Deformation and occurrence of the Che-lung-pu Fault from geomorphic evidence

Abstract

The Chi-chi earthquake that occurred on 21 September 1999 was triggered by the Che-lung-pu active fault. It caused a great deal of land deformation and damaged much of central Taiwan. Although a series of reports on surface ruptures have been published by the Central Geological Survey and earth science researchers, few papers have ever discussed the deformation before the 1999 earthquake or its activities. Therefore, this study seeks to understand the deformation and occurrence of the Che-lung-pu Fault before the Chi-chi earthquake. Aerial photograph interpretation and field observation are the methods used to identify the fault scarp, flexure scarp and range-facing scarp. The fault can be traced along the foothills between the alluvial plains and the hills which stretch from Tung-tou in the south to Cho-lan in the north. By comparing two fault traces between the inferred active Che-lung-pu Fault and the 1999 Che-lung-pu earthquake fault defined by the Central Geological Survey, we found that among the inferred active faults from aerial photographs, 67% coincide with the 1999 earthquake rupture, and about 76% of certainty I faults have ruptured during the 1999 earthquake. The estimation of paleoseismic occurrence in the area south of Ta-li River seems higher than that in the area of the north. However, the land deformation is less severe. All the reactivation and cumulation of active faults and the high percentage of occurrence at the pre-existing location provide useful information for the mitigation of seismic disasters.