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野外考察结果表明 ,1999年 9月 2 1日台湾集集大地震是由车笼埔断层发生逆冲作用造成的。地震产生的地表破裂长约 80km ,具有明显的挤压逆断层特征 ,其活动方式为具左旋性质的逆倾滑动。实测逆冲断层以 30°～ 50°的角向西北逆冲而上。断层的垂直位移量 ,南段约 2～ 3m ,北段约 3～ 8m ;断层的水平位移量 ,南段 0～ 3m ,北段 3～ 5m ;垂直断层的水平缩短量 ,南段 2～ 3m ,北段 3～ 6m。从台湾西部麓山带的地质构造剖面分析 ,地震震源恰好位于台湾西部麓山带中生代基底与其上的沉积盖层的界面的深度 ,而西部麓山带第三纪地层和其下的基底的分离面为一滑动面 (decolle ment)。在菲律宾海板块的挤压作用下 ,沿该区中生代基底之上滑动面的错动导致了地震的发生
The field investigation shows that on September 21, 1999, the Jiji earthquake in Taiwan was caused by the thrusting of the Chegongpu fault. The surface rupture caused by the earthquake is about 80km in length with obvious characteristics of crushed reverse thrust faults. Its active mode is reverse-slip with left-handedness. The measured thrusts are thrust northwest upwards at an angle of 30 ° ~ 50 °. The vertical displacement of the fault is about 2 ~ 3m in the southern section and about 3 ~ 8m in the northern section. The horizontal displacement of the fault is 0 ~ 3m in the southern section and 3 ~ 5m in the northern section. The horizontal shortening of the vertical fault is 2 ~ 3m , North section 3 ~ 6m. From the geological tectonic section of the western foothills of Taiwan, the epicenter is exactly located at the depth of the interface between the Mesozoic basement and the sedimentary capstones on the foothill belt in western Taiwan, whereas that of the Tertiary strata in the Western Foothills and the underlying basement is one Decolle ment. Under the squeezing action of Philippine sea plate, the slip of the sliding surface along the Mesozoic basement in this area led to the earthquake