https://scholars.lib.ntu.edu.tw/handle/123456789/635757
標題: | Strong variation of near-surface seismic anisotropy in Taiwan and its geological implications | 作者: | Lee, Hsin-Yu YUAN-CHENG GUNG Chen, Li Wei WEN-SHAN CHEN Chen, Ying Nien Cai, Sheng Jyun Chen, Hui Chu Liao, Che-Wei |
關鍵字: | borehole array | coda interferometry | crustal structure of Taiwan | orogeny-parallel anisotropy | strength of near-surface anisotropy | stress-aligned anisotropy | 公開日期: | 15-十月-2023 | 卷: | 620 | 來源出版物: | Earth and Planetary Science Letters | 摘要: | We report on the near-surface (< 500 m) seismic structure (Vp, Vs, and Vs anisotropy) of Taiwan using the empirical Green's functions of body waves between vertical station pairs at 60 borehole sites. The near-surface anisotropy in metamorphic rocks and Miocene or older sedimentary strata are mostly categorized as orogeny-parallel anisotropy (OPA), and sites exhibiting stress-aligned anisotropy (SAA) are located in areas with late Quaternary sedimentary deposits or in alluvial coastal plains. The results show that there is a significant variation of the anisotropy strength even within the same geological unit. Since all the major geological units of Taiwan are well sampled by borehole arrays, and drilling data for 52 sites are available, this provides a unique opportunity to investigate the geological implications of strong variations in near-surface anisotropy. The investigation indicates that (1) near-surface anisotropy caused by structural fabric is generally stronger than that resulting from the alignment of stress-induced open cracks, (2) SAA strength in sedimentary rocks, igneous rocks, and gravel sediments is generally higher than that in fine-grained sediments, and (3) the sites with the strongest OPA (> 30%) are located in mountain ranges and the mean OPA strength of these sites is significantly higher than that of foothills, suggesting that foliated metamorphic rocks lead to stronger OPA than do dipping sedimentary strata. The results also suggest that the fluid-saturation of micro-cracks is not a necessary condition for the occurrence of the SAA mechanism in the near-surface depth range. |
URI: | https://scholars.lib.ntu.edu.tw/handle/123456789/635757 | ISSN: | 0012821X | DOI: | 10.1016/j.epsl.2023.118339 |
顯示於: | 地質科學系 |
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