembers of the Madeira hotspot. The peridotite endmember has a highly depleted isotopic composition Sr-87/Sr-86 = 0.7022-0.7026, Nd-143/Nd-144 = 0.5132-0.5135, Pb-206/Pb-204 = 17.4-18.6, Pb-202/Pb-204 = 15.4-15.49, and Pb-208/Pb-204 = 36.8-38.2, whereas the pyroxenite endmember has an enriched composition Sr-87/Sr-86 = 0.7031-0.7035, Nd-143/Nd-144 = 0.5127-0.5130, Pb-206/Pb-204 = 19.9-21.3, Pb-207/Pb-204 = 15.59-15.69, and Pb-208/Pb-204 = 39.6-41.2. Our new data confirm the existence of recycled (pyroxenitic) lithology in the Madeira magma source that was previously interpreted to represent relatively young (<1 Ga) recycled oceanic crust. The isotopically depleted, DMM-like (peridotitic) component sampled by the younger post-erosional stage magmas is thought to reflect the ultramafic portion of the recycled oceanic lithosphere, whereas the HIMU-type pyroxenite of similar age to the peridotite is derived from recycled oceanic crust. Combining our new results with the data from the Canary hotspot, we conclude that the <1 Ga recycled crustal component is common to both plume sources. The Canary volcanism also reflects the presence of older (>1 Ga) recycled crust and a contribution from African subcontinental lithosphere. (C) 2013 Elsevier B.V. All rights reserved.
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Guzman, O., Mugnier, J. L., Vassallo, R., Koci, R., & Jouanne, F. (2013). Vertical slip rates of active faults of southern Albania inferred from river terraces. ANNALS OF GEOPHYSICS, 56(6).
Résumé: Fluvial terraces of Shkumbin, Devoll, Osum and Vjosa rivers (southern Albania and northwestern Greece) are studied in order to quantify the vertical slip rates of the large active faults of the Dinaric-Albanic-Hellenic Alpine fold belt. The spatial and temporal variations of the incision rates along these rivers were estimated from the geomorphological mapping of the Quaternary sediments, the geometry and the dating of the terraces. Eleven terraces levels were identified in Albania from 68 geochronological ages already published or acquired for this work. The five lower terraces of the four studied rivers are well dated (10 new and 23 already published ages). These terraces are younger than 30 ka and their remnants are numerous. Their restoration allows estimating the regional trend of incision rate and the identification of local shifts. We argue that these shifts are linked to the active tectonics when they coincide with the faults already mapped by previous authors. Vertical slip rates for eight active faults in southern Albania are thus estimated for the last 19 ka and vary from similar to 0.1 to similar to 2 mm/a. The Lushnje Tepelene Thrust, that extends more than 120 kilometers, has a throw rate that varies from 0.2 to 0.8 mm/a, whereas the active faults of the extensional domain are segmented but are very active, with throw rates reaching locally 2 mm/a.
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Guzman, O., Vassallo, R., Audemard, F., Mugnier, J. L., Oropeza, J., Yepez, S., et al. (2013). Be-10 dating of river terraces of Santo Domingo river, on Southeastern flank of the Merida Andes, Venezuela: Tectonic and climatic implications. JOURNAL OF SOUTH AMERICAN EARTH SCIENCES, 48, 85–96.
Résumé: In this study, we discuss the first cosmogenic Be-10 dating of river terraces located in the lower reaches of the Santo Domingo river (Southeastern flank of the Merida Andes, Western Venezuela). The geomorphic observations and dating allowed the restoration of the temporal evolution of incision rate, which was analysed in terms of tectonic, climatic and geomorphic processes. The long-term incision rate in the area has been constantly around 1.1 mm/a over the last 70 ka. Taking into account the geologic and geo-morphologic setting, this value can be converted into the Late Pleistocene uplift rate of the Southeastern flank of the Merida Andes. Our results show that the process of terraces formation in the lower reaches of the Santo Domingo river occurred at a higher frequency (10(3)-10(4) years) than a glacial/interglacial cycle (10(4)-10(5) years). According to the global and local climate curve, these terraces were abandoned during warm to cold transitions. (C) 2013 Elsevier Ltd. All rights reserved.
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Haas, A. K., Revil, A., Karaoulis, M., Frash, L., Hampton, J., Gutierrez, M., et al. (2013). Electric potential source localization reveals a borehole leak during hydraulic fracturing. GEOPHYSICS, 78(2), D93–D113.
Résumé: A laboratory experiment was performed to see if passively recorded electric signals can be inverted to retrieve the position of fluid leakages along a well during an attempt to hydraulically fracture a porous block in the laboratory. The cubic block was instrumented with 32 nonpolarizing sintered Ag/AgCl electrodes. During the test, several events were detected corresponding to fluid leakoff along the seal of the well. Each event showed a quick burst in the electric field followed by an exponential-type relaxation of the potential distribution over time. The occurrence of these “electric” events was always correlated with a burst in the acoustic emissions and a change in the fluid pressure. These self-potential data were inverted in two steps: (1) using a deterministic least-square algorithm with focusing to retrieve the position of the source current density in the block for a given snapshot in the electric potential distribution and (2) using a genetic algorithm to refine the position of the source current density on a denser grid. The results of the inversion were found to be in excellent agreement with the position of the well where the hydraulic test was performed and with the localization of the acoustic emissions in the vicinity of this well. This experiment indicates that passively recorded electric signals can be used to monitor fluid flow along the well during leakages, and perhaps monitor fluid flow for numerous applications involving hydromechanical disturbances.
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Hadi, J., Tournassat, C., Ignatiadis, I., Greneche, J. M., & Charlet, L. (2013). Modelling CEC variations versus structural iron reduction levels in dioctahedral smectites. Existing approaches, new data and model refinements. JOURNAL OF COLLOID AND INTERFACE SCIENCE, 407, 397–409.
Résumé: A model was developed to describe how the 2:1 layer excess negative charge induced by the reduction of Fe(III) to Fe(II) by sodium dithionite buffered with citrate-bicarbonate is balanced and applied to nontronites. This model is based on new experimental data and extends structural interpretation introduced by a former model [36-38]. The 2:1 layer negative charge increase due to Fe(III) to Fe(II) reduction is balanced by an excess adsorption of cations in the clay interlayers and a specific sorption of H+ from solution. Prevalence of one compensating mechanism over the other is related to the growing lattice distortion induced by structural Fe(III) reduction. At low reduction levels, cation adsorption dominates and some of the incorporated protons react with structural OH groups, leading to a dehydroxylation of the structure. Starting from a moderate reduction level, other structural changes occur, leading to a reorganisation of the octahedral and tetrahedral lattice: migration or release of cations, intense dehydroxylation and bonding of protons to undersaturated oxygen atoms. Experimental data highlight some particular properties of ferruginous smectites regarding chemical reduction. Contrary to previous assumptions, the negative layer charge of nontronites does not only increase towards a plateau value upon reduction. A peak is observed in the reduction domain. After this peak, the negative layer charge decreases upon extended reduction (>30%). The decrease is so dramatic that the layer charge of highly reduced nontronites can fall below that of its fully oxidised counterpart. Furthermore, the presence of a large amount of tetrahedral Fe seems to promote intense clay structural changes and Fe reducibility. Our newly acquired data clearly show that models currently available in the literature cannot be applied to the whole reduction range of clay structural Fe. Moreover, changes in the model normalising procedure clearly demonstrate that the investigated low tetrahedral bearing nontronites (SWa-1, GAN and NAu-1) all exhibit the same behaviour at low reduction levels. Consequently, we restricted our model to the case of moderate reduction (<30%) in low tetrahedral Fe-bearing nontronites. Our adapted model provides the relative amounts of Na+ (p) and H+ (n(i)) cations incorporated in the structure as a function of the amount of Fe reduction. Two equations enable the investigated systems to be described: p = m/(1 + K-r center dot omega center dot m(rel)) and n(i) = K-r center dot omega center dot m center dot m(rel)/(1 + K-r center dot omega center dot m(rel)); where m is the Fe(II) content, m(rel), the reduction level (m/m(tot)), omega, the cation exchange capacity (CEC, and K-r, an empirical constant specific to the system. (c) 2013 Elsevier Inc. All rights reserved.
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He, J., & Charlet, L. (2013). A review of arsenic presence in China drinking water. JOURNAL OF HYDROLOGY, 492, 79–88.
Résumé: Chronic endemic arsenicosis areas have been discovered in China since 1960s. Up to 2012, 19 provinces had been found to have As concentration in drinking water exceeding the standard level (0.05 mg/L). Inner Mongolia, Xinjiang and Shanxi Province are historical well-known “hotspots” of geogenic As-contaminated drinking water. The goal of this review is to examine, summarize and discuss the information of As in drinking water for all provinces and territories in China. Possible natural As sources for elevating As level in drinking water, were documented. Geogenic As-contaminated drinking water examples were taken to introduce typical environmental conditions where the problems occurred: closed basins in arid or semi-arid areas and reducing aquifers under high pH conditions. Geothermal water or mineral water in mountains areas can be high-As water as well. For undiscovered areas, prediction of potential As-affected groundwater has been carried out by some research groups by use of logistic regression. Modeled maps of probability of geogenic As contamination in groundwater are promising to be used as references to discover unknown areas. Furthermore, anthropogenic As contaminations were summarized and mining, smelters and chemical industries were found to be major sources for As pollution in China. (c) 2013 Elsevier B.V. All rights reserved.
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Hellmann, R., & Pitsch, H. (2013). Proceedings of the Fourteenth International Symposium on Water-Rock Interaction (Vol. 7).
Résumé: This article presents the Proceedings of the Fourteenth International Symposium on Water-Rock Interaction, WRI-14, held from 9-14 June 2013 in the Palais des Papes, Avignon, France. The persons responsible for this volume are: Pierpaolo Zuddas, Secretary General of WRI-14 (Universite P. et M. Curie, Paris-Sorbonne) Roland Hellmann and Helmut Pitsch, Guest Editors of this volume And the members of the Scientific Editorial Review Team: Luc Aquilina (Universite de Rennes) Mohamed Azaroual (Bureau de Recherches Geologiques et Minieres – BRGM) Catherine Beaucaire (Commissariat a l'Energie Atomique et aux Energies Alternatives – CEA) Olivier Bildstein (Commissariat a l'Energie Atomique et aux Energies Alternatives – CEA) Christelle Latrille (Commissariat a l'Energie Atomique et aux Energies Alternatives -CEA) Philippe Negrel (Bureau de Recherches Geologiques et Minisres – BRGM) Helsne Pauwels (Bureau de Recherches Geologiques et Minisres – BRGM) (C) 2012 The Authors. Published by Elsevier
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Hellmann, R., Daval, D., & Wirth, R. (2013). Formation of amorphous silica surface layers by dissolution-reprecipitaton during chemical weathering: implications for CO2 uptake. PROCEEDINGS OF THE FOURTEENTH INTERNATIONAL SYMPOSIUM ON WATER-ROCK INTERACTION, 7, 346–349.
Résumé: Chemical weathering reactions at the Earth's surface and upper crust influence the chemical cycle of elements, chemical erosion rates, the quality of potable water resources, soil formation and nutrient availability, and ore genesis. Chemical weathering is also a major process controlling the regulation of the carbon cycle by CO2 consumption and sequestration by carbonation reactions. Based on nanometer-resolution TEM measurements, chemical weathering of silicates in both the laboratory and the field was found to result in the development of a distinct interfacial phase that is amorphous, hydrated, and silica-rich. An abrupt, step function-like change in chemistry and structure delimits the interface with the unaltered parent mineral, suggesting a dissolution-reprecipitation mechanism. The existence of these precipitated silica layers has important and so far unrecognized implications with respect to natural and industrial carbon sequestration processes, as surface silica layers may decrease the amount of atmospheric CO2 consumed during coupled silicate chemical weathering-carbonation reactions. (C) 2012 The Authors. Published by Elsevier B. V. Selection and/or peer-review under responsibility of Organizing and Scientific Committee of WRI 14 – 2013
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Hewins, R. H., Zanda, B., Humayun, M., Lorand, J. P., Deldicque, D., Pont, S., et al. (2013). PETROLOGY OF NWA 7533: FORMATION BY IMPACT ON ANCIENT MARTIAN CRUST. METEORITICS & PLANETARY SCIENCE, 48, A160.
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Hillers, G., Campillo, M., Ben-Zion, Y., & Landes, M. (2013). Interaction of microseisms with crustal heterogeneity: A case study from the San Jacinto fault zone area. GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, 14(7), 2182–2197.
Résumé: We perform a multicomponent analysis to evaluate the validity and limits of noise imaging in the San Jacinto fault zone (SJFZ) area. Estimates of noise propagation and scattering length scales in the area are combined with a noise correlation-based analysis of variability of noise constituents, excitation regions, and propagation patterns. We evaluate the quality of correlation-phase and -amplitude imaging of tectonic features in the context of observed noise properties. Statistical properties of a regional high-resolution 3-D velocity model indicate that propagation of double-frequency microseism Rayleigh waves is sensitive to medium heterogeneity in the southern California plate boundary area. The analysis of noise correlation functions constructed from records of a regional seismic network suggests stable excitation of microseisms along the southern California coastline. The proximity to the source region together with randomization properties of the heterogeneous medium govern the scattered yet anisotropic character of the wave field. Insignificant travel time errors resulting from the associated imperfect reconstruction of interstation Green's function estimates allow the resolution of a velocity contrast across the SJFZ from noise correlations. However, attenuation estimates are biased by the anisotropic propagation directions. The interaction of the ambient surface wave field with medium heterogeneity facilitates imaging of the velocity structure, but the inversion of the amplitude pattern is limited since it is dominated by wave field instead of medium properties.
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Hirth, G., & Guillot, S. (2013). Rheology and Tectonic Significance of Serpentinite. ELEMENTS, 9(2), 107–113.
Résumé: Serpentinites occur in many active geologic settings and control the rheology of the lithosphere where aqueous fluids interact with ultramafic rocks. The crystal structure of serpentine-group Minerals results in diagnostic physical properties that are important for interpreting a wide range of geophysical data and impart unique rheological behaviors. Serpentinites play an important role during continental rifting and oceanic spreading, in strain localization along lithospheric strike-slip faults, and in subduction zone processes. The rheology of serpentine is key for understanding the nucleation and propagation of earthquakes, and the relative weakness of serpentinite can significantly affect geodynamic processes at tectonic plate boundaries.
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Hobiger, M., Cornou, C., Wathelet, M., Di Giulio, G., Knapmeyer-Endrun, B., Renalier, F., et al. (2013). Ground structure imaging by inversions of Rayleigh wave ellipticity: sensitivity analysis and application to European strong-motion sites. GEOPHYSICAL JOURNAL INTERNATIONAL, 192(1), 207–229.
Résumé: The knowledge of the local soil structure is important for the assessment of seismic hazards. A widespread, but time-consuming technique to retrieve the parameters of the local underground is the drilling of boreholes. Another way to obtain the shear wave velocity profile at a given location is the inversion of surface wave dispersion curves. To ensure a good resolution for both superficial and deeper layers, the used dispersion curves need to cover a wide frequency range. This wide frequency range can be obtained using several arrays of seismic sensors or a single array comprising a large number of sensors. Consequently, these measurements are time-consuming. A simpler alternative is provided by the use of the ellipticity of Rayleigh waves. The frequency dependence of the ellipticity is tightly linked to the shear wave velocity profile. Furthermore, it can be measured using a single seismic sensor. As soil structures obtained by scaling of a given model exhibit the same ellipticity curve, any inversion of the ellipticity curve alone will be ambiguous. Therefore, additional measurements which fix the absolute value of the shear wave velocity profile at some points have to be included in the inversion process. Small-scale spatial autocorrelation measurements or MASW measurements can provide the needed data. Using a theoretical soil structure, we show which parts of the ellipticity curve have to be included in the inversion process to get a reliable result and which parts can be omitted. Furthermore, the use of autocorrelation or high-frequency dispersion curves will be highlighted. The resulting guidelines for inversions including ellipticity data are then applied to real data measurements collected at 14 different sites during the European NERIES project. It is found that the results are in good agreement with dispersion curve measurements. Furthermore, the method can help in identifying the mode of Rayleigh waves in dispersion curve measurements.
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Hooper, A., Pietrzak, J., Simons, W., Cui, H., Riva, R., Naeije, M., et al. (2013). Importance of horizontal seafloor motion on tsunami height for the 2011 M-w=9.0 Tohoku-Oki earthquake. EARTH AND PLANETARY SCIENCE LETTERS, 361, 469–479.
Résumé: It is now clear that the 2011 Tohoku-Oki earthquake ruptured the subduction interface all the way to the Japan Trench. However, there is significant disagreement about just how much slip occurred at the trench, with most geodetic studies locating only a small fraction of the maximum slip there, whereas broadband seismic studies put the majority of the slip near the trench. Measurements of seafloor displacement near the trench also imply more slip there than is estimated by the geodetic studies. Here, by means of a joint inversion of displacement measurements and seafloor pressure data, we show that it is possible to reconcile geodetic and seismic studies and that a considerable amount of slip indeed occurred at the trench, with slip magnitudes reaching 57-74% of the maximum slip. The seafloor displacement predicted by our model agrees very well with independent measurements made close to the trench. We also find good agreement between our tsunami model and independent measurements of tsunami height in the ocean and on land. Re-running of the inversion without the near-field pressure gauge data, however, leads to underprediction of the flooding on land, even when the seafloor geodetic data are still included. Thus, even if the seafloor geodetic measurements had been available in real time, they would still not have allowed reliable prediction of near-field tsunami inundation. Close to the trench, the dip of the plate interface is shallow, which serves to decrease the vertical motion of the sea floor for any given slip. However, the horizontal motion is conversely larger. Because the ocean floor slopes steeply near the trench, it acted like a giant wedge, converting the horizontal motion of the ground into an uplift of the water column and causing the peak initial tsunami wave height to be twice as high as it would have been from vertical displacement alone. (C) 2012 Elsevier B.V. All rights reserved.
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Humayun, M., Nemchin, A., Grange, M., Kennedy, A., Zanda, B., Hewins, R. H., et al. (2013). THE AGE AND COMPOSITION OF THE MARTIAN CRUST FROM NWA 7533. METEORITICS & PLANETARY SCIENCE, 48, A177.
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Inwood, J., Lofi, J., Davies, S., Basile, C., Bjerum, C., Mountain, G., et al. (2013). Statistical classification of log response as an indicator of facies variation during changes in sea level: Integrated Ocean Drilling Program Expedition 313. GEOSPHERE, 9(4), 1025–1043.
Résumé: In this study, a novel application of a statistical approach is utilized for analysis of downhole logging data from Miocene-aged siliciclastic shelf sediments on the New Jersey Margin (eastern USA). A multivariate iterative nonhierarchical cluster analysis (INCA) of spectral gamma-ray logs from Integrated Ocean Drilling Program (IODP) Expedition 313 enables lithology within this siliciclastic succession to be inferred and, through comparison with the 1311 m of recovered core, a continuous assessment of depositional sequences is constructed. Significant changes in INCA clusters corroborate most key stratigraphic surfaces interpreted from the core, and this result has particular value for surface recognition in intervals of poor core recovery. This analysis contributes to the evaluation of sequence stratigraphic models of large-scale clinoform complexes that predict depositional environments, sediment composition, and stratal geometries in response to sea-level changes. The novel approach of combining statistical analysis with detailed lithostratigraphic and seismic reflection data sets will be of interest to any scientists working with downhole logs, especially spectral gamma-ray data, and also provides a reference for the strengths and weaknesses of multi component analysis applied to continental margin lithofacies. The method presented here is appropriate for evaluating successions elsewhere and also has value for hydrocarbon exploration where sequence stratigraphy is a fundamental tool.
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Ito, T., Funato, A., Lin, W. R., Doan, M. L., Boutt, D. F., Kano, Y., et al. (2013). Determination of stress state in deep subsea formation by combination of hydraulic fracturing in situ test and core analysis: A case study in the IODP Expedition 319. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 118(3), 1203–1215.
Résumé: In situ test of hydraulic fracturing (HF) provides the only way to observe in situ stress magnitudes directly. The maximum and minimum horizontal stresses, S-Hmax and S-hmin, are determined from critical borehole pressures, i.e., the reopening pressure P-r and the shut-in pressure P-s, etc, observed during the test. However, there is inevitably a discrepancy between actual and measured values of the critical pressures, and this discrepancy is very significant for P-r. For effective measurement of P-r, it is necessary for the fracturing system to have a sufficiently small compliance. A diagnostic procedure to evaluate whether the compliance of the employed fracturing system is appropriate for S-Hmax determination from P-r was developed. Furthermore, a new method for stress measurement not restricted by the system compliance and P-r is herein proposed. In this method, the magnitudes and orientations of S-Hmax and S-hmin are determined from (i) the cross-sectional shape of a core sample and (ii) P-s obtained by the HF test performed near the core depth. These ideas were applied for stress measurement in a central region of the Kumano fore-arc basin at a water depth of 2054 m using a 1.6 km riser hole drilled in the Integrated Ocean Drilling Program (IODP) Expedition 319. As a result, the stress decoupling through a boundary at 1285 m below seafloor was detected. The boundary separates new upper layers and old lower ones with an age gap of similar to 1.8 Ma, which is possibly the accretionary prism. The stress state in the lower layers is consistent with that observed in the outer edge of accretionary prism. Citation: Ito, T., A. Funato, W. Lin, M.-L. Doan, D. F. Boutt, Y. Kano, H. Ito, D. Saffer, L. C. McNeill, T. Byrne, and K. T. Moe (2013), Determination of stress state in deep subsea formation by combination of hydraulic fracturing in situ test and core analysis: A case study in the IODP Expedition 319, J. Geophys. Res. Solid Earth, 118, 1203-1215, doi: 10.1002/jgrb.50086.
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Jaillard, E., Dumont, T., Ouali, J., Bouillin, J. P., Chihaoui, A., Latil, J. L., et al. (2013). The Albian tectonic “crisis” in Central Tunisia: Nature and chronology of the deformations. JOURNAL OF AFRICAN EARTH SCIENCES, 85, 75–86.
Résumé: The Mid-Cretaceous tectonic “crisis” is a classical feature of the tectono-sedimentary evolution of Tunisia. A reappraisal of synsedimentary deformation observed in the Tajerouine and Kasserine areas shows that deformation began in the earliest Albian, increased during the Early Albian, and culminated in the Middle Albian. Late Albian deposits overly, locally with a strong angular unconformity, Aptian to Early Albian sediments. In the southern part of the studied area, fault tectonics and tilted blocks dominate, whereas in the northern area, the occurrence of slumps and olistoliths suggests deformation related to incipient salt movements at depth. These new chronological constraints suggest that this tectonic event is most probably related to the final opening of the Atlantic Ocean at equatorial latitudes. (C) 2013 Elsevier Ltd. All rights reserved.
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Jardani, A., Revil, A., & Dupont, J. P. (2013). Stochastic joint inversion of hydrogeophysical data for salt tracer test monitoring and hydraulic conductivity imaging. ADVANCES IN WATER RESOURCES, 52, 62–77.
Résumé: The assessment of hydraulic conductivity of heterogeneous aquifers is a difficult task using traditional hydrogeological methods (e.g., steady state or transient pumping tests) due to their low spatial resolution. Geophysical measurements performed at the ground surface and in boreholes provide additional information for increasing the resolution and accuracy of the inverted hydraulic conductivity field. We used a stochastic joint inversion of Direct Current (DC) resistivity and self-potential (SP) data plus in situ measurement of the salinity in a downstream well during a synthetic salt tracer experiment to reconstruct the hydraulic conductivity field between two wells. The pilot point parameterization was used to avoid over-parameterization of the inverse problem. Bounds on the model parameters were used to promote a consistent Markov chain Monte Carlo sampling of the model parameters. To evaluate the effectiveness of the joint inversion process, we compared eight cases in which the geophysical data are coupled or not to the in situ sampling of the salinity to map the hydraulic conductivity. We first tested the effectiveness of the inversion of each type of data alone (concentration sampling, self-potential, and DC resistivity), and then we combined the data two by two. We finally combined all the data together to show the value of each type of geophysical data in the joint inversion process because of their different sensitivity map. We also investigated a case in which the data were contaminated with noise and the variogram unknown and inverted stochastically. The results of the inversion revealed that incorporating the self-potential data improves the estimate of hydraulic conductivity field especially when the self-potential data were combined to the salt concentration measurement in the second well or to the time-lapse cross-well electrical resistivity data. Various tests were also performed to quantify the uncertainty in the inverted hydraulic conductivity field. (C) 2012 Elsevier Ltd. All rights reserved.
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Jayangondaperumal, R., Mugnier, J. L., & Dubey, A. K. (2013). Earthquake slip estimation from the scarp geometry of Himalayan Frontal Thrust, western Himalaya: implications for seismic hazard assessment. INTERNATIONAL JOURNAL OF EARTH SCIENCES, 102(7), 1937–1955.
Résumé: Geometric and kinematic analyses of minor thrusts and folds, which record earthquakes between 1200 AD and 1700 AD, were performed for two trench sites (Rampur Ghanda and Ramnagar) located across the Himalayan Frontal Thrust (HFT) in the western Indian Himalaya. The present study aims to re-evaluate the slip estimate of these two trench sites by establishing a link between scarp geometry, displacements observed very close to the surface and slip at deeper levels. As geometry of the active thrust beneath the scarp is unknown, we develop a parametric study to understand the origin of the scarp surface and to estimate the influence of ramp dip. The shortening estimates of Rampur Ghanda trench by line length budget and distance-displacement (D-d) method show values of 23 and 10-15 %, respectively. The estimate inferred from the later method is less than the line length budget suggesting a small internal deformation. Ramnagar trench shows 12 % shortening by line length budget and 10-25 % by the D-d method suggesting a large internal deformation. A parametric study at the trenched fault zone of Rampur Ghanda shows a slip of 16 m beneath the trailing edge of the scarp, and it is sufficient to raise a 8-m-high scarp. This implies that the Rampur Ghanda scarp is balanced with a single event with 7.8-m-coseismic slip in the trenched fault zone at the toe of the scarp, 8-15 % mean deformation within the scarp and 16-m slip at depth along a 30A degrees ramp for a pre-1400 earthquake event. A 16-m slip is the most robust estimate of the maximum slip for a single event reported previously by trench studies along the HFT in the western Indian Himalaya that occurred between 1200 AD and 1700 AD. However, the Ramnagar trenched fault zone shows a slip of 23 m, which is larger than both line length and D-d methods. It implies that a 13-m-high scarp and 23-m slip beneath the rigid block may be ascribed to multiple events. It is for the first time we report that in the south-eastern extent of the western Indian Himalaya, Ramnagar scarp consists of minimum two events (i) pre-1400 AD and (ii) unknown old events of different lateral extents with overlapping ruptures. If the more optimistic two seismic events scenario is followed, the rupture length would be at least 260 km and would lead to an earthquake greater than Mw 8.5.
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Jolivet, L., Faccenna, C., Huet, B., Labrousse, L., Le Pourhiet, L., Lacombe, O., et al. (2013). Aegean tectonics: Strain localisation, slab tearing and trench retreat. TECTONOPHYSICS, 597, 1–33.
Résumé: We review the geodynamic evolution of the Aegean-Anatolia region and discuss strain localisation there over geological times. From Late Eocene to Present, crustal deformation in the Aegean backarc has localised progressively during slab retreat. Extension started with the formation of the Rhodope Metamorphic Core Complex (Eocene) and migrated to the Cyclades and the northern Menderes Massif (Oligocene and Miocene), accommodated by crustal-scale detachments and a first series of core complexes (MCCs). Extension then localised in Western Turkey, the Corinth Rift and the external Hellenic arc after Messinian times, while the North Anatolian Fault penetrated the Aegean Sea. Through time the direction and style of extension have not changed significantly except in terms of localisation. The contributions of progressive slab retreat and tearing, basal drag, extrusion tectonics and tectonic inheritance are discussed and we favour a model (I) where slab retreat is the main driving engine, (2) successive slab tearing episodes are the main causes of this stepwise strain localisation and (3) the inherited heterogeneity of the crust is a major factor for localising detachments. The continental crust has an inherited strong heterogeneity and crustal-scale contacts such as major thrust planes act as weak zones or as zones of contrast of resistance and viscosity that can localise later deformation. The dynamics of slabs at depth and the asthenospheric flow due to slab retreat also have influence strain localisation in the upper plate. Successive slab ruptures from the Middle Miocene to the late Miocene have isolated a narrow strip of lithosphere, still attached to the African lithosphere below Crete. The formation of the North Anatolian Fault is partly a consequence of this evolution. The extrusion of Anatolia and the Aegean extension are partly driven from below (asthenospheric flow) and from above (extrusion of a lid of rigid crust). (c) 2012 Elsevier B.V. All rights reserved.
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Jolivet, R., Lasserre, C., Doin, M. P., Peltzer, G., Avouac, J. P., Sun, J., et al. (2013). Spatio-temporal evolution of aseismic slip along the Haiyuan fault, China: Implications for fault frictional properties. EARTH AND PLANETARY SCIENCE LETTERS, 377, 23–33.
Résumé: We use 20 years of Synthetic Aperture Radar acquisitions by the ERS and Envisat satellites to investigate the spatial and temporal variations of strain rates along the 35-km long creeping section of the Haiyuan fault, at the north eastern boundary of the Tibetan plateau. We then use the derived displacements to infer the fault's frictional properties and discuss the relationship between creep and the seismic behavior of the fault. Located in between a millennial seismic gap and the 1920 M8 surface rupture trace, this section has an average creep rate of 5 +/- 1 mm/yr, about the interseismic loading rate. The comparison of average surface velocity profiles derived from SAR interferometry across the creeping section reveals a creep rate increase and/or a creep migration to shallower depth between the 1990s and the 2000s. We apply a smoothed time series analysis scheme on Envisat InSAR data to investigate the creep rate variations during the 2004-2009 time period. Our analysis reveals that the creep rate accelerated in 2007, although data resolution does not allow to better constrain the onset of creep acceleration and its amplitude. Both decadal and short term transient behaviors are coeval with the largest earthquakes (M similar to 4-5) along the fault segment in recent years. From the precise mapping of the surface fault trace, we use the fault strike variations and the Mohr circle construction to compute the along-strike distribution of the friction coefficient along the creeping segment and compare it with the observed distribution of the creep rate. We find that the creep rate scales logarithmically with the friction coefficient, in agreement with the rate-and-state friction law in a rate strengthening regime. The estimated value of delta mu/delta log V similar to 2 x 10(-3) indicates that the earthquakes occurring along the creeping section cannot be the cause for a significant change in the overall segment's creep rate and that the recorded micro seismicity is most likely creep-driven. Finally, given the size and frictional properties of the creeping section, we estimate, based on previous models of dynamic rupture simulations, a 0-20% probability for a rupture to break through this section. Together with the geometrical configuration of the Haiyuan fault, these results suggest that the creeping segment may act as a persistent barrier to earthquake propagation. (C) 2013 Elsevier B.V. All rights reserved.
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Jourdan, S., Bernet, M., Tricart, P., Hardwick, E., Paquette, J. L., Guillot, S., et al. (2013). Short-lived, fast erosional exhumation of the internal western Alps during the late early Oligocene: Constraints from geothermochronology of pro- and retro-side foreland basin sediments. LITHOSPHERE, 5(2), 211–225.
Résumé: Apatite and zircon fission-track analysis and single zircon fission-track-U/Pb double dating of Oligocene to Miocene pro- and retro-side foreland basin sedimentary rocks provide evidence for short-lived but fast erosional exhumation of at least 1.5-2 km/m.y. in the internal western Alps between ca. 30 and 28 Ma. This period of fast erosion is seen as a result of rapid surface uplift coupled with increasing orographic precipitation during this phase of orogenesis. Surface uplift may have been caused and sustained by different plate-tectonic processes such as a change in convergence direction, intermediate-depth slab breakoff, and emplacement of the Ivrea body during continental collision. The occurrence of contemporaneous volcanic activity on the pro-side of the western Alps on the subducting European plate between ca. 36 Ma and 30 Ma is seen in connection with slab rollback of the Apennine slab and upwelling of hot mantle material beneath the western Alps. Single zircon double dating shows that the exhumational signal in the detrital thermochronologic data is not compromised by volcanically derived zircons, as volcanic grains can be identified and removed from the zircon fission-track data set to obtain a pure exhumational signal. The signal of fast exhumation is observed in the zircon fission-track data of the pro-side foreland basin and in the apatite fission-track data and published Ar-40-Ar-39 data in the retro-side foreland basin. During late Oligocene times, erosion rates slowed down to rates similar to present-day erosion rates in the western Alps.
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Jousset, P., Budi-Santoso, A., Jolly, A. D., Boichu, M., Surono, Dwiyono, S., et al. (2013). Signs of magma ascent in LP and VLP seismic events and link to degassing: An example from the 2010 explosive eruption at Merapi volcano, Indonesia. JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, 261, 171–192.
Résumé: The link between seismicity and degassing is investigated during the VEI 4 eruptions of Merapi volcano (Indonesia) in October and in early November 2010. Seismicity comprised a large number and variety of earthquakes including Volcano-Tectonic events, a sustained period of Long Period Seismicity (LPS), i.e., Long-Period events (LP), Very Long Period events (VLP) and tremor. LPS seismicity is ascribed to the excitation of fluid-filled cavity resonance and inertial displacement of fluids and magma. We investigate here LPS that occurred between 17 October and 4 November 2010 to obtain insights into the volcano eruption processes which preceded the paroxysmal phase of the eruption on 4-5 November. We proceed to the moment tensor inversion of a well-recorded large VLP event during the intrusion phase on 17 October 2010, i.e., before the first explosion on 26 October. By using two simplified models (crack and pipe), we find a shallow source for this VLP event at about 1 km to the south of the summit and less than 1 km below the surface. We analyze more than 90 LP events that occurred during the multi-phase eruption (29 October-4 November). We show that most of them have a dominant frequency in the range 0.2-4 Hz. We could locate 48 of those LP events; at least 3 dusters of LP events occurred successively. We interpret these observations as generated by different fluid-filled containers in the summit area that were excited while magma rose. We also observe significant variations of the complex frequency during the course of the eruption. We discuss these changes in terms of a variable ratio of fluid to solid densities and/or by possible conduit geometry change and/or permeability of the conduit or the edifice and/or by resonance of different fluid-containers during the release of more than 0.4 Tg of SO2 and large but unknown masses of other volcanic gases. Finally, we also discuss how the major explosions of the eruption were possibly triggered by passing waves resulting from regional tectonic earthquakes on 3 and 4 November. (C) 2013 Elsevier B.V. All rights reserved.
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Jun, Y. S., Fernandez-Martinez, A., Hu, Y. D., Li, Q. Y., & Waychunas, G. A. (2013). In situ probe of interfacial energies for CaCO3 heterogeneously nucleated on environmentally relevant substrates. ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 245.
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Kang, M. L., Ma, B., Bardelli, F., Chen, F. R., Liu, C. L., Zheng, Z., et al. (2013). Interaction of aqueous Se(IV)/Se(VI) with FeSe/FeSe2: Implication to Se redox process. JOURNAL OF HAZARDOUS MATERIALS, 248, 20–28.
Résumé: Since reductive precipitation is considered as the most effective way to immobilize Se-79, interaction of aqueous Se(IV)/Se(VI) with Fe(II)-bearing minerals has received extensive attention. In contrast to the thermodynamic calculations, as well as the prevalence of iron selenide phases observed in soil, sediments and ore deposits, most laboratory experiments have found that Se(0) was the reaction product. In this study, the interaction of Se(IV)/Se(VI) with FeSe/FeSe2 were investigated. The results demonstrate that FeSe and FeSe2 can be oxidized to Se(0) by Se(IV) with relatively fast kinetics, while reaction between Se(VI) and FeSe/FeSe2 only occurs under limited conditions (i.e. in the presence of high ferrous content and higher pH) with much slower kinetics, and there is no evident reaction in most case. Therefore, reduction of Se(IV) by Fe(ll)-bearing minerals, in particular by natural occurring minerals, is envisioned to produce Se(0) at the early stage of experiments, rather than FeSe or FeSe2. Due to the formation of bulk Se(0) and its low solubility, the Fe-Se-O-H2O system will maintain redox disequilibrium in laboratory time-scale. This study also reveals that iron selenides, like iron sulfides, have strong reactivity toward Fe3+. The findings in this study give insight into possible controls on Se redox process. (C) 2013 Elsevier B.V. All rights reserved.
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Karabulut, H., Paul, A., Ergun, T. A., Hatzfeld, D., Childs, D. M., & Aktar, M. (2013). Long-wavelength undulations of the seismic Moho beneath the strongly stretched Western Anatolia. GEOPHYSICAL JOURNAL INTERNATIONAL, 194(1), 450–464.
Résumé: Western Turkey provides spectacular examples of the two end-member models of deformation of the continental lithosphere, with strain localization along the North Anatolian fault and distributed north-south extension along the Aegean coast. To provide constraints on the mechanisms of continental deformation, we present a new high-resolution image of lithospheric structure along a similar to 650 km transect crossing Western Anatolia at 28 degrees E longitude from the Black Sea to the Mediterranean. More than 2600 receiver functions are computed from records of teleseismic earthquakes at 40 broadband seismic stations with an average spacing of 15 km. Lateral variations of crustal thickness and Vp/Vs ratio are inferred from both H-k and common conversion point stacks. We observe long-wavelength variations of Moho depth from similar to 31 km in the Thrace basin to similar to 25 km beneath the Marmara Sea, similar to 32 km beneath the Izmir-Ankara suture, similar to 25 km beneath the Menderes Massif and similar to 20 km on the coast of the Mediterranean. No mid- or lower-crustal interface is visible in the migrated depth section and seismic discontinuities are confined to the shallow crust. The small-amplitude and long-wavelength lateral variations of the Moho topography suggest that viscous flow in a hot lower crust has smoothed out the lateral variations of crustal thickness induced by Cenozoic continent-continent collision. The crust-mantle boundary is flat beneath the central and southern Menderes Massif. The rougher Moho topography and more heterogeneous crust of the Marmara region likely result from transtension in the North Anatolian Fault Zone superimposed onto Aegean extension. The Moho of the subducted African lithosphere is observed dipping northward between similar to 40 and similar to 60 km depth at the southern end of the profile. The abrupt termination of the subducted slab only 50 km to the north of the Mediterranean coast confirms the slab tear inferred from previous tomographic studies.
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Karlstrom, L., Hurwitz, S., Sohn, R., Vandemeulebrouck, J., Murphy, F., Rudolph, M. L., et al. (2013). Eruptions at Lone Star Geyser, Yellowstone National Park, USA: 1. Energetics and eruption dynamics. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 118(8), 4048–4062.
Résumé: Geysers provide a natural laboratory to study multiphase eruptive processes. We present results from a 4day experiment at Lone Star Geyser in Yellowstone National Park, USA. We simultaneously measured water discharge, acoustic emissions, infrared intensity, and visible and infrared video to quantify the energetics and dynamics of eruptions, occurring approximately every 3 h. We define four phases in the eruption cycle (1) a 283min phase with liquid and steam fountaining, with maximum jet velocities of 16-28 m s(-1), steam mass fraction of less than approximate to 0.01. Intermittently choked flow and flow oscillations with periods increasing from 20 to 40 s are coincident with a decrease in jet velocity and an increase of steam fraction; (2) a 268 min posteruption relaxation phase with no discharge from the vent, infrared (IR), and acoustic power oscillations gliding between 30 and 40 s; (3) a 5913 min recharge period during which the geyser is quiescent and progressively refills, and (4) a 6914 min preplay period characterized by a series of 5-10 min long pulses of steam, small volumes of liquid water discharge, and 50-70 s flow oscillations. The erupted waters ascend from a 160-170 degrees C reservoir, and the volume discharged during the entire eruptive cycle is 20.8 +/- 4.1 m(3). Assuming isentropic expansion, we calculate a heat output from the geyser of 1.4-1.5 MW, which is <0.1% of the total heat output from Yellowstone Caldera.
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Kobchenko, M., Hafver, A., Jettestuen, E., Galland, O., Renard, F., Meakin, P., et al. (2013). Drainage fracture networks in elastic solids with internal fluid generation. EPL, 102(6).
Résumé: Experiments in which CO2 gas was generated by the yeast fermentation of sugar in an elastic layer of gelatine gel confined between two glass plates are described and analyzed theoretically. The CO2 gas pressure causes the gel layer to fracture. The gas produced is drained on short length scales by diffusion and on long length scales by flow in a fracture network, which has topological properties that are intermediate between river networks and hierarchical-fracture networks. A simple model for the experimental system with two parameters that characterize the disorder and the intermediate (river-fracture) topology of the network was developed and the results of the model were compared with the experimental results. Copyright (c) EPLA, 2013
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Komorowski, J. C., Jenkins, S., Baxter, P. J., Picquout, A., Lavigne, F., Charbonnier, S., et al. (2013). Paroxysmal dome explosion during the Merapi 2010 eruption: Processes and facies relationships of associated high-energy pyroclastic density currents. JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, 261, 260–294.
Résumé: An 11-minute sequence of laterally-directed explosions and retrogressive collapses on 5 November 2010 at Merapi (Indonesia) destroyed a rapidly-growing dome and generated high-energy pyroclastic density currents (PDCs) spreading over 22 km(2) with a runout of 8.4 km while contemporaneous co-genetic valley-confined PDCs reached 15.5 km. This event formed Stage 4 of the multi-stage 2010 eruption, the most intense eruptive episode at Merapi since 1872. The deposits and the widespread devastating impact of associated high-energy PDCs on trees and buildings show striking similarities with those from historical volcanic blasts (Montagne Pelee, Martinique, Bezymianny, Russia, Mount St. Helens, USA, Soufriere Hills, Montserrat). We provide data from stratigraphic and sedimentologic analyses of 62 sections of the first unequivocal blast-like deposits in Merapi's recent history. We used high resolution satellite imagery to map eruptive units and flow direction from the pattern of extensive tree blowdown. The stratigraphy of Stage 4 consists of three depositional units (U0, U1, U2) that we correlate to the second, third and fourth explosions of the seismic record. Both U1 and U2 show a bi-partite layer stratigraphy consisting each of a lower L1 layer and an upper L2 layer. The lower L1 layer is typically very coarse-grained, fines-poor, poorly-sorted and massive, and was deposited by the erosive waxing flow head. The overlying U layer is much finer grained, fines-rich, moderately to well-sorted, with laminar to wavy stratification. L2 was deposited from the waning upper part and wake of the PDC. Field observations indicate that PDC height reached similar to 330 m with an internal velocity of similar to 100 m s(-1) within 3 km from the source. The summit's geometry and the terrain morphology formed by a major transversal ridge and a funneling deep canyon strongly focused PDC mass towards a major constriction, thereby limiting the loss of kinetic energy. This favored elevated PDC velocities and high particle concentration, promoted overspilling of PDCs across high ridges into other river valleys, and generated significant dynamic pressures to distances of 6 km that caused total destruction of buildings and the forest. The Merapi 2010 eruption highlights that explosive and gravitational disintegration of a rapidly growing dome can generate devastating high-energy, high-velocity PDCs. This constitutes a credible high impact scenario for future multi-stage eruptions at Merapi and at other volcanoes that pose particular monitoring, crisis response, and risk reduction challenges. (C) 2013 Elsevier B.V. All rights reserved.
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Lacroix, P., & Amitrano, D. (2013). Long-term dynamics of rockslides and damage propagation inferred from mechanical modeling. JOURNAL OF GEOPHYSICAL RESEARCH-EARTH SURFACE, 118(4), 2292–2307.
Résumé: Long-term observations of large active rockslides show accelerating deformation over many thousands of years since the last deglaciation. The effect of deglaciation on slope stability is however poorly understood due to (1) limited long-term observations and (2) a complex interaction between glacier retreat and hydrogeological, mechanical, and morphological processes. To assess the sensitivity of rockslide dynamics to these different processes, a model of progressive damage through intact rock mass is developed in this study, based on the finite element method. This model uses time-to-failure laws based on rock laboratory creep experiments. It is able to reproduce progressive damage localization along shear bands associated with strain rate acceleration as observed during tertiary creep. The model reproduces the different phases of deformation associated with morphologies typical of large rockslides. This model is thus suitable for simulating the dynamics of large rockslides and the transition from initiation to rapid sliding. The sensitivity of rockslide kinematics and morphology to different mechanical properties is analyzed. This analysis shows that the time evolution of the rockslide can be inferred with the knowledge of only one time parameter, independent of the knowledge of the mechanical properties of the rock mass. This parameter is here chosen as the time when the summit slope displacement has reached 10 m, a parameter that can be estimated with cosmogenic dating. The model is then used to study the effects of deglaciation on the valley flank stability and the formation of large rockslides. This study shows that the deglaciation velocity can affect the morphology of the rockslide, with the shear band of the rockslide emerging at higher elevation as the velocity decreases. We also show that the response to the deglaciation can last several thousands of years after the glacier retreat.
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Lacroix, P., Zavala, B., Berthier, E., & Audin, L. (2013). Supervised Method of Landslide Inventory Using Panchromatic SPOT5 Images and Application to the Earthquake-Triggered Landslides of Pisco (Peru, 2007, Mw8.0). REMOTE SENSING, 5(6), 2590–2616.
Résumé: Earthquake is one of the dominant triggering factors of landslides. Given the wide areas covered by mega earthquake-triggered landslides, their inventory requires development of automatic or semi-automatic methods applied to satellite imagery. A detection method is here proposed for this purpose, to fit with simple datasets; SPOT5 panchromatic images of 5 m resolution coupled with a freely and globally available DEM. The method takes advantage of multi-temporal images to detect changes based on radiometric variations after precise coregistration/orthorectification. Removal of false alarms is then undertaken using shape, orientation and radiometric properties of connected pixels defining objects. 80% of the landslides and 93% of the landslide area are detected indicating small omission errors but 50% of false alarms remain. They are removed using expert based analysis of the inventory. The method is applied to realize the first comprehensive inventory of landslides triggered by the Pisco earthquake (Peru, 15/08/2007, Mw 8.0) over an area of 27,000 km(2). 866 landslides larger than 100 m(2) are detected covering a total area of 1.29 km(2). The area/number distribution follows a power-law with an exponent of 1.63, showing a very particular regime of triggering in this arid environment compared to other areas in the world. This specific triggering can be explained by the little soil cover in the coastal and forearc regions of Peru. Analysis of this database finally shows a major control of the topography (both orientation and inclination) on the repartition of the Pisco-triggered landslides.
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Lafay, R., Deschamps, F., Schwartz, S., Guillot, S., Godard, M., Debret, B., et al. (2013). High-pressure serpentinites, a trap-and-release system controlled by metamorphic conditions: Example from the Piedmont zone of the western Alps. CHEMICAL GEOLOGY, 343, 38–54.
Résumé: We provide new insights into the geochemistry of serpentinites from the Alpine orogenic wedge representing a paleo-subduction zone. These serpentinites are derived from similar oceanic protoliths, but they have experienced different metamorphic conditions related to three different structural levels of the paleo-subduction zone ((1) obducted: Chenaillet ophiolite, (2) accretionary wedge: Queyras Schistes lustres complex and (3) serpentinite channel: Monviso ophiolite). Metamorphism undergone by these three units is well defined, increasing eastward from sub-greenschist to eclogite facies conditions, and allows us to examine trace element behavior from the oceanic ridge environment to subduction. Serpentinites first record moderate trace element enrichment due to seawater interaction resulting in the replacement of olivine and pyroxene by chrysotile and lizardite below 300 degrees C. In the sediment-dominated accretionary wedge, serpentinites are strongly enriched in fluid-mobile-elements (B, Li, As, Sb, and Cs) and act as a trapping system following the metamorphic gradient (from 300 to 390 degrees C) up to total replacement of the lizardite/chrysotile assemblage by antigorite. Under higher temperature conditions (T>390 degrees C), no enrichment was observed, and some fluid-mobile elements were released (B, Li, Cs, and Sr). Moreover, in the serpentinite channel (T>460 degrees C), most of the fluid-mobile elements are absent due to the scarcity of metasediments which prevent geochemical exchange between metasediments and serpentinites. This is also due to the onset of antigorite breakdown and the release of fluid-mobile elements. Thus, we emphasize that the geochemistry of Alpine serpentinites is strongly dependent on (1) the grade of metamorphism and (2) the ability of metasediments to supply fluid-mobile elements. We conclude that serpentinites act as a trap-and-release system for fluid-mobile elements in a subduction context. (C) 2013 Elsevier B.V. All rights reserved.
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Lafay, R., Montes-Hernandez, G., Janots, E., Chiriac, R., Findling, N., & Toche, F. (2013). Nucleation and Growth of Chrysotile Nanotubes in H2SiO3/MgCl2/NaOH Medium at 90 to 300 degrees C. CHEMISTRY-A EUROPEAN JOURNAL, 19(17), 5417–5424.
Résumé: Herein, we report new insights into the nucleation and growth processes of chrysotile nanotubes by using batch and semi-continuous experiments. For the synthesis of this highly carcinogenic material, the influences of temperature (90, 200, and 300 degrees C), Si/Mg molar ratio, and reaction time were investigated. From the semi-continuous experiments (i.e., sampling of the reacting suspension over time) and solid-state characterization of the collected samples by XRPD, TGA, FTIR spectroscopy, and FESEM, three main reaction steps were identified for chrysotile nucleation and growth at 300 degrees C: 1)formation of the proto-serpentine precursor within the first 2h of the reaction, accompanied by the formation of brucite and residual silica gel; 2)spontaneous nucleation and growth of chrysotile between about 3 and 8h reaction time, through a progressive dissolution of the proto-serpentine, brucite, and residual silica gel; and 3)Ostwald ripening growth of chrysotile from 8 to 30h reaction time, as attested to by BET and FESEM measurements. Complementary results from batch experiments confirmed a significant influence of the reaction temperature on the kinetics of chrysotile formation. However, FESEM observations revealed some formation of chrysotile nanotubes at low temperatures (90 degrees C) after 14days of reaction. Finally, doubling the Si/Mg molar ratio promoted the precipitation of pure smectite (stevensite-type) under the same P (8.2MPa)/T (300 degrees C)/pH (13.5) conditions.
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Lagabrielle, Y., Chauvet, A., Ulrich, M., & Guillot, S. (2013). Passive obduction and gravity-driven emplacement of large ophiolitic sheets: the New Caledonia ophiolite as case study. Bulletin de la Société Géologique de France, 184(4-5), 545–556.
Résumé: The 300 km long allochthonous sheet of oceanic mantle forming the New Caledonia ophiolite displays three specific characters: 1) the ophiolite pile lacks concordant sheeted dykes and pillow basalt layers; 2) the ophiolite, refered to as the Peridotite nappe, is thrusted over the basaltic formations of the Poya terrane which are classicaly thought to originate from a different oceanic environment; 3) The basal contact of the ultramafic sheet is remarkably flat all along New-Caledonia and the Peridotite nappe has not been thickened during obduction, rather it experienced significant extension. This suggests that the peridotites have not been emplaced by a tectonic force applied to the rear. New petrological and geochemical results obtained from mantle rocks finally show that the Poya terrane may originate from the same oceanic basin as the peridotites. In this article, we consider such possible cogenetic links and we propose a simple model for the obduction of the New Caledonia ophiolite in which the Poya basalts represent the original cover of the Peridotite nappe. We infer that continuous uplift of the subducted units buried beneath the oceanic lithosphere in the northern part of New Caledonia drove passive uplift of the ophiolite and led to erosion and to initiation of sliding of the basaltic layer. During the Priabonian (latest Eocene), products of the erosion of the basaltic layer were deposited together with sediments derived from the Norfolk passive oceanic margin. These sediments are involved as tectonic slices into an accretionary wedge formed in response to plate convergence. The volcaniclastic sedimentation ends up with the emplacement of large slided blocks of basalts and rafted mafic units that progressively filled up the basin. Obduction process ended with the gravity sliding of the oceanic mantle sheet, previously scalped from its mafic cover. This process is contemporaneous with the exhumation of the HP-LT units of Pouebo and Diahot. Gravity sliding was facilitated by the occurrence of a continuous serpentine sole resulting from metasomatic hydratation of mantle rocks, which developed during the uplift of the Norfolk basement and overlying Diahot and Pouébo units. Progressive emersion of the obducted lithosphere allowed subsequent weathering under subaerial, tropical conditions.
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Lanari, P., Riel, N., Guillot, S., Vidal, O., Schwartz, S., Pecher, A., et al. (2013). Deciphering high-pressure metamorphism in collisional context using microprobe mapping methods: Application to the Stak eclogitic massif (northwest Himalaya). GEOLOGY, 41(2), 111–114.
Résumé: The Stak massif, northern Pakistan, is a newly recognized occurrence of eclogite formed by the subduction of the northern margin of the Indian continent in the northwest Himalaya. Although this unit was extensively retrogressed during the Himalayan collision, records of the high-pressure (HP) event as well as a continuous pressure-temperature (P-T) path were assessed from a single thin section using a new multiequilibrium method. This method uses microprobe X-ray compositional maps of garnet and omphacitic pyroxene followed by calculations of similar to 200,000 P-T estimates using appropriate thermobarometers. The Stak eclogite underwent prograde metamorphism, increasing from 650 degrees C and 2.4 GPa to the peak conditions of 750 degrees C and 2.5 GPa, then retrogressed to 700-650 degrees C and 1.6-0.9 GPa under amphibolite-facies conditions. The estimated peak metamorphic conditions and P-T path are similar to those of the Kaghan and Tso Morari high- to ultrahigh-pressure (HP-UHP) massifs. We propose that these three massifs define a large HP to UHP province in the northwest Himalaya, comparable to the Dabie-Sulu province in China and the Western Gneiss Region in Norway.
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Langlais, M., Vial, B., & Coutant, O. (2013). Improvement of broadband seismic station installations at the Observatoire de Grenoble (OSUG) seismic network. Advances in Geosciences, 34, 9–14.
Résumé: We describe in this paper different improvements that were brought to the installation of seismic broadband stations deployed by the Observatoire de Grenoble (OSUG) in the northern French Alps. This work was realized in the frame of a French-Italian ALCOTRA project (RISE), aimed at modernizing the broadband seismic networks across our common border. We had the opportunity with this project to improve some of our seismic recording sites, both in term of sensor installation quality, and in term of reliability. We detail in particular the thermal and barometric protection system that we designed and show its effect on the reduction of long period noise above 20 s.
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Lani, S. W., Sabra, K. G., Hodgkiss, W. S., Kuperman, W. A., & Roux, P. (2013). Coherent processing of shipping noise for ocean monitoring. JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, 133(2), EL108–EL113.
Résumé: Ambient noise was recorded on two vertical line arrays (VLAs) separated by 450m and deployed in shallow water (depth similar to 150 m) off San Diego, CA continuously for 6 days. Recordings were dominated by non-stationary and non-uniform broadband shipping noise (250 Hz to 1.5 kHz). Stable coherent noise wavefronts were extracted from ambient noise correlations between the VLAs during all 6 days by mitigating the effect of discrete shipping events and using array beamforming with data-derived steering vectors. This procedure allows the tracking of arrival-time variations of these coherent wavefronts during 6 days and may help in developing future passive acoustic tomography systems. (C) 2013 Acoustical Society of America
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Latour, S., Voisin, C., Renard, F., Larose, E., Catheline, S., & Campillo, M. (2013). Effect of fault heterogeneity on rupture dynamics: An experimental approach using ultrafast ultrasonic imaging. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 118(11), 5888–5902.
Résumé: This study is devoted to the experimental investigation of the interaction of a propagating rupture with one or several mechanical heterogeneities. We developed a friction laboratory experiment where a soft elastic solid slides past a rigid flat plate. The system is coupled to an original medical imaging technique, ultrasound speckle interferometry, that allows observing the rupture dynamics as well as the emitted elastic shear wavefield into the solid body. We compare the dynamics of propagating rupture for a homogeneous flat interface and for three cases of heterogeneous sliding surfaces: (1) an interface with a single point-like barrier made of a small rock pebble, (2) an interface with a single linear barrier that joins the edges of the faults in a direction perpendicular to slip, and (3) an interface with multiple barriers disposed on half of its surface area, creating a heterogeneous zone. We obtain experimental observations of dynamic effects that have been predicted by numerical dynamic rupture simulations and provide experimental observations of the following phenomena: a barrier can stop or delay the rupture propagation; a linear single barrier can change the rupture velocity, increasing or decreasing it; we observe transition from subshear to supershear propagation due to the linear barrier; a large heterogeneous area slows down the rupture propagation. We observe a strong variability of the rupture dynamics occurring for identical frictional conditions, which we impute to heterogeneity of the stress field due to both the loading conditions and memory of the stress field due to previous rupture events.
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Laurendeau, A., Cotton, F., Ktenidou, O. J., Bonilla, L. F., & Hollender, F. (2013). Rock and Stiff-Soil Site Amplification: Dependency on V-S30 and Kappa (kappa(0)). BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA, 103(6), 3131–3148.
Résumé: A ground-motion prediction equation (GMPE) specific to rock and stiff-soil sites is derived using seismic motion recorded on high V-S30 sites in Japan. This GMPE applies to events with 4.5 <= M-w <= 6.9 and V-S30 ranging from 500 to 1500 m/s (stiff-soil to rock sites). The empirical site coefficients obtained and the comparison with the simulated site functions show that seismic motion on rock and stiff-soil sites does not depend only on V-S30, but also on the high-frequency attenuation site properties (kappa(0)). The effects of the site-specific kappa(0) on site amplification are analyzed using stochastic simulations, with the need to take into account both of these parameters for rock-site adjustments. Adding the site-specific kappa(0) into the GMPEs thus appears to be essential in future work. The rock-site stochastic ground-motion simulations show that the sitespecific kappa(0) controls the frequency corresponding to the maximum response spectral acceleration (f(amp)1). This observation is used to link the peak of the response spectral shape to kappa(0) in this specific Japanese dataset and then to add the effects of high-frequency attenuation into the previous GMPE from the peak ground acceleration and up to periods of 0.2 s. The inclusion of kappa(0) allows the observed bias to be corrected for the intraevent residuals and thus reduces sigma. However, this kappa(0) determination is limited to a minimum number of rock-site records with M-w >= 4: 5 and to distances of less than 50 km.
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Lavoue, F., Brossier, R., Garambois, S., Virieux, J., & Metivier, L. (2013). 2D full waveform inversion of GPR surface data: permittivity and conductivity imaging.
Résumé: In this study, we present a frequency-domain full waveform inversion (FWI) algorithm of ground-penetrating radar (GPR) data for the simultaneous reconstruction of the dielectric permittivity and electrical conductivity of the investigated material. The inverse problem is formulated as a quasiNewton optimization scheme, where the influence of the Hessian is approximated by the L-BFGS-B algorithm. Numerical tests on a cross-shaped benchmark from the literature demonstrate the need for an ad hoc scaling between the relative permittivity epsilon(r) and a relative conductivity sigma(r), through a reference conductivity sigma(o). We study the behavior of the inversion with respect to this reference conductivity and to the frequency sampling approach (simultaneous vs. sequential inversion), showing that i) the inversion process should be governed by the permittivity update to respect the natural sensitivity of the cost function and provide a reliable kinematic background soon the early iterations, ii) the value of sigma(o) should be tuned to find a compromise between resolution and noise in the final image of conductivity. We apply our scaling approach in a realistic synthetic example, illustrating that the quasi-Newton method based on the L-BFGS-B algorithm is able to reconstruct both permittivity and conductivity from multi-offset data acquired with a surface-to-surface acquisition configuration.
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Lebrouc, V., Schwartz, S., Baillet, L., Jongmans, D., & Gamond, J. F. (2013). Modeling permafrost extension in a rock slope since the Last Glacial Maximum: Application to the large Sechilienne landslide (French Alps). GEOMORPHOLOGY, 198, 189–200.
Résumé: Recent dating performed on large landslides in the Alps has revealed that the initiation of instability did not immediately follow deglaciation but occurred several thousand years after ice down-wastage in the valleys. This result indicates that debuttressing is not the immediate cause of landslide initiation. The period of slope destabilization appears to coincide with the wetter and warmer Holocene Climatic Optimum, indicating a climatic cause of landslide triggering, although the role of seismic activity cannot be ruled out. A phenomenon which may partly explain the delay between valley deglaciation and gravitational instability is the temporal persistence of thick permafrost layers developed in the Alps since the Last Glacial Maximum (LGM). This hypothesis was tested through 2D thermal numerical modeling of the large Sechilienne landslide (Romanche valley, French Alps) using plausible input parameter values. Simulation results suggest that permafrost vanished in the Sechilienne slope at 10 to 11 ka, 3000 to 4000 years following the total ice down-wastage of the Romanche valley at 14.3 ka. Permafrost persistence could have contributed to the failure delay by temporally strengthening the slope. Numerical simulations also show that the permafrost depth expansion approximately fits the thickness of ground affected by gravitational destabilization, as deduced from geophysical investigations. These results further suggest that permafrost development, associated with an ice segregation mechanism, damaged the rock slope and influenced the resulting landslide geometry. (C) 2013 Elsevier B.V. All rights reserved.
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Leclere, H., Daniel, G., Fabbri, O., Cappa, F., & Thouvenot, F. (2013). Tracking fluid pressure buildup from focal mechanisms during the 2003-2004 Ubaye seismic swarm, France. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 118(8), 4461–4476.
Résumé: Recent studies have shown that the Ubaye seismic swarm that occurred in the French southwestern Alps in 2003-2004 was triggered by fluid overpressures. This contribution provides additional constraints on the temporal and spatial changes in fluid overpressure during this swarm. The orientations of the double-couple nodal planes of an extended set of 74 focal solutions, spanning the whole 2003-2004 episode, are compared with the regional stress field. Based on a Mohr-Coulomb analysis, these comparisons provide estimates of fluid pressures along seismic fault planes. We show that the fluid overpressures required to reactivate the cohesionless fault planes vary through time, with values close to 35MPa at the inception of the swarm. Overpressures then increase up to 55MPa during the burst of seismic activity and lastly decrease down to 20MPa at the end of the crisis. We also show that the fluid overpressures are developed as patches along two parallel faults bordering a releasing bend structure characterized by low to null overpressure. The development of moderate fluid overpressure at the swarm inception enables the reactivation of normal, transtensional, and strike-slip faults while the development of larger fluid overpressures during the burst of seismic activity progressively enables the reactivation of further misoriented normal, transtensional, and transpressional faults. In order to reconcile the spatial and temporal evolution of the fluid overpressures and the seismic activity, we propose that creep compaction could be the process allowing the successive development of fluid overpressure and the migration of seismicity.
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Leroy, P., Devau, N., Revil, A., & Bizi, M. (2013). Influence of surface conductivity on the apparent zeta potential of amorphous silica nanoparticles. JOURNAL OF COLLOID AND INTERFACE SCIENCE, 410, 81–93.
Résumé: Zeta potential is a physicochemical parameter of particular importance in describing ion adsorption and double layer interactions between charged particles. However, for metal-oxide nanoparticles, the conversion of electrophoretic mobility measurements into zeta potentials is difficult. This is due to their very high surface electrical conductivity, which is inversely proportional to the size of the particle. When surface conductivity is similar to or higher than the electrical conductivity of bulk water, it can significantly lower the electrophoretic mobility of the particles. It follows that the magnitude of the apparent zeta potential determined from the Smoluchowski equation (disregarding surface conductivity) can be grossly underestimated. We use a basic Stern model to describe the electrochemical properties and to calculate the true zeta potential of amorphous silica nanoparticles immersed in NaCl solution. The parameters of our surface complexation model are adjusted by potentiometric titration and electrophoretic mobility measurements at high salinity (10(-1) M NaCl). Electrophoretic mobilities are calculated using Henry's electrokinetic transport model with specific surface conductivities and zeta potentials estimated by our surface complexation model. The very good agreement of calculated and measured electrophoretic mobilities confirms that the true zeta potential corresponds to the electrical potential at the outer Helmholtz plane (OHP). Consequently, the shear plane might be located close to the OHP. The assumption of the presence of a stagnant diffuse layer at the amorphous silica/water interface is therefore not required. (C) 2013 Elsevier Inc. All rights reserved.
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Lin, Y. N. N., Sladen, A., Ortega-Culaciati, F., Simons, M., Avouac, J. P., Fielding, E. J., et al. (2013). Coseismic and postseismic slip associated with the 2010 Maule Earthquake, Chile: Characterizing the Arauco Peninsula barrier effect. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 118(6), 3142–3159.
Résumé: Observations of coseismic and postseismic deformation associated with the 2010 Mw=8.8 Maule earthquake in south-central Chile provide constraints on the spatial heterogeneities of frictional properties on a major subduction megathrust and how they have influenced the seismic rupture and postseismic effects. We find that the bulk of coseismic slip occurs within a single elongated patch approximately 460 km long and 100 km wide between the depths of 15 and 40km. We infer three major patches of afterslip: one extends northward along strike and downdip of the major coseismic patch between 40 and 60km depth; the other two bound the northern and southern ends of the coseismic patch. The southern patch offshore of the Arauco Peninsula is the only place showing resolvable afterslip shallower than 20 km depth. Estimated slip potency associated with postseismic slip in the 1.3years following the earthquake amounts to 20-30% of that generated coseismically. Our estimates of the megathrust frictional properties show that the Arauco Peninsula area has positive but relatively low (a-b)sigma(n) values (0.01 similar to 0.22MPa), that would have allowed dynamic rupture propagation into this rate-strengthening area and afterslip. Given the only modestly rate-strengthening megathrust friction in this region, the barrier effect may be attributed to its relatively large size of the rate-strengthening patch. Coseismic and postseismic uplift of the Arauco Peninsula exceeds interseismic subsidence since the time of the last major earthquake in 1835, suggesting that coseismic and postseismic deformation has resulted in some permanent strain in the forearc.
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Lofi, J., Inwood, J., Proust, J. N., Monteverde, D. H., Loggia, D., Basile, C., et al. (2013). Fresh-water and salt-water distribution in passive margin sediments: Insights from Integrated Ocean Drilling Program Expedition 313 on the New Jersey Margin. GEOSPHERE, 9(4), 1009–1024.
Résumé: On the New Jersey shelf (offshore North America), the presence of pore water fresher than seawater is known from a series of bore-holes completed during the 1970s and 1980s. To account for this fresh water, a first hypothesis involves possible present-day active dynamic connections with onshore aquifers, while a second involves meteoritic and/or sub-ice-sheet waters during periods of lowered sea level. Expedition 313 drilled three bore-holes on the middle shelf, offering a unique opportunity for the internal structure of the siliciclastic system to be accessed, at scales ranging from the depositional matrix to the continental margin. This enables the stratigraphic architecture to be correlated with the spatial distribution and salinity of saturating fluids. Expedition 313 revealed both very low salinities (<3 g/L) at depths exceeding 400 m below the seafloor and evidence for a multilayered reservoir organization, with fresh- and/or brackish-water intervals alternating vertically with salty intervals. In this study we present a revised distribution of the salinity beneath the middle shelf. Our observations suggest that the processes controlling salinity are strongly influenced by lithology, porosity, and permeability. Saltier pore waters generally occur in coarse-grained intervals and fresher pore waters occur in fine-grained intervals. The transition from fresher to saltier intervals is often marked by cemented horizons that probably act as permeability barriers. In the lowermost parts of two holes, the salinity varies independently of lithology, suggesting different mechanisms and/or sources of salinity. We present an interpretation of the sedimentary facies distribution, derived from core, logs, and seismic profile analyses, that is used to discuss the margin-scale two-dimensional reservoir geometry and permeability distribution. These proposed geometries are of primary importance when considering the possible pathways and emplacement mechanisms for the fresh and salty water below the New Jersey shelf.
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Mahaney, W. C., Keiser, L., Krinsley, D. H., Pentlavalli, P., Allen, C. C. R., Somelar, P., et al. (2013). Weathering rinds as mirror images of palaeosols: examples from the Western Alps with correlation to Antarctica and Mars. JOURNAL OF THE GEOLOGICAL SOCIETY, 170(5), 833–847.
Résumé: Weathering rinds have been used for decades as relative age indicators to differentiate glacial deposits in long Quaternary sequences, but only recently has it been shown that rinds contain long and extensive palaeoenvironmental records that often extend far beyond mere repositories of chemical weathering on both Earth and Mars. When compared with associated palaeosols in deposits of the same age, rinds often carry a zonal weathering record that can be correlated with palaeosol horizon characteristics, with respect to both abiotic and biotic parameters. As demonstrated with examples from the French and Italian Alps, rinds in coarse clastic sediment contain weathering zones that correlate closely with horizon development in associated palaeosols of presumed Late Glacial age. In addition to weathering histories in both rinds and palaeosols, considerable evidence exists to indicate that the black mat impact (12.8 ka) reached the European Alps, a connection with the Younger Dryas readvance supported by both mineral and chemical composition. Preliminary metagenomic microbial analysis using density gradient gel electrophoresis suggests that the eubacterial microbial population found in at least one Ah palaeosol horizon associated with a rind impact site is different from that in other Late Glacial and Younger Dryas surface palaeosol horizons.
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Malvoisin, B., Brunet, F., Carlut, J., Montes-Hernandez, G., Findling, N., Lanson, M., et al. (2013). High-purity hydrogen gas from the reaction between BOF steel slag and water in the 473-673 K range. INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 38(18), 7382–7393.
Résumé: A novel method for producing hydrogen with water and BOF steel slag was developed. The steel slag was reacted with water during 2-57 days at 50 MPa for temperatures ranging from 473 to 673 K. The quantitative evolution of the slag and gas compositions indicated that the main H-2 producing reaction is: 3FeO + H2O --> Fe3O4 + H-2 At 523 K, approximately 5 NL of H-2 per kg of slag were produced in 3 days. The reaction rate was only 1.5 times faster when the slag was crushed down to an initial particle size below 50 AM. The H-2 production has been also tested on slags carbonated beforehand at 0.142 +/- 0.002 kg of CO2 per kg of slag. The reaction was found to be thermally activated. A high purity hydrogen (99.995%) is produced with non-carbonated steel slag below 573 K whereas CH4 production was measured in all the other experiments. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
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Manceau, A., & Gates, W. P. (2013). Incorporation of Al in iron oxyhydroxides: implications for the structure of ferrihydrite. CLAY MINERALS, 48(3), 481–489.
Résumé: The incomplete miscibility of Al into the ferrihydrite structure has been a recurring issue in understanding the environmental geochemistry of this important oxyhydroxide. During co-precipitation from acidic aqueous solution, ferrihydrite has been observed to accept only up to similar to 25 at.% Al without the formation of multi-phasic Al and Fe oxyhydroxides. Using basic chemistry and crystal-chemical relationships we propose here that the saturation limit of Al substitution in the structure of Fe oxyhydroxides is controlled by Al Al avoidance in a manner that conforms to Pauling's distortion rule. Employing this hypothesis, we show that the predicted miscibility limit for Al incorporation is 25 at.% in ferrihydrite and 33 at.% in goethite, in agreement with previous observations. These results indicate that the classical f-phase model for ferrihydrite best represents observations. Incorrect assignment of Fe site occupancy and other shortcomings of the akdalaite/tohdite model for ferrihydrite are also discussed.
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Manceau, A., Marcus, M. A., Grangeon, S., Lanson, M., Lanson, B., Gaillot, A. C., et al. (2013). Short-range and long-range order of phyllomanganate nanoparticles determined using high-energy X-ray scattering. JOURNAL OF APPLIED CRYSTALLOGRAPHY, 46(1), 193–209.
Résumé: High-energy X-ray scattering (HEXS) is used to explore the pH-dependent structure of randomly stacked manganese oxide nanosheets of nominal formula delta-MnO2. Data are simulated in real space by pair distribution function (PDF) analysis and in reciprocal space by both the Bragg-rod method and the Debye equation in order to maximize the information gained from the total scattering measurements. The essential new features of this triple-analysis approach are (1) the use of a two-dimensional supercell in PDF modeling to describe local distortions around Mn layer vacancies, (2) the implementation in Bragg-rod calculations of a lognormal crystal size distribution in the layer plane and an empirical function for the effect of strain, and (3) the incorporation into the model used with the Debye equation of an explicit elastic deformation of the two-dimensional nanocrystals. The PDF analysis reveals steady migration at acidic pH of the Mn atoms from layer to interlayer sites, either above or below the Mn layer vacancies, and important displacement of the remaining in-layer Mn atoms toward vacancies. The increased density of the vacancy-interlayer Mn pairs at low pH causes their mutual repulsion and results in short-range ordering. The layer microstructure, responsible for the long-range lateral disorder, is modeled with spherically and cylindrically bent crystallites having volume-averaged radii of 20-40 angstrom. The b unit-cell parameter from the hexagonal layer has different values in PDF, Bragg-rod and Debye equation modeling, because of the use of different weighting contributions from long-range and short-range distances in each method. The PDF b parameter is in effect a measure of the average inlayer Mn center dot center dot center dot Mn distance and consistently deviates from the average structure value determined by the Bragg-rod method by 0.02 angstrom at low pH, as a result of the local relaxation induced by vacancies. The layer curvature increases the Bragg-rod value by 0.01-0.02 angstrom with the cylindrical model and as much as 0.04-0.05 angstrom with the spherical model. Therefore, in principle, the diffraction alone can unambiguously determine with good accuracy only a volume-averaged apparent layer dimension of the manganese oxide nanosheets. The b parameter is model dependent and has no single straightforward interpretation, so comparison of b between different samples only makes sense if done in the context of a single specified model.
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Manceau, A., Simionovici, A., Lanson, M., Perrin, J., Tucoulou, R., Bohic, S., et al. (2013). Thlaspi arvense binds Cu(II) as a bis-(L-histidinato) complex on root cell walls in an urban ecosystem. METALLOMICS, 5(12), 1674–1684.
Résumé: Root cell walls accumulate metal cations both during acquisition from the environment and removal from the protoplast to avoid toxicity, but molecular forms of the metals under field conditions remain elusive. We have identified how copper is bound to cell walls of intact roots of native Thlaspi arvense by combining synchrotron X-ray fluorescence and absorption techniques (XANES and EXAFS) at the nano-, micro-, and bulk scales. The plants grew naturally in sediment in a stormwater runoff basin at copper concentrations typical of urban ecosystems. About 90% of acquired copper is bound in vivo to cell walls as a unique five-coordinate Cu(II)-bis(L-histidinato) complex with one L-histidine behaving as a tridentate ligand (histamine-like chelate) and the other as a bidentate ligand (glycine-like chelate). Tridentate binding of Cu(II) would provide thermodynamic stability to protect cells against copper toxicity, and bidentate binding may enable kinetic lability along the cell wall through protein-protein docking with the non-bonded imidazole group of histidine residues. EXAFS spectra are provided as ESI dagger to facilitate further identification of Cu-histidine and distinction of Cu-N from Cu-O bonds in biomolecules.
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Marsan, D., Prono, E., & Helmstetter, A. (2013). Monitoring Aseismic Forcing in Fault Zones Using Earthquake Time Series. BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA, 103(1), 169–179.
Résumé: The dynamics of earthquake occurrences is controlled both by fault interaction processes and by long-term, tectonic loading of the faults. In addition, transient loading can be caused by aseismic deformation episodes, for example during crustal fluid migration or slow slip events. These forcing transients are best revealed by geodetic measurements. However, this type of instrumentation is not always available, or is not always sensitive enough to detect significant anomalies. In such cases, one is better off exploiting the seismicity signature of these transients in order to characterize them. We here explore different ways to do so. Interearthquake time statistics are found to be prone to damping out fluctuations in forcing rate. A more accurate method is developed by comparing the data with a triggering model that accounts for earthquake interactions. The changes in fault loading rates are then well recovered, both in duration and in intensity.
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Marsan, D., Reverso, T., Helmstetter, A., & Enescu, B. (2013). Slow slip and aseismic deformation episodes associated with the subducting Pacific plate offshore Japan, revealed by changes in seismicity. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 118(9), 4900–4909.
Résumé: Aseismic phenomena, including slow slip, can alter the surrounding seismicity. We here investigate how seismicity can be used in order to reveal episodes of aseismic deformation. An objective method is proposed that accounts for both earthquake interactions and transient loading. Applying it to the 1990-2011 (pre-Tohoku) seismicity of the Japan subduction zone, we find several significant instances of aseismic transients. Small-scale and short-duration transients are favored updip of the subducting plate. Large-scale transients are mostly observed offshore Ibaraki prefecture, in a partly decoupled zone that extends downdip. The four most intense of such transients have occurred periodically every 5.9years and are likely due to slow-slip episodes. Other aseismic phenomena, including possible fluid intrusion in the outer rise, are also detected. Finally, the seismicity in January and February 2011, close to the epicenter of the megathrust Tohoku earthquake, is found to be due to aseismic loading, confirming previous studies, although this transient is only one among others and is not the most intense nor the most significant for the 21year long period studied here.
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Marti, J., Pinel, V., Lopez, C., Geyer, A., Abella, R., Tarraga, M., et al. (2013). Causes and mechanisms of the 2011-2012 El Hierro (Canary Islands) submarine eruption. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 118(3), 823–839.
Résumé: El Hierro eruption started on 10 October 2011 after an unrest episode that initiated on 17 July 2011. This is the first eruption in the Canary Islands that has been tracked in real time. Although being submarine and not directly observable, the data recorded allowed its reconstruction and to identify its causes and mechanisms. Seismicity, surface deformation, and petrological data indicate that a batch of basanitic magma coming from a reservoir located at a depth of about 25km below the El Hierro Island was emplaced at shallower depth creating a new reservoir about 10-12km above, where magma evolved until the initiation of the eruption. The characteristics of seismicity and surface deformation suggest that the necessary space to accumulate magma at this shallower position, which coincides with the crust/mantle boundary beneath El Hierro, was created in about 2months by elastic deformation and magma-driven fracturing of the crust. After this first intrusion episode, part of the magma started to migrate laterally toward the SE for nearly 20 km, always keeping the same depth and following a path apparently controlled by stress barriers created by tectonic and rheological contrasts in the upper lithosphere. This lateral migration of magma ended with a submarine eruption at about 5 km offshore from the southern corner of El Hierro Island. The total seismic energy released during the unrest episode was of 8.1 x 10(11) J, and the total uplift previous to the onset of the eruption was of 40 mm. Combining geological, geophysical, and petrological data and numerical modeling, we propose a volcanological model of the causes and mechanisms of El Hierro eruption that shows how the stress distribution in the crust beneath El Hierro, which was influenced by rheological contrasts, tectonic stresses, and gravitational loading, controlled the movement and eruption of magma. We also discuss the implications of this model in terms of eruption forecast in the Canary Islands.
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Martin, C., Debaille, V., Lanari, P., Goderis, S., Vandendael, I., Vanhaecke, F., et al. (2013). REE and Hf distribution among mineral phases in the CV-CK clan: A way to explain present-day Hf isotopic variations in chondrites. GEOCHIMICA ET COSMOCHIMICA ACTA, 120, 496–513.
Résumé: Chondrites are among the most primitive objects in the Solar System and constitute the main building blocks of telluric planets. Among the radiochronometers currently used for dating geological events, Sm-Nd and Lu-Hf are both composed of refractory, lithophile element. They are thought to behave similarly as the parent elements (Sm and Lu) are generally less incompatible than the daughter elements (Nd and Hf) during geological processes. As such, their respective average isotopic compositions for the solar system should be well defined by the average of chondrites, called Chondritic Uniform Reservoir (CHUR). However, while the Sm-Nd isotopic system shows an actual spread of less than 4% in the average chondritic record, the Lu-Hf system shows a larger variation range of 28% [Bouvier A., Vervoort J. D. and Patchett P. J. (2008) The Lu-Hf and Sm-Nd isotopic composition of CHUR: Constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets. Earth Planet. Sci. Lett. 273, 48-57]. To better understand the contrast between Sm-Nd and Lu-Hf systems, the REE and Hf distribution among mineral phases during metamorphism of Karoonda (CK) and Vigarano-type (CV) carbonaceous chondrites has been examined. Mineral modes were determined from elemental mapping on a set of five CK chondrites (from types 3-6) and one CV3 chondrite. Trace-element patterns are obtained for the first time in all the chondrite- forming minerals of a given class (CK chondrites) as well as one CV3 sample. This study reveals that REE are distributed among both phosphates and silicates. Only 30-50% of Sm and Nd are stored in phosphates (at least in chondrites types 3-5); as such, they are not mobilized during early stages of metamorphism. The remaining fraction of Sm and Nd is distributed among the same mineral phases; these elements are therefore not decoupled during metamorphism. Of the whole-rock total of Lu, the fraction held in phosphate decreases significantly as the degree of metamorphism increases (30% for types 3 and 4, less than 5% in type 6). In contrast to Lu, Hf is mainly hosted by silicates with little contribution from phosphates throughout the CK metamorphic sequence. A significant part of Sm and Nd are stored in phosphates in types 3-5, and these elements behave similarly during CK chondrite metamorphism. That explains the robustness of the Sm/ Nd ratios in chondrites through metamorphism, and the slight discrepancies observed in the present-day isotopic Nd values in chondrites. On the contrary, Lu and Hf are borne by several different minerals and consequently they are redistributed during metamorphism-induced recrystallization. The Lu/Hf ratios are therefore significantly disturbed during chondrites metamorphism, leading to the high discrepancies observed in present-day Hf isotopic values in chondrites. (C) 2013 Elsevier Ltd. All rights reserved.
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Maury, R. C., Guille, G., Guillou, H., Chauvel, C., Rossi, P., Pallares, C., et al. (2013). Temporal evolution of a Polynesian hotspot: New evidence from Raivavae (Austral islands, South Pacific ocean). BULLETIN DE LA SOCIETE GEOLOGIQUE DE FRANCE, 184(6), 557–567.
Résumé: A new geological mapping of Raivavae island, Austral-Cook linear chain, French Polynesia, combined with 10 unspiked K/Ar ages measured on its lavas, shows that it was built during two successive volcanic phases : 10.6-7.4 Ma (dykes crosscutting Rairua submarine breccias and younger subaerial Rairua flows) and 6.4-5.4 Ma (Anatonu shield volcano and associated trachytic and phonolitic domes and plugs). Geochemical data from the present study and a previous one [Lassiter et al., 2003] demonstrate that the Rairua alkali basalts, picrobasalts and basanites are more enriched in incompatible elements (especially Th and Nb) than the predominantly tholeiitic Anatonu basalts. The isotopic signature of Rairua lavas displays a strong HIMU flavour, while that of Anatonu lavas is more subdued and intermediate between DMM, HIMU and EM end-members. Rairua mafic lavas show obvious petrologic and geochemical similarities with those of the neighbouring island of Tubuai. Both could result from the partial melting of a predominantly HIMU secondary plume, which formed sucessively Mangaia (19.4-18.4 Ma), the old lavas of Rurutu (12.7-12.1 Ma), Tubuai (10.0-8.8 Ma) and Rairua volcano. The geochemical signature of the younger Anatonu lavas is ascribed to the partial melting, within the same plume, of a distinct filament of more subdued composition. Alternatively, the proportion of pyroxenites with a HIMU character was lower as partial melting degrees increased, generating the Anatonu tholeiites.
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Meslin, P. Y., Gasnault, O., Forni, O., Schroder, S., Cousin, A., Berger, G., et al. (2013). Soil Diversity and Hydration as Observed by ChemCam at Gale Crater, Mars. SCIENCE, 341(6153).
Résumé: The ChemCam instrument, which provides insight into martian soil chemistry at the submillimeter scale, identified two principal soil types along the Curiosity rover traverse: a fine-grained mafic type and a locally derived, coarse-grained felsic type. The mafic soil component is representative of widespread martian soils and is similar in composition to the martian dust. It possesses a ubiquitous hydrogen signature in ChemCam spectra, corresponding to the hydration of the amorphous phases found in the soil by the CheMin instrument. This hydration likely accounts for an important fraction of the global hydration of the surface seen by previous orbital measurements. ChemCam analyses did not reveal any significant exchange of water vapor between the regolith and the atmosphere. These observations provide constraints on the nature of the amorphous phases and their hydration.
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Metivier, L., Brossier, R., Virieux, J., & Operto, S. (2013). FULL WAVEFORM INVERSION AND THE TRUNCATED NEWTON METHOD. SIAM JOURNAL ON SCIENTIFIC COMPUTING, 35(2), B401–B437.
Résumé: Full waveform inversion (FWI) is a powerful method for reconstructing subsurface parameters from local measurements of the seismic wavefield. This method consists in minimizing the distance between predicted and recorded data. The predicted data are computed as the solution of a wave-propagation problem. Conventional numerical methods for the resolution of FWI problems are gradient-based methods, such as the preconditioned steepest descent, or more recently the l-BFGS quasi-Newton algorithm. In this study, we investigate the desirability of applying a truncated Newton method to FWI. The inverse Hessian operator plays a crucial role in the parameter reconstruction. The truncated Newton method allows one to better account for this operator. This method is based on the computation of the Newton descent direction by solving the corresponding linear system through an iterative procedure such as the conjugate gradient method. The large-scale nature of FWI problems requires us, however, to carefully implement this method to avoid prohibitive computational costs. First, this requires working in a matrix-free formalism and the capability of computing efficiently Hessian-vector products. To this purpose, we propose general second-order adjoint state formulas. Second, special attention must be paid to define the stopping criterion for the inner linear iterations associated with the computation of the Newton descent direction. We propose several possibilities and establish a theoretical link between the Steihaug-Toint method, based on trust regions, and the Eisenstat and Walker stopping criterion, designed for a method globalized by linesearch. We investigate the application of the truncated Newton method to two test cases: The first is a standard test case in seismic imaging based on the Marmousi II model. The second one is inspired by a near-surface imaging problem for the reconstruction of high-velocity structures. In the latter case, we demonstrate that the presence of large amplitude multiscattered waves prevents standard methods from converging while the truncated Newton method provides more reliable results.
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Métois, M., Socquet, A., Vigny, C., Carrizo, D., Peyrat, S., Delorme, A., et al. (2013). Revisiting the North Chile seismic gap segmentation using GPS-derived interseismic coupling. GEOPHYSICAL JOURNAL INTERNATIONAL, 194(3), 1283–1294.
Résumé: No major earthquake occurred in North Chile since the 1877 M-w 8.6 subduction earthquake that produced a huge tsunami. However, geodetic measurements conducted over the last decade in this area show that the upper plate is actually deforming, which reveals some degree of locking on the subduction interface. This accumulation of elastic deformation is likely to be released in a future earthquake. Because of the long elapsed time since 1877 and the rapid accumulation of deformation (thought to be 6-7 cm yr(-1)), many consider this area is a mature seismic gap where a major earthquake is due and seismic hazard is high. We present a new Global Positioning System (GPS) velocity field, acquired between 2008 and 2012, that describes in some detail the interseismic deformation between 18 degrees S and 24 degrees S. We invert for coupling distribution on the Nazca-South America subduction interface using elastic modelling. Our measurements require that, at these latitudes, 10 to 12 mm yr(-1) (i.e. 15 per cent of the whole convergence rate) are accommodated by the clockwise rotation of an Andean block bounded to the East by the subandean fold-and-thrust belt. This reduces the accumulation rate on the subduction interface to 56 mm yr(-1) in this area. Coupling variations on the subduction interface both along-strike and along-dip are described. We find that the North Chile seismic gap is segmented in at least two highly locked segments bounded by narrow areas of weak coupling. This coupling segmentation is consistent with our knowledge of the historical ruptures and of the instrumental seismicity of the region. Intersegment zones (Iquique, Mejillones) correlate with high background seismic rate and local tectonic complexities on the upper or downgoing plates. The rupture of either the Paranal or the Loa segment alone could easily produce a M-w 8.0-8.3 rupture, and we propose that the Loa segment (from 22.5 degrees S to 20.8 degrees S) may be the one that ruptured in 1877.
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Mewafy, F. M., Werkema, D. D., Atekwana, E. A., Slater, L. D., Aal, G. A., Revil, A., et al. (2013). Evidence that bio-metallic mineral precipitation enhances the complex conductivity response at a hydrocarbon contaminated site. JOURNAL OF APPLIED GEOPHYSICS, 98, 113–123.
Résumé: The complex conductivity signatures of a hydrocarbon contaminated site, undergoing biodegradation, near Bemidji, Minnesota were investigated. This site is characterized by a biogeochemical process where iron reduction is coupled with the oxidation of hydrocarbon contaminants. The biogeochemical transformations have resulted in precipitation of different bio-metallic iron mineral precipitates such as magnetite, ferroan calcite, and siderite. Our main objective was to elucidate the major factors controlling the complex conductivity response at the site. We acquired laboratory complex conductivity measurements along four cores retrieved from the site in the frequency range between 0.001 and 1000 Hz. Our results show the following: (1) in general higher imaginary conductivity was observed for samples from contaminated locations compared to samples from the uncontaminated location, (2) the imaginary conductivity for samples contaminated with residual and free phase hydrocarbon (smear zone) was higher compared to samples with dissolved phase hydrocarbon, (3) vadose zone samples located above locations with free phase hydrocarbon show higher imaginary conductivity magnitude compared to vadose zone samples from the dissolved phase and uncontaminated locations, (4) the real conductivity was generally elevated for samples from the contaminated locations, but not as diagnostic to the presence of contamination as the imaginary conductivity; (5) for most of the contaminated samples the imaginary conductivity data show a well-defined peak between 0.001 and 0.01 Hz, and (6) sample locations exhibiting higher imaginary conductivity are concomitant with locations having higher magnetic susceptibility. Controlled experiments indicate that variations in electrolytic conductivity and water content across the site are unlikely to fully account for the higher imaginary conductivity observed within the smear zone of contaminated locations. Instead, using magnetite as an example of the bio-metallic minerals in the contaminated location at the site, we observe a clear increase in the imaginary conductivity response with increasing magnetite content. The presence of bio-metallic mineral phases (e.g., magnetite) within the contaminated location associated with hydrocarbon biodegradation may explain the high imaginary conductivity response. Thus, we postulate that the precipitation of bio-metallic minerals at hydrocarbon contaminated sites impacts their complex conductivity signatures and should be considered in the interpretation of complex conductivity data from oil contaminated sites undergoing intrinsic bioremediation. (C) 2013 Elsevier B.V. All rights reserved.
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Mikael, A., Gueguen, P., Bard, P. Y., Roux, P., & Langlais, M. (2013). The Analysis of Long-Term Frequency and Damping Wandering in Buildings Using the Random Decrement Technique. BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA, 103(1), 236–246.
Résumé: The characterization and monitoring of buildings is an issue that has attracted the interest of many sectors over the last two decades. With the increasing use of permanent, continuous, and real-time networks, ambient vibrations can provide a simple tool for the identification of dynamic building parameters. This study is focused on the long-term variation of frequency and damping in several buildings, using the Random Decrement Technique (RDT). RDT provides a fast, robust, and accurate long-term analysis and improves the reliability of frequency and damping measurements for structural health monitoring. This reveals particularly useful information for finding out precisely how far changes in modal parameters can be related to changes in physical properties. This paper highlights the reversible changes of the structure's dynamic parameters, correlated with external forces, such as temperature and exposure to the sun. Contrasting behaviors are observed, including correlation and anticorrelation with temperature variations.
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Mino, L., Gianolio, D., Bardelli, F., Prestipino, C., Kumar, E. S., Bellarmine, F., et al. (2013). EXAFS and XANES investigation of (Li, Ni) codoped ZnO thin films grown by pulsed laser deposition. JOURNAL OF PHYSICS-CONDENSED MATTER, 25(38).
Résumé: Ni doped, Li doped and (Li, Ni) codoped ZnO thin films were successfully grown using a pulsed laser deposition technique. Undoped and doped ZnO thin films were investigated using extended x-ray absorption fine structure (EXAFS) and x-ray absorption near edge spectroscopy (XANES). Preliminary investigations on the Zn K-edge of the undoped and doped ZnO thin films revealed that doping has not influenced the average Zn-Zn bond length and Debye-Waller factor. This shows that both Ni and Li doping do not appreciably affect the average local environment of Zn. All the doped ZnO thin films exhibited more than 50% of substitutional Ni, with a maximum of 77% for 2% Ni and 2% Li doped ZnO thin film. The contribution of Ni metal to the EXAFS signal clearly reveals the presence of Ni clusters. The Ni-Ni distance in the Ni-0 nanoclusters, which are formed in the film, is shorter with respect to the reference Ni metal foil and the Debye-Waller factor is higher. Both facts perfectly reflect what is expected for metal nanoparticles. At the highest doping concentration (5%), the presence of Li favors the growth of a secondary NiO phase. Indeed, 2% Ni and 5% Li doped ZnO thin film shows %Ni-sub = 75 +/- 11, %Ni-met = 10 +/- 8, %NiO = 15 +/- 8. XANES studies further confirm that the substitutional Ni is more than 50% in all the samples. These results explain the observed magnetic properties.
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Montes-Hernandez, G., Renard, F., Chiriac, R., Findling, N., Ghanbaja, J., & Toche, F. (2013). Sequential precipitation of a new goethite-calcite nanocomposite and its possible application in the removal of toxic ions from polluted water. CHEMICAL ENGINEERING JOURNAL, 214, 139–148.
Résumé: This study proposes a simple and innovative synthesis route for a goethite-calcite nanocomposite. This synthesis is summarised by three sequential precipitation reactions: (1) precipitation of nanosized acicular goethite (alpha-FeOOH) using a high OH/Fe molar ratio (=5); (2) instantaneous precipitation of portlandite (Ca(OH)(2)) by adding CaCl2 salt to a goethite alkaline suspension (2NaOH + CaCl2 -> Ca(OH)(2) + 2NaCI) and; (3) sub-micrometric calcite precipitation by injection of CO2 into a goethite-portlandite alkaline suspension (Ca(OH)(2) + CO2 -> CaCO3 + H2O). The XRD patterns have confirmed the goethite and calcite mineral composition in the composite precipitated at 30 and 70 degrees C. FESEM and TEM observations have revealed the formation of nanosized goethite particles well dispersed with sub-micrometric calcite particles, leading to an orange-brown colour nanocomposite with high specific surface area of around 92 m(2)/g for a composite synthesized at 30 degrees C and 45 m(2)/g for a composite synthesized at 70 degrees C. Both values were determined using the conventional BET method on N-2 sorption isotherms. Finally, a goethite/calcite weight ratio equal to 0.8 in the composite was determined by Thermogravimetric Analysis (TGA). Additionally, some adsorption experiments carried out at two different pH values revealed that the goethitecalcite composite has a good sequestration capacity for Cu > Cd > As(III) > Se(IV) > As(V). Conversely, the Se(VI) did not show any chemical affinity with the goethite-calcite composite under the physico-chemical conditions studied. In practice, the goethite-calcite composite can neutralise acidic wastewater by slight calcite dissolution, enhancing the removal of heavy metals (e.g. Cu and Cd) at the calcite-solution interfaces. (C) 2012 Elsevier B.V. All rights reserved.
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Montes-Hernandez, G., Renard, F., & Lafay, R. (2013). Experimental Assessment of CO2-Mineral-Toxic Ion Interactions in a Simplified Freshwater Aquifer: Implications for CO2 Leakage from Deep Geological Storage. ENVIRONMENTAL SCIENCE & TECHNOLOGY, 47(12), 6247–6253.
Résumé: The possible intrusion of CO2 into a given freshwater aquifer due to leakage from deep geological storage involves a decrease in pH, which has been directly associated with the remobilization of hazardous trace elements via mineral dissolution and/or via desorption processes. In an effort to evaluate the potential risks to potable water quality, the present study is devoted to experimental investigation of the effects of CO2 intrusion on the mobility of toxic ions in simplified equilibrated aquifers. We demonstrate that remobilization of trace elements by CO2 intrusion is not a universal physicochemical effect. In fact goethite and calcite, two minerals frequently found in aquifers, could successfully prevent the remobilization of adsorbed Cu(II), Cd(II), Se(IV), and As(V) if CO2 is intruded into a drinking water aquifer. Furthermore, a decrease in pH resulting from CO2 intrusion could reactivate the adsorption of Se(IV) and As(V) if goethite and calcite are sufficiently available in underground layers. Our results also suggest that adsorption of cadmium and copper could be promoted by calcite dissolution. These adsorbed ions on calcite are not remobilized when CO2 is intruded into the system, but it intensifies calcite dissolution. On the other hand, arsenite As(III) is significantly adsorbed on goethite, but is partially remobilized by CO2 intrusion.
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Mora, S., Lesage, P., Albino, F., Soto, G., & Alvarado, G. E. (2013). Continuous subsidence associated to the long lasting eruption of Arenal volcano (Costa Rica) observed by dry tilt stations. Continuous subsidence associated to the long lasting eruption of Arenal volcano (Costa Rica) observed by dry tilt stations. Geological Soc. Am. Special Paper, 498, 45–56.
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Mordret, A., Landes, M., Shapiro, N. M., Singh, S. C., Roux, P., & Barkved, O. I. (2013). Near-surface study at the Valhall oil field from ambient noise surface wave tomography. GEOPHYSICAL JOURNAL INTERNATIONAL, 193(3), 1627–1643.
Résumé: We used 6 hr of continuous seismic noise records from 2320 four-component sensors of the Valhall 'Life of Field Seismic' network to compute cross-correlations (CCs) of ambient seismic noise. A beamforming analysis showed that at low frequencies (below 2 Hz) the seismic noise sources were spatially homogeneously distributed, whereas at higher frequencies (2-30 Hz), the dominant noise source was the oil platform at the centre of the network. Here, we performed an ambient noise surface wave tomography at frequencies below 2 Hz. We used vertical-component geophones CCs to extract and measure the Scholte waves group velocities dispersion curves that were then processed with a set of quality criteria and inverted to build group velocity maps of the Valhall area. Although Scholte wave group velocity depends on S wave, our group velocity maps show features similar to that was previously obtained from P-wave velocity full-waveform inversion of an active seismic data set. Since the dominant noise source at high frequency (above 3 Hz) was the oil platform, we determined a 2-D S-wave velocity model along a profile aligned with the platform by inverting group velocity dispersion curves of Love waves from transverse-component geophones CCs. We found that S-wave velocity down to 20 m was low and varied along the profile, and could be used to estimate S-wave static.
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Mordret, A., Shapiro, N. M., Singh, S., Roux, P., Montagner, J. P., & Barkved, O. I. (2013). Azimuthal anisotropy at Valhall: The Helmholtz equation approach. GEOPHYSICAL RESEARCH LETTERS, 40(11), 2636–2641.
Résumé: We used 6 h of continuous vertical records from 2320 sensors of the Valhall Life of Fields Seismic network to compute 2,690,040 cross-correlation functions between the full set of sensor pair combinations. We applied the Helmholtz tomography approach combined with the ambient noise correlation method to track the wave front across the network with every station considered as a virtual source. The gradient of the interpolated phase travel time gives us an estimate of the local phase speed and of the direction of wave propagation. By combining the individual measurements for every station, we estimated the distribution of Scholte's wave phase speeds with respect to azimuth. The observed cosine pattern indicates the presence of azimuthal anisotropy. The elliptic shape of the fast anisotropy direction is consistent with results of previous shear wave splitting studies and reflects the strong seafloor subsidence due to the hydrocarbon reservoir depletion at depth and is in good agreement with geomechanical modeling.
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Mordret, A., Shapiro, N. M., Singh, S. S., Roux, P., & Barkved, O. I. (2013). Helmholtz tomography of ambient noise surface wave data to estimate Scholte wave phase velocity at Valhall Life of the Field. GEOPHYSICS, 78(2), WA99–WA109.
Résumé: We applied the Helmholtz tomography technique to 6.5 hours of continuous seismic noise record data set of the Valhall Life of Field network. This network, that has 2320 receivers, allows us to perform a multifrequency, high-resolution, ambient-noise Scholte wave phase velocity tomography at Valhall. First, we computed crosscorrelations between all possible pairs of receivers to convert every station into a virtual source recorded by all other receivers. Our next step was to measure phase traveltimes and spectral amplitudes at different periods from crosscorrelations between stations separated by distances between two and six wavelengths. This is done in a straightforward fashion in the Fourier domain. Then, we interpolated these measurements onto a regular grid and computed local gradients of traveltimes and local Laplacians of the amplitude to infer local phase velocities using a frequency dependent Eikonal equation. This procedure was repeated for all 2320 virtual sources and final phase velocities were estimated as statistical average from all these measurements at each grid points. The resulting phase velocities for periods between 0.65 and 1.6 s demonstrate a significant dispersion with an increase of the phase velocities at longer periods. Their lateral distribution is found in very good agreement with previous ambient noise tomography done at Valhall as well as with a full waveform inversion P-wave model computed from an active seismic data set. We put effort into assessing the spatial resolution of our tomography with checkerboard tests, and we discuss the influence of the interpolation methods on the quality of our final models.
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Mousavi, Z., Walpersdorf, A., Walker, R. T., Tavakoli, F., Pathier, E., Nankali, H., et al. (2013). Global Positioning System constraints on the active tectonics of NE Iran and the South Caspian region. EARTH AND PLANETARY SCIENCE LETTERS, 377, 287–298.
Résumé: We present a velocity field compiled from a network of 27 permanent and 20 campaign GPS stations across NE Iran. This new GPS velocity field helps to investigate how Arabia-Eurasia collision deformation is accommodated at the northern boundary of the deforming zone. The present-day northward motion decreases eastward from 11 mm/yr at Tehran (similar to 52 degrees E) to 1.5 mm/yr at Mashhad (similar to 60 degrees E). N-S shortening across the Kopeh Dagh, Binalud and Koh-e-Sorkh ranges sums to 4.5 +/- 0.5 mm/yr at longitude 59 degrees E. The available GPS velocities allow us to describe the rigid-body rotation of the South Caspian about an Euler pole that is located further away than previously thought. We suggest that two new stations (MAVT and MAR2), which are sited far from the block boundaries, are most likely to indicate the full motion of the South Caspian basin. These stations suggest that NW motion is accommodated by right-lateral slip on the Ashkabad fault (at a rate of up to 7 mm/yr) and by up to 4-6 mm/yr of summed left-lateral slip across the Shahroud left-lateral strike-slip system. Our new GPS results are important for assessing seismic hazard in NE Iran, which contains numerous large population centers and possesses an abundant historical earthquake record. Our results suggest that the fault zones along the eastern Alborz and western Kopeh Dagh may accommodate slip at much faster rates than previously thought. Fully assessing the role of these faults, and the hazard that they represent, requires independent verification of their slip-rates through additional GPS measurements and geological fieldwork. (C) 2013 Elsevier B.V. All rights reserved.
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Mueller, S. B., Varley, N. R., Kueppers, U., Lesage, P., Davila, G. A. R., & Dingwell, D. B. (2013). Quantification of magma ascent rate through rockfall monitoring at the growing/collapsing lava dome of Volcan de Colima, Mexico. SOLID EARTH, 4(2), 201–213.
Résumé: The most recent eruptive phase of Volcan de Colima, Mexico, started in 1998 and was characterized by dome growth with a variable effusion rate, interrupted intermittently by explosive eruptions. Between November 2009 and June 2011, activity at the dome was mostly limited to a lobe on the western side where it had previously started overflowing the crater rim, leading to the generation of rockfall events. As a consequence of this, no significant increase in dome volume was perceivable and the rate of magma ascent, a crucial parameter for volcano monitoring and hazard assessment could no longer be quantified via measurements of the dome's dimensions. Here, we present alternative approaches to quantify the magma ascent rate. We estimate the volume of individual rockfalls through the detailed analysis of sets of photographs (before and after individual rockfall events). The relationship between volume and infrared images of the freshly exposed dome surface and the seismic signals related to the rockfall events were then investigated. Larger rockfall events exhibited a correlation between its previously estimated volume and the surface temperature of the freshly exposed dome surface, as well as the mean temperature of rockfall mass distributed over the slope. We showed that for larger events, the volume of the rockfall correlates with the maximum temperature of the newly exposed lava dome as well as a proxy for seismic energy. It was therefore possible to calibrate the seismic signals using the volumes estimated from photographs and the count of rockfalls over a certain period was used to estimate the magma extrusion flux for the period investigated. Over the course of the measurement period, significant changes were observed in number of rockfalls, rockfall volume and hence averaged extrusion rate. The extrusion rate was not constant: it increased from 0.008 +/- 0.003 to 0.02 +/- 0.007 m(3) s(-1) during 2010 and dropped down to 0.008 +/- 0.003 m(3) s(-1) again in March 2011. In June 2011, magma extrusion had come to a halt. The methodology presented represents a reliable tool to constrain the growth rate of domes that are repeatedly affected by partial collapses. There is a good correlation between thermal and seismic energies and rockfall volume. Thus it is possible to calibrate the seismic records associated with the rockfalls (a continuous monitoring tool) to improve volcano monitoring at volcanoes with active dome growth.
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Mugnier, J. L., Gajurel, A., Huyghe, P., Jayangondaperumal, R., Jouanne, F., & Upreti, B. (2013). Structural interpretation of the great earthquakes of the last millennium in the central Himalaya. EARTH-SCIENCE REVIEWS, 127, 30–47.
Résumé: A major question about the Himalaya remains open: does a great earthquake (like the Mw similar to 8.1 1934 earthquake) release all the strain stored by the Tibet-India convergence during the preceding interseismic period and only that strain, or can it also release a background store of energy that remained unreleased through one or more earlier earthquakes and so potentially engender giant events or a relatively random sequence of events? To consider this question, the history of the great earthquakes of the last millennium is investigated here by combining data provided by the historical archives of Kathmandu, trenches through surface ruptures, isoseismal damage mapping, seismites, and the instrumental record. In the Kathmandu basin, the location of the epicenter of the 1934 earthquake was determined from the arrival of high-energy P-waves that caused sedimentary dikes and ground fractures perpendicular to the epicenter azimuth. The epicenter of the Mw similar to 7.61833 earthquake can therefore be determined analogously from dike orientation, and its location to the NE of Kathmandu indicates an overlap with the Mw similar to 8.1 1934 rupture. The 1934 earthquake released strain not released by the 1833 earthquake. Comparison of the historical records of earthquakes in Kathmandu with C-14 ages from paleo-seismic trenches along the Himalayan front suggests that: (I) the 1344 Kathmandu event ruptured the surface as far away as Kumaon and was therefore a giant Mw >= 8.6 earthquake; and (2) the 1255 event that destroyed Kathmandu is attested by surface ruptures in central and western Nepal and by seismites in soft sediment as far away as Kumaon. Geometric and rheologic controls for the different types of ruptures during the medium (Mw similar to 7), great (Mw >= 8), and giant (Mw > 8.4) earthquakes are illustrated in structural cross-sections. It is found that the epicenters of great Himalayan earthquakes are located on the basal thrust farther north or close to the locked zone, which is defined from geodetic measurements of regional deformation during the interseismic period; this suggests that great earthquakes initiate in a wide transition zone between exclusively brittle and exclusively creeping regimes, the extent of which depends on the dip of the Main Himalayan Thrust. The succession of the great earthquakes during the last millennium has released all the 20-m millennial Himalayan convergence; even in the central seismic gap which has been locked since 1505, the millennial seismic release rate is close to the convergence rate. Nonetheless, no evidence of a succession of characteristic earthquakes has been found: the similar to 1100, 1833, and 1934 earthquakes in the eastern Himalaya are characterized neither by constant displacement nor by constant recurrence. Furthermore, some great earthquakes do not release all the strain elastically stored by the Himalayan and Tibetan upper crust: after the 1255 event, there was still the potential for a slip of several meters for the Mw similar to 8.1 1505 event. This suggests a rather random release of seismic energy; great earthquakes could occur anytime and in any part of the central Himalaya. Furthermore, a future giant earthquake of Mw >= 8.6 cannot be excluded. (C) 2013 Elsevier B.V. All rights reserved.
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Munoz, M., Vidal, O., Marcaillou, C., Pascarelli, S., Mathon, O., & Farges, F. (2013). Iron oxidation state in phyllosilicate single crystals using Fe-K pre-edge and XANES spectroscopy: Effects of the linear polarization of the synchrotron X-ray beam. AMERICAN MINERALOGIST, 98(7), 1187–1197.
Résumé: We investigated the influence of linear polarization of the synchrotron X-ray beam on the determination of iron oxidation state in phyllosilicates. Fe K-edge XANES spectra and pre-edge peaks have been recorded for various orientations of single crystals of biotite (Bt), clinochlore (chlorite group; Cli), talc (Tc), and antigorite (serpentine group; Ant). Ab initio XANES calculations, performed for 6 orientations of the biotite structure, support the experimental results. Depending on crystal orientation, the experimental results show, (1) important changes both for XANES and pre-edge peaks, (2) characteristic changes of spectral signatures regardless of the mineral species, (3) uncorrelated changes between XANES and pre-edge peaks, and (4) important changes of the energy position of pre-edge peaks, but with no significant change for their integrated areas. Regarding the crystal orientation, the pre-edge peak centroid varies in energy by similar to 0.4 eV in the case of Bt and Tc, and by similar to 0.2 eV for Cli and Ant. Such variations correspond to XFe3+ (i.e., Fe3+/Fe-total) of 0.22 and 0.15, respectively. Comparison with the analysis of powdered samples show that Fe-redox can be generally framed as follows: -(2/3) XFe3+ < XFe(powder)3+ < +(1/3)XFe3+. In good agreement with the so-called “magic angle” theorem for powdered samples, we propose an ideal orientation of the single crystals that provide similar pre-edge peaks as for powdered samples. With the wavevector (i.e., beam direction) perpendicular to (100) or (010), measurements should be done with an angle of 35 degrees between the electric-field vector and the [001] crystal direction. Moreover, measurements performed with the wavevector perpendicular to (001) systematically result in an overestimation of XFe3+. up to 0.07. Finally, we show that the appropriate positioning of single crystals reduces the XFe3+ uncertainty to the intrinsic error of pre-peak measurements. This approach opens possibilities for in situ analyses of Fe-bearing phyllosilicates in thin sections that are potentially relevant for scientific fields such as hydrothermal/metallogenic, metamorphic, meteoritic or environmental mineralogy.
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Nataf, H. C. (2013). Magnetic induction maps in a magnetized spherical Couette flow experiment. COMPTES RENDUS PHYSIQUE, 14(2-3), 248–267.
Résumé: The DTS experiment is a spherical Couette flow experiment with an imposed dipolar magnetic field. Liquid sodium is used as a working fluid. In a series of measurement campaigns, we have obtained data on the mean axisymmetric velocity, the mean induced magnetic field and electric potentials. All these quantities are coupled through the induction equation. In particular, a strong omega-effect is produced by differential rotation within the fluid shell, inducing a significant azimuthal magnetic field. Taking advantage of the simple spherical geometry of the experiment, I expand the azimuthal and meridional fields into Legendre polynomials and derive the expressions that relate all measurements to the radial functions of the velocity field for each harmonic degree. For small magnetic Reynolds numbers Rm the relations are linear, and the azimuthal and meridional equations decouple. Selecting a set of measurements for a given rotation frequency of the inner sphere (Rm similar or equal to 9.4), I invert simultaneously the velocity and the magnetic data and thus reconstruct both the azimuthal and the meridional fields within the fluid shell. The results demonstrate the good internal consistency of the measurements, and indicate that turbulent non-axisymmetric fluctuations do not contribute significantly to the axisymmetric magnetic induction. (C) 2012 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
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Nehme, C., Voisin, C., Mariscal, A., Gerard, P. C., Cornou, C., Jabbour-Gedeon, B., et al. (2013). The use of passive seismological imaging in speleogenetic studies: an example from Kanaan Cave, Lebanon. INTERNATIONAL JOURNAL OF SPELEOLOGY, 42(2), 97–108.
Résumé: Among many parameters that control the evolution of caves stands the volume of unconsolidated clay sediments generally produced by the alteration of the calcareous rocks. Here we introduce the use of a passive seismological imaging technique to investigate the clay deposits and estimate its total volume in a cave. Applied for the first time for speleogenesis studies, the HVSR (Horizontal / Vertical Spectral Ratio) is a geophysical technique that can help better interpret cave geomorphology. We apply seismological spectral techniques (H/V ratio) on ambient noise vibrations to derive the clay volume, as well as its shape. This technique applied on the clay volume reveals some internal details, such as fallen blocks prior to the deposit accumulation and helps to understand deposit evacuation dynamics. The study focuses on the Kanaan Cave, located in Metn District, Lebanon, and reveals new stages related to the cave speleogenesis. This technique could be applied on 'paragenetic' caves where clay volume is frequently present in order to constrain the clay volume and reconstruct the buried floor shape of the cave, underneath the clay deposit.
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Nguyen, S. T., Jeannin, L., Dormieux, L., & Renard, F. (2013). Fracturing of viscoelastic geomaterials and application to sedimentary layered rocks. MECHANICS RESEARCH COMMUNICATIONS, 49, 50–56.
Résumé: We study analytically the behavior of a viscoelastic brittle solid loaded in tension, in which fractures may grow or not depending on the amount of dissipation allowed by the viscous behavior. We highlight a threshold in extension rate, below which the solid will not be fractured. Applied to sedimentary rocks, this model shows how viscous effects can prevent fracture growth in geological formations. (C) 2013 Elsevier Ltd. All rights reserved.
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Obermann, A., Planes, T., Larose, E., & Campillo, M. (2013). Imaging preeruptive and coeruptive structural and mechanical changes of a volcano with ambient seismic noise. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 118(12), 6285–6294.
Résumé: Forecasting the location of an eruption is of primary importance for risk management in volcanic regions. Locating the underground structural changes associated with a potential eruption is also a key issue to better understand the dynamics at work in a volcano. Using recent results in wave physics, we develop an imaging procedure that is based on the sensitivity of multiply scattered waves to weak changes in heterogeneous media. This procedure allows to locate changes in both mechanical and scattering properties of the studied medium. We study ambient seismic noise from 19 broadband stations at the active volcano Piton de la Fournaise on Reunion Island, recorded from June to December 2010. During this period, two volcanic eruptions occurred at two different locations. We calculate the noise cross correlations and study two types of changes in the coda: apparent velocity variations related to changes in the elastic properties of the medium; and, waveform decoherence associated with variations in the scattering, and thus the geological structures. We observe that the temporal variations of both of these parameters provide potential precursors of volcanic eruptions at Piton de la Fournaise. The locations determined from the preeruptive and coeruptive changes in both parameters are in good agreement with the actual eruptive activities. These data demonstrate that the coda of ambient noise correlations contains deterministic information on the locations of the eruptive processes in an active volcano. Our analysis offers an original and significant constraint for the localization of forthcoming volcanic eruptions.
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Obermann, A., Planes, T., Larose, E., Sens-Schonfelder, C., & Campillo, M. (2013). Depth sensitivity of seismic coda waves to velocity perturbations in an elastic heterogeneous medium. GEOPHYSICAL JOURNAL INTERNATIONAL, 194(1), 372–382.
Résumé: Numerous monitoring applications make use of seismic coda waves to evaluate velocity changes in the Earth. This raises the question of the spatial sensitivity of coda wave-based measurements. Here, we investigate the depth sensitivity of coda waves to local velocity perturbations using 2-D numerical wavefield simulations. We calculate the impulse response at the surface before and after a slight perturbation of the velocity within a thin layer at depth is introduced. We perform a parametric analysis of the observed apparent relative velocity changes, epsilon(obs), versus the depth of the thin perturbed layer. Through the analysis of the decay of epsilon(obs), we can discriminate two different regimes: one for a shallow perturbation and the other for a deep perturbation. We interpret the first regime as the footprint of the 1-D depth sensitivity of the fundamental surface wave mode. To interpret the second regime, we need to model the sensitivity of the multiply scattered body waves in the bulk. We show that the depth sensitivity of coda waves can be modelled as a combination of bulk wave sensitivity and surface wave sensitivity. The transition between these two regimes is governed by mode conversions due to scattering. We indicate the importance of surface waves for the sensitivity of coda waves at shallow depths and at early times in the coda. At later times, bulk waves clearly dominate the depth sensitivity and offer the possibility of monitoring changes at depths below the sensitivity of the surface waves. Based on the transition between the two regimes, we can discriminate a change that occurs at the surface from a change that occurs at depth. This is illustrated for shallow depth perturbations through an example from lunar data.
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Okay, G., Cosenza, P., Ghorbani, A., Camerlynck, C., Cabrera, J., Florsch, N., et al. (2013). Localization and characterization of cracks in clay-rocks using frequency and time-domain induced polarization. GEOPHYSICAL PROSPECTING, 61(1), 134–152.
Résumé: Induced polarization (IP) is a geophysical method that is potentially sensitive to the presence of cracks in porous rocks and therefore to damage. We performed time-domain and frequency domain IP measurements at the Tournemire Underground Research Laboratory (URL, Aveyron, France) in areas where different types of cracks are observed. These cracks correspond to both tectonic fractures and new cracks associated with stress release and desiccation resulting from the excavation of a gallery. These measurements were performed both in eastern and northern galleries of the test site. The eastern gallery was excavated in 1996 while the northern gallery was excavated recently in 2008. This gives us the opportunity to study the electrical characteristics of the excavation damaged zone surrounding the galleries with respect to the age of the excavation. Longitudinal profiles were performed along the floor of the galleries with 48 Cu/CuSO4 electrodes separated by a distance of 20 cm. Chargeability and resistivity were inverted using a Gauss-Newton iterative approach assuming an isotropic heterogeneous clay-rock material. The resulting IP tomograms show a correlation between high values of chargeability and the presence of calcite-filled tectonic fractures. X-ray analysis indicates that the presence of pyrite in these fractures is a potential source of the observed IP signals. The cracks associated with the mechanical damage of the formation exhibit low values of chargeability, on the same order of magnitude than the chargeability of the clay-rock matrix and are therefore hardly observable. A smaller IP response associated with the presence of these cracks is observed in the older gallery and this observation is qualitatively related to the desaturation process associated with these cracks. In a specific area of one of the galleries, the presence of calcareous nodules is observed to be an important source of anomalous chargeability. This signature seems to be associated with the presence of pyrite.
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Pageot, D., Operto, S., Vallee, M., Brossier, R., & Virieux, J. (2013). A parametric analysis of two-dimensional elastic full waveform inversion of teleseismic data for lithospheric imaging. GEOPHYSICAL JOURNAL INTERNATIONAL, 193(3), 1479–1505.
Résumé: The development of dense networks of broad-band seismographs makes teleseismic data amenable to full-waveform inversion (FWI) methods for high-resolution lithospheric imaging. Compared to scattered-field migration, FWI seeks to involve the full seismic wavefield in the inversion. We present a parametric analysis of 2-D frequency-domain FWI in the framework of lithospheric imaging from teleseismic data to identify the main factors that impact on the quality of the reconstructed compressional (P)-wave and shear (5)-wave speed models. Compared to controlled-source seismology, the main adaptation of FWI to teleseismic configuration consists of the implementation with a scattered-filed formulation of plane-wave sources that impinge on the base of the lithospheric target located below the receiver network at an arbitrary incidence angle. Seismic modelling is performed with a hp-adaptive discontinuous Galerkin method on unstructured triangular mesh. A quasi-Newton inversion algorithm provides an approximate accounting for the Hessian operator, which contributes to reduce the footprint of the coarse acquisition geometry in the imaging. A versatile algorithm to compute the gradient of the misfit function with the adjoint-state method allows for abstraction between the forward-problem operators and the meshes that are during seismic modelling and inversion, respectively. An approximate correction for obliquity is derived for future application to real teleseismic data under the two-dimension approximation. Comparisons between the characteristic scales involved in exploration geophysics and in teleseismic seismology suggest that the resolution gain provided by full waveform technologies should be of the same order of magnitude for both applications. We first show the importance of the surface-reflected wavefield to dramatically improve the resolving power of FWI by combining tomography-like and migration-like imaging through the incorporation of the forward-scattered and the backscattered wavefields in the inversion. The resolution of FWI is assessed through checkerboard tests and confirms a resolution of the order of the wavelength for both the P and S speeds, when the full wavefield is incorporated in the inversion. Secondly, we show that computationally efficient strategies, which consist of decimating the number of frequency components involved in the inversion, do not apply to teleseismic acquisitions, because the scattering-angle bandwidth sampled by plane-wave sources can be narrow and coarsely sampled, compared to that provided by dense profiles of point sources in exploration seismology. The waveform inversion is less sensitive to the band of incidence angles spanned by the plane-wave sources and to the sampling of this band. However, the deficit of vertically propagating plane waves hampers the vertical resolution of planar layers. Aliasing artefacts created by coarse arrays of receivers are illustrated. We show how taking into account the Hessian in the inversion and the suitable management of frequencies in the inversion help to mitigate these artefacts. Acceptable reconstructions are shown for both the P- and S-wave speeds for a receiver spacing of up to 20 km in the 0.1-0.4 Hz frequency range. Building a reliable initial model for FWI is a highly non-linear problem in exploration seismology. We show how the low-frequency content of the teleseismic sources allow us to build accurate P- and S-wave speed models starting from simple vertical-gradient velocity models. All of these results are derived using a 2-D realistic synthetic experiment that was performed with noise-free data. Most of conclusions of this parametric study should apply in three dimensions. The impact of noise and the footprint of other experimental parameters such as the estimation of the temporal plane-wave signature and the estimation of the incidence angle of the impinging plane waves, need however to be assessed in the future.
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Paktunc, D., & Manceau, A. (2013). Comment on “New Clues to the Local Atomic Structure of Short-Range Ordered Ferric Arsenate from Extended X-ray Absorption Fine Structure Spectroscopy”. ENVIRONMENTAL SCIENCE & TECHNOLOGY, 47(22), 13199–13200.
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Paktunc, D., Manceau, A., & Dutrizac, J. (2013). Incorporation of Ge in ferrihydrite: Implications for the structure of ferrihydrite. AMERICAN MINERALOGIST, 98(5-6), 848–858.
Résumé: Ferrihydrite is the main form of ferric iron in surficial environments and a key reactive nanoparticle that regulates nutrient availability and the mobility of metal(loid) contaminants, yet its structure is not completely elucidated. Two models exist to date: the “f-phase” in which Fe is fully octahedral and the “akdalaite-model” possessing 20% of the Fe atoms in tetrahedral coordination. In this study, germanium was used as a structural probe to re-examine the validity of the latter model. Germanium-bearing ferrihydrites containing 0.2, 0.6, 1.4, 2.2, 2.9, 3.8, 12, and 15 wt% Ge were synthesized in the laboratory at 25 and 65 degrees C. X-ray diffraction analyses showed all the precipitates to be six-line ferrihydrite. Semi-quantitative energy-dispersive X-ray microanalyses (TEM) indicate that the precipitates made from solutions having Fe/Ge molar ratios of two and four have Fe/Ge atomic ratios of 3.8-3.9 and 4.4-5.1, respectively, which suggest a limit of Ge uptake in ferrihydrite of about 20 at% relative to total cations. Based on TEM examinations, these high Ge-bearing ferrihydrites are homogenous and consist of equant and plate-like crystallites about 5-6 nm in size. Furthermore, it appears that higher Ge concentrations in solution have no significant effect on the crystallite size, supporting the incorporation of Ge in the ferrihydrite structure. Extended X-ray absorption fine structure (EXAFS) spectroscopy indicated that the Fe atoms in both the low and high Ge-bearing ferrihydrites are in octahedral coordination and that Ge occurs in the ferrihydrite structure by filling the empty tetrahedral sites and coordinating to 4 edge-sharing FeO6 trimers through sharing a common oxygen (Ge-O-Fe linkage). Incorporation of the Ge tetrahedra in the ferrihydrite structure requires redistribution of Fe occupancy along the alternating O/OH layers while forming an ordered distribution of octahedral Fe and tetrahedral Ge. The local structure around Ge mimics a Keggin-like motif in two different, yet equivalent, orientations. It appears that the split diffraction peak at 1.46 and 1.51 A is a characteristic feature of Ge-rich ferrihydrite and suggests that it is a fingerprint of increased order due to significant Ge incorporation in the tetrahedral sites. The findings can be rationalized in terms of the incorporation of Ge in the so-called “f-phase” of the classical ferrihydrite model, and demonstrate the flexibility of the model in terms of accommodating a Keggin-like cluster without the need of imposing unrealistic constraints as in the akdalaite model. Direct comparison of the imaginary parts of the Fourier transforms for ferrihydrite and maghemite further confirms the absence of tetrahedral Fe in ferrihydrite. The absence of tetrahedral Fe substantiates the use of goethite-like or akaganeite-like models to describe the polyhedral structure of ferrihydrite used in modeling sorption reactions at the ferrihydrite-water interface.
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Panahi, H., Kobchenko, M., Renard, F., Mazzini, A., Scheibert, J., Dysthe, D., et al. (2013). A 4D Synchrotron X-Ray-Tomography Study of the Formation of Hydrocarbon-Migration Pathways in Heated Organic-Rich Shale. SPE JOURNAL, 18(2), 366–377.
Résumé: Recovery of oil from oil shales and the natural primary migration of hydrocarbons are closely related processes that have received renewed interest in recent years because of the ever tightening supply of conventional hydrocarbons and the growing production of hydrocarbons from low-permeability tight rocks. Quantitative models for conversion of kerogen into oil and gas and the timing of hydrocarbon generation have been well documented. However, lack of consensus about the kinetics of hydrocarbon formation in source rocks, expulsion timing, and how the resulting hydrocarbons escape from or are retained in the source rocks motivates further investigation. In particular, many mechanisms have been proposed for the transport of hydrocarbons from the rocks in which they are generated into adjacent rocks with higher permeabilities and smaller capillary entry pressures, and a better understanding of this complex process (primary migration) is needed. To characterize these processes, it is imperative to use the latest technological advances. In this study, it is shown how insights into hydrocarbon migration in source rocks can be obtained by using sequential high-resolution synchrotron X-ray tomography. Three-dimensional images of several immature “shale” samples were constructed at resolutions close to 5 μm. This is sufficient to resolve the source-rock structure down to the grain level, but very-fine-grained silt particles, clay particles, and colloids cannot be resolved. Samples used in this investigation came from the R-8 unit in the upper part of the Green River shale, which is organic rich, varved, lacustrine marl formed in Eocene Lake Uinta, USA. One Green River shale sample was heated in situ up to 400 degrees C as X-ray-tomography images were recorded. The other samples were scanned before and after heating at 400 degrees C. During the heating phase, the organic matter was decomposed, and gas was released. Gas expulsion from the low-permeability shales was coupled with formation of microcracks. The main technical difficulty was numerical extraction of microcracks that have apertures in the 5- to 30-mu m range (with 5 μm being the resolution limit) from a large 3D volume of X-ray attenuation data. The main goal of the work presented here is to develop a methodology to process these 3D data and image the cracks. This methodology is based on several levels of spatial filtering and automatic recognition of connected domains. Supportive petrographic and thermogravimetric data were an important complement to this study. An investigation of the strain field using 2D image correlation analyses was also performed. As one application of the 4D (space + time) microtomography and the developed workflow, we show that fluid generation was accompanied by crack formation. Under different conditions, in the subsurface, this might provide paths for primary migration.
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Pang, K. N., Arndt, N., Svensen, H., Planke, S., Polozov, A., Polteau, S., et al. (2013). A petrologic, geochemical and Sr-Nd isotopic study on contact metamorphism and degassing of Devonian evaporites in the Norilsk aureoles, Siberia. CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, 165(4), 683–704.
Résumé: Devonian evaporites and associated sedimentary rocks in the Norilsk region were contact metamorphosed during emplacement of mafic sills that form part of the end-Permian (similar to 252 Ma) Siberian Traps. We present mineralogical, geochemical and Sr-Nd isotopic data on sedimentary rocks unaffected by metamorphism, and meta-sedimentary rocks from selected contact aureoles at Norilsk, to examine the mechanisms responsible for magma-evaporite interaction and its relation to the end-Permian environmental crisis. The sedimentary rocks include massive anhydrite, rock salt, dolostone, calcareous siltstones and shale, and the meta-sedimentary rocks comprise calcareous hornfels, siliceous hornfels and minor meta-anhydrite and meta-sandstone. Contact metamorphism took place at low pressure and at maximum temperatures corresponding to the phlogopite-diopside stability field. Calcareous hornfels have high CaO, MgO, CIY2, SIY3, low SiO2 and initial Sr isotopic ratios of 0.7079-0.7092, features indicative of calcareous siltstone protoliths. Siliceous hornfels, in contrast, have high SiO2, Al2O3, Na2O, low in other major element oxides and initial Sr isotopic ratios of 0.7083-0.7152, consistent with pelitic or shaley protoliths. Loss of CO2 in a subset of calcareous hornfels can be explained by decarbonation reactions during metamorphism, but release of SO2 from evaporites cannot be accounted for by a similar mechanism. Occurrences of wollastonite and a variety of hydrous minerals in the calcareous hornfels are consistent with equilibration with hydrous fluid, which was capable of leaching large quantities of anhydrite in the presence of dissolved NaCl. In this way, substantial sediment-derived sulfur could have been mobilized, incorporated into the magmatic system and released to the atmosphere. The release of CO2 and SO2 from Siberian evaporites added to the variety of toxic gases generated during metamorphism of organic matter, coal and rock salt, contributing to the end-Permian environmental crisis.
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Parsons, C., Grabulosa, E. M., Pili, E., Floor, G. H., Roman-Ross, G., & Charlet, L. (2013). Quantification of trace arsenic in soils by field-portable X-ray fluorescence spectrometry: Considerations for sample preparation and measurement conditions. JOURNAL OF HAZARDOUS MATERIALS, 262, 1213–1222.
Résumé: Recent technological improvements have led to the widespread adoption of field portable energy dispersive X-ray fluorescence (FP-XRF) by governmental agencies, environmental consultancies and research institutions. FP-XRF units often include analysis modes specifically designed for the quantification of trace elements in soils. Using these modes, X-ray tube based FP-XRF units can offer almost “point and shoot” ease of use and results comparable to those of laboratory based instruments. Nevertheless, FP-XRF analysis is sensitive to spectral interferences as well as physical and chemical matrix effects which can result in decreased precision and accuracy. In this study, an X-ray tube-based FP-XRF analyser was used to determine trace (low ppm) concentrations of As in a floodplain soil. The effect of different sample preparation and analysis conditions on precision and accuracy were systematically evaluated. We propose strategies to minimise sources of error and maximise data precision and accuracy, achieving in situ limits of detection and precision of 6.8 ppm and 14.4%RSD, respectively for arsenic. We demonstrate that soil moisture, even in relatively dry soils, dramatically affects analytical performance with a signal loss of 37% recorded for arsenic at 20 wt% soil moisture relative to dry soil. We also highlight the importance of the use of certified reference materials and independent measurement methods to ensure accurate correction of field values. (C) 2012 Elsevier B.V. All rights reserved.
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Parsons, C. T., Couture, R. M., Omoregie, E. O., Bardelli, F., Greneche, J. M., Roman-Ross, G., et al. (2013). The impact of oscillating redox conditions: Arsenic immobilisation in contaminated calcareous floodplain soils. ENVIRONMENTAL POLLUTION, 178, 254–263.
Résumé: Arsenic contamination of floodplain soils is extensive and additional fresh arsenic inputs to the pedosphere from human activities are ongoing. We investigate the cumulative effects of repetitive soil redox cycles, which occur naturally during flooding and draining, on a calcareous fluvisol, the native microbial community and arsenic mobility following a simulated contamination event. We show through bioreactor experiments, spectroscopic techniques and modelling that repetitive redox cycling can decrease arsenic mobility during reducing conditions by up to 45%. Phylogenetic and functional analyses of the microbial community indicate that iron cycling is a key driver of observed changes to solution chemistry. We discuss probable mechanisms responsible for the arsenic immobilisation observed in-situ. The proposed mechanisms include, decreased heterotrophic iron reduction due to the depletion of labile particulate organic matter (POM), increases to the proportion of co-precipitated vs. aqueous or sorbed arsenic with alpha-FeOOH/Fe(OH)(3) and potential precipitation of amorphous ferric arsenate. (C) 2013 Elsevier Ltd. All rights reserved.
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Pattier, F., Loncke, L., Gaullier, V., Basile, C., Maillard, A., Imbert, P., et al. (2013). Mass-transport deposits and fluid venting in a transform margin setting, the eastern Demerara Plateau (French Guiana). MARINE AND PETROLEUM GEOLOGY, 46, 287–303.
Résumé: The eastern Demerara Plateau offshore French Guiana was surveyed in 2003 during the GUYAPLAC cruise (multibeam bathymetry and acoustic imagery, 6-channel seismic reflection and 3.5 kHz echo-sounding). The data show the “post-transform” Cenozoic that the series located on the outer part of the plateau (below c. 2000 m) contain at least twelve stacked mass transport deposits (MTDs) that have recorded a history of large-scale slope failure, as well as two main normal fault sets that provide possible pathways for upward fluid migration through the series, reaching at high as the uppermost MTDs. Seabed data show that the area above the failures is characterized by circular-to-elongate (slope-parallel) depressions interpreted as fluid seeps (pockmarks), some of them have been modified by along slope currents. We suggest that the development of the MTDs to results from the combinaiton of the presence of fluid overpressure at depth the geometry of the margin's deep structure, in particular the existence of a 'free borderlateral border' on the outermost plateau. Our results also emphasise the role of stratigraphic decollements within the Cenozoic series. (C) 2013 Elsevier Ltd. All rights reserved.
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Pedersen, H. A., Debayle, E., & Maupin, V. (2013). Strong lateral variations of lithospheric mantle beneath cratons – Example from the Baltic Shield. EARTH AND PLANETARY SCIENCE LETTERS, 383, 164–172.
Résumé: Understanding mechanisms for creation and evolution of Precambrian continental lithosphere requires to go beyond the large-scale seismic imaging in which shields often appear as laterally homogeneous, with a thick and fast lithosphere. We here present new results from a seismic experiment (POLENET-LAPNET) in the northern part of the Baltic Shield where we identify very high seismic velocities (Vs similar to 4.7 km/s) in the upper part of the mantle lithosphere and a velocity decrease of similar to 0.2 km/s at approximately 150 km depth. We interpret this velocity decrease as refertilisation of the lower part of the lithosphere. This result is in contrast to the lithospheric structure immediately south of the study area, where the seismic velocities within the lithosphere are fast down to 250 km depth, as well as to that of southern Norway, where there is no indication of very high velocities in the lithospheric mantle (Vs of similar to 4.4 km/s). While the relatively low velocities beneath southern Norway can tentatively be attributed to the opening of the Atlantic Ocean, the velocity decrease beneath northern Finland is not easily explained with present knowledge of surface tectonics. Our results show that shield areas may be laterally heterogeneous even over relatively short distances. Such variability may in many cases be related to lithosphere erosion and/or refertilisation at the edge of cratons, which may therefore be particularly interesting targets for seismic imaging. (C) 2013 Elsevier B.V. All rights reserved.
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Perrault, M., Gueguen, P., Aldea, A., & Demetriu, S. (2013). Using experimental data to reduce the single-building sigma of fragility curves: case study of the BRD tower in Bucharest, Romania. EARTHQUAKE ENGINEERING AND ENGINEERING VIBRATION, 12(4), 643–658.
Résumé: The lack of knowledge concerning modelling existing buildings leads to signifiant variability in fragility curves for single or grouped existing buildings. This study aims to investigate the uncertainties of fragility curves, with special consideration of the single-building sigma. Experimental data and simplified models are applied to the BRD tower in Bucharest, Romania, a RC building with permanent instrumentation. A three-step methodology is applied: (1) adjustment of a linear MDOF model for experimental modal analysis using a Timoshenko beam model and based on Anderson's criteria, (2) computation of the structure's response to a large set of accelerograms simulated by SIMQKE software, considering twelve ground motion parameters as intensity measurements (IM), and (3) construction of the fragility curves by comparing numerical interstory drift with the threshold criteria provided by the Hazus methodology for the slight damage state. By introducing experimental data into the model, uncertainty is reduced to 0.02 considering S (d) (f (1)) as seismic intensity IM and uncertainty related to the model is assessed at 0.03. These values must be compared with the total uncertainty value of around 0.7 provided by the Hazus methodology.
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Peybernes, C., Giraud, F., Jaillard, E., Robert, E., Masrour, M., Aoutem, M., et al. (2013). Stratigraphic framework and calcareous nannofossil productivity of the Essaouira-Agadir Basin (Morocco) during the Aptian-Early Albian: Comparison with the north-Tethyan margin. CRETACEOUS RESEARCH, 39, 149–169.
Résumé: In the southern Tethyan margin, the Essaouira-Agadir Basin (EAB), south of Morocco, exhibits well-exposed and fossiliferous sections of Aptian-Albian age. Biostratigraphy by ammonoids and sedimentological analysis have been realized for five sections located along an E-W transect in the EAB. The studied successions were dated from the latest Early Aptian to the Early Albian and are characterized by five major sedimentary discontinuities defining at least four main sedimentary sequences. The Late Aptian Early Albian succession can be considered a gently westward-dipping ramp, marked by a deepening upward evolution. A quantitative study of calcareous nannofossils and calcium carbonate content has been performed on three of these sections. At this time, the EAB was located in the tropical-equatorial hot arid belt. The decrease in both calcium carbonate content and Nannoconus abundances at the Aptian Albian transition could be the result of cooler climatic conditions recognized in the EAB, and/or of the associated increasing terrigenous input and nutrients, which hindered carbonate production. In the EAB, the nannofossil productivity is higher below the deposition of dark levels, which are coeval with the Niveau Paquier, recognized as the expression in southern France of the OAE 1b (Early Albian). During the Early Albian, the EAB was characterized by nannofossil fluxes two times lower than the upwelling-influenced Mazagan Plateau (southern Tethyan margin) and eight times lower than the Vocontian Basin (northern Tethyan margin). These results show that, with respect to the northern Tethyan margin, trophic conditions in sea surface waters of the pelagic realm of the southern Tethyan margin were lower. Comparable results obtained by Heldt et al. in the neritic realm of the southern Tethyan margin have been ascribed to more arid climatic conditions. (C) 2012 Elsevier Ltd. All rights reserved.
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Pichavant, M., Di Carlo, I., Rotolo, S. G., Scaillet, B., Burgisser, A., Le Gall, N., et al. (2013). Generation of CO2-rich melts during basalt magma ascent and degassing. CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, 166(2), 545–561.
Résumé: To test mechanisms of basaltic magma degassing, continuous decompressions of volatile-bearing (2.7-3.8 wt% H2O, 600-1,300 ppm CO2) Stromboli melts were performed from 250-200 to 50-25 MPa at 1,180-1,140 A degrees C. Ascent rates were varied from 0.25 to 1.5 m/s. Glasses after decompression show a wide range of textures, from totally bubble-free to bubble-rich, the latter with bubble number densities from 10(4) to 10(6) cm(-3), similar to Stromboli pumices. Vesicularities range from 0 to 20 vol%. Final melt H2O concentrations are homogeneous and always close to solubilities. In contrast, the rate of vesiculation controls the final melt CO2 concentration. High vesicularity charges have glass CO2 concentrations that follow theoretical equilibrium degassing paths, whereas glasses from low vesicularity charges show marked deviations from equilibrium, with CO2 concentrations up to one order of magnitude higher than solubilities. FTIR profiles and maps reveal glass CO2 concentration gradients near the gas-melt interface. Our results stress the importance of bubble nucleation and growth, and of volatile diffusivities, for basaltic melt degassing. Two characteristic distances, the gas interface distance (distance either between bubbles or to gas-melt interfaces) and the volatile diffusion distance, control the degassing process. Melts containing numerous and large bubbles have gas interface distances shorter than volatile diffusion distances, and degassing proceeds by equilibrium partitioning of CO2 and H2O between melt and gas bubbles. For melts where either bubble nucleation is inhibited or bubble growth is limited, gas interface distances are longer than volatile diffusion distances. Degassing proceeds by diffusive volatile transfer at the gas-melt interface and is kinetically limited by the diffusivities of volatiles in the melt. Our experiments show that CO2-oversaturated melts can be generated as a result of magma decompression. They provide a new explanation for the occurrence of CO2-rich natural basaltic glasses and open new perspectives for understanding explosive basaltic volcanism.
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Pili, E., Tisserand, D., & Bureau, S. (2013). Origin, mobility, and temporal evolution of arsenic from a low-contamination catchment in Alpine crystalline rocks. JOURNAL OF HAZARDOUS MATERIALS, 262, 887–895.
Résumé: The reduction to 10 μg/l of the limit for arsenic in drinking water led many resource managers to deal with expensive treatments. In the very common case of arsenic levels close to the recommended maximum concentration, knowing the origin and temporal evolution of As has become of great importance. Here we present a case study from an alpine basin. Arsenic speciation, isotopic compositions of pyrite, sulfate and water, and concentrations of major and trace elements demonstrate a geogenic source for arsenic linked to the dissolution of pyrite. We provide new tools to further study As at low concentrations where many processes may be masked. The observed negative correlation between delta S-34(SO4) and [As] is interpreted as a Rayleigh-type sulfur-isotope fractionation during increasing pyrite dissolution. The observed positive correlation between delta O-18(SO4) and As-V/As-III ill could help to retrieve initial redox conditions. A 3-year long monitoring at high-resolution demonstrated that drought conditions enhance pyrite dissolution whose degradation products are scavenged by recharge water. An increase in As in groundwater may result from droughts due to enhanced oxygen entry in the unsaturated zone. The 2003 European heatwave had a major effect. (C) 2012 Elsevier B.V. All rights reserved.
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Pinel, V., & Albino, F. (2013). Consequences of volcano sector collapse on magmatic storage zones: Insights from numerical modeling. JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, 252, 29–37.
Résumé: Major volcano flank collapses strongly affect the underlying magmatic plumbing system. Here, we consider the magma storage zone as a liquid pocket embedded in an elastic medium, and we perform numerical simulations in two-dimensional axisymmetric geometry as well as in three dimensions in order to evaluate the consequences of a major collapse event. We quantify the pressure decrease induced within and around a magma reservoir by a volcano flank collapse. This pressure reduction is expected to favor replenishment with less evolved magma from deeper sources. We also estimate the impact of the magma pressure decrease, together with the stress field variations around the reservoir, on the eruptive event associated with the edifice failure. We show that, for a given magma reservoir geometry, the collapse of a large strato-volcano tends to reduce the volume of the simultaneous eruption; destabilization of large edifices may even suppress magma emission, resulting in phreatic eruptions instead. This effect is greater for shallow reservoirs, and is more pronounced for spherical reservoirs than for vertically-elongated ones. It is reduced for compressible magmas containing a large amount of volatiles. Over a longer time scale, the modification of pressure conditions for dyke initiation at the chamber wall may also explain an increase in eruption rate as well as an apparent change of magma storage location. (C) 2012 Elsevier B.V. All rights reserved.
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Planes, T., & Larose, E. (2013). A review of ultrasonic Coda Wave Interferometry in concrete. CEMENT AND CONCRETE RESEARCH, 53, 248–255.
Résumé: Concrete is a multicomposite material with heterogeneities ranging in size from micrometers to centimeters.At low frequency (below 50 kHz), ultrasound propagates through concrete without suffering scattering and absorption. On the contrary, above approximate to 100 kHz, the waves strongly interact with all the heterogeneities and enter a multiple scattering regime. This regime induces 1) substantial attenuation of coherent waves (direct waves and ballistic echoes), a feature that disables most conventional imaging techniques; and 2) the onset of late arrival signals that form the ultrasonic coda. An important feature of coda waves is their very high sensitivity to weak changes in the medium. Over the last years Coda Wave Interferometry (CWI) applied to ultrasound in concrete has been widely adopted in the non-destructive testing community. This article reviews several applications based on the precise processing of ultrasonic coda, in the case of thermal and/or stress and/or damage changes. (C) 2013 Elsevier Ltd. All rights reserved.
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Plunian, F., Stepanov, R., & Frick, P. (2013). Shell models of magnetohydrodynamic turbulence. PHYSICS REPORTS-REVIEW SECTION OF PHYSICS LETTERS, 523(1), 1–60.
Résumé: Shell models of hydrodynamic turbulence originated in the seventies. Their main aim was to describe the statistics of homogeneous and isotropic turbulence in spectral space, using a simple set of ordinary differential equations. In the eighties, shell models of magnetohydrodynamic (MHD) turbulence emerged based on the same principles as their hydrodynamic counter-part but also incorporating interactions between magnetic and velocity fields. In recent years, significant improvements have been made such as the inclusion of non-local interactions and appropriate definitions for helicities. Though shell models cannot account for the spatial complexity of MHD turbulence, their dynamics are not over simplified and do reflect those of real MHD turbulence including intermittency or chaotic reversals of large-scale modes. Furthermore, these models use realistic values for dimensionless parameters (high kinetic and magnetic Reynolds numbers, low or high magnetic Prandtl number) allowing extended inertial range and accurate dissipation rate. Using modern computers it is difficult to attain an inertial range of three decades with direct numerical simulations, whereas eight are possible using shell models. In this review we set up a general mathematical framework allowing the description of any MHD shell model. The variety of the latter, with their advantages and weaknesses, is introduced. Finally we consider a number of applications, dealing with free-decaying MHD turbulence, dynamo action, Alfven waves and the Hall effect. (C) 2012 Elsevier B.V. All rights reserved.
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Poli, P., Pedersen, H. A., & Campillo, M. (2013). Noise directivity and group velocity tomography in a region with small velocity contrasts: the northern Baltic shield. GEOPHYSICAL JOURNAL INTERNATIONAL, 192(1), 413–424.
Résumé: Ambient noise tomography (ANT) is widely used to image strong velocity variations within the upper crust. Using careful processing, we obtained a 3-D model of shear velocities in the upper crust beneath northern Finland, where the lateral velocity variations are less than 3 per cent. As part of the tomography, the noise field is analysed. It is strongly heterogeneous but the signal-to-noise ratio is sufficient to obtain stable dispersion curves for all profile azimuths. Our results show that the directions of dominant noise sources of Rayleigh and Love waves are the same, but the amplitude distribution with azimuth is different for the two types of waves. More intriguingly, the high frequency Love waves are dominated by a mixture of higher modes rather than the fundamental mode. The reconstructed 3-D model shows the Lapland Granulite Belt as a high velocity body with a limit at surface in excellent agreement with geological observations at surface. Following this interface at depth, our results are compatible with previous studies suggesting an Archean north oriented subduction.
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Pourteau, A., Sudo, M., Candan, O., Lanari, P., Vidal, O., & Oberhansli, R. (2013). Neotethys closure history of Anatolia: insights from Ar-40-Ar-39 geochronology and P-T estimation in high-pressure metasedimentary rocks. JOURNAL OF METAMORPHIC GEOLOGY, 31(6), 585–606.
Résumé: The multiple high-pressure (HP), low-temperature (LT) metamorphic units of Western and Central Anatolia offer a great opportunity to investigate the subduction-and continental accretion-related evolution of the eastern limb of the long-lived Aegean subduction system. Recent reports of the HP-LT index mineral Fe-Mg-carpholite in three metasedimentary units of the Gondwana-derived Anatolide-Tauride continental block (namely the Afyon Zone, the Oren Unit and the southern Menderes Massif) suggest a more complicated scenario than the single-continental accretion model generally put forward in previous studies. This study presents the first isotopic dates (white mica Ar-40-Ar-39 geochronology), and where possible are combined with P-T estimates (chlorite thermometry, phengite barometry, multi-equilibrium thermobarometry), on carpholite-bearing rocks from these three HP-LT metasedimentary units. It is shown that, in the Afyon Zone, carpholite-bearing assemblages were retrogressed through greenschist-facies conditions at c. 67-62 Ma. Early retrograde stages in the Oren Unit are dated to 63-59 Ma. In the Kurudere-Nebiler Unit (HP Mesozoic cover of the southern Menderes Massif), HP retrograde stages are dated to c. 45 Ma, and post-collisional cooling to c. 26 Ma. These new results support that the Oren Unit represents the westernmost continuation of the Afyon Zone, whereas the Kurudere-Nebiler Unit correlates with the Cycladic Blueschist Unit of the Aegean Domain. In Western Anatolia, three successive HP-LT metamorphic belts thus formed: the northernmost Tavsanli Zone (c. 88-82 Ma), the Oren-Afyon Zone (between 70 and 65 Ma), and the Kurudere-Nebiler Unit (c. 52-45 Ma). The southward younging trend of the HP-LT metamorphism from the upper and internal to the deeper and more external structural units, as in the Aegean Domain, points to the persistence of subduction in Western Anatolia between 93-90 and c. 35 Ma. After the accretion of the Menderes-Tauride terrane, in Eocene times, subduction stopped, leading to continental collision and associated Barrovian-type metamorphism. Because, by contrast, the Aegean subduction did remain active due to slab roll-back and trench migration, the eastern limb (below Southwestern Anatolia) of the Hellenic slab was dramatically curved and consequently teared. It therefore is suggested that the possibility for subduction to continue after the accretion of buoyant (e.g. continental) terranes probably depends much on palaeogeography.
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Prieux, V., Brossier, R., Operto, S., & Virieux, J. (2013). Multiparameter full waveform inversion of multicomponent ocean-bottom-cable data from the Valhall field. Part 1: imaging compressional wave speed, density and attenuation. GEOPHYSICAL JOURNAL INTERNATIONAL, 194(3), 1640–1664.
Résumé: Multiparameter full waveform inversion (FWI) is a challenging quantitative seismic imaging method for lithological characterization and reservoir monitoring. The difficulties in multiparameter FWI arise from the variable influence of the different parameter classes on the phase and amplitude of the data, and the trade-off between these. In this framework, choosing a suitable parametrization of the subsurface and designing the suitable FWI workflow are two key methodological issues in non-linear waveform inversion. We assess frequency-domain visco-acoustic FWI to reconstruct the compressive velocity (V-P), the density () or the impedance (I-P) and the quality factor (Q(P)), from the hydrophone component, using a synthetic data set that is representative of the Valhall oil field in the North Sea. We first assess which of the (V-P, ) and (V-P, I-P) parametrizations provides the most reliable FWI results when dealing with wide-aperture data. Contrary to widely accepted ideas, we show that the (V-P, ) parametrization allows a better reconstruction of both the V-P, and I-P parameters, first because it favours the broad-band reconstruction of the dominant V-P parameter, and secondly because the trade-off effects between velocity and density at short-to-intermediate scattering angles can be removed by multiplication, to build an impedance model. This allows for the matching of the reflection amplitudes, while the broad-band velocity model accurately describes the kinematic attributes of both the diving waves and reflections. Then, we assess different inversion strategies to recover the quality factor Q(P), in addition to parameters V-P and . A difficulty related to attenuation estimation arises because, on the one hand the values of Q(P) are on average one order of magnitude smaller than those of V-P and , and on the other hands model perturbations relative to the starting models can be much higher for Q(P) than for V-P and during FWI. In this framework, we show that an empirical tuning of the FWI regularization, which is adapted to each parameter class, is a key issue to correctly account for the attenuation in the inversion. We promote a hierarchical approach where the dominant parameter V-P is reconstructed first from the full data set (i.e. without any data preconditioning) to build a velocity model as kinematically accurate as possible before performing the joint update of the three parameter classes during a second step. This hierarchical imaging of compressive wave speed, density and attenuation is applied to a real wide-aperture ocean-bottom-cable data set from the Valhall oil field. Several geological features, such as accumulation of gas below barriers of claystone and soft quaternary sediment are interpreted in the FWI models of density and attenuation. The models of V-P, and Q(P) that have been developed by visco-acoustic FWI of the hydrophone data can be used as initial models to perform visco-elastic FWI of the geophone data for the joint update of the compressive and shear wave speeds.
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Prieux, V., Lambare, G., Operto, S., & Virieux, J. (2013). Building starting models for full waveform inversion from wide-aperture data by stereotomography. GEOPHYSICAL PROSPECTING, 61, 109–137.
Résumé: Building an accurate initial velocity model for full waveform inversion (FWI) is a key issue to guarantee convergence of full waveform inversion towards the global minimum of a misfit function. In this study, we assess joint refraction and reflection stereotomography as a tool to build a reliable starting model for frequency-domain full waveform inversion from long-offset (i.e., wide-aperture) data. Stereotomography is a slope tomographic method that is based on the inversion of traveltimes and slopes of locally-coherent events in a data cube. One advantage of stereotomography compared to conventional traveltime reflection tomography is the semi-automatic picking procedure of locally-coherent events, which is easier than the picking of continuous events, and can lead to a higher density of picks. While conventional applications of stereotomography only consider short-offset reflected waves, we assess the benefits provided by the joint inversion of reflected and refracted arrivals. Introduction of the refracted waves allows the construction of a starting model that kinematically fits the first arrivals, a necessary requirement for full waveform inversion. In a similar way to frequency-domain full waveform inversion, we design a multiscale approach of stereotomography, which proceeds hierarchically from the wide-aperture to the short-aperture components of the data, to reduce the non-linearity of the stereotomographic inversion of long-offset data. This workflow which combines stereotomography and full waveform inversion, is applied to synthetic and real data case studies for the Valhall oil-field target. The synthetic results show that the joint refraction and reflection stereotomography for a 24-km maximum offset data set provides a more reliable initial model for full waveform inversion than reflection stereotomography performed for a 4-km maximum offset data set, in particular in low-velocity gas layers and in the deep part of a structure below a reservoir. Application of joint stereotomography, full waveform inversion and reverse-time migration to real data reveals that the FWI models and the reverse-time migration images computed from the stereotomography model shares several features with FWI velocity models and migrated images computed from an anisotropic reflection-traveltime tomography model, although stereotomography was performed in the isotropic approximation. Implementation of anisotropy in joint refraction and reflection stereotomography of long-offset data is a key issue to further improve the accuracy of the method.
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Putnis, C. V., Renard, F., King, H. E., Montes-Hernandez, G., & Ruiz-Agudo, E. (2013). Sequestration of Selenium on Calcite Surfaces Revealed by Nanoscale Imaging. ENVIRONMENTAL SCIENCE & TECHNOLOGY, 47(23), 13469–13476.
Résumé: Calcite, a widespread natural mineral at the Earth's surface, is well-known for its capacity to sequester various elements within its structure. Among these elements, selenium is important because of its high toxicity in natural systems and for human health. In the form of selenite (Se-(IV)), selenium can be incorporated into calcite during growth. Our in situ atomic force microscopy observations of calcite surfaces during contact with selenium-bearing solutions demonstrate that another process of selenium trapping can occur under conditions in which calcite dissolves. Upon the injection of solutions containing selenium in two states of oxidation (either Se-(IV) or Se-(VI)), precipitates were observed forming while calcite was still dissolving. In the presence of selenate (Se-(VI)), the precipitates formed remained small during the observation period. When injecting selenite (Se-(IV)), the precipitates grew significantly and were identified as CaSeO3 center dot H2O, based on SEM observations, Raman spectroscopy, and thermodynamic calculations. An interpretation is proposed where the dissolution of calcite increases the calcium concentration in a thin boundary layer in contact with the surface, allowing the precipitation of a selenium phase. This process of dissolution-precipitation provides a new mechanism for selenium sequestration and extends the range of thermodynamic conditions under which such a process is efficient.
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Quesnel, B., Gautier, P., Boulvais, P., Cathelineau, M., Maurizot, P., Cluzel, D., et al. (2013). Syn-tectonic, meteoric water-derived carbonation of the New Caledonia peridotite nappe. GEOLOGY, 41(10), 1063–1066.
Résumé: Exceptional outcrops recently exposed in the Koniambo massif allow the study of the serpentine sole of the peridotite nappe of New Caledonia (southwest Pacific Ocean). Many magnesite veins are observed, with characteristics indicating that they were emplaced during pervasive top-to-the-southwest shear deformation. The oxygen isotope composition of magnesite is homogeneous (27.4 parts per thousand < delta O-18 < 29.7 parts per thousand), while its carbon isotope composition varies widely (-16.7 parts per thousand < delta C-13 < -8.5 parts per thousand). These new data document an origin of magnesite from meteoric fluids. Laterization on top of the peridotite nappe and carbonation along the sole appear to represent complementary records of meteoric water infiltration. Based on the syn-kinematic character of magnesite veins, we propose that syn-laterization tectonic activity has enhanced water infiltration, favoring the exportation of leached elements like Mg, which has led to widespread carbonation along the serpentine sole. This calls for renewed examination of other magnesite-bearing ophiolites worldwide in order to establish whether active tectonics is commonly a major agent for carbonation.
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Quezada-Reyes, A., Lesage, P., Valdés-González, C., & Perrier, L. (2013). An analysis of the seismic activity of Popocatepetl volcano, Mexico, associated with the eruptive period of December 2002 to February 2003: looking for precursors. Geological Soc. Am.Special Paper, 498, 89–106.
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Rathbun, A. P., & Marone, C. (2013). Symmetry and the critical slip distance in rate and state friction laws. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 118(7), 3728–3741.
Résumé: We performed laboratory experiments to investigate the processes responsible for rate and state friction (RSF) behavior in fault rocks. We focused on the symmetry of the frictional constitutive response to velocity changes and the mechanics of the critical friction slip distance D-c. Experiments were conducted in double direct shear at 1 and 25 MPa normal stress, at room temperature, and for shearing velocity from 1 to 300 μm/s. We studied three granular materials and bare surfaces of Westerly granite. Ruina's law, which predicts frictional symmetry between velocity increases and decreases, better matches our data than Dieterich's law, which predicts that velocity decreases should evolve to steady state at a smaller displacement. However, for granular shear, in some cases D-c is smaller for velocity increases than for velocity decreases, contrary to expectations from either law. On bare granite surfaces, the frictional response is symmetric for velocity increases/decreases. Two distinct length scales for D-c and two-state variables are required for granular shear in some cases. We hypothesize that asymmetry and two-state behavior are caused by shear localization and changes in shear fabric in fault gouge. Our measurements show that during steady state frictional shear, dilation after a velocity increase is smaller than compaction after a decrease. Normal stress oscillations cause a marked decrease in D-c. Reduction of D-c reduces frictional stability, enhancing the possibility of seismic slip. Our experiments show that shear localization and fabric within the fault gouge can influence the RSF parameters that dictate earthquake nucleation and dynamic rupture.
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Rathbun, A. P., Renard, F., & Abe, S. (2013). Numerical investigation of the interplay between wall geometry and friction in granular fault gouge. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 118(3), 878–896.
Résumé: The influence of surface roughness is central in understanding the behavior of various types of shear zones including faults, landslides, and deformation in glacial till. All of these systems contain a non-planar rough wall, which interacts with either a gouge zone or another wall. We use the 3-D discrete element method (DEM) to investigate both the effect of boundary roughness and friction. Granular non-cohesive gouge is sandwiched between rough walls with large grooves, or smooth walls composed of spherical particles that can be adjusted to control roughness. Roughness and gouge properties are scaled to laboratory friction experiments. We vary friction between the particles and the wall and monitor shear strength, height, coordination number, distribution, and orientation of particle forces, localization, and porosity distribution in the shear zone. We find that, on the first-order, strength is controlled by particle-particle friction and mechanical coupling of the fault zone wall to the gouge. Rough boundaries (RMS roughness > grain radius) force more shear within the gouge zone, dilating the layer and sliding more grains, which leads to large stress necessary to shear the layer. When large amplitude roughness is removed, and roughness is at the grain-scale, the coupling, and thus the strength, is controlled by both wall and particle friction as well as fine-scale boundary roughness. These differences are reflected in profiles of shear within the gouge zone and offset at the boundary in smooth models. From our simulations, we quantify how and why rough natural faults will have a higher overall strength.
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Reboulet, S., Giraud, F., Colombie, C., & Carpentier, A. (2013). Integrated stratigraphy of the Lower and Middle Cenomanian in a Tethyan section (Blieux, southeast France) and correlations with Boreal basins. CRETACEOUS RESEARCH, 40, 170–189.
Résumé: A detailed stratigraphic analysis was carried out on the Lower-Middle Cenomanian hemipelagic deposits of the Blieux section (Alpes-de-Haute-Provence; southeast France) in order to identify the Middle Cenomanian event I (MCE I) in the Vocontian Basin. These deposits are represented by five bundles composed of limestone-marl alternations that are separated by thick marly intervals. The Blieux section, which is well exposed, very thick, continuous. and relatively rich in macrofauna, provides an ideal succession for an integrated approach. Biostratigraphy by ammonoids and sequence stratigraphy have been established for the whole succession whereas calcareous nannofossil and geochemical analyses have been carried out on a restricted interval across the Lower/Middle Cenomanian boundary. The uppermost part of the Mantelliceras mantelli Zone, the Mantelliceras dixoni Zone and the lower part of the Acanthoceras rhotomagense Zone have been recognized. The appearance of the genus Cunningtoniceras (C. inerme or C. cunningtoni) is used to place the base of the A. rhotomagense Zone and the Lower/Middle Cenomanian boundary. This boundary is also well characterized by the presence of nannofossil Subzone UC2C. Two orders of hierarchically stacked depositional sequences have been identified. Medium- and large-scale sequences correspond to 400 Icy eccentricity cycles and to third-order cycles, respectively. The duration of the interval studied (from the uppermost part of the M. mantelli to the lower part of the A. rhotomagense zones) is estimated to be 2.8 my. Carbon-isotope values determined from bulk carbonate sediments show a first positive excursion (+0.6 parts per thousand) corresponding to the MCE la, in the lower part of the A. rhotomagense Zone. A subsequent increase (+1.1 parts per thousand) is recorded and could correspond to MCE Ib, but a sharp return to baseline values as expected in an excursion is not observed. The duration of the MCE I is estimated to be less than 400 Icy. The Blieux section is correlated with some classical sections of the Anglo-Paris (Southerham, Folkestone, Cap Blanc-Nez) and Lower Saxony (Baddeckenstedt and Wunstorf) basins using ammonoid biostratigraphy, sequence stratigraphy, and chemostratigraphy. It is proposed as a candidate for the Middle Cenomanian GSSP (Global Boundary Stratotype Section and Point). (C) 2012 Elsevier Ltd. All rights reserved.
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Regnier, J., Cadet, H., Bonilla, L. F., Bertrand, E., & Semblat, J. F. (2013). Assessing Nonlinear Behavior of Soils in Seismic Site Response: Statistical Analysis on KiK-net Strong-Motion Data. BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA, 103(3), 1750–1770.
Résumé: This article investigates the effects of the nonlinear behavior of soils on site response, through various earthquake recordings from the KiK-net database in Japan. This network is composed of more than 688 surface-borehole instruments, from which a characterization of the shear-and compressive-wave velocity profiles down to the borehole depth is available. We selected events with a peak ground acceleration (PGA) at the downhole station of < 10 cm/s(2) in order to characterize the linear soil behavior by computing the surface to downhole spectral ratios at each site. Modifications of site-response curves computed with strong events (PGA > 50 cm/s(2)) compared to the linear characterization are supposed to be caused by nonlinear soil behavior. To describe the effects of soil nonlinear behavior on site response per event, we propose the percentage of modification (either amplification or deamplification) of the site-response curve compared to the linear evaluation (PNLev, percentage of nonlinearity) and the associated shift frequency (Sh(ev)). These parameters are used to estimate the probability that nonlinear site response is significantly different that the linear counterpart. We find that, regardless the site, this probability is important even for low input-motion PGA (values equal to or larger than 30 cm/s(2) at downhole sensor). This indicates that nonlinear soil behavior must be taken into account in site-response evaluation for moderate to strong motion. In addition, for 54 sites of the KiK-net database that have recorded at least two strong events (PGA at the downhole station > 50 cm/s(2)), we define four additional parameters that characterize the effects of soil nonlinear behavior on site responses for each site: (1) a PGA threshold (PGA(th)), defined as the PGA value for which PNLev is higher than 10%; (2) a site-specific PNL for a PGA of 50 cm/s(2) (PNLsite); (3) a site-specific shift of the predominant frequency for a PGA of 50 cm/s(2) (Sh(site)); and (4) a frequency from which we observe deamplification between nonlinear and linear site responses (fNL). We observe that nonlinear soil behavior can increase the amplification at frequencies below fNL. We find that fNL lies in between the fundamental and the predominant resonance frequencies of the site response and that sites having VS contrast close to the surface trigger nonlinear behavior at a lower input-motion PGA threshold. These results suggest that nonlinear behavior occurs mostly in the superficial soil layers. Furthermore, by investigating the nonlinear behavior of soils on earthquake horizontal-to-vertical spectral ratios at the surface, we find that they can give satisfactory results (equivalent to the analysis of borehole site responses) for the evaluation of the fNL frequency and shift frequency (Sh(site)), which indicates that part of the results obtained in this study can be extended to other databases without downhole sensors.
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Regnier, J., Michel, C., Bertrand, E., & Gueguen, P. (2013). Contribution of ambient vibration recordings (free-field and buildings) for post-seismic analysis: The case of the Mw 7.3 Martinique (French Lesser Antilles) earthquake, November 29, 2007. SOIL DYNAMICS AND EARTHQUAKE ENGINEERING, 50, 162–167.
Résumé: Following the Mw 7.3 Martinique earthquake, November 29th, 2007, a post-seismic survey was conducted by the Bureau Central Sismologique Francais (BCSF) for macroseismic intensities assessment. In addition to the inventories, ambient vibration recordings were performed close to the particularly damaged zones in the free-field and the buildings. The objective of the paper is to show the relevancy of performing ambient vibration recordings for post-earthquake surveys. The analyses of the recordings aim at explaining the variability of the damages through site effects, structure vulnerability or resonance phenomena and to help the characterization of the post-seismic building integrity. In three sites prone to site effects, we suspect damage to be related to a concordance between soil fundamental frequency and building resonance frequency. Besides, the recordings of ambient vibrations at La Trinite hospital before and after the earthquake allow us to quantify the damage due to earthquake in terms of stiffness loss. (C) 2013 Elsevier Ltd. All rights reserved.
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Renard, F., Candela, T., & Bouchaud, E. (2013). Constant dimensionality of fault roughness from the scale of micro-fractures to the scale of continents. GEOPHYSICAL RESEARCH LETTERS, 40(1), 83–87.
Résumé: Many faults and fractures in various natural and man-made materials share a remarkable common fractal property in their morphology. We report on the roughness of faults in rocks by analyzing the out-of-plane fluctuations of slip surfaces. They display a statistical power-law relationship with a nearly constant fractal exponent from millimeter scale micro-fractures in fault zones to coastlines measuring thousands of kilometers that have recorded continental breakup. A possible origin of this striking fractal relationship over 11 orders of magnitude of length scales is that all faulting processes in rocks share common characteristics that play a crucial role in the shaping of fault surfaces, such as the effects of elastic long-range stress interactions and stress screening by mechanical heterogeneities during quasi-static fracture growth. Citation: Renard, F., T. Candela, and E. Bouchaud (2013), Constant dimensionality of fault roughness from the scale of micro-fractures to the scale of continents, Geophys. Res. Lett., 40, 83-87, doi: 10.1029/2012GL054143.
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Renard, F., Montes-Hernandez, G., Ruiz-Agudo, E., & Putnis, C. V. (2013). Selenium incorporation into calcite and its effect on crystal growth: An atomic force microscopy study. CHEMICAL GEOLOGY, 340, 151–161.
Résumé: The atomic processes leading to calcite growth are still debated. The presence of foreign impurities in solution is known to change the rate of step propagation during growth as well as the growth mechanism. Among trace elements, selenium, in the form of oxyanions, can incorporate into the calcite structure by replacing the carbonate group. In the present study, we record the effect of organic and inorganic selenium on calcite growth at room temperature by using in-situ time-lapse atomic force microscopy (AFM) and we confirm the observations by performing batch reactor experiments. Our results show that the incorporation of Se(IV) during calcite growth could be observed in-situ and the presence of this element modifies the morphology of growth features formed on a cleaved calcite surface, transforming typical pyramidal spiral growth hillocks into more complex heart-shape and tear-shape patterns. This effect is reversible as changing the solution back to a selenium-free composition recovers the original hillock pattern. Conversely, Se(VI) does not incorporate, but catalyzes the step propagation rate without changing the growth pattern. We have also observed that the presence of organic selenium (Se(-II)), in the form of seleno-L-cystine, has an effect on the nucleation of calcite crystals and their aggregation in clusters, but has no measurable effect on the morphology of growing steps at the calcite surface. These results indicate that calcite could represent a reservoir of selenite, whereas selenate would remain preferentially in solution, as observed in the composition of sea waters worldwide. (C) 2013 Elsevier B.V. All rights reserved.
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Replumaz, A., Guillot, S., Villasenor, A., & Negredo, A. M. (2013). Amount of Asian lithospheric mantle subducted during the India/Asia collision. GONDWANA RESEARCH, 24(3-4), 936–945.
Résumé: Body wave seismic tomography is a successful technique for mapping lithospheric material sinking into the mantle. Focusing on the India/Asia collision zone, we postulate the existence of several Asian continental slabs, based on seismic global tomography. We observe a lower mantle positive anomaly between 1100 and 900 km depths, that we interpret as the signature of a past subduction process of Asian lithosphere, based on the anomaly position relative to positive anomalies related to Indian continental slab. We propose that this anomaly provides evidence for south dipping subduction of North Tibet lithospheric mantle, occurring along 3000 km parallel to the Southern Asian margin, and beginning soon after the 45 Ma break-off that detached the Tethys oceanic slab from the Indian continent. We estimate the maximum length of the slab related to the anomaly to be 400 km. Adding 200 km of presently Asian subducting slab beneath Central Tibet, the amount of Asian lithospheric mantle absorbed by continental subduction during the collision is at most 600 km. Using global seismic tomography to resolve the geometry of Asian continent at the onset of collision, we estimate that the convergence absorbed by Asia during the indentation process is similar to 1300 km. We conclude that Asian continental subduction could accommodate at most 45% of the Asian convergence. The rest of the convergence could have been accommodated by a combination of extrusion and shallow subduction/underthrusting processes. Continental subduction is therefore a major lithospheric process involved in intraplate tectonics of a supercontinent like Eurasia. (C) 2012 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
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Revil, A. (2013). Effective conductivity and permittivity of unsaturated porous materials in the frequency range 1 mHz-1GHz. WATER RESOURCES RESEARCH, 49(1), 306–327.
Résumé: A model combining low-frequency complex conductivity and high-frequency permittivity is developed in the frequency range from 1 mHz to 1 GHz. The low-frequency conductivity depends on pore water and surface conductivities. Surface conductivity is controlled by the electrical diffuse layer, the outer component of the electrical double layer coating the surface of the minerals. The frequency dependence of the effective quadrature conductivity shows three domains. Below a critical frequency f(p), which depends on the dynamic pore throat size Lambda, the quadrature conductivity is frequency dependent. Between f(p) and a second critical frequency f(d), the quadrature conductivity is generally well described by a plateau when clay minerals are present in the material. Clay-free porous materials with a narrow grain size distribution are described by a Cole-Cole model. The characteristic frequency f(d) controls the transition between double layer polarization and the effect of the high-frequency permittivity of the material. The Maxwell-Wagner polarization is found to be relatively negligible. For a broad range of frequencies below 1 MHz, the effective permittivity exhibits a strong dependence with the cation exchange capacity and the specific surface area. At high frequency, above the critical frequency f(d), the effective permittivity reaches a high-frequency asymptotic limit that is controlled by the two Archie's exponents m and n like the low-frequency electrical conductivity. The unified model is compared with various data sets from the literature and is able to explain fairly well a broad number of observations with a very small number of textural and electrochemical parameters. It could be therefore used to interpret induced polarization, induction-based electromagnetic methods, and ground penetrating radar data to characterize the vadose zone. Citation: Revil, A. (2013), Effective conductivity and permittivity of unsaturated porous materials in the frequency range 1 mHz-1GHz, Water Resour. Res., 49, doi:10.1029/2012WR012700.
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Revil, A. (2013). On charge accumulation in heterogeneous porous rocks under the influence of an external electric field. GEOPHYSICS, 78(4), D271–D291.
Résumé: Electric polarization is described as the sum of charge accumulations (free charge density) and orientation of polar molecules such as those of bound and free water molecules (bound charge polarization). Charge accumulation in porous materials cannot be described with Ohm's law alone. Non-equilibrium thermodynamics or the upscaling of the local Nernst-Planck equation imply that the drift of ions in porous media is controlled by the gradient of their electrochemical potentials and not solely by the electric field. In porous media, electrochemical capacitance is at least six to eight orders of magnitude larger than electrostatic capacitance associated with bound charge polarization. In other words, the low-frequency (<1 kHz) effective permittivity entering Ampere's law is six to eight orders of magnitude larger than high-frequency dielectric permittivity (measured for instance at 1 GHz). Low-frequency polarization of porous media, with no metallic particles (no electronic conductors and semiconductors) is controlled by polarization of the inner component of the electrical double layer coating the grains. This layer, called the “Stern layer,” plays a strong role in defining the cation exchange capacity of a material. A polarization model based on the polarization of the Stern layer explains a large number of experimental observations and could be used in the interpretation of hydro-and petroleum geophysical measurements.
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Revil, A., & Lu, N. (2013). Unified water isotherms for clayey porous materials. WATER RESOURCES RESEARCH, 49(9), 5685–5699.
Résumé: We provide a unified model for the soil-water retention function, including the effect of bound and capillary waters for all types of soils, including clayey media. The model combines a CEC-normalized isotherm describing the sorption of the bound water (and the filling of the trapped porosity) and the van Genuchten model to describe the capillary water sorption retention but ignore capillary condensation. For the CEC-normalized isotherm, we tested both the BET and Freundlich isotherms, and we found that the Freundlich is more suitable than the BET isotherm in fitting the data. It is also easier to combine the Freundlich isotherm with the van Genuchten model. The new model accounts for (1) the different types of clay minerals, (2) the different types of ions sorbed in the Stern layer and on the basal planes of 2:1 clays, and (3) the pore size distribution. The model is validated with different data sets, including mixtures of kaolinite and bentonite. The model parameters include two exponents (the pore size exponent of the van Genuchten model and the exponent of the Freundlich isotherm), the capillary entry pressure, and two critical water contents. The first critical water content is the water content at saturation (porosity), and the second is the maximum water content associated with adsorption forces, including the trapped nonbound water.
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Revil, A., & Mahardika, H. (2013). Coupled hydromechanical and electromagnetic disturbances in unsaturated porous materials. WATER RESOURCES RESEARCH, 49(2), 744–766.
Résumé: A theory of cross-coupled flow equations in unsaturated soils is necessary to predict (1) electroosmotic flow with application to electroremediation and agriculture, (2) the electroseismic and the seismoelectric effects to develop new geophysical methods to characterize the vadose zone, and (3) the streaming current, which can be used to investigate remotely ground water flow in unsaturated conditions in the capillary water regime. To develop such a theory, the cross-coupled generalized Darcy and Ohm constitutive equations of transport are extended to unsaturated conditions. This model accounts for inertial effects and for the polarization of porous materials. Rather than using the zeta potential, like in conventional theories for the saturated case, the key parameter used here is the quasi-static volumetric charge density of the pore space, which can be directly computed from the quasi-static permeability. The apparent permeability entering Darcy's law is also frequency dependent with a critical relaxation time that is, in turn, dependent on saturation. A decrease of saturation increases the associated relaxation frequency. The final form of the equations couples the Maxwell equations and a simplified form of two-fluid phases Biot theory accounting for water saturation. A generalized expression of the Richard equation is derived, accounting for the effect of the vibration of the skeleton during the passage of seismic waves and the electrical field. A new expression is obtained for the effective stress tensor. The model is tested against experimental data regarding the saturation and frequency dependence of the streaming potential coupling coefficient. The model is also adapted for two-phase flow conditions and a numerical application is shown for water flooding of a nonaqueous phase liquid (NAPL, oil) contaminated aquifer. Seismoelectric conversions are mostly taking place at the NAPL (oil)/water encroachment front and can be therefore used to remotely track the position of this front. This is not the case for other geophysical methods. Citation: Revil, A., and H. Mahardika (2013), Coupled hydromechanical and electromagnetic disturbances in unsaturated porous materials, Water Resour. Res., 49, doi: 10.1002/wrcr.20092.
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Revil, A., Eppehimer, J. D., Skold, M., Karaoulis, M., Godinez, L., & Prasad, M. (2013). Low-frequency complex conductivity of sandy and clayey materials. JOURNAL OF COLLOID AND INTERFACE SCIENCE, 398, 193–209.
Résumé: Low-frequency polarization of sands and sandstones seems to be dominated by the polarization of the Stern layer, the inner part of the electrical double layer coating the surface of the silica grains and clay particles. We investigate a simple model of Stern layer polarization combined with a simple complexation model of the surface of the grains immersed in a 1:1 electrolyte like NaCl. In isothermal conditions, the resulting model can be used to predict the complex conductivity of clayey materials as a function of the porosity, the cation exchange capacity of the clay fraction (alternatively the specific surface area of the material), and the salinity of the pore water. A new set of experimental data is presented. This dataset comprises low-frequency (1 mHz-45 kHz) complex conductivity measurements of saprolites and sandstones that are well characterized in terms of their petrophysical properties (porosity, permeability, specific surface area or CEC, and pore size). This dataset, together with incorporating additional data from the literature, is used to test the Stern layer polarization model. We find an excellent agreement between the predictions of this model and this experimental dataset indicating that the new model can be used to predict the complex conductivity of natural clayey materials and clay-free silica sands. (C) 2013 Elsevier Inc. All rights reserved.
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Revil, A., Karaoulis, M., Srivastava, S., & Byrdina, S. (2013). Thermoelectric self-potential and resistivity data localize the burning front of underground coal fires. GEOPHYSICS, 78(5), B258–B272.
Résumé: Self-potential signals and resistivity data can be jointly inverted or analyzed to track the position of the burning front of an underground coal-seam fire. We first investigate the magnitude of the thermoelectric coupling associated with the presence of a thermal anomaly (thermoelectric current associated with a thermal gradient). A sandbox experiment is developed and modeled to show that in presence of a heat source, a negative self-potential anomaly is expected at the ground surface. The expected sensitivity coefficient is typically on the order of -0.5 mV degrees C-1 in a silica sand saturated by demineralized water. Geophysical field measurements gathered at Marshall (near Boulder, CO) show clearly the position of the burning front in the electrical resistivity tomogram and in the self-potential data gathered at the ground surface with a negative self-potential anomaly of about -50 mV. To localize more accurately the position of the burning front, we developed a strategy based on two steps: (1) We first jointly invert resistivity and self-potential data using a cross-gradient approach, and (2) a joint interpretation of the resistivity and self-potential data is made using a normalized burning front index (NBI). The value of the NBI ranges from 0 to 1 with 1 indicating a high probability to find the burning front (strictly speaking, the NBI is, however, not a probably density). We validate first this strategy using synthetic data and then we apply it to the field data. A clear source is localized at the expected position of the burning front of the coal-seam fire. The NBI determined from the joint inversion is only slightly better than the value determined from independent inversion of the two geophysical data sets.
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Revil, A., Skold, M., Karaoulis, M., Schmutz, M., Hubbard, S. S., Mehlhorn, T. L., et al. (2013). Hydrogeophysical investigations of the former S-3 ponds contaminant plumes, Oak Ridge Integrated Field Research Challenge site, Tennessee. GEOPHYSICS, 78(4), EN29–EN41.
Résumé: At the Oak Ridge Integrated Field Research Challenge site, near Oak Ridge, Tennessee, contaminants from the former S-3 ponds have infiltrated the shallow saprolite for over 60 years. Two-and three-dimensional DC-resistivity tomography is used to characterize the number and location of the main contaminant plumes, which include high concentration of nitrate. These contaminant plumes have typically an electrical resistivity in the range 2-20 ohm-m while the background saprolite resistivity is in the range 60-120 ohm-m, so the difference of resistivity can be easily mapped using DC-resistivity tomography to locate the contaminant pathways. We develop a relationship to derive the in situ nitrate concentrations from the 3D resistivity tomograms accounting for the effect of surface conductivity. The footprint of the contamination upon the resistivity is found to be much stronger than the local variations associated with changes in the porosity and the clay content. With this method, we identified a total of five main plumes (termed CP1 to CP5). Plume CP2 corresponds to the main plume in terms of nitrate concentration (similar to 50,000 mgL(-1)). We also used an active time constrained approach to perform time-lapse resistivity tomography over a section crossing the plumes CP1 and CP2. The sequence of tomograms is used to determine the changes in the nitrate concentrations associated with infiltration of fresh (meteoritic) water from a perched aquifer. This study highlights the importance of accounting for surface conductivity when characterizing plume distributions in clay-rich subsurface systems.
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Revil, A., Woodruff, W. F., Torres-Verdin, C., & Prasad, M. (2013). Complex conductivity tensor of anisotropic hydrocarbon-bearing shales and mudrocks. GEOPHYSICS, 78(6), D403–D418.
Résumé: A model was recently introduced to describe the complex electrical conductivity and high-frequency dielectric constant of isotropic clayey porous materials. We generalized that approach to the case of anisotropic and tight hydrocarbon-bearing shales and mudrocks by introducing tensorial versions of formation factor and tortuosity. In-phase and quadrature conductivity tensors have common eigenvectors, but the eigenvectors of the dielectric tensor may be different due to influence of the solid phase at high frequencies. In-phase and quadrature contributions to complex electrical conductivity depend on saturation, salinity, porosity, temperature, and cation exchange capacity (alternatively, specific surface area) of the porous material. Kerogen is likely to have a negligible contribution to the cation exchange capacity of the material because all exchangeable sites in the functional groups of organic matter may have been polymerized during diagenesis. An anisotropic experiment is performed to validate some of the properties described by the proposed model, especially to verify that the electrical anisotropy factor is the same for in-phase and quadrature conductivities. We used two samples from the Bakken formation. Experimental data confirm the validity of the model. Also, the range of values for cation exchange capacity determined when implementing the new model with experimental data agree with the known range of cation exchange capacity for the Bakken shale. Measurements indicate that the bulk-space tortuosity in the direction normal to bedding plane can be higher than 100.
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Revil, A., Wu, Y., Karaoulis, M., Hubbard, S. S., Watson, D. B., & Eppehimer, J. D. (2013). Geochemical and geophysical responses during the infiltration of fresh water into the contaminated saprolite of the Oak Ridge Integrated Field Research Challenge site, Tennessee. WATER RESOURCES RESEARCH, 49(8), 4952–4970.
Résumé: At the Oak Ridge Integrated Field Research Challenge (IFRC) site, Tennessee, the saprolitic aquifer was contaminated by leaks from the former S-3 disposal ponds between 1951 and 1983. The chemistry of the contaminant plume is also episodically impacted by fresh meteoritic water infiltrating vertically from a shallow variably saturated perched zone and the ditch surrounding the former S-3 ponds. We performed a column experiment using saprolite from the contaminated aquifer to understand the geochemical and complex electrical conductivity signatures associated with such events. The changes in the pH and pore water ionic strength are responsible for measurable changes in both the in-phase and quadrature conductivities. The pore water conductivity can be related to the nitrate concentration (the main ionic species in the plume) while the release of uranium is controlled by the pH. We developed a simple model to determine the pore water conductivity and pH from the recorded complex conductivity. This model is applied to time-lapse resistivity data at the IFRC site. Time-lapse inversion of resistivity data, performed with an active time constrain approach, shows the occurrence of an infiltration event during the winter of 2008-2009 with a dilution of the pore water chemistry and an increase of the pH. A simple numerical simulation of the infiltration of fresh water into the unconfined contaminated aquifer is consistent with this scenario. Key Points <list list-type=“bulleted”> Complex conductivity is related to pore water and interfacial chemistry Surface conductivity cannot be neglected in ERT Time-lapse ERT is used to monitor an infiltration event.
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Reynard, B., Godard, M., & Guillot, S. (2013). Preface: Serpentinites from mid-oceanic ridges to subduction. LITHOS, 178, 1–2.
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Riel, N., Guillot, S., Jaillard, E., Martelat, J. E., Paquette, J. L., Schwartz, S., et al. (2013). Metamorphic and geochronogical study of the Triassic El Oro metamorphic complex, Ecuador: Implications for high-temperature metamorphism in a forearc zone. LITHOS, 156, 41–68.
Résumé: In the forearc of the Andean active margin in southwest Ecuador, the El Oro metamorphic complex exhibits a well exposed tilted forearc section partially migmatized. We used Raman spectroscopy on carbonaceous matter (RSCM) thermometry and pseudosections coupled with mineralogical and textural studies to constrain the pressure-temperature (P-T) evolution of the El Oro metamorphic complex during Triassic times. Our results show that anatexis of the continental crust occurred by white-mica and biotite dehydration melting along a 10 km thick crustal domain (from 4.5 to 8 kbar) with increasing temperature from 650 to 700 degrees C. In the biotite dehydration melting zone, temperature was buffered at 750-820 degrees C in a 5 km thick layer. The estimated average thermal gradient during peak metamorphism is of 30 degrees C/km within the migmatitic domain can be partitioned into two apparent gradients parts. The upper part from surface to 7 km depth records a 40-45 degrees C/km gradient. The lower part records a quasi-adiabatic geotherm with a 10 degrees C/km gradient consistent with an isothermal melting zone. Migmatites U-Th-Pb geochronology yielded zircon and monazite ages of 229.3 +/- 2.1 Ma and 224.5 +/- 2.3 Ma, respectively. This thermal event generated S-type magmatism (the Marcabeli granitoid) and was immediately followed by underplating of the high-pressure low-temperature (HP-LT) Arenillas-Panupali unit at 225.8 +/- 1.8 Ma. The association of high-temperature low-pressure (HT-LP) migmatites with HP-LT unit constitutes a new example of a paired metamorphic belt along the South American margin. We propose that in addition to crustal thinning, underplating of the Piedras gabbroic unit before 230 Ma provided the heat source necessary to foster crustal anatexis. Furthermore, its MORB signature shows that the asthenosphere was involved as the source of the heat anomaly. S-type felsic magmatism is widespread during this time and suggests that a large-scale thermal anomaly affected a large part of the South American margin during the late Triassic. We propose that crustal anatexis is related to an anomaly that arose during subduction of the Panthalassa ocean under the South American margin. Slab verticalization or slab break-off can be invoked as the origin of the upwelling of the asthenosphere. (C) 2012 Elsevier B.V. All rights reserved.
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Rittgers, J. B., Revil, A., Karaoulis, M., Mooney, M. A., Slater, L. D., & Atekwana, E. A. (2013). Self-potential signals generated by the corrosion of buried metallic objects with application to contaminant plumes. GEOPHYSICS, 78(5), EN65–EN82.
Résumé: Large-amplitude (>100 mV) negative electric (self)-potential anomalies are often observed in the vicinity of buried metallic objects and ore bodies or over groundwater plumes associated with organic contaminants. To explain the physical and chemical mechanisms that generate such electrical signals, a controlled laboratory experiment was carried out involving two metallic cylinders buried with vertical and horizontal orientations and centered through and in the capillary fringe within a sandbox. The 2D and 3D self-potential (SP) data were collected at several time steps along with collocated pH and redox potential measurements. Large dipolar SP and redox potential anomalies developed in association with the progressive corrosion of the vertical pipe, although no anomalies were observed in the vicinity of the horizontal pipe. This discrepancy was due to the orientation of the pipes with the vertical pipe subjected to a significantly larger EH gradient. Accounting for the electrical conductivity distribution, the SP data were inverted to recover the source current density vector field using a deterministic least-squares 4D (time-lapse) finite-element modeling approach. These results were then used to retrieve the 3D distribution of the redox potential along the vertical metallic cylinder. The results of the inversion were found to be in excellent agreement with the measured distribution of the redox potential. This experiment indicated that passively recorded electrical signals can be used to nonintrusively monitor corrosion processes. In addition, vertical electrical potential profiles measured through a mature hydrocarbon contaminated site were consistent with the sandbox observations, lending support to the geobattery model over organic contaminant plumes.
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Rodriguez, M. P., Carretier, S., Charrier, R., Saillard, M., Regard, V., Herail, G., et al. (2013). Geochronology of pediments and marine terraces in north-central Chile and their implications for Quaternary uplift in the Western Andes. GEOMORPHOLOGY, 180, 33–46.
Résumé: In north-central Chile, a wide shore platform is morphologically connected with a high fluvial terrace and a pediment. The eastward extension of Quaternary coastal uplift in the Southern Central Andes is poorly constrained since no age correlation between marine and continental landforms has been reported. We use Al-26 and Be-10 concentrations to constrain the geomorphic evolution of these marine and continental landforms near the Choapa valley (31.6 degrees S). Be-10 ages for the shore platform indicate that this surface was repeatedly reoccupied during sea-level highstands between similar to 800 and 500 ka and uplifted after 500 ka. While 'zero erosion' ages for the pediment between similar to 600 and 300 ka only partly overlap the shore platform age range, more realistic exposure ages calculated for an erosion rate of 1 m/Ma are between similar to 945 and 475 ka, fitting the age range of the correlated shore platform. Be-10 concentrations of the high fluvial terrace are highly scattered evidencing vertical mixing of clasts probably due to slow lowering of the surface. Although it is not possible to determine an age for this landform, the scattering among its Be-10 concentrations implies that this marker is several hundreds of thousands of years old and that the high fluvial terrace began to form at similar to 1200 ka or after. Finally, Be-10 concentrations of the high fluvial terrace, the pediment and the shore platform are of the same order of magnitude, which is consistent with the clear morphologic correlation between these three types of landforms. These data suggest that the marine and continental landforms studied formed synchronously, with some local differences, during a long period of relative tectonic stability between similar to(1200?) 800 and 500 ka and uplifted after 500 ka. Our results confirm recent studies showing a post-400 +/- 100 ka renewal of uplift along the Pacific coast after a Lower to Middle Pleistocene period of slow uplift. Moreover, the extension of the surfaces suggests that a broad region of similar to 40 km has been uplifted ca. 150 m during the Quaternary. (c) 2012 Elsevier B.V. All rights reserved.
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Rodriguez-Marek, A., Cotton, F., Abrahamson, N. A., Akkar, S., Al Atik, L., Edwards, B., et al. (2013). A Model for Single-Station Standard Deviation Using Data from Various Tectonic Regions. BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA, 103(6), 3149–3163.
Résumé: Correctly accounting for the uncertainty in ground-motion prediction is a critical component of probabilistic seismic-hazard analysis (PSHA). This prediction is commonly achieved using empirical ground-motion prediction equations. The differences between the observed and predicted ground-motion parameters are generally assumed to follow a normal distribution with a mean of zero and a standard deviation sigma. Recent work has focused on the development of partially nonergodic PSHA, where the repeatable effects of site response on ground-motion parameters are removed from their total standard deviation. The resulting value is known as single-station standard deviation or single-station sigma. If event-to-event variability is also removed from the single-station standard deviation, the resulting value is referred to as the event-corrected single-station standard deviation (phi(ss)). In this work, a large database of ground motions from multiple regions is used to obtain global estimates of these parameters. Results show that the event-corrected single-station standard deviation is remarkably stable across tectonic regions. Various models for this parameter are proposed accounting for potential magnitude and distance dependencies. The article also discusses requirements for using single-station standard deviation in a PSHA. These include the need for an independent estimate of the site term (e. g., the repeatable component of the ground-motion residual at a given station) and properly accounting for the epistemic uncertainty in both the site term and the site-specific single-station standard deviation. Values for the epistemic uncertainty on phi(ss) are proposed based on the station-to-station variability of this parameter.
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Rostom, F., Royne, A., Dysthe, D. K., & Renard, F. (2013). Effect of fluid salinity on subcritical crack propagation in calcite. TECTONOPHYSICS, 583, 68–75.
Résumé: The slow propagation of cracks, also called subcritical crack growth, is a mechanism of fracturing responsible for a ductile deformation of rocks under crustal conditions. In the present study, the double-torsion technique was used to measure the effect of fluid chemistry on the slow propagation of cracks in calcite single crystals at room temperature. Time-lapse images and measurements of force and load-point displacement allowed accurate characterization of crack velocities in a range of 10(-8) to 10(-4) m/s. Velocity curves as a function of energy-release rates were obtained for different fluid compositions, varying NH4Cl and NaCl concentrations. Our results show the presence of a threshold in fluid composition, separating two regimes: weakening conditions where the crack propagation is favored, and strengthening conditions where crack propagation slows down. We suggest that electrostatic surface forces that modify the repulsion forces between the two surfaces of the crack may be responsible for this behavior. (C) 2012 Elsevier B.V. All rights reserved.
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Rouby, D., Braun, J., Robin, C., Dauteuil, O., & Deschamps, F. (2013). Long-term stratigraphic evolution of Atlantic-type passive margins: A numerical approach of interactions between surface processes, flexural isostasy and 3D thermal subsidence. TECTONOPHYSICS, 604, 83–103.
Résumé: The thermal and flexural evolution of passive margins is impacted by the (un)loading effects of erosion/sedimentation processes, which, in turn, affect their relief and sediment accumulation. These complex couplings are recorded by the stratigraphic trend of the associated sedimentary basins, which is controlled by the balance between sediment accumulation, subsidence and eustasy. Our objective is to constrain the relative contribution of the factors controlling the mechanical response of the lithosphere and the efficiency of the surface processes on parameters such as the denudation/accumulation and uplift/subsidence history and long-term stratigraphic trends. The novel aspect of our approach is to integrate the evolution of both domains in erosion and in sedimentation, using state of the art modeling of the flexure of the lithosphere including the surface processes (erosion/sedimentation) and the thermal evolution, as well as concepts in sequence stratigraphy. We investigated numerically the post-rift evolution of passive margins, testing the influence of the lithosphere's initial geometries, thermal states and stretching profiles as well as the efficiency of the surface processes. In all simulations, the initial flexural rift-shoulder is eroded away within 10 to 20 Myr. In the following stages, the sedimentary supply and the evolution of the margin are mostly controlled by the flexural response to the thermal relaxation of the isotherms by cooling and the (un)loading mass transfer at the surface. Both the sediment accumulation (controlled by relief relaxation) and the subsidence rates decrease exponentially with time. The evolution of their relative values forms a regressive/transgressive sequence. We show that variations in the efficiency of the surface processes may impact the uplift/subsidence histories and the long-term stratigraphic trend within the same range of magnitude as lithospheric parameters such as pre-rift crust thickness or depth dependency of stretching. The initial crustal thickness is then determinant in the denudation/accumulation history whereas the margin width will impact the uplift/subsidence history the second most. Depth of necking and effective elastic thickness are critical mostly during the initial phase of the margin history (syn- and immediate post-rift) whereas bulk sediment density and lithosphere thickness become critical in the late post-rift. (C) 2013 Elsevier B.V. All rights reserved.
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Roux, P., Kuperman, W. A., Cornuelle, B. D., Aulanier, F., Hodgkiss, W. S., & Song, H. C. (2013). Analyzing sound speed fluctuations in shallow water from group-velocity versus phase-velocity data representation. JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, 133(4), 1945–1952.
Résumé: Data collected over more than eight consecutive hours between two source-receiver arrays in a shallow water environment are analyzed through the physics of the waveguide invariant. In particular, the use of vertical arrays on both the source and receiver sides provides source and receiver angles in addition to travel-times associated with a set of eigenray paths in the waveguide. From the travel-times and the source-receiver angles, the eigenrays are projected into a group-velocity versus phase-velocity (Vg-Vp) plot for each acquisition. The time evolution of the Vg-Vp representation over the 8.5-h long experiment is discussed. Group speed fluctuations observed for a set of eigenrays with turning points at different depths in the water column are compared to the Brunt-Vaisala frequency. (C) 2013 Acoustical Society of America.
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Roux, P., Marandet, C., Nicolas, B., & Kuperman, W. A. (2013). Experimental measurement of the acoustic sensitivity kernel. JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, 134(1), EL38–EL44.
Résumé: In the Born approximation, the acoustic scattering from a spherical obstacle of a size comparable to the acoustic wavelength can be evaluated in the framework of the sensitivity kernel approach, which describes the relationship between the pressure-field fluctuation and the position of a local change in the propagation medium. The spatial structure of the sensitivity kernel is here investigated through experimental observations made in a water tank at the ultrasonic scale and compared to an analytical model. The pattern of the sensitivity kernel is discussed in the case of a source-to-receiver wave field that includes a direct path and one surface reflection. (C) 2013 Acoustical Society of America
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Sandikkaya, M. A., Akkar, S., & Bard, P. Y. (2013). A Nonlinear Site-Amplification Model for the Next Pan-European Ground-Motion Prediction Equations. BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA, 103(1), 19–32.
Résumé: A site-amplification model for shallow crustal regions that considers both linear and nonlinear soil effects is proposed. The original functional form of the model was developed by Walling et al. (2008) (WAS08) using stochastic simulations and site-response analysis. The major difference between the proposed model and WAS08 is that our site-amplification expression is entirely based on empirical data. To comply with this objective, a database with the most recent V-S30 information from the pan-European region has been compiled. This feature of the model encourages its use for the future ground-motion prediction equations (GMPEs) that will be devised particularly for this region. Worldwide accelerograms are also considered to have a better representation of the soil behavior under strong-motion excitations. As an auxiliary tool a GMPE for reference-rock sites is also developed to calculate the site-amplification factors. The coefficients of the site-amplification model as well as the reference-rock model are computed by applying the random-effects regression technique proposed by Abrahamson and Youngs (1992). Preliminary results of this article suggest a more comprehensive study for the revision of site factors in Eurocode 8 (European Committee for Standardization [CEN], 2004).
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Sarret, G., Smits, E. A. H. P., Michel, H. C., Isaure, M. P., Zhao, F. J., & Tappero, R. (2013). Use of Synchrotron-Based Techniques to Elucidate Metal Uptake and Metabolism in Plants (Vol. 119).
Résumé: Synchrotron techniques have become key components of the toolbox for studying the mechanisms involved in metal(loid) uptake and metabolism in plants. Most widely used techniques in this field include micro-X-ray fluorescence (mu XRF) for imaging the distribution of elements in plant tissues and cells and quantifying them, and X-ray absorption spectroscopy (XAS) for determining their chemical forms. Recent advances in terms of spatial resolution, sensitivity and versatility of the sample environment have opened new perspectives for the study of trace elements at the micro- and nanoscale with a minimal perturbation of the sample. Sample conditioning remains a key issue for the study of metals in plants. Cryogenic sample environments allow work on hydrated systems, with a limited risk of metal remobilization and changes in speciation. Still, radiation damage should be monitored carefully, especially for high-flux spectrometers. In addition, progress in software for data analysis has facilitated data mining and integration of results from various techniques. This chapter presents the principle and the basics of data analysis for μXRF imaging and tomography, XAS and micro-Fourier transform infrared spectromicroscopy (mu FTIR). Major results obtained on Ni, Cd, Zn, Se, As, Cu, Mn and nanoparticles in hyperaccumulating and nonaccumulating plants are presented. Complementary approaches including histochemical techniques, micro and nanoscopic techniques using electron- or ion beams, and laser ablation coupled with inductively coupled plasma mass spectrometry (ICP-MS) are also presented, and key results reviewed. Finally, there is also great interest in coupling synchrotron techniques, which is possible on more and more beamlines, and also in coupling synchrotron techniques with other approaches such as the ones mentioned above; perspectives in this area are discussed.
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Savelieva, G. N., Batanova, V. G., Berezhnaya, N. A., Presnyakov, S. L., Sobolev, A. V., Skublov, S. G., et al. (2013). Polychronous formation of mantle complexes in ophiolites. GEOTECTONICS, 47(3), 167–179.
Résumé: The paper presents new determinations of the U-Pb zircon age of high-Al chromitite from dunite of the mantle section of the Voikar-Synya massif at the Kershor site in the boundary zone with rocks of the dunite-wehrlite-clinopyroxenite complex. The high-Cr chromitite from dunite in the central part of the same massif contains zircon dated at ca. 0.6 Ga [10]. It is suggested that Paleoproterozoic (2.0-1.9 Ga) zircons from chromitites of the mantle section near the petrological Moho boundary were formed in the course of partial melting of peridotites and/or their interaction with migrating MORB-type melts. The occurrence of Vendian and Paleoproterozoic zircons in chromitites from different parts of the mantle section, as well as previously published petrological, geochemical, and geological data [2, 11, 22] allow us to suggest a complex multistage evolution of the mantle section in ophiolites. The arguments stated below show that chromitites and host dunites could have been formed at different times and were probably related to different processes. Thus, not only various complexes of the pre-Paleozoic oceanic crust reworked in the suprasubduction setting differ in age, but also the mantle rock of similar petrography, vary in the time of their formation.
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Schaeffer, N. (2013). Efficient spherical harmonic transforms aimed at pseudospectral numerical simulations. GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, 14(3), 751–758.
Résumé: In this paper, we report on very efficient algorithms for spherical harmonic transform (SHT). Explicitly vectorized variations of the algorithm based on the Gauss-Legendre quadrature are discussed and implemented in the SHTns library, which includes scalar and vector transforms. The main breakthrough is to achieve very efficient on-the-fly computations of the Legendre-associated functions, even for very high resolutions, by taking advantage of the specific properties of the SHT and the advanced capabilities of current and future computers. This allows us to simultaneously and significantly reduce memory usage and computation time of the SHT. We measure the performance and accuracy of our algorithms. Although the complexity of the algorithms implemented in SHTns are in O(N-3) (where N is the maximum harmonic degree of the transform), they perform much better than any third-party implementation, including lower-complexity algorithms, even for truncations as high as N=1023. SHTns is available at https://bitbucket.org/nschaeff/shtns as open source software.
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Schlegel, M. L., & Manceau, A. (2013). Binding mechanism of Cu(II) at the clay-water interface by powder and polarized EXAFS spectroscopy. GEOCHIMICA ET COSMOCHIMICA ACTA, 113, 113–124.
Résumé: The sorption mechanism of Cu(II) on the 2:1 magnesian clay hectorite, the 2:1 aluminous clay montmorillonite, and the 1:1 aluminous clay kaolinite was investigated at pH 5.4-6.0 and 0.5 M NaCl ionic strength by solution chemistry and powder and polarized XANES and EXAFS spectroscopy. Divalent copper was not photoreduced under the intense synchrotron X-ray beam and retained its usual square (bi)pyramidal coordination with four equatorial oxygens (O-eq) at 1.93-1.96 angstrom and one to two axial oxygens (O-ax) at 2.56-2.58 angstrom. The angular dependence of XANES spectra, the measured angle of 57-58 degrees between the Cu-O-eq atomic pair and the direction perpendicular to the clay layer plane ([001]*), and the detection and polarization dependence of neighboring Al/Mg and Si cationic shells, together indicate that Cu(II) is bonded to the edges of the clay layers as an inner-sphere complex. Based on the number of Mg/Al and Si nearest neighbors, the Cu(O-eq)(4)(O-ax)(1-2) polyhedron is attached to the clay surface by sharing one to three edges with the structural Al/Mg octahedra and zero to three corners with the Si/Al tetrahedra. Copper has an unusually high coordination on the two dioctahedral aluminous clays, explained by the presence at their surface of distorted empty cavities which can accommodate irregular coordination polyhedra. The steric match between the distorted empty octahedral cavities and the Jahn-Teller distorted Cu polyhedra provides a rationale to explain the higher affinity of Cu(II) for Al octahedral sheets, including the hydrargillite sheet of lithiophorite ([Al,Li][MnO2]-O-2[OH](2)) as observed in nature. (c) 2013 Elsevier Ltd. All rights reserved.
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Schmitt, D., Cardin, P., La Rizza, P., & Nataf, H. C. (2013). Magneto-Coriolis waves in a spherical Couette flow experiment. EUROPEAN JOURNAL OF MECHANICS B-FLUIDS, 37, 10–22.
Résumé: The dynamics of fluctuations in a fast rotating spherical Couette flow experiment in the presence of a strong dipolar magnetic field is investigated in detail, through a thorough analysis of the experimental data as well as a numerical study. Fluctuations within the conducting fluid (liquid sodium) are characterized by the presence of several oscillation modes, identified as magneto-Coriolis (MC) modes, with definite symmetry and azimuthal number. A numerical simulation provides eigensolutions which exhibit oscillation frequencies and magnetic signatures comparable to the observation. The main characteristics of these hydromagnetic modes is that the magnetic contribution has a fundamental influence on the dynamical properties through the Lorentz forces, although its importance remains weak in an energetical point of view. Another specificity is that the Lorentz forces are confined near the inner sphere where the dipolar magnetic field is the strongest, while the Coriolis forces are concentrated in the outer fluid volume close to the outer sphere. (C) 2012 Elsevier Masson SAS. All rights reserved.
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Schubnel, A., Brunet, F., Hilairet, N., Gasc, J., Wang, Y. B., & Green, H. W. (2013). Deep-Focus Earthquake Analogs Recorded at High Pressure and Temperature in the Laboratory. SCIENCE, 341(6152), 1377–1380.
Résumé: Phase transformations of metastable olivine might trigger deep-focus earthquakes (400 to 700 kilometers) in cold subducting lithosphere. To explore the feasibility of this mechanism, we performed laboratory deformation experiments on germanium olivine (Mg2GeO4) under differential stress at high pressure (P = 2 to 5 gigapascals) and within a narrow temperature range (T = 1000 to 1250 kelvin). We found that fractures nucleate at the onset of the olivine-to-spinel transition. These fractures propagate dynamically (at a nonnegligible fraction of the shear wave velocity) so that intense acoustic emissions are generated. Similar to deep-focus earthquakes, these acoustic emissions arise from pure shear sources and obey the Gutenberg-Richter law without following Omori's law. Microstructural observations prove that dynamic weakening likely involves superplasticity of the nanocrystalline spinel reaction product at seismic strain rates.
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Schwartz, S., Guillot, S., Reynard, B., Lafay, R., Debret, B., Nicollet, C., et al. (2013). Pressure-temperature estimates of the lizardite/antigorite transition in high pressure serpentinites. LITHOS, 178, 197–210.
Résumé: Serpentine minerals in natural samples are dominated by lizardite and antigorite. In spite of numerous laboratory experiments, the stability fields of these species remain poorly constrained. This paper presents petrological observations and the Raman spectroscopy and XRD analyses of natural serpentinites from the Alpine paleo-accretionary wedge. Serpentine varieties were identified from a range of metamorphic pressure and temperature conditions from sub-greenschist (P<4 kbar, T similar to 200-300 degrees C) to eclogite facies conditions (P>20 kbar, T>460 degrees C) along a subduction geothermal gradient. We use the observed mineral assemblage in natural serpentinite along with the T-max estimated by Raman spectroscopy of the carbonaceous matter in associated metasediments to constrain the temperature of the lizardite to antigorite transition at high pressures. We show that below 300 degrees C, lizardite and locally chrysotile are the dominant species in the mesh texture. Between 320 and 390 degrees C, lizardite is progressively replaced by antigorite at the grain boundaries through dissolution-precipitation processes in the presence of SiO2 enriched fluids and in the cores of the lizardite mesh. Above 390 degrees C, under high-grade blueschist to eclogite facies conditions, antigorite is the sole stable serpentine mineral until the onset of secondary olivine crystallization at 460 degrees C. (C) 2012 Elsevier B.V. All rights reserved.
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Senouci, A., Bard, P., Farsi, M., Beck, E., & Cartier, S. (2013). Robustness and uncertainties of seismic damage estimates at urban scale: a methodological comparison on the example of the city of Oran (Algeria). BULLETIN OF EARTHQUAKE ENGINEERING, 11(4), 1191–1215.
Résumé: The city of Oran is exposed to a significant seismic hazard, as almost all the northern Algeria territory, where numerous casualties and severe damage occurred in the last decades due to several moderate to large earthquakes. A mitigation policy should include the establishment of priorities to reduce the vulnerability of existing buildings based on the knowledge of the actual urban fabrics. The complexity of vulnerability assessment requires a gradual approach from the urban scale to the building scale. The study reported in this paper corresponds to the first step of such an approach, i.e., a preliminary study of the seismic vulnerability and expected damage within an urban district of the city of Oran, based on a non-dedicated data base from a building survey previously performed for other purposes. The main goals of this study are twofold: (1) an assessment of the degree of uncertainty and robustness of such results through a comparison of the results derived from different urban vulnerability methods (GNDT 2; RISK-UE LM1; and VULNERALP 2.0) and (2) an assessment of the actual level of seismic risk in the city of Oran. Cross-method comparisons and correlations highlight a satisfactory agreement between mean damage estimates at the urban scale, despite significant scattering at the single building scale, and uncertainty levels which vary significantly from one method to the other. For a given scenario, the three methods provide damage estimates lying within half an EMS damage degree of one another, with some systematic positive bias for VULNERALP and negative bias for RISK-UE LM1, especially for masonry buildings. The expected mean damage is very important for intensities 9 and 10, with an average damage grade around 3-4 for intensity 9 and 4-5 for intensity 10. The spatial distribution of damage systematically exhibits larger values in the northern, older, commercial area, than in the southern, more recent and more residential area, in relation to the building typology and the existence of several aggravating factors. Some areas of higher vulnerability / damage can be distinguished, which should receive particular attention for retrofitting priorities or urban planning decisions, also taking into account their cultural heritage value.
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Simionovici, A. S., Lemelle, L., Cloetens, P., Sole, V. A., Tresseras, J. A. S., Butterworth, A. L., et al. (2013). Quantification of Element Abundances of Stardust Interstellar Candidates by Synchrotron Radiation X-Ray Fluorescence Spectroscopy. METEORITICS & PLANETARY SCIENCE, 48, A318.
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Simon-Labric, T., Brocard, G. Y., Teyssier, C., van der Beek, P. A., Fellin, M. G., Reiners, P. W., et al. (2013). Preservation of contrasting geothermal gradients across the Caribbean-North America plate boundary (Motagua Fault, Guatemala). TECTONICS, 32(4), 993–1010.
Résumé: Strike-slip plate boundaries juxtapose crustal blocks that may have different geodynamic origins and therefore different thermal structures. Thermo-kinematic modeling of this type of strike-slip plate boundary predicts an asymmetric signature in the low-temperature thermochronologic record across the fault. Age-elevation profiles of zircon (U-Th)/He ages across the Motagua Fault, a 500km long segment of the transform boundary between the North American and Caribbean plates, document a sharp cooling age discontinuity across the fault. This discontinuity could be interpreted as a difference in denudation history on each side of the fault. However, a low-relief Miocene erosional surface extends across the fault; this surface has been uplifted and incised and provides a geomorphic argument against differential denudation across the fault. By integrating magmatic, volcanic, and heat flow data, age-elevation profiles, and thermo-kinematic modeling, we propose that large horizontal displacement along the Motagua Fault has offset a persistent geothermal asymmetry across the fault and explains both the age discontinuities and the age-elevation patterns. This study illustrates how thermochronology can be used to detect large strike-slip displacements and more generally opens new perspectives in understanding the impact of nonuniform thermal structures on thermochronologic results.
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Sissmann, O., Daval, D., Brunet, F., Guyot, F., Verlaguet, A., Pinquier, Y., et al. (2013). The deleterious effect of secondary phases on olivine carbonation yield: Insight from time-resolved aqueous-fluid sampling and FIB-TEM characterization. Chemical Geology, 357, 186–202.
Résumé: Geological storage of CO2 in mafic and ultramafic rocks relies on the dissolution of their silicate components, followed by the precipitation of carbonates, the overall process being commonly referred to as carbonation. To gain a better understanding of the rate-and yield-controlling factors of mineral carbonation, three batch experiments were conducted in CO2-saturated water, at (a) 90 degrees C, (b) 120 degrees C and (c) 170 degrees C, respectively (with citrate ligands added to the 90 degrees C experiment) in a Ti-reactor at pCO(2) = 280 bar, using San Carlos olivine (Fo(88)) as a model mineral of (ultra) mafic environments. Those physicochemical conditions were purposely chosen so as to promote the dissolution rate of olivine. (a) At 90 degrees C, similar to 40 wt.% of olivine were dissolved within 3 weeks, a result which suggests that the passivation barrier evidenced in previous studies carried out in citrate-free media had been overcome. However, while saturation with respect to magnesite was overstepped in this experiment, the carbonation yield remained below similar to 1 wt.%, which we attributed to the slow kinetics of magnesite precipitation. (b) At 120 degrees C, the concentration of Mg and Si monitored by aqueous fluid sampling reached an apparent plateau for over 4 weeks, at conditions close to saturation with respect to amorphous silica, and with Fe concentration being below the detection limit. A resumption of the dissolution process was subsequently observed while the concentration of Fe suddenly increased in solution. The concentration plateau was attributed either to the formation of a protective Si-Fe(III) layer, or to the occurrence of Fe(III) phases clogging the porosity of a secondary silica layer. The resumption of olivine dissolution was ascribed to the increasingly reducing conditions that led to the breakdown of the protective phases. This late resumption led to a carbonation yield slightly above 2 wt.%. (c) At 170 degrees C, Fe was incorporated into a presumably permeable Fe-rich phyllosilicate layer, so that the dissolution process was likely less affected by such an interfacial layer. Nevertheless, carbonate minerals still formed in low quantity (similar to 6 wt.%), while other amorphous phases represented the main sink for Mg cations. Overall, this study emphasizes that achieving carbonation reactions in reducing environments and circum-neutral aqueous solutions may represent a necessary requirement for making olivine carbonation a viable process in these temperature ranges. It also insists on the importance of transitory phases, which form both at the fluid-silicate interface and from the bulk solution. While they may not appear in overall carbonation equations or in thermodynamic data-bases, arguably they can drive the global kinetics of olivine dissolution and its transformation towards magnesite. (C) 2013 Elsevier B. V. All rights reserved.
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Snieder, R., & Larose, E. (2013). Extracting Earth's Elastic Wave Response from Noise Measurements (Vol. 41).
Résumé: Recent research has shown that noise can be turned from a nuisance into a useful seismic source. In seismology and other fields in science and engineering, the estimation of the system response from noise measurements has proven to be a powerful technique. To convey the essence of the method, we first treat the simplest case of a homogeneous medium to show how noise measurements can be used to estimate waves that propagate between sensors. We provide an overview of physics research-dating back more than 100 years-showing that random field fluctuations contain information about the system response. This principle has found extensive use in surface-wave seismology but can also be applied to the estimation of body waves. Because noise provides continuous illumination of the subsurface, the extracted response is ideally suited for time-lapse monitoring. We present examples of time-lapse monitoring as applied to the softening of soil after the 2011 Tohoku-oki earthquake, the detection of a precursor to a landslide, and temporal changes in the lunar soil.
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Song, I., Rathbun, A. P., & Saffer, D. M. (2013). Uncertainty analysis for the determination of permeability and specific storage from the pulse-transient technique. INTERNATIONAL JOURNAL OF ROCK MECHANICS AND MINING SCIENCES, 64, 105–111.
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Soueid Ahmed, A., Jardani, A., Revil, A., & Dupont, J. P. (2013). SP2DINV: A 2D forward and inverse code for streaming potential problems. COMPUTERS & GEOSCIENCES, 59, 9–16.
Résumé: The self-potential method corresponds to the passive measurement of the electrical field in response to the occurrence of natural sources of current in the ground. One of these sources corresponds to the streaming current associated with the flow of the ground water. We can therefore apply the self-potential method to recover non-intrusively some information regarding the ground water flow. We first solve the forward problem starting with the solution of the ground water flow problem, then computing the source current density, and finally solving a Poisson equation for the electrical potential. We use the finite-element method to solve the relevant partial differential equations. In order to reduce the number of (petrophysical) model parameters required to solve the forward problem, we introduced an effective charge density tensor of the pore water, which can be determined directly from the permeability tensor for neutral pore waters. The second aspect of our work concerns the inversion of the self-potential data using Tikhonov regularization with smoothness and weighting depth constraints. This approach accounts for the distribution of the electrical resistivity, which can be independently and approximately determined from electrical resistivity tomography. A numerical code, SP2DINV, has been implemented in Matlab to perform both the forward and inverse modeling. Three synthetic case studies are discussed. (C) 2013 Elsevier Ltd. All rights reserved.
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Stange, K. M., van Balen, R., Carcaillet, J., & Vandenberghe, J. (2013). Terrace staircase development in the Southern Pyrenees Foreland: Inferences from Be-10 terrace exposure ages at the Segre River. GLOBAL AND PLANETARY CHANGE, 101, 97–112.
Résumé: The fluvial network of the Southern Pyrenees is an example of transverse drainage systems in young (alpine) mountain belts and it features well preserved fluvial terrace records. Some of the major Southern Pyrenees tributary rivers have been studied previously and have some age controls on their fluvial terrace levels. We extend these records to one of the largest streams in the Southern Pyrenees, the Segre River. In this paper, we present new GIS data, field observations and exposure ages obtained from in situ produced terrestrial cosmogenic nuclides (Be-10). The focus of this paper is set to unravel the relative impact of climatic controls on the formation of the Segre terrace staircase in the Southern Pyrenees foreland (Ebro Basin). The Pleistocene terrace staircase of the Segre River is built up by seven major terrace levels, which range from 112 to 3 m above the present-day active channel. The prominent upper and middle terraces TQ1, TQ2, TQ3 and TQ4 have been sampled for Be-10 exposure dating. Exposure ages have been calculated using Monte Carlo parameter simulations. Additionally, we applied a Profile Rejuvenation method accounting for variable Be-10 inheritance in the samples, and which yielded comparable results. The Monte Carlo results show Middle to Late Pleistocene exposure ages for TQ1: 202 ka (MIS 7), TQ2: 139 ka (MIS 6), TQ3: 100 ka (MIS 5), and TQ4: 62 ka (MIS 4), involving denudation rates of 3-8 mm ka(-1). The results indicate that the abandonment of Segre paleo-floodplains and the change from aggradation to predominant incision is related with Middle to Late Pleistocene cold-warm climate transitions (or early stages of interglacial periods). Major floodplain aggradation appears to be linked with intense deglaciation at the end of MIS 8, MIS 6, and MIS 4. The exposure of terrace TQ3 (MIS 5) indicates that terrace formation might also occur during relatively warm isotope stages with sufficient climate instability. On a regional scale, the staircase morphology at the Segre River shows similarities with adjacent fluvial systems in the Southern Pyrenees. In addition, previously published chronologies for these systems are consistent with the timing of aggradation and terrace abandonment. Both, staircase morphology and chronology point to regionally synchronous phases of floodplain aggradation and river incision, which seem to be triggered by climate variability and Pleistocene glaciations in the Pyrenees since the Mid Pleistocene Climatic Revolution. (C) 2013 Elsevier B.V. All rights reserved.
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Sucheras-Marx, B., Giraud, F., Fernandez, V., Pittet, B., Lecuyer, C., Olivero, D., et al. (2013). Duration of the Early Bajocian and the associated delta C-13 positive excursion based on cyclostratigraphy. JOURNAL OF THE GEOLOGICAL SOCIETY, 170(1), 107–118.
Résumé: The Early Bajocian, about 172 Ma ago, was a period of tectonic changes, a global carbon-isotope positive excursion, and biological diversification of marine invertebrates (e. g. ammonites, radiolarians and coccolithophores). unfortunately, both the duration of the Early Bajocian and the associated palaeoenvironmental changes are still poorly constrained. We propose here an estimate of the duration of this sub-stage based on a cyclostratigraphic analysis of the carbonate content from the Chaudon-Norante section, French Subalpine Basin, France. The Chaudon-Norante succession has been correlated with Les Dourbes section using greyscale variations to detect possible local hiatuses. The duration estimated here for the entire Early Bajocian is 4.082 Ma. Two intervals were identified in the positive delta C-13 excursion: an increase of carbon isotope values lasting 1.36 Ma and climax isotope values lasting for 2.72 Ma. A cooling at high latitudes and warming at low latitudes may have enhanced the Earth's temperature gradient leading to an increase in humidity, which in turn triggered ocean eutrophication at the origin of the delta C-13 positive excursion.
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Tatard, L., & Grasso, J. R. (2013). Controls of earthquake faulting style on near field landslide triggering: The role of coseismic slip. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 118(6), 2953–2964.
Résumé: We compare the spatial distributions of seven databases of landslides triggered by M-w=5.6-7.9 earthquakes, using distances normalized by the earthquake fault length. We show that the normalized landslide distance distributions collapse, i.e., the normalized distance distributions overlap whatever the size of the earthquake, separately for the events associated with dip-slip, buried-faulting earthquakes, and surface-faulting earthquakes. The dip-slip earthquakes triggered landslides at larger normalized distances than the oblique-slip event of Loma Prieta. We further identify that the surface-faulting earthquakes of Wenchuan, Chi-Chi, and Kashmir triggered landslides at normalized distances smaller than the ones expected from their M(w)7.6 magnitudes. These results support a control of the seismic slip (through amplitude, rake, and surface versus buried slip) on the distances at which landslides are triggered. In terms of coseismic landslide management in mountainous areas, our results allow us to propose distances at which 95 and 75% of landslides will be triggered as a function of the earthquake focal mechanism.
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Tonazzi, D., Massi, F., Culla, A., Baillet, L., Fregolent, A., & Berthier, Y. (2013). Instability scenarios between elastic media under frictional contact. Mechanical Systems And Signal Processing, 40(2), 754–766.
Résumé: This article presents the results of a numerical dynamic analysis of two bodies in sliding contact. The 2D model consists of two finite elastic media separated by a contact interface, governed by classical Coulomb friction law. The aim of this work is to investigate the instability scenarios occurring when friction forces excite the mechanical systems during the relative motion; simulation results show that the coupling between the frictional behaviour at the contact and the global dynamic of the system can bring to either stick-slip phenomena, or mode coupling instability. Complex eigenvalue analysis and transient non-linear simulations highlight how system parameters, like structural damping, affect the macroscopic frictional behaviour, switching from stick-slip phenomena to harmonic vibrations (due to mode coupling instability), up to the stable sliding state. The presented results allow for generalizing the instabilities due to mode coupling, named in brake squeal literature “lock-in” instability, to any mechanical system with frictional contact. The analyses show how maps of the instability scenarios can be drawn as a function of different parameters to help the design of systems in frictional contact. (C) 2013 Elsevier Ltd. All rights reserved.
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Tonnellier, A., Helmstetter, A., Malet, J. P., Schmittbuhl, J., Corsini, A., & Joswig, M. (2013). Seismic monitoring of soft-rock landslides: the Super-Sauze and Valoria case studies. GEOPHYSICAL JOURNAL INTERNATIONAL, 193(3), 1515–1536.
Résumé: This work focuses on the characterization of seismic sources observed in clay shale landslides. Two landslides are considered: Super-Sauze (France) and Valoria (Italy). The two landslides are developed in reworked clay shales but differ in terms of dimensions and displacement rates. Thousands of seismic signals have been identified by a small seismic array in spite of the high-seismic attenuation of the material. Several detection methods are tested. A semiautomatic detection method is validated by the comparison with a manual detection. Seismic signals are classified in three groups based on the frequency content, the apparent velocity and the differentiation of P and S waves. It is supposed that the first group of seismic signals is associated to shearing or fracture events within the landslide bodies, while the second group may correspond to rockfalls or debris flows. A last group corresponds to external earthquakes. Seismic sources are located with an automatic beam-forming location method. Sources are clustered in several parts of the landslide in agreement with geomorphological observations. We found that the rate of rockfall and fracture events increases after periods of heavy rainfall or snowmelt. The rate of microseismicity and rockfall activity is also positively correlated with landslide displacement rates. External earthquakes did not influence the microseismic activity or the landslide movement, probably because the earthquake ground motion was too weak to trigger landslide events during the observation periods.
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Trugman, D. T., Daub, E. G., Guyer, R. A., & Johnson, P. A. (2013). Modeling dynamic triggering of tectonic tremor using a brittle-ductile friction model. GEOPHYSICAL RESEARCH LETTERS, 40(19), 5075–5079.
Résumé: We study the physics of dynamically triggered tectonic tremor by applying a brittle-ductile friction model in which we conceptualize the tremor source as a rigid block subject to driving and frictional forces. To simulate dynamic triggering of tremor, we apply a stress perturbation that mimics the surface waves of remote earthquakes. The tectonic and wave perturbation stresses define a phase space that demonstrates that both the timing and amplitude of the dynamic perturbations control the fundamental characteristics of triggered tremor. Tremor can be triggered instantaneously or with a delayed onset if the dynamic perturbation significantly alters the frictional state of the tremor source.
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Tucker, G. E., & van der Beek, P. (2013). A model for post-orogenic development of a mountain range and its foreland. BASIN RESEARCH, 25(3), 241–259.
Résumé: Decaying mountain ranges often show a surprisingly dynamic pattern of landscape evolution. Although one might expect a simple, monotonic decline in relief over time, evidence from several inactive mountain ranges shows alternating sequences of deposition and erosion in the associated basins, suggesting variations in relief and exhumation rate in the ranges themselves. Examples include the Southern Rocky Mountains, the Pyrenees, the European Alps and the Atlas Mountains. In this paper, we explore the possible origins of post-orogenic landscape dynamics using a simple mathematical model of a mountain range and an adjacent foreland basin. The analysis highlights the importance of mass balance. In particular, a switch from basin exhumation to renewed sedimentation requires either an increase in sediment influx from the range or a decrease in sediment outflux beyond the basin margin. Although it is widely understood that post-orogenic changes in erosion and sediment flux can have multiple causes (including climate change, regional tectonic uplift or tilting, or exhumation of variable lithologies), an important implication of our analysis is that the impact of such changes must differ in sign or magnitude between the range and the basin to be recorded. This requirement places an important constraint on viable explanations for alternating sequences of deposition and erosion in a decaying mountain-basin pair.
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Vandemeulebrouck, J., Roux, P., & Cros, E. (2013). The plumbing of Old Faithful Geyser revealed by hydrothermal tremor. GEOPHYSICAL RESEARCH LETTERS, 40(10), 1989–1993.
Résumé: Old Faithful Geyser in Yellowstone National Park (USA) has attracted numerous scientific investigations for over two centuries to better understand its geological structure, the physics of its eruptions, and the controls of its intermittency. Using data acquired with a seismic array in 1992, we track the sources of hydrothermal tremor produced by boiling and cavitation inside the geyser. The location of seismic sources identifies a previously unknown lateral cavity at 15m below the surface, on the SW side of the vent, and connected to the conduit. This reservoir is activated at the beginning of each geyser eruption cycle and plays a major role in the oscillatory behavior of the water level in the conduit before each eruption.
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Varrica, D., Bardelli, F., Dongarra, G., & Tamburo, E. (2013). Speciation of Sb in airborne particulate matter, vehicle brake linings, and brake pad wear residues. ATMOSPHERIC ENVIRONMENT, 64, 18–24.
Résumé: Insights into the speciation of Sb in samples of brake linings, brake pad wear residues, road dust, and atmospheric particulate matter PM10 and PM2.5 were obtained combining several well established and advanced characterization techniques, such as scanning electron microscopy – energy dispersive spectrometry (SEM-EDS), inductively coupled plasma mass spectrometry (ICP-MS) and synchrotron radiation X-ray absorption spectroscopy (SR-XAS). The advantage of SR-XAS is that samples do not undergo any chemical treatment prior to measurements, thus excluding possible alterations. These analyses revealed that the samples of wheel rims dust, road dust, and atmospheric particulate matter are composed by an admixture of Sb(III) and Sb(V) in different relative abundances. Brake linings turned out to be composed by Sb(III) oxide (Sb2O3) and stibnite (Sb2S3). Stibnite was also detected in some of the particulate matter samples. The obtained data suggest that Sb2S3 during the brake abrasion process is easily decomposed forming more stable compounds such as antimony mixed oxidic forms. Sb redox speciation, in particular and well studied circumstances, may enhance the potential and selectivity of this element as a tracer of motor vehicle emissions in apportioning studies. (C) 2012 Elsevier Ltd. All rights reserved.
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Veludo, I., Teves-Costa, P., & Bard, P. Y. (2013). Damage seismic scenarios for Angra do Heroismo, Azores (Portugal). BULLETIN OF EARTHQUAKE ENGINEERING, 11(2), 423–453.
Résumé: Angra do Heroismo, located in Terceira Island, is the main town of the Central Group of Azores Archipelago and it is classified as World Heritage by Unesco. The preservation of this patrimony, located inside a seismic region, includes the implementation of a policy to protect it against earthquakes. The development of credible damage scenarios could help this objective, as they can be used in prevention measures to minimize the impact of future earthquakes. Two methods were used for seismic damage estimation: the capacity spectrum method and a new method, based on the direct response of a 1D non-linear oscillator to simulate the building seismic performance. Both methods seem to overestimate the damages for the near sources, but this could be due to the empirical model used to estimate the input ground motion. Comparison with the damage observed after the January 1st, 1980 earthquake show a large discrepancy with an underestimation bias, which can be explained, mainly, by the difference of building performance and on the plausible hypothesis of 2D site effects.
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Wallace, A. F., Hedges, L. O., Fernandez-Martinez, A., Raiteri, P., Gale, J. D., Waychunas, G. A., et al. (2013). Microscopic Evidence for Liquid-Liquid Separation in Supersaturated CaCO3 Solutions. SCIENCE, 341(6148), 885–889.
Résumé: Recent experimental observations of the onset of calcium carbonate (CaCO3) mineralization suggest the emergence of a population of clusters that are stable rather than unstable as predicted by classical nucleation theory. This study uses molecular dynamics simulations to probe the structure, dynamics, and energetics of hydrated CaCO3 clusters and lattice gas simulations to explore the behavior of cluster populations before nucleation. Our results predict formation of a dense liquid phase through liquid-liquid separation within the concentration range in which clusters are observed. Coalescence and solidification of nanoscale droplets results in formation of a solid phase, the structure of which is consistent with amorphous CaCO3. The presence of a liquid-liquid binodal enables a diverse set of experimental observations to be reconciled within the context of established phase-separation mechanisms.
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Walter, F., Canassy, P. D., Husen, S., & Clinton, J. F. (2013). Deep icequakes: What happens at the base of Alpine glaciers? Journal Of Geophysical Research-Earth Surface, 118(3), 1720–1728.
Résumé: Basal seismicity cannot be attributed exclusively to glacier stick-slip motion. As shown by previous studies on temperate Alpine glaciers, there also exist basal seismic sources, which are not due to pure shear mechanisms. Their moment tensors have substantial, if not dominant, isotropic components. Based on first motion data of high-quality seismic records from Gornergletscher and Triftgletscher, Switzerland, we argue that the observed isotropic components can be explained by tensile faulting. The implied coseismic volumetric change can be both positive (fracture opening) and negative (fracture collapse). We attribute these observations to hydraulic processes near water-filled cavities, whose connectivity to the subglacial drainage system changes over time. Thus, our proposed icequake source mechanisms cannot be reconciled with pure shear sources at the glacier bed, which would be expected for basal stick-slip motion. This sliding mode has recently been proposed as a realitively common mechanism, which can substantially enhance subglacial erosion. The existence of several seismic source mechanisms (tensile, shear, or some combination of the two) of basal icequakes implies that a solid understanding about the nature of these events is indispensible if conclusions about glacier sliding, subglacial erosion, and other basal processes are to be drawn from observed seismicity.
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Warden, S., Garambois, S., Jouniaux, L., Brito, D., Sailhac, P., & Bordes, C. (2013). Seismoelectric wave propagation numerical modelling in partially saturated materials. GEOPHYSICAL JOURNAL INTERNATIONAL, 194(3), 1498–1513.
Résumé: To better understand and interpret seismoelectric measurements acquired over vadose environments, both the existing theory and the wave propagation modelling programmes, available for saturated materials, should be extended to partial saturation conditions. We propose here an extension of Pride's equations aiming to take into account partially saturated materials, in the case of a water-air mixture. This new set of equations was incorporated into an existing seismoelectric wave propagation modelling code, originally designed for stratified saturated media. This extension concerns both the mechanical part, using a generalization of the Biot-Gassmann theory, and the electromagnetic part, for which dielectric permittivity and electrical conductivity were expressed against water saturation. The dynamic seismoelectric coupling was written as a function of the streaming potential coefficient, which depends on saturation, using four different relations derived from recent laboratory or theoretical studies. In a second part, this extended programme was used to synthesize the seismoelectric response for a layered medium consisting of a partially saturated sand overburden on top of a saturated sandstone half-space. Subsequent analysis of the modelled amplitudes suggests that the typically very weak interface response (IR) may be best recovered when the shallow layer exhibits low saturation. We also use our programme to compute the seismoelectric response of a capillary fringe between a vadose sand overburden and a saturated sand half-space. Our first modelling results suggest that the study of the seismoelectric IR may help to detect a sharp saturation contrast better than a smooth saturation transition. In our example, a saturation contrast of 50 per cent between a fully saturated sand half-space and a partially saturated shallow sand layer yields a stronger IR than a stepwise decrease in saturation.
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Winkel, L. H. E., Casentini, B., Bardelli, F., Voegelin, A., Nikolaidis, N. P., & Charlet, L. (2013). Speciation of arsenic in Greek travertines: Co-precipitation of arsenate with calcite. GEOCHIMICA ET COSMOCHIMICA ACTA, 106, 99–110.
Résumé: The western part of the Chalkidiki peninsula in Northern Greece is a geothermally active area that contains high levels of naturally derived arsenic in its alkaline groundwaters (up to 3760 μg/L). Near wells, equilibration of these groundwaters with atmospheric carbon dioxide leads to the precipitation of travertines that contain very high levels of arsenic (up to 913 mg/kg). To determine the mechanism of arsenic uptake in these travertines, we analyzed two different types of travertine from this region using both bulk and micro-focused X-ray absorption spectroscopy (XAS and mu-XAS) and micro-focused X-ray fluorescence spectroscopy (mu-XRF). Bulk XAS showed that in all of the studied samples arsenic is present in the pentavalent oxidation state (arsenate). mu-XRF analyses indicated that arsenic is closely associated with the calcite matrix and that it generally does not correlate well with iron. The arsenic K-edge XAS spectra of all samples closely matched each other and closely resembled a reference spectrum for arsenate coprecipitated with calcite (rather than adsorbed or pure calcium arsenate). Iron on the other hand was found to be mainly present as a constituent of clay minerals, of presumably detrital origin, suggesting that iron-(hydr)oxides were not sufficiently abundant to act as major scavengers for arsenic in the Chalkidiki travertines. We estimated that calcite in these travertines could sequester at least 25% of aqueous arsenic in the form of As(V) and thus immobilize a substantial part of arsenic present in the geothermal groundwaters. These results may also be relevant for other areas where geothermal groundwaters carry arsenic to the surface and possibly as well for arsenic geochemistry in other environments with CO2-enriched water. (C) 2012 Elsevier Ltd. All rights reserved.
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Xu, Z. Q., Wang, Q., Pecher, A., Liang, F. H., Qi, X. X., Cai, Z. H., et al. (2013). Orogen-parallel ductile extension and extrusion of the Greater Himalaya in the late Oligocene and Miocene. TECTONICS, 32(2), 191–215.
Résumé: Predominant stretching structures in the Greater Himalayan Crystalline Complex (GHC) trend perpendicular to the belt and are linked to the southward exhumation or emplacement of the GHC between the South Tibet Detachment (STD) and the Main Central Thrust. However, our field investigations in southern Tibet reveal the widespread presence of gently dipping shear zones with a penetrative orogen-parallel stretching lineation, which separates the Tethyan Himalayan Sequence and the underlying GHC. The shear zones are well preserved in the upper part of the GHC, south to and structurally lower than the STD. Field criteria, microstructures, and quartz fabrics indicate top-to-the-east shearing in the Yadong shear zone (eastern GHC), coexistence of top-to-the-east and top-to-the-west shearing in the Nyalam shear zone (central GHC), but top-to-the-west shearing in the Pulan shear zone (western GHC). Characteristic microstructures and slip systems of quartz in the high-grade GHC rocks resulted from the lateral flow under upper amphibolite (up to 650-700 degrees C) to greenschist facies conditions. U-Pb ages of metamorphic zircon rims by sensitive high-resolution ion microprobe (SHRIMP) and laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) analyses yield 28-26Ma for the initiation of the Yadong and Nyalam shear zones and 22-15Ma for the activation of the Pulan shear zone. In addition, 40Ar/39Ar cooling ages of biotite and muscovite suggest cessation of ductile sharing at 13-11Ma on the Yadong shear zone, which is coeval with the activation of the STD. Combined with previous studies, we propose that initiation of orogen-parallel extension marks the transition from burial/crustal thickening to exhumation of the GHC. Due to lateral crustal thickness gradients in a thickened crust, orogen-parallel gravitational collapse occurred within the convergent Himalayan orogen in the late Oligocene-Miocene. This tectonic denudation triggered and enhanced partial melting and ductile extrusion of the GHC in the Miocene.
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Yan, Y., Pinel, V., Trouve, E., Pathier, E., Perrin, J., Bascou, P., et al. (2013). Coseismic displacement field and slip distribution of the 2005 Kashmir earthquake from SAR amplitude image correlation and differential interferometry. GEOPHYSICAL JOURNAL INTERNATIONAL, 193(1), 29–46.
Résumé: The coseismic surface displacement field and slip distribution at depth due to the Kashmir earthquake (M-w = 7.6, 2005) have been analysed by different authors using subpixel correlation of synthetic aperture radar (SAR) images and optical images, teleseismic analysis, GPS measurements, as well as in situ field measurements. In this paper, first, we use 23 sets of measurement from subpixel correlation of SAR images and differential interferometry to retrieve the 3-D coseismic surface displacement field. The obtained horizontal and vertical components along the fault trace are then compared, respectively, to equivalent measurements obtained from subpixel correlation of two optical ASTER images and in situ field measurements. Second, the coseismic fault geometry parameters and slip distribution at depth are estimated. In addition to the one segment slip model as reported in previous work, a two segments slip model that better fits the surface fault break is proposed. The improvement of the two segments slip model in interpreting the measured displacement field is highlighted through comparison of residuals of both slip models. Taking advantage of differential interferometry measurements that provide precise and continuous information in the far field of the fault, firstly, a wedge thrust according to Bendick et al. to the Northwest of the main rupture built on our two segments model is tested. According to the obtained results, the residual of the two segments main rupture plus wedge thrust model is slightly smaller than the residual of the two segments model to the Northwest of the Balakot-Bagh fault. Secondly, we test the sensitivity of our slip model to the presence of slip along a decollement as evidenced by Jouanne et al. through post-seismic analysis. The results indicate that the estimations of the coseismic displacement field and slip distribution in this paper are not significantly biased by such post-seismic displacement and that most coseismic displacement is located on a similar to 40 degrees NE-dipping fault, as previously reported.
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Yang, W. B., Niu, H. C., Sun, W. D., Shan, Q., Zheng, Y. F., Li, N. B., et al. (2013). Isotopic evidence for continental ice sheet in mid-latitude region in the supergreenhouse Early Cretaceous. SCIENTIFIC REPORTS, 3.
Résumé: Cretaceous represents one of the hottest greenhouse periods in the Earth's history, but some recent studies suggest that small ice caps might be present in non-polar regions during certain periods in the Early Cretaceous. Here we report extremely negative delta O-18 values of -18.12 parts per thousand to -13.19 parts per thousand for early Aptian hydrothermal zircon from an A-type granite at Baerzhe in northeastern China. Given that A-type granite is anhydrous and that magmatic zircon of the Baerzhe granite has delta O-18 value close to mantle values, the extremely negative delta O-18 values for hydrothermal zircon are attributed to addition of meteoric water with extremely low delta O-18, mostly likely transported by glaciers. Considering the paleoaltitude of the region, continental glaciation is suggested to occur in the early Aptian, indicating much larger temperature fluctuations than previously thought during the supergreenhouse Cretaceous. This may have impact on the evolution of major organism in the Jehol Group during this period.
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Zandomeneghi, D., Aster, R., Kyle, P., Barclay, A., Chaput, J., & Knox, H. (2013). Internal structure of Erebus volcano, Antarctica imaged by high-resolution active-source seismic tomography and coda interferometry. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 118(3), 1067–1078.
Résumé: Erebus volcano, Antarctica has hosted a persistent convecting phonolite lava lake for over 40 years. The lake produces small (VEI 0-1) Strombolian eruptions resulting from gas slugs rising through the upper conduit system. High-resolution (to scale lengths of several hundreds of meters) three-dimensional P-wave tomographic velocity images were obtained to a depth of approximately 600m below the volcano surface. Data were collected using 91 seismographs deployed over an approximately 4 by 4 km area of the summit region. Seismic illumination was provided by 12 chemical shots emplaced in shallow snow and ice boreholes. P-wave direct arrival travel-time measurements were used to invert for strong velocity anomalies (with spatial variations in V-p exceeding +/- 1 km/s) associated with the uppermost few km. Shallow anomalies correlate with fumarolic ice caves, a prominent radial chilled dike, and ring structures associated with the caldera rim. Conduit structures feeding the lava lake and other vents within the Inner Crater are evidently too small (e. g., less than many 10 s of meters) to be imaged under the resolution limits of this experiment. However, combined velocity and coda interferometry scattering intensity images identify near-summit regions with both low velocity and high scattering that are candidates for magma accommodation. Results indicate a nonaxisymmetric near-summit magmatic system that is likely constrained by heterogeneous structures in the uppermost volcano. The most extensive volume of near-summit magma likely resides approximately 500m NW of the active Inner Crater vents at depths of 500m and more below the surface.
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Zhang, H., Ling, M. X., Liu, Y. L., Tu, X. L., Wang, F. Y., Li, C. Y., et al. (2013). High Oxygen Fugacity and Slab Melting Linked to Cu Mineralization: Evidence from Dexing Porphyry Copper Deposits, Southeastern China. JOURNAL OF GEOLOGY, 121(3), 289–305.
Résumé: The Dexing porphyry Cu deposit is the largest Cu deposit in eastern China, with total reserves of 8.4 Mt Cu. The Dexing porphyries have geochemical characteristics typical of adakites: they are similar to examples in the Circum-Pacific Belt and in the Lower Yangtze River Belt but different from adakites from the Dabie Mountains and the Tibetan Plateau. Ce4+/Ce3+ and (Eu/Eu*)(N) values calculated from zircon trace-element compositions vary from 495 N to 1922 and from 0.51 to 0.82, respectively, and reflect high oxygen fugacity similar to that measured in or inferred for porphyry Cu-Au deposits in the South America. The high oxygen fugacity is consistent with abundant anhydrite and magnetite-hematite intergrowths in the porphyry, which indicate that the highest oxygen fugacity of Dexing porphyry reached the hematite-magnetite buffer. Based on the geochemical characteristics and the drifting history of the Pacific Plate, we propose that the Dexing adakitic porphyries formed through slab melting, most likely during subduction of an aseismic ridge in the Pacific Plate in the Mid-Jurassic.
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