Coseismic deformation of the 2010 Jiashian, Taiwan earthquake and implications for fault activities in southwestern Taiwan

Abstract

The March 04, 2010, Jiashian, Taiwan earthquake (M w 6.4) ruptured an unknown fault at depth in southwestern Taiwan. The main shock initiated near the town of Liuquei at 23 km depth and the rupture propagated westward. Measurements of coseismic displacements from Taiwan Continuous GPS Array indicate horizontal displacements of 5–27 mm in the NW–SW directions to the west of the epicenter; while horizontal movements to the east of the epicenter are absent. The GPS vertical displacements show an uplift motion of about 5–25 mm near the epicenter, in contrast to a small movement of about 5–10 mm observed in the far-field GPS sites. We use coseismic GPS displacements and an elastic half-space dislocation model to invert for fault geometries and coseismic slip distribution associated with the Jiashian earthquake. Our preferred model exhibits 0.05–0.1 m of reverse slip and ~ 0.04 m of left-lateral slip on a N324°-trending fault with dip of 40° to NE, consistent with the earthquake focal mechanisms from BATS, USGS/NEIC, and Global CMT. The highest slip of 0.12 m mainly occurs to the west of the epicenter at a depth range of 15–20 km. Given the rigidity modulus of 60 GPa, the geodetic moment is 4.95 × 10 18 N-m, equivalent to a M w 6.4 earthquake and consistent with the seismic moment estimated from seismic waveform inversion. Additionally, we notice that the mainshock rupture area is surrounded by high seismicity between 1991 and 2007, suggesting that the Jiashian earthquake may be triggered by the high stress concentration in the vicinity. The calculated Coulomb stress changes on nearby fault systems imparted by the coseismic slip suggest that the Jiashian earthquake may encourage failures on the Chukou fault and inhibit ruptures on the Hsinhua fault. However, the Coulomb stress changes are more complicated on the Chaochou fault and Chishan fault with both positive and negative stress changes.