Spectral-Element Simulations of Seismic Wave Propagation

研究人员将使用并扩展一种称为“谱元法”（SEM）的数值技术来模拟地震波的传播。由于压缩波速、横波速度和密度的横向变化、三维地壳模型、椭圆性、地形和测深、海洋、衰减、各向异性以及长周期的自转和自引力，该方法包含了一些复杂性。他们建议利用这些能力来研究表面波建模中各向同性和各向异性结构之间的权衡，并分析与各向异性内核相关的长周期PKIKP波形。他们还将基于数值计算的Frechet导数实现全三维质心矩张量（CMT）反演。扫描电镜可以处理有限破裂模型，这对最近几次表现出强指向性的大型事件非常重要。在对振幅异常进行建模时，在弹性聚焦和衰减之间存在着重要的权衡。扫描电镜可以适应弹性和非弹性结构的横向变化，这提供了一种定量评估这种权衡的方法。研究人员将扩展扫描电子显微镜来模拟地震波在沉积盆地中的传播。基于哈佛大学John Shaw教授和他的同事开发的详细的洛杉矶盆地3D模型，他们正在着手对TriNet数据进行波形建模。在拟议的研究期间结束时，将提供盆地软件包供其他研究小组使用。最后，研究人员与日本JAMSTEC的Seiji Tsuboi博士建立了合作关系，其中包括在世界上最大最快的计算机Earth Simulator上进行SEM模拟。该提议的更广泛影响包括用于模拟沉积盆地和全球地震波传播的开源软件包。基于这些包的模拟可以用来研究地震危害和帮助确定震源参数。扫描电镜还可以用来评估和提高地幔层析成像模型的质量，这一努力将增强我们对地球内部物理的理解。最后，提案将支持两名研究生和一名博士后的教育和培训。

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.