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 throughout 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 and at Jih- Feng-Erh-Shan. At Jih-Feng-Erh-Shan, the entire thickness (30-50 m) of the Mio- cene Changhukeng Shale over an area of 1 km 2 slid down its bedding plane for a distance of about 1 km. Initial movement of the landslide was nearly purely trans- lational. We investigate the effect of surface-normal acceleration on the initiation of the Jih-Feng-Erh-Shan landslide using a block slide model. We show that this ac- celeration, currently not considered by dynamic slope-stability analysis methods, significantly influences the initiation of the landslide.