A study of a large earthquake in Taiwan collision zone

点击翻译按钮获取中文摘要

(1) Earthquake observation : We deployed 60 3-component seismographs along a 150-km-long line in central part of Taiwan to observe natural earthquakes. We observed local, regional and teleseismic events. The data show large-scale deformation of the crust, which might be controlled by the collision tectonics in Taiwan. A highly active seismic activity was detected in central part of Taiwan even two year has passed since the 1999 Chi-Chi earthquake.(2) GPS observation : We analyzed a single frequency GPS data to improve accuracy.(3) Geomorphology : We conducted a filed survey, analysis of air-bone photos and 1 : 2,500 geologic maps to evaluate quantitatively the present-day tectonic processes that are acting in the Taiwan. We found an active fold that runs parallel to the Chelungpu fault.(4) Control source seismology : We conducted a 15-km-long reflection survey in central part of Taiwan. We detonated two 50-kg dynamite shot. We imaged a deep crust and a deeper extension of the Chelungpu fault.(5) Geological survey : From the northern borehole of the Chelungpu fault, thin layers of very soft fault clay were found, while pseudotachylyte was found form the southern borehole. The degree of melting of the southern layer is very low, suggesting that high viscosity of the melt is likely to have restrained the smooth slip.(6) Tectonics : The reason why there is a difference in the interplate seismic activity in collision zones are studied from a viewpoint dehydration from the subducted slab.