Three Dimensional Velocity Structure Beneath Taiwan by Using the Data Recorded Along the Central Range of Taiwan in the TAIGER Experiment

• Main Authors: Cheng-lun, Wu, 吳政倫
• Other Authors: Ruey-Chyuan Shih
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/79556653400269842742

碩士 === 國立中正大學 === 應用地球物理研究所 === 101 === Taiwan is located in a convergent boundary between the Eurasian plate and the Philippines sea plate; the subsurface structure is very complicated. Many studies have been conducted in this area to clarify the detailed subsurface structure of the island; however, more works are still needed. In 2008, an active source experiment named Taiwan Integrated Geodynamic Research (TAIGER) was conducted around Taiwan for better understanding the Taiwan arc-continent collision system. The field experiment was successfully accomplished, and an extensive dataset has been collected. In the meantime, there were 108 seismographs installed in the central mountain range of Taiwan, along the principal tectonic structure of Taiwan in the North-South direction to record the valuable data. In this paper, we will present 3D subsurface velocity structure beneath Taiwan, by using the data recorded from the 108 stations. The seismic sources consist of eight large-scale dynamite shots deployed across the recording line in the West-East direction; four shots (N1, N2, N3p, and N4) in the north and another four shots (S1, S2, S3, and S4) in the south, respectively. We have processed the data with editing, amplitude balancing, and filtering to identify the arrival time of seismic waves. The data were then processed by using the 3D inversion program, FAST, developed by Zelt to construct the subsurface velocity structure. An initial model of velocities 4.5 km/s at the surface down to 8.2 km/s at the depth of 80 km was chosen. From the results, we may see that the subsurface velocity structure in the north is much complicated than that in the south. A major boundary of velocity 6.2 km/s could be observed in the velocity structure, and that boundary is deeper in southern Taiwan than that in the north. The overall depth of boundary is approximately from 20 to 30 km. The other major boundary of velocity 7.8 km/s was also seen, but appeared at certain places, which was probably limited by the density of ray coverage. In this study, better coverage area is mainly located on mid Taiwan. Overall distribution of the boundary is approximately from 45 to 60 km. In coverage area, the boundary of velocity 7.8 km/s is deeper in southern Taiwan than in the northern Taiwan. Also, it can find that has deeper boundary under the central mountain range of Taiwan, which is 60 km.