Spectral-Element Simulations of Seismic Wave Propagation

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TrompEAR-0309576The investigators will use and extend a numerical technique called the `spectral-element method' (SEM) to model seismic wave propagation. The method incorporates complications due to lateral variations in compressional-wave speed, shear-wave speed and density, a 3D crustal model, ellipticity, topography and bathymetry, the oceans, attenuation, anisotropy, and, at long periods, rotation and self-gravitation. They propose to use these capabilities to investigate tradeoffs between isotropic and anisotropic structure in surface-wave modeling, and to analyze long-period PKIKP waveforms associated with an anisotropic inner core. They will also implement fully 3D centroid-moment tensor (CMT) inversions based upon numerically calculated Frechet derivatives. The SEM can handle finite rupture models, which turns out to be quite important for several large recent events that exhibit strong directivity. When modeling amplitude anomalies there exist significant tradeoffs between elastic focusing and attenuation. The SEM can accommodate lateral variations in both elastic and anelastic structure, which provides a quantitative means of assessing this tradeoff. The investigators will extend the SEM to simulate seismic wave propagation in sedimentary basins. Based upon a detailed 3D Los Angeles basin model developed by Prof. John Shaw and his co-workers at Harvard, they are embarking on waveform modeling of TriNet data. At the end of the proposed research period the basin software package will be made available for use by other research groups. Finally, the investigators have established a collaboration with Dr. Seiji Tsuboi of JAMSTEC (Japan), which involves SEM simulations on the Earth Simulator, the world's largest and fastest computer.The broader impacts of the proposal include open-source software packages for the simulation of seismic wave propagation in sedimentary basins and the entire globe. Simulations based upon these packages can be used to investigate seismic hazard and aid in the determination of earthquake source parameters. The SEM can also be used to assess and improve the quality of tomographic models of the mantle, an endeavor that will enhance our understanding of the physics of the Earth's interior. Finally, the proposal would support the education and training of two graduate students and one postdoc.