Numerical Simulation of Seismic Wave Propagation and Strong Motions in 3D Heterogeneous Structure

Introduction The heterogeneities in the crust and upper mantle structure as well as the complex source rupture process have an important influence on regional seismic wavefield, particularly for high-frequency waves. Moreover small-scale heterogeneities such as for the sedimentary basin introduce significant amplification of ground motion, which lead to long ground shaking over several minutes in the population centers. In order to see seismic wave behavior imposed by such heterogeneous structures, a high-resolution computer simulation with including a deep plate structure as well as a shallow superficial structure is indispensable. The Earth Simulator made it possible to provide a realistic simulation of strong ground motions in 3D heterogeneous structure. In this report we will show two examples of strong ground motion simulations with illuminated 3D seismic wavefield using a newly developed visualization techniques suitable for the Earth Simulator (Chen et al., 2003). The first example is for the ground motions from the 1983 Kushirooki earthquake (M7.8) which produced anomalous pattern of seismic intensity in wide area of northern Japan due the subduction of low-attenuative (high-Q) Pacific plate. The second example is the modeling of strong ground motions for the 1923 Kanto earthquake (M7.9) to show the amplification effect in low-velocity structure in the basin of Tokyo. The Earth Simulator realized realistic 3D simulation of seismic wave propagations over a regional scale and relatively higher frequencies. In addition, a visualization tool for seismic 3D wavefield made it possible to directly understand the complex regional seismic wavefield imposed by heterogeneities in the crust and upper-mantle structure. We applied the parallel FDM code and visualization tools both are optimized for the Earth Simulator (Furumura and Chen, 2004) for modeling of seismic wave propagation from recent and historically damaging earthquakes, such as for the great 1923 Kanto earthquake (M7.9) and the 1983 Kushiro-Oki earthquake (M7.8), in order to understand the generation process of the strong ground motions in 3D heterogeneous structure. The good agreement in the simulations and observations in the feature of the seismic wavefield and pattern of intensities indicating that the computer simulation is already a suitable level to apply to investigate the pattern of ground motions expecting for future earthquake scenarios.