Moho depth variation in Taiwan from teleseismic receiver functions

摘要

We determine lateral variation of Moho discontinuity, crustal thickness, and Vp/Vs ratios in the vicinity of Taiwan by analyzing all the available teleseismic waveform data collected by the Broadband Array in Taiwan for Seismology network from 1998 to 2004. The crustal thickness and the average crustal Vp/Vs ratio beneath each station are obtained by stacking Ps, PpPs and PpSs + PsPs phases coherently. The best estimated crustal thickness of Taiwan from 27 broadband stations is 30 km on average. The thinnest crust (11-15 km) is found east of the Longitude Valley suture zone, as part of the oceanic crust of the Philippine Sea plate. In other places, the crustal thickness varies from 17-19 km in northern Taiwan to 32-39 km in the southwestern island. The deepest Moho is found to be 53 km beneath station SSLB in central Taiwan. The average crustal Vp/Vs ratio in Taiwan is 1.74, with higher values of 1.74-1.99 in the north and lower values of 1.60-1.74 in the south. The crustal thickness variation is supported by gravity measurements in Taiwan and indicates that the collision between the Philippine Sea plate and Eurasian plate in Taiwan involves the whole crust. The thin crust and high Vp/Vs ratios in northern Taiwan are believed to be related to the volcanism in Tatun and Keelung located in the southwestern extent of the Okinawa Trough.