Kinematics of Taiwan Collision Zone from GPS Observations

• Main Authors: Kuo-En Ching, 景國恩
• Other Authors: Ruey-Juin Rau
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/02744966220089069689

博士 === 國立成功大學 === 地球科學系碩博士班 === 96 === Taiwan, seated at the junction of the Manila and the Ryukyu subduction systems, is a classical case of the ongoing arc-continent collision due to the convergence between the Eurasian and the Philippine Sea plates. In order to understand the kinematics of present-day interseismic crustal deformation of Taiwan, we analyzed GPS observations from 813 campaign-mode GPS stations and 12 continuous-recorded stations. Horizontal velocities relative to the Chinese continental margin station, S01R, reveal a fan-shaped distribution. Their magnitudes gradually decreases northwestward from ~88 mm/yr in SE Taiwan to nearly no deformation in NW Taiwan. According to analysis of velocities, three major NNE-SSW-striking velocity discontinuities were identified along the Longitudinal Valley Fault, the mountain front, and the deformation front, respectively. The kinematics of the sinistral reverse Longitudinal Valley Fault in eastern Taiwan is dominated by the intensity variation of the arc-continent collision. The central segment (the Chihshang fault) of the Longitudinal Valley Fault (23°N - 23.7°N) undergoes a maximum shortening rate of ~25 mm/yr. The 2003 Mw 6.8 Chengkung, Taiwan, earthquake occurred along this fault. Horizontal coseismic displacements of the 2003 Chengkung earthquake, determined with 213 GPS stations, represent the fault-normal shortening across the fault trace and the fault-parallel and the fault-normal lengthening on the hanging wall. This earthquake generates a larger rupture area and a lower stress-drop, suggesting lower than average fault friction. In addition, this model also indicates that the Chihshang fault is divided into a creeping segment in the north and the locked segment in the south. An average recurrence interval of 50 years for a magnitude 6.8 earthquake was estimated for the locked segment of the Chihshang fault. On the other hand, both mountain front and deformation front reveal S-shaped pattern in the western flank of the accretionary wedge, mainly controlled by the configuration of the inherited structures. For the SW Taiwan, velocity field indicates the N-S-trending Chaochou fault acting as nearly pure reverse faulting, the NE-SW-striking Chishan fault (CHNF) as reverse faulting with right-lateral motion, and the Fengshan transfer fault zone (FTFZ) as left-lateral shearing, intersecting aforementioned fault. The movement of FTFZ enhances velocities rotating from nearly westward direction to WSW direction, sub-parallel to the southern edge of the Peikang basement high. A nearly E-W contraction and N-S extension escaping stress regime is accommodated by N-S-trending ductile flow within the upper mantle and by brittle conjugated-type fracture, formed by the CHNF and the FTFZ, within the crust. The mechanism of syn-orogenic extension located from the southern Central Range to the Hengchun peninsula is caused by the growth of the thrust belt at the accretionary prism.