碩士 / 國立臺灣海洋大學 / 應用地球科學研究所 / 105 / Due to the NW convergence and northward subduction of the Philippine Sea Plate (PSP), the sedimentary basement off northeastern Taiwan has been affected by uplifting or stretching. Many faults and shallow earthquakes were formed and disturbed the upper sediments so that the structures of Ryukyu fore-arc area are complicated. Pre-stack depth migration (PSDM) sections and depth-velocity model of the long-offset reflection data, collected during TAICRUST (1995) and TAIGER (2009) projects, were integrated to image the sedimentary thickness across fore-arc basins off northeastern Taiwan. The sedimentary structures constructed from this study will enable us to understand velocity structures, sedimentary structures, the variation of the basement structures, locations of faults and the seismogenic structures below the fore-arc basins off northeastern Taiwan. These results will provide references for the safety evaluation and the early warning system of earthquakes for the metropolitan Taipei. Firstly, long-offset reflection data were analyzed by band-pass filtering, geometry, vertical velocity analysis based on the variation of the seafloor and normal move-out to generate a pre-stack time migration (PSTM) section. Subsequently, sedimentary horizons of the strong seismic signals were picked on the PSTM section for analyzing the horizontal variation of the interval velocity based on the horizon velocity semblances. Finally, PSDM section and the depth-velocity model were built from the picked horizon velocity and analysis of the residual velocity semblances each layer. From a S-N PSDM section at the southern edge of the Nanao Basin, the thickness of the northern accretionary prism beneath the Nanao Basin decreases from south to north in the Ryukyu subduction zone caused by westward compression and N-S shearing from the NW convergence of the PSP . The faults in the Nanao Basin are normal faults which were formed by the strike-slip faults due to the westward component from the NW convergence of the PSP and the subsidence of sediments. Furthermore, the normal faults at the top of the Ryukyu Arc were caused by subduction of the PSP beneath the Ryukyu Trench and West Yaeyama fault zone. Based on the PSDM section across the East Nanao Basin and the Nanao Basement Rise, many faults (1-1.5 km long) might cause shallow (< 20 km depth) earthquakes (such as Hoping Cluster and Nanao Cluster) due to the subducted Gagua Ridge and the NW convergence of the PSP. In particular, the old Suao Basin Strata (P-wave velocity of 3.0-4.4 km/s) has been compressed into the western Hoping Basement Rise. Therefore, we suggest that sediments in three fore-arc basins of the Ryukyu subduction system off northeastern Taiwan have been affected by westward compression and N-S shearing from the NW convergence of the PSP. Many N-S normal faults in the Nanao Basin and the Nanao Basement Rise, might cause shallow (< 20 km depth) earthquakes (such as Nanao Cluster east of Nanao Basin).
| Identifer | oai:union.ndltd.org:TW/105NTOU5135008 |
| Date | January 2017 |
| Creators | Hu, Wan-Ting, 胡菀婷 |
| Contributors | Wang, Tan-Kin, 王天楷 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 54 |
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