Geomorphological identification of pre-existing active Chelungpu Fault in central Taiwan, especially its relation to the location of the surface rupture by the 1999 Chichi earthquake

Abstract

Pre-existing active faults were identified on the Chelungpu Fault, based on airphoto interpretation and field survey, and their precise position was mapped. Active faults are divided into four types from I to IV, depending on certainty of the presence of active faults and accuracy of their location. Most of the Chelungpu Fault shows evidence of Late Quaternary repeated activities. The location of the 1999 Chichi earthquake surface ruptures were plotted from the sites where they were accurately mapped by GPS measurements by the Central Geological Survey, supplemented by our own observations, on the active fault map. There is a very close coincidence between the active fault trace and the 1999 surface rupture, indicating that the mapping of active faults is fundamental for the estimation of location of rupture by future earthquakes.