Strong Motion Prediction Based on the 3-D Basin Structure and Inhomogeneous Source Process of Hypothesized Kego Earthquake in Fukuoka, Japan

Abstract eng:
On March 20, 2006 the City of Fukuoka were jolted by the West off Fukuoka Prefecture earthquake of MJ 7.0 and moderate damage to structures (around 300 heavy damage buildings) were observed. First the seismic records of K-NET, KiK-net, the JMA network, and Fukuoka Prefecture network during this earthquake were collected and analyzed. We then constructed a clear asperity source model on the fault plane. We use a three-dimensional (3-D) deep basin model based on the S-wave velocity structures at four sites, geological data, topographical information, and gravity data. We used forward modeling technique with an assumption of a single asperity located at the southeast of the hypocenter, which is derived from a multi-window kinematic source inversion by Suzuki and Iwata. We found a high speed peak slip velocity in this relatively small asperity. The resultant simulated strong motions show quite similar waveforms with the observed ones. Next we estimated broadband strong ground motions in Fukuoka City by using an improved version of the 3-D basin structure based on a detailed map of gravity anomaly. We simulated strong ground motions during the hypothesized Kego earthquake using hypothesized rupture scenarios derived from the multi-asperity source model obtained for the Hyogo-ken Nanbu (Kobe) earthquake of 1995. The result of our simulation shows that we have to prepare for a severe disaster in the downtown Fukuoka, once such an event would occur. The detailed distribution of high peak ground velocity (PGV) and maximum values inside the high value zone strongly depend on the rupture scenario, however, the downtown Fukuoka is always the region of high PGVs.

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