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A produção de cânulas, materiais utilizados na fabricação de dispositivos médicos, é feita a partir de uma tira de aço inoxidável 304L laminado em tubos e posteriormente soldado por processo GTAW. Após esse procedimento, o tubo sofre uma série de passes de trefilação com recozimento e sem recozimento, para diminuir seu diâmetro. Por fim, são realizadas as etapas de corte, apontamento e limpeza do material. Durante a trefilação, uma série de defeitos chamados “GOUGE” é encontrada, provocando altas perdas nos processos, em função das desconformidades com as especificações técnicas. Inicialmente, no intuito de caracterizar e detectar possíveis causas dos defeitos foram analisadas as características do processo, desde a soldagem até a trefilação sem recozimento. Em seguida, foram feitas análises com microscopia de varredura, para avaliar algumas características metalúrgicas do material. Como o objetivo era caracterizar o defeito, diversas causas possíveis surgiram, como a influência da corrente ou velocidade de soldagem, temperatura de tratamento juntamente com as reações do gás Amônia na geração das desconformidades, a velocidade de trefilação ou a quantidade de óleo lubrificante. Concluiu-se que o processo de soldagem não foi o causador da falha, bem como a trefilação sem recozimento. A possibilidade da causa da descontinuidade ficou com o processo de trefilação com recozimento. Assim, diversas propostas para trabalhos futuros surgiram., Keywords: GOUGE; GTAW; Drawing; Cannulae.

We experimentally determined the hydraulic properties of fractures within various rock types, focusing on a variety of Variscan rocks. Flow-through experiments were performed on slate, graywacke, quartzite, granite, natural fault gouge, and claystone samples containing an artificial fracture with a given roughness. For slate samples, the hydraulic transmissivity of the fractures was measured at confining pressures, pc, at up to 50 MPa, temperatures, T, between 25 and 100 °C, and differential stress, σ, acting perpendicular to the fracture surface of up to 45 MPa. Fracture transmissivity decreases non-linearly and irreversibly by about an order of magnitude with increasing confining pressure and differential stress, with a slightly stronger influence of pc than of σ. Increasing temperature reduces fracture transmissivity only at high confining pressures when the fracture aperture is already low. An increase in the fracture surface roughness by about three times yields an initial fracture transmissivity of almost one order of magnitude higher. Fractures with similar surface roughness display the highest initial transmissivity within slate, graywacke, quartzite and granite samples, whereas the transmissivity in claystone and granitic gouge material is up to several orders of magnitude lower. The reduction in transmissivity with increasing stress at room temperature varies with composition and uniaxial strength, where the deduction is lowest for rocks with a high fraction of strong minerals and associated high brittleness and strength. Microstructural investigations suggest that the reduction is induced by the compaction of the matrix and crushing of strong asperities. Our results suggest that for a given surface roughness, the fracture transmissivity of slate as an example of a target reservoir for unconventional EGS, is comparable to that of other hard rocks, e.g., granite, whereas highly altered and/or clay-bearing rocks display poor potential for extracting geothermal energy from discrete fractures.

Calcite and dolomite are the two most common minerals in carbonate-bearing faults and shear zones. Motivated by observations of exhumed seismogenic faults in the Italian Central Apennines, we used a rotary-shear apparatus to investigate the frictional and microstructural evolution of ca. 3 mm thick gouge layers consisting of 50 wt % calcite and 50 wt % dolomite. The gouges were sheared at a range of slip rates (30 µm s−1–1 m s−1), displacements (0.05–0.4 m), and a normal load of 17.5 MPa under both room-humidity and water-dampened conditions. The frictional behaviour and microstructural evolution of the gouges were strongly influenced by the presence of water. At room humidity, slip strengthening was observed up to slip rates of 0.01 m s−1, which was associated with gouge dilation and the development of a 500–900 µm wide slip zone cut by Y-, R-, and R1-shear bands. Above a slip rate of 0.1 m s−1, dynamic weakening accompanied the development of a localised < 100 µm thick principal slip zone preserving microstructural evidence for calcite recrystallisation and dolomite decarbonation, while the bulk gouges developed a well-defined foliation consisting of organised domains of heavily fractured calcite and dolomite. In water-dampened conditions, evidence of gouge fluidisation within a fine-grained principal slip zone was observed at a range of slip rates from 30 µm s−1 to 0.1 m s−1, suggesting that caution is needed when relating fluidisation textures to seismic slip in natural fault zones. Dynamic weakening in water-dampened conditions was observed at 1 m s−1, where the principal slip zone was characterised by patches of recrystallised calcite. However, local fragmentation and reworking of recrystallised calcite suggests a cyclic process involving formation and destruction of a heterogeneous slip zone. Our microstructural data show that development of well-defined gouge foliation under the tested experimental conditions is limited to high velocities (>0.1 m s−1) and room humidity, supporting the notion that some foliated gouges and cataclasites may form during seismic slip in natural carbonate-bearing faults.

During shearing in geological environments, frictional processes, including the wear of sliding rock surfaces, control the nature of the slip events. Multiple studies focusing on natural samples have investigated the frictional behaviour of a large suite of geological materials. However, due to the varied and heterogeneous nature of geomaterials, the individual controls of material properties on friction and wear remain unconstrained. Here, we use variably porous synthetic glass samples (8, 19 and 30% porosity) to explore the frictional behaviour and development of wear in geomaterials at low normal stresses (≤1 MPa). We propose that porosity provides an inherent roughness to material which wear and abrasion cannot smooth, allowing material at the pore margins to interact with the slip surface. This results in an increase in measured friction coefficient from, info:eu-repo/semantics/published

A major part of the seismicity striking the Mediterranean area and other regions worldwide is hosted in carbonate rocks. Recent examples are the destructive earthquakes of L'Aquila Mw 6.1 2009 and Norcia Mw 6.5 2016 in Central Italy. Surprisingly, within this region, fast (\approx 3km/s) and destructive seismic ruptures coexist with slow (maximum 10 m/s) and non-destructive rupture phenomena. Despite of its relevance for seismic hazard studies, the transitions from fault creep to slow and fast seismic rupture propagation are still poorly constrained by seismological and laboratory observations. Here, we reproduced in the laboratory the complete spectrum of natural faulting on samples of dolostones representative of the seismogenic layer in the region. The transitions from fault creep to slow ruptures and from slow to fast ruptures, are obtained by increasing both confining pressure (P) and temperature (T) up to conditions encountered at 3-5 km depth (i.e., P = 100 MPa and T = 100 $^{o}$C), which corresponds to the hypocentral location of slow earthquake swarms and the onset of regular seismicity in Central Italy. The transition from slow to fast rupture is explained by the increase of the ambient temperature, which enhances the elastic loading stiffness of the fault and consequently the slip velocity during the nucleation stage, allowing flash weakening. The activation of such weakening induces the propagation of fast ruptures radiating intense high frequency seismic waves.

Grain size reduction due to cataclasis is a key process controlling fault frictional properties during the seismic cycle. We investigated the role of cleavage planes on fracturing and microstructural evolution during cataclasis in wet and dry carbonate fault gouges (50 wt% calcite, 50 wt% dolomite) deformed in a rotary-shear apparatus over a wide range of slip rates (30 μms−1 to 1 ms−1) and displacements (0.05–0.4 m). During shearing, progressive strain localization forms a narrow slip zone that undergoes significant frictional heating (at high slip rates), but the bulk gouge always accommodates low finite shear strains and deforms at low temperatures. Microstructural analysis of the bulk gouges indicates that deformation occurred by brittle fracturing and twinning. Microfractures in calcite are closely spaced, often exploit { 10 1 ¯ 4 } cleavage r-rhomb planes, and occur mainly subparallel to the expected principal stress orientation (σ1). Instead, twin planes typically occur sub-perpendicular to σ1. Electron backscatter diffraction analysis of the bulk gouges shows that calcite develops a well-defined crystallographic preferred orientation (CPO) at all investigated deformation conditions. The CPO is defined by a clustering of the calcite c-axes around an orientation sub-parallel to σ1. The calcite CPO is interpreted to result from grain rotation during granular flow, followed by brittle fracturing that occurred preferentially along calcite cleavage planes. This interpretation is supported by measurements of calcite grain shape-preferred orientations that show a population of elongate calcite grains oriented with their long axes sub-parallel to σ1. Our experimental results indicate that well-defined CPOs can form at low temperature in cataclastic fault rocks, and that mineral cleavage can strongly influence the evolution of grain sizes and shapes during comminution.

This work was supported by the Natural Environment Research Council (grant NE/R010846/1) Carbon Storage in Intertidal Environments (C-SIDE) project. A comparison of gouge and hammer coring techniques in intertidal wetland soils highlights a significant effect of soil compaction of up to 28% associated with the widely applied hammer coring method employed in Blue Carbon research. Hammer coring reduces the thickness of the soil profile and increases the dry bulk density, which results in an overestimation of the soil OC stock of up to 22%. In saltmarshes with multiple different soil units, we show that hammer coring is unsuitable for the calculation of OC stocks and should be avoided in favour of Russian or gouge cores. Compaction changes both soil dry bulk density and porosity and we show that resultant radiometric chronologies are compromised, almost doubling mass accumulation rates. While we show that the OC (%) content of these sediments is largely unchanged by coring method, the implication for OC burial rates are profound because of the significant effect of hammer coring on soil mass accumulation rates. Postprint

International audience; Continuous critical loading of pressure equipments can affect the structural stability of these plants. The structural stability and mechanical resistance under pressure loads can also be affected by defects. Fracture mechanics assumptions were applied to aluminium alloys to study their effect on its mechanical behaviours. A 3-point bending standard test was employed and the critical Stress Intensity Factor, K (SIF) in mode I was determined in order to provide a quantitative/qualitative evaluation of the performance. Additional experiments were carried out to validate the numerical results gained from the Finite Element Method (FEM) and the Extended Finite Element Method (X-FEM). The crack propagation process is discussed in this study focussing on the effect of crack tip radius.

International audience; The Nankai Trough Seismogenic Zone Experiment (IODP), SW Japan, aimed at unraveling hydrologic processes at subduction megathrusts and in situ rock and fluid properties to understand the fault zone behavior during earthquake nucleation and rupture propagation. At different sites, characterization of the sediments at high resolution allows tracing fluid-rock reactions that are either associated to early transformations (hydration or dehydration of clay minerals) during the accretion phase or to mineral recrystallization processes linked to deformation phases in gouge zones. In the sedimentary strata at the front of the accretionary prism changes in clay composition are inferred from chemical trends observed in pore fluids, which further indicate the influence of volcanic ash alteration (zeolite formation). Along the megasplay fault, recrystallization processes (e.g. pyrite) are observed in foliated gouge zones at the contact with non-foliated silty clay. The data highlight the importance of small-scale observations for process and reactive phases such as clays in such variable fluid-sediment reactions.

The influence of mechanical damage of the gas transmission pipelines on safe pipelines operation was researched in the article. The paper presents the main pipelines damage types with actual parameters and influence on operational parameters. The main pipeline Kaunas – Kaliningrad part, which was removed as no longer usable, was analysed. This damaged part was removed and changed to a new part by a responsible company. The hardness measurement and micro hardness measurement, chemical analysis, impact strength test, metallography analysis with an optical microscope were used in experiments. The analysed pipeline part was also regenerated by the computer software ANSYS, which works by the finite elements method. Santrauka Straipsnyje nagrinėjama magistralinių dujotiekių mechaninių pažeidimų įtaka saugiam jų eksploatavimui. Darbe pateikti pagrindiniai vamzdynų pažeidimo tipai su jiems būdingais bruožais ir įtaka eksploataciniams parametrams. Ištirta magistralinio dujotiekio Kaunas – Kaliningradas dalis, kuri buvo pašalinta, kaip nebetinkama naudojimui. Tyrimams pasitelktas kietumo ir mikrokietumo matavimas, cheminės analizės tyrimas, smūginio tąsumo bandymas. Mikrostruktūros tyrimams naudotas optinis mikroskopas. Tiriamasis objektas buvo atkurtas kompiuterinės programos, veikiančios baigtinių elementų metodu, ANSYS erdvėje. Raktiniai žodžiai:defektas, dujotiekis, įlenkimas, išskaptavimas, liekamasis resursas, mechaniniai pažeidimai, vamzdynas.

The influence of mechanical damage of the gas transmission pipelines on safe pipelines operation was researched in the article. The paper presents the main pipelines damage types with actual parameters and influence on operational parameters. The main pipeline Kaunas – Kaliningrad part, which was removed as no longer usable, was analysed. This damaged part was removed and changed to a new part by a responsible company. The hardness measurement and micro hardness measurement, chemical analysis, impact strength test, metallography analysis with an optical microscope were used in experiments. The analysed pipeline part was also regenerated by the computer software ANSYS, which works by the finite elements method. Article in Lithuanian. Magistralinio dujotiekio mechaninių pažeidimų įtaka saugiam eksploatavimui Santrauka Straipsnyje nagrinėjama magistralinių dujotiekių mechaninių pažeidimų įtaka saugiam jų eksploatavimui. Darbe pateikti pagrindiniai vamzdynų pažeidimo tipai su jiems būdingais bruožais ir įtaka eksploataciniams parametrams. Ištirta magistralinio dujotiekio Kaunas – Kaliningradas dalis, kuri buvo pašalinta, kaip nebetinkama naudojimui. Tyrimams pasitelktas kietumo ir mikrokietumo matavimas, cheminės analizės tyrimas, smūginio tąsumo bandymas. Mikrostruktūros tyrimams naudotas optinis mikroskopas. Tiriamasis objektas buvo atkurtas kompiuterinės programos, veikiančios baigtinių elementų metodu, ANSYS erdvėje. Reikšminiai žodžiai:defektas, dujotiekis, įlenkimas, išskaptavimas, liekamasis resursas, mechaniniai pažeidimai, vamzdynas.

To determine the role of strain localization during dynamic weakening of calcite gouge at seismic slip rates, single-slide and slide–hold–slide experiments were conducted on 2–3-mm thick layers of calcite gouge at normal stresses up to 26 MPa and slip rates up to 1 m s−1. Microstructures were analyzed from short displacement ( 35 cm ) experiments stopped prior to and during the transition to dynamic weakening. In fresh calcite gouge layers, dynamic weakening occurs after a prolonged strengthening phase that becomes shorter with increasing normal stress and decreasing layer thickness. Strain is initially distributed across the full thickness of the gouge layer, but within a few millimeters displacement the strain becomes localized to a boundary-parallel, high-strain shear band c. 20 μm wide. During the strengthening phase, which lasts between 3 and 30 cm under the investigated conditions, the shear band broadens to become c. 100 μm wide at peak stress. The transition to dynamic weakening in calcite gouges is associated with the nucleation of micro-slip surfaces dispersed throughout the c. 100 μm wide shear band. Each slip surface is surrounded by aggregates of extremely fine grained and tightly packed calcite, interpreted to result from grain welding driven by local frictional heating in the shear band. By the end of dynamic weakening strain is localized to a single 2 – 3 -μm wide principal slip surface, flanked by layers of recrystallized gouge. Calcite gouge layers re-sheared following a hold period weaken nearly instantaneously, much like solid cylinders of calcite marble deformed under the same experimental conditions. This is due to reactivation of the recrystallized and cohesive principal slip surface that formed during the first slide, reducing the effective gouge layer thickness to a few microns. Our results suggest that formation of a high-strain shear band is a critical precursor to dynamic weakening in calcite gouges. Microstructures are most compatible with dynamic weakening resulting from a thermally triggered mechanism such as flash heating that requires both a high degree of strain localization and a minimum slip velocity to activate. The delayed onset of dynamic weakening in fresh calcite gouge layers, particularly at low normal stresses, may inhibit large coseismic slip at shallow crustal levels in calcite-bearing fault zones.

The objective of this study is to demonstrate how fault dynamics may naturally be placed in the context of incremental stress theory, rock textural evolution modeling and standard conservation laws. Casting the fault dynamics problem in this framework naturally introduces rock memory for failure, fluid pressure effects and the autonomous nature of fault evolution. Poroelasticity, nonlinear viscosity and gouge are combined in an incremental stress rheology approach to examine the effect of changes in particle size distribution on fluid pressure in fault zones. © 2003 Elsevier Science B.V. All rights reserved.

Fluid-saturated granular and porous layers can undergo liquefaction and lose their shear resistance when subjected to shear forcing. In geosystems, such a process can lead to severe natural hazards of soil liquefaction, accelerating slope failure, and large earthquakes. Terzaghi's principle of effective stress predicts that liquefaction occurs when the pore pressure within the layer becomes equal to the applied normal stress on the layer. However, under dynamic loading and when the internal permeability is relatively small the pore pressure is spatially heterogeneous and it is not clear what measurement of pore pressure should be used in Terzaghi's principle. Here, we show theoretically and demonstrate using numerical simulations a general criterion for liquefaction that applies also for the cases in which the pore pressure is spatially heterogeneous. The general criterion demands that the average pore pressure along a continuous surface within the fluid-saturated granular or porous layer is equal to the applied normal stress., Fifth Biot Conference on Poromechanics, Vienna : Austria (2013)

The coupled mechanics of fluid-filled granular media controls the behavior of many natural systems such as saturated soils, fault gouge, and landslides. The grain motion and the fluid pressure influence each other: It is well established that when the fluid pressure rises, the shear resistance of fluid-filled granular systems decreases, and as a result catastrophic events such as soil liquefaction, earthquakes, and accelerating landslides may be triggered. Alternatively, when the pore pressure drops, the shear resistance of these systems increases. Despite the great importance of the coupled mechanics of grains-fluid systems, the basic physics that controls this coupling is far from understood. We developed a new multi-scaled model based on the discrete element method, coupled with a continuum model of fluid pressure, to explore this dynamical system. The model was shown recently to capture essential feedbacks between porosity changes arising from rearrangement of grains, and local pressure variations due to changing pore configurations. We report here new results from numerical experiments of a continuously shearing layer of circular two-dimensional grains, trapped between two parallel rough boundaries. The experiments use a fixed confining stress on the boundary walls, and a constant velocity applied to one of the boundaries, as if this system was the interior of a sliding geological fault filled with 'fault gouge'. In addition, we control the layer permeability and the drainage boundary conditions. This paper presents modeling results showing that the localization of shear (into a narrow shear band within the shearing layer) is strongly affected by the presence of fluids. While in dry granular layers there is no preferred position for the onset of localization, drained systems tend to localize shear on their boundary. We propose a scaling argument to describe the pressure deviations in a shear band, and use that to predict the allowable positions of shear localizations as a function of the fault and gouge properties., Comment: Fifth Biot Conference on Poromechanics, Vienna : Austria (2013)

Fault zones are major discontinuities in sedimentary basins. Understanding their role on fluid migrations is an essential issue to (i) characterize the mechanisms and kinematics of deformation and (ii) to determine the parameters which control the distribution of energetic or mineral resources. This work applies to faulting under a temperature range of 200-250°C, corresponding to that of deeply buried reservoirs as well as potentially seismogenic fault zones. The studied faults are normal faults affecting the “Grès d’Annot” Formation, a Priabonian-Rupelian siliclastic turbidite succession of the Alpine foreland basin. They are located in two distinct areas: the Moutière-Restefond area in the eastern part of the basin and the Estrop area in the western part. Vitrinite reflectance outside fault zones indicates maximal temperatures of 240-260°C at Moutière-Restefond and 170-200°C at Estrop, i.e. burial depths around 8 km and 6 km, respectively, assuming a mean geothermal gradient of 30°C/km. Burial was due to underthrusting below the Embrunais-Ubaye Alpine nappes, the difference in burial between the two areas traducing the westward taper of the nappe front.The studied faults affect alternating arkosic sandstone beds and pelite layers with offsets from centimeters to decameters. Two types of core zones are recognized: (1) the foliated core zones of the Moutière-Restefond area, where deformation dominated by pressure solution and synkinematic phyllosilicate neoformation resulted in a foliated fabric, and (2) the core zones of the Estrop area, characterized by dilatant quartz-mineralized veins and breccia. Fault and host rock petrophysical properties were measured on drill plugs, using the water porosity technique and nitrogen permeability technique under 2 Mpa of confining pressure. In the Moutière-Restefond fault zones, plug axes were oriented in three orthogonal directions corresponding to the main deformation axes (X, Y, Z) of the foliated arkose to characterize the effect of structural anisotropy. In the Estrop fault zones, where deformation does not show equivalent anisotropy, the plug axes were oriented according to the main fault plane orientation (i.e., parallel to azimuth, parallel to dip and normal). In each fault zone, the porosity of fault rocks is equivalent to that of host rocks. In the Moutière-Restefond fault zones, the plugs parallel to the X and Z axes of deformation have a permeability similar to that of the host rocks, whereas permeability parallel to the Y axis (i.e. parallel to the foliation and the main fault plane) is one order of magnitude higher. By contrast, the permeability values in the Estrop fault zones are isotropic and equivalent to the host rock values. This study highlights the importance of various types of deformation mechanisms and related fluid-rock interactions in determining different fault rock types within a similar protolith, ultimately controlling distinct petrophysical properties of fault zones., Les zones de failles constituent des discontinuités majeures dans la croûte supérieure. Ce mémoire s’intéresse aux failles actives à des profondeurs de 5-8 km, i.e. dans des conditions pouvant jouer un rôle important (i) sur le comportement mécanique de de la croûte, en particulier sur son potentiel sismogénique et (ii) sur la compartimentation des réservoirs géologiques profondément enfouis.Les failles étudiées sont des failles normales (rejet jusqu’à 50 mètres) affectant des alternances de bancs de grès arkosiques et de pélites dans les Grès d’Annot, une formation turbiditique d’âge priabonien-rupélien du bassin d’avant-chaine alpin. Les Grès d’Annot ont été enfouis sous les nappes de l’Embrunais-Ubaye peu de temps après leur dépôt et exhumés au Miocène moyen-supérieur. L’étude a été réalisée dans deux secteurs des Alpes de Haute-Provence, (1) le secteur de l’Estrop (chaine des Trois Evéchés, dans la partie occidentale du bassin) et (2) le secteur de Point Vert-Restefond (alentours du col de la Bonette, dans la partie orientale du bassin). La réflectance de la vitrinite dans les Grès d’Annot indique des températures maximales de 160-190°C dans le secteur (1) et de 240-260 °C dans le secteur (2) , soit des profondeurs d’enfouissement de 5-6 km et 8-10 km, respectivement, dans l’hypothèse d’un gradient géothermique moyen de 25-30°C/km. A partir des observations microstructurales, de données d’inclusions de fluides, de modélisations thermodynamiques sur chlorites syncinématiques et des indices de cristallinité de l’illite, on a établi que les failles du secteur (1) ont fonctionné à une température d’environ 200°C pour une pression de 0.6Kbar et celles du secteur (2) dans une gamme de température de 200-220°C et de pression comprise entre 0.6 et 1.1 Kba. L’activité de la faille de Point-Vert a été datée par la méthode 40Ar/39Ar au Miocène inférieur (21 Ma). Ces failles sont interprétées comme associées aux premiers stades du soulèvement résultant de l’activité des chevauchements dans le socle sous-jacent.Deux types principaux de roches de failles caractérisent les failles étudiées. Les brèches dilatantes sont majoritaires dans les zones de failles du secteur (1) alors que les arkoses foliées sont majoritaires dans les zones de failles du secteur (2). Les brèches dilatantes témoignent de mécanismes de déformation dominés par la fracturation transgranulaire et la pression-solution des silicates. Ce dernier mécanisme se manifeste principalement par d’abondantes précipitations cycliques de quartz, les stylolites restant peu développés. Les géométries structurales sont associées à l’activation de plans T de Riedel déterminant l’ouverture de relais extensifs et un régime localement dilatant. Nous associons ce type de roche de faille à une faible pression effective au cours de la déformation.La déformation cisaillante exprimée dans les arkoses foliées témoigne de mécanismes de déformation dominés par (i) la fracturation intragranulaire et transgranulaire, (ii) la pressionsolution/ précipitation des silicates, principalement le quartz, (iii) la néoformation de micas blancs liée à l’altération des feldspaths et (iv) la précipitation de chlorite. Ce travail montre également que les transformations minéralogiques liées aux interactions fluide-roche dans la zone de faille (forte augmentation de la proportion des phyllosilicates au dépend des feldspaths) changent radicalementla composition minéralogique de la roche. Nous associons ce type de roche de faille à une forte pression effective au cours de la déformation.La pétrophysique montre que les brèches de failles (secteur 1) ont une perméabilité isotrope et équivalente à celle du protolithe (10-3mD sous 2 MPa de confinement) tandis que les roches foliées (secteur 2) montrent une augmentation de perméabilité (10-2mD) selon l’axe Y de la déformation, d’un ordre de grandeur supérieure aux perméabilités suivant les axes X et Z et dans la roche hôte (10-3mD). Ce drain préférentiel potentiel est associé à l’orientation des phyllosilicates dans la foliation.

During an earthquake, the physical and the chemical transformations along a slip zone lead to alteration and formation of minerals within the gouge layer of a mature fault zone. The gouge contains magnetic minerals, which could be formed under the combined action of friction heat and fluid. Thus, gouge has the capacity to behave as a magnetic recorder during an earthquake. This constitutes a conceivable way to identify earthquakes slip zones. Besides, altered and neoformed magnetic minerals can be used as tracers of some earthquake processes. In this study, we investigate the rock magnetism and paleomagnetism of the Chelungpu fault gouge that hosts the principal slip zone of the Chi-Chi earthquake (Mw 7.6, 1999, Taiwan) using Taiwan Chelungpu-fault Drilling Project (TCDP) hole-B core samples. We also took a Chelungpu fault outcrop sample for identification of nanoparticle, which associated with fracture energy estimation in fault gouge., Lors d'un tremblement de terre, les transformations physiques et chimiques qui surviennent le long d'une zone de glissement vont conduire à l'altération et à la formation de minéraux. La gouge contient des minéraux magnétiques, qui peuvent être formés sous l'action combinée de la chaleur frictionnelle et par l'action chimique en relation avec les fluides. Ainsi, la gouge a la capacité de se comporter comme un enregistreur magnétique pendant un tremblement de terre. Il s'agit là d'une nouvelle méthode pour identifier les zones de tremblements de terre de glissement. En outre,les minéraux magnétiques initiaux, altérés, et néoformés peuvent être utilisés comme traceurs de certains processus physico chimique.Dans cette étude, nous étudions le magnétisme des roches et l'enregistrement paléomagnétique de la gouge de faille active de Chelungpu qui héberge, entre autres,la zone de glissement principale du tremblement de terre de Chi-Chi (Mw 7.6, 1999,Taiwan). Nous avons bénéficié pour cette étude d'échantillons non altérés provenant des carottes du forage B Taiwan Chelungpu-fault Drilling Project (TCDP). Nous avons également échantillonné la faille de Chelungpu à l'affleurement pour une caractérisation des nanoparticules. Cette caractérisation vise à estimer l'énergie de fracture dans la gouge de faille.

International audience; We have investigated the grain size distribution (GSD) of granitoid fault rock by comparing experimentally produced gouge with fault rock from the Nojima Fault Zone. Triaxial experiments were carried out on wet and dry intact samples of Verzasca Gneiss at T = 300 and 500°C, Pc = 500 and 1030 MPa, ε = 0.013-1.6 x 10-4s-1. The GSD has been determined from SEM-micrographs and is characterized by the slope, D, of its log(frequency)-log(radius) histogram. The GSD is not fractal; we observe two slopes for all GSDs. The larger grains in experimentally deformed samples have a D value, D>, of 2.04 and 2.26 for feldspar and quartz gouge. Cracked grains yield values of D = 1.5-1.6.Increasing the confining pressure or temperature decreases the D-value. For grains smaller than ~2 μm another D-value, D = 2.02 for gouge and 1.64 for cracked grains; D< = 0.97. Grain size reduction in fault zones develops by a two-stage process: rupturing creates cracked grains; further displacement of fragments causes further comminution by wear and attrition. Cracked grains have been used to calculate the surface energy associated with faulting; it follows that this energy forms a small fraction in the total energy-budget of earthquakes.

International audience; To understand the behaviour and deformation mechanisms of serpentinites in the seismogenic zone we study the deformation macro- and microstructures of serpentinites along the Santa Ynez Fault in the San Andreas System. At the outcrop scale, deformation is localized in a gouge zone that shows three different structures: (1) micrometric undeformed fragments (clasts) of the previously serpentinized peridotite, (2) localized shear planes (Y and R) and (3) a penetrative schistosity (S). Observations under SEM and TEM reveal that the schistosity corresponds to serpentine fibres, parallel to each other, and whose orientation varies as they wrap around clasts. TEM micro-textures indicate that these long fibres result from continuous syntectonic growth rather than from reorientation of pre-existing fibres implying a slow transfer process that occurs at short distances. We propose a dissolution–diffusion–crystallization process for the formation of the schistosity that corresponds to a low strain-rate creeping process of deformation that can be effective in aseismic fault segments.