ABSTRACT
The 1999 Chi-Chi earthquake with a local magnitude of 7.3 struck central Taiwan and induced more than 30000 cases of landslides covering a total area of more than 8600 ha. In this paper, the ground motion records and threshold conditions of the landslides induced by Chi-Chi earthquake were examined. The relationship between the critical acceleration and threshold displacement to the landslides and ground motion is analyzed for evaluation of the seismic stability of slope. Landslide cases were selected from satellite images/aerial photos identified variations and ground-based investigation cases for which landslide displacements were analyzed. Results of the analysis suggested that the lower bound threshold displacements were about 7 cm with most cases larger than 10 cm. It is proposed that the threshold conditions of critical acceleration ratio of smaller than 0.5 and a toe displacement of 7 cm would be appropriate for defining landslide threshold caused by the Chi-Chi earthquake. To understand the run-out behavior of the earthquake-induced landslide, a two-stage numerical model was used to simulate the sliding behavior of the earthquake-induced landslides. The field cases in the May river basin were used and the resulting run-out displacements were discussed.
