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Albino, F., Pinel, V., Massol, H., & Collombet, M. (2011). Conditions for detection of ground deformation induced by conduit flow and evolution. Journal of Geophysical Research-Solid Earth, 116.
Résumé: At mature andesitic volcanoes, magma can reach the surface through the same path for several eruptions thus forming a volcanic conduit. Because of degassing, cooling, and crystallization, magma viscosity increase in the upper part of the conduit may induce the formation of a viscous plug. We conducted numerical simulations to quantify the deformation field caused by this plug emplacement and evolution. Stress continuity between Newtonian magma flow and elastic crust is considered. Plug emplacement causes a ground inflation correlated to a decrease of the magma discharge rate. A parametric study shows that surface displacements depend on three dimensionless numbers: the conduit aspect ratio (radius/length), the length ratio between the plug and the conduit, and the viscosity contrast between the plug and the magma column. Larger displacements are obtained for high-viscosity plugs emplaced in large aspect ratio conduits. We find that only tiltmeters or GPS located close to the vent (a few hundred meters) might record the plug emplacement. At immediate proximity of the vent, plug emplacement might even dominate the deformation signal over dome growth or magma reservoir pressurization effects. For given plug thicknesses and viscosity profiles, our model explains well the amplitude of tilt variations (from 1 to 25 mu rad) measured at Montserrat and Mt. St. Helens. We also demonstrate that at Montserrat, even if most of the tilt signal is due to shear stress induced by magma flow, pressurization beneath the plug accounts for 20% of the signal.
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Alboussiere, T., Cardin, P., Debray, F., La Rizza, P., Masson, J. - P., Plunian, F., et al. (2011). Experimental evidence of Alfven wave propagation in a Gallium alloy. Physics of Fluids, 23.
Résumé: Experiments with a liquid metal alloy, Galinstan, are reported and show clear evidence of Alfveacuten wave propagation as well as resonance of Alfveacuten modes. Galinstan is liquid at room temperature and, although its electrical conductivity is not as large as that of liquid sodium or NaK, it has still been possible to study Alfveacuten waves, thanks to the use of intense magnetic fields up to 13 T. The maximal values of Lundquist number, around 60, are similar to that of the reference experimental study by Jameson [J. Fluid Mech. 19, 513 (1964)]. The generation mechanism for Alfveacuten waves and their reflection is studied carefully. Numerical simulations have been performed and have been able to reproduce the experimental results, despite the fact that the simulated magnetic Prandtl number was much larger than that of Galinstan. An originality of the present study is that a poloidal disturbance (magnetic and velocity fields) is generated, allowing us to track its propagation from outside the conducting domain, hence without interfering. (C) 2011 American Institute of Physics. [doi:10.1063/1.3633090]
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Allibon, J., Bussy, F., Lewin, E., & Darbellay, B. (2011). The tectonically controlled emplacement of a vertically sheeted gabbro-pyroxenite intrusion: Feeder-zone of an ocean-island volcano (Fuerteventura, Canary Islands). Tectonophysics, 500, 78–97.
Résumé: The Miocene PX1 gabbro-pyroxenite pluton, Fuerteventura, Canary Islands, is a 3.5 x 5.5 km shallow-level intrusion (0.15-0.2 GPa and 1100-1120 degrees C), interpreted as the feeder-zone to an ocean-island volcano. It displays a vertical magmatic banding expressed in five 50 to 100 metre-wide NNE-SSW trending alkaline gabbro sequences alternating with pyroxenites. This emplacement geometry was controlled by brittle to ductile shear zones, generated by a regional E-W extensional tectonic setting that affected Fuerteventura during the Miocene. At a smaller scale, the PX1 gabbro and pyroxenite bands consist of metre-thick differentiation units, which suggest emplacement by periodic injection of magma pulses as vertical dykes that amalgamated, similarly to a sub-volcanic sheeted dyke complex. Individual dykes underwent internal differentiation following a solidification front parallel to the dyke edges. This solidification front may have been favoured by a significant lateral/horizontal thermal gradient, expressed by the vertical banding in the gabbros, the fractionation asymmetry within individual dykes and the migmatisation of the wall rocks. Pyroxenitic layers result from the fractionation and accumulation of clinopyroxene +/- olivine +/- plagioclase crystals from a mildly alkaline basaltic liquid. They are interpreted as truncated differentiation sequences, from which residual melts were extracted at various stages of their chemical evolution by subsequent dyke intrusions, either next to or within the crystallising unit. Compaction and squeezing of the crystal mush is ascribed to the incoming and inflating magma pulses. The expelled interstitial liquid was likely collected and erupted along with the magma flowing through the newly injected dykes. Clinopyroxene mineral orientation – as evidenced by EBSD and micro X-ray tomography investigations – displays a marked pure-shear component, supporting the interpretation of the role of compaction in the generation of the pyroxenites. Conversely, gabbro sequences underwent minor melt extraction and are believed to represent crystallised coalesced magma batches emplaced at lower rates at the end of eruptive cycles. Clinopyroxene orientations in gabbros record a simple shear component suggesting syn-magmatic deformation parallel to observed NNE-SSW trending shear zones induced by the regional tensional stress field. This emplacement model implies a crystallisation time of 1 to 5 years for individual dykes, consistent with PX1 emplacement over less than 0.5 My. A minimum amount of approximately 150 km(3) of magma is needed to generate the pluton, part of it having been erupted through the Central Volcanic Centre of Fuerteventura. If the regional extensional tectonic regime controls the PX1 feeder-zone initiation and overall geometry, rates and volumes of magma depend on other, source-related factors. High injection rates are likely to induce intrusion growth rates larger than could be accommodated by the regional extension. In this case, dyke intrusion by propagation of a weak tip, combined with the inability of magma to circulate through previously emplaced and crystallised dykes could result in an increase of non-lithostatic pressure on previously emplaced mushy dyke walls; thus generating strong pure-shear compaction within the pluton feeder-zone and interstitial melt expulsion. These compaction-dominated processes are recorded by the cumulitic pyroxenite bands. (C) 2010 Elsevier B.V. All rights reserved.
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Allibon, J., Ovtcharova, M., Bussy, F., Cosca, M., Schaltegger, U., Bussien, D., et al. (2011). Lifetime of an ocean island volcano feeder zone: constraints from U-Pb dating on coexisting zircon and baddeleyite, and (40)Ar/(39)Ar age determinations, Fuerteventura, Canary Islands. Canadian Journal of Earth Sciences, 48, 567–592.
Résumé: High-precision isotope dilution – thermal ionization mass spectrometry (ID-TIMS) U-Pb zircon and baddeleyite ages from the PX1 vertically layered mafic intrusion Fuerteventura, Canary Islands, indicate initiation of magma crystallization at 22.10 +/- 0.07 Ma. The magmatic activity lasted a minimum of 0.52 Ma. (40)Ar/(39)Ar amphibole dating yielded ages from 21.9 +/- 0.6 to 21.8 +/- 0.3, identical within errors to the U-Pb ages, despite the expected 1% theoretical bias between (40)Ar/(39)Ar and U-Pb dates. This overlap could result from (i) rapid cooling of the intrusion (i. e., less than the 0.3 to 0.6 Ma 40Ar/39Ar age uncertainties) from closure temperatures (T(c)) of zircon (699-988 degrees C) to amphibole (500-600 degrees C); (ii) lead loss affecting the youngest zircons; or (iii) excess argon shifting the plateau ages towards older values. The combination of the (40)Ar/(39)Ar and U/Pb datasets implies that the maximum amount of time PX1 intrusion took to cool below amphibole T(c) is 0.8 Ma, suggesting PX1 lifetime of 520 000 to 800 000 Ma. Age disparities among coexisting baddeleyite and zircon (22.10 +/- 0.07/0.08/0.15 Ma and 21.58 +/- 0.15/0.16/0.31 Ma) in a gabbro sample from the pluton margin suggest complex genetic relationships between phases. Baddeleyite is found preserved in plagioclase cores and crystallized early from low silica activity magma. Zircon crystallized later in a higher silica activity environment and is found in secondary scapolite and is found close to calcite veins, in secondary scapolite that recrystallised from plagioclase. close to calcite veins. Oxygen isotope delta(18)O values of altered plagioclase are high (+7.7), indicating interaction with fluids derived from host-rock carbonatites. The coexistence of baddeleyite and zircon is ascribed to interaction of the PX1 gabbro with CO(2)-rich carbonatite-derived fluids released during contact metamorphism.
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Amortegui, A., Jaillard, E., Lapierre, H., Martelat, J. - E., Bosch, D., & Bussy, F. (2011). Petrography and geochemistry of accreted oceanic fragments below the Western Cordillera of Ecuador. Geochemical Journal, 45, 57–78.
Résumé: The Western Cordillera of Ecuador consists of Cretaceous crustal fragments of oceanic plateaux and superimposed insular arcs, which were accreted to the northwestern South American margin during the Late Cretaceous and Paleocene. Slices of high-grade metabasites, ultramafic rocks, gabbros and basalts, unmetamorphosed radiolarian cherts and scarce garnet-bearing metasediments were randomly exhumed along Miocene to Recent transcurrent faults crosscutting the Western Cordillera. The basalts show geochemical characteristics of oceanic plateau basalts (flat REE patterns, La/Nb = 0.85). The gabbros differ from the basalts in having lower REE levels, positive Eu anomalies, and negative Nb and Ta anomalies; they are interpreted as resulting from arc magmatism. The amphibolites and banded amphibolites have major and trace element chemistry similar to that of oceanic plateau basalts (flat REE patterns, La/Nb = 0.86) or to cumulate gabbros. The granulite shares with oceanic plateaus similar trace element chemistry (flat REE patterns, La/Nb < 1) and epsilon(Ndi) values (+7.6). Continent-derived metasediments are depleted in heavy REE (La/Y = 4.8) and have a negative Eu anomaly. Foliated Iherzolites, melagabbronorites and pyroxenites consist of serpentinized olivine + cpx + opx +/- Ca-plagioclase. Lherzolites, melagabbronorites and pyroxenites are LREE depleted with positive Eu anomalies, while the harzburgite displays a U-shaped REE pattern. The trace element abundances of the ultramafic rocks are very low (0.1 to 1 times the chonctritic and primitive mantle values). The ultramafic rocks represent fragments of depleted mantle, deformed cpx-rich cumulate, and continental lithospheric mantle or mantle contaminated by subduction-fluid. Except the scarce quartz-rich metasediments, all these rocks likely represent remnants of accreted oceanic crustal fragments and associated depleted mantle. Since these samples were randomly sampled at depth by the fault, we propose that the Western Cordillera and its crustal root are mainly of oceanic nature.
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Angheluta, L., Candela, T., Mathiesen, J., & Renard, F. (2011). Effect of Surface Morphology on the Dissipation During Shear and Slip Along a Rock-Rock Interface that Contains a Visco-elastic Core. Pure and Applied Geophysics, 168, 2335–2344.
Résumé: High resolution topography measurements of the Vuache-Sillingy fault (Alps, France) reveal a characteristic roughness of the fault zone. We investigate the effect of roughness on the rheology of a planar shear configuration by using a model system consisting of a visco-elastic layer embedded into a rigid solid. The model is discussed in the context of several geological cases: a damage fault zone, a fault smeared with a clay layer, and a shear zone with strain weakening. Using both analytical approaches and finite element simulations, we calculate to linear order the relation between wall roughness and the viscous dissipation in the fault zone as well as the average shear rate.
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Aochi, H., Durand, V., & Douglas, J. (2011). Influence of Super-Shear Earthquake Rupture Models on Simulated Near-Source Ground Motion from the 1999 Izmit, Turkey, Earthquake. Bulletin of the Seismological Society of America, 101, 726–741.
Résumé: We numerically simulate seismic wave propagation from the 1999 M(w) 7.4 earthquake in Izmit, Turkey, using a 3D finite difference method based on published finite-source models obtained by waveform inversions. This earthquake has been reported, based on observations at the near-fault station SKR, as an example of supershear rupture propagation toward the east. Although the modeled ground motion does show a characteristic Mach wave from the fault plane, it is difficult to identify any particular effects in terms of peak ground velocity (PGV), an important parameter in earthquake engineering. This is because the fault's spatial heterogeneity is strong enough to mask the properties of supershear rupture, which has been reported through several numerical simulations mostly based on homogeneous fault conditions. This article demonstrates the importance of studying ground motions for known earthquakes through numerical simulations based on finite-fault source models.
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Arambula-Mendoza, R., Lesage, P., Valdes-Gonzalez, C., Varley, N. R., Reyes-Davila, G., & Navarro, C. (2011). Seismic activity that accompanied the effusive and explosive eruptions during the 2004-2005 period at Volcan de Colima, Mexico. Journal of Volcanology and Geothermal Research, 205, 30–46.
Résumé: Volcan de Colima is considered the most active in Mexico. A period of large eruptive activity occurred in 2004-2005. It began as a swarm of long-period events (LPs) in late September 2004, indicating the onset of growth of a new lava dome in its crater. Subsequently, avalanches of incandescent material and pyroclastic flows during a period of approximately 2 months occurred. Then, the activity became more explosive with moderate explosions. Finally, swarms of LPs accompanied the magma ascent and extrusion of small domes and vulcanian explosions with pyroclastic flows in 2005. This eruptive period was investigated with a continuous seismic signal study, cross-correlation of LPs and autoregressive analysis of monochromatic LPs. For the vast majority of the explosions, an increase in the rate of seismic energy was observed with the Seismic Spectral Energy Measurement (SSEM) from 1 to 3 Hz, before each explosive event. This increase in energy is proportional to the increase in the rate of LPs, probably as a result of an increase in the emission rate. Applying the material failure forecasting method (FFM) and using SSEM inverse of parameter, the time of the explosions is estimated as the time when the adjusted line reaches the null value. We observe a systematic delay of a few hours between the real time of occurrence of the explosions and the estimated time. This suggests that more complex processes than pure damaging of the plug occur before the explosions. The swarms associated with the large explosions include a large proportion of LPs with similar waveforms. They form a dozen of families which stay during the whole period of activity and which indicate repetitive sources. Some of the families are active only before the explosions and could therefore be used as early warning. Monochromatic LP events occurred during this period, some of them just some hours before an explosion. However, no clear relationship between their occurrence and the explosions could be found. (C) 2011 Elsevier B.V. All rights reserved.
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Arzhannikova, A., Arzhannikov, S., Jolivet, M., Vassallo, R., & Chauvet, A. (2011). Pliocene to Quaternary deformation in South East Sayan (Siberia): Initiation of the Tertiary compressive phase in the southern termination of the Baikal Rift System. Journal of Asian Earth Sciences, 40, 581–594.
Résumé: The South East Sayan area, W of the Lake Baikal is subjected to a very complex tectonic setting where the extensional stress field of the Baikal Rift System meets the compressional stress field generated by the India-Asia collision further south. Using satellite images, aerial photographs, SRTM DEM, field mapping of geomorphological structures, and published neotectonics and geological data we show that most of the relief in the SE Sayan initiated during Late Pliocene-Pleistocene through compressive reactivation of inherited structures. By Late Quaternary, clockwise rotation of the compressive field generated strike-slip faulting and local, secondary extension still within a general compressional stress field. We demonstrate that the formation of the small-scale extensional basins within the East Sayan range is not linked to general the extension in the Baikal Rift System nor to a possible asthenospheric plume acting at the base of the crust but rather to the rotation of small rigid tectonic blocks driven by the compression. (C) 2010 Elsevier Ltd. All rights reserved.
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Bachaud, P., Berne, P., Renard, F., Sardin, M., & Leclerc, J. R. (2011). Use of tracers to characterize the effects of a CO(2)-saturated brine on the petrophysical properties of a low permeability carbonate caprock. Chemical Engineering Research & Design, 89, 1817–1826.
Résumé: To assess the long-term safety of a geological carbon dioxide storage site, the confining properties of the rocks sealing an underground reservoir (caprocks) and their evolution inthe presence of CO(2) must be characterized. The present study consists in the measurement of the transport parameters of dissolved CO(2) through low permeability carbonate-rich caprocks. The properties of interest are the effective permeability and the diffusion coefficients of carbon dioxide dissolution products in water. The impact of carbon dioxide has been evaluated when altering rock samples by diffusion of a CO(2)-saturated brine under reservoir thermodynamic conditions, and by comparison of the pre- and post-alteration measured values. Permeability was measured by a gas-tracing method and, to study diffusion, radioactive isotopes of carbon ((14)C) and hydrogen ((3)H) were used. Despite a porosity increase observed for all the studied samples, the low values of transport parameters, measured initially, were also measured after alteration, showing a non-catastrophic alteration of the material. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
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Bard, P. - Y. (2011). Seismic loading Engineering characterization of seismic ground motion and key controling factors. European Journal of Environmental and Civil Engineering, 15, 141–184.
Résumé: This paper presents the main ground motion parameters which are used in earthquake engineering to characterize the seismic loading, as well as the key phyisclal phenomena that control their value and their variability. A first section shortly outlines the principles of strong motion measurement and the main networks and databases. The next section describes in detail the main strong motion parameters that are routinely used in earthquake engineering, i.e., peak time domain values and spectral characterizatons (response spectra and Fourier spectra) together with a few additional quantities originally introduced to improve the correlation with actual damage. The last section outlines the sensitivity of these ground motion parameters to the macroscopic factors used to describe the physics of the source (moment magnitude, stress drop, etc.) and of wave propagation at regional and local scales.
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Bardelli, F., Benvenuti, M., Costagliola, P., Di Benedetto, F., Lattanzi, P., Meneghini, C., et al. (2011). Arsenic uptake by natural calcite: An XAS study. Geochimica Et Cosmochimica Acta, 75(11), 3011–3023.
Résumé: As-bearing travertine rocks from Tuscany (Italy), where previous studies suggested the existence of a CO32- double left right arrow AsO33- substitution in the calcite lattice, were investigated with X-ray Absorption Spectroscopy (XAS) at the As K-edge (11,867 eV). In two of the studied samples, XANES indicates that As is in the 5+ oxidation state only, and EXAFS analysis reveals a local environment typical of arsenate species. For these samples, the lack of detectable second shell signals suggests a poorly ordered environment, possibly corresponding to an adsorption onto oxide and/or silicate phases. On the other hand, in the third sample XANES reveals a mixed As oxidation state (III and V). This sample also presents evident next nearest neighbor coordination shells, attributed to As-Ca and As-As contributions. The occurrence of next neighbor shells is evidence that part of As is incorporated in an ordered lattice. Furthermore, the local structure revealed by EXAFS is compatible with As incorporation in the calcite phase, as further supported by DFT simulations. The observation of next neighbors shells only in the As(III)-rich sample suggests the substitution of the arsenite group in place of the carbonate one (CO32- double left right arrow AsO33-). The conclusion of this work is that uptake of As by calcite is in general less favored than adsorption onto iron oxhydroxides, but could become environmentally important wherever the latter phenomenon is hindered. (C) 2011 Elsevier Ltd. All rights reserved.
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Bardelli, F., Cattaruzza, E., Gonella, F., Rampazzo, G., & Valotto, G. (2011). Characterization of road dust collected in Traforo del San Bernardo highway tunnel: Fe and Mn speciation. Atmospheric Environment, 45, 6459–6468.
Résumé: X-ray Absorption Spectroscopy (XAS), X-Ray Diffraction (XRD), Thermo-Gravimetric Analysis (TGA) and Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) techniques were used to determine the composition and the speciation of Fe and Mn in road dust samples collected in the Traforo del San Bernardo highway tunnel. Principal Component Analysis and Least Square Fitting on the XANES region of the absorption spectra and structural refinements on the EXAFS part of the spectra were applied to obtain complementary information on the speciation, average oxidation state, and local structure of Fe and Mn. XRD indicated the presence of silica, calcite, gypsum, and of various phyllosilicates. TGA analysis confirmed the presence of phyllosilicates and also detected a significant amount of organic phases. These findings indicate the co-presence of particles of natural origin along with the organic phases related to vehicular gas exhausts emission. On the other hand, XAS analysis showed that iron is mainly present in the Fe(3)O(4) and FeCl(3) forms, which can be considered to have both anthropic origin, i.e., exhaust emission and salt used to prevent ice formation, respectively. (C) 2011 Elsevier Ltd. All rights reserved.
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Barruol, G., Bonnin, M., Pedersen, H., Bokelmann, G. H. R., & Tiberi, C. (2011). Belt-parallel mantle flow beneath a halted continental collision: The Western Alps. Earth and Planetary Science Letters, 302, 429–438.
Résumé: Constraining mantle deformation beneath plate boundaries where plates interact with each other, such as beneath active or halted mountain belts, is a particularly important objective of “mantle tectonics” that may bring a depth extent to the Earth's surface observation. Such mantle deformation can be mapped at scale lengths of several tens of kilometers through the analysis of seismological data and particularly by mapping seismic anisotropy from the splitting analysis of vertically-propagating SKS waves that largely reflect the strain-induced crystal preferred orientations of the rock-forming minerals within the upper mantle. In the present study, we analyse data from approximately 50 broadband seismic stations covering the Western Alps and we provide a coherent picture of upper mantle anisotropy beneath the belt. The large-scale anisotropy pattern is characterized by fast split directions that closely follow the trend of the belt. Moreover, the maximum anisotropy magnitude is not located beneath the internal zones of the belt but instead beneath external units. All suggests that the anisotropy is likely dominated by sublithospheric mantle deformation. We propose that the observed anisotropy pattern can be explained by recent or active mantle flow around the Eurasian slab presently plunging beneath the inner parts of the Alps. (c) 2010 Elsevier B.V. All rights reserved.
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Batanova, V. G., Belousov, I. A., Savelieva, G. N., & Sobolev, A. V. (2011). Consequences of Channelized and Diffuse Melt Transport in Supra-subduction Zone Mantle: Evidence from the Voykar Ophiolite (Polar Urals). Journal Of Petrology, 52(12), 2483–2521.
Résumé: The well-preserved, 6 km thick mantle section of the Voykar ophiolite in the Polar Urals contains numerous dunite bodies as well as dunite and pyroxenite veins within the host harzburgites. These rocks provide evidence of a composite asthenosphere-lithosphere history of partial melting, plastic deformation, multi-stage melt migration and melt-rock interaction. We investigated the petrology and geochemistry of multiple samples of the different mantle lithologies to define the sequence of mantle melting and melt migration events, as well as the composition of the percolating melts. Spinel harzburgites sampled far from dunite bodies and pyroxenite veins have fairly homogeneous bulk-rock, olivine and Cr-spinel compositions and are interpreted as residues after 14-16% of partial melting, most probably at a mid-ocean ridge. Near the contacts with the dunite bodies and pyroxenite veins, spinel peridotites demonstrate distinct compositional changes marking different stages of melt migration in a supra-subduction environment. At the earliest stage, which probably took place in the lithosphere-asthenosphere boundary of the forearc mantle at temperature between 1050 and 1200 degrees C and a pressure of 1-1 center dot 7 GPa, the dunite bodies formed as a result of stress-driven focused melt flow. The latest stage melts moved in cracks under a conductive cooling regime within the lithospheric mantle section when it was horizontally displaced towards the trench. The trace element composition of the melts that migrated through the mantle section during dunite formation have geochemical characteristics like those of high-Ca boninites. The role of the slab-derived component progressively increased through time and late-stage, pyroxenite-forming melts were conspicuously rich in SiO2 and H2O. These low-viscosity melts impregnated the surrounding harzburgites, modifying or obliterating their primary composition.
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Battaglia, J., Zollo, A., & Got, J. - L. (2011). Rates of similar micro-earthquakes: Comparison between Campi Flegrei (Southern Italy) and other volcanic areas. Journal of Volcanology and Geothermal Research, 200, 62–74.
Résumé: The precise relocation of micro-earthquakes using waveform cross-correlation is an efficient tool for defining the spatial characteristics of seismogenic structures in volcanic areas. To be applied and to provide meaningful results, the technique requires, however, the presence of sufficient amounts of similar events. We examined about 870 earthquakes recorded at the Campi Flegrei (CF) caldera by a temporary digital network during the end of the 1982-1984 bradiseismic crisis. The classification of these earthquakes indicates a surprising low amount of similar events, especially according to the clustered aspect of the seismicity. The relocation technique, allows only to identify 3 elongated patterns that may be interpreted as small faults which are dipping inward toward the center of the caldera. To determine up to which point this low similarity rate is unusual, we examined the rates for several data sets coming from various volcanic areas: Hawaii, Mount Pinatubo (Philippines) and Piton de la Fournaise (La Reunion Island). The results show for all areas, percentages of similar events significantly higher than for CF and indicate that the low rate observed there is not just a matter of low detection threshold or network characteristics. At CF, most of the seismicity appears to be diffused and generated along small fractures rather than along well defined fault structures. The low similarity rate is in good agreement with a seismicity generated in a fractured medium by overpressure in the hydrothermal system and low deviatoric local stress. (C) 2010 Elsevier B.V. All rights reserved.
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Beck, P., Barrat, J. A., Grisolle, F., Quirico, E., Schmitt, B., Moynier, F., et al. (2011). NIR spectral trends of HED meteorites: Can we discriminate between the magmatic evolution, mechanical mixing and observation geometry effects? Icarus, 216, 560–571.
Résumé: The Howardite-Eucrite-Diogenite (HED) suite is a family of differentiated meteorites that provide a unique opportunity to study the differentiation of small bodies. The likely parent-body of this meteorite group, (4) Vesta is presently under study by the Dawn mission, scrutinizing its surface in the visible and NIR infrared range. Here, we discuss how well the magmatic trends observed in HED might be retrieved from NIR spectroscopy, by studying laboratory spectra of 10 HED meteorites together with spectra from the RELAB database. We show that although an exsolution process did occur for most eucrites (i.e. decomposition of a primary calcic pyroxene into a high-Ca and low-Ca pyroxene), it does not affect the “bulk pyroxene” trend retrieved from the location of the pyroxene crystal field bands (Band I with a maximum of absorption around at about 1 mu m and Band II around 2 mu m). Absolute values of the chemical composition appears however to deviate from the expected chemical composition. We show that mechanical mixture (i.e. impact gardening) will produce a linear mixing in the pyroxenes band position diagram (Band I position vs Band II position). This diagram also reveals that howardite are not pure mixtures of an average eucrite and average diogenite. Because asteroid surfaces are expected to show topography, we also study the effect of observation geometry on the NIR spectra of an eucrite and a diogenite by measuring the bi-directional reflectance spectra from 0.4 to 4.6 mu m. Results show that these meteorites tend to act as forward scatterers, leading to a decrease of integrated band area (relative to the continuum) at high phase angles. The position of the two strong crystal field bands shows only small variability with observation geometry. Retrieval of the magmatic trends from the Band I vs Band II diagram should not be affected by observation geometry effects. Finally we performed NIR reflectance measurement on olivine diogenites. The presence of olivine can be suggested by using the Band Area Ratio vs Band I diagram, but this phase might affect the retrieval of pyroxene composition from the position of Band I and Band II. (C) 2011 Elsevier Inc. All rights reserved.
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Beck, P., Quirico, E., Sevestre, D., Montes-Hernandez, G., Pommerol, A., & Schmitt, B. (2011). Goethite as an alternative origin of the 3.1 mu m band on dark asteroids (vol 85, pg 526, 2011). Astronomy & Astrophysics, 530.
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Beck, P., Yabuta, H., Atou, T., Quirico, E., Yoldi-Martinez, Z., Guillot, A., et al. (2011). CO-EVOLUTION OF CHONDRITIC ORGANICS AND MINERALS DURING IMPACT METAMORPHISM. Meteoritics & Planetary Science, 46, A16.
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Ben-Hadj-Ali, H., Operto, S., & Virieux, J. (2011). An efficient frequency-domain full waveform inversion method using simultaneous encoded sources. Geophysics, 76, R109–R124.
Résumé: Three-dimensional full waveform inversion (FWI) still suffers from prohibitively high computational costs that arise because of the seismic modeling for multiple sources that is performed at each nonlinear iteration of FWI. Building supershots by assembling several sources allows mitigation of the number of simulations per FWI iteration, although it adds crosstalk artifacts because of interference between the individual sources of the supershots. These artifacts themselves can be reduced by encoding each individual source with a random phase shift during assembling of the sources. The source encoding method is applied to an efficient frequency-domain FWI, in which a limited number of discrete frequencies or coarsely sampled frequency groups are inverted successively following a multiscale approach. Random codes can be regenerated at each FWI iteration or for each frequency of a group during each FWI iteration, to favor the destructive summation of crosstalk artifacts over FWI iterations. Either a limited number of sources (partial assembling) or the total number of sources (full assembling) can be combined into supershots. Wide-aperture acquisition geometries such as land or marine node acquisitions are considered, to allow one to stack a large number of shots in the full computational domain and to test different partial assembling strategies involving sources that are close to or distant from each other. Two-dimensional case studies show that partial-source assembling of distant shots has a limited sensitivity to noise, for a computational saving that is roughly proportional to the number of shots assembled into the supershots. On the other hand, full assembling is more sensitive to noise, and it requires successive inversions of finely sampled frequency groups with a large number of FWI iterations. In contrast, refining the shot interval to improve the fold degrades the models when full assembling is applied to noisy data. Preliminary 3D application of the method leads to the same conclusions that 2D case studies do, with regard to the footprint of crosstalk noise in the imaging.
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Berger, P., Got, J. - L., Gonzalez, C. V., & Monteiller, V. (2011). Seismic tomography at Popocatepetl volcano, Mexico. Journal of Volcanology and Geothermal Research, 200, 234–244.
Résumé: We performed the first 3D seismic tomography of the Popocatepetl volcano, Mexico, from the inversion of the P-wave arrival times of nearly 1500 earthquakes recorded by up to 11 seismic stations of the permanent CENAPRED-SSN network. We used the Bayesian tomographic algorithm developed by Monteiller et al. (2005) to perform this P-wave travel-time tomography and carefully choose optimal regularization hyper-parameters. Sensitivity tests show that the inversion is correctly constrained under the volcano from -1 to 4 km depth b.s.l.. At these depths, the optimal tomographic model mainly shows low-velocity volumes surrounded by higher-velocity volumes. Lateral heterogeneity is strong: the variation of the P-wave velocity may reach up to +/- 20% of the average value at a given depth. Low-velocity volumes correlate well with results from former geological and geophysical studies. (C) 2011 Elsevier B.V. All rights reserved.
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Bermudez, M. A., van der Beek, P., & Bernet, M. (2011). Asynchronous Miocene-Pliocene exhumation of the central Venezuelan Andes. Geology, 39, 139–142.
Résumé: Constraining the uplift and exhumation history of the Venezuelan Andes is critical for understanding the complex geodynamic evolution of northern South America. We present new apatite fission-track (AFT) data from the Sierra Nevada de Merida in the central Venezuelan Andes and compare the results with previously published AFT data for the Sierra La Culata (El Carmen block) to the north. The AFT data are combined with three-dimensional thermal modeling to constrain the exhumation and relief history of both blocks, which show significant differences. The Sierra Nevada indicates exhumation rates of similar to 1.7 km/m.y. from ca. 10 Ma until 4 Ma, decreasing to similar to 0.4 km/m.y. from 4 Ma to present; the El Carmen block, in contrast, underwent much more rapid recent exhumation, with rates of similar to 1.4 km/m.y. since 4 Ma. The data suggest similar to 4 km of relative rock uplift of the Sierra La Culata with respect to the Sierra Nevada since 4 Ma and support significant uplift of basement blocks along major preexisting discontinuities during transpression in the Northern Andes, linked to accretion of the Panama arc and indentation of the Maracaibo block. Rapid Middle-Late Miocene exhumation in the Sierra Nevada resulted from surface uplift that caused the Late Miocene deflection of the Orinoco River inferred from the Neogene sedimentary record.
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Bernet, M., & Tricart, P. (2011). The Oligocene orogenic pulse in the southern Penninic arc (western Alps): structural, sedimentary and thermochronological constraints. Bulletin De La Societe Geologique De France, 182, 25–36.
Résumé: The Oligocene evolution of the southern branch of the western Alpine arc, more precisely the stack of metamorphic Brianconnais and Piedmont nappes composing the southern Penninic arc (SPA), are the focus of this study. We review published structural, sedimentological and thermochronological data in order to discuss exhumation of the SPA. At first, we compare bedrock zircon and apatite fission-track (FT) data from the SPA with detrital thermochronologic data (zircon FT, white mica (40)Ar/(39)Ar) from Oligocene molasse deposits. Using improved stratigraphic ages for the Barreme basin, samples from the uppermost Rupelian “Conglomerat de Clumanc” and the Chattian “Molasse Rouge” provided zircon FT lag times of similar to 3.5 and 8 m.y., indicating source exhumation rates on the order of similar to 1.5 and similar to 0.75 km/m.y. respectively. These short lag times are consistent with lag times of (40)Ar-(39)Ar ages of detrital white mica from the same formations in the same basin, and also from Oligocene molasse sediments in the Tertiary Piedmont basin. The sediment source for these grains as for the associated clasts of blueschist, is identified as the HP-LT metamorphic units of the SPA. The source cannot be the Ubaye-Embrunais nappes as classically considered, because these nappes do not bear the required metamorphic imprint. This interpretation is consistent with fast Oligocene cooling of the SPA, as attested by in situ zircon and apatite FT analyses. Such fast and relatively old cooling is a peculiarity of the southern branch of the western Alpine arc, when considering the entire arc. A second range of data concerns the structural building of the SPA. The initial stacking of metamorphic nappes in a poorly elevated accretionnary wedge was completed before the end of the Eocene. During the Early Oligocene collision, this wedge was severely refolded, acquiring its fan structure, as visible in cross section, and its curvature in map view. In such a context, we propose that fast exhumation and cooling of the SPA during the Oligocene resulted from active erosion of rapidly raised high topography. This is consistent with the sudden arrival of metamorphic Penninic clasts in the molasse basins along both flanks of the belt. Moreover, detrital and in situ thermochronological ages, suggest a strong slowing down of cooling and exhumation from the Miocene onwards, coinciding with brittle extension that dominates in the SPA during this long period. The brief Early Oligocene rise of a SPA cordillera, contrasts with the preceding and subsequent period of poor relief of the SPA. The mountainous character of the SPA today is not directly inherited from the Oligocene orogenic climax, as modern high relief and elevation are most likely related to rejuvenation under climatic control during the Quaternary.
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Bievre, G., Kniess, U., Jongmans, D., Pathier, E., Schwartz, S., van Westen, C. J., et al. (2011). Paleotopographic control of landslides in lacustrine deposits (Trieves plateau, French western Alps). Geomorphology, 125, 214–224.
Résumé: Paleotopography in Quaternary sedimentary environments can be an important factor that controls landslide movement. This study investigates the relation between paleotopography and landslide activity in two adjacent landslides in glaciolacustrine sediments located in the Trieves area (French western Alps). Although both are in slopes underlain by the same lacustrine deposits, the Avignonet and Harmaliere landslides exhibit major differences in morphology and displacement rates. Through a combination of geological mapping, airborne light detection and ranging (LiDAR) data, aerial photographs, global positioning system (GPS), and seismic noise measurements, a three-dimensional impression was made of both landslides. The analysis reveals that the difference in kinematics between the two mass movements can be traced back to at least 50 years ago. The results show that the Harmaliere slide, which failed catastrophically in 1981, is still much more active than the Avignonet landslide. The fear was that the Avignonet landslide might develop in a similar catastrophic manner, threatening a number of houses constructed on the landslide. A geophysical survey based on ambient noise measurements allowed us to map the base of the lacustrine clays, and the results indicate the presence of a N-S ridge of hard sediments (Jurassic bedrock and/or compact alluvial layers) on the eastern side of the Avignonet landslide. This ridge disappears when approaching the Harmaliere landslide and makes a place to what can be interpreted as a NW-SE oriented paleovalley of the river Drac. We proposed that the ridge acts as a buttress that could mechanically prevent the Avignonet landslide from evolving as fast as the Harmaliere. Furthermore, the NW-SE paleovalley located under the Harmaliere landslide corresponds to the motion direction of the slide. Therefore, the different behaviour of the two landslides is partly controlled by the paleotopographic setting of Lake Trieves during the last Glacial Maximum extension. These results suggest a major influence of the bedrock paleotopography on the kinematics of the landslides. (C) 2010 Elsevier B.V. All rights reserved.
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Boleve, A., Janod, F., Revil, A., Lafon, A., & Fry, J. J. (2011). Localization and quantification of leakages in dams using time-lapse self-potential measurements associated with salt tracer injection. Journal of Hydrology, 403, 242–252.
Résumé: The self-potential method is the only non-intrusive method that is directly sensitive to the flow of the pore water in a porous material. We propose the use of a new protocol of self-potential measurements associated with a brine injection to locate leakages in earth dams and to quantify their permeability. Indeed, a brine solution injection upstream of an earth dam (in the assumed leakage zone) is able to change the electrical conductivity of the medium. In turn, this decreases the magnitude of the electrokinetic contribution of the self-potential signals that are related to the flow of the seepage water. The evolution of this anomalous self-potential signal (expected to be positive with respect to a reference state prior the salt injection) can be measured at the ground surface with a network of non-polarizing electrodes. The seepage flow inside the dam is localized from the evolution in space and time of the resulting transient self-potential signals associated with the transport of the brine. The mean permeability of the preferential flowpath can be determined. This method is first applied to a laboratory test to show how the passage of a salt tracer affects the self-potential response. Then, we apply this new methodology to a field test site (a dam with a proven leakage) located in the south of France. At this test site, self-potential mapping was first performed to locate the preferential flow path. Then, a network of non-polarizing electrodes was used to perform time-lapse self-potential measurements at the dam crest during a brine injection occurring upstream of the seepage zone. We used two lines of 16 non-polarizing electrodes each. From the time-lapse data, the permeability of the leaking area was estimated inside one order of magnitude. (C) 2011 Elsevier B.V. All rights reserved.
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Bonilla, L. F., Tsuda, K., Pulido, N., Regnier, J., & Laurendeau, A. (2011). Nonlinear site response evidence of K-NET and KiK-net records from the 2011 off the Pacific coast of Tohoku Earthquake. Earth Planets and Space, 63, 785–789.
Résumé: We analyzed the acceleration time histories recorded by the K-NET and KiK-net stations of the M(w) 9 Tohoku Earthquake in order to investigate site response issues related to near-source effects. Time-frequency analysis of K-NET stations in the Miyagi prefecture, closest to the rupture area, show that sites having a V(s30) < 400 m/s present a combination of deamplification at frequencies higher than 5 to 10 Hz and cyclic mobility (high acceleration peaks riding over a low frequency carrier). This suggests strong nonlinear site response at these stations. Furthermore, using KiK-net data we are able to compute borehole transfer functions from the mainshock and events having small PGA values from the local dataset. The ratio between weak-motion and strong-motion borehole transfer functions constitutes an indicator of nonlinear site response. This ratio reveals strong dependence on V(s30) and shows that widespread nonlinear behavior took place during this large earthquake.
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Bonnel, J., Gervaise, C., Roux, P., Nicolas, B., & Mars, J. I. (2011). Modal depth function estimation using time-frequency analysis. Journal of the Acoustical Society of America, 130, 61–71.
Résumé: Acoustic propagation in shallow water is characterized by a set of depth-dependent modes, the modal depth functions, which propagate in range according to their horizontal wavenumbers. For inversion purposes, modal depth function estimation in shallow water is an issue when the environment is not known. Classical methods that provide blind mode estimation rely on the singular value decomposition of the received field at different frequencies over a vertical array of transducers. These methods require that the vertical array spans the full water column. This is obviously a strong limitation for the application of such methods in an operational context. To overcome these shortcomings, this study proposes to replace the spatial diversity constraint by a frequency diversity condition, and thus considers the case of a field emanating from an impulsive source. Indeed, because of the discrete nature of the wavenumber spectrum and due to their dispersive behavior, the modes are separated in the time-frequency domain. This phenomenon enables the design of a modal filtering scheme for signals received on a single receiver. In the case of a vertical receiver array, the modal contributions can be isolated for each receiver even when using a partial water column spanning array. This method thus eliminates the receiving constraints of classical methods of modal depth function estimation, although it imposes the use of an impulsive source. The developed algorithm is benchmarked on numerical simulations and validated on laboratory experimental data recorded in an ultrasonic waveguide. Practical applications are also discussed. (C) 2011 Acoustical Society of America. [DOI: 10.1121/1.3592230]
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Boore, D. M., Thompson, E. M., & Cadet, H. (2011). Regional Correlations of VS30 and Velocities Averaged Over Depths Less Than and Greater Than 30 Meters. Bulletin of the Seismological Society of America, 101, 3046–3059.
Résumé: Using velocity profiles from sites in Japan, California, Turkey, and Europe, we find that the time-averaged shear-wave velocity to 30 m (V(S30)), used as a proxy for site amplification in recent ground-motion prediction equations (GMPEs) and building codes, is strongly correlated with average velocities to depths less than 30 m (V(Sz), with z being the averaging depth). The correlations for sites in Japan (corresponding to the KiK-net network) show that V(S30) is systematically larger for a given V(Sz) than for profiles from the other regions. The difference largely results from the placement of the KiK-net station locations on rock and rocklike sites, whereas stations in the other regions are generally placed in urban areas underlain by sediments. Using the KiK-net velocity profiles, we provide equations relating V(S30) to V(Sz) for z ranging from 5 to 29 m in 1-m increments. These equations (and those for California velocity profiles given in Boore, 2004b) can be used to estimate V(S30) from V(Sz) for sites in which velocity profiles do not extend to 30 m. The scatter of the residuals decreases with depth, but, even for an averaging depth of 5 m, a variation in log V(S30) of +/- 1 standard deviation maps into less than a 20% uncertainty in ground motions given by recent GMPEs at short periods. The sensitivity of the ground motions to V(S30) uncertainty is considerably larger at long periods (but is less than a factor of 1.2 for averaging depths greater than about 20 m). We also find that V(S30) is correlated with V(Sz) for z as great as 400 m for sites of the KiK-net network, providing some justification for using V(S30) as a site-response variable for predicting ground motions at periods for which the wavelengths far exceed 30 m.
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Bouchon, M., Karabulut, H., Aktar, M., Ozalaybey, S., Schmittbuhl, J., & Bouin, M. - P. (2011). Extended Nucleation of the 1999 M(w) 7.6 Izmit Earthquake. Science, 331, 877–880.
Résumé: Laboratory and theoretical studies suggest that earthquakes are preceded by a phase of developing slip instability in which the fault slips slowly before accelerating to dynamic rupture. We report here that one of the best-recorded large earthquakes to date, the 1999 moment magnitude (M(w)) 7.6 Izmit (Turkey) earthquake, was preceded by a seismic signal of long duration that originated from the hypocenter. The signal consisted of a succession of repetitive seismic bursts, accelerating with time, and increased low-frequency seismic noise. These observations show that the earthquake was preceded for 44 minutes by a phase of slow slip occurring at the base of the brittle crust. This slip accelerated slowly initially, and then rapidly accelerated in the 2 minutes preceding the earthquake.
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Boulanger, J., Lebihan, N., Catheline, S., & Rossetto, V. (2011). Non-adiabatic geometric phase of elastic waves. The Journal of the Acoustical Society of America, 130, 2514.
Résumé: We study the transport of elastic waves in a waveguide with helical shape. Polarization exhibits a geometric phase (or Berry phase): The polarization plane rotates along the helix following a geometric rule called parallel transport. Whereas this experiment is similar to the first experimental evidence of a Berry phase, by Tomita and Chiao [Phys. Rev. Lett. 57 (1986)], there is a major difference: The evolution of polarization is not adiabatic. This experiment therefore addresses the universality of the geometric phase beyond the adiabatic regime. We show that properties of the observed geometric phase coincide with the ones predicted by the adiabatic theory. The measured value of the phase is consistent (up to experimental uncertainty) with the theoretical value and no dependency with frequency is observable either.
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Brenguier, F., Clarke, D., Aoki, Y., Shapiro, N. M., Campillo, M., & Ferrazzini, V. (2011). Monitoring volcanoes using seismic noise correlations. Comptes Rendus Geoscience, 343, 633–638.
Résumé: In this article, we summarize some recent results of measurements of temporal changes of active volcanoes using seismic noise cross-correlations. We first present a novel approach to estimate volcano interior temporal seismic velocity changes. The proposed method allows to measure very small velocity changes (approximate to 0.1%) with a time resolution as small as one day. The application of that method to Piton de la Fournaise Volcano (La Reunion Island) shows velocity decreases preceding eruptions. Moreover, velocity changes from noise cross-correlations over 10 years allow to detect transient velocity changes that could be due to long-lasting intrusions of magma without eruptive activity or to pressure buildup associated to the replenishing of the magma reservoir. We also present preliminary results of noise cross-correlation waveform perturbation associated with the occurrence of dike injection and volcanic eruption. We show that such an analysis leads us to locate the areas of dike injection and eruptive fissures at Piton de la Fournaise Volcano. These recent results suggest that monitoring volcanoes using seismic noise correlations should improve our ability to forecast eruptions, their intensity and thus potential environmental impact. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
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Brito, D., Alboussiere, T., Cardin, P., Gagniere, N., Jault, D., La Rizza, P., et al. (2011). Zonal shear and super-rotation in a magnetized spherical Couette-flow experiment. Physical Review E, 83.
Résumé: We presentmeasurements performed in a spherical shell filled with liquid sodium, where a 74-mm-radius inner sphere is rotated while a 210-mm-radius outer sphere is at rest. The inner sphere holds a dipolar magnetic field and acts as a magnetic propeller when rotated. In this experimental setup called “Derviche Tourneur Sodium” (DTS), direct measurements of the velocity are performed by ultrasonic Doppler velocimetry. Differences in electric potential and the induced magnetic field are also measured to characterize the magnetohydrodynamic flow. Rotation frequencies of the inner sphere are varied between -30 Hz and +30 Hz, the magnetic Reynolds number based on measured sodium velocities and on the shell radius reaching to about 33. We have investigated the mean axisymmetric part of the flow, which consists of differential rotation. Strong super-rotation of the fluid with respect to the rotating inner sphere is directly measured. It is found that the organization of the mean flow does not change much throughout the entire range of parameters covered by our experiment. The direct measurements of zonal velocity give a nice illustration of Ferraro's law of isorotation in the vicinity of the inner sphere, where magnetic forces dominate inertial ones. The transition from a Ferraro regime in the interior to a geostrophic regime, where inertial forces predominate, in the outer regions has been well documented. It takes place where the local Elsasser number is about 1. A quantitative agreement with nonlinear numerical simulations is obtained when keeping the same Elsasser number. The experiments also reveal a region that violates Ferraro's law just above the inner sphere.
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Brossier, R. (2011). Two-dimensional frequency-domain visco-elastic full waveform inversion: Parallel algorithms, optimization and performance. Computers & Geosciences, 37, 444–455.
Résumé: Full waveform inversion (FWI) is an appealing seismic data-fitting procedure for the derivation of high-resolution quantitative models of the subsurface at various scales. Full modelling and inversion of viscoelastic waves from multiple seismic sources allow for the recovering of different physical parameters, although they remain computationally challenging tasks. An efficient massively parallel, frequency-domain FWI algorithm is implemented here on large-scale distributed-memory platforms for imaging two-dimensional visco-elastic media. The resolution of the elastodynamic equations, as the forward problem of the inversion, is performed in the frequency domain on unstructured triangular meshes, using a low-order finite element discontinuous Galerkin method. The linear system resulting from discretization of the forward problem is solved with a parallel direct solver. The inverse problem, which is presented as a non-linear local optimization problem, is solved in parallel with a quasi-Newton method, and this allows for reliable estimation of multiple classes of visco-elastic parameters. Two levels of parallelism are implemented in the algorithm, based on message passing interfaces and multi-threading, for optimal use of computational time and the core-memory resources available on modern distributed-memory multi-core computational platforms. The algorithm allows for imaging of realistic targets at various scales, ranging from near-surface geotechnic applications to crustal-scale exploration. (C) 2010 Elsevier Ltd. All rights reserved.
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Calandra, H., Plessix, R. E., & Virieux, J. (2011). Special Issue: Modelling Methods for Geophysical Imaging: Trends and Perspectives Foreword. Geophysical Prospecting, 59, 793.
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Campillo, M., Sato, H., Shapiro, N. M., & van der Hilst, R. D. (2011). New developments on imaging and monitoring with seismic noise Foreword. Comptes Rendus Geoscience, 343, 487–495.
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Candela, T., Renard, F., Bouchon, M., Schmittbuhl, J., & Brodsky, E. E. (2011). Stress Drop during Earthquakes: Effect of Fault Roughness Scaling. Bulletin of the Seismological Society of America, 101, 2369–2387.
Résumé: We propose that a controlling parameter of static stress drop during an earthquake is related to the scaling properties of the fault-surface topography. Using high resolution laser distance meters, we have accurately measured the roughness scaling properties of two fault surfaces in different geological settings (the French Alps and Nevada). The data show that fault-surface topography is scale dependent and may be accurately described by a self-affine geometry with a slight anisotropy characterized by two extreme roughness exponents (H(R)), H(parallel to) = 0: 6 in the direction of slip and H(perpendicular to) = 0.8 perpendicular to slip. Disregarding plastic processes like rock fragmentation and focusing on elastic deformation of the topography, which is the dominant mode at large scales, the stress drop is proportional to the deformation, which is a spatial derivative of the slip. The evolution of stress-drop fluctuations on the fault plane can be derived directly from the self-affine property of the fault surface, with the length scale (lambda) as std(Delta sigma)(lambda) proportional to lambda(HR-1). Assuming no characteristic length scale in fault roughness and a rupture cascade model, we show that as the rupture grows, the average stress drop, and its variability should decrease with increasing source dimension. That is for the average stress drop Delta sigma(r) proportional to r(HR-1), where r is the radius of a circular rupture. This result is a direct consequence of the elastic squeeze of fault asperities that induces the largest spatial fluctuations of the shear strength before and after the earthquake at local (small) scales with peculiar spatial correlations.
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Candela, T., Renard, F., Schmittbuhl, J., Bouchon, M., & Brodsky, E. E. (2011). Fault slip distribution and fault roughness. Geophysical Journal International, 187, 959–968.
Résumé: We present analysis of the spatial correlations of seismological slip maps and fault topography roughness, illuminating their identical self-affine exponent. Though the complexity of the coseismic spatial slip distribution can be intuitively associated with geometrical or stress heterogeneities along the fault surface, this has never been demonstrated. Based on new measurements of fault surface topography and on statistical analyses of kinematic inversions of slip maps, we propose a model, which quantitatively characterizes the link between slip distribution and fault surface roughness. Our approach can be divided into two complementary steps: (i) Using a numerical computation, we estimate the influence of fault roughness on the frictional strength (pre-stress). We model a fault as a rough interface where elastic asperities are squeezed. The Hurst exponent H(tau), characterizing the self-affinity of the frictional strength field, approaches H(tau) = H(//)-1, where H(//) is the roughness exponent of the fault surface in the direction of slip. (ii) Using a quasi-static model of fault propagation, which includes the effect of long-range elastic interactions and spatial correlations in the frictional strength, the spatial slip correlation is observed to scale as H(s) = H(tau) + 1, where H(s) represents the Hurst exponent of the slip distribution. Under the assumption that the origin of the spatial fluctuations in frictional strength along faults is the elastic squeeze of fault asperities, we show that self-affine geometrical properties of fault surface roughness control slip correlations and that H(s) = H(//). Given that H(//) = 0.6 for a wide range of faults (various accumulated displacement, host rock and slip movement), we predict that H(s) = 0.6. Even if our quasi-static fault model is more relevant for creeping faults, the spatial slip correlations observed are consistent with those of seismological slip maps. A consequence is that the self-affinity property of slip roughness may be explained by fault geometry without considering dynamical effects produced during an earthquake.
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Catheline, S., Gallot, T., Roux, P., Ribay, G., & de Rosny, J. (2011). Coherent backscattering enhancement in cavities The simple-shape cavity revisited. Wave Motion, 48, 214–222.
Résumé: Coherent backscattering enhancement (CBE) was introduced in disordered, random or chaotic media. In this study, our attention is focused on simple parallelepipedic cavities, as contrary to the widespread opinion, CBE can also be observed for a pure-tone source in a one-dimensional (1-D) cavity. This approach is of two-fold interest. First, analytical calculus predicts a dimensional dependence of the CBE according to a R = (3/2)(d) law, with d = 1,2,3 as the dimensionality of the cavity; these computations have not yet been compared to experiments. Secondly, a ray approach in simple-shape cavities confirms the modal theory and opens new ballistic interpretations, for which each multiply reverberated path is not necessarily associated with one single reciprocal counterpart. The number of associated equal length paths ranges from zero to four in rectangular cavities. (C) 2010 Elsevier B.V. All rights reserved.
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Catinon, M., Ayrault, S., Spadini, L., Boudouma, O., Asta, J., Tissut, M., et al. (2011). Tree bark suber-included particles: A long-term accumulation site for elements of atmospheric origin. Atmospheric Environment, 45, 1102–1109.
Résumé: The deposition of atmospheric elements on and into the bark of 4-year-old Fraxinus excelsior L was studied. The elemental composition of the suber tissue was established through ICP-MS analysis and the presence of solid mineral particles included in this suber was established and described through SEM-EDX. Fractionation of the suber elements mixture was obtained after ashing at 550 degrees C through successive water (C fraction) and HNO(3) 2 M (D fraction) extraction, leading to an insoluble residue mainly composed of the solid mineral particles (E fraction). The triplicated % weight of C. D and E were respectively 34.4 +/- 2.7, 64.8 +/- 2.7 and 0.8 +/- 0.1% of the suber ashes weight. The main component of C was K, of D was Ca. Noticeable amounts of Mg were also observed in D. The E fraction, composed of insoluble particles, was mostly constituted of geogenic products, with elements such as Si, Al, K, Mg, representing primary minerals. E also contained Ca(3)(PO(4))(2) and concentrated the main part of Pb and Fe. Moreover, The SEM-EDX analysis evidenced that this fraction also concentrated several types of fly ashes of industrial origin. The study of the distribution between C, D and E was analysed through ICP-MS with respect to their origin. The origin of the elements found in such bark was either geogenic (clay, micas, quartz...), anthropogenic or biogenic (for instance large amounts of solid Ca organic salts having a storage role). As opposed to the E fraction, the C fraction, mainly composed of highly soluble K+ is characteristic of a biological pool of plant origin. In fraction D, the very high amount of Ca++ corresponds to two different origins: biological or acid soluble minerals such as calcite. Furthermore, the D fraction contains the most part of pollutants of anthropic origin such as Zn, Cu, Ni, Co, Cd. As a whole, the fractionation procedure of the suber samples allows to separate elements as a function of their origin but also gives valuable information on distribution and speciation of trace elements. (C) 2010 Elsevier Ltd. All rights reserved.
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Cederbom, C. E., van der Beek, P., Schlunegger, F., Sinclair, H. D., & Oncken, O. (2011). Rapid extensive erosion of the North Alpine foreland basin at 5-4 Ma. Basin Research, 23, 528–550.
Résumé: An extensive low-temperature thermochronology study of the Swiss part of the North Alpine Foreland Basin has been conducted with the aim of deciphering the late Neogene basin development. Apatite fission-track (AFT) ages from wells located in the distal and weakly deformed Plateau Molasse reveal rapid, km-scale erosion with an onset in early Pliocene times. The distribution of erosion implies that there was a strong gradient in late Miocene deposition rates along the strike of the basin, with an increase towards the northeast. Additionally, renewed tectonic activity and km-scale out-of-sequence thrusting during Plio-Pleistocene times is indicated by AFT data from wells within the thrusted, proximal Subalpine Molasse. Several different mechanisms driving late Neogene basin erosion and accelerated erosional discharge from the European Alps have been considered in the literature. Based on our AFT results, we reevaluate previously published hypotheses, and suggest that a change in climate and/or drainage reorganisation coincided and possibly interacted with preexisting tectonic and geodynamic forces in the Alpine region.
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Cenki-Tok, B., Oliot, E., Rubatto, D., Berger, A., Engi, M., Janots, E., et al. (2011). Preservation of Permian allanite within an Alpine eclogite facies shear zone at Mt Mucrone, Italy: Mechanical and chemical behavior of allanite during mylonitization. Lithos, 125, 40–50.
Résumé: This study addresses the mechanical and chemical behavior of allanite during shear zone formation under high-pressure metamorphism. Understanding physico-chemical processes related to the retention or resetting of Pb isotopes in allanite during geological processes is essential for robust petrochronology. Dating of allanite in meta-granodiorite showing variable amounts of strain (from an undeformed protolith to mylonite) at Monte Mucrone (Sesia Zone, NW Italy) gave surprising results. Based on structural and petrographic observations the shear zones at Mt Mucrone are Alpine, yet allanite located within an eclogite facies mylonite yielded Permian ages ((208)Pb/(232)Th average age: 287 +/- 7 Ma). These mm-sized allanite grains are rimmed by an aggregate of coarse-grained garnet tau phengite, thought to derive from former epidote. These aggregates were immersed in a weak matrix that experienced granular flow, and they were thus chemically and mechanically shielded during Alpine mylonitization. In undeformed samples (8a and 8b), two populations of epidote group minerals were found. Allanite forms either coronas around Permian monazite or individual grains with patchy zoning. Both types yield Permian ages ((208)Pb/(232)Th age: 291 +/- 5 Ma). On the other hand, grains of REF-rich clinozoisite of Cretaceous age are found in undeformed rocks. These grains appear as small fragments with embayed surface outlines and minute satellites or rims around Permian allanite. These (re)crystallized grains are Sr-rich and show mosaic zoning. These results indicate that allanite crystals retained their chemical and isotopic characteristics, and thus their Permian age, as a result of strong strain partitioning between the epidote group porphyroclasts and the eclogite facies matrix in HP-mylonites. The observed partial mobilization of Pb isotopes, which lead to the Cretaceous-aged rims or grains in undeformed samples was facilitated by (re)crystallization of allanite and not by mere Pb diffusion alone under the HP conditions. (C) 2011 Elsevier B.V. All rights reserved.
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Chakraborty, S., Bardelli, F., Mullet, M., Greneche, J. - M., Varma, S., Ehrhardt, J. - J., et al. (2011). Spectroscopic studies of arsenic retention onto biotite. Chemical Geology, 281, 83–92.
Résumé: Biotite is a constituent Fe-bearing mineral of Delta subsoils in India and Bangladesh and has been hypothesized as a primary source of arsenic (As). The adsorption behavior of As onto structural Fe(II, III)-bearing biotite fractions ( <50 mu m) was investigated in the pH range of 4-8 under a CO(2)-free, anoxic condition (O(2)<1 ppmv) using X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS). The batch experiments indicate that As adsorption is strongly pH dependent and that As(V) adsorbs more efficiently than As(III). X-ray Absorption Near-Edge Structure (XANES) spectra show no oxidation or reduction of As by biotite after reaction with As(III) or As(V) solutions for 3 days. Extended X-ray Absorption Fine Structure (EXAFS) spectroscopic results suggest that As(III) forms bidentate mononuclear edge-sharing ((2)E) and bidentate binuclear corner-sharing ((2)C) surface complexes at pH 7.7 as indicated by average As-Fe bond distances at 3.00 +/- 0.02 angstrom and 3.37 +/- 0.03 angstrom respectively. The surface speciation retrieved by XPS does not provide any evidence of reduction of As(V) on biotite after 30 days further confirming the thermodynamic prediction and the XANES results. This study has therefore significant environmental implications for As contaminated areas, where biotite retards the release of As into reducing groundwater. The changes in soil redox conditions and weathering of biotite may likely contribute to the occurrence of high As in groundwater. (C) 2010 Elsevier B.V. All rights reserved.
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Charlet, L., Morin, G., Rose, J., Wang, Y., Auffan, M., Burnol, A., et al. (2011). Reactivity at (nano)particle-water interfaces, redox processes, and arsenic transport in the environment. Comptes Rendus Geoscience, 343, 123–139.
Résumé: Massive deleterious impacts to human health are resulting from the use of arsenic-bearing groundwaters in South-East Asia deltas and elsewhere in the world for drinking, cooking and/or irrigation. In Bangladesh alone, a fifth of all deaths are linked to arsenicosis. In the natural and engineered subsurface environment, the fate of arsenic is, to a large extent, controlled by redox potential, pH, as well as total iron, sulfur and carbonate content, via sorption and coprecipitation on a variety of natural and engineered (nano)particles. In the present article, we address: (1) new insights in the sorption mechanisms of As on Fe(II) and Fe(III) nanophases recognized to play an important role in the microbial cycling of As and Fe; (2) artifacts often encountered in field and laboratory studies of As speciation due to the extreme redox sensitivity of the Fe-As-O-H phases; and (3) as a conclusion, the implications for water treatment. Indeed the specific reactivity of nanoparticles accounts not only for the As bioavailability within soils and aquifers, but also opens new avenues in water treatment. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
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Chauvel, C., Bureau, S., & Poggi, C. (2011). Comprehensive Chemical and Isotopic Analyses of Basalt and Sediment Reference Materials. Geostandards and Geoanalytical Research, 35, 125–143.
Résumé: Geochemical studies of geological samples require the precise determination of their major and trace element contents and, when measured, of their isotopic compositions. It is now commonly accepted that the accuracy and precision of geochemical analyses are best estimated by the concomitant analysis of international reference materials run as unknown samples. Although the composition of a wide selection of basalts is relatively well constrained, this is far from being the case for sedimentary materials. We present here a comprehensive set of major and trace element data as well as Nd, Hf, Sr and Pb isotopic compositions for thirteen commonly used international reference materials – eight magmatic rocks (BHVO-2, BR, BE-N, BR 24, AGV-1, BIR-1, UB-N, RGM-1) and five sediments (JLk-1, JSd-1, JSd-2, JSd-3, LKSD-1). We determined the concentrations of over forty elements in the magmatic rocks together with Sr, Nd, Hf and Pb isotopic compositions. Our trace element results were both accurate (difference < 3%) and precise (reproducibility at 1s < 3%) and the isotopic results were very similar to other published values. In contrast, we observed a significant chemical and isotopic variability in the sedimentary materials, which we attribute to mineral heterogeneities in the powders. Despite the limitation imposed by this heterogeneity, our work presents a complete set of data determined with a precision not yet achieved in the literature for sedimentary material. We also provide the first Nd, Hf and Pb isotopic measurements for the five sediments, which are commonly used by the geochemical community. Our study of both basalt and sediment reference materials represents a comprehensive and self-consistent set of geochemical data and can therefore be considered as a reference database for the community.Les etudes geochimiques des echantillons geologiques exigent la determination precise de leurs teneurs en elements majeurs et traces et, lorsqu'elle est mesuree, de leurs compositions isotopiques. Il est maintenant communement admis que l'exactitude et la precision des analyses geochimiques sont les mieux estimees par l'analyse simultanee, comme echantillons inconnus, de materiaux de reference internationaux. La composition d'une large selection de basaltes est relativement bien contrainte, ce qui est loin d'etre le cas pour les materiaux sedimentaires. Nous presentons ici un jeu complet de donnees d'elements majeurs et traces ainsi que les compositions isotopiques du Nd, de l'Hf, du Sr et du Pb pour treize materiaux de reference internationaux couramment utilises – huit roches magmatiques (BHVO-2, BR, BE-N, BR 24, AGV-1, BIR-1, UB-N, RGM-1) et cinq sediments (JLk-1, JSD-1, JSD-2, JSD-3, LKSD-1). Nous avons determine les concentrations de plus de quarante elements dans les roches magmatiques ainsi que leurs compositions isotopiques du Sr, du Nd, de l'Hf et du Pb. Nos resultats pour les elements traces sont a la fois precis (difference < 3%) et justes (reproducibilitea 1s < 3%) et les resultats isotopiques sont tres similaires aux autres valeurs publiees. En revanche, nous avons observe une variabilite chimique et isotopique significative pour les materiaux sedimentaires, que nous attribuons a la presence d'heterogeneites minerales au sein des poudres. Malgre les limitations imposees par ces heterogeneites, notre travail presente un jeu complet de donnees determine avec une precision encore jamais atteinte dans la litterature pour des materiaux sedimentaires. Nous fournissons egalement les premieres mesures isotopiques du Nd, de l'Hf et d Pb pour les cinq sediments, qui sont couramment utilisees par la communaute geochimique. Notre etude a la fois de basaltes et de sediments de reference represente un ensemble complet et auto-coherent de donnees geochimiques qui peut donc etre considere comme une base de donnees de reference pour la communaute.
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Chauvet, F., Lapierre, H., Maury, R. C., Bosch, D., Basile, C., Cotten, J., et al. (2011). Triassic alkaline magmatism of the Hawasina Nappes: Post-breakup melting of the Oman lithospheric mantle modified by the Permian Neotethyan Plume. Lithos, 122, 122–136.
Résumé: Middle to Late Triassic lavas were sampled within three tectonostratigraphic groups of the Hawasina Nappes in the Oman Mountains. They are predominantly alkali basalts and trachybasalts, associated with minor sub-alkaline basalts, trachyandesites, trachytes and rhyolites. Their major, trace elements and Nd-Pb isotopic compositions are very similar to those of the Permian plume-related high-Ti basalts which also occur in the Hawasina Nappes. The Triassic lavas derive from low-degree melting of an enriched OIB-type mantle source, characterized by epsilon Nd(i) = 0.3-5.3 and ((206)Pb/(204)Pb)(i) = 16.96-19.31 (for t = 230 My). With time, melting depths decreased from the garnet + spinel to the spinel lherzolite facies and the degree of melting increased. The oldest are distinguished from the others by unradiogenic Nd and Pb signatures, with epsilon Nd(i) = -4.5 to -1.2 and ((209)Pb/(204)Pb)(i) = 16.35-17.08, which we attribute to their contamination by Arabo-Nubian lower crust. The lavas likely derived from the Oman lithospheric mantle, the original DMM-HIMU signature of which was overprinted during its pervasive metasomatism by the Permian plume-related melts. We suggest that these lavas were emplaced during post-breakup decompression-triggered melting in the Middle Triassic during global kinematic reorganization of the Tethyan realm. (c) 2010 Elsevier B.V. All rights reserved.
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Chiaraluce, L., Chiarabba, C., De Gori, P., Di Stefano, R., Improta, L., Piccinini, D., et al. (2011). The 2009 L'Aquila (central Italy) seismic sequence. Bollettino Di Geofisica Teorica Ed Applicata, 52, 367–387.
Résumé: On April 6 (01:32 UTC) 2009 a M(W) 6.1 normal faulting earthquake struck the axial area of the Abruzzo region in central Italy. The earthquake heavily damaged the city of L'Aquila and its surroundings, causing 308 casualties, 70,000 evacuees and incalculable losses to the cultural heritage. We present the geometry of the fault system composed of two main normal fault planes, reconstructed by means of seismicity distribution: almost 3000 events with M(L)>= 1.9 occurred in the area during 2009. The events have been located with a 1D velocity model we computed for the area by using data of the seismic sequence. The mainshock, located at around a 9.3 km depth beneath the town of L'Aquila, activated a 50 degrees (+/-3) SW-dipping and similar to 135 degrees NW-trending normal fault with a length of about 16 km. The aftershocks activated the whole 10 km of the upper crust up to the surface. The geometry of the fault is coherent with the mapped San Demetrio-Paganica and Mt. Stabiata normal faults. The whole normal fault system that reached about 40 km of length by the end of December in the NW-trending direction, was activated within the first few days of the sequence when most of the energetic events occurred. The main shock fault plane was activated by a foreshock sequence that culminated with a M(W) 4.0 on March 30 (13:38 UTC), showing extensional kinematics with a minor left lateral component. The second major structure, located to the north close to Campotosto village, is controlled by an M(W) 5.0 event, which occurred on the same day of the main shock (April 6 at 23: 15 UTC), and by an M(W) 5.2 event (April 9 at 00:53 UTC). The fault plane shows a shallower dip angle with respect to the main fault plane, of about 35 degrees with a tendency to flattening towards the deepest portion. Due to the lack of seismicity above a 5 km depth, the connection between this structure and the mapped Monti della Laga fault is not straightforward. This northern segment is recognisable for about 12-14 km of length, always NW-trending and forming a right lateral step with the main fault plane. The result is a en-echelon system overlapping for about 6 km. The seismicity pattern also highlights the activation of numerous minor normal fault segments within the whole fault system. The deepest is located at around a 13-15 km depth, south of the L'Aquila mainshock, and it seems to be antithetic to the main fault plane.
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Chlieh, M., Perfettini, H., Tavera, H., Avouac, J. - P., Remy, D., Nocquet, J. - M., et al. (2011). Interseismic coupling and seismic potential along the Central Andes subduction zone. Journal of Geophysical Research-Solid Earth, 116.
Résumé: We use about two decades of geodetic measurements to characterize interseismic strain build up along the Central Andes subduction zone from Lima, Peru, to Antofagasta, Chile. These measurements are modeled assuming a 3-plate model (Nazca, Andean sliver and South America Craton) and spatially varying interseismic coupling (ISC) on the Nazca megathrust interface. We also determine slip models of the 1996 M(w) = 7.7 Nazca, the 2001 M(w) = 8.4 Arequipa, the 2007 M(w) = 8.0 Pisco and the M(w) = 7.7 Tocopilla earthquakes. We find that the data require a highly heterogeneous ISC pattern and that, overall, areas with large seismic slip coincide with areas which remain locked in the interseismic period (with high ISC). Offshore Lima where the ISC is high, a M(w) similar to 8.6-8.8 earthquake occurred in 1746. This area ruptured again in a sequence of four M(w) similar to 8.0 earthquakes in 1940, 1966, 1974 and 2007 but these events released only a small fraction of the elastic strain which has built up since 1746 so that enough elastic strain might be available there to generate a M(w) > 8.5 earthquake. The region where the Nazca ridge subducts appears to be mostly creeping aseismically in the interseismic period (low ISC) and seems to act as a permanent barrier as no large earthquake ruptured through it in the last 500 years. In southern Peru, ISC is relatively high and the deficit of moment accumulated since the M(w) similar to 8.8 earthquake of 1868 is equivalent to a magnitude M(w) similar to 8.4 earthquake. Two asperities separated by a subtle aseismic creeping patch are revealed there. This aseismic patch may arrest some rupture as happened during the 2001 Arequipa earthquake, but the larger earthquakes of 1604 and 1868 were able to rupture through it. In northern Chile, ISC is very high and the rupture of the 2007 Tocopilla earthquake has released only 4% of the elastic strain that has accumulated since 1877. The deficit of moment which has accumulated there is equivalent to a magnitude M(w) similar to 8.7 earthquake. This study thus provides elements to assess the location, size and magnitude of future large megathurst earthquakes in the Central Andes subduction zone. Caveats of this study are that interseismic strain of the forearc is assumed time invariant and entirely elastic. Also a major source of uncertainty is due to fact that the available data place very little constraints on interseismic coupling at shallow depth near the trench, except offshore Lima where sea bottom geodetic measurements have been collected suggesting strong coupling.
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Connolly, B. D., Puchtel, I. S., Walker, R. J., Arevalo, R., Piccoli, P. M., Byerly, G., et al. (2011). Highly siderophile element systematics of the 3.3 Ga Weltevreden komatiites, South Africa: Implications for early Earth history. Earth and Planetary Science Letters, 311, 253–263.
Résumé: Highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundances, Re-Os isotopic systematics, and major-, minor-, and lithophile trace element abundances are determined for a suite of remarkably fresh komatiites from the Weltevreden Formation (Fm.) of the Barberton Greenstone Belt, South Africa. The komatiite lavas examined are calculated to have contained ca. 31% MgO upon emplacement, and are among the most MgO-rich lavas ever erupted onto Earth's surface. Based on the partitioning behavior of V, indicating reduced conditions of magma formation, as well as the low calculated H(2)O abundance of similar to 0.02% in the mantle source, anhydrous melting for the Weltevreden Fm. komatiites is inferred. The high calculated liquidus temperatures of the emplaced komatiite lavas of ca. 1600 degrees C require an unusually hot (similar to 1800 degrees C) mantle source, >100 degrees C hotter than the ambient contemporaneous mantle. These observations are most consistent with formation of the Weltevreden komatiites via deep (similar to 530 km) melting in a mantle plume. The Re-Os isotopic data for twelve whole-rock samples and an olivine separate define a precise Re-Os isochron age of 3266 +/- 8 Ma (2 sigma(mean)) and an initial (187)Os/(188)Os of 0.10440 +/- 5 (gamma(187)Os = 0.13 +/- 0.05). The Re-Os data, coupled with the relatively high calculated HSE abundances in the mantle source totaling similar to 80% of those in modern Primitive Mantle (PM) estimates, indicate that at least some portions of the deep, early Archean mantle evolved with essentially chondritic Re/Os and absolute HSE abundances that are typical of the sources of late Archean komatiites. If the HSE budget of the terrestrial mantle was established via late accretion of several large planetesimals following the cessation of major chemical interaction between the core and the mantle, our data indicate that by 3.3 Ga, these materials were well homogenized within the mantle domains sampled by the Weltevreden komatiites and, by inference, within the mantle as a whole. (C) 2011 Elsevier B.V. All rights reserved.
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Cossart, E., Bourles, D., Braucher, R., Carcaillet, J., Fort, M., & Siame, L. (2011). Glacier extents within Brianconnais Alps (southern French Alps) from the Last Glacial Maximum to the Holocene: chronological synthesis. Geomorphologie-Relief Processus Environnement, , 123–142.
Résumé: This paper aims to provide an overview of the investigations led in the Upper-Durance catchment (upstream Guillestre), focusing on the disappearance of glaciers after the Last Glacial Maximum. It is based on extensive fieldwork, describing and mapping the geomorphic remnants of past-glaciations, and 35 Cosmic Ray Exposure ages. A four-stage chronological sequence summarises glacial variations during the Late-Glacial/Holocene transition. The main results provide both chronological data (two generations of moraines identified as Younger Dryas and Preboreal) and spatial data (asymmetry of glaciers development in the Upper-Durance catchment during the Late-Glacial), providing new findings that may be useful for palaeo-climatologists.
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Cros, E., Roux, P., Vandemeulebrouck, J., & Kedar, S. (2011). Locating hydrothermal acoustic sources at Old Faithful Geyser using Matched Field Processing. Geophysical Journal International, 187, 385–393.
Résumé: In 1992, a large and dense array of geophones was placed around the geyser vent of Old Faithful, in the Yellowstone National Park, to determine the origin of the seismic hydrothermal noise recorded at the surface of the geyser and to understand its dynamics. Old Faithful Geyser (OFG) is a small-scale hydrothermal system where a two-phase flow mixture erupts every 40 to 100 min in a high continuous vertical jet. Using Matched Field Processing (MFP) techniques on 10-min-long signal, we localize the source of the seismic pulses recorded at the surface of the geyser. Several MFP approaches are compared in this study, the frequency-incoherent and frequency-coherent approach, as well as the linear Bartlett processing and the non-linear Minimum Variance Distorsionless Response (MVDR) processing. The different MFP techniques used give the same source position with better focalization in the case of the MVDR processing. The retrieved source position corresponds to the geyser conduit at a depth of 12 m and the localization is in good agreement with in situ measurements made at Old Faithful in past studies.
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Daniel, G., Prono, E., Renard, F., Thouvenot, F., Hainzl, S., Marsan, D., et al. (2011). Changes in effective stress during the 2003-2004 Ubaye seismic swarm, France. Journal of Geophysical Research-Solid Earth, 116.
Résumé: We study changes in effective stress (normal stress minus pore pressure) that occurred in the French Alps during the 2003-2004 Ubaye earthquake swarm. Two complementary data sets are used. First, a set of 974 relocated events allows us to finely characterize the shape of the seismogenic area and the spatial migration of seismicity during the crisis. Relocations are performed by a double-difference algorithm. We compute differences in travel times at stations both from absolute picking times and from cross-correlation delays of multiplets. The resulting catalog reveals a swarm alignment along a single planar structure striking N130 degrees E and dipping 80 degrees W. This relocated activity displays migration properties consistent with a triggering by a diffusive fluid overpressure front. This observation argues in favor of a deep-seated fluid circulation responsible for a significant part of the seismic activity in Ubaye. Second, we analyze time series of earthquake detections at a single seismological station located just above the swarm. This time series forms a dense chronicle of +16,000 events. We use it to estimate the history of effective stress changes during this sequence. For this purpose we model the rate of events by a stochastic epidemic-type aftershock sequence model with a nonstationary background seismic rate lambda(0)(t). This background rate is estimated in discrete time windows. Window lengths are determined optimally according to a new change-point method on the basis of the interevent times distribution. We propose that background events are triggered directly by a transient fluid circulation at depth. Then, using rate-and-state constitutive friction laws, we estimate changes in effective stress for the observed rate of background events. We assume that changes in effective stress occurred under constant shear stressing rate conditions. We finally obtain a maximum change in effective stress close to -8 MPa, which corresponds to a maximum fluid overpressure of about 8 MPa under constant normal stress conditions. This estimate is in good agreement with values obtained from numerical modeling of fluid flow at depth, or with direct measurements reported from fluid injection experiments.
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Daval, D., Sissmann, O., Menguy, N., Saldi, G. D., Guyot, F., Martinez, I., et al. (2011). Influence of amorphous silica layer formation on the dissolution rate of olivine at 90 degrees C and elevated pCO(2). Chemical Geology, 284, 193–209.
Résumé: For mitigating against rising levels of atmospheric CO(2), carbonation of M(2+)-bearing silicates has been proposed as a possible option for sequestering CO(2) over long time spans. Due to its rapid far-from-equilibrium dissolution rate and its widespread occurrence in mafic and ultramafic rocks, olivine has been suggested as a potentially good candidate for achieving this goal, although the efficacy of the carbonation reaction still needs to be assessed. With this as a goal, the present study aims at measuring the carbonation rate of San Carlos olivine in batch experiments at 90 degrees C and pCO(2) of 20 and 25 MPa. When the reaction was initiated in pure water, the kinetics of olivine dissolution was controlled by the degree of saturation of the bulk solution with respect to amorphous silica. This yet unrecognized effect for olivine was responsible for a decrease of the dissolution rate by over two orders of magnitude. In long-term (45 days) carbonation experiments with a high surface area to solution volume ratio (SA/V=24,600 m(-1)), the final composition of the solution was close to equilibrium with respect to SiO(2)(am), independent of the initial concentration of dissolved salts (NaCl and NaClO(4), ranging between 0 and 1 m), and with an aqueous Mg/Si ratio close to that of olivine. No secondary phase other than a ubiquitous thin (<= 40 nm), Si-rich amorphous layer was observed. These results are at odds with classic kinetic modeling of the process. Due to experimental uncertainties, it was not possible to determine precisely the dissolution rate of olivine after 45 days. but the long term alteration of olivine was indirectly estimated to be at least 4 orders of magnitude slower than predicted. Taken together, these results suggest that the formation of amorphous silica layers plays an important role in controlling the rate of olivine dissolution by passivating the surface of olivine, an effect which has yet to be quantified and incorporated into standard reactive-transport codes. Published by Elsevier B.V.
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De Andrade, V., Susini, J., Salome, M., Beraldin, O., Rigault, C., Heymes, T., et al. (2011). Submicrometer Hyperspectral X-ray Imaging of Heterogeneous Rocks and Geomaterials: Applications at the Fe K-Edge. Analytical Chemistry, 83, 4220–4227.
Résumé: Because of their complex genesis, rocks and geomaterials are commonly polycrystalline heterogeneous systems, with various scale-level chemical and structural heterogeneities. Like most other mu-analytical techniques relying on scanning instruments with pencil-beam, the X-ray absorption near edge structure (XANES) technique allows elemental oxidation states to be probed with high spatial resolution but suffers from long acquisition times, imposing practical limits on the field of view. Now, regions of interest of sample are generally several orders of magnitude larger than the beam size. Here, we show the potential of coupling XANES and full-field absorption radiographies with a large hard X-ray beam. Thanks to a new setup, which allows both the acquisition of a XANES image stack and the execution of polarization contrast imaging, 1 to 4 mega-pixel crystallographic orientations and Fe oxidation state mapping corrected from polarization effects are obtained in a couple of hours on polycrystalline materials with submicrometric resolution. The demonstration is first carried out on complex metamorphic rocks, where Fe(3+)/Fe(total) images reveal subtle redox variations within single mineralogical phases. A second application concerns a bentonite analogue considered for nuclear waste and CO(2) storage. Proportion mappings of finely mixed phases are extracted from hyperspectral data, imaging the spatial progress of reaction processes essential for the safety of such storage systems.
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De Barros, L., Lokmer, I., Bean, C. J., O'Brien, G. S., Saccorotti, G., Metaxian, J. P., et al. (2011). Source mechanism of long-period events recorded by a high-density seismic network during the 2008 eruption on Mount Etna. Journal of Geophysical Research-Solid Earth, 116.
Résumé: One hundred twenty-nine long-period (LP) events, divided into two families of similar events, were recorded by the 50 stations deployed on Mount Etna in the second half of June 2008. During this period lava was flowing from a lateral fracture after a summit Strombolian eruption. In order to understand the mechanisms of these events, we perform moment tensor inversions. Inversions are initially kept unconstrained to estimate the most likely mechanism. Numerical tests show that unconstrained inversion leads to reliable moment tensor solutions because of the close proximity of numerous stations to the source positions. However, single forces cannot be accurately determined as they are very sensitive to uncertainties in the velocity model. Constrained inversions for a crack, a pipe or an explosion then allow us to accurately determine the structural orientations of the source mechanisms. Both numerical tests and LP event inversions emphasise the importance of using stations located as close as possible to the source. Inversions for both families show mechanisms with a strong volumetric component. These events are most likely generated by cracks striking SW-NE for both families and dipping 70 degrees SE (family 1) and 50 NW (family 2). For family 1 events, the crack geometry is nearly orthogonal to the dikelike structure along which events are located, while for family 2 the location gave two pipelike bodies that belong to the same plane as the crack mechanism. The orientations of the cracks are consistent with local tectonics, which shows a SW-NE weakness direction. The LP events appear to be a response to the lava fountain occurring on 10 May 2008 as opposed to the flank lava flow.
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De Cacqueray, B., Roux, P., Campillo, M., Catheline, S., & Boue, P. (2011). Elastic-wave identification and extraction through array processing: An experimental investigation at the laboratory scale. Journal of Applied Geophysics, 74, 81–88.
Résumé: The mix of body waves and surface waves is a recurrent problem for deep exploration in geophysical contexts. As surface waves represent up to 70% of the recorded energy, they hide a large part of the information coming from the sub-surface through body waves. Efforts have been made in the past to better filter or remove surface waves: however, their impact is always far from negligible, especially with strong backscattering contributions. In parallel, taking advantage of an always growing number of channels, geophysical explorations face new opportunities to enhance the quality of Earth imaging. For example, better spatial sampling is a way to better use or remove surface waves. There are compromises to find between higher spatial sampling and operational costs, even for on-field tests. In this context, surface-wave studies at the laboratory scale are a flexible way to evaluate new acquisition designs and processing. This study shows how a gel-based phantom can be used successfully to study elastic-wave mixing in the context of geophysics prospection. Small-scale experiments provide the records of thousands of traces. Using projections in the slowness/angle domain, wave separation and identification algorithms are proposed, with the goal of being able to adapt array processing to geophysical-like designs. (C) 2011 Elsevier B.V. All rights reserved.
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Decou, A., von Eynatten, H., Mamani, M., Sempere, T., & Woerner, G. (2011). Cenozoic forearc basin sediments in Southern Peru (15-18 degrees S): Stratigraphic and heavy mineral constraints for Eocene to Miocene evolution of the Central Andes. Sedimentary Geology, 237, 55–72.
Résumé: A large sedimentary forearc basin developed in Cenozoic times between the present-day Coastal Cordillera and the Western Cordillera of the Central Andes, called Moquegua basin in southern Peru. The basin is filled by Moquegua Group deposits (similar to 50 to 4 Ma) comprising mostly siliciclastic mudstones, sandstones and conglomerates as well as volcanic intercalations. Several facies changes both, along orogenic strike and through time, are described and have led to subdivision into four sedimentary units (Moquegua A, B, C and D). In this paper we present a refined stratigraphic scheme of the Moquegua Group combined with the first provenance analysis of the Moquegua basin based on (i) semi-quantitative analysis of heavy mineral abundance, (ii) electron microprobe (EMP) and laser ablation (LA) ICP-MS analyses of single detrital amphibole and Fe-Ti oxide grains, and (iii) comparative analysis of the different potential source rocks to clearly identify the most likely sources. Results allow us to reconstruct sediment provenance and to relate changes of the erosion-sedimentation system in the Moquegua basin to the evolution of the Andean orogen. At similar to 50 to similar to 40 Ma the Moquegua basin was close to sea level and fed by low energy rivers transporting mainly metamorphic basement and Jurassic-Cretaceous sedimentary detritus from local and distal sources. The latter might be as far as the present Eastern Cordillera. From similar to 35 Ma on the distal sediment sources were cut off by the uplift of the Altiplano and Eastern Cordillera leading to higher energy fluvial systems and increasing importance of local sources, especially the relevant volcanic arcs. From 25 Ma on volcanic arc rocks became the predominant sources for Moquegua Group sediments. The 10 Ma time lag observed between the onset of uplift-induced facies and provenance changes (at similar to 35 Ma) and the onset of intense magmatic activity (at similar to 25 Ma) suggests that magmatic addition was not the main driver for crustal thickening and uplift in the Central Andes during latest Eocene to Oligocene time. (C) 2011 Elsevier B.V. All rights reserved.
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Deguen, R., & Cardin, P. (2011). Thermochemical convection in Earth's inner core. Geophysical Journal International, 187, 1101–1118.
Résumé: The dynamics of Earth's inner core depends critically on whether it is stably stratified or unstably stratified. We propose here a general analysis of the thermal evolution of the inner core. Whether the geotherm in the inner core is superadiabatic or not depends on the inner core solidification rate, on the thermal diffusivity of iron at inner core conditions, and on the ratio of the Clapeyron slope to the adiabatic gradient in the inner core. The temperature field within the inner core can be destabilizing-and could drive convection-if the growth of the inner core is fast enough. The effect of radiogenic heating is probably small, and, perhaps surprisingly, can even stabilize the inner core against convection. The uncertainties are such that it is not possible at present to conclude about the likelihood of thermal convection in the inner core, but recent estimates of the Core-Mantle Boundary (CMB) heat flux and inner core conductivity favour convection. Thermal convection is more likely early in the inner core history, a consequence of the secular decrease in cooling rate of the core. In addition, solidification-induced partitioning of the light elements may induce a stable density stratification within the inner core. We develop a numerical model of thermochemical convection in a growing inner core, which couples the evolution and dynamics of the inner core with the thermal and compositional evolution of the outer core. Melting and crystallization associated with deformation of the Inner Core Boundary (ICB) would be of importance for the style of convection if the viscosity is large, but we focus here on the case of low viscosity for which phase change associated with dynamic topography at the ICB is expected to play a secondary role. In this regime, convection is typical of high Rayleigh number internally heated convection, with cold plumes falling from the ICB. Several possible scenarios can lead to a layered inner core, either because of cessation of thermal convection due to the decrease in cooling rate of the core, or because of a compositional stratification which can confine convection in the deep inner core, or stabilize the whole inner core. For each of these scenarios, it is possible to find plausible sets of parameters (inner core age, viscosity, magnitude of the compositional stratification) for which the radius at which convection stops corresponds to the radius of the seismically inferred innermost inner core.
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Deguen, R., Cardin, P., Merkel, S., & Lebensohn, R. A. (2011). Texturing in Earth's inner core due to preferential growth in its equatorial belt. Physics of the Earth and Planetary Interiors, 188, 173–184.
Résumé: We propose an extension of the model by Yoshida et al., 1996 where deformation in the inner core is forced by preferential growth in the equatorial belt, by taking into account the presence of a stable compositional stratification. Stratification inhibits vertical motion, imposes a flow parallel to isodensity surfaces, and concentrates most deformation in a shallow shear layer of thickness similar to B(-1/5), where B is the dimensionless buoyancy number. The localization of the flow results in large strain rates and enables the development of a strong alignment of iron crystals in the upper inner core. We couple our dynamical model with a numerical model of texture development and compute the time evolution of the lattice preferred orientation of different samples in the inner core. With sufficient stratification, texturing is significant in the uppermost inner core. In contrast, the deeper inner core is unaffected by any flow and may preserve a fossil texture. We investigate the effect of an initial texture resulting from solidification texturing at the ICB. In the present inner core, the deformation rate in the shallow shear layer is large and can significantly alter the solidification texturing, but the solidification texture acquired early in the inner core history can be preserved in the deeper part. Using elastic constants from ab initio calculations, we predict different maps of anisotropy in the modern inner core. A model with both solidification texturing and subsequent deformation in a stratified inner core produces a global anisotropy in reasonable agreement with seismological observations. (C) 2011 Elsevier B.V. All rights reserved.
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Deguen, R., Olson, P., & Cardin, P. (2011). Experiments on turbulent metal-silicate mixing in a magma ocean. Earth and Planetary Science Letters, 310, 303–313.
Résumé: We compare the results of laboratory fluid dynamics experiments with theoretical models of turbulent entrainment in two-phase buoyant plumes and thermals to estimate the amount of mixing between the iron core of a planetesimal or planetary embryo and the molten silicates in a magma pool formed by its impact with a growing planet during accretion. We demonstrate experimentally that turbulent plumes in immiscible fluids fragment into droplets, and that the envelope of the droplet distribution is indistinguishable from the envelope of a turbulent plume in a single phase fluid under the same dynamical conditions, implying that turbulent entrainment concepts are applicable to immiscible fluids mixing. A series of experiments are made on the time evolution of a two-phase turbulent thermal, representing a planetesimal core, falling under its own negative buoyancy in a spherical fluid, representing an impact-produced magma pool. Two stages of mixing are observed in these experiments: the first corresponding to turbulent entrainment during free-fall of the thermal, the second corresponding to entrainment in turbulent gravity currents that form after the thermal reaches the base of the magma pool. We demonstrate that the amount of mixing between metals and silicate liquids in a magma pool depends on the Rouse number of the metal fragments and increases rapidly with the radius of the proto-planet. We derive a similarity model for metal-silicate mixing in a spherical magma pool, assuming a constant entrainment coefficient for the turbulent liquid metal phase. This model supports our experimental finding that a small metal core of an impactor will become diluted (i.e., mix) within a deep magma pool, but a large impacting core will not fully dilute before reaching the base of the magma pool. (C) 2011 Elsevier B.V. All rights reserved.
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Delolme, C., Spadini, L., Muris, M., Causse, B., & Gaudet, J. - P. (2011). Comparison of the acid-base reactivity of free-living Pseudomonas putida cells and biofilm. Chemical Geology, 289, 48–54.
Résumé: The proton reactivity of a soil bacterium, Pseudomonas putida ATCC12633 was investigated in two physiologically different states: (i) as free-living cells, and (ii) as a 5-day biofilm formed in a sandy column. Acid-base data analysis and modeling based on a three-site non-electrostatic model showed that biofilm has a proton exchange capacity 3.8 times higher than that of free-living cells (13.2 mmol/g(protein) corresponding to 5.9 +/- 1.2 mmol/g(dry weight) for biofilm and 3.8 mmol g(protein): 1.56 +/- 0.32 mmol/g(dry weight) for free cells). The higher proton exchange capacity of the biofilm fragments mainly results from the high content of the 'neutral' pK 6.5 sites. This increase was explained through sorption on the biofilm of mineral phosphate residues circulating with the nutrient medium during the 5 days of column biofilm growth. SEM biofilm observations show a dense network of excreted organic materials linking the individual cells and organic residues. On the contrary, free cells are clearly individualized. The differences between the morphology and reactivity of biofilms and free cells strongly indicate that the two substrates have different compositions. In opposition to free cells, acidic conditions lead to non reversible biofilm proton exchange properties that could be explained by biofilm coagulation processes. These results show the importance of the growing conditions of biofilm and especially its development on a solid surface in the determination of biofilm composition and reactivity. (C) 2011 Elsevier B.V. All rights reserved.
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Deschamps, F., Guillot, S., Godard, M., Andreani, M., & Hattori, K. (2011). Serpentinites act as sponges for fluid-mobile elements in abyssal and subduction zone environments. Terra Nova, 23, 171–178.
Résumé: P>Serpentinization of the oceanic lithosphere contributes significantly to the geochemical cycle from spreading ridges to subduction zones. In situ trace element analysis of oceanic serpentinites from the Mid-Atlantic Ridge and the Greater Antilles (Cuba, Dominican Republic) shows that all serpentine minerals are enriched in fluid-mobile elements (FME: As, Sb, B, Li, Cs, Pb, U, Ba, Sr). We observe no loss of these elements from abyssal to subduction environments during prograde metamorphism. Moreover, the transition from lizardite/chrysotile to antigorite during subduction is marked by a strong over-enrichment in As and Sb in antigorite, indicating late contamination by a sedimentary source. This suggests that a second stage of serpentinization occurs in the earlier stages of subduction, when newly formed or reactivated normal faults ease fluid penetration, and/or in the subduction channel. Our study shows that, from spreading ridges to forearc environments, serpentines act as sponges for FME. We posit that, until ultimate antigorite breakdown, serpentinites efficiently transport significant amounts of FME down to great depths in the mantle.
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Doan, M. - L., & Billi, A. (2011). High strain rate damage of Carrara marble. Geophysical Research Letters, 38.
Résumé: Several cases of rock pulverization have been observed along major active faults in granite and other crystalline rocks. They have been interpreted as due to coseismic pervasive microfracturing. In contrast, little is known about pulverization in carbonates. With the aim of understanding carbonate pulverization, we investigate the high strain rate (c. 100 s(-1)) behavior of unconfined Carrara marble through a set of experiments with a Split Hopkinson Pressure Bar. Three final states were observed: (1) at low strain, the sample is kept intact, without apparent macrofractures; (2) failure is localized along a few fractures once stress is larger than 100 MPa, corresponding to a strain of 0.65%; (3) above 1.3% strain, the sample is pulverized. Contrary to granite, the transition to pulverization is controlled by strain rather than strain rate. Yet, at low strain rate, a sample from the same marble displayed only a few fractures. This suggests that the experiments were done above the strain rate transition to pulverization. Marble seems easier to pulverize than granite. This creates a paradox: finely pulverized rocks should be prevalent along any high strain zone near faults through carbonates, but this is not what is observed. A few alternatives are proposed to solve this paradox. Citation: Doan, M.-L., and A. Billi (2011), High strain rate damage of Carrara marble, Geophys. Res. Lett., 38, L19302, doi:10.1029/2011GL049169.
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Doan, M. - L., Conin, M., Henry, P., Wiersberg, T., Boutt, D., Buchs, D., et al. (2011). Quantification of free gas in the Kumano fore-arc basin detected from borehole physical properties: IODP NanTroSEIZE drilling Site C0009. Geochemistry Geophysics Geosystems, 12.
Résumé: The Kumano fore-arc basin overlies the Nankai accretionary prism, formed by the subduction of the Philippine Sea Plate beneath the Eurasian plate offshore the Kii Peninsula, SW Honshu, Japan. Seismic surveys and boreholes within the framework of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) project show evidence of gas hydrates and free gas within the basin. Here we use high-quality borehole sonic data from Integrated Oceanic Drilling Program (IODP) Site C0009 to quantify the free gas distribution in the landward part of the basin. The Brie theory is used to quantify gas content from sonic logs, which are calibrated from laboratory measurements on drill cores. First, we show that the sonic data are mainly sensitive to the fluid phase filling the intergranular pores (effective porosity), rather than to the total porosity that includes water bound to clay minerals. We then compare the effective porosity to lithodensity-derived porosity that acts as a proxy for total porosity. The combination of these two data sets also allows assessment of clay mineralogy of the sediments. Second, we compute free gas saturation and find a gas-rich interval that is restricted to a lithological unit characterized by a high abundance of wood fragments and lignite. This unit, at the base of the fore-arc basin, is a hydrocarbon source that should be taken into account in models explaining gas distribution and the formation of the bottom-simulating reflector within the Kumano fore-arc basin.
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Drouet, S., Bouin, M. - P., & Cotton, F. (2011). New moment magnitude scale, evidence of stress drop magnitude scaling and stochastic ground motion model for the French West Indies. Geophysical Journal International, 187, 1625–1644.
Résumé: In this study we analyse records from the 'Les Saintes' seismic sequence following the M(w) = 6.3 earthquake of 2004 November 11, which occurred close to Guadeloupe (French West Indies). 485 earthquakes with magnitudes from 2 to 6, recorded at distances between 5 and 150 km are used. S-waves Fourier spectra are analysed to simultaneously determine source, path and site terms. The results show that the duration magnitude routinely estimated for the events that occurred in the region underestimate moment magnitude by 0.5 magnitude units over the whole magnitude range. From the inverted seismic moments and corner frequencies, we compute Brune's stress drops. We show that stress drops increase with increasing magnitude. The same pattern is observed on apparent stresses (i.e. the seismic energy-to-moment ratio). However, the rate of increase diminishes at high magnitudes, which is consistent with a constant stress drop model for large events. Using the results of the inversions, we perform ground motion simulations for the entire data set using the SMSIM stochastic simulation tool. The results show that a good fit (sigma = 0.25) with observed data is achieved when the source is properly described by its moment magnitude and stress drop, and when site effects are taken into account. Although the magnitude-dependent stress drop model is giving better results than the constant stress drop model, the interevent variability remains high, which could suggest that stress drop depends on other parameters such as the depth of the hypocentre. In any case, the overall variability is of the same order of magnitude as usually observed in empirical ground motion prediction equations.
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Dubacq, B., Vidal, O., & Lewin, E. (2011). Atomistic investigation of the pyrophyllitic substitution and implications on clay stability. American Mineralogist, 96, 241–249.
Résumé: Predicting phase relations and reactions involving phyllosilicates is of critical importance when modeling geological reservoirs and making thermobarometric estimates at temperatures below 350 C. However, it is difficult to perform experimental studies of phase relations of phyllosilicates because of very slow reaction rates. Simple methods of estimations of thermodynamic properties of minerals such as oxide summation techniques are insufficient to constrain activity models for minerals. In this study, we use a recent atomistic technique that allows constraining activity models in minerals independently from kinetics. Among the various solid solutions occurring in phyllosilicates, the magnitude and the thermodynamic significance of the pyrophyllitic substitution has strong implications on the stability of clay minerals at surface conditions. We have applied a lattice energy estimation method combined with Monte Carlo simulations to estimate the energy of mixing along the muscovite-pyrophyllite solid solution at 25 degrees C and 1 bar. The results suggest a strongly positive and asymmetric Gibbs free energy of mixing, concordant at first order with previous thermodynamic models issued from phase relations and with field observations. The calculated solvus implies that pyrophyllite-rich phyllosilicates are unstable, unless another phenomenon such as hydration stabilizes them. Calculated structures at low muscovite contents present large variations of interlayer occupancies due to short- and long-range ordering. The observed ordering suggests that sub-layers in illite/smectite mixed layers minerals are not independent as the alternation of K-rich and K-depleted sublayers minimizes the Gibbs free energy of the mineral.
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Dumont, T., Simon-Labric, T., Authemayou, C., & Heymes, T. (2011). Lateral termination of the north-directed Alpine orogeny and onset of westward escape in the Western Alpine arc: Structural and sedimentary evidence from the external zone. Tectonics, 30.
Résumé: The initial propagation of the Western Alpine orogen was directed northwestward, as shown by basement-involved and Mesozoic sedimentary cover compressional structures and by the early foreland basins evolution. The crystalline basement of the Dauphine zone recorded three shortening episodes: pre-Priabonian deformation D1 (coeval with the Pyrenean-Provence orogeny), and Alpine shortening events D2 (N-NW directed) and D3 (W-directed). The early Oligocene D2 structures are trending sub-perpendicular to the more recent, arcuate orogen and are interfering with (or truncated by) D3, which marks the onset of westward lateral extrusion. The NW-ward propagating Alpine flexural basin shows earliest Oligocene thin-skinned compressional deformation, with syn-depositional basin-floor tilting and submarine removal of the basin infill above active structures. Gravity enhanced submarine erosion gave birth locally to steep submarine slopes overlain by kilometric-scale blocks slid from the orogenic wedge. The deformations of the basin floor and the associated sedimentary and erosional features indicate a N-NW-ward directed propagation, consistent with D2 in the Dauphine foreland. The Internal zones represent the paleo-accretionary prism developed during this early Alpine continental subduction stage. The early buildup has been curved in the arc and rapidly exhumed during the Oligocene collision stage. Westward extrusion and indenting by the Apulian lithosphere allowed the modern arc to crosscut the western, lateral termination of the ancient orogen from similar to 32 Ma onward. This contrasted evolution leads to propose a palinspastic restoration taking in account important northward transport of the distal passive margin fragments (Brianconnais) involved in the accretionary prism before the formation of the Western Alps arc.
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Dunham-Cheatham, S., Rui, X., Bunker, B., Menguy, N., Hellmann, R., & Fein, J. (2011). The effects of non-metabolizing bacterial cells on the precipitation of U, Pb and Ca phosphates. Geochimica Et Cosmochimica Acta, 75, 2828–2847.
Résumé: In this study, we test the potential for passive cell wall biomineralization by determining the effects of non-metabolizing bacteria on the precipitation of uranyl, lead, and calcium phosphates from a range of over-saturated conditions. Experiments were performed using Gram-positive Bacillus subtilis and Gram-negative Shewanella oneidensis MR-1. After equilibration, the aqueous phases were sampled and the remaining metal and P concentrations were analyzed using inductively coupled plasma-optical emission spectroscopy (ICP-OES); the solid phases were collected and analyzed using X-ray diffractometry (XRD), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS). At the lower degrees of over-saturation studied, bacterial cells exerted no discernable effect on the mode of precipitation of the metal phosphates, with homogeneous precipitation occurring exclusively. However, at higher saturation states in the U system, we observed heterogeneous mineralization and extensive nucleation of hydrogen uranyl phosphate (HUP) mineralization throughout the fabric of the bacterial cell walls. This mineral nucleation effect was observed in both B. subtilis and S. oneidensis cells. In both cases, the biogenic mineral precipitates formed under the higher saturation state conditions were significantly smaller than those that formed in the abiotic controls. The cell wall nucleation effects that occurred in some of the U systems were not observed under any of the saturation state conditions studied in the Pb or Ca systems. The presence of B. subtilis significantly decreased the extent of precipitation in the U system, but had little effect in the Pb and Ca systems. At least part of this effect is due to higher solubility of the nanoscale HUP precipitate relative to macroscopic HUP. This study documents several effects of non-metabolizing bacterial cells on the nature and extent of metal phosphate precipitation. Each of these effects likely contributes to higher metal mobilities in geologic media, but the effects are not universal, and occur only with some elements and only under a subset of the conditions studied. (C) 2011 Elsevier Ltd. All rights reserved.
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Dupuy, B., De Barros, L., Garambois, S., & Virieux, J. (2011). Wave propagation in heterogeneous porous media formulated in the frequency-space domain using a discontinuous Galerkin method. Geophysics, 76, N13–N28.
Résumé: Biphasic media with a dynamic interaction between fluid and solid phases must be taken into account to accurately describe seismic wave amplitudes in subsurface and reservoir geophysical applications. Consequently, the modeling of the wave propagation in heteregeneous porous media, which includes the frequency-dependent phenomena of the fluidsolid interaction, is considered for 2D geometries. From the Biot-Gassmann theory, we have deduced the discrete linear system in the frequency domain for a discontinuous finite-element method, known as the nodal discontinuous Galerkin method. Solving this system in the frequency domain allows accurate modeling of the Biot wave in the diffusive/propagative regimes, enhancing the importance of frequency effects. Because we had to consider finite numerical models, we implemented perfectly matched layer techniques. We found that waves are efficiently absorbed at the model boundaries, and that the discretization of the medium should follow the same rules as in the elastodynamic case, that is, 10 grids per minimum wavelength for a P0 interpolation order. The grid spreading of the sources, which could be stresses or forces applied on either the solid phase or the fluid phase, did not show any additional difficulties compared to the elastic problem. For a flat interface separating two media, we compared the numerical solution and a semianalytic solution obtained by a reflectivity method in the three regimes where the Biot wave is propagative, diffusive/propagative, and diffusive. In all cases, fluid-solid interactions were reconstructed accurately, proving that attenuation and dispersion of the waves were correctly accounted for. In addition to this validation in layered media, we have explored the capacities of modeling complex wave propagation in a laterally heterogeneous porous medium related to steam injection in a sand reservoir and the seismic response associated to a fluid substitution.
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El Atrassi, F., Brunet, F., Bouybaouene, M., Chopin, C., & Chazot, G. (2011). Melting textures and microdiamonds preserved in graphite pseudomorphs from the Beni Bousera peridotite massif, Morocco. European Journal of Mineralogy, 23, 157–168.
Résumé: Over 30 graphite aggregates that represent pseudomorphs after diamond were manually extracted from a garnet pyroxenite layer in the Beni Bousera peridotite massif, northern Morocco. The inclusions present in the aggregates were characterized by combining scanning electron microscopy, micro-Raman spectroscopy and cathodoluminescence. Large composite clinopyroxene-orthopyroxene-garnet inclusions (ca. 500 mu m across) are common in the core of the graphite aggregates. Silicate films with a thickness of a few micrometres occur intercalated between graphite flakes throughout each aggregate. They are of basaltic composition and are interpreted as partial melts formed by in situ melting of the large composite inclusions and, possibly, of the host pyroxenite, during the Beni Bousera massif uplift. In addition, various solid inclusions composed of chlorides, sulphates and carbonates are found to be evenly distributed irrespective of the graphite aggregate texture (coarse in the core, in some instances fine-grained on the rim). Diamond crystals, 0.5-2 mu m in size, were also observed in several aggregates, apparently included in large graphite flakes, and were characterized using cathodoluminescence and Raman micro-spectroscopies. They are interpreted as relics of large mantle-stage diamonds, now heavily graphitized. This finding confirms earlier propositions that the graphite aggregates in Beni Bousera and Ronda garnet pyroxenites are pseudomorphs after diamond and raises questions on the kinetics of graphitization.
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El Haddad, I., Marchand, N., Wortham, H., Piot, C., Besombes, J. L., Cozic, J., et al. (2011). Primary sources of PM(2.5) organic aerosol in an industrial Mediterranean city, Marseille. Atmospheric Chemistry and Physics, 11, 2039–2058.
Résumé: Marseille, the most important port of the Mediterranean Sea, represents a challenging case study for source apportionment exercises, combining an active photochemistry and multiple emission sources, including fugitive emissions from industrial sources and shipping. This paper presents a Chemical Mass Balance (CMB) approach based on organic markers and metals to apportion the primary sources of organic aerosol in Marseille, with a special focus on industrial emissions. Overall, the CMB model accounts for the major primary anthropogenic sources including motor vehicles, biomass burning and the aggregate emissions from three industrial processes (heavy fuel oil combustion/shipping, coke production and steel manufacturing) as well as some primary biogenic emissions. This source apportionment exercise is well corroborated by (14)C measurements. Primary OC estimated by the CMB accounts on average for 22% of total OC and is dominated by the vehicular emissions that contribute on average for 17% of OC mass concentration (vehicular PM contributes for 17% of PM(2.5)). Even though industrial emissions contribute only 2.3% of the total OC (7% of PM(2.5)), they are associated with ultrafine particles (Dp < 80 nm) and high concentrations of Polycyclic Aromatic Hydrocarbons (PAH) and heavy metals such as Pb, Ni and V. On one hand, given that industrial emissions governed key primary markers, their omission would lead to substantial uncertainties in the CMB analysis performed in areas heavily impacted by such sources, hindering accurate estimation of non-industrial primary sources and secondary sources. On the other hand, being associated with bursts of submicron particles and carcinogenic and mutagenic components such as PAH, these emissions are most likely related with acute ill-health outcomes and should be regulated despite their small contributions to OC. Another important result is the fact that 78% of OC mass cannot be attributed to the major primary sources and, thus, remains un-apportioned. We have consequently critically investigated the uncertainties underlying our CMB apportionments. While we have provided some evidence for photochemical decay of hopanes, this decay does not appear to significantly alter the CMB estimates of the total primary OC. Sampling artifacts and unaccounted primary sources also appear to marginally influence the amount of un-apportioned OC. Therefore, this significant amount of un-apportioned OC is mostly attributed to secondary organic carbon that appears to be the major component of OC during the whole period of study.
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Eric, L. (2011). Imaging and monitoring with ambient vibrations: A review. The Journal of the Acoustical Society of America, 130, 2372.
Résumé: The principle of passive imaging and reconstructing the Green functions by means of correlating ambient vibrations or noise will be reviewed. Some basic processing procedures for optimizing the convergence of the correlations, along with the role of multiple scattering, will also be presented. Monitoring with ambient noise constitutes a different goal that relies on different assumptions on the background noise structure. Similarities and differences between the imaging and the monitoring approaches will be addressed.
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Fallourd, R., Harant, O., Trouve, E., Nicolas, J. - M., Gay, M., Walpersdorf, A., et al. (2011). Monitoring Temperate Glacier Displacement by Multi-Temporal TerraSAR-X Images and Continuous GPS Measurements. Ieee Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 4, 372–386.
Résumé: A new generation of space-borne SAR sensors were launched in 2006-2007 with ALOS, TerraSAR-X, COSMO-Sky-Med and RadarSat-2 satellites. The data available in different bands (L, C and X bands), with High Resolution (HR) or multi-polarization modes offer new possibilities to monitor glacier displacement and surface evolution by SAR remote sensing. In this paper, the first results obtained with TerraSAR-X HR SAR image time series acquired over the temperate glaciers of the Chamonix Mont-Blanc test site are presented. This area involves well-known temperate glaciers which have been monitored and instrumented i. e. stakes for annual displacement/ ablation, GPS for surface displacement and cavitometer for basal displacement, for more than 50 years. The potential of 11-day repeated X-band HR SAR data for Alpine glacier monitoring is investigated by a combined use of in situ measurements and multi-temporal images. Interpretations of HR images, analysis of interferometric pairs and performance assessments of target/texture tracking methods for glacier motion estimation are presented. The results obtained with four time series covering the Chamonix Mont-Blanc glaciers over one year show that the phase information is rarely preserved after 11 days on such glaciers, whereas the high resolution intensity information allows the main glacier features to be observed and displacement fields on the textured areas to be derived.
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Ferrage, E., Sakharov, B. A., Michot, L. J., Delville, A., Bauer, A., Lanson, B., et al. (2011). Hydration Properties and Interlayer Organization of Water and Ions in Synthetic Na-Smectite with Tetrahedral Layer Charge. Part 2. Toward a Precise Coupling between Molecular Simulations and Diffraction Data. Journal of Physical Chemistry C, 115, 1867–1881.
Résumé: A specific methodology was developed to collate the interlayer configurations resulting from Grand-Canonical Monte Carlo (GCMC) simulations with experimental X-ray and neutron diffraction data for two synthetic Na-saturated saponites having contrasting layer charge. Numerical simulations were performed assuming different existing sets of atomic partial charge and Lennard-Jones parameters for clay and water. For each parameter set and for the two samples in both the mono- and bihydrated states, the water contents resulting from GCMC simulations were first compared to water vapor desorption gravimetry data. The density distributions of interlayer species were then used to generate 00l intensities that were compared to X-ray and neutron diffraction data, the latter being recorded on both hydrogenated and deuterated specimens. The CLAYFF model [Cygan et al. J. Phys. Chem. B 2004, 108, 1255] is shown to better account for water content and organization compared to the model developed by Skipper et al. (Clays Clay Miner. 1995, 43, 285) and modified by Smith (Langmuir 1998, 14, 5959). However, diffraction patterns calculated for bihydrated samples from CLAYFF simulations did not match satisfactorily the diffraction data. Lennard-Jones parameters were thus modified for oxygen atoms from the clay layer. When combined with the SPC/E water model, this modified version of CLAYFF allows matching experimental water contents and fitting the complete set of diffraction data. Relevant information may thus be derived on the influence of layer charge on the orientational properties of interlayer water molecules which differs for the different clay models. Finally, the approach used in the present study proved powerful for assessing atomic interaction parameters considered for computational simulations.
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Ferrage, E., Vidal, O., Mosser-Ruck, R., & Cathelineau, M. (2011). A reinvestigation of smectite illitization in experimental hydrothermal conditions: Results from X-ray diffraction and transmission electron microscopy-Reply. American Mineralogist, 96, 1903–1904.
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Ferrage, E., Vidal, O., Mosser-Ruck, R., Cathelineau, M., & Cuadros, J. (2011). A reinvestigation of smectite illitization in experimental hydrothermal conditions: Results from X-ray diffraction and transmission electron microscopy. American Mineralogist, 96, 207–223.
Résumé: The hydrothermal reactivity of the <I mu m fraction, K-saturated SWy-2 Wyoming low-charge montmorillonite was studied in the 250-400 degrees C temperature range with reactions lasting between 5 and 120 days, with a solid/solution mass ratio of 1:10, and in 1 mol/L KCI solution. From X-ray diffraction (XRD) profile modeling results on K-saturated and ethylene-glycol solvated samples the illitization process appears to occur as a progressive replacement of expandable layers by layers with illitic behavior, in a single illite-smectite phase. However this treatment overestimates the amount of illite layers because of the presence of smectitic non-expandable layers. This was revealed by calcium exchange of the products, which causes re-expansion of the apparent illite layers. The illitization model then obtained consists of four phases with increasing illite content: discrete smectite, a randomly interstratified mixed-layered mineral (MLM) and two ordered MLMs that progressively replace the phases with less illite content. This polyphase model is consistent with results from transmission electron microscopy and chemical microanalysis, which show several types of particle morphology with different interlayer K content and Al-for-Si substitution that seem to correspond to the several phases detected by XRD. Thus, the actual illitization mechanism of smectite in our experiments is not a progressive reaction but a dissolution-precipitation process following the Ostwald step rule in which metastable smectite transforms into illite through a series of metastable illite-smectite phases.
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Frechet, J., Thouvenot, F., Frogneux, M., Deichmann, N., & Cara, M. (2011). The M(W) 4.5 Vallorcine (French Alps) earthquake of 8 September 2005 and its complex aftershock sequence. Journal of Seismology, 15, 43–58.
Résumé: On 8 September 2005 a moderate MW 4.5 earthquake occurred in the north-western Alps midway between Chamonix (France) and Martigny (Switzerland). The focal mechanism corresponds to a right-lateral strike-slip on a N60 degrees E fault plane. The foreshock-mainshock-aftershock sequence is investigated on the basis of data recorded by a temporary network of 28 stations deployed for 1 month just after the mainshock, and data from permanent, regional seismic networks. Absolute and relative locations of more than 400 events are obtained with a mean uncertainty of approximately 0.2 km. Small foreshocks, the mainshock, and early and late aftershocks are located relative to the main aftershock set. The seismic sequence exhibits a surprisingly complex structure, with at least five clusters on distinct fault planes. The main elongated cluster agrees with the location of the mainshock, its hypocenter being 4.3 km below sea level. We discuss the relationship between the right-lateral fault beneath the Loriaz peak (the source of the Vallorcine event), the nearby normal Remuaz fault, and the regional seismotectonic stress field.
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Froment, B., Campillo, M., & Roux, P. (2011). Reconstructing the Green's function through iteration of correlations. Comptes Rendus Geoscience, 343, 623–632.
Résumé: Correlations of ambient seismic noise are now widely used to retrieve the Earth response between two points. In this study, we reconstruct the surface-wave Green's function by iterating the correlation process over the tail of the noise-based correlation function. It has been demonstrated that the so-called C(3) function shows the surface-wave part of the Green's function. Using data from 150 continuously recording stations in Europe, the C(3) results help in the extraction of the travel-times from noise-based measurements, especially through the suppression of effects caused by non-isotropic source distributions. We present the results of the next iterative step (i.e. C(5)), which show that some coherent signal is still present in the coda of the C(3) function, and we investigate the evolution of the reconstruction of the Green's function throughout the iteration process. Finally, we discuss the interest of combining information from the different correlation functions to improve noise-based tomography analysis. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
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Fulton, P. M., & Rathbun, A. P. (2011). Experimental constraints on energy partitioning during stick-slip and stable sliding within analog fault gouge. Earth and Planetary Science Letters, 308, 185–192.
Résumé: The lack of substantial frictional heat anomalies across major fault zones has been a key observation suggesting that faults support low shear stress during slip. Some studies have suggested that the lack of large thermal anomalies across faults may be a result of considerably less energy going to frictional heat than generally thought and that a large fraction of energy is dissipated by other processes such as the creation of new surface area. We evaluate this hypothesis through the analysis of laboratory shear experiments for both stick-slip (seismic) and stably sliding (aseismic) analog fault gouges. These experiments differ from previous laboratory studies in that they 1) provide independent constraints on frictional heat generation and energy consumed generating new surface area, 2) cover a broader range of shear stresses (2-20 MPa) than most previous studies, and 3) evaluate both stick-slip and stable sliding within granular material. Based on the analysis of high-precision temperature measurements and comparisons with numerical model simulations >90% of the total energy appears to go to frictional heat generation (E(H)) for all of our experiments. We also show based on grain size analysis that similar to 1% of total work is consumed generating new surface area (E(SA)). These results are consistent with assumptions allowing frictional resistance to be inferred from thermal data. Furthermore, we observe no resolvable difference in the fraction of energy going to fracturing or frictional heat between stick-slip and stable sliding experiments. (C) 2011 Elsevier B.V. All rights reserved.
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Gaillard, F., Scaillet, B., & Arndt, N. T. (2011). Atmospheric oxygenation caused by a change in volcanic degassing pressure. Nature, 478(7368), 229–U112.
Résumé: The Precambrian history of our planet is marked by two major events: a pulse of continental crust formation at the end of the Archaean eon and a weak oxygenation of the atmosphere (the Great Oxidation Event) that followed, at 2.45 billion years ago. This oxygenation has been linked to the emergence of oxygenic cyanobacteria(1,2) and to changes in the compositions of volcanic gases(3,4), but not to the composition of erupting lavas-geochemical constraints indicate that the oxidation state of basalts and their mantle sources has remained constant since 3.5 billion years ago(5,6). Here we propose that a decrease in the average pressure of volcanic degassing changed the oxidation state of sulphur in volcanic gases, initiating the modern biogeochemical sulphur cycle and triggering atmospheric oxygenation. Using thermodynamic calculations simulating gas-melt equilibria in erupting magmas, we suggest that mostly submarine Archaean volcanoes produced gases with SO(2)/H(2)S < 1 and low sulphur content. Emergence of the continents due to a global decrease in sea level and growth of the continental crust in the late Archaean then led to widespread subaerial volcanism, which in turn yielded gases much richer in sulphur and dominated by SO(2). Dissolution of sulphur in sea water and the onset of sulphate reduction processes could then oxidize the atmosphere.
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Gaillot, A. - C., Drits, V. A., Veblen, D. R., & Lanson, B. (2011). Polytype and polymorph identification of finely divided aluminous dioctahedral mica individual crystals with SAED. Kinematical and dynamical electron diffraction. Physics and Chemistry of Minerals, 38, 435–448.
Résumé: This work investigates the potential of selected-area electron diffraction (SAED) for the polytype and polymorph identification of finely divided K-bearing aluminous dioctahedral mica. Individual mica crystals may indeed differ by their layer-stacking sequence and by the inner structure of their octahedral sheets (polytypic and polymorphic variants, respectively). This diversity of natural mica is commonly considered to be responsible for their morphological variety. The present article thus analyzes the intensity distribution between hk0 beams as a function of the crystal structure and thickness. The comparison of ED calculations with experimental diffraction data shows that predicted dynamical effects are not observed for finely divided dioctahedral mica. The influence of different structure defects on calculated intensities is analyzed, and their widespread occurrence in natural mica is hypothesized to be responsible for the limitation of dynamical diffraction effects. SAED may thus be used to identify the structure of individual dioctahedral mica crystals using the kinematical approximation to simulate and qualitatively interpret the observed intensities.
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Gallot, T., Catheline, S., & Roux, P. (2011). Coherent backscattering enhancement in cavities. Highlights of the role of symmetry. Journal of the Acoustical Society of America, 129, 1963–1971.
Résumé: Through experiments and simulations, the consequences of symmetry on coherent backscattering enhancement (CBE) are studied in cavities. Three main results are highlighted. First, the CBE outside the source is observed: (a) on a single symmetric point in a one-dimensional (1-D) cavity, in a disk and in a symmetric chaotic plate; (b) on three symmetric points in a two-dimensional (2-D) rectangle; and (c) on seven symmetric points in a three-dimensional (3-D) parallelepiped cavity. Second, the existence of enhanced intensity lines and planes in 2-D and 3-D simple-shape cavities is demonstrated. Third, it is shown how the anti-symmetry caused by the special boundary conditions is responsible for the existence of a coherent backscattering decrement with a dimensional dependence of R – (1/2)(d), with d – 1, 2, 3 as the dimensionality of the cavity. (C) 2011 Acoustical Society of America. [DOI: 10.1121/1.3557029]
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Gallot, T., Catheline, S., Roux, P., Brum, J., Benech, N., & Negreira, C. (2011). Passive Elastography: Shear-Wave Tomography From Physiological-Noise Correlation in Soft Tissues. Ieee Transactions on Ultrasonics Ferroelectrics and Frequency Control, 58, 1122–1126.
Résumé: Inspired by seismic-noise correlation and time reversal, a shear-wave tomography of soft tissues using an ultra-fast ultrasonic scanner is presented here. Free from the need for controlled shear-wave sources, this passive elastography is based on Green's function retrieval and takes advantage of the permanent physiological noise of the human body.
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Garcon, M., Chauvel, C., & Bureau, S. (2011). Beach placer, a proxy for the average Nd and Hf isotopic composition of a continental area. Chemical Geology, 287, 182–192.
Résumé: Beach placer deposits concentrate detrital heavy minerals which are the erosion products of large areas of continental crust Here, we report the first analyses of Nd-Hf isotopic ratios and trace element concentrations that we measured in a beach placer from Camargue, France and in its pure mineral separates. Both the bulk composition of the placer and those of its pure mineral separates were determined. We also report mineral proportions obtained using observations under a binocular microscope and micro X-ray fluorescence mapping. Our results indicate that monazite totally controls the placer's Nd isotopic composition (epsilon(Nd) = -9.3) while zircon dominates its Hf isotopes (epsilon(Hf) = -13.0) even though both mineral phases represent only a small proportion of the heavy mineral assemblage (3.5 and 10% respectively). We demonstrate that the Camargue placer provides a good estimate of the average Nd and Hf isotopic composition of the continental area drained by the Rhone River in Western Europe (epsilon(Nd) approximate to -9 and epsilon(Hf) approximate to -13). Using these values, we calculate two stage model ages and show that almost all the placer minerals are derived from Proterozoic crustal protoliths. This provides valuable information on the history of the continental crust drained by the Rhone River. In particular, it suggests that little juvenile crust was created during the recent geological events that formed the Alps and the Massif Central, the two main massifs from which the placer minerals originate. More generally, we propose that similar measurements made on other worldwide beach placer deposits could provide estimates of the present-day Nd and Hf isotopic composition of large continental areas, values that are difficult to obtain due to the well-known heterogeneity of continental material but are essential to model the growth of continental crust through Earth history or to model the impact of crustal material when recycled into the mantle. (C) 2011 Elsevier B.V. All rights reserved.
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Gasc, J., Brunet, F., Bagdassarov, N., & Morales-Florez, V. (2011). Electrical conductivity of polycrystalline Mg(OH)(2) at 2 GPa: effect of grain boundary hydration-dehydration. Physics and Chemistry of Minerals, 38, 543–556.
Résumé: The effect of intergranular water on the conductivity of polycrystalline brucite, Mg(OH)(2), was investigated using impedance spectroscopy at 2 GPa, during consecutive heating-cooling cycles in the 298-980 K range. The grain boundary hydration levels tested here span water activities from around unity (wet conditions) down to 10(-4) (dry conditions) depending on temperature. Four orders of magnitude in water activity result in electrical conductivity variations for about 6-7 orders of magnitude at 2 GPa and room temperature. Wet brucite samples containing, initially, about 18 wt% of evaporable water (i.e. totally removed at temperatures below 393 K in air), display electrical conductivity values above 10(-2)-10(-3) S/m. A.C. electrical conductivity as a function of temperature follows an Arrhenius behaviour with an activation energy of 0.11 eV. The electrical conductivity of the same polycrystalline brucite material dried beforehand at 393 K (dry conditions) is lower by about 5-6 orders of magnitude at room temperature and possesses an activation energy of 0.8-0.9 eV which is close to that of protonic diffusion in (001) brucitic planes. Above ca. 873 K, a non-reversible conductivity jump is observed which is interpreted as a water transfer from mineral bulk to grain boundaries (i.e. partial dehydration). Cooling of such partially dehydrated sample shows electrical conductivities much higher than those of the initially dry sample by 4 orders of magnitude at 500 K. Furthermore, the corresponding activation energy is decreased by a factor of about four (i.e. 0.21 eV). Buffering of the sample at low water activity has been achieved by adding CaO or MgO, two hygroscopic compounds, to the starting material. Then, sample conductivities reached the lowest values encountered in this study with the activation energy of 1.1 eV. The strong dependency of the electrical conductivity with water activity highlights the importance of the latter parameter as a controlling factor of diffusion rates in natural processes where water availability and activity may vary grandly. Water exchange between mineral bulk and mineral boundary suggests that grain boundary can be treated as an independent phase in dehydroxylation reactions.
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Gasc, J., Schubnel, A., Brunet, F., Guillon, S., Mueller, H. - J., & Lathe, C. (2011). Simultaneous acoustic emissions monitoring and synchrotron X-ray diffraction at high pressure and temperature: Calibration and application to serpentinite dehydration. Physics of the Earth and Planetary Interiors, 189, 121–133.
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Germa, A., Quidelleur, X., Labanieh, S., Chauvel, C., & Lahitte, P. (2011). The volcanic evolution of Martinique Island: Insights from K-Ar dating into the Lesser Antilles arc migration since the Oligocene. Journal of Volcanology and Geothermal Research, 208, 122–135.
Résumé: The Lesser Antilles island arc bifurcates into two lines in its northern part, with an old branch to the east and a recent active branch to the west. Martinique is located at the southern tip of the separation. The two arcs diverge northward, and at maximum divergence are separated by a 50 km wide depression. Despite this separation, which suggests a jump in volcanism, activity has been almost continuous in Martinique Island with a slow displacement of the eruptive centers to the west. Considering timing of emplacement, previous authors defined three cycles of activity, the old, intermediate and recent arcs, of Late Oligocene-Early Miocene, Mid Miocene and Late Miocene to present ages, respectively. The present study investigates the timing of emplacement of the volcanic units in Martinique Island in order to constrain the activity of the old and intermediate Lesser Antilles arcs, as recorded on this island. Unspiked K-Ar age determinations on groundmass and plagioclase separates (Cassignol-Gillot technique) were conducted on 20 samples from the old and intermediate volcanic chains. Martinique has evolved as eight distinct volcanic centers: (I) Basal Complex and Sainte Anne Series (24.8 +/- 0.4-20.8 +/- 0.4 Ma) for the old arc; (2) Vauclin-Pitault Chain (16.1 +/- 02-8.44 +/- 0.12 Ma) and (3) South-western Volcanism (9.18 +/- 0.16-7.10 +/- 0.10 Ma) for the intermediate arc; and (4) Morne Jacob volcano (5.14 +/- 0.07-1.54 +/- 0.03 Ma), (5) Trois llets Volcanism (2.358 +/- 0.034 Ma and 346 +/- 27 ka), (6) Carbet Complex (998 +/- 14 to 322 +/- 6 ka), (7) Mount Conil (543 +/- 8 to 127 +/- 2 ka) and (8) Mount Pelee (126 +/- 2 ka to present) for the recent arc (Germa et al., 2010, 2011a).We propose migration rates of 1.1-1.4 km/Myr westward, toward the back arc region throughout the whole volcanic history of Martinique Island. These rates, together with geochemical evidence for a more enriched signature in the youngest magmas, are consistent with a geodynamic evolution involving the migration of the northern volcanic front away from the trench in response to the subduction of an aseismic ridge, possibly influenced by convergence between North-American and South-American plates. (C) 2011 Elsevier B.V. All rights reserved.
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Germa, A., Quidelleur, X., Lahitte, P., Labanieh, S., & Chauvel, C. (2011). The K-Ar Cassignol-Gillot technique applied to western Martinique lavas: A record of Lesser Antilles arc activity from 2 Ma to Mount Pelee volcanism. Quaternary Geochronology, 6, 341–355.
Résumé: We present 23 new ages from three volcanic complexes of the Lesser Antilles arc in Martinique Island (French West Indies). These ages obtained with the K-Ar Cassignol-Gillot technique are distributed within the whole Quaternary. They allowed us to reconstruct a detailed history of successive volcanic growth and flank collapse stages. Trois Ilets Volcanism has been active during at least 2 Ma, between 2.35 +/- 0.03 Ma and 346 +/- 27 ka, with monogenetic volcanoes of basaltic-andesite to andesitic compositions. We here propose that magma mixing, which characterizes this volcanism, could have been initiated between 617 and 346 ka by the activation of arc-parallel and arc-transverse fault systems. Meanwhile, the Carbet complex was active 25 km to the north from 998 +/- 14 to 322 +/- 6 ka, and was partially destroyed by a flank collapse after 602 +/- 10 ka. Together with geochemical data, our ages show that Mount Conil and Mount Pelee volcanoes are parts of the same edifice sharing a single magmatic reservoir. Mount Conil started to emerge before 543 +/- 8 ka, and andesites erupted until 127 +/- 3, 2 ka, when a flank collapse destroyed the western flank of the edifice, probably triggering the emplacement of Piton Marcel, the last eruption of this first stage. We note that this collapse occurred during the transition from oxygen stages 6 to 5, i.e. during glacial to interglacial change, when eustatic level rapidly increased. After that, and until present, Mount Pelee volcano was built with periods of cone growth intercalated by flank collapse events. We here show that a peak of activity occurred between 550 and 330 ka in western Martinique within the three complexes, which are spaced of 15-25 km. Since 330 ka volcanic activity is limited to the northernmost Mount Conil Mount Pelee complex. Our data are in agreement with the regional scale observations that the whole recent Lesser Antilles arc was subject to a high volcanic activity since 600 ka, probably linked to an increase in magma production. This permanent establishment of rising magma in regularly spaced batches and tectonically controlled, could explain the individual chemical evolution of each edifice and the different eruptive dynamisms occurring at the same time along the recent arc. (C) 2011 Elsevier B.V. All rights reserved.
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Gillet, N., Schaeffer, N., & Jault, D. (2011). Rationale and geophysical evidence for quasi-geostrophic rapid dynamics within the Earth's outer core. PHYSICS OF THE EARTH AND PLANETARY INTERIORS, 187(3-4), 380–390.
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Girard, L., Bouillon, S., Weiss, J., Amitrano, D., Fichefet, T., & Legat, V. (2011). A new modeling framework for sea-ice mechanics based on elasto-brittle rheology. Annals of Glaciology, 52, 123–132.
Résumé: We present a new modeling framework for sea-ice mechanics based on elasto-brittle (EB) behavior. The EB framework considers sea ice as a continuous elastic plate encountering progressive damage, simulating the opening of cracks and leads. As a result of long-range elastic interactions, the stress relaxation following a damage event can induce an avalanche of damage. Damage propagates in narrow linear features, resulting in a very heterogeneous strain field. Idealized simulations of the Arctic sea-ice cover are analyzed in terms of ice strain rates and contrasted to observations and simulations performed with the classical viscous-plastic (VP) rheology. The statistical and scaling properties of ice strain rates are used as the evaluation metric. We show that EB simulations give a good representation of the shear faulting mechanism that accommodates most sea-ice deformation. The distributions of strain rates and the scaling laws of ice deformation are well captured by the EB framework, which is not the case for VP simulations. These results suggest that the properties of ice deformation emerge from elasto-brittle ice-mechanical behavior and motivate the implementation of the EB framework in a global sea-ice model.
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Glotzbach, C., Bernet, M., & van der Beek, P. (2011). Detrital thermochronology records changing source areas and steady exhumation in the Western European Alps. Geology, 39, 239–242.
Résumé: A dramatic increase in sediment flux since ca. 5 Ma has been inferred for the European Alps and worldwide, and is interpreted to reflect a climatically driven increase in erosion rates. However, detrital thermochronology data from the Alpine forelands suggest steady Miocene-Pliocene exhumation, contradicting the sediment budget data. We present new detrital apatite fission-track (AFT) data from the foreland of the Western Alps to better resolve Miocene to present-day exhumation rates and to determine sediment provenance. A shift in AFT lag time from <3 m.y. before 13 Ma to similar to 6 m.y. from 10 Ma on reflects reorganization of the drainage pattern within the Alps. AFT lag times are constant since then. Thermal modeling reveals that our detrital AFT data set is sufficiently sensitive to detect an increase in erosion rate, but our data record overall steady exhumation of the Western Alps since 10 Ma. Hence, increasing climatically controlled erosion may have been balanced by decreasing tectonic activity since ca. 5 Ma.
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Glotzbach, C., van der Beek, P. A., & Spiegel, C. (2011). Episodic exhumation and relief growth in the Mont Blanc massif, Western Alps from numerical modelling of thermochronology data. Earth and Planetary Science Letters, 304, 417–430.
Résumé: The Pliocene-Quaternary exhumational and topographic evolution of the European Alps and its potential climatic and tectonic controls remain a subject of controversy. Here, we apply inverse numerical thermal-kinematic modelling to a spatially dense thermochronological dataset (apatite fission-track and (U-Th)/He) of both tunnel and surface samples across the Mont Blanc massif in the Western Alps, complemented by new zircon fission-track data, in order to better quantify its Neogene exhumation and relief history. Age-elevation relationships and modelling results show that an episodic exhumation scenario best fits the data. Initiation of exhumation in the Mont Blanc massif at 22 +/- 2 Ma with a rate of 0.8 +/- 0.15 km/Myr is probably related to NW-directed thrusting during nappe emplacement. Exhumation rates decrease at 6 +/- 2 Ma to values of 0.15 +/- 0.65 km/Myr, which we interpret to be the result of a general decrease in convergence rates and/or extensive exposure of less erodible crystalline basement rocks from below more easily erodible Mesozoic sediments. Finally, local exhumation rates increase up to 2.0 +/- 0.6 km/Myr at 1.7 +/- 0.8 Ma. Modelling shows that this recent increase in local exhumation can be explained by valley incision and the associated increase in relief at 0.9 +/- 0.8 Ma, leading to erosional unloading, isostatic rebound and additional rock uplift and exhumation. Given the lack of tectonic activity as evidenced by constant thermochronological ages along the tunnel transect, we suggest that the final increase in exhumation and relief in the Mont Blanc massif is the result of climate change, with the initiation of mid-Pleistocene glaciations leading to rapid valley incision and related local exhumation. (C) 2011 Elsevier B.V. All rights reserved.
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Got, J. - L., Monteiller, V., Guilbert, J., Marsan, D., Cansi, Y., Maillard, C., et al. (2011). Strain localization and fluid migration from earthquake relocation and seismicity analysis in the western Vosges (France). Geophysical Journal International, 185, 365–384.
Résumé: To understand the mechanisms of intraplate earthquakes, well-documented seismological and geodynamical studies are needed, to provide information for adequate mechanical modelling. This paper describes a detailed analysis of the earthquake sequence associated with the Rambervillers (France) M similar to 5.4 earthquake (2003 February 22), which occurred in the western Vosges massif (France), some tens of kilometres to the north of the sites of the Epinal (1973-1974) and Remiremont (1984-1985) earthquake sequences. We computed the location of the mainshock and focal mechanism, together with the double-difference locations of 419 aftershocks of the subsequent earthquake sequence, which included 195 well-recorded similar events (earthquakes with similar waveforms). We combined pP phases recorded by remote dense seismic networks with waveform modelling, to accurately determine the mainshock depth (12.5 +/- 1.5 km). Computations of focal mechanisms from regional waveform inversions showed a normal fault plane with a N315 degrees +/- 10 degrees strike and a 45 degrees +/- 15 degrees dip. A detailed space-time analysis allowed two earthquake sequences to be identified: a classic mainshock-aftershock sequence and a secondary sequence that began 250 days after the mainshock. More events were recorded during the secondary sequence than during the main sequence. Very few similar events were recorded during the first 2 days after the mainshock, although data were recorded continuously. Double-difference locations from traveltime differences show that these immediate, non-similar aftershocks occurred in a 4 km x 2 km subhorizontal area at a depth of about 12 km. Similar events were far more numerous during the secondary earthquake sequence. Double-difference relocation of these similar events revealed a N315 degrees striking, 65 degrees dipping fault plane that is compatible with the mainshock source mechanism. During this later sequence, seismicity oscillated over a vertical range of 2-3 km around a mean depth of approximately 12 km. This observation strongly suggests fluid migration. Normal faulting, subhorizontal faulting and fluid transfer at about 12 km depth can be interpreted in terms of the crust's response (mainshock and post-seismic relaxation) to flexural stresses induced by the alpine compression. This relaxation involves weakening and collapse of the crust, and fluid transfer.
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Gouedard, P., Roux, P., Campillo, M., Verdel, A., Yao, H., & van der Hilst, R. D. (2011). Source depopulation potential and surface-wave tomography using a crosscorrelation method in a scattering medium. Geophysics, 76, SA51–SA61.
Résumé: We use seismic prospecting data on a 40 x 40 regular grid of sources and receivers deployed on a 1 km x 1 km area to assess the feasibility and advantages of velocity analysis of the shallow subsurface by means of surface-wave tomography with Green's functions estimated from crosscorrelation. In a first application we measure Rayleigh-wave dispersion curves in a 1D equivalent medium. The assumption that the medium is laterally homogeneous allows using a simple projection scheme and averaging of crosscorrelation functions over the whole network. Because averaging suppresses noise, this method yields better signal-to-noise ratio than traditional active-source approaches, and the improvement can be estimated a priori from acquisition parameters. We find that high-quality dispersion curves can be obtained even when we reduce the number of active sources used as input for the correlations. Such source depopulation can achieve significant reduction in the cost of active source acquisition. In a second application we compare Rayleigh-wave group velocity tomography from raw and reconstructed data. We can demonstrate that the crosscorrelation approach yields group velocity maps that are similar to active source maps. Scattering has an importance here as it may enhance the crosscorrelation performance. We quantify the scattering properties of the medium using mean free path measurements from coherent and incoherent parts of the signal. We conclude that for first-order velocity analysis of the shallow subsurface, the use of crosscorrelation offers a cost-effective alternative to methods that rely exclusively on active sources.
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Grandjean, G., Gourry, J. C., Sanchez, O., Bitri, A., & Garambois, S. (2011). Structural study of the Ballandaz landslide (French Alps) using geophysical imagery. Journal of Applied Geophysics, 75, 531–542.
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Gratier, J. P. (2011). Fault Permeability and Strength Evolution Related to Fracturing and Healing Episodic Processes (Years to Millennia): the Role of Pressure Solution. Oil & Gas Science and Technology-Revue D Ifp Energies Nouvelles, 66, 491–506.
Résumé: Fault Permeability and Strength Evolution Related to Fracturing and Healing Episodic Processes (Years to Millennia): the Role of Pressure Solution – It is well known that fluids flow through faults and fractures but it is also demonstrated that fault zones act as impermeable barriers. Consequently, one must consider that faults are successively open and closed paths for fluids. On the human-activity time scale (years to millennia), studies of the seismic cycle offer the possibility of making a model of such evolution. According to this model, seismic (or hydraulic) fracturing opens fluid paths almost instantaneously through the faults with associated weakening and post-fracturing creep processes. Fault healing processes then progressively close such fluid paths, associated with fault strengthening and fluid pressure recovery. Such transient behaviors have major consequences in the studies of: – the evolution of permeability along faults with application to oilfield reservoir exploitation and fluid and waste storage; – the evolution of fluid fluxes along faults with application to mass balance and climate evolution on the scale of the earth; – the timing of earthquakes and the probability of their occurrence. The aim is to understand and evaluate the kinetics of the processes and the specific characteristic times of the fracturing and healing cycles. Results from laboratory experiments and natural fault studies are presented that show how pressure solution processes can explain both creep and sealing processes and the way they are associated in nature. The various fault-healing processes are discussed with their various characteristics in times from weeks to millennia. It is shown how they can be integrated into creep and sealing laws. Laboratory experiments give the values of some parameters of the laws (kinetics, thermodynamic). Other parameters must always be evaluated from the study of natural structures (geometry of path transfer, pressure and temperature conditions, nature of minerals and fluids). Consequently, the duration of the fracturing and sealing cycle is related to some extent to the geological context of a faulted area. Finally, as the mechanisms of permeability and strength evolution interact and occur on various scales of time and space, they must be integrated into numerical models, which are briefly discussed.
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Gratier, J. P., Richard, J., Renard, F., Mittempergher, S., Doan, M. L., Di Toro, G., et al. (2011). Aseismic sliding of active faults by pressure solution creep: Evidence from the San Andreas Fault Observatory at Depth. Geology, 39, 1131–1134.
Résumé: Active faults in the upper crust can either slide steadily by aseismic creep, or abruptly causing earthquakes. Creep relaxes the stress and prevents large earthquakes from occurring. Identifying the mechanisms controlling creep, and their evolution with time and depth, represents a major challenge for predicting the behavior of active faults. Based on microstructural studies of rock samples collected from the San Andreas Fault Observatory at Depth (California), we propose that pressure solution creep, a pervasive deformation mechanism, can account for aseismic creep. Experimental data on minerals such as quartz and calcite are used to demonstrate that such creep mechanism can accommodate the documented 20 mm/yr aseismic displacement rate of the San Andreas fault creeping zone. We show how the interaction between fracturing and sealing controls the pressure solution rate, and discuss how such a stress-driven mass transfer process is localized along some segments of the fault.
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Guedron, S., Cossa, D., Grimaldi, M., & Charlet, L. (2011). Methylmercury in tailings ponds of Amazonian gold mines (French Guiana): Field observations and an experimental flocculation method for in situ remediation. Applied Geochemistry, 26, 222–229.
Résumé: Sites of monomethylmercury (MMHg) production in Amazonian regions have been identified in hydraulic reservoirs, lake sediments and wetlands, but tailings ponds have not yet received sufficient attention for this purpose. This work evidenced high MMHg production within the water column and the interstitial water of two tailings ponds of French Guiana Au mines located; (i) in a small scale exploitation (Combat) where Hg was used for Au amalgamation, and (ii) in an industrial on-going Au mine (Yaoni) processing without Hg. The (MMHg)(D) maximum (2.5 ng L(-1)) occurred in the oxic water column above the sediment-water interface (SWI) of the most recent tailings pond (Combat), where the substrate was fresh, the redox transition was sharp and the pool of total Hg was large. In the Yaoni pond, the (MMHg)(D) maximum concentration (1.4 ng L(-1)) was located at the SWI where suboxic conditions prevailed. Using the (MMHg)(D) concentration as a proxy for Hg methylation rates, the present results show that Hg methylation may occur in various redox conditions in tailings ponds, and are favored in areas where the organic matter regeneration is more active. A 3-month long laboratory experiment was performed in oxic and anoxic boxes filled with high turbidity waters from the Combat Au mine to simulate tailings ponds. Slaked lime was added in an experimental set (2 mg L(-1))and appeared to be very efficient for the reduction of suspended particulate matter (SPM) to environmentally acceptable concentrations. However, at the end of the experiment, large (MMHg)(D) concentrations were monitored under treated anoxic conditions with the (MMHg)(D) maximum located at the SWI above the Fe-reducing zones. No (MMHg)(D) was detected in oxic experiments. The use of slaked lime for SPM decantation appears to be an efficient and non-onerous process for Au miners to avoid Hg methylation in tailings ponds when it is combined with rapid drainage of the mine waters. A subsequent human intervention is however necessary for the recovery of soil structure through the cover of dried ponds with organic rich materials and reforestation to avoid the stagnation of rain waters and the occurrence of anoxia. (C) 2010 Elsevier Ltd. All rights reserved.
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Guedron, S., Grimaldi, M., Grimaldi, C., Cossa, D., Tisserand, D., & Charlet, L. (2011). Amazonian former gold mined soils as a source of methylmercury: Evidence from a small scale watershed in French Guiana. Water Research, 45, 2659–2669.
Résumé: Total mercury (HgT) and monomethylmercury (MMHg) were investigated in a tropical head watershed (1 km(2)) of French Guiana. The watershed includes a pristine area on the hill slopes and a former gold mined flat in the bottomland. Concentrations of dissolved and particulate HgT and MMHg were measured in rain, throughfall, soil water and at three points along the stream. Samples were taken in-between and during 14 storm events at the beginning and middle of the 2005 and 2006 rainy seasons. Dissolved and particulate HgT concentrations in the stream slightly increased downstream, while dissolved and particulate MMHg concentrations were low at the pristine sub-watershed outlet (median = 0.006 ng L(-1) and 1.84 ng g(-1), respectively) and sharply increased at the gold mined flat outlet (median = 0.056 ng L(-1) and 6.80 ng g(-1), respectively). Oxisols, which are dominant in the pristine area act as a sink of HgT and MMHg from rain and throughfall inputs. Hydromorphic soils in the flat are strongly contaminated with Hg (including Hg droplets) and their structure has been disturbed by former gold-mining processes, leading to multiple stagnant water areas where biogeochemical conditions are favorable for methylation. In the former gold mined flat high dissolved MMHg concentrations (up to 0.8 ng L(-1)) were measured in puddles or suboxic soil pore waters, whereas high dissolved HgT concentrations were found in lower Eh conditions. Iron-reducing bacteria were suggested as the main methylators since highest concentrations for dissolved MMHg were associated with high dissolved ferrous iron concentrations. The connection between saturated areas and stagnant waters with the hydrographic network during rain events leads to the export of dissolved MMHg and HgT in stream waters, especially at the beginning of the rainy season. As both legal and illegal gold-mining continues to expand in French Guiana, an increase in dissolved and particulate MMHg emissions in the hydrographic network is expected. This will enhance MMHg bio-amplification and present a threat to local populations, whose diet relies mainly on fish. (C) 2011 Elsevier Ltd. All rights reserved.
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Gueguen, P., Langlais, M., Foray, P., Rousseau, C., & Maury, J. (2011). A Natural Seismic Isolating System: The Buried Mangrove Effects. Bulletin of the Seismological Society of America, 101, 1073–1080.
Résumé: The Belleplaine test site, located in the island of Guadeloupe (French Lesser Antilles), includes a three-accelerometer vertical array, designed for liquefaction studies. The seismic response of the soil column at the test site is computed using three methods: the spectral ratio method using the vertical array data, a numerical method using the geotechnical properties of the soil column, and an operative frequency domain decomposition (FDD) modal analysis method. The Belleplaine test site is characterized by a mangrove layer overlaid by a stiff sandy deposit. This configuration is widely found at the border coast of the Caribbean region, which is exposed to high seismic hazard. We show that the buried mangrove layer plays the role of an isolation system equivalent to those usually employed in earthquake engineering aimed at reducing the seismic shear forces by reducing the internal stress within the structure. In our case, the flexibility of the mangrove layer reduces the distortion and the stress in the sandy upper layer, and consequently reduces the potential of liquefaction of the site.
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Guemache, M. A., Chatelain, J. - L., Machane, D., Benahmed, S., & Djadia, L. (2011). Failure of landslide stabilization measures: The Sidi Rached viaduct case (Constantine, Algeria). Journal of African Earth Sciences, 59, 349–358.
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Hadziioannou, C., Larose, E., Baig, A., Roux, P., & Campillo, M. (2011). Improving temporal resolution in ambient noise monitoring of seismic wave speed. Journal of Geophysical Research-Solid Earth, 116.
Résumé: The use of ambient seismic noise has been intensively investigated to perform passive tomography at various scales. Besides passive tomography, passive monitoring is another application of seismic noise correlation as was shown by the recent observation of postseismic velocity changes around the San Andreas Fault in Parkfield, California. One of the drawbacks of using ambient noise correlation for passive monitoring is the need to average the correlations over a long time period in order to obtain a sufficient signal-to-noise ratio (SNR) for the phase fluctuations to be measured accurately. For the application to passive monitoring, one wants the possibility of following short-term velocity variations (1 day or less) using noise correlation functions calculated on short time windows. Another difficulty may then appear when the spatial distribution of noise sources also evolves with time. The aim of this paper is to introduce an adaptive filter to the Parkfield data set in order to improve the SNR output of the ambient noise correlation functions. When applied to passive monitoring, the temporal resolution can be increased from 30 days up to 1 day. With this improved temporal resolution, the velocity drop observed at Parkfield is shown to be cosesimic with the 24 September 2004 M(w) = 6.0 event. The relationship between the measured velocity fluctuations and the time evolution of the spatial distribution of the noise wavefield is also investigated. Finally, the error bar in the amplitudes of the velocity variations is compared with a theoretical expectation.
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Hantz, D. (2011). Quantitative assessment of diffuse rock fall hazard along a cliff foot. Natural Hazards and Earth System Sciences, 11, 1303–1309.
Résumé: Many works have shown that the relation between rock fall frequency and volume is well fitted by a power law. Based on this relation, a new method is presented which allows estimating the fall frequency and probability for a wall section in a homogenous cliff, considering all possible rock fall volumes. The hazard for an element located at the foot of the cliff, with a minimal energy, is also estimated. The method has been applied to an itinerary, for which the human risk has also been estimated. Rock fall inventories featuring the location, date, and volume of the falls and the dimensions of the fallen compartments (width, length, and thickness) are needed for better estimating of hazard and risk.
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Hillers, G., & Ben-Zion, Y. (2011). Seasonal variations of observed noise amplitudes at 2-18 Hz in southern California. Geophysical Journal International, 184, 860–868.
Résumé: P>We show that noise amplitudes at frequencies above 1 Hz exhibit strong seasonal variations in a broad southern California region. The results are based on 3-component seismic data recorded between 2002 and 2009 by 30 stations. Focusing on continuous 6-hr night-time segments, the seismograms are bandpass-filtered in nine frequency bands between 2 and 18 Hz. Squared amplitudes are median-filtered to reduce the influence of earthquake signals and integrated to yield half-hourly noise energy estimates. The 6-hr minimum energy values are converted back to ground velocity and used as representative daily noise level amplitudes. Notwithstanding various trends, drifts and other transient complexities, a common feature of the resulting time series in both the horizontal and vertical components are annual amplitude changes at all examined frequencies and all stations. The strength of amplitude variations shows no correlation with distance from the coast and some particularly clear seasonal changes are seen near topographic features in arid uninhabited areas. Comparison to meteorological data suggests that the main sources for the high-frequency noise field are variations of temperature and wind at the surface. In addition to acting directly on topographic irregularities and other surface features, these sources (and especially temperature changes) may also generate high-frequency noise by inducing multitudinous small-scale failures in the shallow crust.
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Hippolyte, J. C., & Mann, P. (2011). Neogene-Quaternary tectonic evolution of the Leeward Antilles islands (Aruba, Bonaire, Curacao) from fault kinematic analysis. Marine and Petroleum Geology, 28, 259–277.
Résumé: Aruba, Bonaire, and Curacao are islands aligned along the crest of a 200-km-long segment of the east-west-trending Leeward Antilles ridge within the broad Caribbean-South America plate boundary zone presently characterized by east-west, right-lateral strike-slip motion. The crust of the Leeward Antilles ridge represents the western segment of the Cretaceous-early Cenozoic Great Arc of the Caribbean, which obliquely collided, with the continental margin of northern South America in early Cenozoic time. Following the collision, the ridge was affected by folding and was segmented by oblique, northwest-striking normal faults that have produced steep-sided, northwest-trending, elongate islands and narrow shelves separated by deepwater, sediment-filled and fault-controlled basins. In this paper, we present the first fault slip observations on the Neogene carbonate rocks that cover large areas of all three islands. Our main objective is to quantify the timing and nature of Neogene to Quaternary phases of faulting and folding that have affected the structure and topography of this area including offshore sedimentary basins that are being explored for their petroleum potential. These data constrain three fault phases that have affected Aruba, Bonaire, and Curacao and likely the adjacent offshore areas: 1) NW-SE-directed late Paleogene compression; 2) middle Miocene syndepositional NNW-SSE to NNE-SSW extension that produced deep rift basins transverse to the east-west-trending Leeward Antilles ridge; and 3) Pliocene-Quaternary NNE-trending compression that produced NW-SE-trending anticlines present on Aruba, Curacao and Bonaire islands. Our new observations – that include detailed relationships between striated fault planes, paleostress tensors, and bedding planes – show that prominent bedding dips of Neogene limestone on Aruba, Bonaire and Curacao were produced by regional tectonic shortening across the entire Leeward Antilles ridge rather than by localized, syndepositional effects as proposed by previous workers. We interpret Pliocene-Quaternary NNE-directed shortening effects on the Leeward Antilles ridge as the result of northeastward extrusion or “tectonic escape” of continental areas of western Venezuela combined with southeastward shallow subduction of the Caribbean plate beneath the ridge. (C) 2009 Elsevier Ltd. All rights reserved.
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Hug, F., Gallot, T., Catheline, S., & Nordez, A. (2011). ELECTROMECHANICAL DELAY IN BICEPS BRACHII ASSESSED BY ULTRAFAST ULTRASONOGRAPHY. Muscle & Nerve, 43, 441–443.
Résumé: Using ultrasound we tested the utility of determining the relative contribution of the main muscle structures/mechanisms to the electromechanical delay in the biceps brachii. Nine subjects underwent electrically evoked contractions with the echographic probe maintained over the muscle and the myotendinous junction. No difference was found between the onset of muscle fascicle motion (Dm, 5.57 +/- 1.37 ms) and the onset of myotendinous junction motion (Dt, 5.47 +/- 1.38 ms), whereas significant differences were found between Dm/Dt and electromechanical delay (approximately 10 ms). Electromechanical delay can be used as a model for studying the effects of neuromuscular disorders or various constraints that affect excitation- contraction coupling and/or muscle force transmission. Muscle Nerve 43: 441-443, 2011
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Huyghe, P., Guilbaud, R., Bernet, M., Galy, A., & Gajurel, A. P. (2011). Significance of the clay mineral distribution in fluvial sediments of the Neogene to Recent Himalayan Foreland Basin (west-central Nepal). Basin Research, 23, 332–345.
Résumé: Clay mineral assemblages of the Neogene Himalayan foreland basin are studied to decipher their significance with respect to tectonic and climate processes. Fluvial deposits of the Siwalik Group (west-central Nepal), and sediment of the Ganga River drainage system were analysed for clay mineralogy. The observed clay mineral assemblages are mainly composed of illite (dominant), chlorite, smectite and kaolinite. Illite and chlorite are chiefly of detrital origin, derived from Himalayan sources. Kaolinite and smectite are authigenic, and mainly developed within pore space and as coating of detrital particles. With increasing burial, diagenetic processes affected the original clay mineral signature. Illitisation of smectite and kaolinite occurred below 2500 and 3500 m depth, respectively. Therefore, illite in the lower parts of the Siwalik Group consists of a mixture of inherited illite and illitised smectite and kaolinite, as suggested by illite crystallinity. Detrital grains that make up the framework of the Siwalik Group sandstones mainly consist of quartz, feldspar and lithic fragments, which are principally of sedimentary and metamorphic origin. Lithoclast content increases over time at the expense of quartz and K-feldspar in response to uplift and erosion of the Lesser Himalaya Series since about 11-10 Ma. Despite mainly felsic source rocks, dominantly physical erosion processes in the Himalayan belt, and high-energy fluvial depositional systems, smectite is abundant in the < 7 Ma Siwalik Group deposits. Analyses of the Siwalik deposits and comparison with the clay mineralogy of the modern drainage system suggest that smectite preferentially formed in floodplains and intermontane valleys during early diagenesis because of downward percolating fluids rich in cations from weathering and soil development. In general, increasing seasonality and aridity linked to variability of the Asian monsoon from about 8 Ma enhanced clay mineral formation and development of authigenic smectite in paleo-plains on the southern side of the Himalaya.
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Inza, L. A., Mars, J. I., Metaxian, J. P., O'Brien, G. S., & Macedo, O. (2011). Seismo-volcano source localization with triaxial broad-band seismic array. Geophysical Journal International, 187, 371–384.
Résumé: Seismo-volcano source localization is essential to improve our understanding of eruptive dynamics and of magmatic systems. The lack of clear seismic wave phases prohibits the use of classical location methods. Seismic antennas composed of one-component (1C) seismometers provide a good estimate of the backazimuth of the wavefield. The depth estimation, on the other hand, is difficult or impossible to determine. As in classical seismology, the use of three-component (3C) seismometers is now common in volcano studies. To determine the source location parameters (backazimuth and depth), we extend the 1C seismic antenna approach to 3Cs. This paper discusses a high-resolution location method using a 3C array survey (3C-MUSIC algorithm) with data from two seismic antennas installed on an andesitic volcano in Peru (Ubinas volcano). One of the main scientific questions related to the eruptive process of Ubinas volcano is the relationship between the magmatic explosions and long-period (LP) swarms. After introducing the 3C array theory, we evaluate the robustness of the location method on a full wavefield 3-D synthetic data set generated using a digital elevation model of Ubinas volcano and an homogeneous velocity model. Results show that the backazimuth determined using the 3C array has a smaller error than a 1C array. Only the 3C method allows the recovery of the source depths. Finally, we applied the 3C approach to two seismic events recorded in 2009. Crossing the estimated backazimuth and incidence angles, we find sources located 1000 +/- 660 m and 3000 +/- 730 m below the bottom of the active crater for the explosion and the LP event, respectively. Therefore, extending 1C arrays to 3C arrays in volcano monitoring allows a more accurate determination of the source epicentre and now an estimate for the depth.
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Jacques, E., Kidane, T., Tapponnier, P., Manighetti, I., Gaudemer, Y., Meyer, B., et al. (2011). Normal Faulting during the August 1989 Earthquakes in Central Afar: Sequential Triggering and Propagation of Rupture along the Dobi Graben. Bulletin of the Seismological Society of America, 101, 994–1023.
Résumé: In August 1989, an earthquake sequence including ten events with 6.3 >= M >= 5. 5 in the first two days produced widespread ground deformation in the Dobi graben of central Afar. Numerous surface breaks with complex geometry, including fresh scarplets with vertical throws up to 30 cm high and open fissures up to 30 cm wide, were observed. Coseismic slip incremented the deformation (normal faulting, block tilting, and counterclockwise rotation of basaltic slices) accumulated in the last 2 m.y. in the transfer zone between the Dobi and Hanle grabens. By combining maps of surface ruptures, relative event relocations with the local Djibouti network, published focal mechanisms, and source sizes, we tentatively relate most of the main-shocks of the sequence to slip on individual faults. The largest shocks at 11h16 on 20 August 1989 (M(S) 6.2) and at 1h09 on 21 August 1989 (M(S) 6.3) ruptured southern segments of the southwestern bounding fault of the graben. A dozen other faults also slipped along the edges of, and inside, the graben. On average, triggered seismic faulting propagated about 35 km northwestward along the graben in about 20 hr. Slip on the main faults was coupled with slip on secondary antithetic faults branching from them at depth. Although the Dobi earthquakes ruptured part of the fault array between the Asal rift (1978 sequence) and the Serdo region (1969 sequence), an approximately 50-km-long gap subsists along the Der'ela half-graben. We infer the patterns of surface faulting in the Dobi sequence, which coinvolved bookshelf-faulting about both horizontal and vertical axes, to typify the complexity of coseismic stress release in central Afar and in other active zones of distributed extension (e.g., Iceland, Abruzzi, Basin and Range).
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Janots, E., Berger, A., & Engi, M. (2011). Physico-chemical control on the REE minerals in chloritoid-grade metasediments from a single outcrop (Central Alps, Switzerland). Lithos, 121, 1–11.
Résumé: This study assesses the effects of fluid, whole-rock composition and oxygen fugacity, on the texture and composition of monazite, allanite, and xenotime. For this purpose, these were investigated in 13 mono-metamorphic metasediments from a single locality of the Central Alps (Switzerland), which record greenschist facies conditions (T similar to 400-450 degrees C). Two of the samples contain hydrothermal veins dominated by quartz and calcite + quartz, respectively. In metasediments devoid of veins, the light rare earth elements (LREE) are concentrated in allanite in all samples except for one metamarl (Ga06). Allanite formation is texturally coeval with apatite, chloritoid and xenotime, during the main tectono-metamorphic stage. Allanite formation implies significant mass transfer of Ca and P via a fluid phase, which is not clearly related to advective transport. In Ga06, elongate monazite grains have a detrital core rimmed by newly formed monazite. Significant arsenic contents are found in newly formed monazite, xenotime and apatite. Monazite texture and composition suggest (re)crystallization by pressure solution, at an oxygen fugacity sufficient to partly oxidize As, S. 11, and Fe. Whether or not monazite is preserved appears to be but weakly dependent on the Ca/Al ratio and thus whole-rock composition at greenschist fades conditions. Samples with veins show peculiar features. Along carbonate-bearing veins allanite occurs as porphyroblasts overgrowing the main foliation of the host rock. As similar allanite porphyroblasts occur in calcite-bearing metamarl, their formation is attributed to environments rich in CO(2)-bearing fluid. A new generation of monazite is found in and along retrograde quartz veins. This study demonstrates that, at least in metasediments up to chloritoid-grade, REE minerals record fluid/rock interaction that occurred at different deformation stages. Arsenic concentrations in REE phosphates appear to reflect conditions of elevated oxygen fugacity. In cases where such conditions are not inherited from the sedimentary protolith, the oxidation reflects a hydrothermal event, the age of which may be directly datable by U/Th-Pb of As-rich monazite. (C) 2010 Elsevier B.V. All rights reserved.
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Janots, E., Gnos, E., Hofmann, B. A., Greenwood, R. C., Franchi, I. A., & Bischoff, A. (2011). Jiddat al Harasis 422: A ureilite with an extremely high degree of shock melting. Meteoritics & Planetary Science, 46, 134–148.
Résumé: The Jiddat al Harasis (JaH) 422 ureilite was found in the Sultanate of Oman; it is classified as a ureilitic impact melt breccia. The meteorite consists of rounded polycrystalline olivine clasts (35%), pores (8%), and microcrystalline matrix (57%). Clasts and matrix have oxygen isotopic values and chemical compositions (major and trace elements) characteristic of the ureilite group. The matrix contains olivine (Fo(83-90)), low-Ca pyroxene (En(84-92)Wo(0-5)), augite (En(71-56)Wo(20-31)), graphite, diamond, Fe-metal, sulfides, chromite, and felsic glass. Pores are partly filled by secondary Fe-oxihydroxide and desert alteration products. Pores are surrounded by strongly reduced silicates. Clasts consist of fine-grained aggregates of polygonal olivine. These clasts have an approximately 250 mu m wide reaction rim, in which olivine composition evolves progressively from the core composition (Fo(79-81)) to the matrix composition (Fo(84-87)). Veins crossing the clasts comprise pyroxene, Fe-oxihydroxide, C-phases, and chromite. Clasts contain Ca-, Al-, and Cr-rich glass along olivine grain boundaries (< 1 mu m wide). We suggest that a significant portion of JaH 422, including olivine and all the pyroxenes, was molten as a result of an impact. In comparison with other impact-melted ureilites, JaH 422 shows the highest melt portion. Based on textural and compositional considerations, clasts and matrix probably originated from the same protolith, with the clasts representing relict olivine that survived, but was recrystallized in the impact melt. During the melt stage, the high availability of FeO and elevated temperatures controlled oxygen fugacity at values high enough to stabilize olivine with Fo(similar to 83-87) and chromite. Along pores, high Mg# compositions of silicates indicate that in a late stage or after melt crystallization FeO became less available and fO(2) conditions were controlled by C-CO + CO(2).
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Jault, D. (2011). PLANETARY SCIENCE Ancient lunar dynamo. Nature, 479, 183–184.
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Jolivet, R., Grandin, R., Lasserre, C., Doin, M. P., & Peltzer, G. (2011). Systematic InSAR tropospheric phase delay corrections from global meteorological reanalysis data. Geophysical Research Letters, 38.
Résumé: Despite remarkable successes achieved by Differential InSAR, estimations of low tectonic strain rates remain challenging in areas where deformation and topography are correlated, mainly because of the topography-related atmospheric phase screen (APS). In areas of high relief, empirical removal of the stratified component of the APS may lead to biased estimations of tectonic deformation rates. Here we describe a method to correct interferograms from the effects of the spatial and temporal variations in tropospheric stratification by computing tropospheric delay maps coincident with SAR acquisitions using the ERA-Interim global meteorological model. The modeled phase delay is integrated along vertical profiles at the ERA-I grid nodes and interpolated at the spatial sampling of the interferograms above the elevation of each image pixel. This approach is validated on unwrapped interferograms. We show that the removal of the atmospheric signal before phase unwrapping reduces the risk of unwrapping errors in areas of rough topography. Citation: Jolivet, R., R. Grandin, C. Lasserre, M.-P. Doin, and G. Peltzer (2011), Systematic InSAR tropospheric phase delay corrections from global meteorological reanalysis data, Geophys. Res. Lett., 38, L17311, doi: 10.1029/2011GL048757.
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Jorry, S. J., & Bievre, G. (2011). Integration of sedimentology and ground-penetrating radar for high-resolution imaging of a carbonate platform. Sedimentology, 58, 1370–1390.
Résumé: Ground-penetrating radar has not been applied widely to the recognition of ancient carbonate platform geometries. This article reports the results of an integrated study performed on an Upper Jurassic outcrop from the south-east Paris basin, where coral bioherms laterally change into prograding depositional sequences. Ground-penetrating radar profiles illustrate the different bedding planes and major erosional unconformities visible at outcrop. A ground-penetrating radar profile conducted at the base of the cliff displays a palaeotopographic surface on which the outcropping bioherms settled. The excellent penetration depths of the ground-penetrating radar (20 m with a monostatic 200 MHz antenna) images the carbonate platform geometries, ranging between outcrop workscale (a few metres) and seismic scale (several hundreds of metres). This study supports recent evidence of icehouse conditions and induced sea-level fluctuations controlling the Upper Jurassic carbonate production.
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Jouanne, F., Audemard, F. A., Beck, C., Van Welden, A., Ollarves, R., & Reinoza, C. (2011). Present-day deformation along the El Pilar Fault in eastern Venezuela: Evidence of creep along a major transform boundary. Journal of Geodynamics, 51, 398–410.
Résumé: The right-lateral strike-slip El Pilar Fault is one of the major structures that accommodate the relative displacement between the Caribbean and South-America Plates. This fault, which trends East-West along the northeastern Venezuela margin, is a seismogenic source, and shows numerous evidence for active tectonics, including deformation of the Quaternary sediments filling the Cariaco Gulf. Because the main El Pilar Fault strand belongs to a set of strike-slip faults and thrusts between the stable Guyana shield (South) and the Caribbean oceanic floor (North), a GPS network was designed and installed to measure the relative motion of the El Pilar Fault and other faults. The results obtained from the comparison of 2003 and 2005 surveys indicate: (i) a lack of significant displacement (especially shortening) in the Serrania del Interior (Neogene cordillera overthrusted above the Guyana craton), (ii) an eastward displacement (relative to fixed south America plate) up to 22 mm/year of benchmarks located north of the El Pilar Fault. Velocities simulations using dislocations in an elastic half-space show: (1) the concentration along the El Pilar Fault of the whole Caribbean-South America relative displacement, (2) the existence of an important component of aseismic displacement along the upper part of the El Pilar Fault. Between 12 km depth and the surface, only 40% of displacement is locked for the western segment and 50% for the eastern segment. This last phenomenon may be related to the existence of serpentinite lenses along the fault zone as observed for segments of San Andreas and North Anatolian faults. (C) 2010 Elsevier Ltd. All rights reserved.
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Jouanne, F., Awan, A., Madji, A., Pecher, A., Latif, M., Kausar, A., et al. (2011). Postseismic deformation in Pakistan after the 8 October 2005 earthquake: Evidence of afterslip along a flat north of the Balakot-Bagh thrust. Journal of Geophysical Research-Solid Earth, 116.
Résumé: The 8 October 2005 Kashmir earthquake ruptured an out-of-sequence Himalayan thrust known as the Balakot-Bagh thrust. The earthquake's hypocenter was located at a depth of 15 km on the ramp close to a possible ramp/flat transition. In the weeks following the earthquake a GPS network was installed to measure postseismic displacement. The initial measurements in November 2005 were followed by other campaigns in January and August 2006, in March and December 2007, and in August 2008 and 2009. Two hypotheses were tested: post-seismic displacements controlled by viscous relaxation of the lower crust or by afterslip along a flat north of the ramp affected by the main shock. A single Newtonian viscosity for the different periods cannot be determined by numerical simulations of viscous relaxation, which may indicate that the viscosity of the lower crust is non-Newtonian or that viscous relaxation does not control postseismic displacements. Numerical simulations using dislocations in a uniform elastic half-space indicate afterslip north of the ramp of the earthquake along a flat connected to the ramp. Slip along the northwestern portion of the flat accrued to about 285 mm between November 2005 and August 2006, while slip along the southeastern portion accrued to 130 mm over the same time period. Residual misfit of the observed and predicted displacements clearly indicated that afterslip is a better explanation for the observations than the hypothesis of viscous relaxation. The time evolution of the afterslip was found to be consistent with that predicted from rate-strengthening frictional sliding.
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Julea, A., Meger, N., Bolon, P., Rigotti, C., Doin, M. - P., Lasserre, C., et al. (2011). Unsupervised Spatiotemporal Mining of Satellite Image Time Series Using Grouped Frequent Sequential Patterns. Ieee Transactions on Geoscience and Remote Sensing, 49, 1417–1430.
Résumé: An important aspect of satellite image time series is the simultaneous access to spatial and temporal information. Various tools allow end users to interpret these data without having to browse the whole data set. In this paper, we intend to extract, in an unsupervised way, temporal evolutions at the pixel level and select those covering at least a minimum surface and having a high connectivity measure. To manage the huge amount of data and the large number of potential temporal evolutions, a new approach based on data-mining techniques is presented. We have developed a frequent sequential pattern extraction method adapted to that spatiotemporal context. A successful application to crop monitoring involving optical data is described. Another application to crustal deformation monitoring using synthetic aperture radar images gives an indication about the generic nature of the proposed approach.
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Kang, M. L., Chen, F. R., Wu, S. J., Yang, Y. Q., Bruggeman, C., & Charlet, L. (2011). Effect of pH on Aqueous Se(IV) Reduction by Pyrite. Environmental Science & Technology, 45, 2704–2710.
Résumé: Interaction of aqueous Se(IV) with pyrite was investigated using persistently stirred batch reactors under O(2)-free (<1 ppm) conditions at pH ranging from similar to 4.5 to similar to 6.6. Thermodynamic calculations, an increase in pH during the experiments, and spectroscopic observation indicate that the reduction of aqueous Se(IV) by pyrite is dominated by the following reaction: FeS(2) + 3.5HSeO(3)(-) + 1.5H(+) = 2SO(4)(2-) Fe(2+) + 3.5Se(0) 2.5H(2)O. The released Fe(II) was partitioned between the bulk solution and pyrite surface at pH approximate to 4.5 and 4.8, with the Fe(2+) density at pyrite-solution interface about 4 orders of magnitude higher than that in the bulk solution, while iron oxyhydroxide precipitated at pH approximate to 6.6, resulting in the decrease of dissolved iron. In the Se(IV) concentration range of the experiments, aqueous Se(IV) reduction rate follows the pseudofirst order which is in the form of In m(Se(IV)) = kappa(1)t + In m(Se(IV))(0), where kappa(1) is apparent rate constant combining the rate constant k and pyrite surface area to mass of solution ratio (AIM). And the aqueous Se(IV) reduction rate constant for a standard system (kappa) with 1 m(2) pyrite surface area per 1 kg solution was obtained to be 1.65 x 10(-4) h(-1), 3.28 x 10(-4) h(-1), and 4.76 x 10(-4) h(-1) at pH around 4.5, 4.8, and 5.1, respectively. The positive correlation between reaction rate and pH disagrees with the theories that protons are consumed when HSeO(3)(-) is reduced to Se, and negative charge density on pyrite surface increases as pH increases. Thus, a ferrous iron mediated electron transfer mechanism is proposed to operate during the reduction of aqueous Se(IV) by pyrite. pH and iron concentration affect significantly on Se(IV) reaction rate and reaction product.
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Karabulut, H., Schmittbuhl, J., Ozalaybey, S., Lengline, O., Komec-Mutlu, A., Durand, V., et al. (2011). Evolution of the seismicity in the eastern Marmara Sea a decade before and after the 17 August 1999 Izmit earthquake. Tectonophysics, 510, 17–27.
Résumé: We review the long term evolution of seismicity in the eastern Marmara Sea over a decade, before and after the 1999 Mw 7.6 Izmit earthquake. We analyze large scale space-time variations of seismicity in the region and illustrate the impact of the recent large strike-slip earthquakes on the background activity composed of distinct pre-existing seismic clusters. Two types of aftershocks activity are observed: the first type of enhancement is on strike-slip fault segments (Izmit Fault, Princes Island section of the Main Marmara Fault, Gemlik Fault) immediately following the main shock and related to Coulomb stress transfer; the second type of enhancement is attached to extensional clusters (Yalova, Tuzla) with a few days delay in the onset of strong activation, probably related to pore pressure increase. We observe a fast decay of the activity on strike-slip segments and slower evolution of seismic clusters with extensional features. Two years after the Izmit earthquake, seismic activity returned to the pre-earthquake pattern with most of the activity occurring within extensional clusters. It appears that the influence of the last large strike-slip event on the spatial seismicity distribution in the eastern Marmara Sea is less significant than the effect of the long term regional extension. (C) 2011 Elsevier B.V. All rights reserved.
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Karaoulis, M., Revil, A., Werkema, D. D., Minsley, B. J., Woodruff, W. F., & Kemna, A. (2011). Time-lapse three-dimensional inversion of complex conductivity data using an active time constrained (ATC) approach. Geophysical Journal International, 187, 237–251.
Résumé: Induced polarization (more precisely the magnitude and phase of impedance of the subsurface) is measured using a network of electrodes located at the ground surface or in boreholes. This method yields important information related to the distribution of permeability and contaminants in the shallow subsurface. We propose a new time-lapse 3-D modelling and inversion algorithm to image the evolution of complex conductivity over time. We discretize the subsurface using hexahedron cells. Each cell is assigned a complex resistivity or conductivity value. Using the finite-element approach, we model the in-phase and out-of-phase (quadrature) electrical potentials on the 3-D grid, which are then transformed into apparent complex resistivity. Inhomogeneous Dirichlet boundary conditions are used at the boundary of the domain. The calculation of the Jacobian matrix is based on the principles of reciprocity. The goal of time-lapse inversion is to determine the change in the complex resistivity of each cell of the spatial grid as a function of time. Each model along the time axis is called a 'reference space model'. This approach can be simplified into an inverse problem looking for the optimum of several reference space models using the approximation that the material properties vary linearly in time between two subsequent reference models. Regularizations in both space domain and time domain reduce inversion artefacts and improve the stability of the inversion problem. In addition, the use of the time-lapse equations allows the simultaneous inversion of data obtained at different times in just one inversion step (4-D inversion). The advantages of this new inversion algorithm are demonstrated on synthetic time-lapse data resulting from the simulation of a salt tracer test in a heterogeneous random material described by an anisotropic semi-variogram.
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Kirsch, R., Fellhauer, D., Altmaier, M., Neck, V., Rossberg, A., Fanghaenel, T., et al. (2011). Oxidation State and Local Structure of Plutonium Reacted with Magnetite, Mackinawite, and Chukanovite. Environmental Science & Technology, 45, 7267–7274.
Résumé: Due to their redox reactivity, surface sorption characteristics, and ubiquity as corrosion products or as minerals in natural sediments, iron(II)-bearing minerals control to a large extent the environmental fate of actinides. Pu-L(III)-edge}CANES and EXAFS spectra were used to investigate reaction products of aqueous (242)Pu(III) and (242)Pu(V) reacted with magnetite, mackinawite, and chukanovite under anoxic conditions. As Pu concentrations in the liquid phase were rapidly;below detection limit, oxidation state and local structure of Pu were determined for Pu associated with the solid mineral phase. Pu(V) was reduced in the presence of all three minerals. A newly identified, highly specific Pu(III)-sorption complex formed with magnetite. Solid PuO(2) phases formed in the presence of mackinawite and chukanovite; in the case of chukanovite, up to one-third of plutonium was also present as Pu(III). This highlights the necessity to consider, under reducing anoxic conditions, Pu(III) species in addition to tetravalent PuO(2) for environmental risk assessment. Our results also demonstrate the necessity to support thermodynamic calculations with spectroscopic data.
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Kobchenko, M., Panahi, H., Renard, F., Dysthe, D. K., Malthe-Sorenssen, A., Mazzini, A., et al. (2011). 4D imaging of fracturing in organic-rich shales during heating. Journal of Geophysical Research-Solid Earth, 116.
Résumé: To better understand the mechanisms of fracture pattern development and fluid escape in low permeability rocks, we performed time-resolved in situ X-ray tomography imaging to investigate the processes that occur during the slow heating (from 60 degrees to 400 degrees C) of organic-rich Green River shale. At about 350 degrees C cracks nucleated in the sample, and as the temperature continued to increase, these cracks propagated parallel to shale bedding and coalesced, thus cutting across the sample. Thermogravimetry and gas chromatography revealed that the fracturing occurring at similar to 350 degrees C was associated with significant mass loss and release of light hydrocarbons generated by the decomposition of immature organic matter. Kerogen decomposition is thought to cause an internal pressure build up sufficient to form cracks in the shale, thus providing pathways for the outgoing hydrocarbons. We show that a 2D numerical model based on this idea qualitatively reproduces the experimentally observed dynamics of crack nucleation, growth and coalescence, as well as the irregular outlines of the cracks. Our results provide a new description of fracture pattern formation in low permeability shales.
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Lacroix, P., & Helmstetter, A. (2011). Location of Seismic Signals Associated with Microearthquakes and Rockfalls on the Sechilienne Landslide, French Alps. Bulletin of the Seismological Society of America, 101, 341–353.
Résumé: The Sechilienne rockslide, in the French Alps, has recently been instrumented with three seismic arrays. This network has recorded numerous rockfalls and local microearthquakes. Because the media is highly fractured, it is difficult to identify and pick first arrivals. Beam-forming methods were therefore used to locate these events. The method has been adapted to take into account the heterogeneity of seismic wave velocities. The location accuracy has been estimated to be about 50 m for epicenters by applying the method to calibration shots. Depth is less constrained due to uncertainties on the velocity model and due to the seismic network geometry. This method of location has then been applied to rockfalls and microearthquakes. Most rockfalls initiate in the most active part of the rockslide called Les Ruines; the others are located on a recent eroded area aside from Les Ruines. The network also allows the estimation of the rockfall trajectory and propagation speed. Finally, 55 microearthquakes have been located within two zones. Microearthquakes are located within the first 250 m below the surface. Most microearthquakes are located in Les Ruines, the most active part of the rockslide, where the velocity has increased from 0.5 m/yr in 1996 to 1.4 m/yr in 2008. These events are located close to three faults that delimit a mass of about 3.6 million m(3). Other events are located close to the summital scarp, in a zone moving at a few centimeters per year. The western part of the rockslide, which moves more slowly, did not produce any event large enough to be detected simultaneously by all stations. This seismic monitoring suggests that only a very small fraction of the deformation is released through seismic events.
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Latour, S., Campillo, M., Voisin, C., Ionescu, I. R., Schmedes, J., & Lavallee, D. (2011). Effective friction law for small-scale fault heterogeneity in 3D dynamic rupture. Journal of Geophysical Research-Solid Earth, 116, 18.
Résumé: We address the problem of modeling dynamic rupture on multiscale heterogeneous faults in 3D. Under the assumption of slip-weakening friction, we numerically construct effective friction laws that integrate the effects of small-scale heterogeneity during the rupture. This homogenization process is based on the description of the initial phase of the rupture by the dominant unstable spectral mode. Its dynamics is influenced by the geometry of the fault, the static friction heterogeneities and the friction law. We first define a periodic small-scale heterogeneous model, introducing heterogeneity in the distribution of the static friction coefficient. We then describe a method for constructing this effective friction law. Applying this new law homogeneously on the fault permits to reproduce the dynamic evolution of the heterogeneous fault. Furthermore, we show that the effective friction law can be used to replace small-scale heterogeneities in two-scale heterogeneous models, while preserving their effects. We study three kinds of two-scale models, with growing complexity: first periodic at both scales, then periodic only at small scale, and finally irregular at both scales. This homogenization method can be adapted to the case where the heterogeneity is introduced in the initial stress rather than in the static friction value. Finally, we show in a simple example that the effective friction law permits to reproduce the transition between subshear and supershear rupture propagation, originally produced by heterogeneities on the fault.
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Latour, S., Gallot, T., Catheline, S., Voisin, C., Renard, F., Larose, E., et al. (2011). Ultrafast ultrasonic imaging of dynamic sliding friction in soft solids: The slow slip and the super-shear regimes. Epl, 96.
Résumé: Ultrafast ultrasonic speckle interferometry, an imaging technique derived from elastography, is used to follow the dynamic of the interface failure in a friction experiment. Experimental results that characterise two slipping regimes are presented: a slow slip regime associated with depinning events at the interface and a supershear rupture regime associated with the emission of Mach waves fronts. These results are discussed in the light of geophysical observations made at the scale of the Earth on the slip dynamics in active faults. Copyright (C) EPLA, 2011
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Lauterbach, S., Brauer, A., Andersen, N., Danielopol, D. L., Dulski, P., Huels, M., et al. (2011). Environmental responses to Lateglacial climatic fluctuations recorded in the sediments of pre-Alpine Lake Mondsee (northeastern Alps). Journal of Quaternary Science, 26, 253–267.
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Lauterbach, S., Brauer, A., Andersen, N., Danielopol, D. L., Dulski, P., Huels, M., et al. (2011). Multi-proxy evidence for early to mid-Holocene environmental and climatic changes in northeastern Poland. Boreas, 40, 57–72.
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Le Roux, O., Jongmans, D., Kasperski, J., Schwartz, S., Potherat, P., Lebrouc, V., et al. (2011). Deep geophysical investigation of the large Sechilienne landslide (Western Alps, France) and calibration with geological data. Engineering Geology, 120, 18–31.
Résumé: A geophysical imaging campaign, including four 950 m electrical profiles and four 470 m long seismic profiles, was performed on the large Sechilienne landslide with the objective of constraining the depth and the volume of the affected zone. Compared to the undisturbed ground, the moving area exhibits lower velocity and higher resistivity values. Comparison with existing geodetic, geomorphic and geological data (investigation gallery and borehole) allowed showing that these geophysical parameter variations result from intense fracturing and the progressive development of air-filled voids within the moving mass. A maximum thickness of 150 m to 200 m was found in the most deconsolidated zones. Locally, near-vertical very low resistivity anomalies were evidenced, related to cataclasis zones filled with clayey material. Applying the Wyllie's experimental law, rock mass porosity images were derived from seismic tomography profiles. Porosity between 30% and 4% was found from the top to the bottom of the deconsolidated zone, explaining the deep water table. Considering a porosity threshold of 3.7% for the sound bedrock, the total volume of the Sechilienne landslide was estimated to about 60 +/- 10 x 10(6) m(3), a more precise bracket than the previous estimations (20 x 10(6) to 100 x 10(6) m(3)). (C) 2011 Elsevier B.V. All rights reserved.
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Lebert, F., Bernardie, S., & Mainsant, G. (2011). Hydroacoustic monitoring of a salt cavity: an analysis of precursory events of the collapse. Natural Hazards and Earth System Sciences, 11, 2663–2675.
Résumé: One of the main features of “post mining” research relates to available methods for monitoring mine-degradation processes that could directly threaten surface infrastructures. In this respect, GISOS, a French scientific interest group, is investigating techniques for monitoring the eventual collapse of underground cavities. One of the methods under investigation was monitoring the stability of a salt cavity through recording microseismic-precursor signals that may indicate the onset of rock failure. The data were recorded in a salt mine in Lorraine (France) when monitoring the controlled collapse of 2 000 000 m(3) of rocks surrounding a cavity at 130m depth. The monitoring in the 30 Hz to 3 kHz frequency range highlights the occurrence of events with high energy during periods of macroscopic movement, once the layers had ruptured; they appear to be the consequence of the post-rupture rock movements related to the intense deformation of the cavity roof. Moreover the analysis shows the presence of some interesting precursory signals before the cavity collapsed. They occurred a few hours before the failure phases, when the rocks were being weakened and damaged. They originated from the damaging and breaking process, when micro-cracks appear and then coalesce. From these results we expect that deeper signal analysis and statistical analysis on the complete event time distribution (several millions of files) will allow us to finalize a complete typology of each signal families and their relations with the evolution steps of the cavity over the five years monitoring.
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Legchenko, A., Descloitres, M., Vincent, C., Guyard, H., Garambois, S., Chalikakis, K., et al. (2011). Three-dimensional magnetic resonance imaging for groundwater. New Journal of Physics, 13.
Résumé: The surface nuclear magnetic resonance method (SNMR) is an established geophysical tool routinely used for investigating one-dimensional (1D) and sometimes 2D subsurface water-saturated formations. We have expanded the tool by developing a 3D application. 3D-SNMR is a large-scale method that allows magnetic resonance imaging of groundwater down to about 80 m. Similar to most surface geophysical methods, 3D-SNMR has limited resolution, but it is effective for investigating water-saturated geological formations larger than several tens of meters. Because the performance of the method depends on variable survey conditions, we cannot estimate it in general. For demonstration purposes, we present an example of numerical modeling under fixed conditions. Results show that under certain conditions it is possible to detect a water volume as small as 500 m(3) and the detection threshold depends on the ambient electromagnetic noise magnitude and on the location of the target volume relative to the SNMR loops. The 3D-SNMR method was used to investigate accumulated water within the Tete Rousse glacier (French Alps). Inversion of the field measurements made it possible to locate the principal reservoir in the central part of the glacier and estimate the volume of accumulated water. These results were verified by 20 boreholes installed after the 3D-SNMR results were obtained and by pumping water out of the glacier. Very good correspondence between the 3D-SNMR and borehole results was observed.
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Lengline, O., & Got, J. L. (2011). Rupture directivity of microearthquake sequences near Parkfield, California. Geophysical Research Letters, 38.
Résumé: [1] The direction of propagation is an important factor that affects the pattern of ground motion generated by an earthquake. Characterizing factors favoring a potential rupture propagation direction is thus an important task. Here we analyze the earthquake directivity of repeating earthquake sequences located on the San Andreas fault near Parkfield, California. All earthquakes of a sequence have very similar waveforms and have overlapping surface ruptures. We show that subtle variations of the transfer function between earthquakes of a common sequence can be interpreted as a change of apparent rupture duration. Relative apparent rupture durations are computed for all pairs of events at all available stations and for each sequence. We invert these measurements to obtain an estimation of the apparent rupture duration for each individual event of the sequence relative to a reference event. Variation of apparent rupture duration with azimuth attests for the rupture directivity. We show that the majority of analyzed microearthquakes presents a rupture in the south-east direction. We also show that, on a given repeating sequence, most earthquakes tend to show the same rupture direction. Citation: Lengline, O., and J.-L. Got ( 2011), Rupture directivity of microearthquake sequences near Parkfield, California, Geophys. Res. Lett., 38, L08310, doi:10.1029/2011GL047303.
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Lessinnes, T., Plunian, F., Stepanov, R., & Carati, D. (2011). Dissipation scales of kinetic helicities in turbulence. Physics of Fluids, 23.
Résumé: A systematic study of the influence of the viscous effect on both the spectra and the nonlinear fluxes of conserved as well as nonconserved quantities in Navier-Stokes turbulence is proposed. This analysis is used to estimate the helicity dissipation scale which is shown to coincide with the energy dissipation scale. However, it is shown using the decomposition of helicity into eigenmodes of the curl operator that viscous effects have to be taken into account for wave vectors smaller than the Kolmogorov wave number in the evolution of these eigencomponents of the helicity. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3567253]
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Levy, C., Jongmans, D., & Baillet, L. (2011). Analysis of seismic signals recorded on a prone-to-fall rock column (Vercors massif, French Alps). Geophysical Journal International, 186, 296–310.
Résumé: A small-aperture (40 m) short-period seismic array was installed during four months on the Vercors massif (Western French Alps) at the top of a limestone column which collapsed one month and a half later. During this monitoring period, 193 seismic events were recorded by the seven seismometers of the array. Signal analysis yielded three main types of nearby seismic events to be identified from temporal and spectral characteristics: microearthquakes (single or multiple events), individual block falls and rock falls. It turned out that 60 per cent of the 193 events were classified as microearthquakes, exhibiting distinct P and S waves, while 17 per cent of these events remained unclassified. Out of the microearthquakes, 40 events with a good signal-to-noise ratio were selected and processed. P- and S-wave traveltimes were picked on the records and the inferred hypocentral distances agree with the two zones of the scarp exhibiting fresh ruptures after the fall. Polarization analysis of the 3-C records, along with numerical simulations, allowed discriminating between the two possible rupture mechanisms (toppling and sliding). Shear rupture (sliding) was the predominant mode in the lower part of the column whereas traction rupture (toppling) affected the upper part. Finally, the comparison between the ground motions recorded on the column and on the rock mass showed a systematic amplification on the column. Signal processing and numerical modelling both suggest that this amplification resulted from the excitation of the natural frequencies of the column and is particularly high (>3) for microearthquakes occurring at the column-to-mass interface.
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Lupker, M., France-Lanord, C., Lave, J., Bouchez, J., Galy, V., Metivier, F., et al. (2011). A Rouse-based method to integrate the chemical composition of river sediments: Application to the Ganga basin. Journal of Geophysical Research-Earth Surface, 116.
Résumé: The Ganga River is one of the main conveyors of sediments produced by Himalayan erosion. Determining the flux of elements transported through the system is essential to understand the dynamics of the basin. This is hampered by the chemical heterogeneity of sediments observed both in the water column and under variable hydrodynamic conditions. Using Acoustic Doppler Current Profiler (ADCP) acquisitions with sediment depth profile sampling of the Ganga in Bangladesh we build a simple model to derive the annual flux and grain size distributions of the sediments. The model shows that ca. 390 (+/- 30) Mt of sediments are transported on average each year through the Ganga at Haring Bridge (Bangladesh). Modeled average sediment grain size parameters D(50) and D(84) are 27 (+/- 4) and 123 (+/- 9) mu m, respectively. Grain size parameters are used to infer average chemical compositions of the sediments owing to a strong grain size chemical composition relation. The integrated sediment flux is characterized by low Al/Si and Fe/Si ratios that are close to those inferred for the Himalayan crust. This implies that only limited sequestration occurs in the Gangetic floodplain. The stored sediment flux is estimated to c.a. 10% of the initial Himalayan sediment flux by geochemical mass balance. The associated, globally averaged sedimentation rates in the floodplain are found to be ca. 0.08 mm/yr and yield average Himalayan erosion rate of ca. 0.9 mm/yr. This study stresses the need to carefully address the average composition of river sediments before solving large-scale geochemical budgets.
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Mahaney, W. C., Hart, K. M., Dohm, J. M., Hancock, R. G. V., Costa, P., O'Reilly, S. S., et al. (2011). Aluminum extracts in Antarctic paleosols: Proxy data for organic compounds and bacteria and implications for Martian paleosols. Sedimentary Geology, 237, 84–94.
Résumé: Pyrophosphate-extractable Al has been used to establish the presence of organically-complexed compounds in middle latitude and tropical soils and paleosols on Earth. As proxy data used to establish the presence of organic molecules and trace movement within profiles, it has proved an accurate indicator of downward translocation in Spodosols (podzols). Antarctic paleosols, dating from Middle to Early Miocene age (15-20 Ma), are mineralic weathering profiles lacking A and B horizons. These profiles exhibit pavement/Cox/Cz/Cu horizons, largely with sandy silt textures, little clay, and exceedingly low concentrations of organic matter. Recent chemical investigations of 33 soil samples from the New Mountain and Aztec Mountain areas near the Inland Ice, adjacent to the Taylor Glacier, show that pyrophosphate-extractable Al concentrations vary in phase with organic carbon as determined by loss-on-ignition. While Al-extract concentrations in selected samples are low (<0.15%), increasing values above nil approximately correlate positively with increases in bacterial populations of several common phylum, the extreme high numbers with more advanced biota including fossil Coleoptera. Available data suggest Al(p) extracts may target samples which may have undergone minor chelation, and which over long periods of time might have a cumulative weathering effect resulting in the accumulation of small concentrations of organic matter. As such, Al(p) extracts may prove useful in targeting the presence of life once in situ investigations of paleosols begin on Mars. (C) 2011 Elsevier B.V. All rights reserved.
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Mahaney, W. C., Krinsley, D., Langworthy, K., Kalm, V., Havics, T., Hart, K. M., et al. (2011). Fired glaciofluvial sediment in the northwestern Andes: Biotic aspects of the Black Mat. Sedimentary Geology, 237, 73–83.
Résumé: Fired glaciofluvial beds in outwash considered to date from the onset of the Younger Dryas Event (similar to 12.9 ka) in the northwestern Venezuelan Andes are considered equivalent to the Black Mat deposits described in other areas of North and South America and Europe. It may be equivalent to sediment recovered from other sites containing beds with spikes of cosmic nuclides and charcoal indicating the presence of widespread fire, one of the signatures of the Black Mat conflagration that followed the proposed breakup of Comet Encke or an unknown asteroid over the Laurentide Icesheet at 12.9 ka. In the northern Andes at Site MUM7B, sediment considered coeval with the Black Mat contains glassy carbon spherules, tri-coatings of C welded onto quartz and feldspar covered with Fe and Mn. Monazite with excessive concentrations of REEs, platinum metals including Ru and Rh, possible pdf's, and disrupted/brecciated and microfractured quartz and feldspar from impacting ejecta and excessive heating summarize the data obtained so far. The purpose of this paper is to document the physical character, mineralogy and biotic composition of the Black Mat. (C) 2011 Elsevier B.V All rights reserved.
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Manceau, A. (2011). Critical evaluation of the revised akdalaite model for ferrihydrite. American Mineralogist, 96, 521–533.
Résumé: The defect-free akdalaite model (fhyd6) for six-line ferrihydrite (6Fh) derived from a pair distribution function (PDF) analysis of high-energy X-ray scattering (HEXS) data was revised (model ferrifh) by Michel et al (2010) using data from a sample produced by heating two-line ferrihydrite (2Fh) at 175 degrees C for 8 h in the presence of citrate. We show here that the scattering pattern for this sample is similar if not the same as that for hydromaghemite, which in turn is a mixture of maghemite (gamma-Fe(2)O(3)), hematite and 6Fh. As in the case of fhyd6, the PDF of ferri fit was regressed using the structure of the weakly hydrated phase akdalaite [Al(10)O(14)(OH)(2)] after substituting Fe for Al as a starting model. We show that the ferrifh model is implausible for the following reasons. (1) It is derived from a sample, ferrith, that appears to be hydromaghemite, not pure 6Fh. (2) It has 20% tetrahedral Fe, a coordination that had been eliminated previously using XANES, Mossbauer, and EELS spectroscopies. (3) 75% of the Fe octahedra have shared edge lengths considerably longer than the shortest unshared edges in violation of Pauling's distortion rule. (4) Three tetrahedral Fe-O bonds are longer than three octahedral Fe-O bonds, inducing significant polyhedral distortions. And (5) the calculated composition [Fe(10)O(14)(OH)(2)center dot 1.2H(2)O] disagrees with literature data on weight loss from dehydration for 6Fh. We present an alternative interpretation of the histogram of Fe-Fe distances up to 3.7 angstrom obtained from the PDF of the fhyd6 ferrihydrite as a mixture of local structures of goethite/akaganeite (alpha/beta-FeOOH) and feroxyhite/hematite (delta-FeOOH/alpha-Fe(2)O(3)). Within this interpretation Fe only occupies octahedra that are bonded to each other by faces, edges, or double-corners. This polyhedral connectivity is confirmed experimentally by analysis of the EXAFS spectra of six-line ferrihydrites measured at room and liquid helium temperature. The Fe-Fe pairs from EXAFS data are described reasonably well by a mixture of approximately 70% feroxyhite (containing some nanohematite) and 30% akaganeite, without resorting to other phases. This set of evidence indicates that HEXS data are consistent with the Drits model for ferrihydrite (Drits et al. 1993a).
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Marandet, C., Roux, P., La Rizza, P., & Nicolas, B. (2011). Understanding the feedback effect through the physics of the diffraction-based sensitivity kernel for a target in shallow water: A small-scale experimental demonstration. The Journal of the Acoustical Society of America, 130, 2410.
Résumé: Using the feedback effect, we experimentally detect a wavelength-sized target in a shallow ultrasonic waveguide between two source-receiver transducers on acoustic feedback. The waveguide represents a 1-km-long, 50-m-deep ocean acoustic channel at the 1/1000 scale. The feedback phenomenon, or Larsen effect, occurs when a source and a receiver are connected both acoustically through the propagation medium and electrically through an amplifier in such a way that the received signal is simultaneously and continuously added to the emitted signal. A resonance is obtained when the emitter and the receiver are in phase. This resonance is very sensitive to any change in the medium which makes it a good observable for target detection. In presence of a target in the waveguide, the numerical gain of the feedback effect has to increase in order to compensate the scattering of the acoustic field from the target. In a separate experiment, the scattered field may also be recorded in a transmission configuration from the same couple of emitter/receiver with an impulse as a source signal. A comparison is made between the two different approaches.
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Marandet, C., Roux, P., Nicolas, B., & Mars, J. (2011). Target detection and localization in shallow water: An experimental demonstration of the acoustic barrier problem at the laboratory scale. Journal of the Acoustical Society of America, 129, 85–97.
Résumé: This study demonstrates experimentally at the laboratory scale the detection and localization of a wavelength-sized target in a shallow ultrasonic waveguide between two source-receiver arrays at 3 MHz. In the framework of the acoustic barrier problem, at the 1/1000 scale, the waveguide represents a 1.1-km-long, 52-m-deep ocean acoustic channel in the kilohertz frequency range. The two coplanar arrays record in the time-domain the transfer matrix of the waveguide between each pair of source-receiver transducers. Invoking the reciprocity principle, a time-domain double-beam-forming algorithm is simultaneously performed on the source and receiver arrays. This array processing projects the multireverberated acoustic echoes into an equivalent set of eigenrays, which are defined by their launch and arrival angles. Comparison is made between the intensity of each eigenray without and with a target for detection in the waveguide. Localization is performed through tomography inversion of the acoustic impedance of the target, using all of the eigenrays extracted from double beamforming. The use of the diffraction-based sensitivity kernel for each eigenray provides both the localization and the signature of the target. Experimental results are shown in the presence of surface waves, and methodological issues are discussed for detection and localization. (C) 2011 Acoustical Society of America. [DOI: 10.1121/1.3514503]
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Marcaillou, C., Munoz, M., Vidal, O., Parra, T., & Harfouche, M. (2011). Mineralogical evidence for H(2) degassing during serpentinization at 300 degrees C/300 bar. Earth and Planetary Science Letters, 303, 281–290.
Résumé: Hydrogen is produced in large amounts during hydrothermal alteration of peridotite in low-spreading-rate mid-ocean ridges. This production is directly linked to reducing conditions in hydrothermal fluids induced by the oxidation of Fe(2+) in primary minerals (olivine and pyroxene) to Fe(3+) in secondary minerals (magnetite and serpentine). A better knowledge of iron speciation in serpentine is therefore crucial to the quantification of hydrogen production during the serpentinization process. For the first time, we have determined the amount of ferric iron in altered peridotite as a function of alteration time. We investigated experimentally the alteration of powdered Iherzolite in pure water at 300 degrees C/300 bar. For each experimental run (0, 7, 18,34 and 70 days), H(2) degassing was measured using in-situ gas chromatography and the experimental products were analyzed using XRD, Raman and X-ray absorption spectroscopy at the iron K-edge. In parallel, aqueous solutions were analyzed by ICP-AES. Our results show quasi-complete scrpentinization at 70 days with replacement of primary olivine and pyroxene by secondary lizardite and magnetite. The Fe(3+)/Fe(total) ratio is linearly dependent on the hydrogen production and ranges from 0 to 0.66 at the end of the experiment. Our results reveal strong variations in Fe3+ in serpentine for different alteration times, from 0 to 100% of ferric iron, including up to 12% of tetrahedral iron. Hydrogen was produced in three main stages: (1) a first stage during which the H(2) production rate reaches a maximum at 18 days and is controlled by the crystallization of magnetite, (2) an intermediate stage during which serpentine incorporates ferric iron and thus plays a major role (up to 50%) in the hydrogen formation, and (3) a final stage during which magnetite amount increases from similar to 2 to similar to 5% of the mineral assemblage. The last alteration stage is accompanied by a slight increase of the Fe(3+)/Fe(total) ratio, while the rate of hydrogen production decreases at the end of the experiment. Consequently, variations of the ferric iron contents in natural oceanic peridotites may constitute a good indicator of the “hydrogen-potential” of various ultramafic hydrothermal fields. (C) 2011 Elsevier B.V. All rights reserved.
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Margheriti, L., Chiaraluce, L., Voisin, C., Cultrera, G., Govoni, A., Moretti, M., et al. (2011). Rapid response seismic networks in Europe: lessons learnt from the L'Aquila earthquake emergency. Annals of Geophysics, 54, 392–399.
Résumé: The largest dataset ever recorded during a normal fault seismic sequence was acquired during the 2009 seismic emergency triggered by the damaging earthquake in L'Aquila (Italy). This was possible through the coordination of different rapid-response seismic networks in Italy, France and Germany. A seismic network of more than 60 stations recorded up to 70,000 earthquakes. Here, we describe the different open-data archives where it is possible to find this unique set of data for studies related to hazard, seismotectonics and earthquake physics. Moreover, we briefly describe some immediate and direct applications of emergency seismic networks. At the same time, we note the absence of communication platforms between the different European networks. Rapid-response networks need to agree on common strategies for network operations. Hopefully, over the next few years, the European Rapid-Response Seismic Network will became a reality.
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Marsan, D., Weiss, J., Metaxian, J. - P., Grangeon, J., Roux, P. - F., & Haapala, J. (2011). Low-frequency bursts of horizontally polarized waves in the Arctic sea-ice cover. Journal of Glaciology, 57, 231–237.
Résumé: We report the detection of bursts of low-frequency waves, typically f=0.025 Hz, on horizontal channels of broadband seismometers deployed on the Arctic sea-ice cover during the DAMOCLES (Developing Arctic Modeling and Observing Capabilities for Long-term Environmental Studies) experiment in spring 2007. These bursts have amplitudes well above the ambient ice swell and a lower frequency content. Their typical duration is of the order of minutes. They occur at irregular times, with periods of relative quietness alternating with periods of strong activity. A significant correlation between the rate of burst occurrences and the ice-cover deformation at the similar to 400 km scale centered on the seismic network suggests that these bursts are caused by remote, episodic deformation involving shearing across regional-scale leads. This observation opens the possibility of complementing satellite measurements of ice-cover deformation, by providing a much more precise temporal sampling, hence a better characterization of the processes involved during these deformation events.
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Martin, C., Brunet, F., Duchene, S., Luais, B., & Deloule, E. (2011). REE and Hf distribution between pyrope and NaCl-bearing water at eclogitic-facies conditions. European Journal of Mineralogy, 23, 343–353.
Résumé: Due to the interaction of oceanic crust with seawater, NaCl is a main component dissolved in aqueous fluid in subduction zones. The effect of dissolved NaCl (1.64 mol/l) on the partitioning of REE and Hf between garnet (pyrope) and aqueous fluid (doped with similar to 500 ppm of REE and similar to 250 ppm of Hf) has been investigated experimentally at 3 GPa, 850 degrees C(i.e., eclogitic UHP conditions) using the diamond trap technique. Trace elements in both pyrope and diamond aggregate were analyzed using LA-ICP-MS to derive fluid/pyrope partition coefficients (D). Mass balance calculation indicates that lanthanum is present in an accessory phase, tornebohmite. Europium and aluminium concentrations are too high in the aggregate to comply with mass balance and solubility data from the literature, respectively. Transport of these species from the mineral powder to the aggregate is inferred. D(MREE) (Gd and Tb) equals 0.39 +/- 0.11 and 0.22 +/- 0.07, respectively. D(HREE) (Dy to Lu) ranges from 0.09 +/- 0.02 to 0.02 +/- 0.01 with a regular decrease from Dy to Lu. D(Hf) is 0.33 +/- 0.09. Lanthanum is found to be incompatible (D(La) is 2.10 +/- 0.95) whereas for the other LREE (from Ce to Sm), D is lower than 1 (D(Ce) = 0.65 +/- 0.15, D(Pr) = 0.74 +/- 0.22, D(Nd) = 0.71 +/- 0.29 and D(Sm) = 0.61 +/- 0.23). Contrary to D(HRE)E and D(MREE), D(LREE) do not fit a near-parabolic dependence on LREE effective ionic radius. The Hf fluid/pyrope partition coefficient (D(Hf) = 0.33 +/- 0.09) indicates that this element favourably partition into garnet. Finally, it is shown that, compared to pure water, the addition of NaCl in water has no significant effect on REE and Hf behaviour.
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Matthieu, R., Stefan, C., & Philippe, R. (2011). One channel spatio-temporal inversion of acoustic wave in reverberant cavities. The Journal of the Acoustical Society of America, 130, 2515.
Résumé: It has been recently shown that it was possible to optimally recover the Green functions from a complex wave field despite of a non-isotropic distribution of the noise sources. The method used is based on a particular use of the inverse filter (IF) formalism which is called the passive IF. Based on this formalism, we have investigated the possibility to control the spatio-temporal degrees of freedom in a reverberant cavity for the focusing of waves (active processes). The understanding of this phenomenon can be very useful in a lot of different applications like in acoustical imaging, seismology, or telecommunications. In the present work, the spatio-temporal focalization of ultrasounds in reverberant cavities is studied using medical arrays and water tanks. Through experiments, a complete spatio-temporal inversion is realized to synthesize optimized emitting signals. The result generalizes the focalization control over a spatial vector and during an arbitrary time window.
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Mewafy, F. M., Atekwana, E. A., Werkema, D. D., Slater, L. D., Ntarlagiannis, D., Revil, A., et al. (2011). Magnetic susceptibility as a proxy for investigating microbially mediated iron reduction. Geophysical Research Letters, 38, 5.
Résumé: We investigated magnetic susceptibility (MS) variations in hydrocarbon contaminated sediments. Our objective was to determine if MS can be used as an intrinsic bioremediation indicator due to the activity of iron-reducing bacteria. A contaminated and an uncontaminated core were retrieved from a site contaminated with crude oil near Bemidji, Minnesota and subsampled for MS measurements. The contaminated core revealed enriched MS zones within the hydrocarbon smear zone, which is related to iron-reduction coupled to oxidation of hydrocarbon compounds and the vadose zone, which is coincident with a zone of methane depletion suggesting aerobic or anaerobic oxidation of methane is coupled to iron-reduction. The latter has significant implications for methane cycling. We conclude that MS can serve as a proxy for intrinsic bioremediation due to the activity of iron-reducing bacteria iron-reducing bacteria and for the application of geophysics to iron cycling studies. Citation: Mewafy, F. M., E. A. Atekwana, D. D. Werkema Jr., L. D. Slater, D. Ntarlagiannis, A. Revil, M. Skold, and G. N. Delin (2011), Magnetic susceptibility as a proxy for investigating microbially mediated iron reduction, Geophys. Res. Lett., 38, L21402, doi:10.1029/2011GL049271.
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Mittempergher, S., Di Toro, G., Gratier, J. P., Hadizadeh, J., Smith, S. A. F., & Spiess, R. (2011). Evidence of transient increases of fluid pressure in SAFOD phase III cores. Geophysical Research Letters, 38.
Résumé: The San Andreas Fault Observatory at Depth (SAFOD) in Parkfield, central California, has been drilled through a fault segment that is actively deforming through creep and microearthquakes. Creeping is accommodated in two fault strands, the Southwest and Central Deforming Zones, embedded within a damaged zone of deformed shale and siltstone. During drilling, no pressurized fluids have been encountered, even though the fault zone acts as a permeability barrier to fluid circulation between the North American and Pacific plates. Microstructural analysis of sheared shales associated with calcite and anhydrite-bearing veins found in SAFOD cores collected at 1.5m from the Southwest Deforming Zone, suggests that transient increases of pore fluid pressure have occurred during the fault activity, causing mode I fracturing of the rocks. Such build-ups in fluid pressure may be related to permeability reduction during fault creep and pressure-solution processes, resulting in localized failure of small fault zone patches and providing a potential mechanism for the initiation of some of the microearthquakes registered in the SAFOD site. Citation: Mittempergher, S., G. Di Toro, J. P. Gratier, J. Hadizadeh, S. A. F. Smith, and R. Spiess (2011), Evidence of transient increases of fluid pressure in SAFOD phase III cores, Geophys. Res. Lett., 38, L03301, doi:10.1029/2010GL046129.
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Moczo, P., Kristek, J., Galis, M., Chaljub, E., & Etienne, V. (2011). 3-D finite-difference, finite-element, discontinuous-Galerkin and spectral-element schemes analysed for their accuracy with respect to P-wave to S-wave speed ratio. Geophysical Journal International, 187, 1645–1667.
Résumé: We analyse 13 3-D numerical time-domain explicit schemes for modelling seismic wave propagation and earthquake motion for their behaviour with a varying P-wave to S-wave speed ratio (V(P)/V(S)). The second-order schemes include three finite-difference, three finite-element and one discontinuous-Galerkin schemes. The fourth-order schemes include three finite-difference and two spectral-element schemes. All schemes are second-order in time. We assume a uniform cubic grid/mesh and present all schemes in a unified form. We assume plane S-wave propagation in an unbounded homogeneous isotropic elastic medium. We define relative local errors of the schemes in amplitude and the vector difference in one time step and normalize them for a unit time. We also define the equivalent spatial sampling ratio as a ratio at which the maximum relative error is equal to the reference maximum error. We present results of the extensive numerical analysis. We theoretically (i) show how a numerical scheme sees the P and S waves if the V(P)/V(S) ratio increases, (ii) show the structure of the errors in amplitude and the vector difference and (iii) compare the schemes in terms of the truncation errors of the discrete approximations to the second mixed and non-mixed spatial derivatives. We find that four of the tested schemes have errors in amplitude almost independent on the V(P)/V(S) ratio. The homogeneity of the approximations to the second mixed and non-mixed spatial derivatives in terms of the coefficients of the leading terms of their truncation errors as well as the absolute values of the coefficients are key factors for the behaviour of the schemes with increasing V(P)/V(S) ratio. The dependence of the errors in the vector difference on the V(P)/V(S) ratio should be accounted for by a proper (sufficiently dense) spatial sampling.
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Montes-Hernandez, G., & Renard, F. (2011). Co-utilisation of alkaline solid waste and compressed-or-supercritical CO(2) to produce calcite and calcite/Se(0) red nanocomposite. Journal of Supercritical Fluids, 56, 48–55.
Résumé: The coal combustion fly-ash and alkaline paper mill waste were previously used to sequester CO(2) via waste-water-CO(2) interactions. For this case, a solid mixture (calcite and un-reacted waste) was obtained after carbonation process. In the present study, we propose a solid-water separation of free lime (CaO) or free portlandite (Ca(OH)(2)) contained in waste prior to carbonation experiments in order to produce pure calcite or calcite/Se(0) red composite. The calcite and carbonate composite syntheses have been also independently studied, but for both cases, a commercial powdered portlandite was used as calcium source. For this study, the extracted alkaline-solution (pH = 12.2-12.4 and Ca concentration = 810-870 mg/L) from alkaline solid waste was placed in contact with compressed or supercritical CO(2) at moderate or high temperature, leading a preferential nucleation-growth of submicrometric particles of calcite (<1 mu m) with rhombohedral morphology at 90 degrees C and 90 bar (9 MPa), whereas a preferential nucleation-growth of nanometric particles of calcite (<0.2 mu m) with scalenohedral morphology at 30 degrees C and 20 bar (2 MPa) were observed. When, the extracted alkaline-solution was placed in contact with supercritical CO(2) (90 bar) at high temperature (90 degrees C) and in presence of unstable seleno-L-cystine compound, the nucleation-growth of calcite/Se(0) red nano-composite taken place. The composite consisted predominantly of spherical, amorphous nanometric-to-submicrometric of elemental red selenium (<500 nm) deposited on the calcite matrix. Here, the calcite was constituted by nano- to microrhombohedral crystals (<2 mu m) and micrometric agglomerates and/or aggregates (<5 mu m). These results on the particle size and morphology of crystal faces are very similar to calcite produced using commercial powdered portlandite as alkaline reactant and calcium source. This study is a nice example of feasibility to obtain possible ecological and economical benefits from waste co-utilisation. (C) 2010 Elsevier B.V. All rights reserved.
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Montes-Hernandez, G., Beck, P., Renard, F., Quirico, E., Lanson, B., Chiriac, R., et al. (2011). Fast Precipitation of Acicular Goethite from Ferric Hydroxide Gel under Moderate Temperature (30 and 70 degrees C). Crystal Growth & Design, 11, 2264–2272.
Résumé: The present study describes a simple and novel synthesis route for submicrometric acicular goethite (alpha-FeOOH) using high OH/Fe molar ratio (=5) and moderate temperature (30 and 70 degrees C). Two different alkaline sources (NaOH and Ca(OH)(2)) and two iron(III) sources (FeCl(3)center dot 6H(2)O and Fe(NO(3))(3)center dot 9H(2)O) were investigated. FESEM, XRD, FTIR, N(2) sorption isotherms, color evolution, and pH monitoring have been used to determine the formation mechanism, the particle size, specific surface area, and morphology of goethite particles. Three pH regions were determined during goethite formation, and each of them was qualitatively associated to (I) the formation of a ferric hydroxide gel, leading to acid conditions (pH < 2.5); (II) the spontaneous nucleation of goethite, leading to alkaline conditions (pH > 11) and fine sedimentable particles; and (III) the growth of goethite in alkaline conditions (11 < pH < 13.5). Both the temperature and the Fe(III) source have a significant effect on the particle size, specific surface area, and morphology of goethite. High acicular goethite particles (<1 mu m in length, moderate specific surface area, S(BET) = 31.2 m(2)/g) were produced after 7 h of reaction at 70 degrees C, while about 24 h of reaction are required to produce low, acicular goethite particles (<0.5 mu m in length, high specific surface area, S(BET) = 133.8 m(2)/g) at 30 degrees C, using in both cases iron chloride. When Ca(OH)(2) particles are used as alkaline source, a complex mineral composite with high specific surface area (87.3 m(2)/g) was synthesized; it was mainly composed of unreacted Ca(OH)(2) coated with nanosized particles (possibly amorphous iron hydroxide), calcium iron oxide chloride hydrate, and calcite. Novel conditions to prepare uniform goethite particles, possibly with high potential as adsorbents or pigments, have been established.
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Montes-Hernandez, G., Sarret, G., Hellmann, R., Menguy, N., Testemale, D., Charlet, L., et al. (2011). Nanostructured calcite precipitated under hydrothermal conditions in the presence of organic and inorganic selenium. Chemical Geology, 290, 109–120.
Résumé: Selenium is an important trace metalloid, whose global cycle is controlled by fluid-rock interactions in the Earth's upper crust, interactions with bin-molecules in soils and living systems, and atmospheric transport in ashes. The cycling of selenium is often intimately associated with carbonate phases, with Se being generally incorporated as an impurity in calcite crystals or adsorbed on carbonate nanoparticles. In order to better understand the interaction of aqueous selenium species with carbonates, we studied the precipitation of calcite under hydrothermal conditions (30-90 degrees C, 25-90 bar) in a CO(2)-H(2)O-Ca(OH)(2) medium in the presence of aqueous inorganic and organic selenium compounds. Aqueous carbonation reactions in the presence of selenium at elevated temperatures and pressures, relevant for long-term CO(2) sequestration in reservoirs and other natural geological systems, have until now not been investigated to the best of our knowledge. Electron microscopy (FESEM and TEM) and synchrotron X-ray absorption spectroscopy (XAS) were used in a complementary manner to investigate crystal size, structural order (crystallinity), morphology of crystal faces, crystal organization, and selenium speciation in the calcite samples. XAS data analysis showed clear evidence for the incorporation of selenite oxyanion (SeO(3)(2-)) into the calcite crystal structure. At low Se content (1.3 mg/g calcite), a single site was observed with Se surrounded by six Ca atoms, whereas additional sites, probably corresponding to surface sorption sites, were found with increasing Se content. XAS also showed that seleno-L-cystine (Secys) was chemically fragmented during carbonation, and the solid phase contained elemental and oxidized Se, in hexagonal or amorphous form depending on the experimental conditions, with a minor proportion of Se(IV). Moreover, FESEM and TEM measurements revealed a very complex effect of Secys on the particle size and aggregation/agglomeration process, leading to the following calcite morphologies: rhombohedra, elongated rhombohedra (c-axis elongation), scalenohedra, star-like and shell-like crystal aggregates, and irregular calcite polycrystals. The aggregates and irregular polycrystals, which we designate as nanostructured calcite material, were constituted of nanometer-sized calcite crystallites (<100 nm). The star and shell-like crystal aggregates, which were observed only in the presence of Secys, may be due to crystal growth in the presence of associated secondary organic compounds due to a simultaneous chemical fragmentation of Secys. Overall, the results from this study show that selenium (of biotic or abiotic origin) can be integrated into the crystallographic structure of calcite under hydrothermal conditions. This has relevance for geological processes in diverse environments, such as hydrothermal systems along mid-ocean ridges, or underground reservoirs associated with massive injection of CO(2) for long-term geological sequestration. (C) 2011 Elsevier B.V. All rights reserved.
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Moore, J. R., Boleve, A., Sanders, J. W., & Glaser, S. D. (2011). Self-potential investigation of moraine dam seepage. Journal of Applied Geophysics, 74, 277–286.
Résumé: Self-potential (SP) and electrical resistivity measurements are used to investigate seepage at a remote moraine dam in the Sierra Nevada of California. The site is a small terminal moraine impounding roughly 300,000 m(3) of water at similar to 3400 m a.s.l. Suspicious fine sediment in a small lake at the dam's downstream toe prompted initial concerns that anomalous seepage may be eroding matrix material from the moraine. 235 individual SP measurements covering the surface of the dam were collected in order to investigate electrokinetic current sources resulting from seepage, while resistivity soundings probed moraine stratigraphy and suggest that the till contains interstitial ice. Contoured SP data reveal a non-uniform voltage distribution over the moraine dam and two distinct negative SP anomalies. The first, located in the central area of the moraine, shows a broad negative SP zone around the crest and increasingly positive SP moving downhill towards both the upstream and downstream toes. This anomaly can be explained by shallow gravitational groundwater flow in the near subsurface combined with upward groundwater flux through evapotranspiration; numerical simulation of the combined effect matches field data well. The second SP anomaly has a tightly localized distribution and can be explained by vertically descending flow into a bedrock fault conduit. Our conceptual seepage model suggests that flow travels from Dana Lake first at the boundary of ice-filled moraine and bedrock before converging on a concentrated channel in the subvertical fault zone. Positive SP near the dam abutments results from groundwater inflow from adjacent hillslopes. Combined analyses suggest that seepage erosion is not currently affecting the moraine dam, and that the sediment observed on the bed of the downstream toe lake is likely a remnant of past outflow events. (C) 2011 Elsevier B.V. All rights reserved.
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Moradi, A. S., Hatzfeld, D., & Tatar, M. (2011). Microseismicity and seismotectonics of the North Tabriz fault (Iran). Tectonophysics, 506, 22–30.
Résumé: We present the results of a microearthquake study conducted in 2004 with 31 portable stations around the city of Tabriz, which is crossed by an active fault and has experienced several destructive earthquakes in the recent history. From April 24 until July 24, we recorded 80 earthquakes by more than 4 stations. We complement these data with earthquakes recorded by the 8 permanent seismological stations of the Tabriz network operated by Institute of Geophysics of the University of Tehran from August 1995 until March 2008. Among a total of 6377 events, only 394 earthquakes were recorded by more than 5 stations and located with statistical uncertainties (ERZ and ERH) less than 5 km and a Gap less than 270 degrees. Most of these earthquakes are located along the Tabriz fault, at a depth ranging from the surface to 20 km, comparable to other studies conducted in Central Alborz. We computed 22 focal mechanisms most of which show right-lateral strike-slip motion along east-southeast planes, consistent with the geologic evidence for Quaternary slip. We do not see any peculiar pattern near the Tabriz pull-apart basin, or at both ends of the North Tabriz fault, where it terminates in EW trending reverse faults. This suggests that the fault is simpler (more mature) at depth than at the surface. (C) 2011 Elsevier B.V. All rights reserved.
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Mugnier, J. L., Huyghe, P., Gajurel, A. P., Upreti, B. N., & Jouanne, F. (2011). Seismites in the Kathmandu basin and seismic hazard in central Himalaya. Tectonophysics, 509, 33–49.
Résumé: Soft-sediment deformation structures have been analyzed at six sites of the Kathmandu valley. Microgranulometric study reveals that silty levels (60 to 80% silt) favor the development of soft-sediment deformation structures, while sandy levels (60 to 80% sand) are passively deformed. Nonetheless well sorted sand levels (more than 80% sand) generate over-fluid pressure during compaction if located beneath a silty cap, leading to fluidization and dike development. 3-D geometry of seismites indicates a very strong horizontal shearing during their development. Using a physical approach based on soil liquefaction during horizontal acceleration, we show that the fluidization zone progressively grows down-section during the shaking, but does not exactly begin at the surface. The comparison of bed-thickness and strength/depth evolution indicates three cases: i) no soft-sediment deformation occurs for thin (few centimeters) silty beds; ii) the thickness of soft-sediment deformation above sandy beds is controlled by the lithological contrast; iii) the thickness of soft-sediment deformation depends on the shaking intensity for very thick silty beds. These 3 cases are evidenced in the Kathmandu basin. We use the 30 cm-thick soft-sediment deformation level formed during the 1833 earthquake as a reference: the 1833 earthquake rupture zone extended very close to Kathmandu, inducing there MMI IX-X damages. A 90 cm-thick sediment deformation has therefore to be induced by an event greater than MMI X. From a compilation of paleo and historic seismology studies, it is found that the great (M similar to 8.1) historical earthquakes are not characteristic of the greatest earthquakes of Himalaya; hence earthquakes greater than M similar to 8.6 occurred. Kathmandu is located above one of the asperities that laterally limits the extent of mega-earthquake ruptures and two successive catastrophic events already affected Kathmandu, in 1255 located to the west of this asperity and in similar to 1100 to the east. (C) 2011 Elsevier B.V. All rights reserved.
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Nagy, K. L., Manceau, A., Gasper, J. D., Ryan, J. N., & Aiken, G. R. (2011). Metallothionein-Like Multinuclear Clusters of Mercury(II) and Sulfur in Peat. Environmental Science & Technology, 45, 7298–7306.
Résumé: Strong mercury(II)-sulfur (Hg-SR) bonds in natural organic matter, which influence mercury bioavailability, are difficult to characterize. We report evidence for two new Hg-SR structures using X-ray absorption spectroscopy in peats from the Florida Everglades with added Hg. The first, observed at a mole ratio of organic reduced S to Hg (S(red)/Hg) between 220 and 1140, is a Hg(4)S(x), type of cluster with each Hg atom bonded to two S atoms at 2.34 angstrom and one Sat 2.53 angstrom, and all Hg atoms 4.12 angstrom apart. This model structure matches those of metal-thiolate clusters in metallothioneins, but not those of HgS minerals. The second, with one S atom at 2.34 angstrom and about six C atoms at 2.97 to 3.28 angstrom, occurred at S(red)/Hg between 0.80 and 4.3 and suggests Hg binding to a thiolated aromatic unit. The multinuclear Hg cluster indicates a strong binding environment to cysteinyl sulfur that might impede methylation. Along with a linear Hg(SR)(2) unit with Hg-S bond lengths of 2.34 angstrom at S(red)/Hg of about 10 to 20, the new structures support a continuum in Hg-SR binding strength in natural organic matter.
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Nemati, M., Hatzfeld, D., Gheitanchi, M. R., Sadidkhouy, A., & Mirzaei, N. (2011). Microseismicity and seismotectonics of the Firuzkuh and Astaneh faults (East Alborz, Iran). Tectonophysics, 506, 11–21.
Résumé: In 2007 and 2008, we installed two local seismological networks of 10 stations around the two active faults of Firuzkuh and Astaneh, which are part of the Sharud fault system located in Central Alborz, similar to 150 km east of Tehran, Iran. These networks were deployed for about 7 months each and recorded 785 and 1194 earthquakes, respectively. We analyzed the seismicity and focal mechanisms together with data from the permanent network of the Institute of Geophysics (University of Tehran). The tectonics of this area shows a pull-apart relay (Bashm and Chashm faults) between the 2 left-lateral strike-slip faults of Firuzkuh and Astaneh. Firstly, we computed the velocity structure which minimizes the travel time residuals and obtained a sedimentary cover of 4 km overlying an 8 km-thick upper-crust with a Moho located at a depth of 33.5 km. Secondly, we located the seismicity which is distributed mainly on the Astaneh fault and Chashm fault Seismicity is also associated with the North Semnan fault located farther south. Cross sections show that the North Semnan fault is dipping north and both the Chashm and Astaneh faults are vertical. The Garmsar, Bashm and North Alborz faults seem to be less active. Focal mechanisms associated with the Chashm and Astaneh faults show mainly strike-slip motion (left-lateral on a NE-SW trending active plane) with no difference between the 2 faults, suggesting they behave similarly. (C) 2011 Elsevier B.V. All rights reserved.
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O'Brien, G. S., Lokmer, I., De Barros, L., Bean, C. J., Saccorotti, G., Metaxian, J. P., et al. (2011). Time reverse location of seismic long-period events recorded on Mt Etna. Geophysical Journal International, 184, 452–462.
Résumé: We present the first application of a time reverse location method in a volcanic setting, for a family of long-period (LP) events recorded on Mt Etna. Results are compared with locations determined using a full moment tensor grid search inversion and cross-correlation method. From 2008 June 18 to July 3, 50 broad-band seismic stations were deployed on Mt Etna, Italy, in close proximity to the summit. Two families of LP events were detected with dominant spectral peaks around 0.9 Hz. The large number of stations close to the summit allowed us to locate all events in both families using a time reversal location method. The method involves taking the seismic signal, reversing it in time, and using it as a seismic source in a numerical seismic wave simulator where the reversed signals propagate through the numerical model, interfere constructively and destructively, and focus on the original source location. The source location is the computational cell with the largest displacement magnitude at the time of maximum energy current density inside the grid. Before we located the two LP families we first applied the method to two synthetic data sets and found a good fit between the time reverse location and true synthetic location for a known velocity model. The time reverse location results of the two families show a shallow seismic region close to the summit in agreement with the locations using a moment tensor full waveform inversion method and a cross-correlation location method.
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Pedoja, K., Ortlieb, L., Devries, T. J., Machare, J., Audin, L., & Regard, V. (2011). Comment on “Tectonic record of strain buildup and abrupt coseismic stress release across the northwestern Peru coastal plain, shelf, and continental slope during the past 200 kyr” by Jacques Bourgois et al. Journal of Geophysical Research-Solid Earth, 116.
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Pili, E., Kennedy, B. M., Conrad, M. E., & Gratier, J. P. (2011). Isotopic evidence for the infiltration of mantle and metamorphic CO(2)-H(2)O fluids from below in faulted rocks from the San Andreas Fault system. Chemical Geology, 281, 242–252.
Résumé: To characterize the origin of the fluids involved in the San Andreas Fault (SAF) system, we carried out an isotope study of exhumed faulted rocks from deformation zones, vein fillings and their hosts and the fluid inclusions associated with these materials. Samples were collected from segments along the SAF system selected to provide a depth profile from upper to lower crust. In all, 75 samples from various structures and lithologies from 13 localities were analyzed for noble gas, carbon, and oxygen isotope compositions. Fluid inclusions exhibit helium isotope ratios ((3)He/(4)He) of 0.1-2.5 times the ratio in air, indicating that past fluids percolating through the SAF system contained mantle helium contributions of at least 35%, similar to what has been measured in present-day ground waters associated with the fault (Kennedy et al., 1997). Calcite is the predominant vein mineral and is a common accessory mineral in deformation zones. A systematic variation of C- and O-isotope compositions of carbonates from veins, deformation zones and their hosts suggests percolation by external fluids of similar compositions and origin with the amount of fluid infiltration increasing from host rocks to vein to deformation zones. The isotopic trend observed for carbonates in veins and deformation zones follows that shown by carbonates in host limestones, marbles, and other host rocks, increasing with increasing contribution of deep metamorphic crustal volatiles. At each crustal level, the composition of the infiltrating fluids is thus buffered by deeper metamorphic sources. A negative correlation between calcite delta(13)C and fluid inclusion (3)He/(4)He is consistent with a mantle origin for a fraction of the infiltrating CO(2). Noble gas and stable isotope systematics show consistent evidence for the involvement of mantle-derived fluids combined with infiltration of deep metamorphic H(2)O and CO(2) in faulting, supporting the involvement of deep fluids percolating through and perhaps weakening the fault zone. There is no clear evidence for a significant contribution from meteoric water, except for overprinting related to late weathering. (C) 2010 Elsevier B.V. All rights reserved.
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Pinel, V. (2011). Influence of pre-existing volcanic edifice geometry on caldera formation. Geophysical Research Letters, 38.
Résumé: Volcanic edifice construction at the Earth's surface significantly modifies the stress field within the underlying crust with two main implications for caldera formation. First, tensile rupture at the Earth's surface is favored at the periphery, which enables ring fault formation. Second, edifice formation amplifies the amount of pressure decrease occurring within a magma reservoir before the eruption stops. Taking into account both of these effects, caldera formation can be initiated during a central eruption of a preexisting volcano even when assuming elastic behaviour for the surrounding crust. Providing the roof aspect ratio is small enough, conditions for caldera formation by reservoir withdrawal can be reached whatever the reservoir shape is. However ring fault initiation is easier for laterally elongated reservoirs. Citation: Pinel, V. (2011), Influence of pre-existing volcanic edifice geometry on caldera formation, Geophys. Res. Lett., 38, L11305, doi: 10.1029/2011GL047900.
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Pinel, V., Hooper, A., De la Cruz-Reyna, S., Reyes-Davila, G., Doin, M. P., & Bascou, P. (2011). The challenging retrieval of the displacement field from InSAR data for andesitic stratovolcanoes: Case study of Popocatepetl and Colima Volcano, Mexico. Journal of Volcanology and Geothermal Research, 200, 49–61.
Résumé: Despite the ability of synthetic aperture radar (SAR) interferometry to measure ground motion with high-resolution, application of this remote sensing technique to monitor andesitic stratovolcanoes remains limited. Specific acquisition conditions characterizing andesitic stratovolcanoes, mainly vegetated areas with large elevation ranges, induce low signal coherence as well as strong tropospheric artefacts that result in small signal-to-noise ratio. We propose here a way to mitigate these difficulties and improve the SAR measurements. We derive ground motions for two of the most active Mexican stratovolcanoes: Popocatepetl and Colima Volcano, from the time series of SAR data acquired from December 2002 to August 2006. The SAR data are processed using a method that combines both persistent scatterers and small baseline approaches. Stratified tropospheric delays are estimated for each interferogram using inputs from the global atmospheric model NARR, up to a maximum of 10 rad/km. These delays are validated using spectrometer data, as well as the correlation between the wrapped phase and the elevation. The tropospheric effect is removed from the wrapped phase in order to improve the unwrapping process. On Popocatepetl, we observe no significant deformation. The Colima summit area exhibits a constant subsidence rate of more than 1 cm/year centered on the summit but enhanced (reaching more than 2 cm/year) around the 1998 lava flow. We model this subsidence considering both a deflating magma source at depth and the effect of the eruptive deposits load. (C) 2010 Elsevier B.V. All rights reserved.
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Plunian, F. and L., T. and Carati, D. and Stepanov, R. (2011). Helicity scalings. In {13TH EUROPEAN TURBULENCE CONFERENCE (ETC13): STATISTICAL ASPECTS, MODELLING AND SIMULATIONS OF TURBULENCE} (Vol. 318).
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Ponty, Y., & Plunian, F. (2011). Transition from Large-Scale to Small-Scale Dynamo. Physical Review Letters, 106.
Résumé: The dynamo equations are solved numerically with a helical forcing corresponding to the Roberts flow. In the fully turbulent regime the flow behaves as a Roberts flow on long time scales, plus turbulent fluctuations at short time scales. The dynamo onset is controlled by the long time scales of the flow, in agreement with the former Karlsruhe experimental results. The dynamo mechanism is governed by a generalized alpha effect, which includes both the usual alpha effect and turbulent diffusion, plus all higher order effects. Beyond the onset we find that this generalized alpha effect scales as O(Rm(-1)), suggesting the takeover of small-scale dynamo action. This is confirmed by simulations in which dynamo occurs even if the large-scale field is artificially suppressed.
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Prieux, V., Brossier, R., Gholami, Y., Operto, S., Virieux, J., Barkved, O. I., et al. (2011). On the footprint of anisotropy on isotropic full waveform inversion: the Valhall case study. Geophysical Journal International, 187, 1495–1515.
Résumé: The validity of isotropic approximation to perform acoustic full waveform inversion (FWI) of real wide-aperture anisotropic data can be questioned due to the intrinsic kinematic inconsistency between short-and large-aperture components of the data. This inconsistency is mainly related to the differences between the vertical and horizontal velocities in vertical-transverse isotropic (VTI) media. The footprint of VTI anisotropy on 2-D acoustic isotropic FWI is illustrated on a hydrophone data set of an ocean-bottom cable that was collected over the Valhall field in the North Sea. Multiscale FWI is implemented in the frequency domain by hierarchical inversions of increasing frequencies and decreasing aperture angles. The FWI models are appraised by local comparison with well information, seismic modelling, reverse-time migration (RTM) and source-wavelet estimation. A smooth initial VTI model parameterized by the vertical velocity V(0) and the Thomsen parameters delta and epsilon were previously developed by anisotropic reflection traveltime tomography. The normal moveout (V(NMO) = V(0) root 1 + 2 delta) and horizontal (V(h) = V(0) root 1 + 2 epsilon) velocity models were inferred from the anisotropic models to perform isotropic FWI. The VNMO models allows for an accurate match of short-spread reflection traveltimes, whereas the Vh model, after updating by first-arrival traveltime tomography (FATT), allows for an accurate match of first-arrival traveltimes. Ray tracing in the velocity models shows that the first 1.5 km of the medium are sampled by both diving waves and reflections, whereas the deeper structure at the reservoir level is mainly controlled by short-spread reflections. Starting from the initial anisotropic model and keeping fixed delta and epsilon models, anisotropic FWI allows us to build a vertical velocity model that matches reasonably well the well-log velocities. Isotropic FWI is performed using either the NMO model or the FATT model as initial model. In both cases, horizontal velocities are mainly reconstructed in the first 1.5 km of the medium. This suggests that the wide-aperture components of the data have a dominant control on the velocity estimation at these depths. These high velocities in the upper structure lead to low values of velocity in the underlying gas layers (either equal or lower than vertical velocities of the well log), and/or a vertical stretching of the structure at the reservoir level below the gas. This bias in the gas velocities and the mispositioning in depth of the deep reflectors, also shown in the RTM images, are required to match the deep reflections in the isotropic approximation and highlight the footprint of anisotropy in the isotropic FWI of long-offset data. Despite the significant differences between the anisotropic and isotropic FWI models, each of these models produce a nearly-equivalent match of the data, which highlights the ill-posedness of acoustic anisotropic FWI. Hence, we conclude with the importance of considering anisotropy in FWI of wide-aperture data to avoid bias in the velocity reconstructions and mispositioning in depth of reflectors. Designing a suitable parameterization of the VTI acoustic FWI is a central issue to manage the ill-posedness of the FWI.
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Radiguet, M., Cotton, F., Vergnolle, M., Campillo, M., Valette, B., Kostoglodov, V., et al. (2011). Spatial and temporal evolution of a long term slow slip event: the 2006 Guerrero Slow Slip Event. Geophysical Journal International, 184, 816–828.
Résumé: P>The Guerrero 2006 Slow Slip Event (SSE), Mexico, one of the world's largest observed SSEs, was recorded at 15 continuous GPS stations. This event provides the opportunity to analyse in detail the spatial and temporal evolution of slip at depth, and to constrain the characteristics of a large SSE. We perform an inversion in two steps. First, we invert the cumulative GPS displacements to retrieve the total slip amplitude. Second, we invert for the initiation time and duration of the slip, using a linearized least-squares inversion procedure and assuming a functional form for the slip function. Our results show that the slip is located on a patch of 300 km x 150 km (parallel and perpendicular to the coast, respectively), and extends from the bottom of the seismogenic zone to the transition zone. This slow slip event has an equivalent moment magnitude of 7.5. The maximum slip over a length scale of 25 km is 15 cm and the mean slip is 5.5 cm. Its lateral extension coincides with the segmentation of the subduction. Our inversion scheme allows us to analyse the spatial variability of the rise time, rupture velocity and slip function. We obtain a continuous image of the spatial and temporal variations of slip on the fault plane. The rupture initiated at a depth of 40 km (transition zone), in the western part of the Guerrero gap. The rupture then propagated from the western to the eastern part of the Guerrero segment with an average velocity of 0.8 km d-1. Our results show that a slip dislocation pulse, characterized by a symmetric ramp function, can model the 2006 SSE. The rise time (local duration of slip) does not show large spatial variations and is equal to about 185 d. The local slip duration is compared to the total duration (11-12 months) of the event, suggesting a large interaction of a large part of the fault during the dynamic process. We find that our inverted slip model is well resolved on the shallow part of the fault and in the central section of the fault.
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Rakotonarivo, S. T., Walker, S. C., Kuperman, W. A., & Roux, P. (2011). Localization of a small change in a multiple scattering environment without modeling of the actual medium. Journal of the Acoustical Society of America, 130, 3566–3573.
Résumé: A method to actively localize a small perturbation in a multiple scattering medium using a collection of remote acoustic sensors is presented. The approach requires only minimal modeling and no knowledge of the scatterer distribution and properties of the scattering medium and the perturbation. The medium is ensonified before and after a perturbation is introduced. The coherent difference between the measured signals then reveals all field components that have interacted with the perturbation. A simple single scatter filter (that ignores the presence of the medium scatterers) is matched to the earliest change of the coherent difference to localize the perturbation. Using a multi-source/receiver laboratory setup in air, the technique has been successfully tested with experimental data at frequencies varying from 30 to 60 kHz (wavelength ranging from 0.5 to 1 cm) for cm-scale scatterers in a scattering medium with a size two to five times bigger than its transport mean free path. (C) 2011 Acoustical Society of America. [DOI: 10.1121/1.3652859]
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Revil, A., & Linde, N. (2011). Comment on 'Streaming potential dependence on water-content in Fontainebleau sand' by V. Allegre, L. Jouniaux, F. Lehmann and P. Sailhac. Geophysical Journal International, 186, 113–114.
Résumé: Allegre et al. recently presented new experimental data regarding the dependence of the streaming potential coupling coefficient with the saturation of the water phase. Such experiments are important to model the self-potential response associated with the flow of water in the vadose zone and the electroseismic/seismoelectric conversions in unsaturated porous media. However, the approach used to interpret the data is questionable and the conclusions reached by Allegre et al. likely incorrect
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Revil, A., & Skold, M. (2011). Salinity dependence of spectral induced polarization in sands and sandstones. Geophysical Journal International, 187, 813–824.
Résumé: In electrolyte-saturated sands, the reversible storage of electrical charges is responsible for a phase lag between the current (injected and retrieved by two current electrodes) and the electrical field recorded by two voltage electrodes. This phenomenon is called 'spectral induced polarization' in geophysics and can potentially be used to monitor salt tracer tests in shallow aquifers to infer their permeability and dispersivity tensors. We demonstrate analytically that the polarization of the inner part of the electrical triple layer coating the surface of the grains (named the Stern layer in electrochemistry) is consistent with available data. We also perform new experiments using silica sands saturated by NaCl and CaCl(2) pore water solutions. The salinity dependence of quadrature conductivity can be modelled using an analytical solution of the triple layer model, which offers a simple way to interpret laboratory and field data. This analytical solution depends on the total site density of the mineral surface, the pH value and the sorption coefficient of the cation in the Stern layer. This model shows that both the specific surface conductivity of the Stern layer and the quadrature conductivity of the porous material depend on the conductivity of the pore water. The quadrature conductivity is becoming independent of the salinity above 1 S m(-1). The parameters entering the analytical model are consistent with independent estimates from titration data and zeta potential measurements, which are two classical methods to characterize the electrical triple layer at the pore water mineral interface.
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Revil, A., Finizola, A., Ricci, T., Delcher, E., Peltier, A., Barde-Cabusson, S., et al. (2011). Hydrogeology of Stromboli volcano, Aeolian Islands (Italy) from the interpretation of resistivity tomograms, self-potential, soil temperature and soil CO(2) concentration measurements. Geophysical Journal International, 186, 1078–1094.
Résumé: To gain a better insight of the hydrogeology and the location of the main tectonic faults of Stromboli volcano in Italy, we collected electrical resistivity measurements, soil CO(2) concentrations, temperature and self-potential measurements along two profiles. These two profiles started at the village of Ginostra in the southwest part of the island. The first profile (4.8 km in length) ended up at the village of Scari in the north east part of the volcano and the second one (3.5 km in length) at Forgia Vecchia beach, in the eastern part of the island. These data were used to provide insights regarding the position of shallow aquifers and the extension of the hydrothermal system. This large-scale study is complemented by two high-resolution studies, one at the Pizzo area (near the active vents) and one at Rina Grande where flank collapse areas can be observed. The Pizzo corresponds to one of the main degassing structure of the hydrothermal system. The main degassing area is localized along a higher permeability area corresponding to the head of the gliding plane of the Rina Grande sector collapse. We found that the self-potential data reveal the position of an aquifer above the villages of Scari and San Vincenzo. We provide an estimate of the depth of this aquifer from these data. The lateral extension of the hydrothermal system (resistivity similar to 15-60 ohm m) is broader than anticipated extending in the direction of the villages of Scari and San Vincenzo (in agreement with temperature data recorded in shallow wells). The lateral extension of the hydrothermal system reaches the lower third of the Rina Grande sector collapse area in the eastern part of the island. The hydrothermal body in this area is blocked by an old collapse boundary. This position of the hydrothermal body is consistent with low values of the magnetization (<2.5 A m(-1)) from previously published work. The presence of the hydrothermal body below Rina Grande raises questions about the mechanical stability of this flank of the edifice.
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Revil, A., Schmutz, M., & Batzle, M. L. (2011). Influence of oil wettability upon spectral induced polarization of oil-bearing sands. Geophysics, 76, A31–A36.
Résumé: The presence of oil in an unconsolidated granular porous material, like a sand, changes both the resistivity of the material and the value of the phase lag between the current and the voltage. We performed laboratory experiments to investigate the influence of oil wettability and water saturation upon the complex resistivity of oil-bearing sands in the frequency range 1 mHz-1 kHz. For a sand saturated by a nonwetting oil, both the resistivity and the magnitude of the phase increase with the oil saturation, as expected from theoretical considerations. In the case of a sand partially saturated by a wetting oil, we found that both the magnitude of the phase and the resistivity decrease with the oil saturation. The quadrature conductivity decreases with the oil with the same trend in presence of wetting and nonwetting oils for relative water saturation above 0.5. In the case of a nonwetting oil, the results are quantitatively predicted by available theories. In the case of a wet oil, our results could be interpreted as resulting from the increase of the cation exchange capacity associated with the presence of a polar component at the oil water interface.
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Revil, A., Woodruff, W. F., & Lu, N. (2011). Constitutive equations for coupled flows in clay materials. Water Resources Research, 47.
Résumé: We first upscale the local transport (Stokes and Nernst-Planck) equations to the scale of a single capillary saturated by a binary 1: 1 electrolyte. These equations are then upscaled to the scale of a network of tortuous capillaries embedded in a homogeneous and continuous mineral matrix, including the influence of the distribution of pore sizes but excluding the effect of connectivity between the pores. One of the features of our theory is to account for transport along the mineral surface in the so-called Stern layer because of recent evidence that this mechanism is effective in describing frequency-dependent electrical conductivity. Real clay materials are, however, not described by a set of capillaries, so we have to modify the model to include the effect of transversal dispersivity, for example. We found no evidence for transport in the Stern layer because of the discontinuity of the solid phase at the scale of a representative elementary volume in clay materials. The effect of the diffuse layer is accounted for through the use of a Donnan equilibrium approach to determine the effective concentrations of the ions in the pore space, which are different from the ionic concentrations of an ionic reservoir in local equilibrium with the porous material. We found that the diffuse layer controls various transport properties, including, for example, the DC electrical conductivity, the osmotic efficiency coefficient, the streaming potential coupling coefficient, and the macroscopic Hittorf numbers. Comparison to a large data set of experimental data, mainly on clay materials, confirms the validity of the derived relationships used to describe the material properties entering into the constitutive equations.
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Ribodetti, A., Operto, S., Agudelo, W., Collot, J. Y., & Virieux, J. (2011). Joint ray plus Born least-squares migration and simulated annealing optimization for target-oriented quantitative seismic imaging. Geophysics, 76, R23–R42.
Résumé: A seismic processing workflow based on iterative ray + Born migration/inversion and target-oriented postprocessing of the migrated image is developed for fine-scale quantitative characterization of reflectors. The first step of the workflow involves linear iterations of the ray + Born migration/inversion. The output of the first step is a true-amplitude migrated image parameterized by velocity perturbations. In a second step, postprocessing of the migrated image is performed through a random search with a very-fast simulated annealing (VFSA) algorithm. The forward problem of the global optimization is a simple convolutional model that linearly relates a vertical profile of the band-limited migrated image after depth-to-time conversion to a 1D velocity model composed of a stack of homogeneous layers of arbitrary velocity and thickness. The aim of the postprocessing is to eliminate the limited bandwidth effects of the source from the migrated image for resolution improvement and enhanced geological interpretation of selected targets. The global optimization approach allows for uncertainty analysis required by the intrinsic nonuniqueness of the velocity model output by the postprocessing. The relevance of the convolutional model when applied to the output of the ray + Born migrated inversion is first illustrated with a one-layer model. The accuracy and the robustness of the workflow to image geologically complicated models are then illustrated with an application to the synthetic Marmousi model. Some practical issues (e. g., the source wavelet estimate and the scaling of the migrated image required by the VFSA optimization) are discussed with an application to a 2D real seismic multichannel reflection data set collected in the Gulf of Guayaquil (Ecuador). The postprocessing is applied to derive the fine-scale velocity structure of a decollement zone on top of the subduction channel. The postprocessing allows for mapping structural variations along different segments of the decollement, which can be associated with changes in fluid content and porosity.
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Rinaldi, A. P., Todesco, M., Vandemeulebrouck, J., Revil, A., & Bonafede, M. (2011). Electrical conductivity, ground displacement, gravity changes, and gas flow at Solfatara crater (Campi Flegrei caldera, Italy): Results from numerical modeling. Journal of Volcanology and Geothermal Research, 207, 93–105.
Résumé: Hydrothermal fluid circulation may cause measurable gravity changes and ground deformation. We extend our previous studies and increase the number of observable parameters to include gas temperature, the rate of diffuse degassing, the extent of the degassing area, and electrical conductivity. We have carried out simulations using TOUGH2/EOS2 of a large scale hydrothermal system, then we have calculated observables arising from changes in hydrothermal fluid circulation. Our results show that fluids affect many observable parameters generating detectable signals. However, a more detailed description of the shallow subsurface is necessary to properly calculate electrical conductivity. Studies at Solfatara volcano (Campi Flegrei caldera, Italy) highlight the presence of an unsaturated layer at depth and allow to determine the position of the water table. Then, we present results from a new, small scale simulation, focused on the crater, and carried out with a new, refined meshgrid taking into account the real topography. Aim of the work is to calculate a detailed electrical conductivity map and reproduce the main features of the Solfatara crater. (C) 2011 Elsevier B.V. All rights reserved.
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Rivet, D., Campillo, M., Shapiro, N. M., Cruz-Atienza, V., Radiguet, M., Cotte, N., et al. (2011). Seismic evidence of nonlinear crustal deformation during a large slow slip event in Mexico. Geophysical Research Letters, 38.
Résumé: Repeated cross-correlations of ambient seismic noise indicate a long-term seismic velocity change associated with the 2006 M7.5 slow-slip event (SSE) in the Guerrero region, Mexico. Because the SSE does not radiate seismic waves, the measured velocity change cannot be associated with the response of superficial soil layers to strong shaking as observed for regular earthquakes. The perturbation observed maximized at periods between 7 s and 17 s, which correspond to surface waves with sensitivity to the upper and middle crust. The amplitude of the relative velocity change (similar to 10(-3)) was much larger than the volumetric deformation (similar to 10(-6)) at the depths probed (similar to 5-20 km). Moreover, the time dependence of the velocity perturbation indicated that it was related to the strain rate rather than the strain itself. This suggests that during strong slow-slip events, the deformation of the overlying crust shows significant nonlinear elastic behavior. Citation: Rivet, D., M. Campillo, N. M. Shapiro, V. Cruz-Atienza, M. Radiguet, N. Cotte, and V. Kostoglodov (2011), Seismic evidence of nonlinear crustal deformation during a large slow slip event in Mexico, Geophys. Res. Lett., 38, L08308, doi:10.1029/2011GL047151.
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Rizza, M., Ritz, J. F., Braucher, R., Vassallo, R., Prentice, C., Mahan, S., et al. (2011). Slip rate and slip magnitudes of past earthquakes along the Bogd left-lateral strike-slip fault (Mongolia). Geophysical Journal International, 186, 897–927.
Résumé: We carried out morphotectonic studies along the left-lateral strike-slip Bogd Fault, the principal structure involved in the Gobi-Altay earthquake of 1957 December 4 (published magnitudes range from 7.8 to 8.3). The Bogd Fault is 260 km long and can be subdivided into five main geometric segments, based on variation in strike direction. West to East these segments are, respectively: the West Ih Bogd (WIB), The North Ih Bogd (NIB), the West Ih Bogd (WIB), the West Baga Bogd (WBB) and the East Baga Bogd (EBB) segments. Morphological analysis of offset streams, ridges and alluvial fans-particularly well preserved in the arid environment of the Gobi region-allows evaluation of late Quaternary slip rates along the different faults segments. In this paper, we measure slip rates over the past 200 ka at four sites distributed across the three western segments of the Bogd Fault. Our results show that the left-lateral slip rate is similar to 1 mm yr(-1) along the WIB and EIB segments and similar to 0.5 mm yr(-1) along the NIB segment. These variations are consistent with the restraining bend geometry of the Bogd Fault. Our study also provides additional estimates of the horizontal offset associated with the 1957 earthquake along the western part of the Bogd rupture, complementing previously published studies. We show that the mean horizontal offset associated with the 1957 earthquake decreases progressively from 5.2 m in the west to 2.0 m in the east, reflecting the progressive change of kinematic style from pure left-lateral strike-slip faulting to left-lateral-reverse faulting. Along the three western segments, we measure cumulative displacements that are multiples of the 1957 coseismic offset, which may be consistent with a characteristic slip. Moreover, using these data, we re-estimate the moment magnitude of the Gobi-Altay earthquake at M(w) 7.78-7.95. Combining our slip rate estimates and the slip distribution per event we also determined a mean recurrence interval of similar to 2500-5200 yr for past earthquakes along the different segments of the western Bogd Fault. This suggests that the three western segments of the Bogd Fault and the Gurvan Bulag thrust fault (a reverse fault bounding the southern side of the Ih Bogd range that ruptured during the 1957 earthquake) have similar average recurrence times, and therefore may have ruptured together in previous earthquakes as they did in 1957. These results suggest that the western part of the Bogd Fault system, including the Gurvan Bulag thrust fault, usually behaves in a 'characteristic earthquake' mode.
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Robert, X., van der Beek, P., Braun, J., Perry, C., & Mugnier, J. - L. (2011). Control of detachment geometry on lateral variations in exhumation rates in the Himalaya: Insights from low-temperature thermochronology and numerical modeling. Journal of Geophysical Research-Solid Earth, 116.
Résumé: The Himalayan range is commonly presented as largely laterally uniform from west to east. However, geological structures, topography, precipitation rate, convergence rates, and low-temperature thermochronological ages all vary significantly along strike. Here, we focus on the interpretation of thermochronological data sets in terms of along-strike variations in geometry and kinematics of the main crustal detachment underlying the Himalaya: the Main Himalayan Thrust (MHT). We report new apatite fission track (AFT) ages collected along north-south transects in western and eastern central Nepal (at the latitudes of the Annapurna and Langtang massifs, respectively). AFT ages are consistently young (<3 Ma) along both N-S transects in the high-relief zone of the Higher Himalaya and increase (4 to 6 Ma) toward the south in the Lesser Himalaya. We compare our new data to published low-temperature thermochronological data sets for Nepal and the Bhutan Himalaya. We use the full data set to perform both forward and inverse thermal kinematic modeling with a modified version of the Pecube code in order to constrain potential along-strike variations in the kinematics of the Himalayan range. Our results show that lateral variations in the geometry of the MHT (in particular the presence or absence of a major crustal-scale ramp) strongly control the kinematics and exhumation history of the orogen.
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Roddaz, M., Said, A., Guillot, S., Antoine, P. - O., Montel, J. - M., Martin, F., et al. (2011). Provenance of Cenozoic sedimentary rocks from the Sulaiman fold and thrust belt, Pakistan: implications for the palaeogeography of the Indus drainage system. Journal of the Geological Society, 168, 499–516.
Résumé: The provenance of middle Eocene to early Miocene sedimentary rocks cropping out in the Sulaiman fold and thrust belt has been determined examining the mineralogy, bulk-rock major and trace elements, and Nd-Sr isotopes. The older (50-30 Ma) deposits are characterized by a mixed orogenic provenance with a major contribution from the Karakorum and the Tethyan belt (c. 80%). As the 50-30 Ma deposits have a provenance distinct from that of coeval Subathu, Khojak and Ghazij shallow marine formations of India and Pakistan, we propose that they were deposited as a distinct delta system that once fed the Palaeo-Indus fan. We document a major change in provenance that occurred before the early-late Oligocene transition at c. 30 Ma. This change in provenance is marked by the appearance of chlorite and monazite and a shift toward more radiogenic Nd-Sr isotopic compositions. We interpret this change as the result of the exhumation and erosion of the proto-Higher Himalaya. The 30-15 Ma sampled rocks are characterized by a major contribution from the Tethyan belt and the Higher Himalayan Crystallines (70-90%) and a subordinate contribution (10-30%) from the Karakorum, Ophiolitic Suture and Trans-Himalaya. As the epsilon Nd(0) values of our 30-15 Ma samples are similar to those of the Palaeo-Indus fan deposits, we suggest that the 30-15 Ma sedimentary rocks of the Sulaiman fold and thrust belt were the fluvial onshore record of the Indus fan. Other coeval deposits of India and Pakistan recorded similar increasing exhumation of the Higher Himalaya range, so that we postulate that these sedimentary rocks all derived from the Palaeo-Indus drainage basin. This would suggest that the modern Indus drainage basin is no younger than 30 Ma.
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Rodriguez-Marek, A., Montalva, G. A., Cotton, F., & Bonilla, F. (2011). Analysis of Single-Station Standard Deviation Using the KiK-net Data. Bulletin of the Seismological Society of America, 101, 1242–1258.
Résumé: Estimates of single-station standard deviation can be used as a lower bound to probabilistic seismic hazard analyses that remove the ergodic assumption on site response. This paper presents estimates of single-station standard deviation using data from the KiK-net network. The KiK-net network has a dense array of stations that recorded a large number of earthquakes over the period of study, both at the surface and at colocated borehole instruments. The large number of records implies that there are a large number of stations with recordings from multiple events; hence, site terms and single-station standard deviations can be properly estimated. Borehole instruments permit a breakdown of residuals, considering the effect of amplification in the shallow surface layers. Random-effects regression was first used to develop a ground-motion prediction equation (GMPE) using both the surface and borehole data. The GMPE was constrained such that event terms were the same at the surface and borehole. Residuals were then computed and the within-event (intraevent) residuals were separated into a repeatable site-term and a remaining residual, for both the ground motion itself and for the empirical amplification factor between surface and borehole. Results show that single-station standard deviations are considerably lower than standard deviations using the ergodic assumption, and these standard deviations are further reduced if only a small bracket of station-to-event azimuths is considered for each station such that path variability is minimized. Moreover, analyses of residuals indicate that most of the differences between ergodic standard deviations of surface and borehole data are the results of a poor parametrization of shallow site effects. However, the contribution of site-to-site variability in the empirical amplification factor is only limited. Finally, a comparison with results from other studies at different tectonic regions indicates that the values of single-station standard deviations are strikingly similar for all studies.
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Romdhane, A., Grandjean, G., Brossier, R., Rejiba, F., Operto, S., & Virieux, J. (2011). Shallow-structure characterization by 2D elastic full-waveform inversion. Geophysics, 76, R81–R93.
Résumé: Assessing the effectiveness of elastic full-waveform-inversion (FWI) algorithms when applied to shallow 2D structures in the presence of a complex topography is critically important. By using FWI, we overcome inherent limitations of conventional seismic methods used for near-surface prospecting (acoustic tomography and multichannel spectral analysis of surface waves). The elastic forward problem, formulated in the frequency domain, is based on a mixed finite-element P0-P1 discontinuous Galerkin method to ensure accurate modeling of complex topography effects at a reasonable computing cost. The inversion problem uses an FWI algorithm to minimize the misfit between observed and calculated data. Based on results from a numerical experiment performed on a realistic landslide model inspired from the morphostructure of the Super-Sauze earthflow, we analyzed the effect of using a hierarchical preconditioning strategy, based on a simultaneous multifrequency inversion of damped data, to mitigate the strong nonlinearities coming from the surface waves. This strategy is a key point in alleviating the strong near-surface effects and avoiding convergence toward a local minimum. Using a limited-memory quasi-Newton method improved the convergence level. These findings are analogous to recent applications on large-scale domains, although limited source-receiver offset ranges, low-frequency content of the source, and domination of surface waves on the signal led to some difficulties. Regarding the impact of data decimation on the inversion results, we have learned that an inversion restricted to the vertical data component can be successful without significant loss in terms of parameter imagery resolution. In our investigations of the effect of increased source spacing, we found that a sampling of 4 m (less than three times the theoretical maximum of one half-wavelength) led to severe aliasing.
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Rossetto, V., Margerin, L., Planes, T., & Larose, E. (2011). Locating a weak change using diffuse waves: Theoretical approach and inversion procedure. Journal of Applied Physics, 109.
Résumé: We describe a time-resolved monitoring technique for heterogeneous media. Our approach is based on the spatial variations of the cross-coherence of diffuse waves acquired at fixed positions but at different dates. The technique applies to all kind of waves, provided that waveforms can be acquired with a sampling frequency much larger than the wave frequency. To locate and characterize a weak change that occurred between successive acquisitions, we use a maximum likelihood approach combined with a diffusive propagation model. We characterize this technique, locating a weak change using diffuse waves, called LOCADIFF, with the aid of numerical simulations. In several illustrative examples, we show that the change can be located with a precision of a few wavelengths and that its effective scattering cross-section can be retrieved. We investigate how the accuracy and precision of the method depends on the number of source-receiver pairs, on the time window used to compute the cross-correlation and on the errors in the propagation model. Applications can be found in nondestructive testing, seismology, radar, and sonar location. (C) 2011 American Institute of Physics. [doi:10.1063/1.3544503]
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Roux, P., Iturbe, I., Nicolas, B., Virieux, J., & Mars, J. I. (2011). Travel-time tomography in shallow water: Experimental demonstration at an ultrasonic scale. Journal of the Acoustical Society of America, 130, 1232–1241.
Résumé: Acoustic tomography in a shallow ultrasonic waveguide is demonstrated at the laboratory scale between two source-receiver arrays. At a 1/1 000 scale, the waveguide represents a 1.1-km-long, 52-m-deep ocean acoustic channel in the kilohertz frequency range. Two coplanar arrays record the transfer matrix in the time domain of the waveguide between each pair of source-receiver transducers. A time-domain, double-beamforming algorithm is simultaneously performed on the source and receiver arrays that projects the multi-reflected acoustic echoes into an equivalent set of eigenrays, which are characterized by their travel times and their launch and arrival angles. Travel-time differences are measured for each eigenray every 0.1 s when a thermal plume is generated at a given location in the waveguide. Travel-time tomography inversion is then performed using two forward models based either on ray theory or on the diffraction-based sensitivity kernel. The spatially resolved range and depth inversion data confirm the feasibility of acoustic tomography in shallow water. Comparisons are made between inversion results at 1 and 3 MHz with the inversion procedure using ray theory or the finite-frequency approach. The influence of surface fluctuations at the air-water interface is shown and discussed in the framework of shallow-water ocean tomography. (C) 2011 Acoustical Society of America. [DOI: 10.1121/1.3621271]
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Roux, P., Kuperman, W. A., & Sabra, K. G. (2011). Ocean acoustic noise and passive coherent array processing. Comptes Rendus Geoscience, 343, 533–547.
Résumé: Broadband correlation processing for extracting time-domain Green's functions and coherent wavefronts from random ocean noise has been demonstrated recently using experiments and numerical simulations that are consistent with theoretical predictions. Ocean acoustic noise processing presents additional challenges over its seismological counterpart. Mainly, the ocean environment is temporally non-stationary and it is spatially heterogeneous. Further, in the lower underwater acoustic frequency regime of about 20 to 500 Hz, space-time episodic shipping is the dominant noise source. The data from different publications and research groups are gathered here, with the goal being to review recent underwater acoustic research that demonstrates the viability and potential applications of passive coherent array processing in the ocean. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
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Roux, P., Marandet, C., La Rizza, P., & Kuperman, W. A. (2011). Application of acoustic feedback to target detection in a waveguide: Experimental demonstration at the ultrasonic scale. Journal of the Acoustical Society of America, 130, 13–19.
Résumé: People are familiar with the acoustic feedback phenomenon, which results in a loud sound that is heard when a musician plays an electric instrument directly into a speaker. Acoustic feedback occurs when a source and a receiver are connected both acoustically through the propagation medium and electrically through an amplifier, such that the amplified received signal is continuously re-emitted by the source. The acoustic feedback can be initiated from a continuous sine wave. When the emitter and the receiver are in phase, resonance is obtained, which appears to be highly sensitive to any fluctuation of the propagation medium. Another procedure consists in initiating the acoustic feedback from a continuous loop of ambient noise. It then generates an unstable self-sustained feedback oscillator (SFO) that is tested here as a method for monitoring temperature fluctuations of a shallow-water oceanic environment. The goal of the present study is to reproduce and study the SFO at the laboratory scale in an ultrasonic waveguide. The experimental results demonstrate the potential applications of the SFO for the detection of a target in the framework of the acoustic-barrier problem in shallow-water acoustics. (C) 2011 Acoustical Society of America. [DOI: 10.1121/1.3593365]
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Roux, P., Wathelet, M., & Roueff, A. (2011). The San Andreas Fault revisited through seismic-noise and surface-wave tomography. Geophysical Research Letters, 38.
Résumé: We present here surface-wave tomography results for the San Andreas Fault in the Parkfield area, California, USA, that were extracted from microseismic noise in the 0.15 Hz to 0.35 Hz frequency band using passive seismic-correlation techniques. Using directive noise incoming from the Pacific Ocean, passive seismic-noise tomography was performed using three-component sensors from a dense seismic network. A rotation algorithm was applied to the nine-component noise-correlation tensor that optimally forced each station pair to re-align in the noise direction, a necessary condition to extract unbiased travel-times from passive seismic processing. After the rotation was performed, an optimal surface-wave tensor is obtained from which Love waves were extracted for tomography inversion. Dispersion curves were then inverted to obtain a three-dimensional shear-velocity map showing vertical geological structures and a 1.3-km wide low seismic velocity dip, which are in agreement with previous tomography studies in the same area. Citation: Roux, P., M. Wathelet, and A. Roueff (2011), The San Andreas Fault revisited through seismic-noise and surface-wave tomography, Geophys. Res. Lett., 38, L13319, doi:10.1029/2011GL047811.
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Saillard, M., Hall, S. R., Audin, L., Farber, D. L., Regard, V., & Herail, G. (2011). Andean coastal uplift and active tectonics in southern Peru: (10)Be surface exposure dating of differentially uplifted marine terrace sequences (San Juan de Marcona, similar to 15.4 degrees S). Geomorphology, 128, 178–190.
Résumé: Along the San Juan de Marcona Bay of southern Peru, two spectacular sequences of preserved marine terraces record net Quaternary uplift. Previous geomorphic analysis of these paleo-shorelines has revealed evidence of upper plate deformation and regional uplift. However, in the absence of a robust absolute dating method, these studies contain substantial uncertainties concerning the numerical dating of these marine markers and thus the corresponding calculated surface uplift rates. However, field mapping, surveying the neotectonic features and (10)Be dating of abraded surfaces contained within two sequences of marine terraces along this margin should allow for the robust calculation of Pleistocene uplift rates. The San Juan de Marcona Bay lies on the southern flank of the subducting and south-migrating aseismic Nazca Ridge where the maximum rates of coastal uplift are expected. In this locality, we measure high uplift rates ranging from 0.4 m/ka to 0.9 m/ka during the Pleistocene. Margin-parallel normal faults displace several marine terraces and influence the development of bays, thereby contributing to the configuration of paleo-and present-day coastlines. The faults have relatively low slip rates, <0.1 m/ka over 400 ka, and have been inactive for the last 80 ka. The presence and activity of these normal faults can be directly linked to subduction zone processes, with the release and accommodation of short-term coseismic compression during megathrust subduction-zone events. In contrast, the regional permanent uplift is probably controlled by post-seismic and/or interseismic strain accumulation over longer time-scales due to inelastic behavior of the upper plate. Since at least the latest Pliocene, the San Juan de Marcona area has experienced long-term regional tectonic uplift that has increased since about 800 ka due to the southward migration of the subducting Nazca Ridge. Based on migration velocity and geometry of the ridge, the influence of the Nazca Ridge on the uplift of the forearc should account for similar to 0.4 m/ka within 145 km south of the ridge axis. Hence, most of the post-400 ka mean uplift rate of the San Juan de Marcona area could be explained by the Nazca Ridge subduction. (C) 2011 Elsevier B.V. All rights reserved.
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Sanchez-Sesma, F. J., Rodriguez, M., Iturraran-Viveros, U., Luzon, F., Campillo, M., Margerin, L., et al. (2011). A theory for microtremor H/V spectral ratio: application for a layered medium. Geophysical Journal International, 186, 221–225.
Résumé: Microtremors are produced by multiple random sources close to the surface of the Earth. They may include the effects of multiple scattering, which suggests that their intensities could be well described by diffusion-like equations. Within this theoretical framework, the average autocorrelation of the motions at a given receiver, in the frequency domain, measures average energy density and is proportional to the imaginary part of the Green's function (GF) when both source and receiver are the same. Assuming the seismic field is diffuse we compute the H/V ratio for a surface receiver on a horizontally layered medium in terms of the imaginary part of the GF at the source. This theory links average energy densities with the GF in 3-D and considers the H/V ratio as an intrinsic property of the medium. Therefore, our approach naturally allows for the inversion of H/V, the well-known Nakamura's ratio including the contributions of Rayleigh, Love and body waves. Broad-band noise records at Texcoco, a soft soil site near Mexico City, are studied and interpreted using this theory.
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Sanchez-Sesma, F. J., Weaver, R. L., Kawase, H., Matsushima, S., Luzon, F., & Campillo, M. (2011). Energy Partitions among Elastic Waves for Dynamic Surface Loads in a Semi-Infinite Solid. Bulletin of the Seismological Society of America, 101, 1704–1709.
Résumé: We examine the energy partitions among elastic waves due to dynamic normal and tangential surface loads in a semi-infinite elastic solid. While the results for a dynamic normal load on the surface of a half-space with Poisson ratio of 1/4 is a well-known result by Miller and Pursey (1955), the corresponding results for a dynamic tangential load are almost unknown. The partitions for the normal and tangential loads were computed independently by Weaver (1985) versus Poisson ratio (0 <= v <= 1/2), using diffuse-field concepts within the context of ultrasonic measurements. The connection with the surface load point was not explicit, which partially explains why these results did not reach the seismological and engineering literature. The characteristics of the elastic radiation of these two cases are quite different. For a normal load, about 2/3 of the energy leaves the loaded point as Rayleigh surface waves. On the other hand, the tangential load induces a similar amount in the form of body shear waves. It is established that the energies injected into the elastic half-space by concentrated normal and tangential harmonic surface loads are proportional to the imaginary part of the corresponding components of the Green's tensor when both source and receiver coincide. The relationship between the Green's function and average correlations of motions within a diffuse field is clearly established.
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Schaeffer, N., & Pais, M. A. (2011). On symmetry and anisotropy of Earth-core flows. Geophysical Research Letters, 38.
Résumé: Quasi-geostrophic (QG) flows are a recently developed and very promising paradigm for modeling decadal secular variation (SV). Here we examine the effects of allowing anisotropy and departures of the flow from quasigeostrophy. We perform dedicated numerical experiments of the flow dynamics and magnetic induction inside the Earth's liquid core at time scales characteristic of secular variation of the geomagnetic field. Obtained results motivate new flow inversion regularization featuring an equatorially anti-symmetric component superimposed to quasi-geostrophic columns, and stronger latitudinal than longitudinal flow gradients. Applying these constraints allows to explain the observed SV for the whole period 1840-2010, and most significantly, provides a clearly improvement in prediction for decadal length-of-day variations for the period 1980-2000. Furthermore, the trace of the inner-core appears clearly without any assumption for the 1997-2010 period covered by satellite geomagnetic data. Our results support QG being the appropriate description of the force balance within the core on decadal time scales and large spatial scales. Citation: Schaeffer, N., and M. A. Pais (2011), On symmetry and anisotropy of Earth-core flows, Geophys. Res. Lett., 38, L10309, doi:10.1029/2011GL046888.
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Schlagenhauf, A., Manighetti, I., Benedetti, L., Gaudemer, Y., Finkel, R., Malavieille, J., et al. (2011). Earthquake supercycles in Central Italy, inferred from (36)Cl exposure dating. Earth and Planetary Science Letters, 307, 487–500.
Résumé: We use (36)Cl surface exposure dating to determine the slip release pattern over the last similar to 15 kyr for the Velino-Magnola fault, a major active normal fault in Central Italy. We sampled the fault at five well-separated sites along its length, and modeled the (36)Cl concentrations measured in the 376 samples. We find that the fault broke in at least 9 large earthquakes that occurred in two 5-6 ka-long supercycles. Each cycle included a 4-5 ka-long phase of relative quiescence, followed by a cluster of at least 3 large earthquakes or earthquake sequences that released most of the accumulated strain in similar to 1 ka. All 9 identified events broke the entire fault and produced maximum surface slips of 2-3 m. Though the Velino-Magnola fault seems presently in a stage of relative quiescence, it may re-enter a phase of paroxysmal seismic activity in a few hundred of years. (C) 2011 Elsevier B.V. All rights reserved.
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Schmutz, M., Ghorbani, A., Vaudelet, P., & Revil, A. (2011). Spectral Induced Polarization Detects Cracks and Distinguishes between Open- and Clay-filled Fractures. Journal of Environmental and Engineering Geophysics, 16, 85–91.
Résumé: Spectral induced polarisation (SIP) is applied to the detection and localization of fractures located in the roof of an abandoned quarry at Saint-Germain-la-Riviere (Gironde, southwest France). Two types of fracture are observed in the roof of the galleries: open (mostly clay-free) and clay-filled. The phase between current and voltage is used to detect the presence of these fractures and can differentiate those with or without clays. The amplitude and phase of complex conductivity can be analysed using a Cole-Cole model of relaxation times. Open fractures are characterized by very low chargeability and a high relaxation time in the order of 3 ms. Clay-filled fractures are characterized by high chargeability and a low relaxation time.
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Simionovici, A., Allen, C., Bajt, S., Bastien, R., Bechtel, H., Borg, J., et al. (2011). SYNCHROTRON X-RAY IRRADIATION OF Stardust INTERSTELLAR CANDIDATES: FROM “NO” TO “LOW” DAMAGE EFFECTS. Meteoritics & Planetary Science, 46, A213.
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Skold, M., Revil, A., & Vaudelet, P. (2011). The pH dependence of spectral induced polarization of silica sands: Experiment and modeling. Geophysical Research Letters, 38.
Résumé: In electrolyte-saturated sands, the storage of electrical charges under an alternating electrical field (called “induced polarization”) is responsible for a phase lag between the applied current and the resulting electrical field. Because a variety of polarization mechanisms exists in porous materials, the underlying physics of induced polarization is somehow unclear and the field data difficult to interpret quantitatively. Measurements at various pHs and salinities can be used to discriminate between different competing mechanisms at low frequencies (1 mHz-1 kHz) in porous media in the absence of electronic conductors. New experimental data point out that, in addition to the polarization of the Stern layer (the inner part of the electrical double layer coating the surface of the silica grains), there is another polarization mechanism possibly associated with a hopping process of the protons on the silica surface. We propose that such a process could follow a Grotthuss cooperation mechanism (as in ice) involving the bound water of the silica surface. Our data also rule out a mechanism based on the diffuse layer. The new polarization mechanism may be applied to quantifying induced-polarization data collected over acidic contaminant plumes. Citation: Skold, M., A. Revil, and P. Vaudelet (2011), The pH dependence of spectral induced polarization of silica sands: Experiment and modeling, Geophys. Res. Lett., 38, L12304, doi:10.1029/2011GL047748.
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Sobolev, A. V., Hofmann, A. W., Jochum, K. P., Kuzmin, D. V., & Stoll, B. (2011). A young source for the Hawaiian plume. Nature, 476, 434–483.
Résumé: Recycling of oceanic crust through subduction, mantle upwelling, and remelting in mantle plumes is a widely accepted mechanism to explain ocean island volcanism(1). The timescale of this recycling is important to our understanding of mantle circulation rates. Correlations of uranogenic lead isotopes in lavas from ocean islands such as Hawaii or Iceland, when interpreted as model isochrons, have yielded source differentiation ages between 1 and 2.5 billion years (Gyr)(2-5). However, if such correlations are produced by mixing of unrelated mantle components(6) they will have no direct age significance. Re-Os decay model ages take into account the mixing of sources with different histories(7,8), but they depend on the assumed initial Re/Os ratio of the subducted crust, which is poorly constrained because of the high mobility of rhenium during subduction(9). Here we report the first data on (87)Sr/(86)Sr ratios for 138 melt inclusions in olivine phenocrysts from lavas of Mauna Loa shield volcano, Hawaii, indicating enormous mantle source heterogeneity. We show that highly radiogenic strontium in severely rubidium-depleted melt inclusions matches the isotopic composition of 200-650-Myr-old sea water. We infer that such sea water must have contaminated the Mauna Loa source rock, before subduction, imparting a unique 'time stamp' on this source. Small amounts of seawater-derived strontium in plume sources may be common but can be identified clearly only in ultra-depleted melts originating from generally highly (incompatible-element) depleted source components. The presence of 200-650-Myr-old oceanic crust in the source of Hawaiian lavas implies a timescale of general mantle circulation with an average rate of about 2 (+/- 1) cm yr(-1), much faster than previously thought. [GRAPHICS] .
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Sobolev, O., Cuello, G. J., Scheinost, A. C., Johnson, M. R., Nikitenko, S., Le Forestier, L., et al. (2011). The short-range order of ions in clay minerals: Sm(3+) coordination. Physica Status Solidi a-Applications and Materials Science, 208, 2293–2298.
Résumé: Experimental techniques as neutron diffraction (ND) with isotopic substitution (NDIS), extended X-ray absorption fine structure spectroscopy (EXAFS), and quasielastic neutron scattering (QENS), in combination with molecular dynamics (MD) simulations, are usually applied to the study of non-crystalline solids, but they are also very useful for the study of complex systems, where the short range order provides an insight of its structure and dynamics. Here, they are used in the study of the coordination of the Sm(3+) in the interlayer of hydrated synthetic montmorillonite and hectorite. The ND results indicate that not all oxygen atoms in the first coordination shell of the Sm(3+) belong to water molecules, supporting the formation of the Sm(3+) inner-sphere complex. On the other hand, the other techniques suggest that the adsorbed Sm(3+) cations form outer-sphere complexes with the clay surface. The hypothesis making compatible all results is that there are different Sm species adsorbed in the clay interlayer: a part of Sm is in the Sm(3+) cationic form, forming outer-sphere adsorption complexes, another part is hydrolyzed and present in the interlayer space as Sm(OH)(2+), Smd(OH)(2)(+), or Smd(OH)(3)(0) species. The latter are more hydrophobic than Sm(3+) cations and can be dehydrated and are able to stick to the clay surface. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Sobolev, S. V., Sobolev, A. V., Kuzmin, D. V., Krivolutskaya, N. A., Petrunin, A. G., Arndt, N. T., et al. (2011). Linking mantle plumes, large igneous provinces and environmental catastrophes. Nature, 477, 312–380.
Résumé: Large igneous provinces (LIPs) are known for their rapid production of enormous volumes of magma (up to several million cubic kilometres in less than a million years)(1), for marked thinning of the lithosphere(2,3), often ending with a continental break-up, and for their links to global environmental catastrophes(4,5). Despite the importance of LIPs, controversy surrounds even the basic idea that they form through melting in the heads of thermal mantle plumes(2,3,6-10). The Permo-Triassic Siberian Traps(11)-the type example and the largest continental LIP(1,12)-is located on thick cratonic lithosphere(1,12) and was synchronous with the largest known mass-extinction event(1). However, there is no evidence of pre-magmatic uplift or of a large lithospheric stretching(7), as predicted above a plume head(2,6,9). Moreover, estimates of magmatic CO(2) degassing from the Siberian Traps are considered insufficient to trigger climatic crises(13-15), leading to the hypothesis that the release of thermogenic gases from the sediment pile caused the mass extinction(15,16). Here we present petrological evidence for a large amount (15 wt%) of dense recycled oceanic crust in the head of the plume and develop a thermomechanical model that predicts no pre-magmatic uplift and requires no lithospheric extension. The model implies extensive plume melting and heterogeneous erosion of the thick cratonic lithosphere over the course of a few hundred thousand years. The model suggests that massive degassing of CO(2) and HCl, mostly from the recycled crust in the plume head, could alone trigger a mass extinction and predicts it happening before the main volcanic phase, in agreement with stratigraphic and geochronological data for the Siberian Traps and other LIPs(5).
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Sourbier, F., Haidar, A., Giraud, L., Ben-Hadj-Ali, H., Operto, S., & Virieux, J. (2011). Three-dimensional parallel frequency-domain visco-acoustic wave modelling based on a hybrid direct/iterative solver. Geophysical Prospecting, 59, 834–856.
Résumé: We present a parallel domain decomposition method based on a hybrid direct-iterative solver for 3D frequency-domain modelling of visco-acoustic waves. The method is developed as a modelling engine for frequency-domain full waveform inversion. Frequency-domain seismic modelling reduces to the solution of a large and sparse system of linear equations, resulting from the discretization of the heterogeneous Helmholtz equation. Our approach to the high-performance, scalable solution of large sparse linear systems is to combine direct and iterative methods. Such a hybrid approach exploits the advantages of both direct and iterative methods. The iterative component uses a small amount of memory and provides a natural way for parallelization. The direct part has favourable numerical properties for multiple right-hand side modelling. The domain decomposition is based upon the algebraic Schur complement method, which allows for the iterative solution of a reduced system, the solution of which is the wavefield at the interfaces between the subdomains. Once the interface unknowns have been computed, the wavefield at the interior of each subdomain is efficiently computed by local substitutions. The reduced Schur complement system is solved with the generalized minimum residual method and is preconditioned by an algebraic additive Schwarz preconditioner. A direct solver is used to factorize local impedance matrices defined on each subdomain. Theoretical analysis shows that the time complexity of the hybrid solver is the same as that of iterative solver and time-domain approaches for single frequency modelling. Simulations are performed in the SEG/EAGE overthrust and the salt models for frequencies up to 12.5 Hz. The number of iterations increases linearly with the number of subdomains for a given computational domain but the elapsed time of the iterative resolution remains almost constant. The number of iterations also increases linearly with frequencies, when the grid interval is adapted to the frequencies and the size of the subdomains is kept constant over frequency. These results make the cost of the hybrid solver of the same order as that of finite-difference time-domain modeling for one-frequency modelling. Although the hybrid approach allows one to tackle larger problems than the direct-solver approach, further improvements are needed to mitigate the computational burden of the iterative component in the context of multisource modelling. On the numerical side, the use of block iterative solvers and of incremental two-level deflating preconditioners and on the parallel implementation side, the use of two levels of parallelism in the domain decomposition method should mitigate this computational burden.
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Souriau, A., Chaljub, E., Cornou, C., Margerin, L., Calvet, M., Maury, J., et al. (2011). Multimethod Characterization of the French-Pyrenean Valley of Bagneres-de-Bigorre for Seismic-Hazard Evaluation: Observations and Models. Bulletin of the Seismological Society of America, 101, 1912–1937.
Résumé: A narrow rectilinear valley in the French Pyrenees, affected in the past by damaging earthquakes, has been chosen as a test site for soil response characterization. The main purpose of this initiative was to compare experimental and numerical approaches. A temporary network of 10 stations has been deployed along and across the valley during two years; parallel various experiments have been conducted, in particular ambient noise recording, and seismic profiles with active sources for structure determination at the 10 sites. Classical observables have been measured for site amplification evaluation, such as spectral ratios of horizontal or vertical motions between site and reference stations using direct S waves and S coda, and spectral ratios between horizontal and vertical (H/V) motions at single stations using noise and S-coda records. Vertical shear-velocity profiles at the stations have first been obtained from a joint inversion of Rayleigh wave dispersion curves and ellipticity. They have subsequently been used to model the H/V spectral ratios of noise data from synthetic seismograms, the H/V ratio of S-coda waves based on equipartition theory, and the 3D seismic response of the basin using the spectral element method. General good agreement is found between simulations and observations. The 3D simulation reveals that topography has a much lower contribution to site effects than sedimentary filling, except at the narrow ridge crests. We find clear evidence of a basin edge effect, with an increase of the amplitude of ground motion at some distance from the edge inside the basin and a decrease immediately at the slope foot.
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Straface, S., Chidichimo, F., Rizzo, E., Riva, M., Barrash, W., Revil, A., et al. (2011). Joint inversion of steady-state hydrologic and self-potential data for 3D hydraulic conductivity distribution at the Boise Hydrogeophysical Research Site. Journal of Hydrology, 407, 115–128.
Résumé: We combine sedimentological, hydraulic and geophysical information to characterize the 3D distribution of transport properties of an heterogeneous aquifer. We focus on the joint inversion of hydraulic head and self-potential measurements collected during an extensive experimental campaign performed at the Boise Hydrogeophysical Research Site (BHRS), Boise, Idaho, and involving a series of dipole tests. While hydraulic head data obtained from piezometric readings in open wells represent a depth-averaged value, self-potential signals provide an estimate of the water table location. The aquifer is conceptualized as a multiple-continuum, where the volumetric fraction of a geo-material within a cell of the numerical flow model is calculated by Multiple Indicator Kriging. The latter is implemented on the basis of available sedimentological information. The functional format of the indicator variograms and associated parameters are estimated on the basis of formal model identification criteria. Self-potential and hydraulic head data have been embedded jointly within a three-dimensional inverse model of groundwater flow at the site. Each identified geo-material (category) is assumed to be characterized by a constant hydraulic conductivity. The latter constitute the set of model parameters. The hydraulic conductivity associated with a numerical block is then calculated as a weighted average of the conductivities of the geo-materials which are collocated in the block by means of Multiple Indicator Kriging. Model parameters are estimated by a Maximum Likelihood fit between measured and modeled state variables, resulting in a spatially heterogeneous distribution of hydraulic conductivity. The latter is effectively constrained on the sedimentological data and conditioned on both self-potential and borehole hydraulic head readings. Minimization of the Maximum Likelihood objective function allows estimating the relative weight of measurement errors associated with self-potential and borehole-based head data. The procedure adopted allowed a reconstruction of the heterogeneity of the site with a level of details, which was not obtained in previous studies and with relatively modest computational efforts. Further validation against dipole tests which were not used in the inversion procedure supports the robustness of the results. (C) 2011 Elsevier B.V. All rights reserved.
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Thevenon, F., Guedron, S., Chiaradia, M., Loizeau, J. - L., & Pote, J. (2011). (Pre-) historic changes in natural and anthropogenic heavy metals deposition inferred from two contrasting Swiss Alpine lakes. Quaternary Science Reviews, 30, 224–233.
Résumé: Continuous high-resolution sedimentary record of heavy metals (chromium (Cr), copper (Cu), lead (Pb), zinc (Zn), manganese (Mn), and mercury (Hg)), from lakes Lucerne and Meidsee (Switzerland), provides pollutant deposition history from two contrasting Alpine environments over the last millennia. The distribution of conservative elements (thorium (Th), scandium (Sc) and titanium (Ti)) shows that in absence of human disturbances, the trace element input is primarily controlled by weathering processes (i.e., runoff and erosion). Nonetheless, the enrichment factor (EF) of Pb and Hg (that are measured by independent methods), and the Pb isotopic composition of sediments from the remote lake Meidsee (which are proportionally more enriched in anthropogenic heavy metals), likely detect early mining activities during the Bronze Age. Meanwhile, the deposition of trace elements remains close to the range of natural variations until the strong impact of Roman activities on atmospheric metal emissions. Both sites display simultaneous increases in anthropogenic trace metal deposition during the Greek and Roman Empires (ca 300 BC to AD 400), the Late Middle Ages (ca AD 1400), and the Early Modern Europe (after ca AD 1600). However, the greatest increases in anthropogenic metal pollution are evidenced after the industrial revolution of ca AD 1850, at low and high altitudes. During the twentieth century, industrial releases multiplied by ca 10 times heavy metal fluxes to hydrological systems located on both sides of the Alps. During the last decades, the recent growing contribution of low radiogenic Pb further highlights the contribution of industrial sources with respect to wood and coal burning emissions. (C) 2010 Elsevier Ltd. All rights reserved.
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Thomas, P., Eric, L., Vincent, R., & Ludovic, M. (2011). Tracking a defect in the multiple scattering regime. The Journal of the Acoustical Society of America, 130, 2378.
Résumé: We describe a time-resolved monitoring technique for heterogeneous media, especially multiply scattering media. Our approach is based on the spatial variations of the cross-coherence of diffuse waves acquired at fixed positions but at different dates. The technique applies to all kind of waves, but a particular attention will be paid to ultrasound propagating in concrete. To locate and characterize a defect occurring between successive acquisitions, we use a maximum likelihood approach combined with a diffusive propagation model. We quantify the performance of this technique called LOCADIFF with numerical simulations. In several illustrative examples, we show that the change can be located with a precision of a few wavelengths and that its effective scattering cross-section can be retrieved. We investigate how the accuracy and precision of the method depends on the number of source-receiver pairs, on the time window used to compute the cross-correlation and on the errors in the propagation model. Applications can be found in nondestructive testing (civil engineering), seismology, radar, and sonar location.
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Traversa, P., Lengline, O., Macedo, O., Metaxian, J. P., Grasso, J. R., Inza, A., et al. (2011). Short term forecasting of explosions at Ubinas volcano, Peru. Journal of Geophysical Research-Solid Earth, 116.
Résumé: Most seismic eruption forerunners are described using Volcano-Tectonic earthquakes, seismic energy release, deformation rates or seismic noise analyses. Using the seismic data recorded at Ubinas volcano (Peru) between 2006 and 2008, we explore the time evolution of the Long Period (LP) seismicity rate prior to 143 explosions. We resolve an average acceleration of the LP rate above the background level during the 2-3 hours preceding the explosion onset. Such an average pattern, which emerges when stacking over LP time series, is robust and stable over all the 2006-2008 period, for which data is available. This accelerating pattern is also recovered when conditioning the LP rate on the occurrence of an other LP event, rather than on the explosion time. It supports a common mechanism for the generation of explosions and LP events, the magma conduit pressure increase being the most probable candidate. The average LP rate acceleration toward an explosion is highly significant prior to the higher energy explosions, supposedly the ones associated with the larger pressure increases. The dramatic decay of the LP activity following explosions, still reinforce the strong relationship between these two processes. We test and we quantify the retrospective forecasting power of these LP rate patterns to predict Ubinas explosions. The prediction quality of the forecasts (e.g. for 17% of alarm time, we predict 63% of Ubinas explosions, with 58% of false alarms) is evaluated using error diagrams. The prediction results are stable and the prediction algorithm validated, i.e. its performance is better than the random guess.
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Trepreau, J., de Rosny, E., Duboc, C., Sarret, G., Petit-Hartlein, I., Maillard, A. P., et al. (2011). Spectroscopic Characterization of the Metal-Binding Sites in the Periplasmic Metal-Sensor Domain of CnrX from Cupriavidus metallidurans CH34. Biochemistry, 50, 9036–9045.
Résumé: CnrX, the dimeric metal sensor of the three-protein transmembrane signal transduction complex CnrYXH of Cupriavidus metallidurans CH34, contains one metal-binding site per monomer. Both Ni and Co elicit a biological response and bind the protein in a 3N2O1S coordination sphere with a nearly identical octahedral geometry as shown by the X-ray structure of CnrXs, the soluble domain of CnrX. However, in solution CnrXs is titrated by 4 Co-equiv and exhibits an unexpected intense band at 384 nm that was detected neither by single-crystal spectroscopy nor under anaerobiosis. The data from a combination of spectroscopic techniques (spectrophotometry, electron paramagnetic resonance, X-ray absorption spectroscopy) showed that two sites correspond to those identified by crystallography. The two extra binding sites accommodate Co(II) in an octahedral geometry in the absence of oxygen and are occupied in air by a mixture of low-spin Co(11) as well as EPR-silent Co(III). These extra sites, located at the N-terminus of the protein, are believed to participate to the formation of peroxo-bridged dimers. Accordingly, we hypothesize that the intense band at 384 nm relies on the formation of a binuclear mu-peroxo Co(III) complex. These metal binding sites are not physiologically relevant since they are not detected in full-length NccX, the closest homologue of CnrX. X-ray absorption spectroscopy demonstrates that NccX stabilizes Co(H) in two-binding sites similar to those characterized by crystallography in its soluble counterpart. Nevertheless, the original spectroscopic properties of the extra Co-binding sites are of interest because they are susceptible to be detected in other Co-bound proteins.
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Trouve, E., Nicolas, J. - M., Ferro-Famil, L., Gay, M., Pinel, V., Doin, M. - P., et al. (2011). EFIDIR: extraction and fusion of information for displacement measurement from radar imagery. Traitement Du Signal, 28, 375–416.
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Uzu, G., Sobanska, S., Sarret, G., Sauvain, J. J., Pradere, P., & Dumat, C. (2011). Characterization of lead-recycling facility emissions at various workplaces: Major insights for sanitary risks assessment. Journal of Hazardous Materials, 186, 1018–1027.
Résumé: Most available studies on lead smelter emissions deal with the environmental impact of outdoor particles, but only a few focus on air quality at workplaces. The objective of this study is to physically and chemically characterize the Pb-rich particles emitted at different workplaces in a lead recycling plant. A multi-scale characterization was conducted from bulk analysis to the level of individual particles, to assess the particles properties in relation with Pb speciation and availability. Process PM from various origins were sampled and then compared; namely Furnace and Refining PM respectively present in the smelter and at refinery workplaces. Emissions PM present in channeled emissions. These particles first differed by their morphology and size distribution, with finer particles found in emissions. Differences observed in chemical composition could be explained by the industrial processes. All PM contained the same major phases (Pb, PbS, PbO, PbSO(4) and PbO center dot PbSO(4)) but differed on the nature and amount of minor phases. Due to high content in PM, Pb concentrations in the CaCl(2) extractant reached relatively high values (40 mg L(-1)). However, the ratios (soluble/total) of CaCl(2) exchangeable Pb were relatively low (< 0.02%) in comparison with Cd (up to 18%). These results highlight the interest to assess the soluble fractions of all metals (minor and major) and discuss both total metal concentrations and ratios for risk evaluations. In most cases metal extractability increased with decreasing size of particles, in particular, lead exchangeability was highest for channeled emissions. Such type of study could help in the choice of targeted sanitary protection procedures and for further toxicological investigations. In the present context, particular attention is given to Emissions and Furnace PM. Moreover, exposure to other metals than Pb should be considered. (C) 2010 Elsevier B.V. All rights reserved.
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Valla, P. G., Shuster, D. L., & van der Beek, P. A. (2011). Significant increase in relief of the European Alps during mid-Pleistocene glaciations. Nature Geoscience, 4, 688–692.
Résumé: Some of Earth's greatest relief occurs where glacial processes act on mountain topography(1,2). This dramatic landscape is thought to be an imprint of Pleistocene glaciations(3,4). However, whether the net effect of glacial erosion on mountains is to increase(5-7) or decrease(8-10) relief remains disputed. It has been suggested that in the European Alps, the onset of widespread glaciation since the mid-Pleistocene climate transition(11) led to the growth of large, long-lived and strongly erosive alpine glaciers(12,13) that profoundly influenced topography(14). Here we use (4)He/(3)He thermochronometry(15) and thermal-kinematic models to show that the Rhone Valley in Switzerland deepened by about 1-1.5 km over the past one million years. Our results indicate that while the valley was incised and back-cut, high-altitude areas were preserved from erosion. We find an approximately two-fold increase in both local topographic relief and valley concavity, which occurred around the time of the mid-Pleistocene transition. Our results support the proposed link(12-14) between the onset of efficient glacial erosion in the European Alps and the transition to longer, colder glacial periods at the middle of the Pleistocene epoch.
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Valla, P. G., van der Beek, P. A., & Braun, J. (2011). Rethinking low-temperature thermochronology data sampling strategies for quantification of denudation and relief histories: A case study in the French western Alps. Earth and Planetary Science Letters, 307, 309–322.
Résumé: We assess the importance of thermochronometric data sampling and modeling strategies for correctly estimating mountain belt exhumation. Thermochronological age-elevation profiles have been widely used to infer orogenic exhumation histories: however, recent studies have shown that this sampling strategy may not be the most pertinent for quantifying both denudation and relief history. Here, we investigate the ability of combining different thermochronology data sampling schemes with numerical modeling to better constrain denudation rates and relief changes. We produce synthetic thermochronology datasets for real Alpine topography under a specific exhumation and relief scenario using the thermal-kinematic model Pecube. We then adopt an inverse approach based on the Neighborhood Algorithm to quantitatively assess the resolution of different thermochronology datasets collected following elevation profiles, long transects and valley bottom sampling. We also test the effect of the modeling approach on denudation and relief predictions, in particular the influence of the topographic grid resolution and of potential constraints on the geothermal gradient. Our results show that sampling along a single elevation profile does not allow to quantitatively constrain both denudation and relief histories. Numerical outputs clearly evidence tradeoffs that limit the capacity of simultaneously resolving denudation rates and relief change. Quantitative predictions are only slightly different when combining elevation profiles along different valleys, but are highly improved when using long transects or valley-bottom samples combined with an elevation profile. The resolution with which relief evolution can be predicted may be increased by a factor of 2 by using spatially distributed datasets. Results of thermal parameter inversions suggest that the geothermal gradient may be better estimated using elevation profiles or long-transect sampling rather than using valley bottom samples. Simulations with different model topography resolutions show that degrading the resolution for computational efficiency may result in a loss of quantitative information on denudation rates and relief history. In summary, we highlight that both thermochronological sampling strategies and the choice of thermal parameters or model topography resolution have a significant influence on predicted denudation and relief histories. Ideally, the sampling strategy should be designed using preliminary modeling of expected denudation and relief histories, and a sensitivity study on assumed thermal parameters and model resolution should be performed when modeling the data. Although our modeling is based on a particular case study of relief evolution in the French western Alps, we believe that these inferences have general relevance for thermochronological studies within mountain belts. (C) 2011 Elsevier B.V. All rights reserved.
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Van Daele, M., van Welden, A., Moernaut, J., Beck, C., Audemard, F., Sanchez, J., et al. (2011). Reconstruction of Late-Quaternary sea- and lake-level changes in a tectonically active marginal basin using seismic stratigraphy: The Gulf of Cariaco, NE Venezuela. Marine Geology, 279, 37–51.
Résumé: The Gulf of Cariaco is a marginal basin located between the Cariaco Basin and the Paria Gulf, offshore NE Venezuela, along a system of active right-lateral strike-slip faults. It is connected to the Caribbean Sea via a shallow 58-m-deep sill implying that the gulf was disconnected from the global ocean during eustatic lowstands. A dense grid of high-resolution reflection seismic profiles has been used to determine the overall tectonic structure of the gulf and to establish the seismic stratigraphy of its sedimentary infill. Six unconformity-bounded seismic-stratigraphic units were identified in the upper similar to 200 m of the sedimentary infill. Detailed seismic-stratigraphic and seismic-facies analysis allowed defining a series of sedimentary features that can be used as indicators of past sea or lake level in the Gulf of Cariaco: i) delta offlap breaks, ii) evaporites, and iii) erosional unconformities. Using accurate measurements of these various indicators at several locations in the gulf and a simple total subsidence model, a relative sea/lake-level history encompassing the last 130 kyr could be reconstructed. In periods of connection with the open ocean, reconstructed relative sea level correlates well with eustatic sea level. In times of disconnection, distinct lake-level fluctuations occurred, which sometimes resulted in total dessication of the gulf. Lake-level fluctuations appear to correlate with major Heinrich Events, stadials and interstadials. MIS 4, the LGM and the Younger Dryas were thus identified in the Gulf of Cariaco sedimentary record. The last reconnection to the Caribbean Sea occurred during MWP1b (around 11.5 kyr). The very good fit of the Cariaco sea/lake-level curve with the eustatic sea-level curves (both in terms of amplitude and of timing) underscores potential for future paleoclimate research of the sedimentary record contained in this marginal basin, despite its active tectonic setting. (C) 2010 Elsevier B.V. All rights reserved.
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Van Houtte, C., Drouet, S., & Cotton, F. (2011). Analysis of the Origins of kappa (Kappa) to Compute Hard Rock to Rock Adjustment Factors for GMPEs. Bulletin of the Seismological Society of America, 101, 2926–2941.
Résumé: The observable decay with frequency (f) of Fourier amplitude spectra for ground-motion recordings is controlled by a parameter kappa: exp (-pi kappa f). We analyze data from the KiK-net network, which is composed of stations with paired ground-motion sensors, one at the surface and one in a borehole. This study estimates kappa for all KiK-net stations, using earthquakes recorded between 1998 and 2006. An inversion scheme is used to separate site, source, and path contributions to kappa. We correlate the site component of kappa (kappa(0)), estimated at the surface and the depth, with different S-wave velocity measures and with the fundamental resonant frequency of the site. The results show that the best correlations involve shallow soil S-wave velocity measures. The superficial layers of the soil predominantly influence kappa(0), but a remaining component with a deep origin is also observed. The source component of kappa is small and presents a clear regional dependence, while no correlations with magnitude or depth of the earthquake are observed. Data from the Next Generation of Attenuation (NGA) database are also used to estimate kappa(0) (surface site component) at the stations with a measured V(S30) value. The V(S30)-kappa couples estimated from both KiK-net and NGA data are compared with results from the literature, and a new correlation is established. Most of the ground-motion prediction equations (GMPEs) for stable continental regions are derived for very hard rock sites (V(S30) > 2000 m/s). In order to use these equations for standard rock sites (V(S30) around 800 m/s), conversion factors are required. Using the new correlation V(S30)-kappa and the host-to-target adjustment method of Campbell (2003), we compute amplification factors from very hard rock to rock sites. We show that in these conversions, the effects of both V(S30) and kappa have to be taken into account.
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Vassallo, R., Ritz, J. - F., & Carretier, S. (2011). Control of geomorphic processes on (10)Be concentrations in individual clasts: Complexity of the exposure history in Gobi-Altay range (Mongolia). Geomorphology, 135, 35–47.
Résumé: The dating of alluvial landforms by cosmogenic nuclides requires distinguishing the pre-deposition inheritance from the post-deposition history of the clasts in the studied marker. Moreover, estimating catchment-scale erosion rates from the concentrations of cosmogenic nuclides in active alluvia requires a good knowledge of the local/regional relationships between rock exhumation and transport through space and time. This is still poorly known for timescales of tens of thousand years. In order to document the evolution of clast exhumation and transport rates through time, we analyze in situ (10)Be concentrations in boulders and cobbles from hillslopes to outlet of an arid mountainous catchment located in Gobi-Altay, Mongolia, strongly affected by global climatic changes during the Pleistocene-Holocene period. Samples were collected on bedrock, abandoned alluvial deposits, active colluvia and alluvia. Our results show a large (10)Be scattering in the active river bed, consistent with a low and discontinuous catchment erosion rate dominated by mass wasting and fluvial incision. On the contrary, pre-exposure signal within abandoned terraces is much more homogeneous, consistent with climatic pulses responsible of strong erosional events on hillslopes and rapid fluvial transport. These results show that exhumation/transport processes at the catchment scale vary in style and intensity through time as a consequence of climatic oscillations. The occurrence of abrupt climatic changes during short periods of time recorded by (10)Be concentrations in abandoned alluvia raise questions about the temporal applicability of catchment erosion rates derived from cosmogenic nuclide concentrations measured in sediments of active rivers. On the other hand, strong and short erosion events limit and homogenize the pre-exposure (10)Be signal in associated deposits like debris-flows, making them particularly suitable markers for dating in active tectonic and paleoclimatic studies. (C) 2011 Elsevier B.V. All rights reserved.
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Vaudelet, P., Revil, A., Schmutz, M., Franceschi, M., & Begassat, P. (2011). Changes in induced polarization associated with the sorption of sodium, lead, and zinc on silica sands. Journal of Colloid and Interface Science, 360, 739–752.
Résumé: Low-frequency dielectric spectroscopy can be measured in terms of a conductance and a phase lag between the electrical current and the electrical field. This conductance and phase lag can be written as into a complex conductivity with both an in-phase and quadrature components that are frequency dependent. In sands, the low-frequency (10 mHz-40 kHz) spectra of the complex conductivity are dominated by the polarization of the electrical double layer (especially the internal part of the electrical double layer called the Stern layer) and the Maxwell-Wagner polarization (typically above 100 Hz). We present a polarization that is able to explain the complex conductivity spectra including the grain size distribution, the porosity, and the complexation of the mineral surface with the ions of the pore water. To test this model, we investigate the sorption of various cations (Na, Pb, Zn) characterized by different affinities with the surface of silica. Sand column experiments were carried out to see the change in the complex conductivity during the advective/dispersive transport of a lead nitrate solution and a zinc sulfate solution, replacing a sodium chloride solution in the pore space of the sand. The complex conductivity model is able to explain the change of the phase over time. (C) 2011 Elsevier Inc. All rights reserved.
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Vaudelet, P., Revil, A., Schmutz, M., Franceschi, M., & Begassat, P. (2011). Induced polarization signatures of cations exhibiting differential sorption behaviors in saturated sands. Water Resources Research, 47.
Résumé: Two sets of experiments were designed to understand the change in induced polarization associated with the sorption of copper and sodium, exhibiting distinct sorption behavior on a silica sand. A sand column experiment was firs performed to see the change in the complex conductivity during the advective transport of a copper sulfate solution. A second set of experiments was done with the sand at equilibrium with various solutions of NaCl and CuSO(4). In the firs experiment, the copper sulfate solution replaced a sodium chloride solution, keeping the electrical conductivity of the solution nearly constant. During the passage of the copper sulfate solution, the apparent phase angle decreased from 3 +/- 0.2 to 0.5 +/- 0.2 mrad, while the magnitude of the conductivity of the sand remained nearly constant. A quantitative model is proposed to explain the change in the complex conductivity as a function of the chemistry assuming a polarization mechanism associated with the Stern layer (the inner part of the electrical double layer coating the water-mineral interface). The Stern layer polarization is combined with a complexation model describing the competitive sorption of copper and sodium at the pore water interface. The change of the phase lag is directly associated with the ion exchange between sodium and copper at the surface of the silica grains. The explanation of the observed phase differences between Na and Cu relies on their different complexation behaviors, with Na being loosely absorbed, while Cu forms relatively strong complexation with both inner (monodentate) and outer sphere (bidentate) complexes. The replacement of Cu(2+) by Na(+) is less favorable; therefore, the kinetics of such a replacement is much slower than for the opposite replacement (Na(+) by Cu(2+)). We were able to reproduce the changes in the phase lags at thermodynamic equilibrium near the relaxation frequency and in the frequency domain. These measurements and modeling results open the door to the quantitative interpretation of spectral induced polarization data in the fiel in terms of quantificatio of the sorption processes.
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Verlaguet, A., Goffe, B., Brunet, F., Poinssot, C., Vidal, O., Findling, N., et al. (2011). Metamorphic veining and mass transfer in a chemically closed system: a case study in Alpine metabauxites (western Vanoise). Journal of Metamorphic Geology, 29, 275–300.
Résumé: In western Vanoise (French Alps), karstic pockets of Triassic-to-Jurassic metabauxites embedded in carbonate rocks and containing several generations of metamorphic veins were studied. During blueschist facies metamorphism, a cumulative amount of similar to 13 vol% of water is inferred to have been produced locally by successive dehydration reactions, and part of this fluid remained in the bauxitic lenses during most of the metamorphic cycle. Field and geochemical evidence show that these rocks have been isolated from large-scale fluid flow (closed-system behaviour). It is proposed that the internally derived fluid has promoted the opening of fluid-filled open spaces (as attested by the euhedral habits of vein minerals) and served as medium for mass transfer from rock to vein. Indeed, the vein infill is obviously the result of chemical interactions, at the millimetre-to-centimetre scale, between the rock minerals and the locally produced aqueous fluid. Two vein types can be distinguished based on mineralogical and textural features: (i) some veins are filled with newly formed products of either prograde (chloritoid) or retrograde (chlorite) metamorphic reactions; in this case, fluid-filled open spaces seem to offer energetically favourable nucleation/growth sites; (ii) the second vein type is infilled with cookeite or pyrophyllite, that were present in the host rock prior to the vein formation. In this closed chemical system, the components for the vein infill minerals have been transferred from rock to vein through the fluid, in a dissolution-transport-precipitation process, possibly stress-assisted. These different vein generations all contain Al-rich mineral infills, suggesting that Al was a mobile element (cm scale) during metamorphism. In these HP rocks, fluid flow may have been restricted, and if so mass transfer occurred by diffusion in an almost stagnant fluid. Metamorphic veins can be seen as witnesses of fluid and mass redistribution that partly accommodate the rock deformation (lateral segregation).
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Virieux, J., Calandra, H., & Plessix, R. - E. (2011). A review of the spectral, pseudo-spectral, finite-difference and finite-element modelling techniques for geophysical imaging. Geophysical Prospecting, 59, 794–813.
Résumé: Modelling methods are nowadays at the heart of any geophysical interpretation approach. These are heavily relied upon by imaging techniques in elastodynamics and electromagnetism, where they are crucial for the extraction of subsurface characteristics from ever larger and denser datasets. While high-frequency or one-way approximations are very powerful and efficient, they reach their limits when complex geological settings and solutions of full equations are required at finite frequencies. A review of three important formulations is carried out here: the spectral method, which is very efficient and accurate but generally restricted to simple earth structures and often layered earth structures; the pseudo-spectral, finite-difference and finite-volume methods based on strong formulation of the partial differential equations, which are easy to implement and currently represent a good compromise between accuracy, efficiency and flexibility and the continuous or discontinuous Galerkin finite-element methods that are based on the weak formulation, which lead to more accurate earth representations and therefore to more accurate solutions, although with higher computational costs and more complex use. The choice between these different approaches is still difficult and depends on the applications. Guidelines are given here through discussion of the requirements for imaging/inversion.
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Wagani, I., Pagel, M., Janots, E., & Gnos, E. (2011). DETRITAL MONAZITE IN THE TIM MERSOI BASIN, NIGER: PROVENANCE AND CONTRIBUTION TO THE URANIUM BUDGET IN SILICICLASTIC SEDIMENTS. Canadian Mineralogist, 49, 487–501.
Résumé: A detailed study using back-scattered electron imaging and electron-microprobe analysis shows that grains of detrital monazite are present in the Carboniferous, Permian, Triassic and Jurassic sediments of the Tim Mersoi basin, Niger. Despite variations in the size and shape of monazite grains, the U-Th-Pb chemical ages obtained by electron microprobe fall in a narrow range, 425 to 650 Ma. These ages indicate that the monazite grains are issued from the erosion of Pan-African granites and metamorphic rocks from the Air Mountains, and probably also from the basement near Zinder and in Nigeria, a hypothesis in good agreement with paleocurrent reconstruction. The uranium content of monazite from sediments is high (up to 1.7 wt% UO(2)), but low in adjacent rhyolite. Some monazite grains from the sandstone show evidence of alteration, especially to florencite. We conclude that detrital monazite is a major reservoir of uranium in some sandstones from the Tim Mersoi Basin.
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Walpersdorf, A., Cotte, N., Kostoglodov, V., Vergnolle, M., Radiguet, M., Antonio Santiago, J., et al. (2011). Two successive slow slip events evidenced in 2009-2010 by a dense GPS network in Guerrero, Mexico. Geophysical Research Letters, 38.
Résumé: A large slow slip event (SSE) had been expected for the Guerrero gap for 2010. It was actually observed with an onset in July 2009. Comparison with the preceding large SSEs, which occurred in 2002 and 2006, highlights both persistent characteristics of the Guerrero SSEs (e.g. the localization of slip in the seismogenic part of the subduction interface), and also particularities of the 2009/2010 event (namely two distinct slip patches on the fault interface moving consecutively). The long GPS time series and the density of the GPS network provide evidence that the Guerrero SSEs, like classical earthquakes, have complex features. Despite having very short and relatively regular repeat times (similar to 4 yr), Guerrero SSEs appear aperiodic. A shorter loading time before the 2009/2010 event than before the 2006 SSE seems to produce consistently reduced surface displacements for a group of stations in a core zone.
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Weaver, R. L., Hadziioannou, C., Larose, E., & Campillo, M. (2011). On the precision of noise correlation interferometry. Geophysical Journal International, 185, 1384–1392.
Résumé: P>Long duration noisy-looking waveforms such as those obtained in randomly multiple scattering and reverberant media are complex; they resist direct interpretation. Nevertheless, such waveforms are sensitive to small changes in the source of the waves or in the medium in which they propagate. Monitoring such waveforms, whether obtained directly or obtained indirectly by noise correlation, is emerging as a technique for detecting changes in media. Interpretation of changes is in principle problematic; it is not always clear whether a change is due to sources or to the medium. Of particular interest is the detection of small changes in propagation speeds. An expression is derived here for the apparent, but illusory, waveform dilation due to a change of source. The expression permits changes in waveforms due to changes in wave speed to be distinguished with high precision from changes due to other reasons. The theory is successfully compared with analysis of a laboratory ultrasonic data set and a seismic data set from Parkfield California.
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Werner, M. J., Helmstetter, A., Jackson, D. D., & Kagan, Y. Y. (2011). High-Resolution Long-Term and Short-Term Earthquake Forecasts for California. Bulletin of the Seismological Society of America, 101, 1630–1648.
Résumé: We present two models for estimating the probabilities of future earthquakes in California, to be tested in the Collaboratory for the Study of Earthquake Predictability (CSEP). The first is a time-independent model of adaptively smoothed seismicity that we modified from Helmstetter et al. (2007). The model provides five-year forecasts for earthquakes with magnitudes M >= 4.95. We show that large earthquakes tend to occur near the locations of small M >= 2 events, so that a high-resolution estimate of the spatial distribution of future large quakes is obtained from the locations of the numerous small events. We further assume a universal Gutenberg-Richter magnitude distribution. In retrospective tests, we show that a Poisson distribution does not fit the observed rate variability, in contrast to assumptions in current earthquake predictability experiments. We therefore issued forecasts using a better-fitting negative binomial distribution for the number of events. The second model is a time-dependent epidemic-type aftershock sequence (ETAS) model that we modified from Helmstetter et al. (2006) and that provides next-day forecasts for M >= 3.95. In this model, the forecasted rate is the sum of a background rate (proportional to the time-independent model rate) and of the expected rate of triggered events due to all prior earthquakes. Each earthquake triggers events with a rate that increases exponentially with its magnitude and decays in time according to the Omori-Utsu law. An isotropic kernel models the spatial density of aftershocks for small (M <= 5.5) events, while for larger quakes, we smooth early aftershocks to forecast later events. We estimate parameter values by optimizing retrospective forecasts and find that the short-term model realizes a probability gain of about 6.0 per earthquake over the time-independent model.
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Westall, F., Cavalazzi, B., Lemelle, L., Marrocchi, Y., Rouzaud, J. - N., Simionovici, A., et al. (2011). Implications of in situ calcification for photosynthesis in a similar to 3.3 Ga-old microbial biofilm from the Barberton greenstone belt, South Africa. Earth and Planetary Science Letters, 310, 468–479.
Résumé: Timing the appearance of photosynthetic microorganisms is crucial to understanding the evolution of life on Earth. The ability of the biosphere to use sunlight as a source of energy (photoautotrophy) would have been essential for increasing biomass and for increasing the biogeochemical capacity of all prokaryotes across the range of redox reactions that support life. Typical proxies for photosynthesis in the rock record include features, such as a mat-like, laminated morphology (stratiform, domical, conical) often associated with bulk geochemical signatures, such as calcification, and a fractionated carbon isotope signature. However, to date, in situ, calcification related to photosynthesis has not been demonstrated in the oldest known microbial mats. We here use in situ nanometre-scale techniques to investigate the structural and compositional architecture in a 3.3 billion-year (Ga) old microbial biofilm from the Barberton greenstone belt, thus documenting in situ calcification that was most likely related to anoxygenic photosynthesis. The Josefsdal Chert Microbial Biofilm (JCMB) formed in a littoral (photic) environment It is characterised by a distinct vertical structural and compositional organisation. The lower part is calcified in situ by aragonite, progressing upwards into uncalcified kerogen characterised by up to 1% sulphur, followed by an upper layer that contains intact filaments at the surface. Crystallites of pseudomorphed pyrite are also associated with the biofilm suggesting calcification related to the activity of heterotrophic sulphur reducing bacteria. In this anoxygenic, nutrient-limited environment, the carbon required by the sulphur reducing bacteria could only have been produced by photoautotrophy. We conclude that the Josfsdal Chen Microbial Biofilm was formed by a consortium of anoxygenic microorganisms, including photosynthesisers and sulphur reducing bacteria. (C) 2011 Elsevier B.V. All rights reserved.
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Woodruff, W. F., & Revil, A. (2011). CEC-normalized clay-water sorption isotherm. Water Resources Research, 47.
Résumé: A normalized clay-water isotherm model based on BET theory and describing the sorption and desorption of the bound water in clays, sand-clay mixtures, and shales is presented. Clay-water sorption isotherms (sorption and desorption) of clayey materials are normalized by their cation exchange capacity (CEC) accounting for a correction factor depending on the type of counterion sorbed on the mineral surface in the so-called Stern layer. With such normalizations, all the data collapse into two master curves, one for sorption and one for desorption, independent of the clay mineralogy, crystallographic considerations, and bound cation type; therefore, neglecting the true heterogeneity of water sorption/desorption in smectite. The two master curves show the general hysteretic behavior of the capillary pressure curve at low relative humidity (below 70%). The model is validated against several data sets obtained from the literature comprising a broad range of clay types and clay mineralogies. The CEC values, derived by inverting the sorption/adsorption curves using a Markov chain Monte Carlo approach, are consistent with the CEC associated with the clay mineralogy.
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Yan, Y., Trouve, E., Mauris, G., Pinel, V., & Ieee. (2011). Fuzzy vs probability uncertainty analysis of seismic displacement measurements issued from D-InSAR and SAR image correlation measurements Application to the Kashmir earthquake (2005). In 2011 Ieee International Instrumentation and Measurement Technology Conference (pp. 114–118). IEEE Instrumentation and Measurement Technology Conference.
Résumé: An emerging way to reduce the geodetic parameter uncertainty is to combine the large numbers of data provided by satellite radar images. However, the measurements by radar images are subjected both to random and epistemic uncertainties. Thus, mathematical theories which are adequate for each type of uncertainty representation and handling have to be selected. Probability theory is known as the adequate theory for uncertainties corresponding to random variables, but questionable for epistemic uncertainties, arising from information incompleteness. Fuzzy theory being a generalization of interval mathematics, it is more adapted to such uncertainty. Moreover it provides a bridge with probability theory by its ability to represent a family of probability distributions. Therefore, we consider here the conventional probability and the fuzzy approaches for handling the random and epistemic uncertainties of D-InSAR and SAR correlation measurements. The applications are performed on the measurement of displacement field due to the Kashmir earthquake (2005).
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Yoldi-Martinez, Z., Beck, P., Montes-Hernandez, G., Chiriac, R., Quirico, E., Bonal, L., et al. (2011). HYDROUS MINERALOGY OF CARBONACEOUS CHONDRITES FROM THERMOGRAVIMETRY ANALYSIS. Meteoritics & Planetary Science, 46, A258.
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Zigone, D., Voisin, C., Larose, E., Renard, F., & Campillo, M. (2011). Slip acceleration generates seismic tremor like signals in friction experiments. Geophysical Research Letters, 38.
Résumé: Since their discovery nearly a decade ago, the origin of seismic tremor remains unclear. Recent studies indicate that various driving phenomena such as Earth and ocean tides, regional and teleseismic earthquakes enhance tremor activity. Observations of the coincidence with slow-slip events and of fast migrations of tremors have led frictional slip to be considered as the possible source of tremors. Indeed, laboratory friction experiments succeeded in generating and recording tremor like signals (TLS). Here we show a systematic correlation between the onset of slip acceleration and the emission of TLS in a laboratory friction experiment. TLS are generated when the shear stress reaches the peak static resistance and the dilatancy meets its maximum that is when the mature interface is close to failure. This robust result provides a comprehensive image of how natural seismic tremors might be generated and/or triggered by passing seismic waves, tides or even slow slip events. Citation: Zigone, D., C. Voisin, E. Larose, F. Renard, and M. Campillo (2011), Slip acceleration generates seismic tremor like signals in friction experiments, Geophys. Res. Lett., 38, L01315, doi:10.1029/2010GL045603.
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