A study of a large earthquake in Taiwan collision zone

(1)地震观测：我们在台湾中部150公里长的线路上部署了60台三分量地震仪，以观测天然地震。我们观察到了地区性、区域性和远震事件。这些资料显示了地壳的大规模形变，这可能受台湾地区碰撞构造的控制。1999年集集地震发生两年后，台湾中部地区仍有高度活跃的地震活动。(2)GPS观测：我们对单频GPS数据进行了分析，以提高精度。(3)地貌：我们进行了实地调查，分析了航空骨片和1：2500地质图，以定量评价台湾现今的构造作用。我们发现了一条与车龙铺断裂平行的活动褶皱。(4)控制源地震学：我们在台湾中部进行了长达15公里的反射调查。我们引爆了两枚50公斤重的炸药。(5)地质调查：在车龙铺断裂的北部钻孔发现了薄层的极软断层粘土，而在南部的钻孔中发现了假硅质岩。南部层的熔融程度很低，表明熔体的高粘度可能抑制了滑移。(6)构造：从俯冲板块脱水的角度研究了碰撞带板间地震活动差异的原因。

(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.