Rôle des hétérogénéité géométriques et rhéologiques sur les ruptures sismiques

par Kristel Chanard

Thèse de doctorat en Géologie

Sous la direction de Raúl Madariaga.


  • Résumé

    Les données expérimentales et les observations de terrain suggèrent que la géométrie et les propriétés de friction le long d'une faille ont un rôle déterminant dans la propagation des ruptures dynamiques et sur le champ d'ondes rayonnées. Cependant les ruptures sont souvent modélisées par un glissement sur une faille complexes (branches). De plus le glissement peut être stable ou instable selon la friction. Cette thèse propose donc un étude de l'influence de la géométrie et de la rhéologie sur les ruptures sismiques, en utilisant de la modélisation numérique et analytique.

  • Titre traduit

    Seasonal deformation of the earth induced by variations in hydrology, impact on seismicity


  • Résumé

    In this thesis, we aimat modeling accurately seasonal deformation of the Earth induced byredistribution of hydrosphere masses. We take advantage of seasonal ground displacementsmeasured by continuous stations of the Global Positioning System (cGPS) and the estimate ofthe spatio-temporal evolution of surface hydrology derived from the Gravity and RecoveryClimate Experiment (GRACE) measurements. Precise geophysical models of the seasonaldeformation, discussed in Chapter 1, of the Earth have far-reaching implications in defininginternational terrestrial reference frame, detecting potential transient deformation withcomparable period or even understanding the link between induced stress perturbations andseasonal seismicity. In Chapter 2, we show that seasonal ground displacements recorded bycGPS stations in the Himalaya are fairly well explained by the Earth’s response to seasonalhydrology derived fromGRACE, which induces coherent surface displacements, in first orderapproximation, with horizontal and vertical observations simultaneously, provided that arealistic elastic, spherical and layered model for Earth is used. We extend the model to a globalscale in Chapter 3, and compare displacements induced by the seasonal load at 195 cGPSstations globally distributed. We account for the degree-1 contribution in GRACE using resultsfrom Swenson et al. (2008). We find that, while the vertical displacements are well predictedby themodel, the horizontal components are systematically underpredicted and out-of-phasewith the observations. We show a significant improvement when we do not apply a prioridegree-1 coefficients but estimate and apply a posteriori a Helmert transformto the horizontalcomponents. The fit in phase and amplitude of the seasonal deformation model to thehorizontal components is improved and does not affect the fit to the verticalmeasurements.We conclude that horizontalmisfits result mostly from degree-one deformation plus referenceframe differences betweenmodel and observations, and not from the limited spatial resolutionof GRACE. However, the amplitude of global seasonal horizontal displacement remains slightlyunderpredicted. We show that mantle volume variations due to mineral phase transitions mayplay a role in the seasonal deformation and, as a by-product, use this seasonal deformationto provide a lower bound of the transient astenospheric viscosity. Finally, in order to testthe impact of seasonal forcing on seismicity, we estimate the amplitude of periodic stressperturbations induced by seasonal loading. To further investigate the question, we performaset of triaxial deformation experiments on water-saturated Fontainebleau sandstones. Rocksamples are loaded by the combined action of steps of constant stress, intended to simulatetectonic loading and small sinusoidal pore pressure variations, analogous to tides or seasonalloading. Our experimental results suggest that the correlation of small stress perturbationsand acoustic emissions depends primarily on the state stress of the rock and that emissionsoccur more likely when cracks are unclamped. In other words, our observations suggest thattidal triggeringmight occur favorably during the long nucleation phase of earthquake.


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  • Bibliothèque : Ecole normale supérieure. Bibliothèque électronique.
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