Numerical modelling of ground motion in the Taipei Basin: basin and source effects

Abstract

The Taipei basin in northern Taiwan is located in a high seismicity region and was affected by several earthquakes in the past (ML= 7.3 on 1909 April 15; ML= 6.8 on 1986 November 15; the Chi-Chi ML= 7.3 earthquake on 1999 September 21 and ML= 6.8 on 2002 March 31). The main characteristic of the Taipei basin is its complex shape with a deep western and shallow eastern part. The uppermost Sungshan formation with its low shear wave velocities (90–200 m s−1) is also a distinct feature of the basin. Based on the large data base of earthquake records obtained from the Taiwan Strong Motion Instrumentation Program network, many studies on ground motion within the Taipei basin exist. However, the influence of the various subsurface structures on the observed ground motions as well as the variability of ground motion with respect to earthquake location is not fully understood. We apply a 3-D finite-difference method to simulate wave propagation up to 1 Hz for a small earthquake close to the basin in order to resolve these open questions. By varying source and structural parameters, we explore the variability of ground motion.