Three-dimensional seismic velocity structure of the crust and uppermost mantle beneath Taiwan

A new tomographic method has been applied to infer the fine 3-D P- and S-wave velocity structures beneath Taiwan. Results show the existence of a low velocity zone in the uppercrust of west Taiwan. This zone is consistent with the thick sediments in the area. A low-velocity zone has been inferred underneath the extinct volcano regions, and it is due to the remnant geothermal effect after past volcanic activities. A low-velocity zone with a relatively homogeneous distribution of P-wave velocities, extending to a depth of about 30-35 km, is found beneath the Central Range. This feature might have resulted from the heat intrusion from the oceanic upper mantle of the Philippine Sea plate, which has been colliding with the Eurasian plate, and the effect of partial melting. The thickness of the crust of Taiwan is estimated to be 30-35 km and that for the Philippine Sea plate is 15-20 km.