碩士 / 國立臺灣大學 / 海洋研究所 / 100 / The Southern Okinawa Trough (SOT) east of Taiwan is the place where initial arc-continent collision occurred, as the collision center moved southwestward and the Ryukyu backarc extension developed toward Taiwan, the present SOT is in post-collision and extension stage. The structural evolution and the nature of the SOT crust are thus important issues. In this study, we use advanced seismic data processing techniques to process the large offset multichannel seismic reflection data for better imaging and understanding the geological processes and velocity structures of the SOT crust. Radon filter and eigenvector filter have been used to eliminate the multiples on the seismic profiles, and pre-stack depth migration and iterative migrate velocity analysis have been performed to produce better seismic images and correct velocity structures. Our results show that the upper crustal velocity structures in the SOT can be roughly divided into three layers. The top layer consists of the most recent sediments that show velocities from 1.5 km/s to 2.35 km/s；the second layer consists of compacted sediments with velocities from 2.8 km/s to 3 km/s；the third layer is basement with high velocities of 4.5 km/s or greater. The most recent sediment layer is thicker in the central part of the SOT than in the eastern SOT. The layer of compacted sediments is thickest in the East China Sea continental shelf. Velocities of the intrusive volcanic zone show a thin sedimentary layer with velocities from 1.5 km/s-1.9 km/s on top. Velocity of the deeper strata increases from 1.9 to 3 km/s with a gradient of 0.9, and then gradually increased to 5 km/s further deep. In certain areas, velocity may increase suddenly then drop down. This is due to igneous rocks intruded into sedimentary strata in forms of sills. After advanced seismic data processing, signals in the deeper strata are much clear, and that help us not only to observe the contact relationships of igneous rocks and sediments, but also to comprehend the velocity difference of the different strata. Comparing the character of the crustal velocity structure of the SOT derived from this study with the oceanic crust velocity (White et al., 1992) and the extensional continental crust velocity (Christensen and Mooney., 1995), it appears that the crustal velocity character in the SOT is similar to the extensional continental crust. Thus, we suggest that the nature of the crust in the SOT is extensional continental crust.
| Identifer | oai:union.ndltd.org:TW/100NTU05279018 |
| Date | January 2012 |
| Creators | Mei-Chi Fan, 范美琪 |
| Contributors | Char-Shine Liu, 劉家瑄 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 98 |
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