Seismogenic structures of the 1999 Mw7.6 Chi-Chi, Taiwan, earthquake and its aftershocks

Abstract

High-resolution 3-D Vp and Vs velocity models around the source region of the Mw7.6 Chi-Chi, Taiwan, earthquake show significant lateral and vertical variations. The mainshock occurred along the Chelungpu Fault within a narrow low-velocity zone. A sudden increase of velocity and seismicity took place across the Shuilikeng Fault to the east. Most aftershocks were located in remote areas, with high Vp and Vs anomalies from the mainshock epicenter. A sharp east-dipping zone extends from the Shuilikeng Fault on the surface to a depth of about 15 km, and this zone separates the subsurface structures into western low velocity material from eastern high velocity material. An apparent west-dipping seismic zone lies at depths of 15?0 km beneath the Central Range. Numerous aftershocks with normal faulting were located west of the middle segment of the Chelungpu Fault. These are assumed to occur along some unexposed normal faults, which may have been reactivated structures triggered by large stress perturbations following the failure along the Changhwa Fault that resulted in the Chi-Chi earthquake.