| Summary: | 碩士 === 國立臺灣大學 === 海洋研究所 === 104 === We apply ambient noise analysis to continuous seismic waveform data recorded by ocean-bottom seismometers (OBS) deployed in the Huatung Basin and adjacent regions off the east coast of Taiwan. Taiwan is a young and active orogenic belt resulting from the oblique subduction and collision between the Eurasian Plate and the Philippine Sea Plate. Sitting on the westernmost edge of the Philippine Sea Plate, the Huatung Basin is directly involved in the subduction-collision processes. The structural characteristics of the basin provide important constraints not only on its own history but the tectonic evolution in this complex region. We first analyze the noise signals by stacking cross-correlation functions from station pairs between OBS stations and between land and OBS stations. We find that, unsurprisingly, the noise power of the offshore OBS stations is larger than that of onshore stations. Further, we integrate the OBS data with selected land station data along the east coast, deriving Rayleigh wave Green’s functions from cross-correlation between all available station pairs. We measure phase velocity dispersion at periods from 4 to 20 sec, and invert for 2-D anisotropic phase velocity maps based on a wavelet-based multi-scale inversion scheme. Our results show that, at periods 12-20 s, significant seismic anisotropy is present in the Huatung Basin close to Taiwan’s southeast coast, with fast direction sub-parallel to the direction of convergence. On the other hand, to the north across the Ryukyu trench, anisotropy becomes weaker and the fast direction appears to rotate clockwise toward NW-SE to N-S directions. These characteristics represent the property of the mantle lithosphere of the Huatung Basin, implying for current influence of asthenospheric flow due to currently the PSP plate motion.
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