Abstract
AbstractStrong ground motions caused by the Mj 7.4 2004 earthquake that occurred in the Nankai Trough to the southeast of the Kii Peninsula, Japan are simulated by a three-dimensional (3D) finite-difference method (FDM) using a fault-rupture model obtained by inversion of teleseismic seismograms and a 3D subsurface structure model for central Japan. Through simulations of the foreshock (Mj 7.1), the structural model is refined by comparison with observations, and the modified model is used to simulate the mainshock. The simulation provides a reasonable reproduction of the ground motions caused by the mainshock, including site amplification effects in the sedimentary basins of Osaka and Noubi. However, the current simulation model has limitations in producing the large and extended ground motion due to long-period Love waves in the Kanto Plain, as the model does not account for the sharp frequency selectivity for Love waves in the surficial structure of the Bouso Peninsula. It therefore appears necessary to develop a better model for longer-period waves.
Highlights
A large Mj 7.4 earthquake occurred in the Nankai trough to the southeast of the Kii Peninsula on 5 September 2004 at 23:57 Japan Standard Time (JST) (Fig. 1)
A notable feature of the 2004 earthquake was that longperiod ground motions of 2–10 s or longer were observed in major population centers such as Osaka, Nagoya, and Tokyo, sites located on large sedimentary basins
Comparison between the waveforms recorded by the Kik-net station on the Bouso Peninsula (CHBH10) for the mainshock and foreshock events reveal the difference in the source spectrum and amplification characteristics of longperiod signals in Tokyo during the small (Mj 7.1) and large (Mj 7.4) events (Fig. 3)
Summary
A large Mj 7.4 earthquake occurred in the Nankai trough to the southeast of the Kii Peninsula on 5 September 2004 at 23:57 Japan Standard Time (JST) (Fig. 1). No such large responses were observed in Tokyo or on the Bouso Peninsula during the foreshock event (Fig. 2(a)), even though both earthquakes have similar source locations and mechanisms.
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