Frictional measurements were made on natural fault gouge at seismic slip rates using a high-speed rotary-shear apparatus to study effects of slip velocity, acceleration, displacement, normal stress, and water content. Thermal-, mechanical-, and fluid-flowcoupled FEM models and microstructure observations were implemented to analyze experimental results. Slightly sheared starting material (Unit 1) and a strongly sheared and foliated gouge (Unit 2) are produced when frictional heating is insignificant and the coefficient of sliding friction is 0.4 to 0.6. A random fabric gouge with rounded prophyroclasts (Unit 3) and an extremely-fine, microfoliated layer (Unit 4) develop when significant frictional heating occurs at greater velocity and normal stress, and the coefficient of sliding friction drops to approximately 0.2. The frictional behavior at coseismic slip can be explained by thermal pressurization and a temperature-dependent constitutive relation, in which the friction coefficient is proportional to 1/T and increases with temperature (temperature-strengthening) at low temperature conditions and decreases with temperature (temperature-weakening) at higher temperature conditions. The friction coefficient, normal stress, pore pressure, and temperature within the gouge layer vary with position (radius) and time, and they depend largely on the frictional heating rate. The critical displacement for dynamic weakening is approximately 10 m or less, and can be understood as the displacement required to form a localized slip zone and achieve a steady-state temperature condition. The temporal and spatial evolution of hydromechanical properties of recovered from the Nankai Trough (IODP NanTroSEIZE Stage 1 Expeditions) have been investigated along different stress paths, which simulate the natural conditions of loading during sedimentation, underthrusting, underplating, overthrusting, and exhumation in subduction systems. Porosity evolution is relatively independent of stress path, and the sediment porosity decreases as the yield surface expands. In contrast, permeability evolution depends on the stress path and the consolidation state, e.g., permeability reduction by shear-enhanced compaction occurs at a greater rate under triaxialcompression relative to uniaxial-strain and isotropic loading. In addition, experimental yielding of sediment is well described by Cam-Clay model of soil mechanics, which is useful to better estimate the in-situ stress, consolidation state, and strength of sediment in nature.

L'existence de glissements lents a été observé pour la première fois en Californie, sur une portion de la faille de San Andreas (Steinbrugge et al., 1960,Tocher 1960). Ils ont ensuite été détéctés dans les années 90s avec l'avènement des GPS. Les interactions entre glissement lents, ou glissements asismiques (qui n'émettent pas d'ondes élastiques) et les glissements sismiques est cependant mal connue.Pourtant, cette question est fondamentale puisque des glissements lents ont été observés avant plusieurs séismes.Par exemple, l’installation d’un glissement lent avant le séisme d’Izmit de 1999 en Turquie a été mise en évidence grâce à l’analyse de signaux répétitifs (Bouchon et al., 2011). De même, en étudiant le comportement des séismes répétitifs avant le méga-séisme de Tohoku de 2011, deux séquences de glissement lent en direction du point d’initiation ont été observées (Kato et al., 2012). D’autres glissements lents précédents des séismes de grandes ampleurs ont été reportés, notamment au Mexique, avant le séisme de Papanoa (Radiguet et al., 2016) de magnitude 7.3 et au Chili, avant le séisme d’Iquique de 2014 de magnitude 8.2 (Ruiz et al., 2014).L'objectif de ce travail de thèse est de mieux caractériser les interactions qui existent entre glissements sismiques et asismiques dans une zone de subduction très largement instrumentée: le Japon.La très grande densité des réseaux Japonais (sismique courte et longue période, GPS) autorise des seuils de détection des glissements sismiques ou lents très bas, et permet d'utiliser des méthodes de réseaux afin de maximiser le rapport signal sur bruit. La recherche d'épisodes de déformation lente est basée sur plusieurs types d'observables et de méthodes, et est complétée par l'analyse des changements de taux de sismicité accompagnant ces épisodes. Cette thèse vise ainsi à mieux comprendre comment du glissement lent peut -ou non- accélérer l'occurrence de grands séismes, et les conditions requises pour se faire. / Transient aseismic slip events (that do not emit elastic waves) were first discovered on the San Andreas fault in central California in 1960 (Steinbrugge et al., 1960, Tocher 1960) and were later confirmed by the development and installation of GPS stations. Aseismic slip can occur on continental faults as well as on subduction zones. However, the interactions between aseismic and seismic slips are not fully captured yet. Understanding the mechanisms at stake on fault planes is fundamental since several large earthquakes were preceded by aseismic slip episodes.For example, the setting of a slow slip event before the 1999 Izmit earthquake in Turkey was evidenced by the observation of repeating signals at one station (Bouchon et al., 2011). Also, by studying repeating earthquakes before the 2011 Tohoku earthquake, two slow slip episodes that migrated towards the rupture intitiation were observed (Kato et al., 2012). Other transient slips preceding large earthquakes occurred, including in Mexico, before the M7.3 Papanoa earthquake (Radiguet et al., 2016) and in Chile, before the 2014 Iquique earthquake (Ruiz et al., 2014).The aim of this thesis is to better characterize the interactions between seismic and aseismic slip that can occur in a subduction zone largely instrumented: Japan.The very high density of the japanese monitoring networks(seismic networks, both at short and long periods, and GPS network), allows the detection ofseismic and aseismic slip events with low intensity / size, and is amenable to the use of arraymethods to improve the signal-to-noise ratio. The search for episodes of transient deformation will be based on several observables andtechniques, and is complemented by the analysis of the changes in earthquake rates concomittent to these episodes. This work thus gives new clues on how aseismic deformation can -or not- accelerate the occurrence of strong earthquakes, and on what are the conditions (tectonic, dynamic) for this to happen.

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