A Study of Aftershocks of the 17 July 1998 Ruey-Li, Chiayi Earthquake

Abstract

On 17 July 1998, an earthquake of magnitude 6.2 (ML) occurred near Chiayi, southwestern Taiwan. Two days after the occurrence of the mainshock, a temporary digital seismic network was deployed near its epi center for 24 days to monitor the aftershock activity. The events within and near the network were first located using a traditional single-event location and then relocated using a joint hypocentral determination (JHD) tech nique to determine the significance of lateral velocity variations and to im prove earthquake locations. The station corrections obtained from the JHD analysis vary from 0.30 to -0.18 sec for the P-waves and from 0.51 to -0.58 sec for the S-waves. The patterns of station corrections suggest that upper crustal velocities on the eastern side of the study area are relatively higher than those on the western side. The depth cross-section of the relocated aftershocks shows a clear pattern of southeast-dipping distribution of the hypocenters. The focal mechanisms and hypocentral distribution of the relocated aftershocks reveal a close relationship between seismicity and the known faults in •the study area.