Localization of subsurface seismic events on the San Jacinto faultusing a dense array of sensors

Abstract : The focus of this thesis is the detection and localization of weak sources on the San Jacinto Fault Zone. The primary targets of interest are sources in the shallow crust, with depth down to a few kilometers. For sources at these depths high frequency content and low energy are expected. Surface sources present on and around the array site are also studied in order to discriminate them from weak seismic sources at depth.We rely on a methodology based on array processing to detect and localize shallow and weak seismic events in the fault zone complex environment. We use Match field Processing on data recorded from a dense array of 1108 vertical component geophones in a 600m x 600m area on the Clark branch of the San Jacinto Fault. We first test the method on a set of chosen events at depth and at the surface. Source epicentral positions and associated apparent velocities are then inverted for surface and seismic sources for 26 days, with the intention of determining if shallow sources are present. Inverting only for these three parameters is less expensive in terms of computational cost and is suitable for a first approach. However, this first inversion leaves us unable to conclude on the presence of shallow sources. As the resolution at depth is insufficient when all three source coordinates are inverted with a classical homogeneous velocity model, we finally investigate strategies to improve resolution at depth without increasing computational cost.
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Chloé Gradon. Localization of subsurface seismic events on the San Jacinto faultusing a dense array of sensors. Earth Sciences. Université Grenoble Alpes, 2019. English. ⟨NNT : 2019GREAU001⟩. ⟨tel-02148230⟩

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