11:45 〜 12:00
[S13-2-06] Crustal stress field in Taiwan inferred from regional-scale damped inversion of a newly derived homogeneous earthquake focal mechanism dataset
A regional seismic stress field of the crust in Taiwan has been obtained by applying the damped stress inversion algorithm to a newly derived focal mechanism dataset. To construct this homogeneous dataset, which is composed of more than 3000 centroid moment tensor solutions, we have developed a new multiple solution method to invert the high quality broadband waveforms collected in the past two decades. Only solutions with high quality and shallower focal depth (<40 km) are selected in the stress inversion. To test the reliability of the stress field, we implement a series of checkerboard tests with various grid spacing. Our results show that the maximum principle seismic stress, signma-1, is dominated by the NW-SE collision direction between the Eurasia plate and the Philippine Sea plat. It presents a fan-shape distribution in the western part of Taiwan. A dramatic change of sigma-1 direction at ~24.3N along the eastern coast, which may mark the transition from collision to subduction in the NE Taiwan area. In addition, we also notice that there is an S-shape trajectory across the Central Range that is suspected to be associated with spatial rheology heterogeneity. Normal faultings are mainly observed in the Okinawa Trough, Central Range, and SW offshore Taiwan, which are referred to different tectonic processes in this region. Obvious interface focal mechanisms in the eastern offshore region are also delineated with their NS striking and shallow angle thrusting pattern. Our principle seismic stress axes are comparable with the principle strain axes derived from GPS observation, implying that the crust in Taiwan may deform largely in an elastic manner. However, remarkable rotational patterns of sigma-1 presented in Ilan and Pingtung area may reflect the complicated tectonic forces and geological settings in the Taiwan region.