Subduction-continent collision in southwestern Taiwan and the 2010 Jiashian earthquake sequence

We integrated a regional tomography model, 20-year seismicity and earthquake focal mechanisms of the 4 March 2010 M _L 6.4 Jiashian earthquake source region to delineate the seismogenic structure and mechanics of a relatively rare damaging inland earthquake that occurred in the southwestern fold-and-thrust belt of Taiwan. The main shock of the Jiashian earthquake occurred at a depth of 23km beneath the slate belt of the southern Central Range with a sinistral thrust mechanism. Based on seismic tomography and seismicity, the Jiashian earthquake sequence occurred in the Chishan transfer fault zone, which we interpret to be located near the transition zone between the subducted Eurasian plate to the south and the arc-continent Taiwan collision to the north. The distribution of the Jiashian aftershocks define a WNW-ESE striking fault plane that dips 30-40° NNE which is consistent with the optimal fault plane of the GPS-derived coseismic slip model. Focal mechanisms and inverted stress results of the earthquake sequence indicate both thrust and strike-slip motions with the maximum compressive stress at nearly 90° to the regional compressive stress and thus sub-parallel to the strike of the Taiwan orogen. We propose that the 2010 Jiashian earthquake resulted from rupturing of a buried oblique fault within the Chishan transfer fault zone at the subduction-collision transition zone in southern Taiwan. The orogen-parallel P-axis of the 2010 Jiashian earthquake represents collision-related lateral compression, although a local stress deviation is also possible.