Large-scale parallel simulation of seismic wave propagation and strong ground motions for the past and future earthquakes in Japan

Large-scale parallel finite-difference method (FDM) simulations of seismic wave propagation have been conducted using the Earth Simulator in order to clarify the complex seismic wavefield resulting from heterogeneities in structures and the source rupture process during the Hyogo-ken Nanbu (Kobe) earthquake (Mj 7.2; Mw 6.9) in 1995. High-resolution simulation using 240 nodes (1920 processing elements) of the Earth Simulator for seismic waves from the Kobe earthquake provided a very good reproduction of strong ground motions and a narrow zone of larger intensity (damage belt) appearing in the Awaji Island and KobeHanshin region. Thus, the current simulation model is considered to be suitable for application in predicting strong ground motions for possible future earthquakes, such as the occurrence of a large earthquake in Tokyo. The Tokyo metropolitan area is located over a tectonically complicated region, in which M7 inland earthquakes and M8 plate earthquakes have frequently occurred. However, no large earthquake has occurred for the past 80 years. Simulation results for a hypothetical earthquake in Tokyo indicate that most population centers would be affected by significant ground shaking of Japan Meteorological Agency (JMA) intensity greater than 6 due to the strong amplification of ground motions in the thick sediments below Tokyo. Large earthquakes also produce strong shaking for relatively longer periods of approximately 6 to 8 s due to the resonance of seismic waves in the thick sedimentary basin. Such long-period ground motions would be most damaging to large-scale man-made structures, such as high-rise buildings, long bridges, and large oil reserve tanks, which were constructed in Tokyo after the 1923 Kanto earthquake.