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Seismic Hazard Analysis using Seismic Noise


April 29, 2015, noon - 12:50 p.m.
Geology 1707

Presented By:
Marine Denolle
UCSD

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Rapid growth of populated urban environments increases exposure to earthquake hazard. In particular, major metropolitan area such as Los Angeles and Tokyo, sit on deep sedimentary basin and are subject to high seismic hazard with the nearby active plate boundaries. Ground motion prediction is central to seismic hazard analysis. Two approaches currently exist to predict ground motion; one is purely empirical and the other is purely physics-based. To validate and constrain both approaches, we propose a third strategy that respects the physics and that takes advantage of large amount of seismic data. The continuously recorded ambient seismic field carries information on three-dimensional wave propagation. We develop a new method that extracts the coherent wavefield buried in seismic noise and that constructs long-period seismograms from virtual earthquakes. In the Los Angeles sedimentary basin, we validate it against past M5 earthquakes in southern California and predict ground motion for a M7+ virtual earthquake on the southern San Andreas Fault. We find that strong seismic amplification patterns concord with basin shape and that finite source directivity couples with three-dimensional structure to intensify seismic amplification far from the fault. In the Kanto sedimentary basin that underlies Tokyo, we take advantage of dense seismic arrays to unravel the effects of focusing and reflection within the basin. We find the resonance frequency of the Kanto Basin, build linear relations between peak ground motion and basin depth, and highlight the variability in amplification pattern with the origin virtual source.