地球シミュレータによるスペクトル要素法を用いた全球広帯域理論地震波伝播計算

抄録

We use a Spectral-Element Method implemented on the Earth Simulator in Japan, to simulate broadband seismic waves generated by various earthquakes. The spectral-element method is based on a weak formulation of the equations of motion and has both the flexibility of a finite-element method and the accuracy of a pseudospectral method (Komatitsch and Tromp, 2002a, b). The method has been developed on a large PC cluster and optimized on the Earth Simulator. We perform a numerical simulation of seismic wave propagation for fully three-dimensional Earth model, which incorporate 3D variations in compressional wave velocity, shear-wave velocity and density, attenuation, anisotropy, ellipticity, topography and bathymetry, and crustal thickness. We use model S20 RTS of the mantle (Ritsema et al., 1999), model CRUST2.0 of the crust (Basin et al., 2000), and topography and bathymetry model ETOPO5. The simulation is performed on 4056 processors, which requires 507 out of 640 nodes of the Earth Simulator. We use a mesh with 206 million spectral-elements, for a total of 13.8 billion global integration grid points (i. e., almost 36.6 billion degrees of freedom). This translates into an approximate grid spacing of 2.0km along the Earth's surface. On this number of nodes, a simulation of 15 minutes of wave propagation accurate at periods of 3.5 seconds and longer requires about 6 hours of CPU time. We show examples of simulation for several large earthquakes and discuss its future application in seismological studies.