Articles présents dans [Web of Knowledge

Résumé: The 2016 Mw 6.1 Parina earthquake ruptured a shallow-crustal normal fault within the high Andes of south Peru. We use high-resolution DEMs and field mapping of the surface ruptures generated by the earthquake, in combination with co-seismic and post-seismic InSAR measurements, to investigate how different features of the geomorphology at Parina are generated by the earthquake cycle on the Parina Fault. We systematically mapped 12 km of NW-SE trending surface ruptures with up to similar to 27 cm vertical displacement and similar to 25 cm tensional opening along strike, separated by a gap with no observable surface ruptures. Co- and post-seismic InSAR measurements require slip below this gap in surface ruptures, implying that surface offsets observed in paleoseismic trenches may not necessarily be representative of slip at seismogenic depths, and will typically yield an underestimate of paleo-earthquake magnitudes. The surface ruptures developed along 10-20 m high cumulative scarps cutting through late Quaternary fluvio-glacial deposits and bedrock. The 2016 Parina earthquake did not rupture the full length of the late Quaternary scarps, implying that the Parina Fault does not slip in characteristic, repeat earthquakes. At Parina, and across most of the Peruvian Altiplano, normal faults are most-easily identified from recent scarps cutting late Quaternary moraine crests. In regions where there are no recently-deposited moraines, faults are difficult to identify and lack time constraints to quantify rates of fault slip. For this reason, current fault maps may underestimate the seismic hazard in the Altiplano.

Résumé: In December 2019, the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group (V-MOD) adopted the thirteenth generation of the International Geomagnetic Reference Field (IGRF). This IGRF updates the previous generation with a definitive main field model for epoch 2015.0, a main field model for epoch 2020.0, and a predictive linear secular variation for 2020.0 to 2025.0. This letter provides the equations defining the IGRF, the spherical harmonic coefficients for this thirteenth generation model, maps of magnetic declination, inclination and total field intensity for the epoch 2020.0, and maps of their predicted rate of change for the 2020.0 to 2025.0 time period.

Résumé: We modeled water exsolution from a growing and crystalizing felsic magma body using a conductive thermal model with simplified physical mechanisms of volatile transport. Magma solidification leads to the release of the water initially dissolved in the melt. Solidification behaviour depends, in turn, on dissolved water content. The water is channeled where the magma is solidified enough to form a crystal network and rapidly ascends until it encounters solid rock or liquid-rich magma. The rate of water exsolution depends on the basal magma emplacement rate, the cooling rate, and the magma initial water content. Water-rich layers form and are eventually trapped in the solid rock as cooling and crystallization proceeds. We ran our model with a quasi-eutectic granite composition and a non-eutectic monzogranite composition. The non-eutectic magma crystallizes on a wider range of temperature than the eutectic magma, produces more mush, and is more prone to the formation of water-rich lenses. Exsolved water accumulates on the sides of the chamber for both tested compositions and also above the top of the chamber for the non-eutectic composition. The actual presence of these water-rich layers in nature and their lifetime depend on whether the water is further released by fracturing. Our results account for the observed decoupling of volatiles from magma and for the episodic nature of volcano deformation. It has implications for the interpretation of magma chambers tomography as water-rich lenses would be difficult to distinguish from melt-rich lenses. (c) 2020 Elsevier B.V. All rights reserved.

Résumé: The subduction of the Nazca plate has specific features that impact the geophysical structure beneath Ecuador. In addition to the convexity of the trench between Peru and Ecuador, the Carnegie ridge and the Grijalva scarp are associated with strong heterogeneities in the plate that interfere with the subduction process. We have taken advantage of the large amount of manually picked P and S wave arrival times accumulated over time thanks to the national RENSIG network to perform an inversion for both event locations and seismic velocities over Ecuador within lat. 1.5 degrees N and 5 degrees S and long. 77 degrees W and 82 degrees W. After data filtering, the model presented in this article results from the inversion of 335,498 P and 111,457 S arrival times, corresponding to 25,410 events between 1988 and 2016. The intermediate depth seismicity outlines a continuous Wadati-Benioff zone in southern Ecuador that clearly defines the topography of the Farallon plate and its plunge towards the north-east at the Puyo nest, whereas in the northern part of the slab its pattern is more heterogeneous and is dominated by three nests at depths ranging between 75 km and 110 km, the Guayaquil, La Mana and Maldonado nests. The velocity model reveals a discontinuity of the Nazca plate along an axis oriented N110 degrees E, starting in the seismogenic zone at the southern limit of the occurrence of large earthquakes. This tear is associated with an overlap of the southern Farallon part of the slab by its younger northern part. We propose that it is the result of plate buckling due to lateral compression at depth caused by the sharp bend of the trench line between Peru and Ecuador.

Résumé: Understanding the transformations of highly reduced enstatite chondrites (EC) in terrestrial environments, even on very short timescales, is important to make the best use of the cosmochemical and mineralogical information carried by these extraterrestrial rocks. Analogs of EC meteorites were synthesized at high pressure and high temperature. Then, their aqueous alterations, either abiotic or in the presence of the bacteria Acidithiobacillus ferrooxidans or Acidithiobacillus thiooxidans, were studied under air, at pH similar to 2, 20 degrees C, and atmospheric pressure. They stayed in shaken batch reactors for 15 days. Reference experiments were carried out separately by altering only one mineral phase among those composing the synthetic EC (i.e., sulfides: troilite or Mg-Ca-rich sulfides, enstatite, and Fe70Si30). Composition of the alteration aqueous media and microstructures of the weathered solids were monitored by inductively coupled plasma atomic emission spectroscopy and by scanning electron microscopy, respectively. Alteration sequence of the different mineral components of the synthetic EC was found to occur in the following order: magnesium-calcium sulfides > troilite > iron-silicon metallic phase > enstatite regardless of the presence or absence of the microorganisms. Such small biological effects might be due to the fact that the alteration conditions are far from biologically optimal, which is likely the case in most natural environments. The exposed surfaces of an EC meteorite falling on Earth in a wet and acidic environment could lose within a few hours their Ca- and Mg-rich sulfides (oldhamite and niningerite). Then, in <1 week, troilite and kamacite could be altered. In a wet and acidic environment, only the enstatite would remain intact and would weather on a much slower geological timescale.

Résumé: Velocity variations obtained from ambient seismic noise are sensitive to many factors. We aimed to disentangle these processes in a 10-year-long recording of seismic noise from a single station in the Pollino region, in southern Italy. This region is characterized by aquifers and by a relatively short period of high seismic activity that included slow slip events and a M(W)5.0 earthquake that occurred on October 25, 2012. We apply two models that estimate the water level inside an aquifer, which show a good correlation with the measured delta upsilon/upsilon, showing that the velocity variations are inversely proportional to the pore pressure inside the aquifer. Our interpretation is further confirmed by geodetic measurements that show that in a direction parallel to the strike angle of the fault rupture, the expansion-contraction displacement of the zone follows the same patterns observed in the models and in the velocity variations, as a result of the pressure generated by the water on its interior. Going one step further, we analyze the nature of the small discrepancies between the measured and modeled velocity variations. These correlate well with the rainfall and with the vertical geodetic measures, which indicates an elastic response of the zone to the loading generated by the rainwater. Comparisons between these variables allow us to clearly identify the period of the seismic activity in the zone, which is represented by the characteristic drop in the seismic velocity in the period from the beginning of 2012 to mid-2013.

Résumé: The sulfur cycle is driven by redox processes, among which sulfate reduction is of primary importance. Sulfate is reduced to sulfide either abiotically by Thermochemical Sulfate Reduction (TSR) or biotically by Microbial Sulfate Reduction (MSR). Although these two processes occur at different temperature regimes (>100 degrees C and <80 degrees C, respectively), they generate similar by-products (e.g., sulfides, elemental sulfur). The S-34/S-32 ratio is often used as the sole criterion to identify the origin of reduced sulfur compounds, but overlaps prevent unambiguous conclusions. Contrary to MSR, the multiple sulfur isotopic signatures (delta S-33, delta S-34, delta S-36) of natural TSR remains uncharacterized. Here, we performed multiple sulfur isotopes analyses of sulfates, sulfides, and elemental sulfur from six sites in the Alpine Triassic evaporites formation to better constrain the isotopic signatures of TSR. Unlike MSR, TSR can induce slight negative deviations (Delta S-33 down to -0.08 parts per thousand) relative to the initial sulfate Delta S-33 value, which significantly discriminates between these two processes. Isotopic equilibria between anhydrite and either elemental sulfur or sulfides (pyrite or chalcopyrite) were verified according to their mass-fractionation exponents ((33/34)theta= 0.5140 and 0.5170, respectively). Using sulfate-elemental sulfur (Delta S-34(SO4)2- (-S8)) or sulfate-sulfide (Delta S-34(SO4)2- (2-)(-S)) fractionation pairs and respective fractionation factors ((34)alpha) for samples that fulfilled the criteria of isotopic equilibrium, we determined the precipitation temperatures of elemental sulfur and sulfides (pyrite or chalcopyrite) to be 194 +/- 14 degrees C and 293-488 degrees C, respectively. Interestingly, the obtained temperature of elemental sulfur precipitation corresponds exactly to the solidliquid phase transition of native sulfur. Using Delta S-33 vs. delta S-34 and Delta S-33 vs. Delta S-36 diagrams, we are able to fully explain the isotopic signatures of disequilibrium sulfides by the mixing of sulfate with either elemental or organic sulfur in the aqueous fluid. Mixing curves allow the determination of the relative proportions of sulfate and organic and elemental sulfur, the latter being formed by the recombination of polysulfides during cooling. It appears that the sulfides' signatures are best explained by a 33% contribution of polysulfides (i.e., elemental sulfur signatures), consistent with the relative proportion of dissolved polysulfides previously measured in fluid inclusions from this formation at >200 degrees C. Finally, no sulfur mass independent fractionation (S-MIF) is observed in this evaporitic formation, consistent with the TSR signature generated both at equilibrium and by mixing. This implies that TSR does not generate S-MIFs. Our results thus provide multiple sulfur isotopes signatures of TSR, which may be used to reliably identify this process in variable geological settings. (C) 2021 Elsevier B.V. All rights reserved.

Résumé: Understanding sub-seabed fluid flow mechanisms is important for determining their significance for ocean chemistry and to define fluid pathways above sub-seafloor CO2 storage reservoirs. Many active seabed fluid flow structures are associated with seismic chimneys or pipes, but the processes linking structures at depth with the seabed are poorly understood. We use seismic anisotropy techniques applied to ocean bottom seismometer (OBS) data, together with seismic reflection profiles and core data, to determine the nature of fluid pathways in the top tens of meters of marine sediments beneath the Scanner pockmark in the North Sea. The Scanner pockmark is 22 m deep, 900 m x 450 m wide and is actively venting methane. It lies above a chimney imaged on seismic reflection data down to similar to 1 km depth. We investigate azimuthal anisotropy within the Scanner pockmark and at a nearby reference site in relatively undisturbed sediments, using the PS converted (C-) waves from a GI gun source, recorded by the OBS network. Shear-wave splitting is observed on an OBS located within the pockmark, and on another OBS nearby, whereas no such splitting is observed on 23 other instruments, positioned both around the pockmark, and at an undisturbed reference site. The OBSs that show anisotropy have radial and transverse components imaging a shallow phase (55-65 ms TWT after the seabed) consistent with PS conversion at 4-5 m depth. Azimuth stacks of the transverse component show amplitude nulls at 70 degrees and 160 degrees N, marking the symmetry axes of anisotropy and indicating potential fracture orientations. Hydraulic connection with underlying, over pressured gas charged sediment has caused gas conduits to open, either perpendicular to the regional minimum horizontal stress at 150-160 N or aligned with a local stress gradient at 50-60 N. This study reports the first observation of very shallow anisotropy associated with active methane venting.

Résumé: We present the results of a paleoseismic survey of the Incapuquio Fault System, a prominent transpressional fault system cutting the forearc of South Peru. High-resolution Digital Elevation Models, optical satellite imagery, radiocarbon dating, and paleoseismic trenching indicate that at least 2-3 m of net slip occurred on the Incapuquio Fault generating a complex, similar to 100-km long set of segmented fault scarps in the early 15th century (similar to 1400-1440 CE). We interpret the consistent along-strike pattern of fault scarp heights, geometries and kinematics to reflect a surface rupture generated by a single M-w 7.4-7.7 earthquake, suggesting that brittle failure of the forearc poses a significant, yet mostly overlooked, seismic hazard to the communities in coastal areas of Peru. The timing of this earthquake coincides with the collapse of the Chiribaya civilization in similar to 1360-1400 CE, and we present evidence of damaged buildings along the fault trace that may be of Chiribayas age. Our surface faulting observations, when combined with observations of deformation in the forearc from geodesy and seismology, also demonstrate that the forearc in South Peru experiences a complex, time-varying pattern of permanent strain, with evidence for trench-parallel shortening, trench-parallel extension, and trench-perpendicular shortening all in close proximity but in different periods of the megathrust earthquake cycle. The kinematics of recent slip on the Incapuquio Fault are consistent with the sense of interseismic strain within the forearc measured by GPS, suggesting the fault is loaded toward failure between megathrust earthquakes.

Résumé: The North Anatolian Fault (NAF) in the Marmara region is composed of three parallel strands all separated by similar to 50 km. The activity of the middle strand, which borders the southern edge of the Marmara Sea, is much debated because of its present-day very low seismicity. This contrasts with historical, archeological and paleoseismological evidence, which suggest several destructive earthquakes have occurred during the last 2000 years. Our study aims to better constrain seismic hazard on the middle strand by exploring its Holocene paleoseismicity. For this, we mapped 148 km of the eastern part of the middle strand, using high-resolution satellite imagery. A series of landforms offset by the middle strand activity have been systematically measured to recover the past ruptures. Three Late Pleistocene-Holocene terraces have been dated with the terrestrial cosmogenic nuclide method, constraining a horizontal slip rate of 4.4-2.8+10.6 mm/yr. The statistical analysis of the offsets evidences several major ruptures preserved in the landscape, with coseismic lateral displacements ranging between 3 and 6.5 m. This corresponds to Mw similar to 7.3 earthquakes able to propagate along several fault segments. Historical seismicity and paleoseismology data suggest that the last large earthquakes along the middle strand of the NAF (MNAF) happened in 1065 CE and between the 14th and 18th centuries CE. Since then, the MNAF may have accumulated enough stress to generate a destructive rupture.

Résumé: New detrital apatite and zircon fission-track thermochronology ages were determined in four rivers (Onzaga, Los Micos, Mogoticos, and Chaguaca) located along the southern termination of the Bucaramanga Fault System in the Eastern Cordillera of Colombia. Younger populations of apatite fission-track (AFT) ages were found in the Onzaga and Los Micos rivers, both draining the central zone of a transpressive system. The detrital thermochronological data are used to estimate erosion rates, assuming topographic steady-state and spatially variable conditions. We also tested the link between long-to short-term erosion patterns employing Hotspot and Cluster Analysis (HCA) of Hack's stream length index (SL), which enables us to detect transient signals related to landsliding, lithologic variability, or tectonic processes. Based on this classification, we identified 175 SL-HCA anomalies distributed across the study area but mainly concentrated on the western side of the Chicamocha River where gigantic landslides are present. This topographic analysis reveals knickzones where higher erosion rates are expected. Consequently, those hotspots are the source of much of the sediment being evacuated through the Chicamocha River system. This favours the hypothesis that the area has spatially variable topographic conditions over time. To test this, we compare observed and predicted detrital age distributions derived from 3D thermal-kinematic inversions of existing in-situ thermochronological data assuming the two different topography conditions. We show that exhumation rates calculated with the bootstrapping method are closer to the predictions obtained from our 3D thermal-kinematic models with a spatially variable topography assumption. Furthermore, for the Onzaga River, the comparison of cumulative density functions between observed and predicted ages are statistically similar, which validates our hypothesis. Our results demonstrate that the topography has been variable over time, mainly from 40 Ma to the present. Exhumation rates in the study area evolved from similar to 2 km/m.y. between similar to 40 and 30 Ma, decreasing to values below 0.1 km/m.y. from 30 to 25 Ma, before increasing to 0.5 km/m.y. from similar to 20 Ma to the present. The results also indicate that a paleotopography representing 10 to 50% of the current topography was present from 80 to 40 Ma. During the interval between 40 Ma to the present, the model suggests that more than 50% of the present-day topography was created.

Résumé: The Avignonet landslide in the Trieves area is made of Quaternary paraglacial sediments among which imbricated till, glacio-lacutrine and fluviatil layers. Numerous boreholes (drillings and corings) were conducted during the mid-1980s and the mid-2000s to assess the geological and geotechnical setting of the inhabited, southern part of this slow-moving earthslide. Heterogeneous paramaters available from these different boreholes make interpretation difficult. Gamma-ray logging along with magnetic susceptibility and pocket vane tests on core samples allowed to distinguish between the different lithological and geotechnical units. Mechanical strength obtained from drilling parameter recording acquired during drilling was correlated to corings and their combination, along with outcrop observations, was used to delineate the lithological units and shear surfaces. The joint analysis of the dataset with outcrop observations and chronological data reveals a high geological complexity with the intrication of various sedimentary units. Two ancient landslides, several tens of metres in width, were furthermore identified within the large Avignonet landslide, almost 2 km in width. All the results point toward a high lithological and hydrogeological complexity that impacts the dynamics of the landslide. This work shows the interest of a multi-proxy approach in studies involving Quaternary sedimentary units. The methodology developed here could be applied to other sites with different palaeoenvironmental contexts initially exhibiting sedimentary compaction, such as lacustrine or coastal environments.

Résumé: In the Western Alps, the Penninic frontal thrust (PFT) is the main crustal-scale tectonic structure of the belt. This thrust transported the high-pressure metamorphosed internal units over the non-metamorphosed European margin during the Oligocene (34-29 Ma). Following the propagation of the compression toward the European foreland, the PFT was later reactivated as an extensional detachment associated with the development of the High Durance extensional fault system (HDFS). This inversion of tectonic displacement along a major tectonic structure has been widely emphasized as an example of extensional collapse of a thickened collisional orogen. However, the inception age of the extensional inversion remains unconstrained. Here, for the first time, we provide chronological constraints on the extensional motion of an exhumed zone of the PFT by applying U-Pb dating on secondary calcites from a fault zone cataclasite. The calcite cement and veins of the cataclasite formed after the main fault slip event, at 3.6 +/- 0.4-3.4 +/- 0.6 Ma. Crosscutting calcite veins featuring the last fault activity are dated at 2.6 +/- 0.3-2.3 +/- 0.3 Ma. delta C-13 and delta O-18 fluid signatures derived from these secondary calcites suggest fluid percolation from deep-seated reservoir at the scale of the Western Alps. Our data provide evidence that the PFT extensional reactivation initiated at least similar to 3.5 Myr ago with a reactivation phase at similar to 2.5 Ma. This reactivation may result from the westward propagation of the compressional deformation toward the external Alps, combined with the exhumation of external crystalline massifs. In this context, the exhumation of the dated normal faults is linked to the eastward transla- tion of the HDFS seismogenic zone, in agreement with the present-day seismic activity.

Résumé: Ambient Vibration-Based Structural Health Monitoring (AVB-SHM) studies on prone-to-fall rock compartments have recently succeeded in detecting both pre-failure damaging processes and reinforcement provided by bolting. The current AVB-SHM instrumentation layout is yet generally an overkill, creating cost and power issues and sometimes requiring advanced signal processing techniques. In this article, we paved the way toward an innovative edge-computing approach tested on ambient vibration records made during the bolting of a similar to 760 m(3) limestone rock column (Vercors, France). First, we established some guidelines for prone-to-fall rock column AVB-SHM by comparing several basic, computing-efficient, seismic parameters (i.e., Fast Fourier Transform, Horizontal to Vertical and Horizontal to Horizontal Spectral Ratios). All three parameters performed well in revealing the unstable compartment's fundamental resonance frequency. HHSR appeared as the most consistent spectral estimator, succeeding in revealing both the fundamental and higher modes. Only the fundamental mode should be trustfully monitored with HVSR since higher peaks may be artifacts. Then, the first application of a novelty detection algorithm on an unstable rock column AVB-SHM case study showed the following: the feasibility of automatic removing the adverse thermomechanical fluctuations in column's dynamic parameters based on machine learning, as well as the systematic detection of clear, permanent change in column's dynamic behavior after grout injection and hardening around the bolts (i(1) and i(2)). This implementation represents a significant workload reduction, compared to physical-based algorithms or numerical twin modeling, and shows better robustness with regard to instrumentation gaps. We believe that edge-computing monitoring systems combining basic seismic signal processing techniques and automatic detection algorithms could help facilitate AVB-SHM of remote natural structures such as prone-to-fall rock compartments.

Résumé: Komatiites and sedimentary rocks sampled during the International Continental Drilling Program (BARB1-2-3-4-5) in the Barberton greenstone belt, South Africa, were analyzed for Sm-146-Nd-142 systematics. Resolved negative μNd-142 values (down to -7.7 +/- 2.8) were identified in komatiites from the 3.48 Ga Komati Formation and this signature correlates with low Hf/Sm ratios measured in these samples. The negative μNd-142 point to a source with subchondritic Sm/Nd ratio which formed during the Hadean. No analytically resolvable Nd-142 anomalies were measured in crustal detritus-rich, Si-rich, Ca-Fe-rich sediments and cherts from the Buck Reef (3.42 Ga) and the Fig Tree Group (3.23-3.28 Ga). Our new measurements are incorporated into a larger set of Sm-147-Nd-143 and Lu-176-Hf-176 data to better understand the Nd-142,Nd-143-Hf-176 isotope signatures in the mantle source at the time of komatiite crystallization. Our calculations show that the Nd-142,Nd-143-Hf-176 isotope signatures and Hf/Sm ratios cannot be produced by recycling into the komatiite source of detrital sediments like those sampled in the Barberton area. Only cherts have the required trace element characteristics – low Hf/Sm, radiogenic epsilon Hf-176 -but the trace element concentrations in the cherts are so low that unrealistic amounts of chert would need to be added. We propose a four-stage model for the formation of these rocks. Negative μNd-142 and low Hf/Sm ratios developed during the crystallization of a deep magma ocean soon after Earth accretion. The material that ultimately became the source of komatiites was a residual liquid produced by 50% crystallization leaving a bridgmanite/ferropericlase/Ca-perovskite cumulate. The Lu-Hf and Sm-Nd isotope systems were decoupled at this stage. After extinction of Sm-146 around 4 Ga, parent/daughter ratios fractionated during a melt extraction event. With this model we explain the positive epsilon Hf-176 and slightly negative epsilon Nd-143 in these samples. The 3.55 Ga Schapenburg komatiites in another part of the Barberton belt share similar chemical signatures, supporting our model of fractionation in a deep magma ocean early in Earth's history. (C) 2021 Elsevier Ltd. All rights reserved.

Résumé: The Earth's mantle exhibits marked chemical heterogeneity. We provide an examination of thallium systematics in ocean island basalts (OIB): new high-precision trace element analyses, including Tl, and Tl isotopic compositions for 48 OIB spanning the entire range of observed Sr-Nd-Hf-Pb isotope ratios. All investigated OIB are characterised by ubiquitous Tl depletion requiring OIB mantle sources to have Tl concentrations as low as 0.2 ng/g, which is an order of magnitude lower than estimates for the primitive mantle and similar to Tl concentrations inferred for the depleted mantle. The low Tl concentrations inferred for OIB mantle sources are interpreted to reflect near quantitative removal of Tl during subduction and inefficient Tl recycling into the deeper mantle. If true, the Tl isotopic composition of surface materials may not be readily translated to the mantle sources of OIB. The new OIB dataset shows a >10 epsilon-unit range in primary isotopic variation, from epsilon Tl-205 = -6.4 to +6.6. However, the majority of samples (32 of 48) are within uncertainty of mantle values (epsilon Tl-205 = -2d +/- 1), and show no co-variation with radiogenic isotopic composition. Notably, OIB with only minor Tl depletion (11 samples) have Tl isotopic compositions outside the mantle range. The Tl concentration contrast between the mantle and inputs such as sediments and altered basalt is so great that minor additions (<1% by mass) of high-Tl material will dominate the isotopic budget of a lava, with decoupling of Tl and radiogenic isotopic compositions as an expected result. Thallium isotopic compositions of OIB are therefore difficult to link directly to radiogenic isotope variations and the mantle components they may reflect. Indeed, if isotopically distinct Tl from altered oceanic crust and/or sediments were efficiently recycled into the mantle and sampled via OIB, more variation in the Tl isotopic composition of OIB would be expected than is observed. The markedly unsystematic primary Tl isotopic variations in OIB therefore likely reflect the residual Tl isotopic composition of subducted material, and/or Tl acquired en route to the surface via shallow-level crustal assimilation. (C) 2021 Elsevier Ltd. All rights reserved.

Résumé: Continental sedimentation was widespread across the Central Anatolian Plateau in MiocenePliocene time, during the early stages of plateau uplift. Today, however, most sediment produced on the plateau is dispersed by a well-integrated drainage and released into surrounding marine depocenters. Residual long-term (10(6)-10(7) yr) sediment storage on the plateau is now restricted to a few closed catchments. Lacustrine sedimentation was widespread in the Miocene-Pliocene depocenters. Today, it is also restricted to the residual closed catchments. The present-day association of closed catchments, long-term sediment storage, and lacustrine sedimentation suggests that the Miocene-Pliocene sedimentation also occurred in closed catchments. The termination of sedimentation across the plateau would therefore mark the opening of these closed catchments, their integration, and the formation of the present-day drainage. By combining newly dated volcanic markers with previously dated sedimentary sequences, we show that this drainage integration occurred remarkably rapidly, within 1.5 m.y., at the turn of the Pliocene. The evolution of stream incision documented by these markers and newly obtained Be-10 erosion rates allow us to discriminate the respective contributions of three potential processes to drainage integration, namely, the capture of closed catchments by rivers draining the outer slopes of the plateau, the overflow of closed lakes, and the avulsion of closed catchments. Along the southern plateau margin, rivers draining the southern slope of the Central Anatolian Plateau expanded into the plateau interior; however, only a small amount of drainage integration was achieved by this process. Instead, avulsion and/or overflow between closed catchments achieved most of the integration, and these top-down processes left a distinctive sedimentary signal in the form of terminal lacustrine limestone sequences. In the absence of substantial regional climate wetting during the early Pliocene, we propose that two major tectonic events triggered drainage integration, separately or in tandem: the uplift of the Central Anatolian Plateau and the tectonic completion of the Anatolian microplate. Higher surface uplift of the eastern Central Anatolian Plateau relative to the western Central Anatolian Plateau promoted more positive water balances in the eastern catchments, higher water discharge, and larger sediment fluxes. Overflow/avulsion in some of the eastern catchments triggered a chain of avulsions and/or overflows, sparking sweeping integration across the plateau. Around 5 Ma, the inception of the full escape of the Anatolian microplate led to the disruption of the plateau surface by normal and strike-slip faults. Fault scarps partitioned large catchments fed by widely averaged sediment and water influxes into smaller catchments with more contrasted water balances and sediment fluxes. The evolution of the Central Anatolian Plateau shows that top-down processes of integration can outcompete erosion of outer plateau slopes to reintegrate plateau interior drainages, and this is overlooked in current models, in which drainage evolution is dominated by bottom-up integration. Top-down integration has the advantage that it can be driven by more subtle changes in climatic and tectonic boundary conditions than bottom-up integration.

Résumé: Regime shifts are major reorganization of ecological processes, creating new sets of mechanisms that drive the new ecological regime. Such rearrangements can affect how and how much the system responds to pressures other than those that created the shift (interactive carryover). Lake Geneva still exhibits high levels of productivity despite reductions in phosphorus to its reference baseline; the continued high productivity is likely due to the synergistic effects of climate change. We tested whether the contemporary Lake Geneva plankton community response to air temperature, one symptom of climate change, differed from the responses to past changes in air temperature. We used paleoecology to quantify the changes in plankton communities, as a proxy of general ecological changes, over the past 1500 years. Our results show that from 563 AD (beginning of the record) to the twentieth century, the cladoceran assemblage remained stable, despite climate variability of 3 degrees C in air temperature. The plankton community of Lake Geneva appeared to shift for the first time in the 1500 year record in 1946, and dynamic linear models suggested that 1958-1961 was a critical transition period when the ecosystem changed state. Littoral species were lost, and the assemblage became dominated by pelagic species. The shift took place around the beginning of the current long-term monitoring program, when local perturbations (eutrophication) were escalating. Our results suggest that eutrophication acted as a switch towards a lake more vulnerable to climate change.

Résumé: Fluid-escape structures within sedimentary basins permit pressure-driven focused fluid flow through inter-connected faults, fractures and sediment. Seismically-imaged chimneys are recognised as fluid migration path-ways which cross-cut overburden stratigraphy, hydraulically connecting deeper strata with the seafloor. How-ever, the geological processes in the sedimentary overburden which control the mechanisms of genesis and temporal evolution require improved understanding. We integrate high-resolution 2D and 3D seismic reflection data with sediment core data to characterise a natural, active site of seafloor methane venting in the UK North Sea and Witch Ground Basin, the Scanner pockmark complex. A regional assessment of shallow gas distribution presents direct evidence of active and palaeo-fluid migration pathways which terminate at the seabed pock-marks. We show that these pockmarks are fed from a methane gas reservoir located at 70 m below the seafloor. We find that the shallow reservoir is a glacial outwash fan, that is laterally sealed by glacial tunnel valleys. Overpressure generation leading to chimney and pockmark genesis is directly controlled by the shallow geological and glaciogenic setting. Once formed, pockmarks act as drainage cells for the underlying gas accu-mulations. Fluid flow occurs through gas chimneys, comprised of a sub-vertical gas-filled fracture zone. Our findings provide an improved understanding of focused fluid flow and pockmark formation within the sediment overburden, which can be applied to subsurface geohazard assessment and geological storage of CO2.

Résumé: The main event responsible for the deposition of tungsten at Panasqueira was closely associated with strong tourmalinization of the wall rocks. Tourmaline is coeval with a W-rich rutile (up to 8-10 wt % W), and both minerals record an early introduction of W in the system, just before the main W deposition. Uranium-Pb dating of the rutile by LA-ICP-MS yielded an age of 305.2 +/- 5.7 Ma, which is 6 to 10 m.y. older than the K-Ar age of 296.3 +/- 1.2 Ma obtained on muscovite, which was therefore not coeval with wolframite. Major and trace element concentration variations in tourmaline record fluid mixing between two end members, both considered to be of metamorphic derivation on the basis of rare earth element profiles. We report evidence for a fluid rich in Co, Cu, Pb, Sc, Sr, V, Cr, Nb, Ta, and Sn interpreted to be of local origin-e.g., well equilibrated with the host formations-and a fluid rich in Li, F, Fe, Mn, and W inferred to be of deep origin and related to biotite dehydration. The second fluid carried the metals (in particular Fe and Mn) that were necessary for wolframite deposition and that were not necessarily inherited from the wall rocks through fluid-rock interaction. Micrometer-scale variations in tourmaline and rutile crystal chemistry are indicative of pulsatory fluid input during tourmalinization.

Résumé: An unusually damaging Mw 4.9 earthquake occurred on November 11, 2019 in the south east of France within the lower Rhone river valley, an industrial region that hosts several operating nuclear power plants. The hypocentre of this event occurred at an exceptionally shallow depth of about 1km. Here we use far-field seismological observations to demonstrate that the rupture properties are consistent with those commonly observed for large deeper earthquakes. In the absence of strong motion sensors in the fault vicinity, we perform numerical predictions of the ground acceleration on a virtual array of near-fault stations. These predictions are in agreement with independent quantitative estimations of ground acceleration from in-situ observations of displaced objects. Both numerical and in-situ analyses converge toward estimates of an exceptional level of ground acceleration in the fault vicinity, that locally exceeded gravity, and explain the unexpectedly significant damage. The 2019 Le Teil earthquake caused shaking and ground acceleration exceeding gravity and far greater than the levels expected for such a moderate sized earthquake, according to a combination of numerical predictions and in-situ observations.

Résumé: Subsurface habitats on Earth host an extensive extant biosphere and likely provided one of Earth's earliest microbial habitats. Although the site of life's emergence continues to be debated, evidence of early life provides insights into its early evolution and metabolic affinity. Here, we present the discovery of exceptionally well-preserved, similar to 3.42-billion-year-old putative filamentous microfossils that inhabited a paleo-subseafloor hydrothermal vein system of the Barberton greenstone belt in South Africa. The filaments colonized the walls of conduits created by low-temperature hydrothermal fluid. Combined with their morphological and chemical characteristics as investigated over a range of scales, they can be considered the oldest methanogens and/or methanotrophs that thrived in an ultramafic volcanic substrate.

Résumé: An emerged coral reef terrace sequence flanks the northern coast of Sumba Island in Indonesia. The sequence was created by the joint effects of uplift and Quaternary sea level oscillations. Since its emergence, it undergoes chemical erosion, which is facilitated by its carbonate lithology. The morphology is dissected by multiple catchments drained by deep canyons, whose stream profiles display several knickpoints. We applied a multi-methods approach using high-resolution topographic data (Pleiades imagery), geomorphological analysis and denudation rates derived from Cl-36 cosmogenic nuclide concentrations to characterize the dynamics of these coastal drainages. We specifically investigate (1) the channel response to eustatic forcing, by analyzing knickpoint dynamics along a longitudinal river profile, and (2) the control of internal and external forcing over the catchment-scale erosion. Firstly, knickpoints form at the distal edge of the emergent reef at each regressive stage following a sea level highstand. The knickpoint propagates and rotates upward by regressive erosion. Knickpoint propagation rate decreases sharply over time until it becomes negligible before the next sea-level rise, which implies a marked decline in knickpoint retreat rate before its resorption. We attribute the inability of the river at Cape Laundi to fully propagate eustatic oscillations to its low stream discharge and low sediment supply, related to its small drainage area, to the karstic nature of the coral reef terraces composing the sequence, and to the high frequency of eustatic forcing. Secondly, average denudation rates calculated from Cl-36 cosmogenic nuclide concentrations of sands collected at the outlet of five catchments draining the sequence amount to 69 +/- 8 mm.ka(-1). We emphasize the role of canyon areas in driving the denudation of the major catchments. However, no first-order correlation has been observed between catchment metrics, uplift rates and denudation rates. Finally, our correlations between catchment finite eroded volumes and uplift rates highlight the tendency of catchments to widen with low uplift rate and to lengthen while incising the sequence deeply with higher uplift rates. (c) 2021 Elsevier B.V. All rights reserved.

Résumé: Opal is a mineral of great interest for tracing the aqueous Mars' history. Detection of opal on Mars is based on the near infrared (NIR) absorption bands related to the presence of water and hydroxyl. Because pressure and temperature can affect the amount and configuration of water in hydrated minerals, the associated absorption bands vary according to the environmental conditions at the surface of Mars. In this study, the effects of Mars' relevant surface pressure and temperature on opal's NIR signature was investigated. By exposing opal samples to pressures varying between 1 and 8 mbar, and temperatures between -51.1 and -96.5 degrees C, significant changes in opal samples' NIR features were observed. It was demonstrated that opal releases molecular water at low pressure, inducing changes on all NIR bands, as observed in previous studies. However, such dehydration was not systematic, as it was observed for only six out thirteen opal samples. When exposed to low temperature, water molecules in opal froze, inducing significant variation in shape and position of the bands at 5200 cm(-1) and 7000 cm(-1) (1.9 μm and 1.4 μm respectively). Low temperature experiments demonstrate that opal, and particularly opal-CT, can exhibit a water ice-like spectral signature. Such experimental data were compared with silica signature detected on Mars by CRISM and it was evident that martian opaline silica has a spectral signature specific of water ice, notably a shoulder near 5100 cm(-1) (1.96 μm) and a wider 7000 cm(-1) (1.4 μm) feature. We show that opal can retain water under martian conditions, an interesting property for sample return missions. (C) 2021 Elsevier B.V. All rights reserved.

Résumé: We propose a new surface wave tomography approach that benefits from densely sampled active-source arrays and brings together elements from active-source seismic-wave interferometry, full waveform inversion and dense-array processing. In analogy with optical interferometry, seismic Michelson interferometer (SMI) uses seismic interference patterns given by the data-based diffraction kernels in an iterative inversion scheme to image a medium. SMI requires no traveltime measurements and no spatial regularization, and it accounts for bent rays. Furthermore, the method does not need computation of complex synthetic models, as it works as a data-driven inversion technique that makes it computationally very fast. In an automatic way, it provides high-resolution phase-velocity maps and their error estimation. SMI can complete traditional surface wave tomography studies, as its use can be easily extended from land active seismic data to the virtual source gathers of ambient-noise-based studies with dense arrays.

Résumé: The Tolhuaca hydrothermal system is one of the few attested geothermal resources in Chile. While recent investigations provided some insights into the depth and temperature of the geothermal reservoirs and the chemical and mineralogical evolution of the hydrothermal system, little is still known about the CO2 degassing of the system and the local and shallow control of fluid pathways. Here, we document the soil CO2 degassing and soil temperature distributions in the southern part of the Tolhuaca hydrothermal system and at one of its northern fumaroles, and provide a first estimate of its total CO2 release. The surveyed area is responsible for a total CO2 emission of up to 30 t d(-1). Hydrothermal CO2 emissions (similar to 4-27 t d(-1)) are mostly restricted to the thermal manifestations or generally distributed along NNW trending lineaments, sharing the same orientation as the volcanic vents and thermal springs and fumaroles. Hydrothermal CO2 fluxes, fumaroles and thermal springs are generally encountered in topographic lows, in close vicinity of streams and often in clay-rich pyroclastic units, highlighting a relation between landscape evolution and the activity of the hydrothermal system. We suggest that glacial unloading and incision of the stream inside the clay-rich units have likely enhanced locally the permeability, creating a preferential pathway for the migration of deeper fluid to the surface. As several hydrothermal systems in the Andes are found on the flank of volcanoes hosting glaciers, we propose that they could have had a similar development to that of the Tolhuaca hydrothermal system. (C) 2021 The Author(s). Published by Elsevier B.V.

Résumé: Remote sensing techniques are leading methodologies for landslide characterization and monitoring. However, they may be limited in highly vegetated areas and do not allow for continuously tracking the evolution to failure in an early warning perspective. Alternative or complementary methods should be designed for potentially unstable sites in these environments. The results of a six-month passive seismic monitoring experiment on a prone-to-fall quartzite tower are here presented. Ambient seismic noise and microseismicity analyses were carried out on the continuously recorded seismic traces to characterize site stability and monitor its possible irreversible and reversible modifications driven by meteorological factors, in comparison with displacement measured on site. No irreversible modifications in the measured seismic parameters (i.e., natural resonance frequencies of the tower, seismic velocity changes, rupture-related microseismic signals) were detected in the monitored period, and no permanent displacement was observed at the tower top. Results highlighted, however, a strong temperature control on these parameters and unusual preferential vibration directions with respect to the literature case studies on nearly 2D rock columns, likely due the tower geometric constraints, as confirmed by 3D numerical modeling. A clear correlation with the tower displacement rate was found in the results, supporting the suitability of passive seismic monitoring systems for site characterization and early waning purposes.

Résumé: The continental shelf north of Central Venezuela is partially or completely structurally controlled by major right lateral strike slip active faults (e.g San Sebastian fault), comprising three physiographic provinces, from west to east: The Golfo Triste Playorm, the Choroni Basin and the La Guaira Platform. The two mentioned platforms are of erosional type while the Choroni basin is a deep depression, which is incised by submarine canyons. These canyons seem to be related to turbidity currents with greater flows during the Pleistocene wetter periods. "Wowing several authors, there submarine canyons are partially or completely structurally controlled by major structures present in the north-central coastal range of Venezuela. Five major regional uncon-formities and/or seismostratigraphic limits have been identified GVe propose to correlate the most recent to MIS 2 (Last Glacial Maximum similar to 20 ka) lowstand. The chronological significance of the deepest detected major uncomformity (strong erasion) is tentatively attributed to MIS 6 (similar to 130 ka) lowstand. Based on the present-day position of the later one, we propose an estimation of similar to 1.2 mm.y(-1) of the mean subsidence rate in the La Guaira Shelf; considering that the obtained value may locally represent a minor vertical component of the dominantly horizontal displacement along the San Sebastian Fault. The San Sebastian fault shows a linear deformation in the eastern profiles. In contrast to the west, we observe in some profiles an intense deformation zone.

Résumé: Volcanoes are traditionally considered isolated with an activity that is mostly independent of the surrounding, with few eruptions only (<2%) associated with a tectonic earthquake trigger. Evidence is now increasing that volcanoes forming clusters of eruptive centers may simultaneously erupt, show unrest, or even shut-down activity. Using infrared satellite data, we detail 20 years of eruptive activity (2000-2020) at Klyuchevskoy, Bezymianny, and Tolbachik, the three active volcanoes of the Klyuchevskoy Volcanic Group (KVG), Kamchatka. We show that the neighboring volcanoes exhibit multiple and reciprocal interactions on different timescales that unravel the magmatic system's complexity below the KVG. Klyuchevskoy and Bezymianny volcanoes show correlated activity with time-predictable and quasiperiodic behaviors, respectively. This is consistent with magma accumulation and discharge dynamics at both volcanoes, typical of steady-state volcanism. However, Tolbachik volcano can interrupt this steady-state regime and modify the magma output rate of its neighbors for several years. We suggest that below the KVG the transfer of magma at crustal level is modulated by the presence of three distinct but hydraulically connected plumbing systems. Similar complex interactions may occur at other volcanic groups and must be considered to evaluate the hazard of grouped volcanoes.

Résumé: The adsorption of two pharmaceuticals, carbamazepine and paracetamol, onto the expandable clay mineral saponite has been studied through the combination of kinetic experiments, X-ray diffraction, and theoretical modeling. Kinetic experiments indicate low adsorption for carbamazepine and paracetamol on expandable smectite clay. Accordingly, X-ray diffraction experiments show that neither compound enters smectite interlayer space. Molecular dynamics simulations were carried out to understand the interactions between the two pharmaceuticals and the saponite basal surface in the presence of Na+ cations. Calculations reveal that paracetamol almost does not coordinate solution cations, whereas a rather low coordination to cation is observed for carbamazepine. As a result, the adsorption onto the clay surface results mainly from van der Waals interactions for both pharmaceuticals. Carbamazepine does adsorb the surface via two configurations, one involving cation coordination, which corresponds to a rather stable adsorption compared to paracetamol. This is confirmed by structural analyses completed with desorption free energy profile.

Résumé: On November 11, 2019, a M-w 4.9 earthquake hit the region close to Montelimar (lower Rhone Valley, France), on the eastern margin of the Massif Central close to the external part of the Alps. Occuring in a moderate seismicity area, this earthquake is remarkable for its very shallow focal depth (between 1 and 3 km), its magnitude, and the moderate to large damages it produced in several villages. InSAR interferograms indicated a shallow rupture about 4 km long reaching the surface and the reactivation of the ancient NE-SW La Rouviere normal fault in reverse faulting in agreement with the present-day E-W compressional tectonics. The peculiarity of this earthquake together with a poor coverage of the epicentral region by permanent seismological and geodetic stations triggered the mobilisation of the French post-seismic unit and the broad French scientific community from various institutions, with the deployment of geophysical instruments (seismological and geodesic stations), geological field surveys, and field evaluation of the intensity of the earthquake. Within 7 days after the mainshock, 47 seismological stations were deployed in the epicentral area to improve the Le Teil aftershocks locations relative to the French permanent seismological network (RESIF), monitor the temporal and spatial evolution of microearthquakes close to the fault plane and temporal evolution of the seismic response of 3 damaged historical buildings, and to study suspected site effects and their influence in the distribution of seismic damage. This seismological dataset, completed by data owned by different institutions, was integrated in a homogeneous archive and distributed through FDSN web services by the RESIF data center. This dataset, together with observations of surface rupture evidences, geologic, geodetic and satellite data, will help to unravel the causes and rupture mechanism of this earthquake, and contribute to account in seismic hazard assessment for earthquakes along the major regional Cevenne fault system in a context of present-day compressional tectonics.

Résumé: Temporal reconstruction of Hg deposition from sediment archives is relatively straightforward in organic-rich or high sedimentation rate environments, such as lakes and ocean margins. To retrieve long-term records at regional or global scales, deep-sea sediments are more appropriate, but such records are scarce and their reliability has been questioned because of possible post-depositional Hg diagenetic remobilization. Here, we investigated the accumulation of Hg in the Balearic Abyssal Plain (2850 m deep) of the Western Mediterranean through a comprehensive characterization of the chemical and isotopic composition (organic carbon, nitrogen, sulfur, major and redox-sensitive elements) of sediment trap material and sediment cores. The analysis of material collected in the sediment traps, deployed at 250, 1440, and 2820 m, indicates that Hg is (i) partially re-emitted to the atmosphere and mobilized in the twilight zone and that (ii) the Hg downward flux depends on the primary production in surface waters, suggesting that organic matter (OM) acts as the main Hg-carrier phase. As the Hg concentrations of material collected in the traps vary little with depth but the Hg: C-org ratio of the settling particulate matter decreases with depth, Hg must be re-adsorbed onto the more refractory fraction of the settling OM. Results of selective chemical extractions of the sediment indicate that Hg is very weakly coupled to the iron cycle but strongly associated with sulfur, supporting the assumption that its vertical distribution was only weakly altered by diagenetic remobilization. In addition, the distributions of S and delta S-34 in the sedimentary column exclude the possibility that local volcanism impacted on Hg enrichment of the sediments. Accordingly, a reconstruction of Hg accumulation rates (Hg-AR) during the Late Holocene is readily achieved. Biological mixing and smoothing of the sediment record, as revealed by the distribution of radionuclides in surface sediments, was considered in the interpretation of the Hg-AR record. The first anthropogenic Hg signal recorded in the studied cores corresponds to the Iron Age and the Roman Empire period, as Hg-ARs rose from the baseline (0.7 +/- 0.2 μg m(-2) yr(-1)) to an average value of 2.2 +/- 0.5 μg m(-2) yr(-1). The Hg-ARs return to baseline values at the decline of the Roman Empire, display a small increase during the Medieval Period (1.5 +/- 0.5 μg m(-2) yr(-1)), increase abruptly at the onset of the Industrial Era, leading to a similar to 10-fold increase in Hg deposition in the last 120 years (8.9 +/- 1.4 μg m(-2) yr(-1)), and retreat progressively over the past 50 years. (C) 2021 Elsevier Ltd. All rights reserved.

Résumé: Repeated periods of inflation-deflation in the vicinity of Mt. thorn orbjorn-Svartsengi, SW-Iceland, were detected in January-July, 2020. We used seismic ambient noise and interferometry to characterize temporal variations of seismic velocities (dv/v, %). This is the first time in Iceland that dv/v variations are monitored in near real-time during volcanic unrest. The seismic station closest to the inflation source center (similar to 1 km) showed the largest velocity drop (similar to 1%). Different frequency range measurements, from 0.1 to 2 Hz, show dv/v variations, which we interpret in terms of varying depth sensitivity. The dv/v correlates with deformation measurements (GPS, InSAR), over the unrest period, indicating sensitivity to similar crustal processes. We interpret the velocity drop to be caused by crack opening triggered by intrusive magmatic activity. We conclude that single-station cross-component analyses provide the most robust solutions for early detection of magmatic activity.

Résumé: In recent years, the permanent seismic networks worldwide have largely increased, raising the amount of earthquake signals and the applications using seismic records. Although characterization of the soil properties at recording stations has a large impact on hazard estimates, it has not been implemented so far in a standardized way for reaching high-level metadata. To address this issue, we built an online questionnaire for the identification of the indicators useful for a reliable site characterization at a seismic station. We analysed the answers of a large number of experts in different fields, which allowed us to rank 24 different indicators and to identify the most relevant ones: fundamental frequency (f(0)), shear-wave velocity profile (V-S), time-averaged Vs over 30 m (V-S30), depth of seismological and engineering bedrock (H-seis bed and H-engbed), surface geology and soil class. Moreover, the questionnaire proposed two additional indices in terms of cost and difficulty to obtain a reliable value of each indicator, showing that the selection of the most relevant indicators results from a complex balance between physical relevancy, average cost and reliability. For each indicator we propose a summary report, provided as editable pdf, containing the background information of data acquisition and processing details, with the aim to homogenize site metadata information at European level and to define the quality of the site characterization (see companion paper Di Giulio et al. 2021). The selected indicators and the summary reports have been shared within European and worldwide scientific community and discussed in a dedicated international workshop. They represent a first attempt to reach a homogeneous set of high-level metadata for site characterization.

Résumé: Which physical parameters are the most influential when predicting earthquake ground motions in a 3-D sedimentary basin? We answer quantitatively by doing a global sensitivity analysis of two quantities of interest: the peak ground motions (PGMs) and a time frequency representation (the S transform) of ground motions resulting from the synthetic anelastic responses of the EUROSEISTEST. This domain of interest is modeled by two layers with uncertain depth-dependent mechanical properties and is illuminated by a plane S-wave propagating vertically upward in an uncertain homogeneous elastic bedrock. The global sensitivity analysis is conducted on 800+ physics-based simulations of the EUROSEISTEST requiring 8+ million core-hours (i.e. approximate to 900 yr of mono-core computation). The analysis of the PGMs at the free surface displays the spatial influence of the uncertain input parameters over the entire basin scale, while the analysis of the time-frequency representation shows their influence at a specific location inside the basin. The global sensitivity analysis done on the PGMs points out that their most influential parameter in the middle of the basin is the quality factor Qs (it controls up to 80 per cent of the PGMs in certain locations where the sediments thickness is larger than 200 m). On the other hand, the geological layering configuration (here represented by the depth of a geological interface controlling the geological layering) strongly influences the PGMs close to the basin edges, up to 90 per cent. We also found that the shear wave velocity at the free surface of the basin and the one of the bedrock underlying the basin are to be considered on an equal footing, both influencing the PGMs in the middle of the basin and close to its edges. We highlight that the bedrock to basin amplification of the PGMs shows a clear increase with respect to the thickness of the sediments, but this amplification saturates from 200 m of sediments around the value of three and is frequency dependent. This PGMs amplification starts from about one tenth of the mean S-wavelength propagating in the basin. The global sensitivity analysis done on the S transform of the ground motions shows that (i) the own effect of the parameters fully controls the first S-wave train and mostly controls the direct arrival of the basin-induced surfaces waves, (ii) the quality factor Qs controls 40-60 per cent of the decay of amplitude of coda waves, the remaining part being mainly controlled by interaction effects due to the coupling effect of several parameters and (iii) the interaction effects between the parameters increases with time, suggesting under the hypotheses of our study that the own effects control the ballistic wave propagation while the interaction effects control the diffusive wave propagation.

Résumé: Rare earth elements (REE) speciation in laterites are commonly estimated from sequential extraction procedure (SEP). In this study, the selectivity of a 5-steps SEP protocol was evaluated on individual synthetic Ce-material and applied to a well-characterized lateritic profile developing over a granite bedrock (Madagascar). The synthetic Ce-materials are representative of laterite minerals: Ce-doped oxyhydroxides and kaolinite, cerianite, Cerhabdophane and Ce-bastnasite. The morphology, specific surface area, Ce sorption concentrations were thoroughly characterized prior to SEP. X-Ray absorption spectroscopy on synthetic material indicates that Ce(III) dominates apart for cerianite and Mn-oxide. The evaluation of the 5-steps SEP scheme shows that reagent selectivity is generally good, but the use of hydroxylamine hydrochloride is strongly discouraged. First, distinction between Ce sorbed at the surface of Mn- and amorphous or crystalline Fe-oxyhydroxides remains ambiguous. Second, Ce-rhabdophane (phosphate) and Ce-bastnasite (carbonate) dissolve partially with this reagent. These experimental results combined with previous mineralogical and geochemical characterization were fundamental to interpret SEP results in the laterite profile from Madagascar. In the three laterite samples from the A-, B- and C-horizons, it is proposed that REE mainly distribute in authigenic phosphates and Fe- and (Mn-) oxyhydroxides. In the oxidized B-horizon, there is a significant LREE/HREE and Ce(IV)/Ce(III) fractionation between laterite minerals. While LREE-Ce is mainly concentrated in phosphates (alunite-jarosite supergroup), it is proposed that HREE and Ce(IV) uptake is dominated by oxyhydroxides. In the A- and C-horizons, the LREE and HREE speciations are similar, indicating no significant LREE/HREE fractionation in laterite minerals and organic matter. In all horizons, the REE ion exchangeable is negligible, although kaolinite is a main mineral of the A- and B-horizons.

Résumé: Many applications related to ground-motion studies and engineering seismology benefit from the opportunity to easily download large dataset of earthquake recordings with different magnitudes. In such applications, it is important to have a reliable seismic characterization of the stations to introduce appropriate correction factors for including site amplification. Generally, seismic networks in Europe describe the site properties of a station through geophysical or geological reports, but often ad-hoc field surveys are missing and the characterization is done using indirect proxy. It is then necessary to evaluate the quality of a seismic characterization, accounting for the available site information, the measurements procedure and the reliability of the applied methods to obtain the site parameters.In this paper, we propose a strategy to evaluate the quality of site characterization, to be included in the station metadata. The idea is that a station with a good site characterization should have a larger ranking with respect to one with poor or incomplete information. The proposed quality metric includes the computation of three indices, which take into account the reliability of the available site indicators, their number and importance, together with their consistency defined through scatter plots for each single pair of indicators. For this purpose, we consider the seven indicators identified as most relevant in a companion paper (Cultrera et al. 2021): fundamental resonance frequency, shear-wave velocity profile, time-averaged shear-wave velocity over the first 30 m, depth of both seismological and engineering bedrock, surface geology and soil class.

Résumé: The southern part of the French Alps is studied for years in mapping and understanding of large-scale gravitational deformations. The identification and the knowledge of large-scale slope deformation (deep-seated gravitational slope deformation or DSGSD and deep-seated landslide or DSL) in the previous work of Jomard (2006) and Zerathe (2013) open a new vision of landslide processes with the reinterpretation of their dynamics and the characterization of the time scales involved. We identify DSGSD (10.10(9) m(3)) in the Var Valley associated with geological and geomorphological anomalies linked to the Messinian Salinity Crisis (MSC) and the alpine orogenesis. We use field observations, geological information (geological map, boreholes), and topographic analysis performed in a GIS environment in order to describe these anomalies. This old and partly eroded slide mass is associated with three typical DSGSD features: (1) a double-crested ridge, the Sinne Valley, (2) a large formation (2.7 x 10(8) m(3)) of slope deposit dated from the Messinian (Carros breccia), and (3) the kilometric deviation (1 to 2 km) of the Var River. We relate all these anomalies to the MSC (5.97 to 5.46 Ma) and the incision of deep canyons during this period related to this major eustatic variation (approximate to 1300 m). The incision of the canyon triggered the collapse process of the DSGSD of the Sinne Valley and so destabilized the entire massif. At present, three DSLs resulting from the DSGSD deformation are still present in the area in a dormant state. Indeed, since the infilling of the Var Canyon during the Pliocene, the activity of the DSGSD has stopped.

Résumé: We developed a high-resolution MIKE SHE/MIKE 11 model of a 231.3 ha headwater catchment in the granitic uplands of the French Massif Central to estimate the contribution of groundwater upwelling to the water balance of the Dauges mire, an acidic valley mire of international importance for nature conservation. We estimated that groundwater upwelling from the underlying weathered granite formations – mostly an approximately 55 m deep fissured zone – provides 27.1 % of total long-term inflows to the mire. This contribution increases to 37.2 % in September when total inflows are small. Overland boundary inflow accounts for an average of 40.2 % of total inflows. However, most of this originates from groundwater seepage through mineral soils along the mire margins or in small non-channelised valleys upslope of the mire. A sensitivity analysis showed that model performance in terms of the simulation of mire groundwater levels was most sensitive to parameters describing the mineral soils and weathered granite formations rather than the overlying peat layer. Variation partitioning demonstrated that groundwater upwelling was the most important factor driving simulated monthly groundwater table depth within the mire. Sustained groundwater upwelling maintains the mire water table close to or at ground level for most of the year. As a result, precipitation and overland boundary inflows quickly leave the wetland as saturation-excess runoff. There was close agreement between the observed distribution of mire habi- tats and areas where the simulated long-term groundwater seepage rate was larger than zero in September. Our results demonstrate that, contrary to the assumed small contribution of groundwater to the hydrology of hard-rock regions, groundwater upwelling from underlying weathered formations can be a quantitatively important and functionally critical element of the water balance of valley mires in granitic headwater catchments. These results have important legal and management implications.

Résumé: The spatial incoherence of ground motion during an earthquake can have a significant effect on the dynamic response of engineering structures such as bridges, dams, nuclear power plants and lifeline facilities. The main objective of this paper is to study the effect of anisotropic heterogeneities in a soil layer overlying homogeneous bedrock on the lagged coherency of surface ground motion. A set of numerical experiments is performed based on 2D spatial variability of shear-wave velocities modeled as a homogeneous stationary random field and discretized by the EOLE method (Expansion Optimal Linear Estimation). Seismic ground motions were simulated using FLAC(2D) software in the 1-25 Hz band for a plane wave excitation with SV polarization. The soil is characterized by horizontal and vertical autocorrelation distances ranging between 5 and 20 m and 1 and 2 m, respectively, and a coefficient of variation of the shear-wave velocity varying between 5% and 40%. The synthetic seismograms calculated for 9 parameter sets (100 realizations each) clearly show seismic waves scattering and surface waves diffracted locally by the ground heterogeneities, generating large spatial variations in coherence mainly controlled by the coefficient of variation of shear-wave velocity. Consistently with existing models and experimental data, the numerical coherency curves decrease with frequency and receiver distance, however at a rate which is lower than that observed in the experimental data. This difference is probably due to intrinsic attenuation that is not accounted for in the simulations and/or to our 2D simulations that do not reproduce the complete wavefield. The numerical average coherency curves for each parameter set exhibit maxima within narrow frequency bands caused by the vertically trapped body waves and surface wave propagation properties within the average ground model. This interpretation is supported by experimental data recorded in the Koutavos-Argostoli valley (Greece).

Résumé: The Cheshmeh-Bid ophiolitic massif in the Khajeh-Jamali district (Southern Iran) is dominated by harzburgite-dunite tectonites locally intruded by orthopyroxenite dikes. 'Mese latter are composed of dominant coarse orthopyroxene with minor olivine, Cr-spinel, clinopyroxene and amphibole. Estimated equilibrium temperatures for Mg-hornblende and edenitic amphibole reveal a late stage magmatic origin. The Cheshmeh-Bid orthopyroxenites are characterized by very low Al2O3, CaO, Na2O and TiO2 abundances coupled to relatively high MgO and SiO2 contents. They display U-shaped REE patterns, selective LILE enrichment and positive Pb and Sr anomalies. The host harzburgites are highly refractory mantle residues resulting from fluid-assisted melting. Field observations and mineral assemblages suggest that the pyroxenites formed by melt injection along fractures within rather cold ambient harzburgites and chromitites at moderate pressure (P> 1 GPa). Based on bulk-rock compositions and mineral chemistry, we infer that the Cheshmeh-Bid orthopyroxenites originated from the intrusion and crystallization of hydrous Si-rich, low-Ca melts with a boninite signature in a suprasubduction environment. Fine-grained neoblastic domains developed in the pyroxenites in response to subsolidus ductile deformation and recrystallization, which were most likely related to the exhumation of the Cheshmeh-Bid ophiolite massif.

Résumé: In the Cheshmeh-Bid district of the Khajeh-Jamali ophiolitic massifs (Southern Iran), mantle peridotites are intruded by abundant pyroxenite dykes. A few of these dykes are remarkable for the occurrence of native copper associated with the development of a metasomatic reaction zone. The dykes are progressively reacted, from their margins towards the center, with an amphibole + antigorite selvage, followed by a centimeter-thick clinopyroxene + antigorite assemblage and, finally, by the native copper-bearing zone consisting of clinopyroxene + chlorite + antigorite. Native Cu occurs along cleavages and partially healed fractures in clinopyroxene, and as massive grains intergrown with antigorite. Copper isotope signatures and thermodynamic calculations show that the main driver for reaction zone formation is Ca-metasomatism. Native copper forms at the expense of chalcocite in the reaction zone. Such a reaction can only occur in reducing conditions, in agreement with the analysis of fluid inclusions composition displaying H-2 and CH4. Such fluids presumably originated from the hydration of mantle rocks. The observed reaction zone and native copper mineralization are thus interpreted as the result of Ca-metasomatism during hydrothermal alteration of the oceanic lithosphere. This is consistent with U/Pb dating of titanite, suggesting formation during the Albian when the dykes were exposed on the seafloor in a supra-subduction setting. The source for copper mineralization, as revealed by Cu isotopes, is probably mantle-like. (C) 2020 Elsevier B.V. All rights reserved.

Résumé: Understanding diagenetic reactions in accreted sediments is critical for establishing the balance of fluid sources and sinks in accretionary prisms, which is in turn important for assessing the fluid pressure field and the ability for faults to host seismic slip. For this reason, we studied diagenetic reactions in deformation bands (shear zones and veins) within deep mud sediments from the Nankai accretionary prism (SW Japan) drilled at site C0001 during IODP Expedition 315, by means of microscopic observation, X-ray diffraction, and major- and trace-element analyses. Deformation bands are not only more compacted than the host sediment but are also enriched in framboidal pyrite, as observed under microscopy and confirmed by chalcophile-element enrichments (Fe, S, Cu, As, Sb, Pb). In tandem, one shear zone sample displays a destabilization of smectite or illite-smectite mixed layers and a slight crystallization of illite relative to its sediment matrix, and another sample shows correlated increases in B and Li in shear zones and veins compared to the host sediment, both effects suggesting a transformation of smectite into illite in deformation bands. The two diagenetic reactions of sulfide precipitation and smectite-to-illite transformation are explained by a combined action of sulfate-reducing and methanogen bacteria, which strongly suggests an increased activity of anaerobic microbial communities localized in deformation bands. This local bacterial proliferation was possibly enhanced by the liberation of hydrogen from strained phyllosilicates. We suggest that the proliferation of anoxic bacteria, boosted by deformation, may contribute to the pore water freshening observed at depth in accretionary prisms. Deformation-enhanced metabolic reactions may also explain the illitization observed in major faults of accretionary prisms. Care is therefore needed before interpreting illitization, and other diagenetic reactions as well, as evidence of shear heating, as these might be biogenic instead of thermogenic.

Résumé: Lebanon is a densely populated country crossed by major faults. Historical seismicity shows the potential of earthquakes with magnitudes 7, but large earthquakes have never been instrumentally recorded in Lebanon. Here, we propose a method to simulate near-fault broadband ground motions for a potential Mw 7 earthquake on the Yammouneh fault (YF)-the largest branch of the Dead Sea Transform fault that bisects Lebanon from north to south. First, we performed the first 3D tomography study of Lebanon using ambient noise correlation, which showed that Lebanon could be approximated by a 1D velocity structure for low-frequency (LF) ground-motion simulation purposes. Second, we generated suites of kinematic rupture models on the YF, accounting for heterogeneity of the rupture process, and uncertainty of the rupture velocity and hypocenter location. The radiated seismic energy was next propagated in the inferred 1D velocity model to obtain suites of LF ground motions (<1 Hz) at four hypothetical near-fault seismic stations. These LF simulations included the main features of near-fault ground motions, such as the impulsive character of ground velocity due to the rupture directivity or fling-step effects (so-called pulse-like ground motions). Third, to obtain broadband ground motions (up to 10 Hz), we proposed a hybrid technique that combined the simulated LF ground motions with highfrequency (HF) stochastic simulations, which were empirically calibrated using a worldwide database of near-fault recordings. Contrary to other hybrid approaches, in which the LF and HF motions are generally computed independently, the characteristics of stochastic HF ground motions were conditioned on those of LF ground motions (namely on the characteristics of the velocity pulse, if it existed, or on the absence of a pulse). The simulated peak ground accelerations were in agreement with the ones reported in the Next Generation Attenuation-West2 (NGA-West2) database for similar magnitude and distances and with three NGA-West2 ground-motion prediction equations.

Résumé: The recycling of oceanic crust, with distinct isotopic and chemical signature from the pyrolite mantle, plays a critical role in the chemical evolution of the Earth with insights into mantle circulation. However, the role of the mantle transition zone during this recycling remains ambiguous. We here combine the unique resolution reflected body waves (P410P and P660P) retrieved from ambient noise interferometry with mineral physics modeling, to shed new light on transition zone physics. Our joint analysis reveals a generally sharp 660-km discontinuity and the existence of a localized accumulation of oceanic crust at the bottom mantle transition zone just ahead of the stagnant Pacific slab. The basalt accumulation is plausibly derived from the segregation of oceanic crust and depleted mantle of the adjacent stagnant slab. Our findings provide direct evidence of segregated oceanic crust trapped within the mantle transition zone and new insights into imperfect whole mantle circulation. By combining ambient noise interferometry with mineral physics modeling, this work sheds new light on mantle transition zone physics. Their findings provide new evidence of segregated oceanic crust subducted and trapped within the mantle transition zone, implying complex mantle circulation modes.

Résumé: We discuss the drivers of the Pyrenean post-orogenic exhumation, including drainage migration, flexural rebound and tectonic reactivation.We provide new low-temperature thermochronological data and inverse thermal modeling from both the hinterland and foreland of the western Pyrenees. Our new thermochronological ages range from 6.6 to 61.4 Ma and reveal a Late Miocene exhumation phase in several massifs. The contrasting thermal histories define a domain of focused exhumation in the western Pyrenees that coincides with the present-day extensional tectonics in a region to the north of the Axial Zone. Based on the inferred cooling rates and paleogradient estimates, we highlight an exhumation phase of c. 1 mm yr(-1) between 11 and 9 Ma in the Axial Zone, well above rates expected for a post-orogenic evolution. The thermal evolution inferred from three boreholes of the Aquitaine foreland basin reveals that sediments eroded from the hinterland did not accumulate in the Piedmont region but were transported offshore in the Bay of Biscay. We infer that the significant c. 10 Ma post-orogenic exhumation event must be related to the modern normal faulting regime of the western Pyrenees, associated with contrasting crustal thickness and densities, inherited from the Mesozoic rift evolution of the northern Pyrenees.

Résumé: Knowledge about ambient noisewavefield, through decomposition into different participant waves and determination of precise singularities in ellipticity curves, could be very beneficial to improve the obtained subsurface velocity structures. In this paper, two array processing methods; WaveDec and high-resolution Rayleigh three-component beamforming (RTBF) and four single-station methods; Horizontal-to-Vertical Spectral Ratio (HVSR) or H/V, HVTFA (H/V using time frequency analysis), RayDec (Random Decrement Technique) and DOP-E (Degree Of Polarization) are applied to decompose ambient noise wavefield and to extract dispersion and ellipticity curves of surfacewaves. Two siteswith different geological and geophysical conditions are chosen to examine the results of the measurements. The first selected site is in the south of Tehran, Iran, as a site with a low impedance contrast structure. The second one is in the Colfiorito basin, Italy, as a major impedance contrast structure site. Wavefield decomposition resulted in Rayleigh and Love wave separation and also mode distinction. The decomposed modes of surface waves and ellipticity curves of Rayleigh waves are used in a joint inversion process. The retrieved shear-wave velocity profiles are in close agreement with previous studies in the mentioned sites. (C) 2020 Elsevier B.V. All rights reserved.

Résumé: In the high mountain rock walls of the Mont Blanc massif, changes in the granite surface colour are related to its exposure age. The light grey colour of fresh rock surfaces turns orange when is long exposed to weathering. In order to study this colour/age relationship, reflectance spectroscopy was performed on 73 samples, and Terrestrial Cosmogenic Nuclide (TCN) dating was used to obtain their surface exposure age. The standard deviation of the reflectance values was calculated for each wavelength of the visible spectrum to study the behaviour of each spectral region. The aim was to find two colour regions that showed opposite behaviour, and once they are combined, they could provide a representative index of the rock colour changes that are linked to the degree of weathering. As an adaptation of the Green Red Vegetation Index used to measure colour changes in vegetation, the GReenInfrared GRanite Index (GRIGRI), a normalized difference between the granite 770 nm and 530 nm reflectance values, was developed. The GRIGRI value of a weathered granite surface has a close relationship with its exposure age (R2 = 0.85). The reflectance spectra of seven samples for which TCN dating failed and two samples for which the TCN age was considered to be an outlier were used to calculate their GRIGRI value to assess the colour-based ages, that were plausible according to rock wall morphology and the TCN exposure ages of the surrounding surfaces. We propose a new method of surface dating for the rock walls of the Mont Blanc massif using reflectance spectroscopy.

Résumé: The formation of iron- and/or manganese-rich dark patinas on sandstones is a common natural phenomenon that occurs also on building stones. Luneville chateau, in eastern France, presents such patinas that developed either under natural conditions (rain and time) or after an accidental fire and exposure to significant amounts of water as part of attempts to extinguish the fire. The present study aimed at characterizing both types of patinas in an effort to determine their formation mechanisms and Mn sources. In both cases, Mn required for patina formation likely derives from the reductive dissolution of Mn-rich minerals present in pristine sandstones, as suggested by the contrasting mineralogy and chemistry of Mn-rich phases present in the bulk and in the patina of a given building block. Reduced Mn species then migrate to the exposed surface of building blocks where they are re-oxidized via undetermined processes. Patinas developing “naturally” over time result from the alternation of wetting-reducing and drying-oxidizing cycles and appear to be composed of birnessite. Patinas formed after the 2003 fire result from this single accidental event and form a much thinner, heterogeneous, and discontinuous layer of poorly crystalline lithiophorite at the sandstone surface (similar to 0-150 μm compared to similar to 300-600 μm for “natural” patinas). The lack of Mn-rich patinas on areas of Luneville chateau is likely related to the lower Mn content of pristine sandstone blocks.

Résumé: We present porosity and free gas estimates and their uncertainties at an active methane venting site in the UK sector of the North Sea. We performed a multi-disciplinary experiment at the Scanner Pockmark area in about 150 m water depth to investigate the physical properties of fluid flow structures within unconsolidated glaciomarine sediments. Here, we focus on the towed controlled source electromagnetic (CSEM) data analysis with constraints from seismic reflection and core logging data. Inferred background resistivity values vary between 0.6-1 Omega m at the surface and 1.9-2.4 Omega m at 150 mbsf. We calibrate Archie's parameters with measurements on cores, and estimate porosities of about 50 +/- 10% at the seafloor decreasing to 25 +/- 3% at 150 mbsf which matches variations expected for mechanical compaction of clay rich sediments. High reflectivity in seismic reflection data is consistent with the existence of a gas pocket. A synthetic study of varying gas content in this gas pocket shows that at least 33 +/- 8% of free gas is required to cause a distinct CSEM data anomaly. Real data inversions with seismic constraints support the presence of up to 34 +/- 14% free gas in a 30-40 m thick gas pocket underneath the pockmark within the stratigraphic highs of a till layer above the glacial unconformity in the Aberdeen Ground Formation.

Résumé: Located at the northern tip of the Altiplano, the Abancay Deflection marks abruptly the latitudinal segmentation of the Central Andes spreading over the Altiplano to the south and the Eastern Cordillera northward. The striking morphological contrast between the low-relief Altiplano and the high-relief Eastern Cordillera makes this area a well-suited place to determine spatiotemporal variations in surface and/or rock uplift and discuss the latest phase of the formation of the Central Andes. Here, we aim to quantify exhumation and uplift patterns in the Abancay Deflection since 40 Ma and present new apatite (U-Th)/He and fission track data from four altitudinal profiles and additional individual samples. Age-elevation relationships and thermal modeling both document that the Abancay Deflection experienced a moderate, spatially uniform, and steady exhumation at 0.2 +/- 0.1 km/Myr between 40 and similar to 5 Ma implying common large-scale exhumation mechanism(s). From similar to 5 Ma, while the northern part of the Eastern Cordillera and the Altiplano registered similar ongoing slow exhumation, the southern part of the Eastern Cordillera experienced one order-of-magnitude of exhumation acceleration (1.2 +/- 0.4 km/Myr). This differential exhumation since similar to 5 Ma implies active tectonics, river capture, and incision affecting the southern Eastern Cordillera. 3D thermokinematic modeling favors a tectonic decoupling between the Altiplano and the Eastern Cordillera through backthrusting activity of the Apurimac fault. We speculate that the Abancay Deflection, with its “bulls-eye” structure and significant exhumation rate since 5 Ma, may represent an Andean protosyntaxis, similar to the syntaxes described in the Himalaya or Alaska.

Résumé: In this paper, a number of spectral and ordinary ground motion intensity measures (IMs) are tested for use in structural performance assessment. Real strong motion values recorded at the top and the bottom of US, Japanese and Romanian buildings are analyzed in order to identify the source of uncertainties in the prediction of engineering demand parameters (i.e. structural drift) for given IMs (i.e. sigma EDP|IM). The efficiency and sufficiency of each IM from a large set of building and earthquake motion data are tested for different criteria characterizing the seismic source (magnitude and source-to-site distance), and considering several building classes and a specific single-building analysis including aging due to cumulative earthquake damage over time. The spectral values at co-seismic resonance frequencies was found to be the most efficient IMs for the range of buildings and earthquakes investigated, particularly for velocity with a reduction of approximately 50% of the sigma EDP|IM value. Conversely, most IMs are relatively insufficient.

Résumé: Recent work in the field of cryo-seismology demonstrates that high-frequency (> 1 Hz) seismic waves provide key constraints on a wide range of glacier processes, such as basal friction, surface crevassing, or subglacial water flow. Establishing quantitative links between the seismic signal and the processes of interest, however, requires detailed characterization of the wavefield, which, at high frequencies, necessitates the deployment of large and dense seismic arrays. Although dense seismic array monitoring has recently become increasingly common in geophysics, its application to glaciated environments remains limited. Here, we present a dense seismic array experiment made of 98 three-component seismic stations continuously recording during 35 days in early spring 2018 on the Argentiere Glacier, French Alps. The seismic dataset is supplemented with a wide range of complementary observations obtained from ground-penetrating radar, drone imagery, Global Navigation Satellite Systems positioning, and in situ measurements of basal glacier sliding velocities and subglacial water discharge. We present first results through conducting spectral analysis, template matching, matched-field processing, and eikonal-wave tomography. We report enhanced spatial resolution on basal stick slip and englacial fracturing sources as well as novel constraints on the heterogeneous nature of the noise field generated by subglacial water flow and on the link between crevasse properties and englacial seismic velocities. We outline in which ways further work using this dataset could help tackle key remaining questions in the field.

Résumé: This article presents findings from two episodes of seismicity and gas emission that occurred on 7 October 2015 and 6 December 2019 in Campi Flegrei caldera. This caldera has been affected by long-term unrest since 2004. The 6 December 2019 episode, consisting of a swarm of 38 earthquakes (maximum duration magnitude 3.1, the largest between 1984 and March 2020), occurred at the end of a one month period characterized by an increase in the ground uplift rate from 0.19 +/- 0.01 to 0.72 +/- 0.05 mm/day. A sudden increase in the fumarolic tremor amplitude, which is a proxy of gas emission related parameters recorded at Solfatara?Pisciarelli hydrothermal area (e.g., CO2 air concentration), was observed during the seismicity episode. The uplift rate decreased immediately after the swarm (0.10 +/- 0.01 mm/day), whereas the fumarolic tremor amplitude remained higher than that observed prior to the swarm. Through analyzing the time series of uplift recorded in Pozzuoli (central area of the caldera) from differential measurements on tide gauges, we were able to identify the 2015 episode. This episode was characterized by increasing uplift rates that culminated in a seismic swarm of 33 earthquakes on 7 October, which was followed by decreasing uplift rates. We computed double-difference locations of earthquakes from the two swarms and found that they located along a conduit-like path, coinciding with a high-resistivity contrast zone, previously identified by audiomagnetotelluric measurements. The focal mechanisms of the major earthquakes of both swarms indicate fault planes radial with respect to the maximum uplift area. These phenomena can be interpreted as episodes of the volcanic and (or) hydrothermal system pressurization that culminate in an injection of fluids along the conduit-like path, which behaves as a valve that allows fluid discharge and the temporary depressurization of the source region.

Résumé: The reactivity of iron(II/III) oxide surfaces may be influenced by their interaction with silica, which is ubiquitous in aquatic systems. Understanding the structure-reactivity relationships of Si-coated mineral surfaces is necessary to describe the complex surface behavior of nanoscale iron oxides. Here, we use Si-adsorption isotherms and Fourier transform infrared spectroscopy to analyze the sorption and polymerization of silica on slightly oxidized magnetite nanoparticles (15% maghemite and 85% magnetite, i.e., similar to 2 maghemite surface layers), showing that Si adsorption follows a Langmuir isotherm up to 2 mM dissolved Si, where surface polymerization occurs. Furthermore, the effects of silica surface coatings on the redox-catalytic ability of magnetite are analyzed using selenium as a molecular probe. The results show that for partially oxidized nanoparticles and even under different Si surface coverages, electron transfer is still occurring. The results indicate anion exchange between silicate and the sorbed Se-IV and Se-VI. X-ray absorption near-edge structure analyses of the reacted Se indicate the formation of a mixed selenite/Se-0 surface phase. We conclude that neither partial oxidation nor silica surface coatings block the sorption and redox-catalytic properties of magnetite nanoparticles, a result with important implications to assess the reactivity of mixed-valence phases in environmental settings.

Résumé: Tectonic pseudotachylytes are thought to be unique to certain water-deficient seismogenic environments and their presence is considered to be rare in the geological record. Here, we present field and experimental evidence that frictional melting can occur in hydrothermal fluid-rich faults hosted in the continental crust. Pseudotachylytes were found in the >40 km-long Bolfin Fault Zone of the Atacama Fault System, within two ca. 1 m-thick (ultra)cataclastic strands hosted in a damage-zone made of chlorite-epidote-rich hydrothermally altered tonalite. This alteration state indicates that hydrothermal fluids were active during the fault development. Pseudotachylytes, characterized by presenting amygdales, cut and are cut by chlorite-, epidote- and calcite-bearing veins. In turn, crosscutting relationship with the hydrothermal veins indicates pseudotachylytes were formed during this period of fluid activity. Rotary shear experiments conducted on bare surfaces of hydrothermally altered rocks at seismic slip velocities (3 m s(-1)) resulted in the production of vesiculated pseudotachylytes both at dry and water-pressurized conditions, with melt lubrication as the primary mechanism for fault dynamic weakening. The presented evidence challenges the common hypothesis that pseudotachylytes are limited to fluid-deficient environments, and gives insights into the ancient seismic activity of the system. Both field observations and experimental evidence, indicate that pseudotachylytes may easily be produced in hydrothermal environments, and could be a common co-seismic fault product. Consequently, melt lubrication could be considered one of the most efficient seismic dynamic weakening mechanisms in crystalline basement rocks of the continental crust.

Résumé: Detailed reconstruction of deep crustal targets by seismic methods remains a long-standing challenge. One key to address this challenge is the joint development of new seismic acquisition systems and leading-edge processing techniques. In marine environments, controlled-source seismic surveys at a regional scale are typically carried out with sparse arrays of ocean bottom seismometers (OBSs), which provide incomplete and down-sampled subsurface illumination. To assess and minimize the acquisition foot-print in high-resolution imaging process such as full wave-form inversion, realistic crustal-scale benchmark models are clearly required. The deficiency of such models prompts us to build one and release it freely to the geophysical community. Here, we introduce GO3DOBS – a 3D high-resolution geomodel representing a subduction zone, inspired by the geology of the Nankai Trough. The 175km x 100km x 30km model integrates complex geological structures with a viscoelastic isotropic parameterization. It is defined in the form of a uniform Cartesian grid containing similar to 33.6e9 degrees of freedom for a grid interval of 25 m. The size of the model raises significant high-performance computing challenges to tackle large-scale forward propagation simulations and related inverse problems. We describe the workflow designed to implement all the model ingredients including 2D structural segments, their projection into the third dimension, stochastic components, and physical parameterization. Various wavefield simulations that we present clearly reflect in the seismograms the structural complexity of the model and the footprint of different physical approximations. This benchmark model is intended to help to optimize the design of next-generation 3D academic surveys – in particular, but not only, long-offset OBS experiments – to mitigate the acquisition footprint during high-resolution imaging of the deep crust.

Résumé: Seismic velocities in the shallow crust down to a few kilometers depth show a remarkable sensitivity to stress perturbations due to the presence of compliant pores, cracks, fractures, and faults. Monitoring temporal changes of seismic velocities can thus provide key insights on dynamic processes affecting the shallow crust such as those related to the atmosphere (rainfall, barometric pressure, and temperature) and those with deeper tectonic and volcanic origins. In this work, we investigate the specific response of the near surface down to 300 m depth to atmospheric pressure variations. We conduct a four month passive seismic monitoring experiment in the desert of Oman using continuous noise recorded at geophones located within five wells. The results show a clear, direct correlation between seismic velocities and barometric pressure variations for monthly transients. At a longer, seasonal temporal scale, seismic velocities are stable, whereas atmospheric pressure shows a clear positive trend. We use the undrained coupled poroelastic theory to model these observations and find that the lack of seasonal velocity changes can be partly explained by the atmospheric pressure that diffuses into the pores with a strong hydraulic diffusivity likely higher than 100 m2=s consistent with the local geology referring to carbonates. Finally, the comparison between the modeled and observed velocity changes leads to estimate a velocity-stress sensitivity on the order of 6:3 x 10-7 Pa-1 which is consistent with previous studies. Using this result for calibration, we find that a sudden step-change drop of velocity of 0.015% occurring in the beginning of October 2019 and corresponding to a stress perturbation likely larger than 240 Pa affected the entire studied area. This small change could be related to a perturbation at greater depth associated with variations in the production rates within the underlying reservoir.

Résumé: The activation of tectonics and anthropogenic swarms in time and space and size remains challenging for seismologists. One remarkably long swarm is the Lacq swarm. It has been ongoing since 1969 and is located in a compound oil-gas field with a complex fluid manipulation history. Based on the overlap between the volumes where poroelastic model predicts stresses buildup and those where earthquakes occur, gas reservoir depletion was proposed to control the Lacq seismic swarm. The 2016 M-w 3.9, the largest event on the site, is located within a few kilometers downward the deep injection well. It questions the possible interactions between the 1955-2016 wastewater injections and the Lacq seismicity. Revisiting 60 yr of fluid manipulation history and seismicity indicates that the impacts of the wastewater injections on the Lacq seismicity were previously underevaluated. The main lines of evidence toward a wastewater injection cause are (1) cumulative injected volume enough in 1969 to trigger M-w 3 events, onset of Lacq seismicity; (2) 1976 injection below the gas reservoir occurs only a few years before the sharp increase in seismicity. It matches the onset of deep seismicity (below the gas reservoir, at the injection depth); (3) the (2007-2010) 2-3 folds increase in injection rate precedes 2013, 2016 top largest events; and (4) 75% of the 2013-2016 events cluster within 4-8 km depths, that is, close to and downward the 4.5 km deep injection well. As quantified by changepoint analysis, our results suggest that timely overlaps between injection operations and seismicity patterns are as decisive as extraction operations to control the Lacq seismicity. The seismicity onset is contemporary to cumulative stress changes (induced by depletion and injection operations) in the 0.1-1 MPa range. The interrelation between injection and extraction is the most probable cause of the Lacq seismicity onset and is sustenance over time. The injected volume-largest magnitude pair for Lacq field is in the same range (90% confidence level) than wastewater volume-magnitude pairs reported worldwide, in a wide variety of tectonic settings.

Résumé: Paleoglacier reconstructions in the northern and southern forelands of the European Alps indicate a synchronous Late Pleistocene glacial maximum during Marine Isotope Stage (MIS) 2, in phase with global ice volume records. However, strong controversy remains for the western foreland, where scarce and indirect dating as well as modeling studies suggest glacial maxima out of phase with the rest of the Alps. New luminescence dating brings the first direct Late Pleistocene glacial chronology for the western Alpine foreland and reveals two major glacier advances of similar maximum extent, at ca. 75-60 and ca. 40-30 ka, coinciding with MIS 4 and late MIS 3. We propose that asynchrony in glacial maxima between the western and the northern and southern Alpine forelands results from a progressive spatial reorganization of the atmospheric circulation over the North Atlantic in response to Northern Hemisphere ice-sheet fluctuations. While such a feedback mechanism has emerged from general circulation models, our Late Pleistocene paleoglacial reconstruction permits tracking of the spatiotemporal evolution of moisture advection patterns over Western Europe.

Résumé: Copper, silver, and gold exploitation has been a foundation of economic and socio-cultural development of Andean societies, at least for the last three millennia. The main centers of pre-colonial metallurgy are well-known from archeological artifacts, but temporal gaps inherent in this record handicap a finer understanding of the modalities of ore exploitation by succeeding civilizations. A continuous record over time of trace metals emitted during ore smelting operations make lake sediments excellent candidates to fill those gaps. Two millennia of metallurgy were reconstructed from atmospherically derived metals together with lead (Pb) isotope ratios in two dated sediment cores from Lake Titicaca. The first evidence for metallurgy is found during the apogee of the Tiwanaku state (AD 800-1150), with a higher copper (Cu) accumulation that can be attributed to the smelting of local Cu ores, based on Pb isotopic fingerprinting. During the Late Intermediate Period (AD 1150-1450), recorded peaks in metal deposition that persisted for similar to twenty years show that mining activities were intensive but discontinuous. Pb isotope ratios suggest diversified extractive activities, mainly located in the southern part of the central Altiplano. Finally, the most intense mining epoch began during the Inca Empire (ca. AD 1500) and lasted until the end of the Colonial Period (AD 1830), with unprecedented metal deposition over this interval. Pb isotope fingerprinting shows that mining operations occurred mainly in the Lake Titicaca and Potosi areas and were responsible for metal emissions recorded in the entire Altiplano, as evidenced by other studies. (C) 2021 Elsevier Ltd. All rights reserved.

Résumé: In this article, we analyze the rotation rates in a building derived from a network of translation sensors and recorded by a rotation sensor. The building is Grenoble city hall, a reinforced concrete structure with permanent accelerometric translation sensors at the top and bottom of the building. A temporary experiment was conducted, consisting in installing a BlueSeis-3A rotation sensor for more than 24 h at the top of the structure. The ambient vibrations were analyzed. The amplitudes of translation accelerations and rotation rates at the top and bottom of the building, along with their variations over time, were analyzed. The acceleration/rotation ratios were then compared with the impulse wave velocities derived from seismic interferometry by deconvolution between the top and bottom. Perspectives with regard to building imaging, time monitoring of structural integrity and understanding the contribution of rotations to the structure's response are discussed, offering new suggestions for research projects.

Résumé: Ice sheet evolution depends on subglacial conditions, with the ice-bed interface's strength exerting an outsized role on the ice dynamics. Along fast-flowing glaciers, this strength is often controlled by the deformation of subglacial till, making quantification of spatial variations of till strength essential for understanding ice-sheet contribution to sea-level. This task remains challenging due to a lack of in situ observations. We analyze continuous seismic data from the Whillans Ice Plain (WIP), West Antarctica, to uncover spatio-temporal patterns in subglacial conditions. We exploit tidally modulated stick-slip events as a natural source of sliding variability. We observe a significant reduction of the till seismic wave-speed between the WIP sticky-spots. These observations are consistent with a poroelastic model where the bed experiences relative porosity and effective pressure increases of >11% during stick-slips. We conclude that dilatant strengthening appears to be an essential mechanism in stabilizing the rapid motion of fast-flowing ice streams.

Résumé: In mountainous, cold temperate and polar sites, the presence of snow cover can affect relative seismic velocity changes (dV/V) derived from ambient noise correlation, but this relation is relatively poorly documented and ambiguous. In this study, we analyzed raw seismic recordings from a snowy flat field site located above Davos (Switzerland), during one entire winter season (from December 2018 to June 2019). We identified three snowfall events with a substantial response of dV/V measurements (drops of several percent between 15 and 25 Hz), suggesting a detectable change in elastic properties of the medium due to the additional fresh snow. To better interpret the measurements, we used a physical model to compute frequency-dependent changes in the Rayleigh wave velocity computed before and after the events. Elastic parameters of the ground subsurface were obtained from a seismic refraction survey, whereas snow cover properties were obtained from the snow cover model SNOWPACK. The decrease in dV/V due to a snowfall was well reproduced, with the same order of magnitude as observed values, confirming the importance of the effect of fresh and dry snow on seismic measurements. We also observed a decrease in dV/V with snowmelt periods, but we were not able to reproduce those changes with our model. Overall, our results highlight the effect of the snow cover on seismic measurements, but more work is needed to accurately model this response, in particular for the presence of liquid water in the snowpack.

Résumé: The main objective of this study is to demonstrate that Electron Spin Resonance (ESR) dating of Quaternary sediments can be performed at Venezuelan Laboratory (Laboratorio de Fisica de la Materia Condensada – Instituto Venezolano de Investigaciones Cientificas). The dating was carried out using quartz samples extracted from sedimentary Quaternary fill of three alluvial terraces (Qt12, Qt9 and Qt7) located along the Santo Domingo River (Merida Andes, Western Venezuela), that have been previously studied and dated by Terrestrial Cosmogenic Isotope (Be-10). The sedimentological characteristics of the Qt9 terrace fill indicate that the transport and sedimentation process of the sediments was under stable and high energy conditions. Our ESR dating suggest a maximum age of 85 +/- 16 ka for this terrace, which is consistent with the Be-10 ages previously published. In the case of the Qt12 and Qt7 terraces, field observations suggest a sediment transport process by debris flows, with rapid deposition. In this case, our ESR ages (228 +/- 93 ka, 108 +/- 33 ka, for Qt12 and Qt7, respectively) seem to be overestimated compared with the Be-10 ages reported in previous studies. These results confirm that the sedimentary material to be used for dating through this technique must be deposited under stable conditions involving long-term sediment transport processes. This will allow the “optical bleaching” of paramagnetic centers to occur before the material is buried, as seems to have happened with the Qt9 terrace sample. The results discussed in this work support the existence of the technological and human resources necessary to carry out numerical dating of Quaternary sediments in Venezuela.

Résumé: Potassium feldspars (KAlSi3O8) are ubiquitous minerals in the Earth's upper crust. This family of minerals has been the subject of numerous experimental and theoretical investigations concerning their dissolution kinetics and the mechanisms controlling chemical alteration at acid and neutral pH, and at temperatures ranging from ambient to hydrothermal conditions. On the other hand, considerably less research on the dissolution behavior of K-feldspars has been carried out at alkaline conditions, in particular at pH > 9 and elevated temperatures. Filling in this gap in knowledge is the major motivation for this study. More specifically, we wanted to document and understand how the K-feldspar interface structurally and chemically evolves during alteration in order to determine the mechanism of dissolution. In this study we examined interfaces of orthoclase samples that were altered in separate experiments in a Ca(OH)(2)-H2O solution (pH(25 degrees C) 12.4) at 190 degrees C for 24 h. We used a combination of focused ion beam (FIB) milling and advanced analytical transmission electron microscopy (TEM) techniques to investigate the structure and chemistry of the near surface region of post-reaction grains, with particular attention being given to the fluid-solid interface. Even though each grain diminishes in volume due to dissolution, high-resolution TEM imaging indicates that the feldspar structure itself remains completely intact and crystalline, as evidenced by lattice fringes that abruptly terminate at the grain edge. Nanometer-scale chemical composition measurements and mapping by TEM-EDXS (energy dispersive X-ray spectroscopy) and EFTEM (energy filtered TEM) show that the chemistry of the parent feldspar also remains unchanged at the interface. In particular, there is no evidence for the incursion of Ca from the fluid solvent into the structure, either by interdiffusion or by a replacement process. Taken together, the TEM observations point to a sharp chemical reaction front characterized by the congruent (i.e. stoichiometric) release of all elements from the feldspar structure. Nanometer-scale measurements by high resolution analytical TEM also reveal that a surface alteration layer (SAL) of amorphous material forms in situ at the expense of the feldspar structure. The interface demarcates a spatially coincident and nm-sharp chemical and structural discontinuity between the parent feldspar and the amorphous phase. The amorphous SAL has a variable thickness, from under 10 nm up to similar to 200 nm. This is likely one of the first observed occurrences of a significant surface amorphous layer on feldspar due to alteration in an alkaline solvent. The lack of a gap between the two phases points to an interfacial dissolution-reprecipitation process that continuously operates during hydrothermal alteration, and mostly likely right from the onset of contact with the fluid. After the initial formation of the amorphous layer, a 1-2 μm-thick porous amalgam of secondary crystalline phases comprised of calcite, tobermorite, and hydrogrossular, as well as other minor phases, precipitated over the SAL. These authigenic crystalline minerals formed during the experiment (hydrothermal alteration, followed by fluid loss due to evaporation) by a classical thermodynamically-controlled precipitation process as the reactor bulk fluid became increasingly concentrated. We propose that a coupled interfacial dissolution-reprecipitation (CIDR) mechanism best explains the chemical and structural properties of the interface and the formation of an amorphous surface layer. In fact, many recent studies postulate that a CIDR process controls feldspar dissolution and the formation of SALs at acid and circumneutral pH over a wide range of temperatures. Combining these previous results with our new observations supports the idea that a unique and unifying mechanism likely controls chemical alteration of feldspars in all aqueous fluids.

Résumé: Memory effects in seismology-such as the occurrence of aftershock sequences-are implicitly assumed to be governed by the time since the main event. However, experiments are yet to identify if memory effects are structural or time-dependent mechanisms. Here, we use laser interferometry to examine the fluctuations of deformation which naturally emerge along an experimental shear fault within a compressed frictional granular medium. We find that deformation occurs as a succession of localized micro-slips distributed along the fault. The associated distributions of released seismic moments, as well as the memory effects in strain fluctuations and the time correlations between successive events, follow exactly the empirical laws of natural earthquakes. We use a methodology initially developed in seismology to reveal at the laboratory scale the underlying causal structure of this behavior and identify the triggering kernel. We propose that strain, not time, controls the memory effects in our fault analog. Deformation experiments using glass beads generate nano-earthquakes that mimic the spatio-temporal pattern of strain in natural seismicity and suggest memory effects associated with strain fluctuations are strain-dependent rather than time-dependent.

Résumé: Arc magmas derived from mantle melting often have trace element and isotopic signatures that indicate crustal contributions. The origin and extent of crustal contributions are critical constraints for quantifying crust-mantle recycling at subduction zones; however, it is difficult to distinguish between inputs from the downgoing oceanic slabs and that of the over-riding arc crust. Here we present a novel study using stable potassium (K) isotopes to fingerprint the long-debated crustal signatures in lavas from Martinique Island, Lesser Antilles arc. We find delta K-41 of Martinique lavas varies from -0.66 to 0.01 parts per thousand and correlates with chemical parameters and radiogenic isotope ratios. These correlations cannot be produced by assimilation of arc crust during magma ascent. Rather, they reflect mantle sources that have been modified by the input of subducted sediments. Most lavas display a strong negative correlation between delta K-41 and radiogenic isotopic compositions, from typical mantle values of -0.37 parts per thousand to much lower values of -0.66 parts per thousand , suggesting the addition of <1% to 5% subducted sediments to their mantle sources. Notable divergence in this correlation occurs for three samples with variably high delta K-41 (-0.28 to 0.01 parts per thousand), which is likely caused by the addition of isotopically heavy K-bearing fluids derived from slab dehydration. Our study indicates that a substantial fraction of large ion lithophile elements, including K in arc magmas and thus nascent crust, is inherited from subducted crust; K isotopes are useful tracers of this cycling process. (C) 2020 Elsevier Ltd. All rights reserved.

Résumé: In this work, we explored the feasibility of predicting the structural drift from the first seconds of P-wave signals for On-site Earthquake Early Warning (EEW) applications. To this purpose, we investigated the performance of both linear least square regression (LSR) and four non-linear machine learning (ML) models: Random Forest, Gradient Boosting, Support Vector Machines and K-Nearest Neighbors. Furthermore, we also explore the applicability of the models calibrated for a region to another one. The LSR and ML models are calibrated and validated using a dataset of similar to 6,000 waveforms recorded within 34 Japanese structures with three different type of construction (steel, reinforced concrete, and steel-reinforced concrete), and a smaller one of data recorded at US buildings (69 buildings, 240 waveforms). As EEW information, we considered three P-wave parameters (the peak displacement, Pd, the integral of squared velocity, IV2, and displacement, ID2) using three time-windows (i.e., 1, 2, and 3 s), for a total of nine features to predict the drift ratio as structural response. The Japanese dataset is used to calibrate the LSR and ML models and to study their capability to predict the structural drift. We explored different subsets of the Japanese dataset (i.e., one building, one single type of construction, the entire dataset. We found that the variability of both ground motion and buildings response can affect the drift predictions robustness. In particular, the predictions accuracy worsens with the complexity of the dataset in terms of building and event variability. Our results show that ML techniques perform always better than LSR models, likely due to the complex connections between features and the natural non-linearity of the data. Furthermore, we show that by implementing a residuals analysis, the main sources of drift variability can be identified. Finally, the models trained on the Japanese dataset are applied the US dataset. In our application, we found that the exporting EEW models worsen the prediction variability, but also that by including correction terms as function of the magnitude can strongly mitigate such problem. In other words, our results show that the drift for US buildings can be predicted by minor tweaks to models.

Résumé: Based on the diffuse field concept for a horizontal-to-vertical spectral ratio of earthquakes (eHVSR), the effectiveness of eHVSRs to invert P- and S-wave velocity structures down to the seismological bedrock (with the S-wave velocity of 3 km/s or higher) has been shown in several published works. An empirical method to correct the difference between eHVSR and a horizontal-to-vertical ratio of microtremors (mHVSR), which is called earthquake-to-microtremor ratio (EMR), has also been proposed for strong-motion sites in Japan. However, the applicability of EMR outside of Japan may not be warranted. We test EMR applicability for the Grenoble basin in France with plentiful microtremor data together with observed weak-motion recordings at five sites. We thereby establish a systematic procedure to estimate the velocity structure from microtremors and delineate the fundamental characteristics of the velocity structures. We first calculate the EMR specific for the Grenoble basin (EMRG) and calculate pseudo eHVSR (pHVSR) from EMRG and mHVSR. We compare the pHVSRs with the eHVSRs at five sites and find sufficient similarity to each other. Then, we invert velocity structures from eHVSRs, pHVSRs, and mHVSRs. The velocity structures from eHVSRs are much closer to those from pHVSRs than those from mHVSRs. We need to introduce a number of layers with gradually increasing S-wave velocities below the geological basin boundary from a previous gravity study because the theoretical eHVSR of the model with a large velocity contrast has larger peak amplitudes than the observed. The depth of the S-wave velocity of 1.3 km/s (Z(1.3)) shows a strong, linear correlation with the geological boundary depth. Finally, we apply our validated methodology and invert velocity structures using pHVSRs at 14 sites where there are no observed earthquakes. The overall picture of Z(1.3) at a cross section in the northeastern part of the basin corresponds to the geological boundary.

Résumé: Granitic melts may form either directly, by melting of pre-existing crustal rocks, or by fractionation of mafic to intermediate magmas, typically mantle-derived. Each model is applicable to distinct portions of the Earth at different times. Whenever there is an important flux of mafic magmas from the mantle, differentiation of basaltic magmas dominates. In contrast, locations with a lower mafic magma flux, elevated thermal gradients and/or a fertile, thick crust are dominated by crustal melting and reworking. This only partly overlaps with the dichotomy between magmatic arcs and collision zones, as places like e.g. inverted back-arcs also feature large-scale crustal melting, whereas post-collisional domains include a sizeable mantle-derived component. Petrogenesis of individual granitic suites probably cannot be accounted for by pure, end-member models, as these suites typically feature a fair proportion of hybrid or ambiguous granitoids. Thus, we explore various petrogenetic and geological scenarios leading to the formation of hybrid granitoids at various scales. Finally, we outline possibilities to quantify the respective contributions of crust and mantle involved in their formation – hopefully, paving the way for a better understanding and more rigorous discussion of the mechanisms of crustal growth and recycling.

Résumé: We investigate the origin of a long-lived earthquake cluster in the Fars arc of the Zagros Simply Folded Belt that is colocated with the major Shanul natural gas field. The cluster emerged in January 2019 and initially comprised small events of M-n similar to 3-4. It culminated on 9 June 2020 with a pair of M-w 5.4 and 5.7 earthquakes, which was followed by >100 aftershocks. We assess the spatiotemporal evolution of the earthquake sequence using multiple event hypocenter relocations, waveform inversions, and Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) measurements and models. We find that the early part of the sequence is spatially distinct from the 9 June 2020 earthquakes and their aftershocks. Moment tensors, centroid depths, and source parameter uncertainties of 15 of the largest (M-n >= 4.0) events show that the sequence is dominated by reverse faulting at shallow depths (mostly <= 4 km) within the sedimentary cover. InSAR modeling shows that the M-w 5.7 mainshock occurred at depths of 2-8 km with a rupture length and maximum slip of similar to 20 km and similar to 0.5 m, respectively. Our results suggest that the 2019-2020 Khalili earthquake sequence was likely influenced by operation of the Shanul field, though elevated natural seismicity in the Zagros makes the association difficult to prove. Understanding how to distinguish man-made from natural seismicity is helpful for hazard and risk assessment, notably in the Zagros, which is both seismically active and rich in oil and gas reserves. Plain Language Summary Earthquakes caused by human activities have been documented in a growing number of regions worldwide, but recognizing these events in areas of naturally elevated seismicity remains challenging. We investigate the origin of a long-lived earthquake cluster in the Fars arc of the Zagros Simply Folded Belt-one of the world's most seismically active mountain belts-that is colocated with a major natural gas field. The seismicity led to public concern and speculation that nearby natural gas extraction was responsible for the seismicity. We assess the spatiotemporal evolution of the earthquake sequence using satellite geodesy and seismology measurements and models. Our results support these being anthropogenic earthquakes, most probably related to operations in the gas field. We suggest that the exploitation of the reservoirs in Iran should be preceded by risk assessment studies and accompanied by the implementation of dedicated, sophisticated monitoring, which would allow seismicity to be detected early and tracked more closely.

Résumé: The Billecocha plateau (4000 m a.s.l.) lies in the high elevation Ecuadorian Andes volcanic arc. It overhangs by 2000 m above the interandean valley. Both the plateau and surrounding volcanoes are heavily affected by active faulting characterized by straight, sharp and discontinuous scarps within a 6 km wide and 24 km long corridor. Contrasting interpretations have been proposed to explain the expression at surface of the so-called Billecocha fault system (BFS), from normal faulting related to postglacial elastic rebound or gravitational processes, to rightlateral faulting compatible with the North-Andean Sliver tectonic regime. The instrumental seismicity recorded around the BFS is low, however, a M similar to 7 earthquake heavily struck the region in 1868. With the aim to discuss the kinematic and coseismic nature of the encountered deformations as well as the seismogenic character of the BFS, we performed (1) morphological analysis to map and quantify evidence of active faulting and (2) paleoseismological investigations across the longer segment of the fault system. In three trenches, we show that surface deformations are at least partly coseismic in origin during the Holocene with a minor lateral component, the last paleoseismic event being compatible in date with the 1868 earthquake. In addition, some of the enlightened paleoseismic events could have occurred in relationship with volcanic eruptions of the surrounding volcanoes. While field evidence of reverse and strike slip faulting suggests that regional tectonics could be involved, the geomorphological signature of the BFS at the mountain scale, as seen on the digital surface model, can partly be related to the development of deep seated gravitational deformations, hence suggesting an interaction between boundary (i.e. tectonic, volcanic) and body forces (i.e. gravity, post-glacial rebound). Further studies are however mandatory to better address the influence of each process at the BFS, in particular geodetic and seismological surveys. Given the available data, we suggest that the BFS could actually correspond to the distributed surface expression of the tectonic reactivation of the inherited Pujili suture, enhanced by gravitational phenomenon. In this light, paleoearthquakes identified along the BFS may help evidencing the recurrence of major events in the region. However, it also imply that surface deformations along the BFS shall not be used without a careful and more detailed field work to derive fault slip rates for seismic hazard calculations.

Résumé: Full-waveform inversion (FWI) applications on 3D oceanbottom cable (OBC) data from the Valhall oil field in the North Sea have demonstrated the importance of appropriately accounting for attenuation. The Valhall field contains unconsolidated shallow sediments and a low-velocity anomaly in its center – indicative of gas clouds – which have a significant attenuation imprint on the data. Our challenge is to perform time-domain viscoacoustic 3D FWI, which requires more sophisticated tools than in the frequency domain wherein attenuation can be incorporated in a straightforward manner. The benefit of using a viscoacoustic, instead of a purely acoustic, modeling engine is illustrated. We have determined that, in the frequency band used (2.5-7.0 Hz), it is better to reconstruct the velocity only keeping the attenuation lixed because simultaneous inversion of the velocity and quality factor Q does not provide reliable Q updates. We develop an efficient time-domain workflow combining a random source decimation algorithm, modeling using standard linear solid mechanisms, and wavefield preconditioning. Our results are similar to those obtained from state-of-the-art frequency-domain algorithms, at a lower computational cost compared to conventional check-pointing techniques. We clearly illustrate the improvement in terms of imaging and data fit achieved when accounting for attenuation.

Résumé: The Oman Drilling Project “Multi-Borehole Observatory” (MBO) samples an area of active weathering of tectonically exposed peridotite. This article reviews the geology of the MBO region, summarizes recent research, and provides new data constraining ongoing alteration. Host rocks are partially to completely serpentinized, residual mantle harzburgites, and replacive. Dunites show evidence for “reactive fractionation,” in which cooling, crystallizing magmas reacted with older residues of melting. Harzburgites and dunites are 65%-100% hydrated. Ferric to total iron ratios vary from 50% to 90%. In Hole BA1B, alteration extent decreases with depth. Gradients in water and core composition are correlated. Serpentine veins are intergrown with, and cut, carbonate veins with measurable C-14. Ongoing hydration is accompanied by SiO2 addition. Sulfur enrichment in Hole BA1B may result from oxidative leaching of sulfur from the upper 30 m, coupled with sulfate reduction and sulfide precipitation at 30-150 m. Oxygen fugacity deep in Holes BA3A, NSHQ14, and BA2A is fixed by the reaction 2H(2)O = 2H(2) + O-2 combined with oxidation of ferrous iron in serpentine, brucite, and olivine. fO(2) deep in Holes BA1A, BA1D, and BA4A is 3-4 log units above the H2O-H-2 limit, controlled by equilibria involving serpentine and brucite. Variations in alteration are correlated with texture, with reduced, low SiO2 assemblages in mesh cores recording very low water/rock ratios, juxtaposed with adjacent veins recording much higher ratios. The proportion of reduced mesh cores versus oxidized veins increases with depth, and the difference in fO(2) recorded in cores and veins decreases with depth. Plain Language Summary The Oman Drilling Project developed a “Multi-Borehole Observatory” (MBO) in an area of active weathering of tectonically exposed peridotite, to study the geochemistry, mechanics, and hydrology of peridotite alteration, which modifies the mineralogy, composition, density, and rheology of mantle lithologies, creates and sustains plate boundaries, and forms dramatic redox gradients. In turn, these redox conditions support a unique subsurface microbial ecosystem, form free H-2 gas, facilitate methane generation, and potentially play a role in the origin of life on this and other planets. This paper provides an overview of the geology of the area within and surrounding the MBO, a summary of recent research on core and fluids from three new cored boreholes and four new rotary boreholes in the MBO, together with older Omani water monitoring well NSHQ14, and new data and calculations constraining ongoing peridotite alteration in this area. We constrain the igneous history of the mantle rocks, the extent to which they have been hydrated, carbonated, and oxidized. Highlights include new hypotheses on mechanisms of shallow sulfur depletion and deeper enrichment, and new insights into the interaction of water and minerals that controls the partial pressures of oxygen and hydrogen in this important geochemical environment.

Résumé: The growth of global ground-motion databases has allowed generation of non-ergodic ground-motion prediction equations (GMPEs) based on specific on-site recordings. Several studies have investigated the differences between the hazard estimates from ergodic versus non-ergodic GMPEs. Here instead we focus on the impact of non-ergodic PSHA estimates on the seismic risk of nonlinear single-degree-of-freedom systems representing ductile structures and compare it with the traditional risk estimates obtained using ergodic GMPEs. The structure-and-site-specific risk estimates depend not only on the difference in the hazard estimates but also on the different hazard-consistent ground-motion record selection that informs the response calculation. The more accurate structure-and-site-specific non-ergodic risk estimates show that traditional ones may be biased in a way impossible to predict a priori. Hence, the use of the non-ergodic approach is recommended, whenever possible. However, further advancements of non-ergodic GMPEs are necessary before being routinely utilized in real-life risk assessment applications.

Résumé: Rockfalls generate seismic signals that can be used to detect and monitor rockfall activity. Event locations can be estimated on the basis of arrival times, amplitudes, or polarization of these seismic signals. However, surface topography variations can significantly influence seismic wave propagation and hence compromise results. Here, we specifically use the signature of topography on the seismic signal to better constrain the source location. Seismic impulse responses are predicted using Spectral Element based simulation of three-dimensional wave propagation in realistic geological media. Subsequently, rockfalls are located by minimizing the misfit between simulated and observed inter-station energy ratios. The method is tested on rockfalls at Dolomieu crater, Piton de la Fournaise volcano, Reunion Island. Both single boulder impacts and distributed granular flows are successfully located, tracking the complete rockfall trajectories by analyzing the signals in sliding time windows. Results from the highest frequency band (here 13-17 Hz) yield the best spatial resolution, making it possible to distinguish detachment positions less than 100 m apart. By taking into account surface topography, both vertical and horizontal signal components can be used. Limitations and the noise robustness of the location method are assessed using synthetic signals. Precise representation of the topography controls the location resolution, which is not significantly affected by the assumed impact direction. Tests on the network geometry reveal best resolution when the seismometers triangulate the source. We conclude that this method can improve the monitoring of rockfall activity in real time once a simulated database for the region of interest is created.

Résumé: The analysis of the seismicity catalog (1996 to 2019) covering the region from the Jura mountains to Corsica provides a first-order image of the distribution of earthquakes, highlighting large structures such as the Brianconnais and Piedmontais seismic arcs, the eastward deepening of the focal depths through the Western Alps, several large active faults (e.g. Belledonne. Middle Durance, Ligure). Over this period the magnitudes are moderate and the focal mechanisms of the main events display a diversity of seismic behaviors that can be explained by the complexity of the different geological domains with a more or less strong structural inheritage, by variable theological characteristics at the scale of the crust and by the joint action of different mechanisms of deformation. The distribution of the historical events is in fairly good agreement with the instrumental seismicity, but several earthquakes of M > 6 are highlighted since the 14th century until the beginning of the 20th.

Résumé: Twenty-two ammonite species are identified in the upper Albian Mortoniceras (Subschloenbachia) rostratum, Mortoniceras (Subschloenbachia) perinflatum and Stoliczkaia (Shumarinaia) africana Zones, and in the lower Cenomanian Mantelliceras mantelli Zone. The species Placenticeras Saadensis Thomas and (Thomas and Peron, 1890, 1890 is revised, including Engonoceras Thomasi Pervinquiere, 1907, and is placed within the genus Hypengonoceras Spath, 1922. This accurate biostratigraphic framework allowed to evidence, at the Albian-Cenomanian transition (S. (S.) africana Zone), a significant sea level drop, responsible for emergence and erosion to the SE, and for deposition of a Lowstand wedge to the NW, fed by erosional channels on the shelf slope. Plesiosaur remains found in the upper Albian series (base of M. (S.) rostratum Zone) represent one of the few elasmosaurids known worldwide in the Albian, and the first plesiosaurian reported from Tunisia. (c) 2021 Elsevier Ltd. All rights reserved.

Résumé: Monitoring landslides is essential to understand their dynamics and to reduce the risk of human losses by raising warnings before a failure. A decade ago, a decrease of apparent seismic velocity was detected several days before the failure of a clayey landslide, that was monitored with the ambient noise correlation method. It revealed its potential to detect precursor signals before a landslide failure, which could improve early warning systems. To date, nine landslides have been monitored with this method, and its ability to reveal precursors before failure seems confirmed on clayey landslides. However three challenges remain for operational early-warning applications: to detect velocity changes both rapidly and with confidence, to account for seasonal and daily environmental influences, and to check for potential instabilities in measurements. The ability to detect a precursory velocity change requires to adapt the processing workflow to each landslide: the key factors are the filtering frequency, the correlation time window, and the choice of temporal resolution. Other optional processing steps are described, to better measure rapid velocity changes, improve signal-to-noise ratio, or estimate the measurement uncertainty. The velocity also fluctuates seasonally, by 1 to 6% on the reviewed landslide studies, due to environmental influences. This review reveals a linear trend between the amplitude of seasonal fluctuations and the filtering frequency over the 0.1?20 Hz range, encompassing both landslide and non-landslide studies. The environmental velocity fluctuations are caused mostly by groundwater levels and soil freezing/thawing, but could also be affected by snow height, air temperature and tide depending on the site. Daily fluctuations should also occur on landslides, and can be an issue when seeking to obtain a sub-daily resolution useful for earlywarning systems. Finally, spurious fluctuations of apparent velocity?unrelated to the material dynamics?should be verified for. They can be caused by changes in noise sources (location or spectral content), in site response (change of scatterers, attenuation, or resonance frequency due to geometrical factors), or in inter-sensor distance. As a perspective, the observation of seismic velocity changes could contribute in assessing a landslide stability across time, both during the different creeping stages occurring before a potential failure, and during its reconsolidation after a failure.

Résumé: We present a 3-D shear wave velocity model of the Mauleon and Arzacq Basins from the surface down to 10 km depth, inverted from phase velocity maps at periods between 2 and 9 s. These phase velocity maps were obtained by analyzing coherent surface wave fronts extracted from ambient seismic noise recorded by the large-N Maupasacq seismic array with a matched filtering approach. This new model is in good agreement with a local earthquake tomography study performed on the same acquisition dataset. Our passive imaging models reveal the upper crustal architecture of the Mauleon and Arzacq Basins, with new details on the basement and its relationship with the overlying sedimentary cover. Combining these new tomographic images with surface and subsurface geological information allows us to trace major orogenic structures from the surface down to the basement. In the basin, the models image the first-order basin architecture with a kilometric resolution. At depth, high velocity anomalies suggest the presence of dense deep crustal and mantle rocks in the hanging wall of north-vergent Pyrenean Thrusts. These high velocity anomalies spatially coincide with a positive gravity anomaly in the western Mauleon Basin. In addition, our models reveal major changes from the Chainons Bearnais to the western Mauleon Basin across a set of orogen-perpendicular structures, the Saison and the Barlanes transfer zones. These changes reflect the along-strike variation of the orogenic evolution that led to the preservation of the former rifted domain and its underlying mantle in the orogenic wedge of the Western Pyrenees. We discuss the implications of these results for the 3-D architecture of the Mauleon Basin and its underlying basement.

Résumé: The high-precision X-ray diffraction setup for work with diamond anvil cells (DAC5) in interaction chamber 2 (IC2) of the High Energy Density instrument of the European X-ray Free-Electron Laser is described. This includes beamline optics, sample positioning and detector systems located in the multipurpose vacuum chamber. Concepts for pump-probe X-ray diffraction experiments in the DAC are described and their implementation demonstrated during the First User Community Assisted Commissioning experiment. X-ray heating and diffraction of Bi under pressure, obtained using 20 fs X-ray pulses at 17.8 keV and 2.2 MHz repetition, is illustrated through splitting of diffraction peaks, and interpreted employing finite element modeling of the sample chamber in the DAC.

Résumé: Denudation of volcanic ocean islands creates remarkable landscapes and contributes to Earth's carbon cycle, since the chemical alteration of basalts is a CO2 sink. Because many volcanic islands have large climate gradients and relatively low variations in lithology and tectonic history, they represent excellent natural laboratories for studying climatic effects on landscape evolution. However, little is known about the control of denudation rates in ocean islands and the respective influences of climatic gradients and morphological parameters. Here, we present new measurements of long-term denudation rates from Santo Antao Island, Cape Verde (17 degrees N). In this 779 km(2) island, mean annual precipitation ranges from 40 mm.yr(-1) in the southwest to 1100 mm.yr(-1) in the north. To constrain the spatial distribution of denudation rates, we measured the cosmogenic He-3 concentration in river-transported pyroxene grains from 23 river bedload samples. We obtained basin wide denudation rates ranging from 2.7 +/- 0.1 to 57.5 +/- 0.3 m/Ma. The denudation rates display a significant spatial variability, with the highest rates in catchments located in the northeast side of the island where modern precipitation are the highest and low denudation rates in the southern and western dry basins. Our study shows that precipitation is the main control on denudation and landscape development of the Santo Antao volcanic island. This study provides for the first time the spatial distribution of denudation rates across a volcanic island located in a tropical zone. (C) 2020 Elsevier B.V. All rights reserved.

Résumé: This paper shows the complementarity of two nonlinear ultrasonic imaging methods to characterize closed macro cracks in concrete. A time reversal mirror is used to locally probe and image the nonlinearity of a cracked region. Two nonlinear parameters are extracted to map the cracked region. The image obtained using the first parameter relates the harmonic generation due to the contact and frictional behaviors at the crack lips, correlated with vibro-thermography imaging of the same crack. The image obtained using the second parameter is based on the conditioning of the material induced by distributed micro cracks arising from the fracture process zone. These results show a great potential for characterization of fracture processes in concrete, with the possibility to uncouple the effects of the crack itself from surrounding distributed micro damage.

Résumé: We explore nonlinear site effects in the new Japanese ground-motion dataset compiled by Bahrampouri et al. (2020). Following the approach of Seyhan and Stewart (2014), we evaluate the decrease of soil amplification according to the increasing and corresponding ground motion on surface rock (V-S30 = 760 m/s). To better predict the rock ground motion associated with each record, we take into account the between-event variability of the ground motion, and to better evaluate the impact of nonlinearity, we correct observed ground motion on soil by the site-specific linear amplification. Instead of grouping the stations by site-response proxy, we focus on individual stations with several strong-motion records. We develop a framework to test recently published nonlinear site amplification models against a linear site amplification model and compare the results with recent building codes that include nonlinearity. The results show that the site response varies greatly from site to site, indicating that conventional site proxies, such as V-S30, are not sufficient to characterize nonlinear site response. Out of all of the Kiban-Kyoshin network stations, 20 stations are selected as having recorded sufficient data to be used in the test. Out of these 20 stations, five stations show signs of nonlinearity, that is, the nonlinear models performed better than the linear-amplification model for all periods T. For most sites, however, the linear site amplification models get the best score. This suggest that, for the range of predicted rock motion considered in this study (peak ground acceleration <0.2g), nonlinearity may not have a sufficiently large impact on soil ground motion to justify the use of nonlinear site terms in ground-motion functional forms and seismic building codes for such moderate-level shaking.

Résumé: Fe-III-containing aluminosilicate zeolites are present in cement-relevant and natural environments. Although Fe-III is known to occur in framework tetrahedral sites where it substitutes isomorphically (AlO4)-O-III or in extra-framework octahedral sites as free Fe(H2O)(6)(3+), the structural incorporation process of Fe-III into different sites is little known. We aim to discern feasible pathways of Fe-III incorporation using hydrothermal synthesis methods and synchrotron-based spectroscopic analyses. Results showed that introducing either Fe3+ or Fe2O3 center dot xH(2)O initially during zeolite nucleation did not lead to Fe-III incorporation into the zeolites but only Fe2O3 center dot xH(2)O prevailed in both cases. However, Fe(NO3)(3), FeCl3, and Fe2O3 center dot xH(2)O affected the kind of zeolite formed. A feasible pathway to incorporate tetrahedral Fe-III in the zeolite framework was to introduce firstly Fe-III in the cage of faujasite-Y followed by a phase transformation to chabazite. This study facilitates understanding of Fe-III uptake in zeolites and of Fe-III functional sites that can contribute to immobilization of contaminants.

Résumé: Earthquake ground motion often triggers landslides in mountainous areas. A simple, robust method to quickly evaluate the terrain's susceptibility of specific locations to earthquake-triggered landslides is important for planning field reconnaissance and rescues after earthquakes. Different approaches have been used to estimate coseismic landslide susceptibility using Newmark's sliding block model. This model requires an estimate of the landslide depth or thickness, which is a difficult parameter to estimate. We illustrate the use of Newmark sliding block's critical acceleration for a glaciated valley affected by the 2015 Gorkha earthquake in Nepal. The landslide data came from comparing high-resolution pre- and post-earthquake digital elevation models (DEMs) derived from Spot 6/7 images. The areas where changes were detected provided an inventory of all the landslides triggered by the earthquake. The landslide susceptibility was modeled in a GIS environment using as inputs the pre-earthquake terrain and slope angles, the peak ground acceleration from the 2015 Gorkha earthquake, and a geological map. We exploit the depth information for the landslides (obtained by DEM difference) to apply the critical acceleration model. The spatial distribution of the predicted earthquake-triggered landslides matched the actual landslides when the assumed landslide thickness in the model is close to the median value of the actual landslide thickness (2.6 m in this case). The landslide predictions generated a map of landslide locations close to those observed and demonstrated the applicability of critical acceleration for rapidly creating a map of earthquake-triggered landslides.

Résumé: The European Alps are the site where classic geologic concepts such as nappe theory, continental subduction and slab breakoff have been first proposed. However, the deep tectonic structure of the Alps has long been poorly constrained by independent geophysical evidence. This review paper summarizes the main results of the CIFALPS passive seismic experiment, that was launched by Chinese, French and Italian scientists in the 2010s to provide new insights on the deep tectonic structure of the Alpine region. The application of a wide range of tomographic methods to the analysis of a single fossil subduction zone makes the CIFALPS experiment a potential reference case for the analysis of other orogenic belts. Major results include: (i) the first seismic evidence of European continental crust subducted into the Adriatic upper mantle, beneath the place where coesite was first recognized in continental (U)HP rocks in the Alps; (ii) evidence of a major involvement of the mantle wedge during (U)HP rock exhumation; (iii) evidence of a serpentinized plate interface favoring continental subduction; (iv) evidence of a continuous slab beneath the Western and Central Alps, ruling out the classic model of slab breakoff magmatism; (v) evidence of a polyphase development of anisotropic fabrics in the Alpine mantle, either representing active mantle flows or fossil fabrics inherited from previous rifting stages. Detection of these major tectonic features allows to propose interpretive geologic cross-sections at the scale of the lithosphere and upper mantle, providing a baseline for future analyses of active continental margins.

Résumé: The hydration of mantle rocks occurs at mid-ocean ridges, in subduction zones and in ophiolites where it strongly modifies the properties of the oceanic lithosphere. The nanostructure of the reaction products is poorly constrained, but it is very important, as it controls fluid transport during solid volume increase, and it influences phase reactivity during further fluid/rock interaction at low temperature. We image contacts between olivine and its hydration products at the nanoscale, in a dunite collected during the Oman Drilling Project that underwent nearly isochemical serpentinisation and solid volume increase. Olivine first reacts to form a similar to 100 nm thick coating composed of a brucite/serpentine mixture, suggesting isochemical serpentinisation at this scale too. Lizardite columns similar to 1 μm wide replace this mixture at its margin. The columns are embedded in a brucite-rich assemblage containing a high density of nanopores that may favourfluid transport during reaction. We interpret these observations as a nanometre-scale, two-step process. Fluid pathways are formed rather than clogged by reaction products thanks to mass transfer at a scale limited to less than 100 nm. The preservation of the fluid pathways during solid volume increase explains the observed high extents of reaction. The presence of brucite in high porosity regions may explain its preferential reaction during low temperature fluid/rock interaction. (C) 2021 Elsevier B.V. All rights reserved.

Résumé: A long-standing challenge in tectonics is to evaluate the role of inheritance and define the initial conditions of a geodynamic system, which are prerequisites to understand and model its evolution with some accuracy. Here we revisit the concept of “inheritance” by distinguishing “interface shape inheritance”, which includes the transient thermal state and gravitational potential energy, and “persisting inheritance”, which encompasses long-lasting structural and compositional inheritance. This new approach allows us to investigate, at each stage of a Wilson Cycle, the interplay between inheritance (innate/“genetic code”) and the physical processes at play (extension/compression, magmatism etc.). The aim of this paper is to provide a conceptual framework that integrates the role of inheritance in the study of rifts, rifted margins and collisional orogens based on the work done in the OROGEN project, which focuses on the Biscay-Pyrenean system. The Biscay-Pyrenean rift system resulted from a multistage rift evolution that developed over a complex lithosphere pre-structured by the Variscan orogenic cycle. There is a general agreement that the Pyrenean-Cantabrian orogen resulted from the reactivation of an increasingly mature rift system along-strike, ranging from mature rifted margins in the west to an immature and segmented hyperextended rift in the east. However, different models have been proposed to explain the preceding rifting and its influence on the subsequent reactivation. Results from the OROGEN project highlight the sequential reactivation of rift-inherited decoupling horizons and identify the specific role of exhumed mantle, hyperextended and necking domains during compressional reactivation. They also highlight the contrasting fate of rift segment centres versus segment boundaries during convergence, explaining the non-cylindricity of internal parts of collisional orogens. Results from the OROGEN project also suggest that the role of inheritance is more important during the initial stages of collision, which may explain the higher complexity of internal parts of orogenic systems with respect to their external parts. In contrast, when the system involved in the orogeny is more mature, the orogenic evolution is mostly controlled by first-order physical processes as described in the Coulomb Wedge theory, for instance. This may account for the simpler and more continuous architecture of external parts of collisional orogens and may also explain why most numerical models can reproduce mature orogenic architectures with a better accuracy compared to those of initial collisional stages. The new concepts developed from the OROGEN research are now ready to be tested at other orogenic systems that result from the reactivation of rifted margins, such as the Alps, the Colombian cordilleras and the Caribbean, Taiwan, Oman, Zagros or Timor.

Résumé: Although fish is an important source of nutrients, including some of the healthiest proteins, long-chain fatty acids, and essential selenium, species at the top of the food chain frequently contain large amounts of toxic mercury (Hg). The provisional tolerable weekly intake (PTWI) of Hg from fish consumption is calculated from the total concentration of Hg and assuming that all Hg is speciated as organic methylmercury (MeHg). Using high energy-resolution X-ray absorption near-edge structure (HR-XANES) spectroscopy, we show that blue marlin (Makaira sp.), a common top predator consumed by humans, contains high concentrations of inorganic Hg(II) complexed as 57 +/- 10% Hg-tetraselenolate [Hg(Sec)(4)] and 43 +/- 10% tiemannite (HgSe). The stable Hg-Se chemical bond likely attenuates the bioavailability of Hg and counteracts some of its health hazards to consumers. Thus, monitoring the concentration of MeHg, rather than total Hg, in top predators such as marlin would provide a more robust measure of potential Hg exposure and may be sufficient for food safety controls. The bonding of Hg atoms to four selenocysteine (Sec) residues in the Hg(Sec)(4) complex severely depletes the stock of bioavailable Se, and quantification shows that blue marlin is not a chief source of dietary Se essential to selenoenzyme synthesis and activity.

Résumé: A prerequisite for environmental and toxicological applications of mercury (Hg) stable isotopes in wildlife and humans is quantifying the isotopic fractionation of biological reactions. Here, we measured stable Hg isotope values of relevant tissues of giant petrels (Macronectes spp.). Isotopic data were interpreted with published HR-XANES spectroscopic data that document a stepwise transformation of methylmercury (MeHg) to Hg-tetraselenolate (Hg(Sec)(4)) and mercury selenide (HgSe) (Sec = selenocysteine). By mathematical inversion of isotopic and spectroscopic data, identical delta Hg-202 values for MeHg (2.69 +/- 0.04 parts per thousand), Hg(Sec)(4) (-1.37 +/- 0.06 parts per thousand), and HgSe (0.18 +/- 0.02 parts per thousand) were determined in 23 tissues of eight birds from the Kerguelen Islands and Ade ' lie Land (Antarctica). Isotopic differences in delta Hg-202 between MeHg and Hg(Sec) 4 (-4.1 +/- 0.1 parts per thousand) reflect mass-dependent fractionation from a kinetic isotope effect due to the MeHg. Hg(Sec)(4) demethylation reaction. Surprisingly, Hg(Sec)(4) and HgSe differed isotopically in delta Hg-202 (+1.6 +/- 0.1 parts per thousand) and mass-independent anomalies (i.e., changes in Delta Hg-199 of <= 0.3 parts per thousand), consistent with equilibrium isotope effects of mass-dependent and nuclear volume fractionation from Hg(Sec)(4) -> HgSe biomineralization. The invariance of species-specific delta Hg-202 values across tissues and individual birds reflects the kinetic lability of Hg-ligand bonds and tissue-specific redistribution of MeHg and inorganic Hg, likely as Hg(Sec)(4). These observations provide fundamental information necessary to improve the interpretation of stable Hg isotope data and provoke a revisitation of processes governing isotopic fractionation in biota and toxicological risk assessment in wildlife.

Résumé: In vivo and in vitro evidence for detoxification of methylmercury (MeHg) as insoluble mercury selenide (HgSe) underlies the central paradigm that mercury exposure is not or little hazardous when tissue Se is in molar excess (Se:Hg > 1). However, this hypothesis overlooks the binding of Hg to selenoproteins, which lowers the amount of bioavailable Se that acts as a detoxification reservoir for MeHg, thereby underestimating the toxicity of mercury. This question was addressed by determining the chemical forms of Hg in various tissues of giant petrels Macronectes spp. using a combination of high energy-resolution X-ray absorption near edge structure and extended X-ray absorption fine structure spectroscopy, and transmission electron microscopy coupled to elemental mapping. Three main Hg species were identified, a MeHg-cysteinate complex, a four-coordinate selenocysteinate complex (Hg(Sec)(4)), and a HgSe precipitate, together with a minor dicysteinate complex Hg(Cys)(2). The amount of HgSe decreases in the order liver > kidneys > brain = muscle, and the amount of Hg(Sec)(4) in the order muscle > kidneys > brain > liver. On the basis of biochemical considerations and structural modeling, we hypothesize that Hg(Sec)(4) is bound to the carboxy-terminus domain of selenoprotein P (SelP) which contains 12 Sec residues. Structural flexibility allows SelP to form multinuclear Hgx(Se,Sec) y complexes, which can be biomineralized to HgSe by protein self-assembly. Because Hg(Sec)(4) has a Se:Hg molar ratio of 4:1, this species severely depletes the stock of bioavailable Se for selenoprotein synthesis and activity to one μg Se/g dry wet in the muscle of several birds. This concentration is still relatively high because selenium is naturally abundant in seawater, therefore it probably does not fall below the metabolic need for essential selenium. However, this study shows that this may not be the case for terrestrial animals, and that muscle may be the first tissue potentially injured by Hg toxicity.

Résumé: Numerous fault slip models for several large strike-slip earthquakes indicate a reduction of slip along the uppermost part of the fault (Shallow Slip Deficit, SSD). In this paper, we investigate the possibility that the SSD is an artifact due to the simplifications made when we model the medium. Using a set of synthetic data for the 1992 Landers earthquake, we show that while neglecting the topography of the Landers area has a moderate impact on the retrieved slip model, neglecting variations in elastic properties, in particular the variation with depth, leads to significant bias on the slip model and can produce 25% of artificial SSD (whereas neglecting the fault damage zone has a smaller impact). We further show that a lack of data coverage around the fault further increases the amount of artificial SSD. Moreover, we find that correlated data noise with maximum amplitude as low as 5% of the maximum surface displacement can also produce significant artificial SSD. We conclude that simple elastic forward modeling in a homogeneous medium may be inappropriate for resolving slip-variability with depth, even in areas of limited topography or lateral variation in elastic properties. Finally, we argue that the estimation of model uncertainty due to data error should be systematic in inversion studies to avoid any misinterpretation of the slip distribution. (C) 2020 Elsevier B.V. All rights reserved.

Résumé: Probabilistic seismic hazard assessment relies on long-term earthquake forecasts and ground-motion models. Our aim is to improve earthquake forecasts by including information derived from geodetic measurements, with an application to the Colombia-Ecuador megathrust. The annual rate of moment deficit accumulation at the interface is quantified from geodetically based interseismic coupling models. We look for Gutenberg-Richter recurrence models that match both past seismicity rates and the geodetic moment deficit rate, by adjusting the maximum magnitude. We explore the uncertainties on the seismic rates (a- and b-values, shape close to M-max) and on the geodetic moment deficit rate to be released seismically. A distribution for the maximum magnitudeMmax bounding a series of earthquake recurrence models is obtained for the Colombia-Ecuador megathrust. Models associated with Mmax values compatible with the extension of the interface segment are selected. We show that the uncertainties mostly influencing the moment-balanced recurrence model are the fraction of geodetic moment released through aseismic processes and the form of the Gutenberg-Richter model close to M-max. We combine the computed moment-balanced recurrence models with a ground-motion model, to obtain a series of uniform hazard spectra representative of uncertainties at one site on the coast. Considering the recent availability of a massive quantity of geodetic data, our approach could be used in other well-instrumented regions of the world.

Résumé: Seismicity quiescences are best observed during sequences with multiple mainshocks and often emerge with some delay after an initial phase of aftershock triggering. The mechanisms controlling this delay are poorly understood, due to a lack of systematic and precise estimation of the duration of the triggering phase which is made complicated by the rapidly changing magnitude of completeness after the mainshock. Here, we analyze how such a delayed quiescence developed during the 2019 Ridgecrest (California) sequence, using a refined earthquake data set obtained by template matching and relative relocation. A method that allows estimating the aftershock occurrence rate after correcting for the change in detection (completeness magnitude) is applied. We find that an immediate seismicity shutdown was triggered by the second (M7.1) mainshock at the tips of the north-east trending cross-cut fault that hosted most of the slip of the first (M6.4) mainshock. This shutdown progressed toward the central part of this fault over the following days. The overall shutdown of the aftershock sequence of the M6.4 by the M7.1 rupture is consistent with static Coulomb stress modeling. This inverse migration is a unique observation, best explained by an enhanced spatial stress change variability in this central part where the cross-cut fault intersects the main fault of the M7.1 shock, hence a strongly damaged zone there. This further confirms previous observations of an enhanced structural disorder in this central part of the cross fault, showing that structural disorder has a first-order control on the seismicity dynamics at the scale of days.

Résumé: Unmodified timber is susceptible to biodegradation in the marine environment by wood-boring molluscs and crustaceans. Wood is a renewable resource and has a much lower carbon footprint than other alternative materials that are suitable for marine applications, such as concrete and steel. However, biodegradation causes expensive damage to wooden structures and protection by broad spectrum biocides entails environmental risks. Furfurylation offers an effective alternative protection from marine wood-borers. We investigate the changes in feeding rate, behaviour and digestion of the marine wood-boring crustacean, the gribble, on furfurylated wood under laboratory conditions. Pinus radiata was impregnated with furfuryl alcohol in a methanol solvent and polymerised at elevated temperatures. Wood was leached in seawater and then tested in a laboratory setting against the gribble Limnoria quadripunctata, by measuring its feeding rate (faecal pellet production), vitality and mortality. The wood samples were analysed using Attenuated Total Reflectance Infrared Spectroscopy (ATR-IR), while faecal pellets were analysed by Atomic Force Microscopy Infrared Spectroscopy (AFM-IR). A reduction in band intensity ascribed to carbonyl vibration was seen during leaching, possibly due to loss of hemicellulose or acetyl groups therein. Untreated wood faecal pellets showed a decrease in C-O absorbance in the 1100-1000 cm(-1) range interpreted as a loss of cellulose and an increase in signal in the 1700-1600 cm(-1) range interpreted as increase in lignin modification products. For furfurylated wood similar tendencies were seen, but to a smaller extent. Faecal pellet production was reduced on treated wood and a lack of burrowing behaviour was observed. Mortality began to increase after a month of decreased feeding rates which is comparable to mortality rates of starved gribble. Disruption to enzymatic activity within the gut and/or increased hardness of the wood could be the mechanisms protecting furfurylated wood from biodegradation by gribble. Modification of wood, such as by furfurylation, offers promising levels of protection against such degradation without the reliance on broad spectrum biocides and can reduce costs associated with damaged wooden structures.

Résumé: Due to the low to moderate seismicity of the European Western Alps, few focal mechanisms are available in this region to this day, and the corresponding current seismic stress and strain fields remain partly elusive. The development of dense seismic networks in past decades now provides a substantial number of seismic records in the 0-5 magnitude range. The corresponding data, while challenging to handle due to their amount and relative noise, represent a new opportunity to increase the spatial resolution of seismic deformation fields. The aim of this paper is to quantitatively assess the current seismic stress and strain fields within the Western Alps, from a probabilistic standpoint, using new seismotectonic data. The dataset comprises more than 30 000 earthquakes recorded by dense seismic networks between 1989 and 2013 and more than 2200 newly computed focal mechanisms in a consistent manner. The global distribution of P and T axis plunges confirms a majority of transcurrent focal mechanisms in the entire western Alpine realm, combined with pure extension localized in the core of the belt. We inverted this new set of focal mechanisms through several strategies, including a seismotectonic zoning scheme and grid procedure, revealing extensional axes oriented obliquely to the strike of the belt. The Bayesian inversion of this new dataset of focal mechanisms provides a probabilistic continuous map of the style of seismic deformation in the Western Alps. Extension is found to be clustered, instead of continuous, along the backbone of the belt. Robust indications for compression are only observed at the boundary between the Adriatic and Eurasian plates. Short-wavelength spatial variations of the seismic deformation are consistent with surface horizontal Global Navigation Satellite System (GNSS) measurements, as well as with deep lithospheric structures, thereby providing new elements with which to understand the current 3D dynamics of the belt. We interpret the ongoing seismotectonic and kinematic regimes as being controlled by the joint effects of far-field forces – imposed by the anticlockwise rotation of Adria with respect to Europe – and buoyancy forces in the core of the belt, which together explain the short-wavelength patches of extension and marginal compression overprinted on an overall transcurrent tectonic regime.

Résumé: We quantify the spatial distribution of fracture networks throughout six in situ X-ray tomography triaxial compression experiments on crystalline rocks at confining stresses of 5-35 MPa in order to quantify how fracture development controls the final macroscopic failure of the rock, a process analogous to those that control geohazards such as earthquakes and landslides. Tracking the proportion of the cumulative volume of fractures with volumes > 90th percentile to the total fracture volume, n-ary sumation v(90)/v(tot) indicates that the fracture networks tend to increase in localization toward these largest fractures for up to 80% of the applied differential stress. The evolution of this metric also matches the evolution of the Gini coefficient, which measures the deviation of a population from uniformity. These results are consistent with observations of localizing low magnitude seismicity before large earthquakes in southern California. In both this analysis and the present work, phases of delocalization interrupt the general increase in localization preceding catastrophic failure, indicating that delocalization does not necessarily indicate a reduction of seismic hazard. However, the proportion of the maximum fracture volume to the total fracture volume does not increase monotonically. Experiments with higher confining stress tend to experience greater localization. To further quantify localization, we compare the geometry of the largest fractures, with volumes > 90th percentile, to the best fit plane through these fractures immediately preceding failure. The r (2) scores and the mean distance of the fractures to the plane indicate greater localization in monzonite than in granite. The smaller mean mineral diameter and lower confining stress in the granite experiments may contribute to this result. Tracking these various metrics of localization reveals a close association between macroscopic yielding and the acceleration of fracture network localization. Near yielding, n-ary sumation v(90)/v(tot) and the Gini coefficient increase while the mean distance to the final failure plane decreases. Macroscopic yielding thus occurs when the rate of fracture network localization increases.

Résumé: Two key parameters control the localization of deformation and seismicity along and surrounding crustal faults: the strength and roughness of the pre-existing fault surface. Using 3-D discrete element method simulations, we investigate how the anisotropy and amplitude of roughness control the mechanical behaviour of healed faults within granite blocks during quasi-static triaxial compression. We focus on models in which the uniaxial compressive strength of the healed faults is about 25 per cent of that strength of the surrounding host rock. These models provide insights into the evolution of fracture network localization, fault roughness, gouge production, fault slip and stress concentrations along initially healed faults of varying roughness. In contrast to expectations, the uniaxial compressive strengths of models that host faults with root-mean-squared roughness amplitudes of 0.2-1.4 mm do not vary more than the change produced by variations in particle packing. To assess if this lack of influence arises from the evolving roughness of the faults, we track the roughness amplitudes parallel and perpendicular to the downdip direction throughout fault failure and slip. The de facto roughness does not provide an explanation for the lack of influence of roughness on compressive strength because the roughness of the faults does not evolve to similar values with slip. Rather, smoother faults remain smoother than rougher faults throughout the simulation. However, the rougher faults produce larger volumes of gouge than the smoother faults. The gouge lubricates the fault and thereby reduces the influence of roughness on compressive strength. These observations suggest that fault topography and the asperities that build this topography do not exert a significant impact on deformation. To quantify the influence of asperities on slip, we calculate correlation coefficients between the fault surface topography and components of the slip vectors. The observed negative correlation coefficients between the fault topography and fault-plane parallel slip quantify the degree to which asperities slow slip in the downdip direction. The observed positive correlation coefficients between the topography and fault-plane perpendicular movement quantify the degree to which asperities promote opening. Thus, this analysis shows how asperities control slip by acting as speed bumps that hinder fault-plane parallel slip and promote fault-plane normal opening as the healed faults slide. The asperities do not significantly control fault movement during the unlocking and failure of the healed faults, but only following the peak axial stress as the faults slide and damage zones develop. These models thus provide unparalleled access to the dynamics of reactivated healed faults.

Résumé: Rock deformation experiments performed at X-ray synchrotrons provide unique insights into the nature of fracture network development. However, these insights depend on the limitations of the X-ray tomography data. Here, we examine how spatial resolution and noise influence the calculated fracture network properties. To assess the influence of spatial resolution, we acquire two overlapping X-ray tomograms with spatial resolution that differ by an order of magnitude. To assess the influence of noise, we produce sets of synthetic tomograms with varying degrees of noise, including point-source noise and blurring noise. In the absence of noise, the differing spatial resolutions produce calculated porosities that differ by 0.05%, or 30% of the porosity measured in the high-resolution data. The fracture property that changes the most in the datasets of varying resolution is the fracture surface area, rather than the volume, length, or aperture. The two types of noise influence the porosity and fracture characteristics in opposite ways. In the synthetic tomograms in which higher values indicate fractures, added point noise increases the porosity while blurring noise decreases the porosity. In volumes with a mapping of gray values in which fractures have lower values, this trend would be reversed. This study is the first to quantify differences in fracture network properties extracted from X-ray tomograms due to spatial resolution and noise.

Résumé: The Trans-Mexican Volcanic Belt (TMVB) is a calc-alkaline volcanic arc cut by different active crustal fault systems that have originated several destructive historical earthquakes. Located in the central part of Mexico this region offers exceptional climatic, and fertility of soil conditions, which is the reason why more than 50% of the Mexican population now live here, increasing the seismic risk. Determining the seismic potential of these fault systems is important in the western section of the TMVB, in the vicinity of the city of Guadalajara, where more than 5 million inhabitants are concentrated in a densely populated urban area. We focus here on the epicentral area of the MW 7.2 sixteenth century Ameca earthquake, one of the first earthquakes described to take place in the American continent and which also may be the largest crustal earthquake to have occurred in the TMVB in the historical record. According to some historical sources, this earthquake would be associated with the Ameca-Ahuisculco Fault but no neotectonic study has been carried out so far to characterize this fault. Here, we describe the geomorphology of the fault escarpment and the characteristics of different fault segments. This first step allowed to select a suitable site for a paleoseismological study to track the historic event. The results of the interpretation of two trenches are consistent, showing evidence of net activity of the fault in the tectono-sedimentary record with two and possibly three seismic events. The older one of these is not well recorded and interpreted as a possible event that could have occurred after 27,91 ? 0,4 cal ka BP and before 5,67 ? 0,064 cal ka BP. The second one and best recorded event occurred around 5,67 ? 0,064 cal ka BP whilst the last one occurred after 0,985 ? 0,065 cal ka BP and is likely to be the geological record of the Ameca sixteenth century earthquake. Considering the potential rupture lengths and the coseismic displacement measured in the trenches, this fault system seems capable of generating earthquakes of magnitude 6.9 to 7.3 and represents a major source of earthquake hazard to the city of Guadalajara.

Résumé: Mercury (Hg), one of the elements most toxic to biota, accumulates within organisms throughout their lifespan and biomagnifies along trophic chain. Due to their key role in marine systems, cephalopods constitute a major vector of Hg in predators. Further, they grow rapidly and display complex behaviours, which can be altered by neurotoxic Hg. This study investigated Hg concentrations within 81 cephalopod specimens sampled in the Bay of Biscay, which belonged to five species: Eledone cirrhosa, Sepia officinalis, Loligo vulgaris, Todaropsis eblanae and Illex coindetii. Hg concentrations were measured in the digestive gland, the mantle muscle and the optic lobes of the brain. The digestive gland and themantlewere tissueswith themost concentratedHg among all species considered (up to 1.50 μg.g(-1) dw), except E. cirrhosa. This benthic cephalopod had 1.3-fold higher Hg concentrations in the brain (up to 1.89 μg.g(-1) dw) than in the mantle, while other species had 2-fold lower concentrations of Hg in the brain than in the mantle. Brain-Hg concentrations can be predicted from muscleHg concentrations for a given species, which facilitates the assessment of Hg toxicokinetics in cephalopods. In the most contaminated E. cirrhosa individual, the chemical form of Hg in its digestive gland, mantle muscle and optic lobes, was determined using High energy-Resolution X-ray Absorption Near Edge Structure (HR XANES) spectroscopy. In the digestive gland, 33 +/- 11% of total Hg was inorganic Hg speciated as a dicysteinate complex (Hg(Cys)(2)), which suggested that the demethylation of dietary MeHg occurs in this organ. All Hg found in the mantle muscle and the optic lobes is methylated and bound to one cysteinyl group (MeHgCys complex), which implies that dietary MeHg is distributed to these tissues via the bloodstream. These results raised the questions regarding interspecific differences observed regarding Hg brain concentrations and the possible effect of Hg on cephalopod functional brain plasticity and behaviour. (C) 2020 Elsevier B.V. All rights reserved.

Résumé: The weathering of primary silicates, and their carbonation in particular, is key for the geochemical cycling of elements, strongly affecting the C cycle and the long-term regulation of the Earth's climate. The knowledge on the controlling factors and mechanisms of aqueous carbonation of primary silicates is however still far from complete. This precludes a better understanding of their chemical weathering in nature and is a strong handicap to implement effective Carbon Capture and Storage (CCS) strategies. Here, dissolution-carbonation reactions of two abundant Ca-Mg pyroxenes, augite and diopside, have been investigated in experiments conducted at hydrothermal conditions, in the presence/absence of different carbonate sources (NaHCO3 and Na2CO3). We show that the main reaction products are low-magnesium calcite and amorphous silica. A higher conversion of augite (similar to 38 wt%) than diopside (similar to 15 wt%) was achieved. The presence of abundant Fe and Al (and minor Na) in the former pyroxene strongly enhances the release of cations to the solution, and contributes to the formation of abundant secondary crystalline and amorphous silicates as well as carbonates (Na-phillipsite and magnesium silicate hydrate, MSH, as well as calcite). In particular, Na-phillipsite nucleates in etch pits exerting a crystallization pressure similar to 100 MPa exceeding the tensile strength of augite (i.e, failure under tension due to breaking of inter-atomic bonds as well as opening and propagation of subcritical fractures or flaws) and causing extensive fracturing. This takes place via an interface-coupled dissolutionprecipitation mechanism, despite the bulk system being undersaturated with respect to this phase. Limited reactioninduced fracturing was also observed following MSH precipitation within diopside crystals. Reaction-induced fracturing increases exposed reactive surface area and creates channels for solution flow, thereby contributing to the progress of the reaction via a positive feedback loop. Ultimately, our results help to understand differences in the kinetics and mechanisms of chemical weathering of these two abundant rock forming inosilicates relevant for CCS strategies, showing that secondary phase formation (other than carbonates) are fostered by moderately alkaline pH and the presence of alkali metals, resulting in reaction-driven fracturing that enables the progress of silicate carbonation for an effective, safe, and permanent CO2 mineral storage. We also show that under our experimental conditions the precipitation of amorphous silica and calcite cannot generate sufficient pressure as to create fracturing, an effect that limits carbonation of Mg-Ca-Fe pyroxenes. (C) 2021 Elsevier Ltd. All rights reserved.