許 華杞 台湾・大漢技術学院大学, 防災研究中心, 教授
IIZUKA Susumu TOKAI University, School of marine Science and Technology, Professor, 海洋学部, 教授 (40055918)
IWASHITA Atsushi Kyusyu TOKAI University, School of Engineering, Professor, 工学部, 教授 (40266383)
HWA-CHU Sheu DAHAN Institute of Technology, The Research Center for Disaster Prevention, Professor
|Budget Amount *help
¥2,500,000 (Direct Cost: ¥2,500,000)
Fiscal Year 2003: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2002: ¥1,100,000 (Direct Cost: ¥1,100,000)
Geology and tectonics of the region between the southwestern Ryukyu arc and the eastern Taiwan are characterized by subduction or collision of the Philippine Sea plate and Eurasian plate. The present collision boundary in Taiwan is located along the Longitudinal Valley between Hualien and Taitung, but the plate boundary of the region between the northeast off Taiwan and the southwestern Ryukyu arc is not yet clear and still controversial. In order to make clear the plate boundary or configuration and tectonics in the region, it is indispensable to study the accurate seismic activities, in other words, precise hypocenter distributions, focal mechanisms, and so on.
We, therefore, have been able to obtain more accurate or detailed hypocenter distributions in this region. As the results, our hypocenter locations show a large discrepancy with those of Japan Meteorological Agency and Taiwan Central Weather Bureau, which may be due to biased station networks, complex lithospheric structures and others, in this area. Recently, within a half year, four large earthquakes occurred near Yonaguni Is. (Dec.18 2001, M7.3), near Ishigaki Is. (Mar.15 2002, M6.6), and off east coast of Taiwan (Mar.31 2002, M7.2, and May.15 2002, M6.8). These earhtquake focal zones seem to align along the plate boundary, and their focal mechanisms are reflected on a complicated tectonics in the region. We describe the precise hypocentral distribution, and fault plane model of earthquake. Also we make consideration about the cause of the activity and the tectonics.