Lateral variations of Pn velocity and anisotropy in Taiwan from travel-time tomography

Abstract

In this study, the P arrivals of 1726 ray paths with the epicentral distances longer than 200 km from 539 earthquakes that occurred in Taiwan are used to investigate the variation of P n velocity. The results show that the lateral variation of P n velocity in Taiwan is quite similar to the pattern of gravity anomaly and strongly related to several features of Taiwan's geological structure. The crust is a little thicker (about 39 km) in the Central Range and somewhat thinner toward the east and west. A relatively thin crust (about 35 km) is obtained in the area of Peikang High; however, an unexpected thick crust of greater than 40 km is also found at the corner of southwestern Taiwan. The degree of anisotropy of P n velocity is found less than 10% and the fast direction is generally in the E-W direction. This direction is parallel to the axis of compressional stress or the direction of plate motion, indicating that the anisotropy results from the deformation of the upper mantle.

Three‐dimensional P velocity structures of the lithosphere beneath Taiwan from the analysis of TAIGER and related seismic data sets

“…The integrative nature of arrival time tomography does not allow the precise identification of an interface like the Moho. In Taiwan, several investigations [ Ma and Song , 1997; Chen et al , 2003; Liang et al , 2007] aimed at the derivation of Moho velocity and they estimated a Pn‐velocity of 7.8–8.0 km/sec using mainly earthquake data. The rapidly varying velocity structures across Taiwan however render the direct measurement of Pn difficult.…”

Three‐dimensional seismic anisotropy in the crust and uppermost mantle beneath the Taiwan area revealed by passive source tomography

“…This observation is consistent with a previous study by Chen et al . [] who presented an anisotropy map beneath Taiwan based on the analysis of Pn traveltimes. Same orientations of anisotropy are reported by Huang et al .…”

“…In particular, Chen et al . [] performed tomography studies for Pn waves and obtained clear coast‐perpendicular orientation for anisotropy just below the crust. This seems to be consistent with the results of Huang et al .…”

Crust and Lithospheric Structure - Global Crustal Structure

“…This technique, which is similar to medical tomography, has the potential to provide a 3-D picture of the crust and uppermost mantle. Local studies mainly provide information about the upper crust and middle crust (Lei and Zhao, 2005;Mandal et al, 2004;Salah and Zhao, 2003;Thurber, 1993; Table 3), whereas regional studies have better resolution within the uppermost mantle, especially for Pn velocity (Al-Lazki et al, 2003, 2004Bannister et al, 1991;Calvert et al, 2000;Chen et al, 2003;Hearn and Ni, 1994;Hearn et al, 2004;Liang et al, 2004;McNamara et al, 1997;Mele, 1998;Nolet, 1987a,b;Parolai et al, 1997;Ritzwoller et al, 2002a,b;Sandoval et al, 2004;Sandvol et al, 2001Sandvol et al, , 2008. A second technique uses teleseismic data and generally provides an image that extends to greater depth (100 þ km) but lacks high resolution of structure within the crust (Allen et al, 2002;Benoit et al, 2003;Bijwaard et al, 1998;Lippitsch et al, 2003;Liu et al, 2005;Petit et al, 1998).…”