Relocation of the 2006 Pingtung Earthquake sequence and seismotectonics in Southern Taiwan

We combine the arrival time data from eleven ocean bottom seismometers (OBS) and from permanent stations of the Central Weather Bureau Seismic Network (CWBSN) and the Taiwan Strong Motion Instrumentation Program (TSMIP) to improve the three-dimensional Vp and Vp/Vs structures in the Taiwan region, relocate hypocenters of earthquakes in southern Taiwan including the 2006 Pingtung Earthquake sequence, and determine the focal mechanisms of some of the larger events. Our tomography result suggests that in the region south of Taiwan the Eurasian continental lithosphere is being subducted beneath the oceanic Philippine Sea plate, leading to a region of low P-wave speed with seismicity on top of a relatively high P-wave speed zone. The hypocentral distribution of the Pingtung Earthquake sequence indicates that the first event in the initial two largest shocks was a normal-faulting quake caused by the bending of the subducting lithosphere. The second event, perhaps triggered by the first one, was a strike-slip earthquake.