Frictional Instabilities and Carbonation of Basalts Triggered by Injection of Pressurized H2O- and CO2- Rich Fluids

The safe application of geological carbon storage depends also on the seismic hazard associated with fluid injection. In this regard, we performed friction experiments using a rotary shear apparatus on precut basalts with variable degree of hydrothermal alteration by injecting distilled H2O, pure CO2, and H2O + CO2fluid mixtures under temperature, fluid pressure, and stress conditions relevant for large-scale subsurface CO2storage reservoirs. In all experiments, seismic slip was preceded by short-lived slip bursts. Seismic slip occurred at equivalent fluid pressures and normal stresses regardless of the fluid injected and degree of alteration of basalts. Injection of fluids caused also carbonation reactions and crystallization of new dolomite grains in the basalt-hosted faults sheared in H2O + CO2fluid mixtures. Fast mineral carbonation in the experiments might be explained by shear heating during seismic slip, evidencing the high chemical reactivity of basalts to H2O + CO2mixtures

Dynamic weakening and amorphization in serpentinite during laboratory earthquakes

The mechanical properties of serpentinites are key factors in our understanding of the dynamics of earthquake ruptures in subduction zones, especially intermediate-depth earthquakes. Here, we performed shear rupture experiments on natural antigorite serpentinite, which showed that friction reaches near-zero values during spontaneous dynamic rupture propagation. Rapid coseismic slip (>1 m/s), although it occurs over short distances (<1 mm), induces significant overheating of microscale asperities along the sliding surface, sufficient to produce surface amorphization and likely some melting. Antigorite dehydration occurs in the fault walls, which leaves a partially amorphized material. The water generated potentially contributes to the production of a low-viscosity pressurized melt, explaining the near-zero dynamic friction levels observed in some events. The rapid and dramatic dynamic weakening in serpentinite might be a key process facilitating the propagation of earthquakes at intermediate depths in subduction zones

Development and Recovery of Stress-Induced Elastic Anisotropy During Cyclic Loading Experiment on Westerly Granite

International audienceIn the upper crust, where brittle deformation mechanisms dominate, the development of Q4 Q5 crack networks subject to anisotropic stress fields generates stress-induced elastic anisotropy. Here a rock specimen of Westerly granite was submitted to differential stress cycles (i.e., loading and unloading) of increasing amplitudes, up to failure and under upper crustal conditions. Combined records of strains, acoustic emissions, and P and S elastic wave anisotropies demonstrate that increasing differential stress promotes crack opening, sliding, and propagation subparallel to the main compressive stress orientation. However, the significant elastic anisotropies observed during loading (≥20%) almost vanish upon stress removal, demonstrating that in the absence of stress, crack-related elastic anisotropy remains limited (≤10%). As a consequence, (i) crack-related elastic anisotropies measured in the crust will likely be a strong function of the level of differential stress, and consequently (ii) continuous monitoring of elastic wave velocity anisotropy along faults could shed light on the mechanism of stress accumulation during interseismic loading. Plain Language Summary In the upper crust, large strains are accommodated by brittle deformation mechanisms, leading to macroscopic faults embedded within a substantially damaged rock medium. The development of crack damage affects both the strength and the elastic and transport properties of rocks. Nowadays, the evolution of rock elastic properties is commonly used to estimate the direction of the maximum stress along faults and evaluate seismic hazard of seismogenic area. Up to Q6 now, stress-induced anisotropy was expected to be irreversible and observable by geophysics method even after unloading or exhumation of the rocks. In this study, we demonstrate for the first time that unloading induces an almost complete recovery of both stress-induced anisotropy and stress-induced damage. Our results suggest that elastic properties estimated from wave velocity measurement could then underestimate both damage and anisotropy of the crust under shallow depth conditions

Frictional Instabilities and Carbonation of Basalts Triggered by Injection of Pressurized H2O- and CO2- Rich Fluids

The safe application of geological carbon storage depends also on the seismic hazard associated with fluid injection. In this regard, we performed friction experiments using a rotary shear apparatus on precut basalts with variable degree of hydrothermal alteration by injecting distilled H2O, pure CO2, and H2O + CO2 fluid mixtures under temperature, fluid pressure, and stress conditions relevant for large-scale subsurface CO2 storage reservoirs. In all experiments, seismic slip was preceded by short-lived slip bursts. Seismic slip occurred at equivalent fluid pressures and normal stresses regardless of the fluid injected and degree of alteration of basalts. Injection of fluids caused also carbonation reactions and crystallization of new dolomite grains in the basalt-hosted faults sheared in H2O + CO2 fluid mixtures. Fast mineral carbonation in the experiments might be explained by shear heating during seismic slip, evidencing the high chemical reactivity of basalts to H2O + CO2 mixtures

Experimental study of seismic rupture

Les phénomènes de ruptures dynamiques, incluant les tremblements de terre, peuventêtre observés de l’échelle atomique jusqu’à l’échelle des failles crustales sismogéniques.Les ruptures dynamiques sont généralement induites par une diminution de la résistancedes failles quand le glissement et la vitesse de glissement augmentent. Au coursde ce travail de thèse, nous avons utilisé des méthodes expérimentales novatrices permettantde reproduire des micro-tremblements de terre en laboratoire (Stick-Slip) dans desconditions de pression proche de la réalité. Les expériences utilisées nous ont permisd’explorer différents stades du cycle sismique, depuis l’activité précurseur des microséismes,la propagation de la rupture, jusqu’à l’endommagement cosismique au niveaude la zone de glissement. Les résultats expérimentaux ont été comparés avec des observationssismologiques et la théorie de la mécanique de la fracture élastique linéaire. Laplupart des résultats présentés ici suggèrent que le paramètre controllant la complexitédes mécanismes de rupture est l’état de contrainte initial. Pour résumer, une augmentationde la contrainte initiale induit (i) l’apparition de précurseurs pendant la phase denucléation, (ii) la transition entre des ruptures de type sub-Rayleigh et supershear, (iii)l’activation de mécanismes d’affaiblissement pendant les séismes, (iv) une augmentationde l’endommagement pendant le glissement sismique.Dynamic rupture phenomena, including earthquakes, can be observed from the atomicscale up to the scale of seismogenic crustal faults. Dynamic ruptures are generatedbecause fault strength drops with increasing slip and slip-rate. During this PhD,we used experimental methods allowing reproduction of earthquakes at the scale of thelaboratory under crustal stress conditions. Experiments used allowed the study of differentstages of the seismic cycle, from the nucleation to the propagation of the seismicrupture, and to study the energy budget of laboratory earthquakes. Experimental resultswere compared to natural observations and to current theory. Most of the results presentedin this manuscript tend to show that the main parameter controlling the complexityof rupture processes is the stress acting on the fault plane. To summarize, increasingnormal stress leads to (i) the occurence of foreshocks during the onset of instability, (ii)the transition between sub-Rayleigh and supershear ruptures, (iii) the activation of weakeningmechanisms during faulting, (iv) the increase of damage along the fault duringearthquakes

La place du père dans l'allaitement maternel (enquête auprès de patients de médecine générale)

LYON1-BU Santé (693882101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

On the Scale Dependence in the Dynamics of Frictional Rupture.

International audienceWhen an earthquake nucleates in the earth crust, the potential energy accumulated during the inter-seismic period is released into breakdown work, heat energy and radiated energy. Often the breakdown work is considered a seismological equivalent of the fracture energy. However, discrepancies related to the definition of the two are not yet fully solved. To this end, we reproduced frictional ruptures in the laboratory to study the relationship between these two energies. A dual strength weakening is observed, reflected in a scale dependent evolution of breakdown work with fault slip, contrarily to fracture energy which is, by definition, scale independent. This behavior shows to be probably caused by thermal weakening (i.e. flash heating) activated during slip and to be well described by the recently developed unconventional theory of frictional ruptures (i.e. rupture driven by a non-square root singularity). Importantly, these results highlight, from an experimental point of view, the presumable unconventional nature of earthquakes, solving the discrepancies between breakdown work and fracture energy. Moreover, it suggests that an analysis of the propagating rupture in the framework of linear elastic fracture mechanics could prove to be not always sufficiently exhaustive when frictional weakenings occur, as it is expected along crustal faults

On the Scale Dependence in the Dynamics of Frictional Rupture.

International audienceWhen an earthquake nucleates in the earth crust, the potential energy accumulated during the inter-seismic period is released into breakdown work, heat energy and radiated energy. Often the breakdown work is considered a seismological equivalent of the fracture energy. However, discrepancies related to the definition of the two are not yet fully solved. To this end, we reproduced frictional ruptures in the laboratory to study the relationship between these two energies. A dual strength weakening is observed, reflected in a scale dependent evolution of breakdown work with fault slip, contrarily to fracture energy which is, by definition, scale independent. This behavior shows to be probably caused by thermal weakening (i.e. flash heating) activated during slip and to be well described by the recently developed unconventional theory of frictional ruptures (i.e. rupture driven by a non-square root singularity). Importantly, these results highlight, from an experimental point of view, the presumable unconventional nature of earthquakes, solving the discrepancies between breakdown work and fracture energy. Moreover, it suggests that an analysis of the propagating rupture in the framework of linear elastic fracture mechanics could prove to be not always sufficiently exhaustive when frictional weakenings occur, as it is expected along crustal faults

Can Precursory Moment Release Scale With Earthquake Magnitude? A View From the Laboratory

Today, earthquake precursors remain debated. While precursory slow slip is an important feature of earthquake nucleation, foreshock sequences are not always observed, and their temporal evolution remains poorly constrained. We report on laboratory earthquakes conducted under upper-crustal stress and fluid pressure conditions. The dynamics of precursors (slip, seismicity, and fault coupling) prior to the mainshock are dramatically affected by slight changes in fault conditions (fluid pressure and slip history). A relationship between precursory moment release and mainshock magnitude is systematically observed, independent of fault conditions. Based on nucleation theory, we derive a semiempirical scaling relationship which explains this trend for laboratory earthquakes. Several natural observations of earthquakes ranging from similar to M-w 6.0-9.0, where precursory moment release could be estimated, seem to follow the extrapolation of the laboratory-derived scaling law. Notwithstanding spatiotemporal complexity in natural seismicity, some moderate to large earthquake magnitudes might be estimated through integrated seismological and geodetic measurements of both seismic and aseismic slips during nucleation. Plain Language Summary Understanding the preparation phase that precedes earthquake ruptures (nucleation) is crucial for seismic hazard assessment because it might provide information on the impending earthquake. Here, we show that the temporal evolution of laboratory earthquake precursors (precursory slow slip, precursory seismicity, and fault coupling) is of little use in assessing an impending earthquake's size. Nevertheless, independent of fault slip behavior (seismic or aseismic) and environmental conditions (stress state and fluid pressure and slip history), the amount of moment released during the preparation phase scales with the earthquake's magnitude. This property is demonstrated by laboratory observations and earthquake nucleation theory and seems compatible with several natural observations of earthquakes ranging from M-w 6.0 to M-w 9.0. As a consequence, if earthquakes exhibit a preparation phase, it could be possible that this phase is larger or longer for higher magnitude earthquakes and consequently, more likely to be detectable