Relationships between surface ruptures and lithologic characteristics of the Wenchuan Ms 8.0 earthquake
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摘要: 2008年汶川8.0级地震沿龙门山断裂带内的映秀—北川断裂和灌县—安县断裂分别形成约230 km和70 km的地表破裂带.震后地质考察研究表明，伴随地震断层出露地表的滑动面大多沿炭质泥岩和煤层发育.与1∶5万区域地质图进行对照，显示映秀—北川地震破裂带的西南段（虹口—清平段）和灌县—安县地震地表破裂带的展布与龙门山地区上三叠统须家河组煤系地层的出露范围相一致.龙门山地区的上三叠统须家河组地层中的薄煤层、炭质泥岩层以及志留系、寒武系的炭质页岩层是易于产生滑动的柔性岩层，易形成滑脱面或成岩片夹于断层带中.汶川地震产生的复杂地表破裂带是龙门山逆冲推覆构造带沿地表构造层中夹有煤层等柔性岩层的断层产生B型滑动的结果.Abstract: Two co-seismic surface rupture zones, 230 km and 70 km long, are produced by the 2008 Wenchuan Ms 8.0 earthquake along the pre-existing Yingxiu-Beichuan fault and the Guanxian-Anxian fault, respectively, in the Longmen Shan fault zone. The post-earthquake geological study shows that the exposed fault planes accompanying with co-seismic scarps usually occurred along the coal seams and carbonaceous shales. In this paper we present the observed results of fault scarps and the slip surface in some typical locations along the co-seismic rupture zones. Comparing with the 1:50000 regional geological map, it shows that the distribution of the major section (the southwest part) of the Yingxiu-Beichuan co-seismic rupture zone and the Guanxian-Anxian co-seismic rupture zone are corresponding with the exposed area of the Upper Triassic Xujiahe coal-bearing strata in the Longmen Shan region. The Upper Triassic Xujiahe coal seam and the Middle-Lower Triassic and Silurian, Cambrian shales in the Longmen Shan region are the flexible rock layers, which are easy to slide and form detachment surface or detritus within the fault zone. The co-seismic rupture zone produced by the May 12 Wenchuan Ms 8.0 great earthquake resulted from a B-type sliding along the flexible rock layers in the shallow crust level.
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