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

Abstract

We present a 3-D anisotropic seismic model of the crust and uppermost mantle beneath the Taiwan region based on the tomographic inversion of traveltime data from regional earthquakes. In the crust beneath eastern Taiwan, we observe coast-parallel anisotropy that perfectly delineates the major geological structures. In westernmost Taiwan, we distinguish a crustal block corresponding to the Peikang High at the margin of the Eurasian Plate, where coast-perpendicular anisotropy within a high-velocity anomaly is observed. In the uppermost mantle, the direction of anisotropy beneath central Taiwan turns perpendicular to the coast, which may indicate eastward underthrusting of the Peikang Block that was induced by collisional processes. To the NE of Taiwan, the anisotropy forms circular patterns coinciding with the shape of the Ryukyu arc, which may reflect the distribution of the deformations and fractures in the accretion and arc complex.