The Hyogoken-nanbu earthquake in 1995 has led to numereous slope failures both in Rokko mountain and Awaji island. The features of slope failures related to lateral faulting or horizontal acceleration by the earthquake are discussed, and their change by subsequent rainfall events are followed.
The earthquake has induced to the numerous slope failures at steep slope segments or near shoulders in dry state. The slip surfaces were shallow and plannar, suggesting that the failures were largely controlled by friction. The failed slopes were located almost at a particular site where the movement of fault or fault blocks made the landmass unstable. The situation is remarkable especially at east-faced slopes located at the northwest side of right-lateral faults, and at the east or north-faced slopes of the northeastern Rokko mountain.
An enlargement or renewed occurrence of slope failures by the subsequent rainfall events has occured in proportion to the number of slope failures due to the earthquake. The portions with intensive slope failures by the earthquake show also the subsequent enlargement and the renewed occurrence of the slope failures by the rainfall events. This means that the failures by the rain are supplementary to those by the earthquake, and also the tendency that they increase reciprocally to the number of the latter.