Influence of surface-normal ground acceleration on the initiation of the Jih-Feng-Erh-Shan landslide during the 1999 Chi-Chi, Taiwan, earthquake

The 1999 Chi-Chi, Taiwan, earthquake triggered numerous landslides througho ut a large area in the Central Range, to the east, southeast, and south of the fault rupture. Among them are two large rock avalanches, at Tsaoling an d at Jih-Feng-Erh-Shan. At Jih-Feng-Erh-Shan, the entire thickness (30-50 i n) of the Miocene Changhukeng Shale over an area of 1 km(2) slid down its b edding plane for a distance of about I km. Initial movement of the landslid e was nearly purely translational. We investigate the effect of surface-nor mal acceleration on the initiation of the Jih-Feng-Erh-Shan landslide using a block slide model. We show that this acceleration, currently not conside red by dynamic slope-stability analysis methods, significantly influences t he initiation of the landslide.