1995年兵庫県南部地震の断層モデルと震源近傍における強振動シミュレーション

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The 1995 Hyogo-ken Nanbu earthquake struck Kobe and adjacent cities, one of the most densely populated area in western Japan, and killed more than 6,400 people and destroyed more than 150,000 buildings and houses and tens of highway and railroad bridges. It is very important to examine the ground motion characteristics in the severely damaged area during the mainshock for understanding how buildings and bridges performed and why they reached collapse. Unfortunately very few strong ground motions were recorded in the severely damaged areas during the mainshock. In this study, we attempt to estimate ground motion at severely damaged sites by using the empirical Green's function method (EGF method). We derive a best source model with three asperities after several try and error with forward modeling by the EGF method. We estimate strong ground motions at sites, where the mainshock was not recorded, using aftershock records. The synthesized motions in the near-fault region in Kobe were characterized by two large long-period (1 to 3 seconds) pulses due to the forward rupture directivity. Peak horizontal acceleration and velocity of the synthesized motions at the heavily damaged sites are about 1,000 cm/sec^2 and 130 cm/sec, respectively, while those at a rock site in near-fault region show about 300 cm/sec^2 and 60 cm/sec. The reason why so strong motions hit the heavily damaged sites is that the large long-period pulses which come from two asperities in the Kobe-side segment of the fault were further amplified by the basin edge effects.
1997-10-30

1995年兵庫県南部地震の断層モデルと震源近傍における強振動シミュレーション

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