Articles in Web of Science for 2024

Résumé: Dyke propagation is a mechanism for more rapid ascent of felsic magmas through the crust than is possible via diapirs or percolative flow. As it ascends, the magma undergoes complex physical and chemical transformations induced by decompression and cooling. These processes dramatically change the magma density and viscosity, which in turn affect magma ascent rate and the depth at which the dyke arrests. We present a mathematical model of dyke propagation for silicic magmas taking into account the presence of multiple volatile species (H2O and CO2), bubble growth, heat advection and loss, crystallization and latent heat release. We consider conditions for dykes associated with porphyry ore deposits, which may represent an end-member in rapid ascent of felsic magmas from depth. In particular, we simulate the propagation of dykes launched from a deep (900 MPa), volatile-saturated magma source, testing the effects of the magma H2O/CO2 content, temperature and mass on its ascent rate and final emplacement depth. The model predicts short ascent times (hours to days), with a large increase in viscosity at shallow depth, leading to stagnation and solidification of the dyke. Higher initial water content, higher temperature and larger mass of the magma in the dyke promote faster propagation and shallower arrest. Volatile loss from ascending magma remains limited until the stagnation depth, providing a potential mechanism for transfer of deep volatiles to hypabyssal blind intrusions associated with porphyry ore deposits. Our findings are applicable to the problem of silicic magma ascent through the crust more generally.

Résumé: On 16 April 2013, an M-w = 7.7 earthquake struck the border of Iran and Pakistan in the central part of the Makran subduction zone with a reported depth of 80 km by USGS. This rare event in this poorly instrumented region helps to shed light on the kinematics of the subducting slab. We investigate source parameters of the Saravan intraslab normal earthquake using RADARSAT-2 SAR images in three ascending tracks, nine permanent GNSS sites and teleseismic data. The maximum coseismic displacement occurred at the SRVN GNSS station with 54.1 mm southeast horizontal and 42.7 mm upward vertical displacements. The coseismic ascending InSAR displacement maps illustrate a continuous and smooth NE-trending elliptical shape deformation pattern with a maximum of similar to 29 cm of displacement away from the satellite. We use 25 broad-band teleseismic P-waveforms to estimate the focal mechanism of the main shock. A joint uniform inversion of InSAR, GNSS and teleseismic data reveals a NW-dipping SW-striking fault and a primarily normal-faulting earthquake with a minor right-lateral strike-slip component. The static slip distribution of the InSAR coseismic maps localizes variable slip at depths between 50 and 81 km with a maximum amplitude >3 m at 60-75.5 km depth, rupturing the oceanic crust of the subducted slab. The kinematic slip distribution exhibits a well-constrained slip pattern with a nucleation depth of 65 km. The source time function indicates that the earthquake reaches its maximum moment tensor release at similar to 8 and similar to 16 s. The NE-trend of the Saravan earthquake slip pattern, the orientation of the volcanic arc, and the distribution of the intraslab intermediate-depth normal earthquakes provide new insights into slab geometry in the central Makran subduction zone. We suggest that the slab bending at the hinge of subducting Arabian Plate is oblique along a NE-SW direction parallel to the volcanic arc rather than the shoreline or deformation front, and it is likely to be the reason for an oblique volcanic arc in the Makran subduction zone. These new constraints on the Makran slab geometry will help further studies in establishing realistic coupling maps for seismic hazard assessment.

Résumé: Warmer temperatures and higher sea level than today characterized the Last Interglacial interval [Pleistocene, 128 to 116 thousand years ago (ka)]. This period is a remarkable deep-time analog for temperature and sea-level conditions as projected for 2100 AD, yet there has been no evidence of fossil assemblages in the equatorial Atlantic. Here, we report foraminifer, metazoan (mollusks, bony fish, bryozoans, decapods, and sharks among others), and plant communities of coastal tropical marine and mangrove affinities, dating precisely from a ca. 130 to 115 ka time interval near the Equator, at Kourou, in French Guiana. These communities include ca. 230 recent species, some being endangered today and/or first recorded as fossils. The hyperdiverse Kourou mollusk assemblage suggests stronger affinities between Guianese and Caribbean coastal waters by the Last Interglacial than today, questioning the structuring role of the Amazon Plume on tropical Western Atlantic communities at the time. Grassland- dominated pollen, phytoliths, and charcoals from younger deposits in the same sections attest to a marine retreat and dryer conditions during the onset of the last glacial (ca. 110 to 50 ka), with a savanna- dominated landscape and episodes of fire. Charcoals from the last millennia suggest human presence in a mosaic of modern-like continental habitats. Our results provide key information about the ecology and biogeography of pristine Pleistocene tropical coastal ecosystems, especially relevant regarding the-widely anthropogenic- ongoing global warming. Significance The Last Interglacial interval (128 to 116 ka) is a remarkable deep- time analog for temperature and sea- level conditions as projected for 2100, that had not been documented in the equatorial Atlantic thus far. Here, we report hyperdiverse fossil communities of coastal marine and mangrove affinities, dating back from this interval and unearthed at the Europe's Spaceport in Kourou, French Guiana. Mollusk assemblages suggest stronger ecological affinities between Guianas and the Caribbean than today. Grassland- dominated pollen, phytoliths, and charcoals from younger deposits in the same sections attest to a marine retreat and dryer conditions during the Last Glacial Period (100 to 50 ka). These records provide key ecological and biogeographic information about Late Pleistocene tropical coastal ecosystems prior to human influence.

Résumé: Creeping landslides may fail catastrophically, posing significant threats to infrastructure and lives. Landslides weaken over time through rock mass damage processes that may occur by steady-state creep or transient accelerations of slip, called creep bursts. Creep bursts may control landslide stability by inducing short-term damage and strain localization. This study focuses on the & Aring;knes landslide in Norway, which moves up to 6 cm per year and could potentially trigger a large tsunami in the fjord below. An 11-year data set is compiled and analyzed, including kinematic, seismic, and hydrogeological data acquired at the landslide surface and in a series of boreholes. An annual average of two creep bursts with millimeter amplitude has been recorded within the shear zone in each borehole, accounting for approximately 11% of the total displacement. Creep bursts detected simultaneously in multiple boreholes are preceded by increased seismic activity and rising water pressure. However, most creep bursts are observed in only one or a few boreholes. These bursts often happen during seasonal high and low groundwater levels in autumn and spring, respectively, correlating with local peaks in water pressure. No such correlation is observed during summer. We propose that creep bursts can have different causes and hypothesize that rock degradation leads to some creep bursts independent of water pressure variations. In contrast, the largest creep bursts are correlated with variations in absolute water pressure or gradients of water pressure within the shear zone. Our findings emphasize the complexity of a dense data set requiring multiple mechanisms to explain creep burst dynamics.

Résumé: Kaolinite naturally contains radiation-induced electron defects in its structure induced by ionizing radiations and can be analyzed with electron paramagnetic resonance spectroscopy (EPR). They include the so-called A-center, which is crucial for geochronological applications due to its stability at the scale of geological periods. Indeed, previous studies have substantiated the thermal stability of naturally occurring A-centers in kaolinite through annealing experiments. However, the stability of artificially created A-centers, which are used to determine paleodose through calibration via irradiation experiments and subsequent dating of kaolinite formation, still needs to be more adequately specified to confirm their relevance. Therefore, this research probed the thermal stability of A-centers produced by ionizing 1.5 MeV He+ beams in two samples, i.e., the reference KGa-2 and a very disordered lateritic soil kaolinite. Heating experiments showed that the annealing of irradiated samples at 250 degrees C was relevant to determining A-center concentration. Second, the annealing of artificial A-centers at higher temperatures was found to be a second-order process, as for natural A-centers. Annealing parameters such as activation energy (2-2.6 eV) were determined with estimates of half-life at 300 K, which was found to be >10(12) years for natural and artificial A-centers. Thus, the parameters for artificial A-centers are consistent with the thermal annealing behavior of their natural counterparts. These new findings affirm that artificially generated A-centers mimic natural ones in terms of EPR spectra and thermal stability, enhancing the reliability and precision of the EPR dating methodology used in kaolinite dating.

Résumé: We present observations showing that during episodes of volcanic tremors, the phase of inter-station cross-correlations becomes stable. We propose a new quantity, the phase coherence, to identify the differential phase stability in recordings obtained from a single pair of stations, which is extrapolated to the seismic network. Then, we present a new approach based on the estimation of differential travel times through the differential phase measurements, to locate the sources of tremors occurring at the end of 2015 at the Klyuchevskoy Volcanic Group in Kamchatka, Russia. We present evidence supporting the existence of two types of activity happening simultaneously during the tremor episode: the main tremor source, originating from a region located between 7 and 9 km depth under the main volcanoes, and the widespread occurrence of weak low-frequency earthquakes occurring at random locations. We show how the phase coherence and the differential phases can be used to provide information on the stability of the tremor source position and to estimate its location.

Résumé: We introduce BPMF (backprojection and matched filtering)-a complete and fully automated workflow designed for earthquake detection and location, and distributed in a Python package. This workflow enables the creation of comprehensive earthquake catalogs with low magnitudes of completeness using no or little prior knowledge of the study region. BPMF uses the seismic wavefield backprojection method to construct an initial earthquake catalog that is then densified with matched filtering. BPMF integrates recent machine learning tools to complement physics-based techniques, and improve the detection and location of earthquakes. In particular, BPMF offers a flexible framework in which machine learning detectors and backprojection can be harmoniously combined, effectively transforming single-station detectors into multistation detectors. The modularity of BPMF grants users the ability to control the contribution of machine learning tools within the workflow. The computation-intensive tasks (backprojection and matched filtering) are executed with C and CUDA-C routines wrapped in Python code. This leveraging of low-level, fast programming languages and graphic processing unit acceleration enables BPMF to efficiently handle large datasets. Here, we first summarize the methodology and describe the application programming interface. We then illustrate BPMF's capabilities to characterize microseismicity with a 10 yr long application in the Ridgecrest, California area. Finally, we discuss the workflow's runtime scaling with numerical resources and its versatility across various tectonic environments and different problems.

Résumé: Onboard NASA's Curiosity rover, the ChemCam LIBS instrument has provided a wealth of information on the chemistry of rocks within Gale crater. Here, we use ChemCam in order to search for carbonates among the >3500 individual targets analyzed by this instrument. Because the carbon-lines are a combination of signal from the CO2-rich atmosphere and possible carbon from the targets, we developed a laboratory-based univariate calibration obtained under Mars-like atmosphere. We measured different type of carbon-bearing samples (sediments, coals, carbonates) and their mixture with a basaltic powder. Based on this work, the preferred approach to qualitatively assess carbon under a CO2-rich atmosphere is to use a ratio to an oxygen line (777 nm) and the estimated limit of detection for carbon in a single LIBS point are found to be of 4.5 wt% and 6.9 wt% for reduced and organic carbon, respectively. Considering carbonate, this LOD correspond to about 50 wt% carbonate in the analyzed volume.Analysis of data obtained on Mars by ChemCam up to sol 3350 reveals the presence of a correlation between the intensity of carbon and oxygen lines, as observed in the laboratory, confirming that most carbon signal is related to ionization of the atmosphere. Some variability in the carbon signal appears related to the physical state of the atmosphere (density, temperature).Based on a combined analysis of carbon lines and major element compositions (Ca, Fe, Mg), there was no detection of carbonate in the ChemCam dataset up to sol 3355. Therefore, we conclude that carbonate was not present as a major constituent (>50%) in the ChemCam LIBS targets, and that soils are not enriched in carbon beyond the limit of detection. The dominant salts present are sulfate, chlorides, and the lack of carbonates in Gale, while observed in Jezero, may at least partly be related to a difference in protolith.

Résumé: Many volcanoes show continuous but variable deformation over timescales of years to decades. Variations in uplift rate are typically interpreted as changes in magma supply rate and/or a viscoelastic response of the host rock. Here we conduct analogue experiments in the laboratory to represent the inflation of a silicic magma body at a constant volumetric flux, and measure the chamber pressure and resulting surface displacement field. We observe that dyke intrusions radiating from the magma body cause a decrease in the peak uplift rate, but do not significantly affect the spatial pattern of deformation or spatially averaged uplift rate. We identify 4 distinct phases: 1) elastic inflation of the chamber, 2) a gradual decrease in the rate of uplift and pressurisation, associated with the formation of visible cracks 3) propagation of a dyke by mode 1 failure at the crack tip and 4) a pressure decrease within the chamber. Phase 2 can be explained by either a) crack damage, which reduces the elastic moduli of the surrounding rock or b) magma filling pre-existing cracks. Thus these experiments provide alternative mechanisms to explain observed variations in uplift rate, with important implications for the interpretation of deformation patterns at volcanoes around the world.

Résumé: Background and aims It is unclear if cadmium (Cd) is loaded into cacao beans directly from the roots and stem or rather via reallocation from leaves and stem via the phloem. Here, a split-root experiment with a stable isotope Cd-108 tracer was set up to determine the short-term circulation in the vegetative tissues of Cd in Theobroma cacao L. seedlings. Methods Roots of cacao seedlings were split into two parts, each growing in separate containers. The compartments contained an equal volume of nutrient solution with a low-dose Cd concentration of 20 nM, and were either (+) or not (-) enriched in stable Cd-108. Seedlings were grown for two weeks and periodically harvested. Results On day 1 after labelling, there was a rise in the Cd-108 isotopic abundance (IA) in the roots in the labelled compartment whereas the Cd-108 IA was unaffected in other plant parts. After 7 days, about 75% of the tracer Cd-108 in the plant had been translocated to the shoots and the largest fraction of tracer was recovered in the stem. The Cd-108 IA in the roots in the non-labelled compartment rose after day 11, demonstrating that Cd was phloem mobile and reallocated to developing tissues. The isotopic abundance of Cd-108 in developing leaves was similar to that in the older leaves, suggesting that Cd originated from leaves rather than directly from roots. Conclusions We corroborated Cd pathways previously studied in mature cacao trees and demonstrated that Cd is reallocated to sink organs via the phloem.

Résumé: Detecting phase arrivals and pinpointing the arrival times of seismic phases in seismograms is crucial for many seismological analysis workflows. For land station data, machine learning methods have already found widespread adoption. However, deep learning approaches are not yet commonly applied to ocean bottom data due to a lack of appropriate training data and models. Here, we compiled an extensive and labeled ocean bottom seismometer (OBS) data set from 15 deployments in different tectonic settings, comprising similar to 90,000 P and similar to 63,000 S manual picks from 13,190 events and 355 stations. We propose PickBlue, an adaptation of the two popular deep learning networks EQTransformer and PhaseNet. PickBlue joint processes three seismometer recordings in conjunction with a hydrophone component and is trained with the waveforms in the new database. The performance is enhanced by employing transfer learning, where initial weights are derived from models trained with land earthquake data. PickBlue significantly outperforms neural networks trained with land stations and models trained without hydrophone data. The model achieves a mean absolute deviation of 0.05 s for P-waves and 0.12 s for S-waves, and we apply the picker on the Hikurangi Ocean Bottom Tremor and Slow Slip OBS deployment offshore New Zealand. We integrate our data set and trained models into SeisBench to enable an easy and direct application in future deployments. Ocean bottom seismometers (OBS) are seismic stations on the seafloor. Just like their counterparts on land, they record many earthquakes on three component sensors but are additionally equipped with underwater hydrophones. To determine the location of an earthquake, seismologists must precisely measure the arrival times of seismic waves. For onshore data, machine learning (ML) has been highly successful in determining earthquake arrival times. However, the noise and the signal are different in the ocean environment. For example, the recordings can contain whale songs and water layer reverberations and are disturbed by ocean bottom currents. We have assembled an extensive database of ocean bottom recordings and trained artificial neural networks to use the underwater hydrophone information and cope with the ocean noise environment. We demonstrate that the resulting ML picker picks are similar to those of human experts and outperform phase pickers based on land data only. We compare earthquake catalogs based on different pickers created from an OBS deployment offshore New Zealand and demonstrate that PICKBLUE outperforms previous pickers. We make the database and ML picker available with a standard interface so that it is easy for other scientists to apply them in their studies. We assembled a database of ocean Bottom Seismometer (OBS) waveforms and manual P and S picks, on which we train PickBlue, a deep learning pickerOur picker significantly outperforms pickers trained with land-based data with confidence values reflecting the likelihood of outlier picksThe picker and database are available in the SeisBench platform, allowing easy and direct application to OBS traces and hydrophone records

Résumé: We performed a passive seismic monitoring of the La Praz similar to 14,000 m3 unstable slope (French Alps) spanning over 10 years. During the last 6 months prior to collapse, we detected a clear 24% decrease in the slope's fundamental resonance frequency, f0, caused by a reduction in overall rock mass stiffness. The combined study of f0 and slope deformation suggested the alternating importance of sudden brittle failure processes versus more ductile phases with possible sliding. Seismic monitoring revealed slope damage that remained ambiguous or undetected with ground surface deformation monitoring, and highlighted critical periods with intense damage. Only some of these critical damage periods could be related to clear external forcing factors such as intense rainfall episodes. These new insights into rock slope's structural condition at depth represent an asset for future monitoring systems. Surface deformation and passive seismic stiffness tracking combined could reveal active slopes with ongoing damage processes. Forecasting the time of rockfalls is of critical importance for risk mitigation operators in order to preserve the safety of persons and the integrity of infrastructure. Most monitoring systems are based on ground deformation measurements, which may fail when the surface motion does not accurately reflect changes in slope stiffness with time. In this work, we used a seismic sensor that passively recorded ground vibrations on top of a similar to 14,000 m3 unstable slope. We detected a significant decrease in the slope's first resonance frequency (-24%) during the 6 months preceding complete collapse. We also revealed details of slope damage processes acting within the slope, showing sudden breakage phases alternating with smoother deformation and sliding phases. These processes would not have been suspected with slope deformation monitoring alone. The use of a new parameter that combines passive seismic tracking and surface deformation measurements could help revealing active slopes with ongoing damage processes. This inovative approach represents an asset for future practical rock slope monitoring. We observed a 24% decrease in rock slope fundamental frequency during the 6 months preceding a similar to 14,000 m3 collapse New insights into slope degradation processes revealed the alternate control of two damage regimes with contrasting rate Results revealed slope damage phases that would not have been suspected on the basis of slope deformation monitoring alone

Résumé: We review the modeling and mathematical properties of compressible viscous flows, ranging from single-phase systems to two-phase systems, with a focus on the occurrence of oscillations and/or concentrations. We explain how establishing the existence of nonlinear weak stability ensures that no such instabilities occur in the solutions because of the system formulation. When oscillation/concentration are inherent to the nature of the physical situation modeled, we explain how the averaging procedure by homogenization helps to understand their effect on the averaged system. This review addresses systems of progressive complexity. We start by focusing on nonlinear weak stability-a crucial property for numerical simulations and well posedness-in single-phase viscous systems. We then show how a two-phase immiscible system may be rewritten as a single-phase system. Conversely, we show then how to derive a two-phase averaged system from a two-phase immiscible system by homogenization. As in many homogenization problems, this is an example where physical oscillation/concentration occur. We then focus on two-phase averaged viscous systems and present results on the nonlinear weak stability necessary for the convergence of numerical schemes. Finally, we review some singular limits frequently developed to obtain drift-flux systems. Additionally, the appendix provides a crash course on basic functional analysis tools for partial differential equation (PDE) and homogenization (averaging procedures) for readers unfamiliar with them. This review serves as the foundation for two subsequent papers (Part I and Part II in this same volume), which present averaged two-phase models with phase exchange applicable to magma flow during volcanic eruptions. Part I introduces the physical processes occurring in a volcanic conduit and establishes a two-phase transient conduit flow model ensuring: (1) mass and volatile species conservation, (2) disequilibrium degassing considering both viscous relaxation and volatile diffusion, and (3) dissipation of total energy. The relaxation limit of this model is then used to obtain a drift-flux system amenable to simplification. Part II revisits the model introduced in Part I and proposes a 1.5D simplification that addresses issues in its numerical implementation. Model outputs are compared to those of another well-established model under conditions typical of an effusive eruption at an andesitic volcano.

Résumé: In a review paper in this same volume, we present the state of the art on modeling of compressible viscous flows ranging from single-phase to two-phase systems. It focuses on mathematical properties related to weak stability because they are important for numerical resolution and on the homogenization process that leads from a microscopic description of two separate phases to an averaged two-phase model. This review serves as the foundation for Parts I and II, which present averaged two-phase models with phase exchange applicable to magma flow during volcanic eruptions. Part I establishes a two-phase transient conduit flow model ensuring: (1) mass and volatile species conservation, (2) disequilibrium degassing considering both viscous relaxation and volatile diffusion, and (3) dissipation of total energy. The relaxation limit of this model is then used to obtain a drift-flux system amenable to simplification. Here, in Part II, we summarize this model and propose a 1.5D simplification of it that alleviates three issues causing difficulties in its numerical implementation. We compare our model outputs to those of another steady-state, equilibrium degassing, isothermal model under conditions typical of an effusive eruption at an andesitic volcano. Perfect equilibrium degassing is unreachable with a realistic water diffusion coefficient because conduit extremities always contain melt supersaturated with water. Such supersaturation has minor consequences on mass discharge rate. In contrast, releasing the isothermal assumption reduces significantly mass discharge rate by cooling due to gas expansion, which in turn increases liquid viscosity. We propose a simplified system using Darcy's law and omitting several processes such as shear heating and liquid inertia. This minimal system is not dissipative but approximates the steady-state mass discharge rate of the full system within 10%. A regime diagram valid under a limited set of conditions indicates when this minimal system captures the ascent dynamics of effusive eruptions. Interestingly, the two novel aspects of the full model, diffusive degassing and heat balance, cannot be neglected. In some cases with high diffusion coefficients, a shallow region where porosity and velocities tend toward zero develops initially, possibly blocking an eventual steady state. This local porosity loss also occurs when a steady-state solution is subjected to a change in shallow permeability. The resulting shallow porosity loss features many characteristics of a plug developing prior to a Vulcanian eruption.

Résumé: This review explores the potential for establishing valley incision chronologies from alluvium-filled cave systems, and covers a total of 30 case studies since 1997. Caves in limestone develop very fast (similar to 10(4) years) when conditions for bedrock solution are optimal, and many contain alluvium deposited by allogenic sinking streams, preserving the sediment thereafter for millions of years. Cave networks display a vertical succession of sub-horizontal passages which indicate past positions of the water table, with the stream in- and outlet caves indicating the former elevation of the adjacent valley floor. Abandoned cave levels are expected to multiply as valley incision increases local relief (descending speleogenesis), but sediment aggradation or glacier ice accumulation may also raise the local base level and flood older caves or generate new ones (ascending speleogenesis). Establishing the age of alluvial sediment hosted by caves relies on burial dating of quartz-rich clasts using two terrestrial cosmogenic nuclides (TCNs) – commonly Al-26 and Be-10 – measured in the same sample. Systematic examination of age-elevation data patterns in the existing literature reveals situations ranging from intuitively consistent valley incision histories to counter-intuitive age inversions and other anomalies. Here those anomalies are analyzed and classified in order to establish the extent to which the corresponding inconsistencies are avoidable, thereby providing a methodical catalogue of foreseeable difficulties and pitfalls. Three domains of uncertainty are emphasized. The first relates to karst processes: cave network geometry, cave passage response to vadose and phreatic processes, and diachronous links between cavity age and sediment. The multiple pathways of speleogenesis are reviewed. They highlight ambiguities behind the concept of 'cave level', which, as a proxy for base-level paleoelevations, may be less precise than subaerial information provided by fluvial fill or strath terraces. The second source of uncertainty lies in the chronological information provided by the alluvium. Sediment dynamics in subterranean karst generate complicated stratigraphic configurations, with opportunities for postdepositional sediment reworking within or between cave levels. Furthermore, a TCN burial age is valid for a population of quartz grains but not necessarily for the entire stratigraphic sequence containing them nor for the cave that contains it. The third source of uncertainty lies in the burial dating method itself, because Al-26 and Be-10 nuclide inventories cannot unequivocally document whether older burial events might have occurred prior to final burial in the cave. The review recommends that (i) sampling strategies should be contingent on a diagnosis of speleogens and speleothems, and on a detailed sedimentological and stratigraphic analysis of the alluvial fills; (ii) dating should focus on individual bedload clasts rather than on sand because this helps to discriminate between pebble populations and to detect sediment mixing; (iii) Al-26/Be-10 ratios in modern channel alluvium and in older deposits stored in the catchment should be measured for the purpose of detecting whether certain features endemic to the sediment cascade could explain apparent burial age anomalies in the cave sediments. In situations where Al-26/Be-10 determinations generate wide age dispersion, four scenarios are discussed in which either the oldest or the youngest age should be retained.

Résumé: Modelling seismic wavefields in complex 3-D elastic media is the key in many fields of Earth Science: seismology, seismic imaging, seismic hazard assessment and earthquake source mechanism reconstruction. This modelling operation can incur significant computational cost, and its accuracy depends on the ability to take into account the scales of the subsurface heterogeneities varying. The theory of homogenization describes how the small-scale heterogeneities interact with the seismic waves and allows to upscale elastic media consistently with the wave equation. In this study, an efficient and scalable numerical homogenization tool is developed, relying on the similarity between the equations describing the propagation of elastic waves and the homogenization process. By exploiting the optimized implementation of an elastic modelling kernel based on a spectral-element discretization and domain decomposition, a fully scalable homogenization process, working directly on the spectral-element mesh, is presented. Numerical experiments on the entire SEAM II foothill model and a 3-D version of the Marmousi II model illustrate the efficiency and flexibility of this approach. A reduction of two orders of magnitude in terms of absolute computational cost is observed on the elastic wave modelling of the entire SEAM II model at a controlled accuracy.

Résumé: Ferroan brucite, (Mg,Fe)(OH)(2), is among the potential mineral candidates for low temperature (<423 K) abiotic H-2 production in ultramafic rocks. To verify this assumption, synthetic ferroan brucite with grain size similar to that observed in natural samples (40-100 nm) was reacted with pure water at temperatures ranging from 348 to 573 K. Experimental products are consistent with the reaction 3 Fe(OH)(2)(brucite) = Fe3O4 + H-2 + 2 H2O. This reaction reached completion in similar to 2 months at 378 K and is thermally activated with an activation energy of 145 +/- 1 kJ/mol. The standard state formation enthalpy and the third law entropy of amakinite, Fe(OH)(2), were refined from the experimental dataset. The new thermodynamic parameters imply that ferroan brucite is stable at significantly lower hydrogen activity than previously calculated. The alteration of Fe-brucite produces H-2 at rates compatible with present day observations of H-2 emissions in natural settings (ophiolite and mid-oceanic ridges). However, efficient fluid renewal is required, as opposed to H-2 production through olivine serpentinisation, which can proceed in static hydraulic conditions.

Résumé: Zinc(II)-phenanthroline complexes are widely used as building blocks to prepare solid-phase chiral catalysts. Adsorbing these complexes on montmorillonite – a green solid support with large external and interlayer surfaces – with the possibility of modulating the structure and the immobilization geometry would allow controlling the reactivity towards the substrate. Here, a series of [ZnPhenx]2+ complexes prepared by varying the phenanthroline/Zn2+ molar ratio in solution were adsorbed onto montmorillonite with the aim to grasp relationships between solution composition and the speciation and structure of the adsorbed complexes. The solid samples were characterized by elemental and chemical analysis, X-rays diffraction, thermogravimetric analysis, and NMR measurements. Atomic scale calculations based on Density Functional Theory (DFT) were also performed to define the structuring of the montmorillonite interlayer in the presence of different intercalated [ZnPhenx]2+ complexes. It was found that [ZnPhenx]2+ complexes were intercalated in a fashion which depends on the composition of the starting zinc(II)-phenanthroline solutions, without being its mirror. Properly tuning the phenanthroline/Zn2+ molar ratio in solution, however, the [ZnPhen]2+, [ZnPhen2]2+ and [ZnPhen3]2+ species and their mixtures were immobilized on montmorillonite in a predictable and reproducible way. This has been achieved through a careful control of the immobilization conditions of the complexes and characterization of the resulting materials. The interlayer structure was also characterized with a modelling approach. This work outlines the procedure to obtain the desired catalytic ZnII-montmorillonite hybrid materials useful as nanosized reaction environments from a starting solution containing several different species in equilibrium. This is a valuable tool for obtaining tailored “green” catalysts, as ZnII complexes have been proven to be effective for a wide variety of organic and polymerization reactions.

Résumé: Dynamic recrystallization can have a strong impact on texture development during the deformation of polycrystalline materials at high temperatures, particularly for materials with strong viscoplastic anisotropy such as ice. Owing to this anisotropy, recrystallization is essential for ensuring strain compatibility, and the development of textures leads to anisotropic softening. Accurate prediction of the effect of recrystallization on the texture evolution of ice is therefore crucial to adequately account for texture-induced mechanical anisotropy in large-scale models of glacial ice flow. However, this prediction remains a challenge. We propose a new formulation for modeling texture evolution due to dynamic recrystallization on the basis of observations of the evolution of the microstructure and texture of ice deforming by dislocation creep and dynamic recrystallization. This formulation relies on an orientation attractor that maximizes the resolved shear stress on the easiest slip system in the crystal. It is implemented in the equation describing the evolution of the crystal orientation with deformation and is coupled with an anisotropic viscoplastic law that provides the mechanical response of the ice crystal. This set of equations, which is the core of the R(3)iCe model is solved by a finite-element method with a semi-implicit scheme coded using the Rheolef library. The resulting open-source software R(3)iCe is validated by comparison with laboratory creep data for ice polycrystals under uniaxial compression, simple shear, and uniaxial tension. It correctly reproduces the texture evolution and mechanical softening observed in the experiment during tertiary creep. Although the present formulation is too time-consuming for direct implementation in large-scale ice flow models, R(3)iCe can be used to adjust the parameterization used to implement texture-induced anisotropy in these models. The validation was performed for ice, but the R(3)iCe implementation is generic and applies to any material whose behavior may be adequately described using an anisotropic flow law. .

Résumé: The loss of fine particles can induce mechanical instabilities in granular soils subjected to internal fluid flow. An appealing countermeasure consists of the re-injection of fine grains with the objective of achieving retention in the soil matrix. In this study, both gravity- and fluid-driven infiltration of fine particles into coarse-grain columns with different solid fraction phi\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\phi$$\end{document} and size ratios R have been studied using coupled pore-scale finite volume (PFV) and discrete element method (DEM) schemes. Three clogging regimes, surface clogging, deep infiltration, and percolation are detected, and the characteristic infiltration depths L0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$L_{0}$$\end{document} are found to grow exponentially with R under gravity- and fluid-driven cases. A probabilistic model derived from pore-constriction size statistics is then put forward, which could efficiently interpret the decaying distribution of fine retention for a given size ratio R and packing density. The mean transit velocity of fine grains follows an increasing trend with R under fixed phi\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\phi$$\end{document} and can be collapsed over an almost constant value with the appropriate scaling of phi/R\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\phi /\sqrt{R}$$\end{document}. Compared to gravitational percolation, more lateral dispersion is found in fluid-driven conditions, and an estimation of the related lateral dispersion coefficient D is provided based on phi\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\phi$$\end{document} and R.

Résumé: Megathrust earthquakes along subduction zones present significant hazards. Evidence from the South Chile subduction zone suggests that the structure and fluid distribution of the megathrust interface governs the size and timing of large earthquakes.

Résumé: The unprecedentedly dense current sampling of the upper mantle with seismic data offers an opportunity for determining representative seismic velocity models for the Earth's main tectonic environments. Here, we use over 1.17 million Rayleigh- and 300,000 Love-wave, fundamental-mode, phase-velocity curves measured with multimode waveform inversion of data available since the 1990s, and compute phase-velocity maps in a 17-310 s period range. We then compute phase-velocity curves averaged over the globe and eight tectonic environments, and invert them for 1D seismic velocity profiles of the upper mantle. The averaged curves are smooth and fit by V-S models with very small misfits, under 0.1%, at most periods. For phase-velocity curves extending up to 310 s, Rayleigh waves resolve V-SV structure down to the shallow lower mantle. Love-wave sampling is shallower, and V-SH and, thus, radial anisotropy profiles are resolved down to 375-400 km depth. The uncertainty of the V-S models is dominated by the trade-offs of V-S at neighboring depths. Using the model-space-projection approach, we quantify the uncertainty of V-S in layers of different thickness and at different depths, and show how it decreases with the increasing thickness of the layers. Example 1D V-S models that fit the data display the expected increase of the lithospheric seismic velocity with the age of the oceanic lithosphere and with the average age of the continental tectonic type. Radial anisotropy in the global and most tectonic-type models show a flip of the sign from positive (V-SH>V-SV) to negative at 200-300 km depth. Negative anisotropy is also observed in the shallow mantle lithosphere beneath oceans down to 45-55 km depth. We also compute a global model with the minimal structural complexity, which fits the data worse than the best-fitting one but does not include a sublithospheric low-velocity zone, providing a simple reference for seismic studies.

Résumé: The Gruneisen parameter is an important parameter for the thermal state and evolution of the core, but its uncertainties and their implications are sometimes overlooked. Several formalisms using different parameters values have been used in different studies, making comparison between studies difficult. In this paper, we use previously published data sets to test the sensitivity of modelling the thermal state of the early core to the different formalisms and parameter values used to describe the evolution of the Gruneisen parameter with density. The temperature of the core obtained in our models is less sensitive to the uncertainties of the parameters used in Al'Tshuler et al. formalism than the uncertainties of the parameters used in Anderson formalism.

Résumé: Coastal sediments constitute a major reservoir for natural and anthropogenic mercury (Hg) and can be used as geochronological records of past Hg deposition. They may also act as secondary Hg sources for pelagic ecosystems via the efflux of toxic methylmercury (MeHg) diffusing from sediment porewaters and/or mobilized by sediment resuspension. In Toulon Bay sediments, which are known as one of the Hg hot spots of the northwestern Mediterranean Sea, we explored Hg species accumulation and mobility. The total Hg concentrations averaged 0.014 μg g- 1 ca. 2000 years ago, then exhibited three major peaks during the Medieval Period, the Early Modern Period of Europe, and the Industrial Era, reaching 0.06, 0.07, and 13 μg g- 1, respectively. The Medieval peak is attributed to the massive development of metallurgy in Europe accompanied by the burning of soil and vegetation, the second peak to the optimum of Hg extraction in Europe (Almade<acute accent>n mine), and the resumption of deforestation after the great plague. The third most recent Hg enrichment is associated with Hg-fulminate production, the scuttling of the French navy fleet during World War II, and ship salvaging and removal in the post-war years. Sampling of the dissolved phase at high vertical resolution above and below the sediment-water interface (SWI) enables us to conclude that MeHg was produced in situ by microbiological pathways and its diffusion across the SWI was negligible. On the other hand, ex-situ resuspension experiments showed that sorption and/or photodemethylation restrict MeHg from the dissolved phase.

Résumé: Since the end of the 20th century, each decade has been warmer than the previous one in the European Alps. As a consequence, Alpine rock walls are generally facing high rockfall activity, likely due to permafrost degradation. We use a unique terrestrial laser scanning derived rockfall catalog over 18 years (2005-2022) compared with photographs (1859-2022) to quantify the evolution of the east face of Tour Ronde (3440-3792 m a.s.l.) in the Mont-Blanc massif (western European Alps) that is permafrost-affected. Overall, 210 rockfalls were identified, from 1 to 15 500 m(3). Forty-five events were >100 m(3) while cumulated volume of events <10 m(3) represents <1% of the fallen rocks. The rockfall magnitude-frequency distribution of the overall inventory follows a power law, with a mean exponent b of 0.44 +/- 0.03, characterizing a high contribution of large rockfalls. The depth of failure ranges from a few centimeters to more than 20 m while 95% of the rockfalls depth is <5 m, highlighting the role of the active layer. The mean rock wall erosion rate is 18.3 +/- 0.2 mm yr(-1) for the 2005-2022 period and ranks in the top range of reported values in the Alps. It has greatly increased between the periods 2006-2014 and 2016-2022, probably in relation to a series of summer heat waves. The exceptional erosion rate of 2015 is driven by one large rockfall in August. Since 2006, an ice apron that covered 16 100 m(2) has now almost vanished, and the surface of the glacier du G & eacute;ant at the rock wall foot has lowered by several tens of meters. The retreat of these two ice masses contributed to the rock wall instability as more than 35% of the rockfall volume detached from the deglaciated surfaces.

Résumé: To design user-centred and scientifically high-quality outreach products to inform about earthquake-related hazards and the associated risk, a close collaboration between the model developers and communication experts is needed. In this contribution, we present the communication strategy developed to support the public release of the first openly available European Seismic Risk Model and the updated European Seismic Hazard Model. The backbone of the strategy was the communication concept in which the overall vision, communication principles, target audiences (including personas), key messages, and products were defined. To fulfil the end-users' needs, we conducted two user testing surveys: one for the interactive risk map viewer and one for the risk poster with a special emphasis on the European earthquake risk map. To further ensure that the outreach products are not only understandable and attractive for different target groups but also adequate from a scientific point of view, a two-fold feedback mechanism involving experts in the field was implemented. Through a close collaboration with a network of communication specialists from other institutions supporting the release, additional feedback and exchange of knowledge was enabled. Our insights, gained as part of the release process, can support others in developing user-centred products reviewed by experts in the field to inform about hazard and risk models.

Résumé: This study examined the arc and line shapes produced in the fault ruptures of the 2016 Mw7.8 Kaikoura earthquake in New Zealand and the 2023 Mw7.8 and Mw7.6 East Anatolian Fault earthquakes in Turkey-Syria. Theoretical fault mechanisms and physical laws of movement were used to interpret the conceptual geometry of the arc and line shapes, and kinematics force movement. Using computer-aided design (CAD) on the Universal Transverse Mercator (UTM) metric projection, this paper presents earthquake parameters defining the fault geometry, including straight lines and arc shapes with specific measurements such as radius, length, angles, and normal/perpendicular vectors. Comparative analysis revealed distinctions between the two seismic events. Specifically, the Kaikoura earthquake exhibited a smaller normal vector compared to the Turkey-Syria earthquakes. Further interpretation uncovered that the Kaikoura earthquake resulted from pressure exerted by the radius arc vector from both the south-east and northwest, aligning with the continuation of the north-easternmost fault rupture. This suggests that the primary fault vector aligns with the fault trend. In contrast, the Turkey-Syria earthquakes displayed two independent circuit systems. The first event in the TurkiyeSyria rupture underwent an orientation change or bending of about 137 degrees (from N24oE to N68oE). The normal vector of the second earthquake originated from the bending angle of the first earthquake, close to its hypocenter. The rupture of the Kaikoura earthquake followed a lineament orientation of N47oE, forming an approximately 10-km wide corridor, comprising both straight lines and arc shapes.

Résumé: In the Southern Hemisphere, the prevalence of oceans and the difficulty of access to land result in reduced coverage of seismological stations, limiting our detailed knowledge of Earth 's structures and of large earthquakes sources. This situation is exacerbated inside the antarctic continent, where only two permanent seismic stations are currently available (IU.QSPA at South Pole and G.CCD). The CCD station, built in early 2000s with state -of -theart surface instrumentation and located at the French -Italian Concordia base (75 degrees S, 123 degrees E), has been providing seismological data since 2008. However, it suffers from several problems: the vault is deformed by the hydrostatic pressure of the snow, the firn waveguide traps anthropogenic noise from the base causing strong noise below 1 s, and a coupling defect limits the performance above 30 s on the horizontal channels. To ensure the continuity of CCD and to improve its overall performance, we started in 2014 to plan the installation of a borehole seismometer at the site. In this article, we describe in detail this renovation of CCD and some examples of data analysis. The new borehole sensor shows that short -period disturbances are largely attenuated ( -20 dB at 0.1 s) compared to the surface installation and that the horizontal channels have a lower noise level at long periods ( -8 dB at 100 s). Data for all components are below the standard noise model between 0.1 and 0.2 s, which makes this sensor one of the quietest installations in the world for this bandwidth. For periods > 600 s we observe atmospheric pressure-related perturbations on the vertical component. Despite this problem, the new CCD borehole station is a success with better-than-expected performances at all periods < 600 s. The data produced are now distributed in the world 's data centers as G.CCD.20 and we encourage the scientific community to use the data for all studies requiring seismograms from Antarctica.

Résumé: Extracting, processing, and delivering energy requires energy itself, which reduces the net energy available to society and yields considerable socioeconomic implications. Yet, most mitigation pathways and transition models overlook net energy feedbacks, specifically related to the decline in the quality of fossil fuel deposits, as well as energy requirements of the energy transition. Here, we summarize our position across 8 key points that converge to form a prevailing understanding regarding EROI (Energy Return on Investment), identify areas of investigation for the Net Energy Analysis community, discuss the consequences of net energy in the context of the energy transition, and underline the issues of disregarding it. Particularly, we argue that reductions in net energy can hinder the transition if demand-side measures are not implemented and adopted to limit energy consumption. We also point out the risks posed for the energy transition in the Global South, which, while being the least responsible for climate change, may be amongst the most impacted by both the climate crisis and net energy contraction. Last, we present practical avenues to consider net energy in mitigation pathways and Integrated Assessment Models (IAMs), emphasizing the necessity of fostering collaborative efforts among our different research communities.

Résumé: Understanding the historical context of rainfall erosivity enhances comprehension of climate and environmental changes, guiding strategies to address global environmental challenges. However, the understanding of the interplay between modern-era environmental hydrology, climate change, and storm evolution remains limited, despite the pivotal role of storm disasters in global environmental change, especially in inland-basin areas. To address this knowledge gap, we present the longest interannual rainfall erosivity history in France, with a specific focus on the area of Clermont-Ferrand, covering the period 1858-2022. Using the Integrated Rainfall Erosivity Model (IREM) approach, refined with process-based insights and expert knowledge, we analyzed the erosivity data and correlated them with environmental and climatic changes. Our findings indicate a rapid and abrupt change in rainfall erosivity around 1964, which we attribute to the negative phase of the North Atlantic Oscillation and a positive phase shift of the Dipole Mode Index. Moreover, the Mann-Kendal statistic demonstrates a significant positive trend in extreme rainfall erosivity (95th percentile) over the entire time-series. A notable finding is the strong coevolution observed between the erosivity density indicator and particulate organic carbon, modulated by multidecadal environmental hydrology in the Rhone River Basin (RRB). These results shed light on the complex interactions among storms, climate, and sediment organic matter, offering insights for environmental management and conservation strategies in the RRB and other regions with similar hydrological characteristics.

Résumé: This study investigates the potential for natural hydrogen (H2) production across western continental Europe and the eastern Mediterranean, focusing on ophiolitic and ultramafic massifs. Our approach integrates geophysical, geological and geochemical parameters to identify regions where serpentinization could be a key natural process for H2 generation. Based on these parameters, we have developed a comprehensive probabilistic model to assess the likelihood of abiotic H2 production at depth. This model incorporates parameters such as geothermal heat flux, magnetic anomalies and the existence of hyperalkaline springs, each weighted according to their possible influence on serpentinization. This weighting is derived from a case study in Albania, where H2 degassing has been observed. The model has been applied to several ophiolitic and ultramafic complexes, including the Ordenes (Spain), the Alter-do-Ch & atilde;o (Portugal), the Ronda (Spain), the northwestern Alps, the Apennine (Italy), the Dinarides, the Hellenides (e.g. Vourinos and Pindos ophiolites in Greece), Troodos (Cyprus), K & imath;z & imath;lda & gbreve;, Bassit, Hatay (Turkey) and Leka (Norway). A ranking has been proposed in terms of the probability of finding H2 at these locations. Subsequently, in order to underscore the potential need for region-specific adaptations of the model, the model was applied to the well-documented Samail Ophiolite in Oman, where H2 seepages are observed. While the model provides a framework for H2-targeted exploration, it also acknowledges its current limitations, emphasizing the necessity for continuous refinement and validation against new observations. The inherent uncertainties in geological processes call for a dynamic modelling strategy to accurately predict and explore geological H2 resources.

Résumé: Most of the current helium (He) reserves originate from fortuitous discoveries, mainly made during oil and gas exploration in sedimentary basins. As helium generation depends on U and Th alpha-decay, old geological provinces gather key ingredients for high He accumulation. However, numerous He-rich springs have also been documented in much younger rocks, such as Variscan granites (320-250 Ma). These latter discoveries question the current exploration guidelines and require revisiting some of the longstanding paradigms. Here, is investigated He migration along a major fault rooted in the Corso-Sardinian batholith (France). Two thermal springs, Caldanelle and Guagno-Les-Bains, show significant outgassing activities of crustal sourced He with concentrations up to 1.45 vol% and flow rates of 110 m3 STP 4He/year. Besides He, the gas phase is dominated by N2 (approximate to 98 vol%) and minor CH4. Based on a survey employing multidisciplinary methodologies, it is revealed that (a) Variscan rocks represent efficient 4He source rocks, (b) the main source of He comes from the underlying Eo-Variscan basement, (c) A deeply rooted fault and dense fractures networks drain the He, (d) the helium loss is limited, (e) faults and fractures may act as partial traps, and finally (f) the presence of an efficient trap could promote a He-rich reservoir with high flux but low reserves. In that sense, young post-orogenic granites represent promising helium plays. The geological context in which Caldanelle and Guagno-Les-Bains are embedded is ubiquitous in European Variscan batholiths. This case study is therefore intended to serve as a guide for helium exploration and to provide insights into helium behavior within a Variscan geological context. Helium, a crucial commodity for various industries, is mainly discovered by chance during oil and gas explorations. However, some thermal springs show high helium concentrations in young Variscan granites, opening new perspectives for helium exploration. This study examined helium migration along a major fault in the Corso-Sardinian batholith. Two thermal springs, Caldanelle and Guagno-Les-Bains, emit substantial crust-derived helium, reaching concentrations up to 1.45% by volume and a flow rate of 110 cubic meters per year of helium. These springs also contain mostly nitrogen (about 98%) and minor methane. The results show that Variscan rocks are potential plays for helium exploration. The primary helium source lies beneath these rocks. A deep fault zone associated with dense fracture networks facilitates helium drainage with minimal loss. Moreover, faults and fractures might also partially retain helium and contribute to its accumulation. The geological context observed in Caldanelle and Guagno-Les-Bains is widespread in European Variscan batholiths; thus, understanding helium behavior in these settings could guide future exploration strategies. Combined geological, geophysical and geochemical analysis of two Corsican He-rich thermal springs Deep faults and dense fracture networks allow for efficient fluid migration with limited loss Variscan geological context could be promising helium plays

Résumé: The textural properties of synthetic and natural clays in the sodium form and exchanged with tetramethylammonium cations (TMA+) were characterized using N2 and Ar physisorption isotherms at cryogenic temperatures. Specific surface areas and micro/mesoporous volumes were determined using the BET and the t-plot models. The t-plot analysis requires the use of reference isotherms measured at the same temperature on the surface of non-porous materials with an identical chemical composition. In order to better assess the effects of chemical heterogeneities in the clay particles, reference isotherms representative of silica surfaces were taken into account in the analysis of the t-curve and corrected to account for variations in curvature at the interface of the film adsorbed in the micropores. In addition, high-resolution Ar adsorption isotherms at 87 K were analyzed using the Derivative Isotherm Summation (DIS) method to quantify the energy contributions of adsorption sites and determine the fractions of basal and lateral surfaces of clay particles. The high-energy adsorption sites, identified in the low-pressure range, were attributed to intra-particle microporosity due to stacking defects and/or open inter-layer spaces. These sites were differentiated from those on the lateral and basal surfaces of the particles. A modification of the DIS method was proposed to measure these contributions and improve the fit with the experimental data. The results show that TMA+ cation exchange significantly increases the microporosity of clays compared to their sodic form, which can be attributed to the increased contribution of intra-particle adsorption sites due to interlayer expansion.

Résumé: In this paper, we address the numerical solution of the quadratic optimal transport problem in its dynamical form, the so-called Benamou-Brenier formulation. When solved using interior point methods, the main computational bottleneck is the solution of large saddle point linear systems arising from the associated Newton-Raphson scheme. The main purpose of this paper is to design efficient preconditioners to solve these linear systems via iterative methods. Among the proposed preconditioners, we introduce one based on the partial commutation of the operators that compose the dual Schur complement of these saddle point linear systems, which we refer to as the BB-preconditioner. A series of numerical tests show that the BB-preconditioner is the most efficient among those presented, despite a performance deterioration in the last steps of the interior point method. It is in fact the only one having a CPU time that scales only slightly worse than linearly with respect to the number of unknowns used to discretize the problem.

Résumé: The heat flux across the core-mantle boundary (CMB) is a fundamental variable for Earth evolution and internal dynamics. Seismic tomography provides access to seismic heterogeneities in the lower mantle, which can be related to present-day thermal heterogeneities. Alternatively, mantle convection models can be used to either infer past CMB heat flux or to produce statistically realistic CMB heat flux patterns in self-consistent models. Mantle dynamics modifies the inertia tensor of the Earth, which implies a rotation of the Earth with respect to its spin axis, a phenomenon called true polar wander (TPW). This rotation must be taken into account to link the dynamics of the mantle to the dynamics of the core. In this study, we explore the impact of TPW on the CMB heat flux over long timescales ( similar to 1 Gyr) using two recently published mantle convection models: one model driven by a plate reconstruction and a second that self-consistently produces a plate-like behaviour. We compute the geoid in both models to correct for TPW. In the plate-driven model, we compute a total geoid and a geoid in which lateral variations of viscosity and density are suppressed above 350 km depth. An alternative to TPW correction is used for the plate-driven model by simply repositioning the model in the original paleomagnetic reference frame of the plate reconstruction. The average TPW rates range between 0.4 and 1.8 degrees Myr – 1 , but peaks up to 10 degrees Myr – 1 are observed. We find that in the plate-driven mantle convection model used in this study, the maximum inertia axis produced by the model does not show a long-term consistency with the position of the magnetic dipole inferred from paleomagnetism. TPW plays an important role in redistributing the CMB heat flux, notably at short timescales ( <= 10 Myr). Those rapid variations modify the latitudinal distribution of the CMB heat flux, which is known to affect the stability of the magnetic dipole in geodynamo simulations. A principal component analysis (PCA) is computed to obtain the dominant CMB heat flux pattern in the different cases. These heat flux patterns are representative of the mantle convection cases studied here and can be used as boundary conditions for geodynamo models.

Résumé: The pressure and temperature conditions at which precipitation of diamond occurs from hydrocarbon mixtures is important for modelling the interior dynamics of icy planets. However, there is substantial disagreement from laboratory experiments, with those using dynamic compression techniques finding much more extreme conditions are required than in static compression. Here we report the time-resolved observation of diamond formation from statically compressed polystyrene, (C8H8)n, heated using the 4.5 MHz X-ray pulse trains at the European X-ray Free Electron Laser facility. Diamond formation is observed above 2,500 K from 19 GPa to 27 GPa, conditions representative of Uranus's and Neptune's shallow interiors, on 30 μs to 40 μs timescales. This is much slower than may be observed during the similar to 10 ns duration of typical dynamic compression experiments, revealing reaction kinetics to be the reason for the discrepancy. Reduced pressure and temperature conditions for diamond formation has implications for icy planetary interiors, where diamond subduction leads to heating and could drive convection in the conductive ice layer that has a role in their magnetic fields. Experiments using high-intensity X-ray pulses incident on high-pressure hydrocarbons suggest that diamond formation can occur at shallower depths in icy planets and may play a role in the internal convection that generates their magnetic fields.

Résumé: A key question for those who study magmatic and volcanic processes is: 'How fast can a magmatic intrusion travel?' Observations and models indicate ranges between 10-2 and 1 m s-1 depending on several parameters, including magma buoyancy (or driving pressure), viscosity and rock fracture toughness (Kc). However, Kc values are difficult to constrain, as effective values inferred from large magmatic intrusions may be 2-3 orders of magnitude larger than measured values from small laboratory samples. This can be attributed to non-elastic processes that dissipate energy at different rates, depending on factors such as the fracture dimension and fracture propagation velocity. Here, we aim to investigate this aspect and provide a scheme for estimating effective fracture toughness values (Keff) by considering fluid-filled fracture processes across different ranges of propagation velocities. To do so, we combine (i) analogue laboratory experiments involving the propagation of oil- and air-filled cracks within a solidified gelatin block, with (ii) numerical simulations, reproducing the crack shape and velocity and providing an estimate of the energy dissipated by the fluid flow between the crack walls. We show that even at the scale of our experiments, Keff values exhibit significant variations spanning over an order of magnitude. Over the velocity ranges relative to our two sets of experiments, we identify two empirical relations for an effective, velocity-dependent fracture energy (triangle Ef (v)), showing that when such an empirical relation is implemented into the numerical model, it improves the prediction of velocities and velocity variations. Following a similar procedure and building empirical relations for triangle Ef (v) or Keff(v) at the scale of magmatic intrusions would improve predictions on dyke propagation velocities in the crust. In order to do so, a considerable amount of observations on the geometry and propagation velocity of magmatic dykes should be gathered.

Résumé: We study the long-period earthquakes that occur at the crust-mantle boundary beneath the Klyuchevskoy volcano group in Kamchatka in order to reconstruct their source mechanisms. These earthquakes are observed at frequencies between 1 and 4 Hz and the phases of their seismograms are strongly affected by the high-pass filtering required to remove the microseismic noise. Therefore, we decided to use an inversion method based on amplitude ratios between S- and P-waves. Considering the uncertainties associated with this method and potentially leading to non-uniqueness of the inversion, we decided not to explore the full space of the source parameters but to test a set of “elementary” mechanisms corresponding to processes possibly occurring within magmatic systems of volcanoes and their surroundings. Also, after measuring the raw amplitudes of P- and Swaves we corrected them for the site amplification effects. Based on the results of the inversion, the generation of the DLP earthquakes beneath Klyuchevskoy by shear faulting (as would be the case in thermomechanical stresses associated with cooling of deep intrusions) can be reasonably excluded. The observed signal amplitudes can be better explained with source mechanisms containing strong volumetric or single force components. The former can be associated with the pressure perturbation withing magmatic reservoirs or conduits and the latter with the sudden acceleration of the magma movement. The ensemble of our observations is compatible with the configuration when the magma is stored in nearly horizontal sills near the crust-mantle boundary and penetrates into the crust through conduits dipping south-southwest, in agreement with previously reported connection of the deep magmatic reservoir with the Bezymanny and Tolbachik volcanoes.

Résumé: In densely populated urban areas, the pressure on water resources is considerable and will tend to intensify over the next decades. Preserving water resources therefore seems fundamental, but many questions remain as to the transfer of contaminants to subsurface waters in these largely sealed areas. Because of their toxicity and persistence in the environment, this work focused on the study of polycyclic aromatic hydrocarbons (PAHs), ubiquitous pollutants mainly produced by human activities. To better understand the main factors leading to the retention or transport of these pollutants in urban environments, vertical transects, from the surface to several meters down, were established on three study sites in or near Paris (France), selected according to an urbanization gradient. Soil samples collected at the surface and urban secondary carbonate deposits (USCD), similar to cave speleothems, sampled underground in quarries and aqueducts were analyzed. As the hydrophobic properties of PAHs favor their sorption onto organic matter, the latter was also studied using organic carbon analysis and UV fluorescence spectroscopy. The USCD located closest to the urbanized surface contained high concentrations of PAHs (76.8 +/- 5.3 ng g(- 1)), while the USCD located at greater depth with organic soil on the surface contained the lowest amount of PAHs (2.9 +/- 0.4 ng g(- 1)), and no PAHs with log KOC > 5. The results highlight the predominant role played by the presence of organic topsoil at the surface in retaining and storing large amounts of PAHs (1914-2595 ng. gsoil(- 1) ), particularly the most hydrophobic ones (i.e. 60% of the 15 PAHs are characterized by a Log KOC >5), which are also the most toxic. The lithology and thickness of the bedrock (between the surface and the USCD) also play an important role in the retention of PAHs, particularly those adsorbed on the particulate phase.

Résumé: Our study aims to understand the palaeohydrological history of Lake Iznik and unravel the complex interplay between climatic, tectonic, and environmental factors that have shaped this Turkish basin. Through the analysis of seismic stratigraphy and sediment cores, we reveal a significant lowstand, indicating a lake level 60 m lower than today at -70 ka BP. Subsequently, a major phase of stepwise transgression is evidenced by 13 buried palaeoshorelines between -70 and 45 ka BP. From 45 to -10 ka cal BP, strong currents controlled the sedimentation in the lake, as evidenced by the occurrence of contourite drifts. Between -14 and 10 ka cal. BP, a major lowstand indicating a drier climate interrupted the current-controlled sedimentation regime. From -10 ka cal. BP, the subsequent increase in lake level occurred at the same time as the reconnection between the Mediterranean and Black seas. Archaeological evidence, including submerged structures of a basilica, establishes a link between lake-level changes and human settlement during the last millennium. The level of Lake Iznik has since continued to fluctuate due to climate change, tectonic events, and human activity. (c) 2024 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Résumé: Egg -tempera painting was a pictorial technique widespread in the Middle Ages. In this work, Sienna earth and yolk have been used to formulate tempera paints according to historical recipes. Micro- and macroscopic properties were investigated to understand the interactions between the pigment and the binder. The pigment, inorganic part of the paint, was characterized by X -Ray Diffraction (XRD), thermal analysis (TG-DTA), Fourier Transform Infrared (FT -IR) Spectroscopy, granulometry, as well as Scanning Electron Microscopy (SEM). Then lecithin adsorption onto pigment particles was probed to understand yolk interaction with Sienna earth, pure kaolinite and goethite particles. NMR-Relaxometry was used to investigate the behavior and accessibility of the mineral surfaces to yolk and water. Macroscopic rheological properties of the paint systems were finally investigated.

Résumé: Assessing or predicting seismic damage in buildings is an essential and challenging component of seismic risk studies. Machine learning methods offer new perspectives for damage characterization, taking advantage of available data on the characteristics of built environments. In this study, we aim (1) to characterize seismic damage using a classification model trained and tested on damage survey data from earthquakes in Nepal, Haiti, Serbia and Italy and (2) to test how well a model trained on a given region (host) can predict damage in another region (target). The strategy adopted considers only simple data characterizing the building (number of stories and building age), seismic ground motion (macroseismic intensity) and a traffic-light-based damage classification model (green, yellow, red categories). The study confirms that the extreme gradient boosting classification model (XGBC) with oversampling predicts damage with 60% accuracy. However, the quality of the survey is a key issue for model performance. Furthermore, the host-to-target test suggests that the model's applicability may be limited to regions with similar contextual environments (e.g., socio-economic conditions). Our results show that a model from one region can only be applied to another region under certain conditions. We expect our model to serve as a starting point for further analysis in host-to-target region adjustment and confirm the need for additional post-earthquake surveys in other regions with different tectonic, urban fabric and socio-economic contexts.

Résumé: X-ray free electron laser (XFEL) sources coupled to high-power laser systems offer an avenue to study the structural dynamics of materials at extreme pressures and temperatures. The recent commissioning of the DiPOLE 100-X laser on the high energy density (HED) instrument at the European XFEL represents the state-of-the-art in combining x-ray diffraction with laser compression, allowing for compressed materials to be probed in unprecedented detail. Here, we report quantitative structural measurements of molten Sn compressed to 85(5) GPa and similar to 3500 K. The capabilities of the HED instrument enable liquid density measurements with an uncertainty of similar to 1 % at conditions which are extremely challenging to reach via static compression methods. We discuss best practices for conducting liquid diffraction dynamic compression experiments and the necessary intensity corrections which allow for accurate quantitative analysis. We also provide a polyimide ablation pressure vs input laser energy for the DiPOLE 100-X drive laser which will serve future users of the HED instrument.

Résumé: Eruptions in basaltic volcanoes are often preceded by increasing seismicity and surface deformation, which progressively damage and weaken the volcanic edifice. We show how damage and crack interaction produce the inverse Omori-Utsu law for earthquakes during pre-eruptive periods. Rock mass continuity, representing damage, is shown to decrease exponentially with the earthquake number; we interpret it as a general form of the Omori-Utsu law. Pre-eruptive earthquake time series are shown to be controlled by heterogeneity distribution, finite-size effect and crack interaction, and by the feeding system characteristic time. Magma-edifice coupling is described by state variables that depend on the continuity and the feeding system characteristic time. Pre-eruptive seismicity of the 2004-2017 24 summit/proximal eruptions of Piton de la Fournaise volcano was well modeled by an inverse Omori-Utsu law. It allowed identifying two cases: (a) strong crack interaction and earthquake number acceleration, when failure in strong intact rock and finite-size effects dominate the brittle fracture process; in that case the magma-edifice interaction power exhibits a maximum before the eruption; (b) weak crack interaction, generating an almost constant earthquake rate and corresponding to a brittle fracture process at constant strain in a weak, fractured rock mass. In this latter case eruptions occurred when the continuity reached a critical value, close to 0.25. Specific times are identified, from the time variations of the state variables; they define estimators that provide values of the eruption time within 10% of the true value in 60%-75% of the cases studied, from the complete time series. Eruptions in basaltic volcanoes are often preceded by increasing seismicity and surface deformation. In this article we study the processes at work in the volcanic edifice rock mass. A rock mass, deformed and fractured, weakens: this process is called damage. Rock elastic characteristics decrease with damage. The way damage evolves under the effect of magma pressure contributes to determine the time evolution of the pre-eruptive deformation. We show that continuity, a measure of damage, is a decreasing exponential of the cumulative number of earthquakes; this relationship is comparable to the definition of Boltzmann entropy. A model of initially elastic edifice, damaged under the pressure of a viscous, incompressible, magma in a reservoir has been developed. It is shown that, when fractures interact, continuity and magma pressure strongly drops, magma flux increases and the power of the magma-edifice interaction reaches a maximum before the eruption. A relation between the time of this maximum and the eruption time has been established and checked using 24 summit eruptions at Piton de la Fournaise; it provided an estimation within 10% of the eruption time in 60%-75% of the cases. Checking this relation with very numerous eruptions on basaltic volcanoes will allow knowing its reliability. Rock mass continuity decreases exponentially with earthquake number and controls magma pressure and flow Pre-eruptive earthquake time series are controlled by heterogeneity distribution and crack interaction for quasi-static deformation When crack interact, magma-edifice interaction power exhibits a maximum before the eruption, used to estimate the eruption time at PdF

Résumé: Arsenic (As) and mercury (Hg) are highly toxic contaminants whereas selenium (Se) is both an essential trace element and potentially harmful at higher concentrations. The hyper-saline lakes of southern Bolivian Altiplano, which are ecological niches for endemic species, are also expected to be enriched in these toxic trace elements. The biogeochemistry of As, Hg, and Se in such high-altitude extreme environments (e.g., high UV radiation and salt content) remains poorly understood. In this study, we investigated the concentrations and chemical forms (speciation) of As, Hg, and Se in sediment, water, and air samples of Lagunas Colorada (LC), Verde (LV), and Blanca (LB) in the South Lipez region (>4200 m a.s.l.). We compared them with the repartition of biodiversity (invertebrates, algae, and bacteria). Extreme As concentrations were found in water (up to 82 mg L-1), and the main As species was inorganic As(V), with neither biogenic methylated As nor volatile As forms being detected in water and air, respectively. Se concentrations in water were of 0.1 to 1.4 μg L-1, and Se existed under different redox states, i.e., Se(IV), Se(VI), and reduced Se (0, -II), including biogenic methylated Se(-II) (trimethyl selenonium). Volatile Se compounds (e.g., dimethyl selenide) were detected in water and air samples. Hg was enriched in the surface water (6 to 30 ng L-1) compared to other regional water bodies, and a significant amount of methyl-Hg and gaseous Hg(0) was detected. The drastic disparity between As, Se and Hg concentrations and speciation between lakes has important implications for their cycling in these extreme aquatic systems. While As mostly accumulated in its oxidized and non-volatile form, Hg and Se concentrations can be controlled by significant conversion to reduced and methylated forms, allowing efficient evasion to the atmosphere. Finally, the salinity, including major ions, and high levels of As were among the main drivers of biodiversity repartition between lakes.

Résumé: A promising superparamagnetic nanomagnetite dipped with Gd was synthesized for possible medical applications. Its size and morphology are independent of Gd content ranging from 1 to 5%. Gadolinium (III) replaced Fe(III) in the lattice. The sizes of Gd-doped nanoparticles ranged from 5 to 50 nm and exhibited a pure magnetite mineralogical phase.

Résumé: Polythermal glaciers can trap considerable volumes of liquid water with the potential to generate devastating outburst floods. This study aims to identify water-filled subglacial reservoirs from ambient seismic noise collected by moderate-cost surveys. The horizontal-to-vertical spectral ratio technique is highly sensitive to impedance contrasts at interfaces, thus commonly used to estimate glacier thickness. Here, we focus on the inverse ratio, that is, the V/H spectral ratio (VHSR), whose high values indicate a low impedance volume beneath the surface, suggesting subglacial cavities. We analyze VHSR peaks from a seismic array of 60 nodes installed on the Tete-Rousse Glacier (Mont Blanc massif, French Alps); data were gathered over 15 days. Mapping the VHSR amplitude over the free surface reveals the main cavity locations and the basal areas affected by melting within the glacier. Results obtained in the field are supported by a conceptual model based on 3D finite-element simulations. Considerable volumes of liquid water may be trapped within cavities in polythermal glaciers. If these cavities rupture, the resulting outburst flood has the potential to cause devastation in populated mountain areas. With the aim of testing methods to locate such cavities, we installed 60 small 3-component seismic sensors on the Tete-Rousse Glacier (Mont Blanc massif, French Alps), which is known to contain such cavities. We used these sensors to test a detection method based on ambient seismic noise. For 3 weeks, the sensors recorded vibrations within the glacier. On a glacier without cavities, these vibrations ought to be predominantly in the horizontal direction. In the presence of a cavity, we expect the ice above the cavity to vibrate mostly vertically-like a bridge. In this paper, we highlight areas on the glacier where vertical vibrations were stronger than horizontal vibrations. These areas fit well with the locations of the main known cavities in this glacier, and with areas affected by basal melting. We supported our field observations with modeling based on 3D simulations, paving the way to a new method to locate water-filled cavities within glaciers. Spectral analysis from ambient seismic noise is complementary to other geophysical methods for investigating glaciers at depth Results suggest that the vertical-to-horizontal spectral ratio is a reliable proxy to locate subglacial cavities Experimental results were confirmed using a simplified numerical model

Résumé: We explore how variation of slip rates in fault source models affect computed earthquake rates of the Pallatanga-Puna fault system in Ecuador. Determining which slip rates best represent fault -zone seismicity is vital for use in probabilistic seismic hazard assessment (PSHA). However, given the variable spatial and temporal scales slip rates are measured over, significantly different rates can be observed along the same fault. The Pallatanga- Puna fault in southern Ecuador exemplifies a fault where different slip rates have been measured using methods spanning different spatial and temporal scales, and in which historical data and paleoseismic studies provide a record of large earthquakes over a relatively long time span. We use fault source models to calculate earthquake rates using different slip rates and geometries for the Pallatanga-Puna fault, and compare the computed magnitude-frequency distributions (MFDs) to earthquake catalog MFDs from the fault zone. We show that slip rates measured across the entire width of the fault zone, either based on geodesy or long-term geomorphic offsets, produce computed MFDs that compare more favorably with the catalog data. Moreover, we show that the computed MFDs fit the earthquake catalog data best when they follow a hybrid -characteristic MFD shape. These results support hypotheses that slip rates derived from a single fault strand of a fault system do not represent seismicity produced by the entire fault zone.

Résumé: Ethyl silicate (tetraethoxysilane, TEOS) is commonly used for consolidating construction materials containing siliceous components such as sandstone, cement mortars and concrete structures. This is especially due to its high compatibility with the substrates ' silicate matrix. Its lack of bonding to calcareous substrates is however considered an important handicap. Here we investigate the consolidation effectiveness and durability of a combined TEOS-nanolime treatment applied on weathered biocalcarenite stone. We report evidence of physical and chemical interactions between the two consolidant materials resulting in limited drying shrinkage and the formation of calcium silicate hydrate (C-S-H) gel, responsible for improving the treated carbonate substrate mechanical properties and treatment durability as compared to both products used separately. The results of this experimental study are promising and could be the foundation for further studies toward obtaining a compatible, effective, and long-lasting consolidation treatment for porous calcareous building materials.

Résumé: Full-waveform inversion (FWI) has emerged as the state-of-the art high resolution seismic imaging technique, both in seismology for global and regional scale imaging and in the industry for exploration purposes. While gaining in popularity, FWI, at an operational level, remains a heavy computational process involving the repeated solution of large-scale 3-D wave propagation problems. For this reason it is a common practice to focus the interpretation of the results on the final estimated model. This is forgetting FWI is an ill-posed inverse problem in a high dimensional space for which the solution is intrinsically non-unique. This is the reason why being able to qualify and quantify the uncertainty attached to a model estimated by FWI is key. To this end, we propose to extend at an operational level the concepts introduced in a previous study related to the coupling between ensemble Kalman filters (EnKFs) and FWI. These concepts had been developed for 2-D frequency-domain FWI. We extend it here to the case of 3-D time-domain FWI, relying on a source subsampling strategy to assimilate progressively the data within the Kalman filter. We apply our strategy to an ocean bottom cable field data set from the North Sea to illustrate its feasibility. We explore the convergence of the filter in terms of number of elements, and extract variance and covariance information showing which part of the model are well constrained and which are not. Analysing the variance helps to gain insight on how well the final estimated model is constrained by the whole FWI workflow. The variance maps appears as the superposition of a smooth trend related to the geometrical spreading and a high resolution trend related to reflectors. Mapping lines of the covariance (or correlation matrix) to the model space helps to gain insight on the local resolution. Through a wave propagation analysis, we are also able to relate variance peaks in the model space to variance peaks in the data space. Compared to other posterior-covariance approximation scheme, our combination between EnKF and FWI is intrinsically scalable, making it a good candidate for exploiting the recent exascale high performance computing machines.

Résumé: This study examines the role of advanced remote sensing technologies, such as LiDAR, SfM, GB-InSAR, and thermal imaging, in enhancing rockfall hazard assessment. These tools have revolutionized the analysis of rock structures, allowing for detailed characterization and quantification of rockfall frequency and volume, essential for accurate hazard evaluation. The paper acknowledges challenges in current hazard assessments. It discusses the use of temporal probability calculations for known rockfall sources and the importance of understanding rock mass degradation mechanisms. Techniques like high-resolution 3D tracking are highlighted for capturing cyclic deformations and hysteresis effects, influenced by environmental factors. The study also explores the evolving efforts in characterizing discontinuity sets from 3D point clouds and the application of the rock mass structure scale extract from GSI for estimating power-law parameters. Overall, the paper provides an overview of remote sensing in rockfall destabilization studies, with a special focus on the emerging field of thermal imaging.

Résumé: The Lacq area in southwest France has been associated with continuous moderate induced seismic activity since 1969. However, the mechanisms driving this induced seismicity are not fully understood: reservoir depletion has been proposed as the main factor, and more recently wastewater injection has been suggested to play a more important role. The interpretation of these mechanisms relies heavily on the quality of earthquake locations, which we prove to be weak due to a lack of local instrumentation for several years. In order to provide the most complete and reliable induced event catalogue for the studies of the Lacq induced seismicity mechanisms and seismic hazard, we made an exhaustive compilation, analysis and improvement of all available catalogues. We also provided new earthquake detections and relocations in a 3-D velocity model from past and present temporary deployments never used for studying the Lacq area. Important remaining location uncertainties lead us to also carefully sort the events according to their location confidence, defining 3 classes of events (unconstrained location, location constrained within 2-3 km and 1-2 km, respectively). This new harmonized catalogue and the identification of well-constrained events, covering 50 yr of induced seismicity, allow us to propose that wastewater injection is almost certainly the main mechanism driving the seismicity, with (i) most of the constrained events located within the reservoir boundaries and (ii) the released seismic energy variations following variations in injection operations at different scales. In particular, we have also highlighted a change in the injection-seismicity relationship around 2010-2013. From 2013, despite lower injection volumes, seismicity remained persistent and some clusters of earthquakes were detected predominantly in spring, summer and early autumn, except in winter periods. From 2016, we observed a strong temporal relationship between days with higher rate/volume injections (approximately above 400 m3 d-1) and both clustered events and higher magnitude earthquakes (greater than 2.4).

Résumé: Detailed study of field sections and extensive ammonite collection allowed to specify the sedimentary evolution and age of the Albian series of the Western Atlas (Morocco). After a significant hiatus of earliest Albian age, the Albian transgression began in the late Douvilleiceras leightonense Zone with partly clastic deposits. A transgressive pulse gave way to clayey marl deposits (Douvilleiceras mammillatum Zone), which evolved upward to partly carbonate, laminated deposits of late early Albian to earliest middle Albian age (Lyelliceras pseudolyelli to early Lyelliceras lyelli zones). A major hiatus that encompassed most of the middle Albian, was followed by a new transgression marked first by sandy deposits (Dipoloceras cristatum and Pervinquiria pricei zones), and then by clayey marl and limestone nodules (Pervinquieria inflata Zone). A sharp sea level fall (late Pervinquieria inflata to early Pervinquieria fallax zones) led to the development of a shallow marine carbonate shelf (Kechoula Formation). A last transgressive pulse allowed deposition of outer shelf clayey marls (Pervinquieria rostrata to Arrhaphoceras briacensis (?) zones), interrupted near the Albian-Cenomanian boundary by a sea level fall and hiatus. Anoxic to disoxic conditions are recorded in the latest early Albian and the late Albian, which correlate with the Leenhardt and Breistroffer levels, respectively. Correlations with Albian successions in North Africa and southern Europe suggest a mainly eustatic origin for the most important sedimentary discontinuities, although the late Albian sea-level drop may be tectonically enhanced. (c) 2024 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Résumé: Seismic hazard assessment in low-to-moderate seismicity regions can benefit from theknowledge of surface deformation rates to better constrain earthquake recurrence mod-els. This, however, amounts to assuming that the known seismicity rate, generallyobserved over historical times (i.e., up to a few centuries in Europe), provides a represen-tative sample of the underlying long-term activity. We here investigate how this limitedsampling can affect the estimated seismic hazard and whether it can explain the disagree-ment between the seismic moment loading rate as seen by nowadays Global NavigationSatellite Systems (GNSS) measurements and the seismic moment release rate by pastearthquakes, as is sometimes observed in regions with limited activity. We approach thisissue by running simulations of earthquake time series over very long timescales thataccount for temporal clustering and the known magnitude-frequency distribution in suchregions, and that those are constrained to a seismic moment rate balance between geo-detic and seismicity estimates at very long timescales. We show that, in the example ofsoutheastern Switzerland, taken here as a case study, this sampling issue can indeedexplain this disagreement, although it is likely that other phenomena, including aseismicdeformation and changes in strain rate due to erosional and/or glacial rebound, may alsoplay a significant role in this mismatch

Résumé: We develop a method to estimate relative seismic moments M0 and corner frequencies fc of acoustic emission events recorded in laboratory experiments from amplitude spectra of signal's coda composed of reverberated and scattered waves. This approach has several advantages with respect to estimations from direct waves that are often clipped and also are difficult to separate in experiments performed on small samples. Also, inversion of the coda spectra does not require information about the source locations and mechanisms. We use the developed method to analyze the data of two experiments: (a) on granite from the Voronezh crystal massif and (b) on Berea sandstone. The range of absolute corner frequencies estimated in both experiments is around 70 – -700 kHz. The range of relative seismic moments covers 103.5. The relation between fc and M0 observed on the first stages of both experiments, consisted of increasing isotropic confining pressure, approximately follow M0 similar to fc-3 ${M}{0}\sim {f}{c}<^>{-3}$ scaling and the b-value of the Gutenberg-Richter distribution was found close to 1. This can be interpreted as rupturing of preexisting material defects with a nearly constant stress-drop and has a similarity with observations of “natural” earthquakes. Deviations from this “earthquake-like” behavior observed after applying axial loading and initiation of sample damaging can be interpreted as changes in stress-drop. Lower stress-drops prevail for sandstone and higher for granite sample respectively that can be related to the strength of corresponding material. Earthquakes generation mechanisms and conditions favoring their occurrence are still debated. Inability to observe these processes in-situ and long lasting earthquake preparation period favor using laboratory experiments to verify quickly the adequacy of proposed hypotheses. Fracturing of small rock samples with high pressures and recording acoustic waves from their micro-fractures is among them. In most cases, the laboratory acoustic emission (AE) is analyzed and compared to natural seismicity statistically, demonstrating similar Gutenberg-Richter power-law magnitude distribution. More advanced analyses can include source characteristics (corner frequencies, seismic moments, and stress-drops), responsible for the source size, forces acting there and stress changes. Ensembles of these characteristics can give ideas on the common generation mechanisms. In laboratory, several technical limitations slow down the implementation of such analyses, widely used in Earth's seismology. We propose a method that use coda waves (signal's decaying part) to estimate source parameters of the laboratory AE. We tested it on two similar experiments conducted on different rock types. Source analyses revealed the high similarity of well-studied tectonic earthquakes and fracturing of pre-existing inhomogeneties in the rock samples by applying equally distributed external pressure to it. The active production of new fractures under high one-directional pressure in contrary deviated significantly. Coda of acoustic emission (AE) waveforms can be used for the source characterization Scaling between the corner frequency fc and seismic moment M0 varies in function of loading regime and rock type The M0 – fc scaling of AE events was found similar to that of tectonic earthquakes when isotropic confining pressure applied to intact rocks

Résumé: This study presents the findings of a splitting analysis conducted on core-refracted teleseismic shear waves (SKS, SKKS and PKS, called together as XKS) and local shear waves, obtained from a dense seismological network spanning the Kamchatka Peninsula. The objective of the study is to examine the pattern of mantle flow beneath the study area through the investigation of seismic anisotropy. The peninsula is situated at the northeastern end of the Kuril-Kamchatka subduction zone, where the Kuril trench intersects with the western boundary of the Aleutian trench. The data set utilized in this study comprises waveform data from a dense network of seismic stations (99 broad-band and short-period stations for the local shear wave splitting analysis and 69 broad-band stations for the SKS splitting analysis). The seismograms were downloaded from publicly available data repositories including the IRIS Data Management Center and the GFZ Data Services (GEOFON program). The dense station coverage allows us to investigate the lateral variations in anisotropy, providing insights into the flow patterns within the mantle. The processing of the combined data sets of local shear wave and teleseismic XKS waves allowed us to partially decipher the source of anisotropy in the mantle. Small delay (splitting) times (similar to 0.35 s) observed from the local-S data suggest that anisotropy in the mantle wedge is relatively weak with lateral variations. Larger splitting times (similar to 1.1 s) observed for the XKS waves relative to local S suggest that the main part of splitting on the XKS waves occurs in the subslab mantle. On the other hand, the rotational pattern of seismic anisotropy observed by both the local S and XKS waves suggests the presence of a toroidal flow at the NE edge of the subducting slab, which affects both the mantle wedge and subslab mantle. For the regions away from the edge of the slab, the mantle flow seems to be governed mainly by the drag of the lithospheric plate over the underlying asthenosphere.

Résumé: The early stages of mineralization continue to be in the focus of intensive research due to their inherent importance for natural and engineered environments. While numerous observations have been reported for single steps in the pathways of various crystallizing phases in previous studies, the complexity of the underlying processes and their elusive character have left central questions unanswered in most cases. In the present work, we provide a detailed view on the nucleation of calcium sulfate mineralization-an abundant mineral with broad use in construction industry-in aqueous systems at ambient conditions. As experimental basis, a co-titration procedure with potentiometric, turbidimetric and conductometric detection was developed, allowing solution speciation and the formation of crystallization precursors to be monitored quantitatively as the level of nominal (super)saturation gradually increases. The nature and spatiotemporal evolution of these precursors was further elucidated by time-resolved small-angle X-ray scattering (SAXS) and analytical ultracentrifugation (AUC) experiments, complemented by cryogenic transmission electron microscopy (cryo-TEM) as a direct imaging technique. The results reveal how ions associate into nanometric primary species, which subsequently aggregate and develop anisotropic order by intrinsic structural reorganization. Our observations challenge the common understanding of fundamental notions such as the nucleation barrier or the meaning of supersaturation, with broad implications for mineralization phenomena in general and the formation of calcium sulfate in geochemical settings and industrial applications in particular.

Résumé: Recent updates of pan-European seismic hazard and risk maps adopted the partially non-ergodic Kotha et al. (Bull Earthq Eng 18:4091-4125, 2020) ground-motion model. This model was regressed from the Engineering Strong Motion dataset, containing ground-motion data of MW >= 3 events mostly from Italy, Turkey, Greece, and in smaller fractions from rest of the active shallow crustal tectonic regions of Europe. Through mixed-effects regressions, the non-ergodic model partially resolved the spatial variability of attenuation characteristics across most of seismically active Europe, but not in France due to the then lack of a regional dataset. With the availability of a manually processed dataset from R & eacute;sif network, and a computationally viable Bayesian inferencing algorithm, this study aims to extend the non-ergodic applicability of the model to M-W<3 earthquakes, attenuating regions, tectonic localities, and sites located in France. In process, a few important deci-sions had to be made concerning the updating methodology, and the interpretation of spa-tial variability of attenuation-specifically, that of the tectonic localities producing earth-quakes. The methodology and results are discussed, emphasising the need to revise the current ground-motion regionalisation approach, and to tailor the updating procedure to be application specific. This study anticipates and supports a shift from frequentist to Bayes-ian approach of ground-motion modelling, in order to maintain continuity of knowledge regressed from various ground-motion datasets.

Résumé: The western Alpine belt is the focal point of moderate but constant seismic activity. Numerous geodynamic and seismological studies underline the many scientific questions linked to Alpine dynamic processes and the associated rate of deformation resulting from late continental collision phases, and the assessment of seismic hazard and its associated risks. Seismic monitoring in the northern French Alps was launched in 1987 with the installation of the first seismological network, hosted by the Earth Science Observatory at Grenoble Alpes University. Since then, the network has been updated over the years, keeping pace with technical developments in seismic instrumentation, monitoring and data management. The homogenization of information described in this scientific data paper is motivated by the need for a single instrumental seismic catalogue, consisting in arrival times picks and hypocenters using the same velocity model. The final catalogue SISMalp-1987-2023 (CC-BY-4.0) contains 50,822 weak-to-moderate earthquakes with local magnitude between -1.8 and 5.0; it can serve as a basis for all general seismotectonic and risk assessment studies in the region.

Résumé: A Ground-Motion Model (GMM)'s apparent aleatory variability is inflated by errors in its pre-dictor parameters, specifically the moment magnitude ( MW ). Multiple MW values can be available for an event (direct or deduced) and various MW defini-tion approaches have been proposed to assign a unique MW value to an event. In this study, we investigate the impact of MW definition on a pan-European Engineering Strong Motion dataset based Fourier GMM, using two datasets with MW defined by two distinct approaches: [1] the ranking strategy of the Euro-Mediterranean Earthquake Catalogue (EMEC 2019) and [2] the multi-strategy (standardization, ranking, unification, averaging) approach to MW definition of Laurendeau et al., (Geophys J Int 230:1980-2002, 2022). Large discrepan-cies in MW values can be observed especially between MW ranging from 4.0 to 5.0. While the GMM median predictions remain unchanged irrespective of dataset, we report a large reduction in between-event variability of the GMM at low frequencies (< 1.8 Hz) when strategy [2] is adopted over [1] (18% at 0.35 Hz). This reduction applies to frequencies before the corner-frequency of the Fourier spectrum, as this part of the spectrum depends primarily on seismic moment. We attribute this reduction to the use of direct MW values in [2] instead of deduced MW values in [1], the priority scheme in the ranking strategy, and the unification strategy. Our study suggests that the approach used to define a unique MWin the GMM dataset may have a significant impact on its predictions in seismic hazard assessment. Highlights center dot Moment magnitude ( MW ) definition approach significantly influences the prediction variability of ground-motion models. A unification-ranked approach to defining MW reduces the pan-European variability by up to 18% at low fre-quencies. Centroid Moment Tensor services for MW are preferable to specific studies for statistic seismic hazard assessment.

Résumé: On Venus, radar observations of the surface have highlighted two categories of craters: bright-floored, interpreted as pristine, and dark-floored, interpreted as being partially filled by lava. While volcanic resurfacing occurs within and outside craters in the plains, it seems mainly concentrated within the interior of dark-floored craters in the crustal plateaus, suggesting that the magma is negatively buoyant there. Indeed, crater unloading may facilitate vertical ascent of a negatively buoyant magma by decompressing the underlying crust. However, the crater topography also generates a shear stress which would tend to horizontalize the vertical propagation of a dyke. We use numerical simulations of magma ascent in an axisymmetric crater stress field to demonstrate that, depending on the crust thickness and the magma-crust density contrast, a negatively buoyant magma can indeed erupt only in the crater interior while remaining stored in the crust elsewhere. In particular, we identify four different behaviors depending on if and where a magma-filled crack ascending below a crater reaches the surface. We draw a regime diagram as a function of two characteristic dimensionless numbers. For eruption to occur only in the crater interior requires a crust thinner than 45 km and a limited range of magma-crust density contrasts, between 40 and 280 kg m-3 for crust thicknesses between 20 and 45 km, the permissible range decreasing for increasing crustal thicknesses. These results suggest that the crustal plateaus may not be particularly thick and could be slightly differentiated, but probably not very felsic. The Magellan mission revealed two categories of impact craters at the surface of Venus: the pristine bright-floored and the dark-floored craters, which are interpreted as craters partially filled by smooth lava after their formation. In the crustal plateaus of Venus, the magma reaches the surface mainly within craters, suggesting that it is denser than the crust. Because of the crater negative topography, the underlying crust is decompressed relative to its surroundings, which, in turn, facilitates magma ascent below the crater despite its negative buoyancy. We first gather surface observations on a set of craters located in the crustal plateaus of Venus to construct a characteristic fresh crater topography. We then use a model of magma ascent below a crater in the crust of Venus to constrain the magma and crust densities as well as the initial magma storage depth that allow for magma eruption within the crater interior only. We show that magma reaches the surface only in the interior of the crater if the crust is slightly less dense than the magma and if it is not too thick (<= 45 km in thickness). We identify four different behaviors for magma-filled crack propagation below craters We draw a behavior diagram as a function of two dimensionless numbers characterizing dyke propagation below a crater Magma infilling of dark-floored craters in Venus' plateaus requires a crustal thickness <= 45 km and a small crust-magma density contrast

Résumé: Global warming leads to drastic glaciers shrinkage worldwide, hence affecting the global water balance. Small mountain glaciers are the most widespread types of glaciers but have received less attention compared to larger ones, despite their importance for the regional hydrological cycle. To better understand the forcing underlying their dynamics, we investigated the glacial activity in the Hengduan Mountains in the SE Tibetan Plateau over the last 2000 years by analysing sediments from the Yunzhu proglacial lake. Five sediment cores were retrieved and dated using short-lived radionuclides, 14C, and analyses of Earth's magnetic field palaeosecular variations. A multiproxy analysis was performed on sediment cores, including geochemical, sedimentological, and hyperspectral analyses. As the sediment was relatively homogeneous and poor in organic material, geochemical ratios and pigment analysis were used to track the evolution of terrigenous inputs and lake photosynthetic activity. Sedimentation is dominated by clastic inputs, which are traced by K flux, while the authigenic components are traced by chlorophyll pigments. During the Little Ice Age (LIA), anoxic conditions prevailed at the bottom of the lake, leading to the preservation of millimetric laminae in the sediment and a bloom of purple sulphur bacteria, visible through abundant bacteriochlorophyll a pigment. We attribute this to persisting ice cover preventing water column mixing over most of the year. During cold periods such as the LIA or the Dark Ages, the relative amount of terrigenous inputs increased at the expense of lake bioproductivity. We interpret the observed erosion increases during cold periods as the consequence of glacial activity, consistent with other sparse glacial records available on the Tibetan Plateau. We show that glacial extent was mainly controlled by temperature in the past two millennia rather than by precipitation, yielding potential widespread melting in the next decades as well as more irregular water supply downstream.

Résumé: The ambient-temperature compressibility and room-pressure thermal expansion of two Mg 3 (PO 4 ) 2 polymorphs (farringtonite = Mg 3 (PO 4 ) 2 -I, with 5- and 6-fold coordinated Mg, and chopinite = “Mg-sarcopside” = [ 6 ] Mg 3 (PO 4 ) 2 -II), three Mg 2 PO 4 OH polymorphs (althausite, hydroxylwagnerite and epsilon -Mg 2 PO 4 OH, all with [ 5 ] Mg and [ 6 ] Mg) and phosphoellenbergerite ( [ 6 ] Mg) were measured on synthetic powders using a synchrotron-based multi-anvil apparatus to 5.5 GPa and a laboratory high-temperature diffractometer, with whole-pattern fitting procedures. Bulk moduli range from 64.5 GPa for althausite to 88.4 GPa for hydroxylwagnerite, the high-pressure Mg 2 PO 4 OH polymorph. Chopinite, based on an olivine structure with ordered octahedral vacancies ( K 0 = 81.6 GPa), and phosphoellenbergerite, composed of chains of face-sharing octahedra ( K 0 = 86.4 GPa), are distinctly more compressible than their homeotypical silicate (127 and 133 GPa, respectively). The compressibility anisotropy is the highest for chopinite and the lowest for phosphoellenbergerite. First-order parameters of quadratic thermal expansions range from v 1 = 2.19 x 10 – 5 K – 1 for epsilon -Mg 2 PO 4 OH to v 1 = 3.58 x 10 – 5 K – 1 for althausite. Phosphates have higher thermal-expansion coefficients than the homeotypical silicates. Thermal anisotropy is the highest for farringtonite and the lowest for hydroxylwagnerite and chopinite. These results set the stage for a thermodynamic handling of phase-equilibrium data obtained up to 3 GPa and 1000 degrees C in the MgO-P 2 O 5 -H 2 O and MgO-Al 2 O 3 -P 2 O 5 -H 2 O systems.

Résumé: Cemented granular materials play an important role in both natural and engineered structures, as they are able to resist traction forces. However, modeling the mechanical behavior of such materials is still challenging, and most of existing constitutive models follow phenomenological approaches that unavoidably disregard the microstructural mechanisms taking place on the bonded grains scale. This paper presents a multiscale approach applicable to any kind of granular materials with solid bonds between particles. Inspired from the H-model, this approach allows simulating the behavior of cemented materials along various loading paths, by describing the elementary mechanisms taking place between bonded grains. In particular, the effect of local bond failure process on the macroscopic response of the whole specimen is investigated according to the bond strength characteristics.

Résumé: The 2024 moment magnitude 7.5 Noto Peninsula (Japan) earthquake caused devastation to communities and was generated by a complex rupture process. Using space geodetic and seismic observations, we have shown that the event deformed the peninsula with a peak uplift reaching 5 meters at the west coast. Shallow slip exceeded 10 meters on an offshore fault. Peak stress drop was greater than 10 megapascals. This devastating event began with a slow rupture propagation lasting 15 to 20 seconds near its hypocenter, where seismic swarms had surged since 2020 because of lower-crust fluid supply. The slow start was accompanied by intense high-frequency seismic radiation. These observations suggest a distinct coseismic slip mode reflecting high heterogeneity in fault properties within a fluid-rich fault zone.

Résumé: Although blind normal faults are common in subduction environments, their rheology, kinematics and interaction with the upper crust are poorly constrained. A month-long shallow normal faulting sequence in the Ibaraki-Fukushima prefectural border (IFPB), northeast Japan, which followed the Mw9.0 Tohoku-Oki earthquake (TOE) and culminated in the Mw6.7 Iwaki earthquake, provides a window into megathrust-to-normal fault interaction. Stress change calculations indicate that direct triggering by the TOE co- and post-seismic slip does not provide a plausible explanation for the IFPB earthquake sequence. In quest for an alternative triggering mechanism, we analyzed post-TOE GNSS data from eastern IFPB. A key step in this analysis is the removal of the large-scale post-TOE displacement field, after which a distinct highly-localized strain along the coastline becomes apparent. The accumulation of this strain was mostly aseismic, and migrated with time prior to the Iwaki earthquake in a manner that correlates well with post-TOE local seismicity. We attribute the pre-Iwaki earthquake strain accumulation to aseismic slip along low-angle seaward dipping blind normal fault, activated by the TOE. Stresses transferred by this slip episode accelerated the failure along the IFPB shallow normal faults. This indirect triggering of the Iwaki earthquake sequence by the TOE highlights the complexity of stress transfers in subduction environments. The 11 March 2011, Mw9.0 Tohoku-Oki megathrust earthquake (TOE) triggered widespread seismicity throughout north-east Japan. One of the most intense inland TOE aftershock sequences occurred along the Ibaraki-Fukushima prefectural border (IFPB) during the first month following the TOE. That sequence, which ended a long period of seismic quiescence in the IFPB area, culminated with the damaging 11 April 2011, Mw6.7 Iwaki earthquake. The IFPB sequence is dominated by shallow normal faulting, suggesting regional extension. Due to its distance from the TOE slip area, activity in the IFPB cannot be explained solely due to the TOE co- or post-seismic slip. Here we analyze dense GNSS data and show that early post-seismic aseismic strain that accumulated in the IFPB greatly exceeded the seismic strain due to the IFBP shallow normal faulting. We associate that strain with slip along a low-angle seaward dipping normal fault that is situated between the subduction interface and the IFPB. We show that the low-angle normal fault's response to the TOE static stress change manifested in a month-long slip transient with an equivalent moment magnitude equal to Mw6.7. We suggest that slip along the low angle normal fault greatly enhanced the failure of the shallow IFPB normal faults. GNSS data analysis reveals a much larger aseismic than seismic strain in the Ibaraki-Fukushima Prefectural border The observed strain field resulted from transient slip on a blind low-angle normal fault offshore the study area Among on- and off-megathrust sources, the low angle normal fault is the primary source to static stress driving the Ibaraki-Fukushima swarm

Résumé: This article presents a Python-based program, DFT2FEFFIT, to regress theoretical extended X-ray absorption fine structure (EXAFS) spectra calculated from density functional theory structure models against experimental EXAFS spectra. To showcase its application, Ce-doped fluorapatite [Ca-10(PO4)(6)F-2] is revisited as a representative of a material difficult to analyze by conventional multi-shell least-squares fitting of EXAFS spectra. The software is open source and publicly available.

Résumé: In the northern Andes, partitioning of oblique subduction of the Nazca plate beneath the South American continent induces a northeastward motion of the North Andean Sliver. The strain resulting from this motion is absorbed by crustal faults, which have produced magnitude 7+ earthquakes historically in the Andean Cordillera of Ecuador and southern Colombia. In order to quantify the strain in that area, we derive a high-resolution surface velocity map using InSAR time-series processing. We analyzed 6-8 yr of Sentinel-1 data and combined different satellite line-of-sight directions to produce a reliable velocity map in the east direction. We use interpolated GNSS data to express the velocity map with respect to Stable South America and remove the long-wavelength pattern due to the postseismic deformation following the 2016 M-w 7.8 Pedernales earthquake. The InSAR velocity map finds high east-west shortening strain rates along north-south trending structures within the Western Cordillera and the Interandean valley, with little deformation taking place east of them. This result strengthens the previous proposition of a similar to 350 km long Quito-Latacunga tectonic block, forming a restraining bend in the overall right-lateral strike-slip fault system accommodating the northeastward escape motion of the North Andean Sliver. However, the high spatial resolution provided by InSAR indicates that previously proposed boundaries for this block need to be revised. In particular, InSAR results highlight high strain rates (>300 nstrain yr(-1)) along undescribed active structures, south and west of the proposed limits for the Quito-Latacunga block, respectively, in Peltetec and Ibarra regions. Interestingly, the two areas with the largest strain rates spatially correlate with the proposed areas of large historical earthquakes. Modeling of the InSAR and GNSS velocities in these areas suggests shallow coupling and high slip rates on structures which, previously, were not identified as active. We also demonstrate a slow-down of the shallow aseismic slip on the Quito fault after the Pedernales earthquake, suggesting that stress changes following large megathrust events might trigger transient slip behaviors on crustal faults. The high-resolution strain map provided by this work provides a new basis for future tectonic models in the Ecuadorian and southern Colombian Andes, and will contribute to the seismic hazard assessment in this highly populated area of the Andes.

Résumé: In the Western Alps, a first Late Cretaceous to Eocene “Pyrenean-Provencal” compressive phase accommodating N-S shortening resulting from the convergence between Africa and Eurasia is classically described. It is followed by the Neogene “Alpine phase” accommodating E-W shortening. Since this major tectonic change is not explained by a modification of the global Africa-Eurasia convergence, it should be explained instead by more local causes, possibly by the subduction of the Ligurian Ocean that initiated in the Oligocene beneath the European and Iberian plates. In this paper, we present analogue models simulating the Neogene evolution of this subduction zone, in order to understand how it impacted the regional tectonics. Although models do not include the lithospheric plate overriding the subduction zone, their surface deformations share many similarities with the Neogene tectonics of Western Europe and Iberia. We observe that the tectonic evolution is largely controlled by the roll-back of the slab, that occurred much faster than the Africa-Eurasia convergence. Models reproduce the opening of the Western Mediterranean Basins and the dispersion of the AlKaPeCa continental fragments (Alboran, Kabylian, Peloritan and Calabrian blocks). They also show that the subduction of the Ligurian Ocean favors the counterclockwise rotation of Adria. In more elaborated models, we introduced a pre-existing weakness along the Africa and Adria margins, to reproduce the break-off of the oceanic slab that followed the beginning of continental subduction both in Northern Africa and Adria. Slab break-off is followed by the exhumation of the subducted continent. We observe that the influence of subduction on the kinematics of Adria largely decreases following slab break-off. In the models, the total counterclockwise rotation of Adria varies between 7 degrees and more than 30 degrees, depending on the timing of slab break-off. Since the process of subduction modifies the displacement of Adria, it also impacts the tectonic evolution of surrounding regions, especially in the Alpine belt: Our models show that during slab-roll back and before the Ligurian slab break-off, the azimuth of convergence between Adria and Europe shifts from similar to N-S to similar to ENE-WSW. Hence, they suggest that the oceanic subduction in the Western Mediterranean may contribute to the “Oligocene revolution” described by Dumont et al. (2011), leading to E-W shortening in the Western Alps and to the activation of the Periadriatic right-lateral shear zones in the Central Alps. We conclude that the western Mediterranean region is a spectacular example showing how the tectonics of mountain ranges and plate boundaries may be controlled by distant subduction processes. Dans les Alpes occidentales, on decrit classiquement une phase tectonique “pyreneo-provencale” ancienne, du Cretace superieur a l'eocene, accommodant un raccourcissement N-S resultant de la convergence entre l'Afrique et l'Eurasie. Elle est suivie par la “phase alpine” Neogene, qui correspond a un raccourcissement E-W. Comme ce changement tectonique majeur ne resulte pas d'un changement de convergence entre l'Afrique et l'Eurasie, il doit etre explique par des causes plus locales, en particulier par la subduction de l'Ocean Ligure qui s'est produite a partir de l'Oligocene sous les plaques europeenne et iberique. Nous presentons des modeles analogiques simulant l'evolution de cette zone de subduction, afin de determiner dans quelle mesure elle a modifie la tectonique regionale. Bien que ces modeles ne comportent pas de plaque lithospherique chevauchant la zone de subduction, nous observons que leurs deformations de surface presentent de nombreuses similitudes avec la tectonique neogene de l'Europe occidentale et de l'Iberie, qui est largement controlee par le recul du plan de subduction. En effet, celui-ci a ete beaucoup plus rapide que la convergence Afrique-Eurasie. Les modeles reproduisent l'ouverture des bassins de Mediterranee occidentale et la dispersion des fragments continentaux AlKaPeCa (Alboran, Kabylie, bloc peloritain et Calabre). Ils montrent egalement que la subduction de l'Ocean Ligure a favorise la rotation antihoraire de la plaque Adria. Dans certains modeles, nous avons introduit une faiblesse preexistante au niveau des marges africaine et adriatique, afin de reproduire le detachement de la plaque oceanique qui s'est produit suite a la subduction continentale, sous l'Afrique du Nord et Adria. Le detachement de la plaque oceanique entraine l'exhumation du continent subduit. L'influence de la subduction sur la cinematique de la plaque Adria diminue fortement apres que le detachement se soit produit. Dans les modeles, la rotation antihoraire totale d'Adria varie entre 7 degrees et plus de 30 degrees, en fonction de la chronologie du detachement de la plaque plongeante. Puisque le processus de subduction modifie le deplacement d'Adria, il impacte aussi l'evolution tectonique des regions qui bordent cette plaque, en particulier dans les Alpes: Nos modeles montrent que pendant le recul de la plaque plongeante, et avant le detachement oceanique, l'azimut de convergence Adria-Europe tourne de similar to N-S a similar to ENE-WSW. Ils suggerent donc que la subduction oceanique de Mediterranee occidentale a contribue a “revolution oligocene” decrite par Dumont et al. (2011), conduisant a un raccourcissement E-W dans les Alpes occidentales et a l'activation des zones de cisaillement dextres peri-adriatiques dans les Alpes centrales. Il apparait que la region mediterraneenne occidentale est un exemple remarquable montrant comment la tectonique des chaines de montagnes et des frontieres de plaques peut etre controlee par des processus de subduction lointains.

Résumé: By demonstrating that extensional inheritance plays a decisive role in the formation of orogens, recent studies have questioned the ability of a unique, complete Wilson cycle model to explain the diversity of collisional orogens. For 5 years, the OROGEN Research Project had therefore the ambition to challenge this classical Wilson cycle model. By focusing on the diffuse Africa-Europe plate boundary in the Biscay-Pyrenean-Western Mediterranean system, the project questioned the preconceived “Orogen singularity” assumption and investigated the role of divergent and convergent maturities in orogenic and post-orogenic processes. This work led us to rethink the development of collisional orogens in a genetic (or process-driven) way and to propose an updated version of the “ classical Wilson cycle”, the Wilson Cycle 2.0, and the ORO-Genic ID concept presented in this paper. The particularity of the Wilson Cycle 2.0 is to take into account the divergence and convergence maturity reached during extensional and orogenic processes in proposing different tectonic tracks associated with different ORO-Genic ID numbers. The ORO-Genic ID is composed of a letter (or track), corresponding to the maturity of divergence reached and a number corresponding to the maturity of convergence reached during the formation of the orogen. This new concept relies on the observed pre- and syn- convergent tectono- stratigraphic and magmatic record and deformation history and can be identified in using diagnostic criteria presented in this paper. It represents therefore a powerful tool that can be used to characterize the evolution and the architectural type of an orogenic system. Moreover, as a mappable concept, it can be easily used worldwide and can help us to explain differences in the style of deformation at crustal scale between orogens. En d & eacute;montrant que l'h & eacute;ritage extensional joue un r & ocirc;le d & eacute;cisif dans la formation des orog & egrave;nes, des & eacute;tudes r & eacute;centes ont remis en question le cycle de Wilson et sa capacit & eacute;, en tant que mod & egrave;le unique, & agrave; expliquer la diversit & eacute; des orog & egrave;nes collisionnels. Pendant 5 ans, le projet de recherche OROGEN s'est donc donn & eacute; pour ambition de questionner ce mod & egrave;le classique du cycle de Wilson. En se concentrant sur la fronti & egrave;re diffuse entre les plaques Afrique-Europe dans le syst & egrave;me Golfe de Gascogne-Pyr & eacute;n & eacute;es-M & eacute;diterran & eacute;e occidentale, le projet a remis en cause l'hypoth & egrave;se pr & eacute;con & ccedil;ue de la << singularit & eacute; orog & eacute;nique >> et a explor & eacute; le r & ocirc;le de la maturit & eacute; divergente et de la maturit & eacute; convergente dans les processus orog & eacute;niques et post-orog & eacute;niques. Ce travail nous a amen & eacute;s & agrave; repenser le d & eacute;veloppement des orog & egrave;nes collisionnels d'un point de vue g & eacute;n & eacute;tique (ou ax & eacute; sur les processus) et nous a amen & eacute; & agrave; proposer une version actualis & eacute;e du << cycle de Wilson classique >>, appel & eacute;e Cycle de Wilson 2.0 et le concept d'ID ORO-g & eacute;nique pr & eacute;sent & eacute; dans cet article. La particularit & eacute; du Cycle de Wilson 2.0 est de prendre en compte la maturit & eacute; de la divergence et la maturit & eacute; de la convergence atteinte au cours des processus d'extension et d'orog & eacute;n & egrave;se, en proposant diff & eacute;rents parcours tectoniques associ & eacute;s & agrave; diff & eacute;rents num & eacute;ros d'identit & eacute; ORO-g & eacute;nique. Le num & eacute;ro d'identit & eacute; ORO-g & eacute;nique est compos & eacute; d'une lettre (ou d'un parcours), correspondant & agrave; la maturit & eacute; de la divergence atteinte, et d'un num & eacute;ro correspondant & agrave; la maturit & eacute; de la convergence atteinte lors de la formation de l'orog & egrave;ne. Ce nouveau concept repose sur l'enregistrement tectono-stratigraphique et magmatique avant et pendant la phase de convergence, ainsi que sur l'histoire de la d & eacute;formation observ & eacute;e, et peut & ecirc;tre identifi & eacute; en utilisant les crit & egrave;res diagnostiques pr & eacute;sent & eacute;s dans cet article. Il constitue donc un outil puissant pouvant & ecirc;tre utilis & eacute; pour caract & eacute;riser l'& eacute;volution et le type architectural d'un syst & egrave;me orog & eacute;nique. De plus, en tant que concept cartographiable, il peut & ecirc;tre facilement utilis & eacute; dans le monde entier et nous aider & agrave; expliquer les diff & eacute;rences de style de d & eacute;formation & agrave; l'& eacute;chelle crustale entre les orog & egrave;nes.

Résumé: Non-reciprocal interactions of discrete or continuous systems may induce surprising responses such as flutter instabilities. It is shown in this paper that a finite one-dimensional lattice under non-symmetrical elastic interactions may flutter for sufficiently strong unsymmetrical interactions. An exact solution is presented for the vibration of such one-dimensional lattices with direct and non-symmetrical elastic interactions. An internal force controlling the interactions is included in the model as an additional force for each mass, which acts proportionally to the elongation of a spring at its position. This non-conservative problem due to this circulatory interaction is solved from the resolution of a linear difference equation for this unsymmetrical repetitive lattice. It is possible to derive the exact eigenfrequency dependence with respect to the unsymmetrical interaction parameter, which plays the role of a bifurcation parameter. Divergence and flutter instabilities of this fixed-fixed non-conservative axial lattice under non-Hermitian interactions are theoretically predicted, from a direct approach or by solving the difference equation whatever the number of masses of the lattice. It is shown that the system may flutter for sufficiently strong unsymmetrical interactions, whatever the size of the system, for even or odd number of masses. However, divergence instability may arise in such a system only for even number of masses. The drastic change of response of the present system for odd or even number of particles is specific of the discrete nature of the dynamic system.

Résumé: Previous studies show that the total volume of fractures increases non-linearly during loading as rocks approach failure in triaxial compression at stress and temperature conditions representative of the upper crust. However, the factors that control the critical volume of fractures or the critical spatial organization of the fracture network that trigger macroscopic failure remain unclear. To identify the fracture characteristics that determine the timing of macroscopic failure and localization of the fracture networks, we analyze data from six X-ray tomography experiments on Westerly granite with varying confining stress, fluid pressure, and amounts of preexisting damage. We develop machine learning models to predict 1) the timing of failure, 2) the localization of the fracture networks as measured with the Gini coefficient of the fracture volume, and 3) the change in localization from one differential stress step to the next. When the models only have access to individual fracture characteristics, the fracture length produces the best predictions of the distance to failure. When the models have access to the fracture length and sets of other characteristics, the fracture volume, aperture, and distance between fractures produce the best predictions of the distance to failure. The characteristics that describe the time or loading in the experiment, the axial strain and differential stress, produce some of the best predictions of the Gini coefficient. The results are generally consistent among the different experiments, suggesting that the fracture characteristics that determine the timing of macroscopic failure, and the localization of the fracture network, are independent of the range of confining stress, fluid pressure, and amount of preexisting damage tested here. Our results are consistent with the idea that monitoring the spatial distribution of deformation and changes in the seismic wave properties indicative of fracture growth may improve forecasting efforts of failure in the crust.

Résumé: High-resolution seismic imaging at all scales using full waveform inversion is now routinely used in the industry and in the academy. One key element for the success of this approach is a numerical method, named adjoint state method, originally designed for optimization problems constrained by partial differential equations, a category to which full waveform inversion belongs. This method provides an efficient way to compute the gradient of the full waveform inversion misfit function, which is the most computationally demanding task in the implementation of full waveform inversion. While well known, the complete and rigorous mathematical derivation of the adjoint state method for full waveform inversion remains missing in the scientific bibliography. The aim of this study is to remedy this lack. The derivation is performed in general settings, that is in the elastodynamics approximation, with and without considering viscosity. Through the calculus, the mechanism of the adjoint state strategy makes clear the connection between the incident and adjoint fields, especially regarding their initial and boundary conditions. The impact of introducing the viscosity is carefully analysed. The resulting gradient formulas are analysed and shown to be consistent with already published ones. The generic approach which is adopted also makes it possible to derive misfit function gradients with respect to other quantities than the subsurface mechanical parameters, for instance with respect to the initial or the boundary conditions, which could be of interest for specific applications where the reconstructed parameters are not only volumetric mechanical parameters but boundary parameters or initial field values.

Résumé: Using GNSS horizontal surface velocities and Sentinel -1 interferometry line -of -sight velocities, we quantify the current velocity field of the Potwar Plateau Salt Range fold -and -thrust belt. From this velocity field indicating a creep of the Potwar Plateau along the Main Himalayan Thrust, we inferred a weak subhorizontal de<acute accent>collement level formed by a massive Precambrian salt layer. To the south of the Plateau, the Salt Range is uplifted along the Salt Range Thrust, conditioned by the presence of an inherited normal fault. The Kalabagh Fault, which forms the western boundary of the Salt Range and Potwar Plateau, exhibits a creep rate of 3.3 mm/yr. Numerical modelling enabled us to characterise the slip distribution and coupling along the faults, showing the presence of a large asperity along the de<acute accent>collement level beneath the Potwar Plateau and several asperities along the eastern part of this basal thrust. The model also indicated an alternation of coupled and decoupled zones along the Kalabagh Fault, suggesting that this strike -slip fault can be characterised by creep and the occurrence of earthquakes and/ or slow slip events. Considering the lack of instrumental and historical large -magnitude earthquakes in this area, the Main Himalayan Thrust and Kalabagh Fault are likely to be affected by earthquakes of magnitude Mw larger than 7.5. A slip rate of 20 mm/yr is modelled along the southern and superficial parts of the Salt Range Thrust, which is larger than the 14 mm/yr slip rate along the Main Himalayan Thrust at depth. This observation suggests the existence of a southward flow of massive salt along the Salt Range Thrust.

Résumé: In August 2019, a multistage hydraulic fracturing (HF) operation was carried out at Preston New Road, United Kingdom. HF caused abundant seismic activity that culminated with an ML 2.9 event. The seismic activity was recorded by a downhole array of 12 sensors located in a nearby monitoring well. About 55,556 events were detected and located in real time during the operation by a service company. In this study, we first improve the number of detections by applying template matching and later calculate the moment magnitude of the associated earthquakes. Then we show that by separately analyzing the periods during and immediately after injection, distinct patterns can be identified. We observe an increase in the delay and decrease in amplitude of peak seismicity during subsequent phases of injection. After injection, the seismicity decay can be described by the Omori-Utsu law. The decay rate tends to slow with each successive injection, in particular during the later injection stages. In addition, the frequency-magnitude distribution evolves from a tapered distribution (lack of large events) to a bilinear distribution (excess of large events). This evolution is gradual, with the corner magnitude increasing with each injection. We interpret these patterns as the result of the combined effect of two factors: (1) the stimulated volume becoming increasingly aseismic and (2) the gradual increase in its size, which increases the probability of triggered events on preexisting faults. More generally, these patterns suggest that seismic activity during injection is strongly influenced by the injection history and is modulated by local conditions such as stress state, fault structure, and permeability.

Résumé: Catastrophe bonds (cat bond in short) are an alternative risk-transfer instrument used to transfer peril-specific financial risk from governments, financial institutions, or (re)insurers, to the capital market. Current approaches for cat bond pricing are calibrated on seismic mainshocks, and thus do not account for potential effects induced by earthquake sequences. This simplifying assumption implies that damage arises from mainshocks only, while aftershocks yield no damage. Postearthquake field surveys reveal that this assumption is inaccurate. For example, in the 2011 Christchurch Earthquake sequence and 2016-2017 Central Italy Earthquake sequence, aftershocks were responsible for higher economic losses when compared to those caused by mainshocks. This article proposes a time-dependent aggregate loss model that takes into account seismicity clustering and damage accumulation effects in the computation of damage. The model is calibrated on the seismic events recorded during the recent 2016-2017 Central Italy Earthquake sequence. Furthermore, the effects of earthquake sequence on cat bond pricing is explored by implementing the proposed model on five Italian municipalities. The investigation showed that neglecting time-dependency may lead to higher difference (up to 45%) in the cat bond price when compared to standard approaches.

Résumé: The production of engineered magnesite (MgCO3) under mild conditions remains an important fundamental challenge in order to store permanently the industrial captured CO2. Because, the magnesite is the more-knownstable carbonate at the Earth surface conditions and it is ready-to-use as profitable construction materials. In the present study, time-resolved Raman spectroscopy experiments have been conducted to characterize magnesite formation from nesquehonite slurry at 90 degrees C in an ionic carbonate alkaline medium (CO32-/HCO3- close to 1) using four different soluble Mg salts (acetate, sulphate, nitrate and chloride of magnesium). The investigated experimental conditions have revealed that only nesquehonite (MgCO3 & sdot;3H2O) via un amorphous phase transformation is produced at room temperature. However, magnesite was systematically formed from nesquehonite slurry when temperature increase to 90 degrees C (heat-ageing step). Here, hydromagnesite (Mg5(CO3)4(OH)2 & sdot;4H2O) and eitelite (Na2Mg(CO3)2) with long lifetimes were the main characterized transient phases prior to magnesite formation depending of the counterions. Moreover, eitelite rare mineral has not been reported as transient phase during magnesite formation. In summary, the imposed carbonate concentration, carbonate speciation, counterions, competitive divalent cations and pH have played a critical role on the magnesite formation at 90 degrees C. The discovered experimental mild conditions are promising; however, 2-3 days were required in single Mg system, except when dissolved calcium is added (Ca/Mg.,:-.10.15) in the chloride counterion system; for such case only one hour is required to produce Ca -magnesite and protodolomite at 90 degrees C, i.e., the production of anhydrous Mg -Ca carbonates phases in very reduced time. In this latter case, the monohydrocalcite (CaCO3 & sdot;H2O) and the nesquehonite precursors produced at room temperature were rapidly transformed via concurrent dissolution into Ca -magnesite (CaxMg1-xCO3) and protodolomite (Ca0.5Mg0.5CO3). In conclusion, these novel insights are relevant for fundamental (direct monitoring of multi-nucleation events in complex ionic and/or slurries systems) and applied (permanent storage of CO2) research on the formation of anhydrous Mg carbonates (e.g., magnesite and dolomite) debated in the last two centuries.

Résumé: Thermal convection in planetary solid (rocky or icy) mantles sometimes occurs adjacent to liquid layers with a phase equilibrium at the boundary. The possibility of a solid-liquid phase change at the boundary has been shown to greatly help convection in the solid layer in spheres and plane layers and a similar study is performed here for a spherical shell with a radius-independent central gravity subject to a destabilizing temperature difference. The solid-liquid phase change is considered as a mechanical boundary condition and applies at either or both horizontal boundaries. The boundary condition is controlled by a phase change number, Phi, that compares the timescale for latent heat exchange in the liquid side to that necessary to build a topography at the boundary. We introduce a numerical tool, available at https://github.com/amorison/stablinrb, to carry out the linear stability analysis of the studied setup as well as other similar situations (Cartesian geometry, arbitrary temperature and viscosity depth-dependent profiles). Decreasing Phi makes the phase change more efficient, which reduces the importance of viscous resistance associated to the boundary and makes the critical Rayleigh number for the onset of convection smaller and the wavelength of the critical mode larger, for all values of the radii ratio, gamma. In particular, for a phase change boundary condition at the top or at both boundaries, the mode with a spherical harmonics degree of 1 is always favoured for Phi less than or similar to 10-1. Such a mode is also favoured for a phase change at the bottom boundary for small (gamma less than or similar to 0.45) or large (gamma greater than or similar to 0.75) radii ratio. Such dynamics could help explaining the hemispherical dichotomy observed in the structure of many planetary objects.

Résumé: Terraces are highly developed along the Albanian rivers and eleven levels of terraces are recognized in the area, nine occurring during the last glacial cycle (MIS 5d to end of MIS 2). An allostratigraphy study of the fluvial terraces shows a large variety of the geometry of the sedimentary units beneath this set of terraces. This variety is controlled by the respective amount of the three parameters: lateral erosion, aggradation and difference between incision and aggradation. Active faults offset the paleoriver profiles at throw rates locally greater than 1 mm<middle dot>yr-1 and the tectonic uplift influences the long term incision: Nested strath terraces or nested filled terraces with substratum risers occur in zones of high uplift rate (greater than 0.4 mm<middle dot>yr-1), superposed units and nested fill terraces with hidden substratum risers occur in the weakly uplifted zones of the intramountainous graben-like structures. Most of the Albanian terraces are located above straths (nearly flat erosional surfaces) linked to phases of lateral beveling. The thickness of the sedimentary units above the strath surfaces is mostly influenced by the altitudinal distribution of the river catchments: thin strath terraces are found in the low elevation catchments, while thick fill terraces are found in large catchments and we suggest here that the deposition of fill terrace sediments occurred very rapidly at the cold-warm transitions when the high elevation areas of the large catchments were not protected by vegetation and heavily affected by hillslope processes that delivered a large volume of sediments. The thick Holocene valley fill, locally affected by fill-cut terraces, extends several tens kilometer within the mountain valleys and is probably linked to the mid-Holocene sea-level highstand.

Résumé: High-relief glacial valleys shape the modern topography of the Southern Patagonian Andes, but their formation remains poorly understood. Two Miocene plutonic complexes in the Andean retroarc, the Fitz Roy (49 degrees S) and Torres del Paine (51 degrees S) massifs, were emplaced between 16.9-16.4 Ma and 12.6-12.4 Ma, respectively. Subduction of oceanic ridge segments initiated ca. 16 Ma at 54 degrees S, leading to northward opening of a slab window with associated mantle upwelling. The onset of major glaciations caused drastic topographic changes since ca. 7 Ma. To constrain the respective contributions of tectonic-mantle dynamics and fluvio-glacial erosion to rock exhumation and landscape evolution, we perform inverse thermal modeling of a new data set of zircon and apatite (U-Th)/He from the two massifs, complemented by apatite 4He/3He data for Torres del Paine. Our results show rapid rock exhumation recorded only in the Fitz Roy massif between 10 and 8 Ma, which we ascribe to local mantle upwelling forcing surface uplift and intensified erosion around 49 degrees S. Both massifs record a pulse of rock exhumation between 7 and 4 Ma, which we interpret as enhanced erosion during the beginning of Patagonian glaciations. After a period of erosional and tectonic quiescence in the Pliocene, increased rock exhumation since 3-2 Ma is interpreted as the result of alpine glacial valley carving promoted by reinforced glacial-interglacial cycles. This study highlights that glacial erosion was the main driver to rock exhumation in the Patagonian retroarc since 7 Ma, but that mantle upwelling might be a driving force to rock exhumation as well. The isotopic system (U-Th)/He in apatite and zircon record the ages in which a rock experiences relatively low temperatures (200-60 degrees C) at shallow crustal depths (6-1 km). We present a new data set of low-temperature thermochronometers for rocks of the Fitz Roy and Torres del Paine mountains in the Southern Patagonian Andes. Fast rock cooling can be forced by intensified surface erosion, and/or tectonic and mantle activity. An episode of fast cooling between 10 and 8 Ma was identified in the Fitz Roy mountains, and mantle upwelling forcing surface uplift, combined with high fluvial erosion may have caused fast rock exhumation. A regional episode of fast rock cooling between 7 and 4 Ma causing 1-3 km of exhumation in the Fitz Roy and Torres del Paine is coincident with the onset of Patagonian glaciations, which would have enhanced erosion and, thus, rock exhumation. An episode of fast rock cooling in the Quaternary is recorded in Torres del Paine rocks, interpreted as enhanced fluvio-glacial erosion during the Plio-Pleistocene climate transition toward faster glacial/interglacial cycles. Therefore, we were able to quantify separately the effects of tectonics and climate changes on rock exhumation, what is usually difficult due to simultaneously occurring processes. Mantle upwelling in Southern Patagonia is the most likely mechanism forcing rock exhumation between 10 and 8 Ma in the Fitz Roy massif Apatite (U-Th)/He data reveal glacial erosion as the main driver to the exhumation of the Fitz Roy and Torres del Paine between 7 and 4 Ma Apatite 4He/3He data reveal intensified fluvio-glacial erosion in Torres del Paine as a result of the Plio-Pleistocene climate transition

Résumé: In a review paper in this same volume, we present the state of the art on modeling of compressible viscous flows ranging from single-phase to two-phase systems. It focuses on mathematical properties related to weak stability because they are important for numerical resolution and on the homogenization process that leads from a microscopic description of two separate phases to an averaged two-phase model. This review serves as the foundation for Parts I and II, which present averaged two-phase models with phase exchange applicable to magma flow during volcanic eruptions. Here, in Part I, after introducing the physical processes occurring in a volcanic conduit, we detail the steps needed at both microscopic and macroscopic scales to obtain a two-phase transient conduit flow model ensuring: (1) mass and volatile species conservation, (2) disequilibrium degassing considering both viscous relaxation and volatile diffusion, and (3) dissipation of total energy. The resulting compressible/incompressible system has eight transport equations on eight unknowns (gas volume fraction and density, dissolved water content, liquid pressure, and the velocity and temperature of both phases) as well as algebraic closures for gas pressure and bubble radius. We establish valid sets of boundary conditions such as imposing pressures and stress-free conditions at the conduit outlet and either velocity or pressure at the inlet. This model is then used to obtain a drift-flux system that isolates the effects of relative velocities, pressures, and temperatures. The dimensional analysis of this drift-flux system suggests that relative velocities can be captured with a Darcy equation and that gas-liquid pressure differences partly control magma acceleration. Unlike the vanishing small gas-liquid temperature differences, bulk magma temperature is expected to vary because of gas expansion. Mass exchange being a major control of flow dynamics, we propose a limit case of mass exchange by establishing a relaxed system at chemical equilibrium. This single-velocity, single-temperature system is a generalization of an existing volcanic conduit flow model. Finally, we compare our full compressible/incompressible system to another existing volcanic conduit flow model where both phases are compressible. This comparison illustrates that different two-phase systems may be obtained depending on the governing unknowns chosen. Part II presents a 1.5D version of the model established herein that is solved numerically. The numerical outputs are compared to those of another steady-state, equilibrium degassing, isothermal model under conditions typical of an effusive eruption at an andesitic volcano.

Résumé: The occurrence of aseismic creep along seismogenic faults significantly impacts seismic hazard assessment by releasing accumulated stress and reducing the slip deficit. Since the 1999 M(w)7.6 Izmit earthquake on the North Anatolian Fault in Turkiye, while aseismic creep has been observed as a postseismic response to the Izmit rupture, additional slow slip events were detected in 2015 and 2016, accommodating several millimeters of relative displacement over periods of approximately one month. By automating Interferometry Synthetic Aperture Radar time series processing from 2016 to 2021 (FLATSIM project) and applying specific post-processing, we extract the tectonic signal to estimate the slip dynamics of the Izmit segment, including the detection and characterization of slow slip events. Modeling the slip distribution at depth on a 2D fault interface within a layered elastic half-space, we estimate a locking depth of 11 km and steady creep between 2 and 5 km. Above the steady creep zone, we identify two new shallow slow slip events in March 2018 and November 2019, with moment magnitudes of 4.3 and 4.4, respectively. Based on creepmeter measurements, we estimate a lateral propagation velocity of 6.4 km/day for the 2019 event. The location of these shallow slow slip events above the sedimentary-bedrock interface suggests a critical role of variations in frictional properties in the occurrence of transient slip events.

Résumé: Artisanal and small-scale gold mining (ASGM) is a major source of mercury (Hg) contamination in Amazonian ecosystems, due to remobilization of geogenic Hg from mined soil, and anthropogenic Hg used for gold amalgamation. To assess these two relative contributions, Hg stable isotope composition together with geochemical variables were determined in sediment samples collected in the early 2000s across the main watersheds of French Guiana. Mercury in sediment was found associated with organic matter and Fe/Al oxides. Total Hg concentrations were correlated (p < 0.001) to both mass-dependent (delta Hg-202) and odd-mass-independent fractionation (Delta Hg-199) indicating that the Hg isotopic composition of river sediments reflects the extent of contamination, with two isotopic end-members for pristine or geogenic (delta Hg-202 = -2.53 +/- 0.23 parts per thousand, Delta Hg-199 = -0.62 +/- 0.10 parts per thousand) and for ASGM contaminated (delta Hg-202 = -0.42 +/- 0.20 parts per thousand, Delta Hg-199 = -0.01 +/- 0.07 parts per thousand) sediments. A binary mixing model showed that the contribution of anthropogenic Hg in river sediments varied widely (ca. 0 to 100%) and reflected the geographical and historical monitoring of ASGM activities in French Guiana. These results highlight that Hg isotopic measurements in archived sediments allow retrospective assessment of Hg pollution in ASGM-impacted regions and evaluation of its temporal evolution.

Résumé: Inselbergs are isolated rock bodies that develop as a result of differential weathering and erosion advances during topographic etchplain formation. The timing and rate of inselberg growth are key for constraining external controls on landscape evolution, particularly in etching terrains associated with elevated plateaus carved on granitic lithologies, and in tectonically active provinces in tropical climate zones (e.g., Antioque & ntilde;o Plateau, AP). We applied new morphostratigraphic and geomorphometric analyses, along with Be-10 terrestrial cosmogenic nuclide (TCN) measurements, to in situ rock samples from the Pe & ntilde;ol de Guatap & eacute; Inselberg (PGI), in the AP of the Colombian Andes to address the chronological framework of bornhardt formation in this tropical setting. The PGI is located in a rejuvenated landscape between middle Miocene to late Mio-Pliocene erosion surfaces. Erosion rates inferred from Be-10 analyses ranged between similar to 0.0024 +/- 0.0001 and 0.24 +/- 0.0283 mm/yr. This broad range is consistent with the long-term erosion rate of similar to 0.04 mm/yr and mid-term erosion rates of 0.01-0.08 mm/yr previously documented for the region using low-temperature thermochronology. Our findings indicate that the PGI emerged as an important landscape feature over a period of similar to 0.5-2.0 Myr and has protruded high above the average AP surface since the Pliocene. The new TCN-derived erosion-rate estimates for the AP Inselberg enable us to better understand the role of weathering and erosional processes that controlled the evolution of landscape surfaces during Andean orogenic cycles documented in the region.

Résumé: The formation of imogolite nanotubes is reported to be a kinetic process involving intermediate roof-tile nanostructures. Here, the structural evolution occurring during the synthesis of aluminogermanate double-walled imogolite nanotubes is in situ monitored, thanks to an instrumented autoclave allowing the control of the temperature, the continuous measurement of pH and pressure, and the regular sampling of gas and solution. Chemical analyses confirm the completion of the precursor's conversion with the release of CO2, ethanol, and dioxane as main side products. The combination of microscopic observations, infrared, and absorption spectroscopies with small and wide-angle X-ray scattering experiments unravel a unique growth mechanism implying transient single-walled nanotubes instead of the self-assembly of stacked proto-imogolite tiles. The growth formation of these transient nanotubes is followed at the molecular level by Quick-X-ray absoprtion specotrscopy experiments. Multivariate data analysis evidences that the near neighboring atomic environment of Ge evolves from monotonous to a more complex one as the reaction progresses. The following transformation into a double-walled nanotube takes place at a nearly constant mean radius, as demonstrated by the simulation of X-ray scattering diagrams. Overall, transient nanotubes appear to serve for the anchoring of a new wall, corresponding to a mechanism radically different from that proposed in the literature. The growth mechanism during the synthesis of double-walled (DW) imogolite nanotubes is described, thanks to an instrumented autoclave. The sampling during the synthesis enables to trap unexpected single-walled nanotubes that further convert into DW ones. This nonclassical growth mechanism by transient nanotubes is radically different from that proposed in the literature since inorganic nanotubes are usually formed from 2D materials.image

Résumé: The application of foliar sprays of suspensions of relatively insoluble essential element salts is gradually becoming common, chiefly with the introduction of nano-technology approaches in agriculture. However, there is controversy about the effectiveness of such sparingly soluble nutrient sources as foliar fertilizers. In this work, we focussed on analysing the effect of adding Ca-carbonate (calcite, CaCO3) micro- and nano-particles as model sparingly soluble mineral compounds to foliar fertilizer formulations in terms of increasing the rate of foliar absorption. For these purposes, we carried out short-term foliar application experiments by treating leaves of species with variable surface features and wettability rates. The leaf absorption efficacy of foliar formulations containing a surfactant and model soluble nutrient sources, namely Ca-chloride (CaCl2), magnesium sulphate (MgSO4), potassium nitrate (KNO3), or zinc sulphate (ZnSO4), was evaluated alone or after addition of calcite particles. In general, the combination of the Ca-carbonate particles with an essential element salt had a synergistic effect and improved the absorption of Ca and the nutrient element provided. In light of the positive effects of using calcite particles as foliar formulation adjuvants, dolomite nano- and micro-particles were also tested as foliar formulation additives, and the results were also positive in terms of increasing foliar uptake. The observed nutrient element foliar absorption efficacy can be partially explained by geochemical modelling, which enabled us to predict how these formulations will perform at least in chemical terms. Our results show the major potential of adding mineral particles as foliar formulation additives, but the associated mechanisms of action and possible additional benefits to plants should be characterised in future investigations.

Résumé: We develop an algorithm to detect and locate sources of long-period (25-100 s) seismic signals. Our method is based on the analysis of seismological data recorded at global networks, plus all available stations at latitude larger (smaller) than 60 degrees (-60 degrees). We use a delay and stack method to identify coherent Rayleigh waves generated at the free surface of the Earth. The application of our approach to 13 yr of continuous data permitted us to detect more than 36,000 events. After a precise analysis to classify known events and to remove spurious detections, we report more than 1700 previously unidentified source of long-period seismic signals. Each source is characterized by its location (with associated uncertainty) and moment magnitude. This new catalog mainly reveals sources in the polar regions likely associated with glaciers dynamics but also volcanic activity, landslides, and regular earthquakes located in remote areas of the planet. Our study reveals the importance of maintaining global seismic networks and exploring the recorded data, beyond providing new observations that can be the basis to future studies to better characterize physical processes occurring at the free surface of our planet.

Résumé: There are still open questions about the deep structure beneath the Western Alps. Seismic velocity tomographies show the European slab subducting beneath the Adria plate, but all these images did not clarify completely the possible presence of tears, slab windows, or detachments. Seismic anisotropy, considered an indicator of mantle deformation and studied using data recorded by dense networks, allows a better understanding of mantle flows in terms of location and orientation at depth. Using the large amount of shear wave-splitting and splitting-intensity measurements available in the Western Alps, collected through the CIFALPS2 temporary seismic network, together with already available data, some new patterns can be highlighted, and gaps left by previous studies can be filled. Instead of the typical seismic anisotropy pattern parallel to the entire arc of the Western Alps, this study supports the presence of a differential contribution along the belt that is only partly related to the European slab steepening. A nearly north-south anisotropy pattern beneath the external Western Alps, a direction that cuts the morphological features of the belt, is clearly found with the new CIFALPS2 measurements. It is, however, confirmed that the asthenospheric flow from central France towards the Tyrrhenian Sea is turning around the southern tip of the European slab.

Résumé: The undesired precipitation of minerals from solution poses challenges in various industrial and domestic applications, including water treatment, desalination, dishwashers and boilers. To mitigate this, threshold inhibitors – small quantities of water-soluble additives-are commonly employed to inhibit the precipitation of inorganic phases. However, concerns about the persistence of traditional additives like phosph(on)ates) in natural environments and stricter regulations warrant the development of more sustainable alternatives. We present a high-throughput approach using a UV-Vis spectrophotometer and automated data analysis to assess the scale inhibiting potential of numerous candidates and their combinations. The robustness and versatility of this method were validated by measuring the kinetics of alkaline-earth metal carbonates precipitating from simulated hard waters and seawaters across an extended range of experimental parameters. This approach allows for straightforward evaluation and quantification of each antiscaling additive's effectiveness and operational range, enabling direct comparison of different additives and blends of additives. Moreover, it facilitates the study of scaling processes in both bulk solutions and at liquid/solid interfaces. By providing a rapid and reliable means of screening potential additives and formulations, our versatile toolbox will expedite the identification of effective scale inhibitors, thereby contributing to the advancement of sustainable practices in various industries reliant on water treatment and mineral precipitation control.

Résumé: The decay of surface-wave coda in ambient noise cross correlations can facilitate the estimation of seismic attenuation. The coda quality factor (Q(c)) can be measured in longer period bands using ambient noise cross correlations, which is the main advantage of using them over earthquakes. The classic model of Aki and Chouet (1975) has been applied previously to estimate coda Q in the Alps using ambient noise cross correlations. The Alps represents an ideal environment for ambient noise study, because it has very high and near-uniform station density, and the region is away from oceanic noise sources. However, many regions around the world do not have uniform station density and may be seismically more active than the Alps. One such region is the Hellenic subduction zone (HSZ), because it has a high rate of seismicity, sparser station coverage, and is surrounded by seas from outside and within. In this study, we estimate ambient seismic noise Q(c) in 2.5-5, 5-10, and 10-20 s period bands for the HSZ, which did not exist previously. Then, we mitigate the effects of lapse time and window length, distance, azimuth, as well as the number of stacked days on the Q(c). Mapping of Q(c) measurements in such a geographically heterogeneous setting poses additional challenges, which we solve using a novel approach that adaptively selects paths based on their lengths and azimuthal distribution. The major tectonic zones are identified in the resulting Q(c) maps in the form of low Qc such as the North Anatolian fault, the Kefalonia transform zone, the Gulf of Corinth, the volcanic centers, and so on. The results also show a good correlation with large topographical features such as the Hellenides and the Thessalian plains, which have also been noticed from Q(c) analysis in other parts of the world.

Résumé: Conditions of sediment transport and deposition in highly dynamic fluvio-glacial environments enhance incomplete bleaching of luminescence signals during sunlight exposure. Whatever the geomorphic context or application, partial bleaching has been widely reported and remains a methodological limitation for application of Optically Stimulated Luminescence (OSL) dating methods, potentially resulting in sediment -burial age overestimation. This study focuses on the highly dynamic Se <acute accent>veraisse River (SW French Alps) where modern-day alluvial sands of a braided reach were sampled to assess the degree of quartz-OSL partial bleaching associated with superficial pre- and post -deposition geomorphic processes. Our original approach combines (i) a photogrammetry-based survey, (ii) sediment grain -size analysis, and (iii) measurements of both portable OSL luminescence signals and conventional quartz OSL equivalent doses in modern superficial (from 0.1 to 1 cm) and sub -surface (up to 30 cm) alluvial sands exposed to sunlight for at least 19 days. Our results show high but spatially variable residual luminescence signals at the surface, measured in all grain -size fractions with both the portable luminescence reader ( >= 5 x10 6 cts/g) and conventional quartz-OSL doses ( >= 80 Gy), even within the uppermost millimetres of the exposed alluvial surface. Our data thus highlight poor luminescence bleaching in the Se <acute accent>veraisse 's modern sands, during both pre -depositional transport and post -depositional exposure. In addition, our study reveals, for the first time, the significant sunlight attenuation over a few millimetres within modern alluvial sediments, perhaps conditioned by dark sand grains, and/or by superficial blanketing by silts (i. e. waning flow stage) that leads to a porosity decrease and very low sunlight penetration. We suggest the occurrence of a critical sediment layer (i.e. only a few mm thick) that could play a key role in bleaching processes for alluvial surfaces, with strong implications for our understanding of residual doses in braided systems ' sandy deposits and the dynamics of such alluvial surfaces.

Résumé: Here we present the new experimental stations devoted to the studies of matter under extreme conditions at the X-ray absorption beamlines BM23 and ID24-DCM that were recently refurbished within the ESRF – Extremely Brilliant Source (EBS) upgrade program. In comparison with the stations before the EBS upgrade, they exhibit outstanding performances in terms of sample positioning capabilities, acceptance of multi-detection systems and complex sample environments. In addition, significant improvements regarding the photon flux and focusing capabilities down to the submicron size have been achieved. These stations are now coupled with the new ESRF double crystal monochromators that exhibit an exceptional beam position and energy stability and that permit quick micro-EXAFS measurements down to one EXAFS/second, and hyperspectral EXAFS mapping. In this contribution, we discuss the choices regarding the sample and detector stages and illustrate the potential of the new setups for extreme conditions studies based on selected preliminary results.

Résumé: Retrieval of modern and ancient environmental DNA (eDNA) from sediments has revolutionized our ability to study past and present ecosystems. Little emphasis has been placed, however, on the fundamentals of the DNA-sediment associations in environmental settings. Consequently, our understanding of mineralogic controls and geochemical processes that take place on the DNA-sediment interface, and its implications for eDNA taphonomy and provenance, remain extremely limited. Here, we apply interfacial geochemical principles to elucidate how depositional processes and the stability of DNA-sediment associations in different environments can influence our interpretation and identify possible interpretational biases arising from neglecting mineral and geochemical controls on eDNA taphonomy. We use atomic force microscopy to show how interfacial geochemical interactions drive DNA adsorption behavior and we outline how to increase the scope and resolution of ecological interpretations from eDNA by combining mineralogic composition information with experimental adsorption data. We bring the concepts together and propose how to integrate sediment provenance as well as mineralogic and geochemical principles in eDNA taphonomy analysis for improved reconstruction of past ecosystems and monitoring of modern ecosystems from eDNA data. We provide a conceptual understanding of how eDNA taphonomy and sediment provenance can be addressed and further applied to enhance the scope, resolution, and accuracy of modern and past ecological reconstructions based on eDNA data.

Résumé: Here, we present a synthetic validation for the inversion of transient fluid motions at the surface of Earth's core. It is based on a numerical simulation of the geodynamo in which the main time-scales (based on rotation, magnetic field and velocity) are sufficiently separated to give rise to a variety of hydro-magnetic waves. We focus the study on wave-like motions with periods commensurate to the Alfve ' n time, which is based on the strength of the magnetic field in the core interior. Synthetic magnetic data are generated over 90 Alfve ' n times, representative of the era covered by observatory and satellite measurements. These synthetic data are inverted to estimate a magnetic field model. Thereafter, we apply the pygeodyn data assimilation tool to recover core surface flows. We investigate the quality of their reconstruction as a function of their time scale. The success of the reconstruction depends on the data accuracy and coverage and on the magnitude of the flow. We also retrieve axisymmetric torsional Alfve ' n waves, despite their relatively weak magnitude. We use the synthetic data to investigate the exchanges of angular momentum between core and mantle that induce length-of-day (LOD) changes. These exchanges result from the electromagnetic torque between the fluid core and the mantle and the gravitational torque between the inner core and the mantle. The inverted flows convincingly predict LOD variations in the dynamo calculation. We find that core surface zonal motions match well with the geostrophic (axially invariant) motions at the origin of the LOD changes, on all considered timescales. We also investigate the different contributions to the electro-magnetic torque. In the dynamo simulation, only a small part can be attributed to the leakage torque caused by electrical currents flowing from the core to the mantle. The relative contribution from the poloidal field induced in the mantle, which amounts to about 1/ 3 of the total torque, is significantly larger than estimated in previous studies, based on geomagnetic observations. The remaining torque, which is associated with the toroidal induced field, mostly stems from the solid body rotation interacting with the radial magnetic field up to spherical harmonic degree 30.

Résumé: In collision belts, the first-order role of the mantle in localizing deformation has remained elusive, as the resolution of geophysical imaging remains too low to constrain crustal geometry. To address this issue, we geologically interpret a recent high-resolution shear-wave velocity model from ambient-noise tomography of Western Alps. We show that the lower crustal Alpine geometry is highly variable at depth, evolving from a preserved European crustal slab in the South to a smooth crustal root in the North. Moho morphology is controlled by numerous pre-existing major faults reactivated during the Alpine orogeny. Two mantle indenters located above the subducted European plate at different depths appear to control the locus of active deformation. The rigid nature of Adria mantle explains the localization of brittle deformation that is transferred towards the upper crust. The strain-field partitioning results in a combination of strike-slip with either shortening or extension controlled by the anticlockwise rotation of Adria. Deep indentation of the western Alps by the mantle portion of the Adria plate is responsible for the current stress partitioning in an anticlockwise rotational context, according to shear-wave tomography combined with stress field analysis.

Résumé: The seismic potential of the Lesser Antilles subduction zone is poorly known and highly debated. Only two damaging earthquakes have been reported in the historical period, in 1839 and 1843, but their sources and magnitude are still uncertain. Global Navigation Satellite Systems and coral data contradict each other, and no conclusion has been reached on the coupling ratio of the plate interface. Given the threat posed by the possible occurrence of a large megathrust earthquake, it is crucial to gain information on prehistorical events. We present the results of a submarine paleoseismological study that covers an exceptional similar to 120 Kyr-long period. We studied the sediments sampled in six up to 26 m-long piston cores collected in deep fore-arc basins located over the epicentral region of the 1843 earthquake. Using a multiproxy approach combining geophysical, geochemical, and sedimentological analysis, biostratigraphy and radiocarbon dating, we identified, characterized, and dated numerous event deposits that we then correlated with the sampled basins over an up to 160 km-long area. We show that at least 33 earthquakes likely triggered these sediment remobilizations in the last 120 Kyr. Four of these events promoted exceptional deposits of turbidites + homogenites. From peak ground acceleration calculated for potential earthquakes occurring on various faults, and the absence of deposits linked to the historical earthquakes, we propose that the sources are likely megathrust earthquakes. Over the last 60 Kyr, we inferred at least three 15-25 Kyr-long seismic cycles in which the recurrence times of earthquakes shortens from similar to 5 to similar to 2 Kyr. Paleoseismology based on identification of turbidites and homogenites along the Lesser Antilles subduction zone Several megathrust earthquakes have been highlighted over the last 120 Kyrs offshore Guadeloupe Four major earthquakes triggered up to 8 m-thick homogenite deposits

Résumé: Reconstructing mountainous landscape evolution throughout the Quaternary is challenging because of the poor long-term preservation of geomorphic records in a context of rapid surface dynamics and topographic rejuvenation. The Quaternary geomorphic evolution of the western European Alps has been strongly controlled by climatic oscillations between glacial and interglacial periods. Significant erosion and sediment remobilization during these glacial/interglacial cycles have left very few sedimentary archives to quantify the surface dynamics and paleo-environmental conditions within the mountain belt over the last hundreds of thousands of years. Alpine valleys within the periglacial zone are potential candidates to target long-term geological archives, since they may contain alluvial deposits that have been preserved from subsequent glaciations. In the Drac valley (French western Alps), three generations of paleo-valleys are preserved, each of which was filled with alluvial and lacustrine sediments in response to glacial damming downstream. The valleys were incised during subsequent times of glacial retreat, leading to the formation of epigenetic valleys. Detailed 3D mapping of the paleovalleys was carried out using photogrammetric models to constrain their geometry. Mapping was combined with luminescence dating of alluvial deposits to reconstruct the temporal evolution of the Drac valley. This chronological framework, together with additional data from the literature, allowed us to quantitatively constrain the complex alluvial dynamics along the Drac river during the last ca. 230 ka. Poly -phased alluvial deposition occurred in the most recent paleo-valley between ca. 90 and 20 ka (i.e., from late MIS 5 to MIS 2) in a context of global climate cooling and major Alpine glaciation. Sediment infilling of the intermediate paleo-valley is dated at around 130 ka; i.e., during the late -glacial phase of the penultimate glaciation, at the abrupt warming transition between MIS 6 and MIS 5. Finally, the oldest paleo-valley was filled around 230 ka (during a sub -stage of MIS 7) probably in a cooling and glacial context. The overall alluviation pattern and chronology of the study area highlight the asynchronous and partially contrasting glacial dynamics between the different glacier systems (i.e., Drac, Bonne and Romanche/Ise `re glaciers) within the Ecrins-Pelvoux massif of the French western Alps.

Résumé: In many geological systems, the porosity of rock or soil may evolve during mineral precipitation, a process that controls fluid transport properties. Here, we investigate the use of 4D neutron imaging to image flow and transport in Bentheim sandstone core samples before and after in-situ calcium carbonate precipitation. First, we demonstrate the applicability of neutron imaging to quantify the solute dispersion along the interface between heavy water and a cadmium aqueous solution. Then, we monitor the flow of heavy water within two Bentheim sandstone core samples before and after a step of in-situ mineral precipitation. The precipitation of calcium carbonate is induced by reactive mixing of two solutions containing CaCl2 and Na2CO3, either by injecting these two fluids one after each other (sequential experiment) or by injecting them in parallel (co-flow experiment). We use the contrast in neutron attenuation from time-resolved tomograms to derive three-dimensional fluid velocity field by using an inversion technique based on the advection-dispersion equation. Results show mineral precipitation induces a wider distribution of local flow velocities and leads to alterations in the main flow pathways. The flow distribution appears to be independent of the initial distribution in the sequential experiment, while in the co-flow experiment, we observed that higher initial local fluid velocities tended to increase slightly following precipitation. The outcome of this study contributes to progressing the knowledge in the domain of reactive solute and contaminant transport in the subsurface using the promising technique of neutron imaging. Flow and mixing processes in porous media control many natural and industrial systems, such as microbial clogging, oil extraction, and effluent disposal. In many systems, the porosity may evolve during mineral precipitation, such as in rocks, and control fluid transport properties. Here, we use time-lapsed three-dimensional neutron imaging to explore fluid transport into Berea sandstone core samples during in-situ carbonate precipitation. Neutron imaging can track fluid flow inside the rock, whereas X-ray imaging illuminates the regions where mineral precipitation occurs. We control the precipitation of calcium carbonate in the rock through reactive mixing between solutions containing CaCl2 and Na2CO3. By solving the adverse advection-diffusion equation using the contrast in neutron attenuation from time-lapse images, we derive the 3D velocity field of the injected fluids. Results show that under the effect of mineral precipitation, a wide range of local flow velocities develop in the sample, and we quantify the distribution of flow velocities in the sample. The finding of this experimental study is useful in progressing the knowledge in the domain of reactive solute and contaminant transport in the subsurface. 4D neutron imaging is used to image flow and transport in porous rock and investigate the effect of carbonate precipitation The velocity field of injected fluid is estimated by solving the advection-dispersion equation using the contrast in neutron attenuation Carbonate precipitation widens the distribution of fluid velocities due to local pore-clogging

Résumé: We utilize train tremors as P-wave seismic sources to investigate velocity-strain sensitivity near the San Jacinto Fault Zone. A dense nodal array deployed at the Pi & ntilde;on Flat Observatory is used to detect and identify repeating train energy emitted from a railway in the Coachella valley. We construct P-wave correlation functions across the fault zone and estimate the spatially averaged dt/t versus strain sensitivity to be 6.25 x 104. Through numerical simulations, we explore how the sensitivity decays exponentially with depth. The optimal solution reveals a subsurface sensitivity of 1.2 x 105 and a depth decay rate of 0.05 km-1. This sensitivity aligns with previous findings but is toward the higher end, likely due to the fractured fault-zone rocks. The depth decay rate, previously unreported, is notably smaller than assumed in empirical models. This raises the necessity of further investigations of this parameter, which is crucial to study stress and velocity variations at seismogenic depth. The speed at which seismic waves travel can be affected by Earth's tidal strains. Understanding this relationship is beneficial for studying tectonic strain accumulation and earthquake nucleation. When freight trains run, they produce powerful seismic energy that can be detected tens of kilometers away. We use these signals to measure how solid Earth tides affect seismic wave speed. Our study focusing on the San Jacinto Fault Zone in southern California reveals that the velocity-strain sensitivity is consistent, albeit at the higher end of previously reported values measured in other regions. Additionally, our numerical simulations examine how this sensitivity varies with depth. We find that the rate at which sensitivity decreases with depth is smaller than what is typically assumed. Stable P-wave correlation functions are constructed from selected train tremors The covariance between tidal strain and P-wave travel-time is used to estimate the velocity-strain sensitivity Full-waveform simulations of correlation functions are performed to constrain the depth dependence of the velocity-strain sensitivity

Résumé: Explosive silicic eruptions pose a significant threat to society, yet the development and destabilization of the underlying silicic magmatic systems are still controversial. Zircons provide simultaneous information on the trace element composition and age of silicic magmatic systems, while melt inclusions in quartz and plagioclase yield important constraints on their volatile content as well as magma storage depth. Melt inclusions in zircons (MIZs) combine these data from a single mineral grain, recording the age, storage depth, temperature, and composition of magmas, and thus provide unique constraints on the structure and evolution of silicic magmatic systems. We studied MIZs from the Laguna del Maule (LdM) volcanic field in the southern Andes that is among the most active Pleistocene-Holocene rhyolitic volcanic centers worldwide and a potentially hazardous system displaying inflation rates in excess of 25 cm/yr. The host zircon ages suggest that the LdM MIZ record extends to similar to 30 kyr before eruption, in contrast to the melt inclusions in LdM plagioclase and quartz crystals that formed only decades to centuries before eruption. The major element compositions of MIZs are minimally affected by post-entrapment crystallization, and agree well with the LdM rhyolitic whole rock data. The MIZs record long-term differences in zircon-saturated melt composition between two eruptive units (rdm: Rhyolite of the Laguna del Maule vs. rle: Rhyolite of Los Espejos). The more evolved major element composition of rle MIZs than rdm MIZs, suggests a long-term deeper connection of the rdm crystal mush to a more primitive magma body than that of the rle. The evidence of slow H diffusion observed in MIZs suggest that their H2O contents are not significantly affected by diffusion of H through the host zircon. The magma storage pressures of 1.1 to 2.8 kbars recorded by the H2O contents of rdm and rle MIZs are consistent with the optimal emplacement window (2.0 +/- 0.5 kbar) of silicic magma reservoir growth, storage, and eruptibility based on thermomechanical modeling (Huber et al. 2019).

Résumé: Subduction-zone fluid-rock interactions have a direct impact onto elemental and isotopic homogeneity of progressively buried and exhumed crustal lithologies by providing an interface for local mass-transfer and enhancing metamorphic reactions. In order to assess the scales of fluid mobility, chemical and isotopic inheritance, as well as resulting degrees of isotopic heterogeneity in the exhumed high-pressure lithologies, we performed the detailed mineralogical, in-situ trace-element and Rb-Sr isotope studies, combined with P-T-X thermodynamic modelling of representative eclogites from the Alag Khadny accretionary complex (SW Mongolia). The eclogites (garnet + omphacite + phengite + rutile + quartz + retrograde amphibole and clinozoisite) display records of subduction-related burial to 540-625 degrees C and 1.7-2.1 GPa, with the enclosed phengite supposed to be in equilibrium at prograde-to-peak conditions. Trace-element signatures, including Cs/Rb (0.03-0.08) and Ba/Rb (7.1-13.8) ratios of phengite, are consistent with moderately to strongly altered protoliths of eclogites, which is supported by elevated delta O-18 values and in-situ Rb-Sr constraints on the initial (Sr-87/Sr-86)(I) ratios of phengite within 0.70549-0.70957. Partial backward rehydration (similar to 0.5-1.0 wt% of H2O added) during decompression from 1.6 to 1.2 GPa produced amphibole- and clinozoisite-bearing assemblages, did not significantly affect LILE systematics and variable Rb-87/Sr-86 ratios of phengite. Limited Rb and Ba loss from phengite during recrystallization is suspected in the evidently deformed eclogites based on the LILE mineral-fluid and phengite-amphibole partitioning data. No exclusive evidence is found in amphibole for LILE-rich metasedimentary fluid with high (Sr-87/Sr-86)(I) released into eclogites. Instead, unradiogenic Sr-87/Sr-86 (0.70279-0.70301) of clinozoisite highlights metasomatic addition from the underlying mafic crust or dehydrated peridotitic mantle. Variable deformation-enhanced fluid-rock interaction during early exhumation was recorded by in-situ phengite Rb-Sr geochronology at 568 +/- 9 Ma, which is considered a direct fluid flow snapshot and place a new minimum age constraint for the peak subduction burial. We argue that, except cases of apparent metasomatic origin of phengite, its (Sr-87/Sr-86)(I) ratios may be a sensitive tracer for the eclogite precursor alteration due to limited Sr mobility. Sample-scale Rb-Sr isotopic heterogeneities may be preserved in the orogenic eclogites due to multi-stage retrograde hydration and should be taken into account while interpreting the bulk-rock Sr isotope data.

Résumé: Here, we show that calcium sulfate dihydrate (gypsum) can be directly, rapidly and reversibly converted to calcium sulfate hemihydrate (bassanite) in high salinity solutions (brines). The optimum conditions for the efficient production of bassanite in a short time (<5 min) involve the use of brines with c(NaCl) > 4 M and maintaining a temperature, T > 80 degrees C. When the solution containing bassanite crystals is cooled down to around room temperature, eventually gypsum is formed. When the temperature is raised again to T > 80 degrees C, bassanite is rapidly re-precipitated. This contrasts with the better-known behaviour of the bassanite phase in low-salt environments. In low-salinity aqueous solutions, bassanite is considered to be metastable with respect to gypsum and anhydrite, and therefore gypsum-to-bassanite conversion does not occur in pure water. Interestingly, the high-salinity transformation of gypsum-to-bassanite has been reported by many authors and used in practice for several decades, although its very occurrence actually contradicts numerical thermodynamic predictions regarding solubility of calcium sulfate phases. By following the evolution of crystalline phases with in situ and time-resolved X-ray diffraction/scattering and Raman spectroscopy, we demonstrated that the phase stability in brines at elevated temperatures was inaccurately represented in the thermodynamic databases. Most notably for c(NaCl) > 4 M, and T > 80 degrees C gypsum becomes readily more soluble than bassanite, which induces the direct precipitation of the latter from gypsum. The fact that these transformations are controlled by the solution provides extensive opportunities for precise manipulation of crystal formation. Our experiments confirmed that bassanite remained the sole crystalline phase for many hours before reverting into gypsum. This property is extremely advantageous for practical processing and efficient crystal extraction in industrial scenarios.

Résumé: Cratonic peridotites are typically depleted but have overall higher modal orthopyroxene than young oceanic and continental peridotites. The origin of this enrichment remains debatable. Here we focus on a spinel harzburgite block from the Mogok metamorphic belt, Myanmar, presenting major and trace element data for 27 harzburgite samples. Twelve samples are clinopyroxene-free but have high modal orthopyroxene (mostly 25.3-30.4%); The remaining fifteen are clinopyroxene-bearing (<4%), with only 10.8-22.7% orthopyroxene. The clinopyroxenefree samples display higher Mg# (91.8-92.5) than those with clinopyroxene (91.1-92.1). All samples yield a positive correlation between modal orthopyroxene and bulk Mg#, overlapping with the trend defined by refractory cratonic peridotite xenoliths. This correlation is unlikely explained by post-melting metasomatism, mechanical sorting, or serpentinization. Instead, it is consistent with non-pyrolitic, silica-rich mantle melting. Thermodynamic modeling shows that high-pressure melting (similar to 15-35 kbar) of the silica-rich mantle proceeds through an orthopyroxene-forming peritectic reaction, leaving residues with higher Mg# compared to those produced at lower pressures. Our harzburgite samples are compatible with this model, with high-Mg# orthopyroxene-rich samples formed at higher pressures (similar to 20-40 kbar) than the orthopyroxene-poor ones (similar to 10-20 kbar). We suggest that high-Mg# orthopyroxene-rich cratonic peridotites are likely an important component of the primordial cratonic mantle. Their formation might occur through anhydrous extensive melting of the silicarich mantle at relatively high pressures, corresponding to the elevated potential temperatures characteristic of the Archean mantle. Progressive mantle cooling from the Archean to the present can account for the rarity of young analogues of high-Mg# orthopyroxene-rich cratonic mantle.