대만지역의 3차원 속도구조와 지진위치 재결정을 통한 판의 섭입과 충돌에 관한 연구

Abstract

3-D Vp and Vs models for the crust and upper mantle beneath the Taiwan area have been determined. All earthquakes in the Taiwan Central Weather Bureau&apos;s catalogue are then relocated using the resultant 3-D Vp and Vs models. The 3D models and the relocated seismicity provide an opportunity to explore tectonic structure and its evolution in the Taiwan region. The depth of the Moho varies significantly, especially along the E-W direction. In the western Coastal Plain and Western Foothills the depth of the Moho is around 35 km, which deepens gradually eastward, reaches a maximum depth of ~55 km beneath the eastern Central Range, shallows up rapidly beneath the Longitudinal Valley and Coastal Range, and merges with the thin Philippine Sea Plate offshore of eastern Taiwan. In central Taiwan, the Central Range is bounded to the east and west by two steeply westward dipping active faults extending from near surface to a depth ~30 km. Therefore, the uplifted and thickened Central Range serves as a backstop for the converging Eurasian and Philippine Sea plates. The crust beneath the Central Range is characterized by a brittle, high-velocity and seismically active upper crust (<15 km) and a ductile, low-velocity and aseismic mid-to-lower crust (below 15 km). Active collision is initialized apparently from SE Taiwan along a SE dipping collision zone reaching from near surface to a depth ~25 km which is, however, transferred into a NW dipping fault zone near Hualien region in central Taiwan. Continue to the north of the northern collision zone, active northwesterly subduction becomes apparent. Upper mantle beneath the collision suture, the Longitudinal Valley, is elevated separating the deformed continental and oceanic crust. Thus, the high geothermal activity from the excess heat supplied from the hot upper mantle beneath the thin suture zone to the east, from the surrounding hotter upper mantle beneath the thickened continental crust, and from shear heating during active colli