Investigation on the 921 Ji-Ji Earthquake, Taiwan, of 21 September 1999

这项研究是由15名研究人员在1999年10月初至12月期间为调查损害和收集资料和数据而进行的。调查结束后，以下情况变得清晰起来：*菲律宾海板块沿着琉球海沟俯冲到欧亚板块之下。亚欧大陆板块向菲律宾海板块下方俯冲，从而引发了地震。地面测得的最大位移量垂直约10米，水平数米。*地震前，台湾交通运输部中央气象局已分布和维护了700多个强震观测站。在震中附近，记录到了非常强的加速度，超过900加仑。此外，断层北端附近的加速度记录综合结果的速度记录超过300公里。*许多交通设施(包括公路桥、铁路桥和隧道)遭到破坏。可以推测，破坏的最主要控制因素是断层引起的地表垂直方向和水平方向的差异位移。*地表断层破坏了混凝土重力坝。这将引发基础设施抗断层位移抗震的新技术课题。*台湾的供电系统集中在一个开关场，地震直接袭击了它。因此，电力系统的冗余是必要的。

This research was carried out by 15 researchers for the investigation into the damage and collection of information and data during early October to December 1999. The following became clear after the investigation.* The Philippine Sea plate subducts along the Ryukyu Trench beneath the Eurasian plate. The Eurasian plate is underthrusting beneath the Philippine Sea plate, this caused the earthquake. The maximum dislocation measured at ground surface was about 10 meters vertically, and several meters horizontally.* Before the earthquake, more than 700 strong motion observation stations have been distributed and maintained by the Central Weather Bureau, Ministry of Transportation and Communications, Taiwan. Near the epicenter, very strong acceleration, over 900 gals, was recorded. Furthermore, the velocity record from the integrated result of the acceleration record near the northern end of the fault was over 300 kine.* Many transportation facilities (including highway bridges, railway bridges and tunnels) suffered damage. It can be guessed that the most governmental factor of the damage is differential ground displacements in vertical and horizontal directions caused by the faulting.* The concrete gravity dam was damaged by the surface faulting. This will rise a new technical subject of the earthquake resistance of infrastructures against fault displacements.* The power supply system in Taiwan is concentrated on the one switching yard, and the earthquake hit it directly. Therefore the redundancy of the power system is necessary.