Seismic tomography of Taiwan: Improved constraints from a dense network of strong motion stations

[1] In this study, a large collection of 41,141 S-P times from the untapped records of the Taiwan Strong Motion Instrumentation Program (TSMIP) network is combined with the P and S wave arrival times from the Taiwan Central Weather Bureau Seismic Network (CWBSN) to image the Vp and Vp/Vs structures beneath Taiwan. The records from the 680 TSMIP stations throughout Taiwan in the past 15 years enhance the path coverage and the resolution in the tomography inversions tremendously. Our result for the Vp structure largely confirms previous studies but brings better constraint on the Vp/Vs structure. The colliding Luzon volcanic arc is characterized by a belt of high Vp and high Vp/Vs with high seismicity that includes the offshore islands of Lutao and Lanyu and the Coastal Ranges in eastern Taiwan, at the depth between about 13 and 25 km. This high Vp/Vs belt can be traced to the subduction zone in the region between Hualian and Ilan in the deeper portion. The shallow portions of the southwestern coastal plain and the Pingtung region are also characterized by a belt of high Vp/Vs with lower seismicity. Most of the events occurred at the base of the high Vp/Vs zones. We suggest that material strength in those regions may be too low to accumulate stress, which may indicate water-saturated young sediments. Finally, the Central Range region is characterized by a low Vp/Vs belt.