Geomorphic evidence for prior earthquakes: Lessons from the 1999 Chichi earthquake in central Taiwan

The September 21, 1999, Mw 7.6 Chichi earthquake destroyed several thousand buildings and caused more than 2000 fatalities in central Taiwan. The earthquake occurred along the Chelungpu fault, a thrust fault on the western flank of the Taiwan fold-andthrust belt. The surface rupture was more than 90 km long, and vertical displacements ranged from 3 to 8 m. Although pre-existing scarps were identified along the Chelungpu fault, the fault had previously been categorized as a less important active fault, owing to the lack of geochronologic evidence and the failure to recognize fault-related geomorphic features. Identifying geomorphic features at active faults in Taiwan will permit the delineation of future surface ruptures and the determination of past magnitudes of past earthquakes, thus contributing to hazard assessment.