碩士 / 國立中央大學 / 地球科學學系 / 103 / The tectonics of southeastern China and its surrounding regions involve two active subduction systems (the Manila and Ryukyu subductions) and one collision system (the Taiwan orogen). In this study, we use teleseismic SKS/SKKS splitting as a tool for investigating seismic anisotropy. The splitting parameters, fast-polarization azimuth (ϕf) and delay time (δt), can provide key information for understanding the geodynamic process in this region. Measurements of δt and ϕf can be used as indicators for the information of the product of deformation magnitude and strain direction. In previous studies, only few seismic stations in this region were available for the analysis. Therefore, in this study we selected 17 seismic stations along the Fujian coastline to obtain more shear wave measurements. Two methods (transverse minimization and splitting intensity method) are applied to obtain the splitting parameters for testing the reliability of the results. Transverse minimization method [Silver and Chan, 1991] utilizes a grid search approach to determine the pair of splitting parameters (ϕf, δt) by miniming the energy on the transverse component. Splitting intensity method, also named Multichannel method [Vinnik et al., 1989; Chavrot, 2000], is defined as the amplitude of the transverse component relative to the time derivative of the radial component. According to the sinusoidal function S=δt sin2(ϕ_b-ϕ_f ), splitting intensity (S) depends on the angle of back-azimuth (ϕb) and ϕf and on the δt between the two shear waves.
From transverse minimization method (SC), the results indicate that the average delay time of teleseismic shear waves observed from 17 stations is 2.4 s and the maximum is 3.8 s, suggesting that seismic anisotropy at least down to 300 km depth. The average split time delay (2.4 s) beneath Fujian coastline is greater than the average result observed from Taiwan and also indicates stronger seismic anisotropy. The disorder distribution of fast directions observed from 17 stations may be caused by different back-azimuths with different teleseismic events, and reveal the fact of complex geodynamic mechanisms beneath southeastern China. From splitting intensity method (SI), each station can observe a pair of splitting parameter (ϕf, δt) by sinusoidal curve fitting. The average split time delay is 1.04 s, which is lower than the result (2.4 s) observed from transverse minimization method. The fast directions can be discussed in two parts. As a result, along the Fujian coastline, compared with the global tomography, it can be explained that the variations of fast-polarizations (ϕf) could relate to the EW mantle flow created by NS collision between the India and Eurasian Plates, influenced by the Taiwan orogen (the collision between Eurasian and Philippine sea plates) and two subduction systems (the Manila and Ryukyu subductions).
| Identifer | oai:union.ndltd.org:TW/103NCU05134008 |
| Date | January 2015 |
| Creators | Hsiao-Chuan Peng, 彭筱涓 |
| Contributors | Hao Kuo-Chen, 郭陳澔 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 144 |
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