| Summary: | 碩士 === 國立臺灣海洋大學 === 應用地球科學研究所 === 103 === Study of gas hydrate in Taiwan has focused on the offshore area, especially in southwest off Taiwan. Amounts of sediments with high concentrations of methane-rich gas are provided from the accretionary wedge at Hengchun Ridge and the continental margin in the South China Sea. In addition, bottom-simulating reflectors （BSRs） were observed from seismic reflection profiles, which preferred drilling sites for gas hydrate will be located in this area. This research analyzed Ocean Bottom Seismic (OBS) data collected from Ocean researcher 1 at the Yuan-An Ridge in May, 2014. We built the P-wave and Vp/Vs velocity sedimentary models by using travel-time inversion of OBS data after considering the Poisson's ratio near the active margins from the previous researches. The results show that the P-wave velocity above the BSR is 1.8~2.0 km/s in the Yuan-An Ridge. Furthermore, the Vp/Vs model shows the range of Vp/Vs about 1.7~2.3 above the BSR. Estimation of the P-wave and S-wave velocities suggests that methane gas migrated through the cracks, gathered and then became the gas hydrate at the west side of the ridge.
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