| 龙门山断裂带北段南坝地区上地壳S波分裂特征 |
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| 引用本文： | 郑拓,丁志峰,常利军,宁杰远,张辉,王兴臣.龙门山断裂带北段南坝地区上地壳S波分裂特征[J].地球物理学报,2018,61(5):2054-2065. |
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| 作者姓名： | 郑拓 丁志峰 常利军 宁杰远 张辉 王兴臣 |
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| 作者单位： | 1. 中国地震局地球物理研究所, 北京 100081;
2. 北京大学地球与空间科学学院, 北京 100871;
3. 中国地震局地震观测与地球物理成像重点实验室, 北京 100081;
4. 山东省昌邑地震台, 山东潍坊 261300 |
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| 基金项目： | 国家自然科学基金（41774061，41474088），中国地震局地球物理研究所基本科研业务专项（DQJB15A03，DQJB17B10）及国家留学基金委联合资助. |
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| 摘 要： | 基于汶川科钻4号井孔（WFSD-4）附近的较小尺度的南坝微震台阵以及较大尺度的川西流动台站和区域台网的固定台站记录到的近震波形资料，通过横波窗内的S波分裂计算，分析了龙门山断裂带北段南坝地区的上地壳介质各向异性特征，并对区域应力场及构造特征展开讨论.S波分裂计算的结果显示研究区快波偏振方向主要表现为NE-NEE向，与北川断裂的走向一致，也与区域主压应力方向一致.小尺度密集分布的南坝微震台阵的计算结果进一步显示，靠近北川断裂的台站，其快波偏振方向与断裂走向一致，而距北川断裂较远的西北部台站的快波偏振方向与断裂走向不一致，反映了上地壳各向异性特征与地表的活动断裂结构密切相关.从南坝微震台阵的归一化时间延迟随时间的变化情况可以发现，在一个震中位于台阵布设范围内的地震事件发生前后，时间延迟有明显的变化，表明时间延迟随时间变化较为敏感，地震的能量影响了介质的性质.对比龙门山断裂带中段的科钻3号井孔周边地区的S波分裂计算结果，归一化时间延迟与本文结果一致，表明龙门山断裂带中段和北段的上地壳介质各向异性强度基本相同.
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| 关 键 词： | 地壳各向异性 S波分裂 龙门山断裂 汶川科钻 |
| 收稿时间： | 2017-09-15 |
Characteristics of S-wave splitting in upper crust of the Nanba region in the northern Longmenshan fault |
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| ZHENG Tuo,DING ZhiFeng,CHANG LiJun,NING JieYuan,ZHANG Hui,WANG XingChen.Characteristics of S-wave splitting in upper crust of the Nanba region in the northern Longmenshan fault[J].Chinese Journal of Geophysics,2018,61(5):2054-2065. |
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| Authors: | ZHENG Tuo DING ZhiFeng CHANG LiJun NING JieYuan ZHANG Hui WANG XingChen |
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| Affiliation: | 1. Institute of Geophysics, China Earthquake Administration, Beijing 100081, China;
2. School of Earth and Space Sciences, Peking University, Beijing 100871, China;
3. Key Laboratory of Seismic Observation and Geophysical Imaging, China Earthquake Administration, Beijing 100081, China;
4. Shandong Province Changyi Seismic Station, Shandong Weifang 261300, China |
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| Abstract: | Based on the seismic data of the small-scale Nanba micro-seismic array (near the No.4 borehole of the Wenchuan Fault Scientific Drilling Project, WFSD-4), and the large-scale portable seismic stations in western Sichuan and regional permanent stations, we perform a S-wave splitting analysis to reveal the upper crustal anisotropy characteristics beneath the northern Longmenshan fault as well as the relationship with regional stress field and tectonic features. The anisotropic parameters, fast polarization directions and delay time are determined by means of analyzing particle motion in the S-wave window. The resultant fast polarization orientations mainly show NE-NEE direction, consistent with the strike of the Beichuan fault and regional maximum principal compressive stress. The results of Nanba micro-seismic array further demonstrate that fast polarization under the Beichuan fault is parallel or sub-parallel to the fault strike, while that far away from the Beichuan fault is inconsistent with the fault trend, meaning the upper crustal anisotropy is closely related to the active fault structures.The normalized delay time variations of the Nanba micro-seismic array show an obvious change before and after the earthquake. This pattern indicates that the delay time is highly sensitive to the time variation and the earthquake energy may affect the crustal properties. The consistency of the measured delay time implies that the anisotropic degrees of the upper crust in the southern and the central Longmenshan fault are largely the same. |
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| Keywords: | Crustal seismic anisotropy S-wave splitting Longmenshan Fault WFSD |
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