Seismogenic Structure around the Epicenter of the May 12,2008 Wenchuan Earthquake from Micro-seismic Tomography |
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| Authors: | AN Meijian FENG Mei DONG Shuwen LONG Changxing ZHAO Yue YANG Nong ZHAO Wenjin ZHANG Jizhong Institute of Geomechanics Chinese Academy of Geological Sciences Beijing China Chinese Academy of Geological Sciences Beijing China |
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| Institution: | AN Meijian~(1,*),FENG Mei~1,DONG Shuwen~2,LONG Changxing~1,ZHAO Yue~1,YANG Nong~1,ZHAO Wenjin~2 and ZHANG Jizhong~1 1 Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China 2 Chinese Academy of Geological Sciences,Beijing 100037,China |
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| Abstract: | A three-dimensional local-scale P-velocity model down to 25 km depth around the main shock epicenter region was constructed using 83821 event-to-receiver seismic rays from 5856 aftershocks recorded by a newly deployed temporary seismic network. Checkerboard tests show that our tomographic model has lateral and vertical resolution of -2 km. The high-resolution P-velocity model revealed interesting structures in the seismogenic layer: (1) The Guanxian-Anxian fault, Yingxiu-Beichuan fault and Wenchuan-Maoxian fault of the Longmen Shan fault zone are well delineated by sharp upper crustal velocity changes; (2) The Pengguan massif has generally higher velocity than its surrounding areas, and may extend down to at least ～10 km from the surface; (3) A sharp lateral velocity variation beneath the Wenchuan-Maoxian fault may indicate that the Pengguan massirs western boundary and/or the Wenchuan-Maoxian fault is vertical, and the hypocenter of the Wenchuan earthquake possibly located at the conjunction point of the NW dipping Yingxiu-Beichuan and Guanxian-Anxian faults, and vertical Wenchuan-Maoxian fault; (4) Vicinity along the Yingxiu-Beichuan fault is characterized by very low velocity and low seismicity at shallow depths, possibly due to high content of porosity and fractures; (5) Two blocks of low-velocity anomaly are respectively imaged in the hanging wall and foot wall of the Guanxian-Anxian fault with a ～7 km offset with ～5 km vertical component. |
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| Keywords: | Wenchuan earthquake seismogenic structure micro-seismic tomography Pengguan massif Longmen Shan fault zone |
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