A joint inversion of focal mechanisms and GPS displacements for absolute crustal stress and coseismic fault slip using data from the 1999 Chi-Chi, Taiwan, earthquake

Inversion of coseismic surface displacements has become a standard tool for estimating fault geometry and coseismic slip distribution on the seismogenic fault plane. Recently, Sun et al. (paper in review) have developed a method for inverting for fault geometry and slip from coseismic surface displacements assuming a uniform stress drop on a fault in an elastic half space. In reality, coseismic stress drops are probably not uniform. Additional insight into the state of stress on and off the fault can be obtained from inversions of focal mechanisms for a reduced stress tensor. The purpose of this study is to solve the mixed linear-nonlinear inversion problem for shear stress drop on the fault plane and stress in the surrounding crust using coseismic surface displacements and focal mechanisms solutions. We apply this method to data from the 1999 Chi-Chi, Taiwan earthquake and compare with previous studies.