Three-Dimensional Seismic Velocity Structure of the Crust and Uppermost Mantle beneath Taiwan.

Abstract

Taiwan is located in a complex, tectonically active region where the Philippine Sea. plate is subducting northwestward along the Ryukyu Trench while the Eurasian plate is subducting eastward along the Manila Trench. The Central Weather Bureau Seismographic Network (CWBSN), which is composed of 75 stations with three-component instruments, has been operated over the island of Taiwan since March of 1991. This dense seismic network provides high-quality P-and S-wave arrival times of local earthquakes, and, thus, gives us a good opportunity to determine the velocity structure of the crust and upper mantle structures beneath Taiwan. We have applied a new tomographic method 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. We infer that 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.

Strong ground motion and damage in the Taipei basin from the Moho reflected seismic waves during the March 31, 2002, Hualien, Taiwan earthquake

“…[17] A number of studies have been completed for the crustal structure [Rau and Wu, 1995;Ma et al, 1996] and Pn velocity [Ma and Song, 1997;Huang et al, 1998] beneath Taiwan. Therefore a simplified single layer over the half space velocity structure for northern Taiwan can be constructed and a focal depth of 28 km estimated from waveform modeling (Ma, personal communication) was used for calculating theoretical travel time curves for each respective phase arrival.…”

Moho Depth Derived from Gravity Data in the Taiwan Strait Area

“…The other seis mic ob ser va tion (B-B') along the west ern coast of Tai wan is ob tained from tomographic in ver sion by jointly us ing the seis mic data set of the CWBSN and two tem po rary seis mic ar rays in Hualien and Pingtung (Kim et al 2005). We as sume that the Vp = 7.5 km s -1 , taken as the av er age ve loc ity of three seis mic tomography re sults (Rau and Wu 1995;Ma et al 1996;Wu et al 2007), is the dis con tin ued in ter face be tween the lower crust and up per man tle. The depth of in ter face es ti mated from the ve loc ity struc tures range from 32 to 34 km (Fig.…”

Real-Time Estimation of Fault Rupture Extent Using Envelopes of Acceleration

“…The distribution of stations is shown in Figure 1. Table 1 describes the crustal model for P-wave and S-wave velocity in central Taiwan (Ma et al, 1996). P-wave and S-wave arrival time for the predicted envelope are computed with this 1D layered crustal model.…”