Deep Processes and Dynamic Responses Associated with the Wenchuan Ms8.0 Earthquake of 2008
Deep Processes and Dynamic Responses Associated with the Wenchuan Ms8.0 Earthquake of 2008
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DOI：
10.1002/cjg2.1347
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
J. Teng;Denghai Bai;Hui Yang;Yafen Yan;Hongshuang Zhang;Yongqi Zhang;Xiaoyan Ruan
中科院分区：
文献类型：
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作者：
J. Teng;Denghai Bai;Hui Yang;Yafen Yan;Hongshuang Zhang;Yongqi Zhang;Xiaoyan Ruan
2008年汶川8.0级地震发生在龙门山构造带上，从现有的资料来看，龙门山构造带似乎不是很活跃。据报道，在这一事件之前没有观察到明显的前兆。这可能意味着与这次巨大地震有关的深部地壳形变在地表或浅部地下没有可检测的表现。本文试图从深层分析这次地震的酝酿和发生过程，从而解释这次特大地震的原因。在构造上，印度-欧亚板块碰撞是中国西南地区大地震最重要的动力学背景。东喜马拉雅构造结正迅速向北北东方向进入青藏高原，迫使深部物质向东流动。由于受四川盆地西北缘北东向龙门山构造带的阻挡，部分油气流向转向东南。龙门山是地形和地壳结构的明显分界线，其高差达3500±500 m，地壳厚度西60±5 km，东40±2 km。因此，它必须经历强烈的变形和应力积累，虽然非常缓慢，没有明显的表现。根据已有资料推测，下地壳和上地幔盖层物质沿两个深部滑动面向东沿着流动，其中一个滑动面为低速低阻层（20~25 km），另一个滑动面为地幔软流层顶部。由于受到盆地下刚性物质的阻碍，下地壳和上地幔物质的覆盖层在龙门山的流动转为高角度逆冲推覆。龙门山以西可见三条逆冲断层，深达20 km，在此汇聚成一条活动带。因此，龙门山构造带是浅部地下断层滑动与下地壳物质流和上地幔盖层物质流耦合的场所。在强烈的物质和能量交换作用下，震源介质突然大规模破裂，释放出巨大的弹性应变，导致汶川8.0级地震。
The Wenchuan Ms8.0 earthquake of 2008 occurred on the Longmen Shan tectonic zone which seems not very active from available data. And it is reported that no noticeable precursors have been observed before this event. It might imply that the crustal deformation at depth associated with this gigantic shock had no expression on the surface or shallow subsurface which was detectable. In this article, we attempt to analyze the processes of brewing and generation of this event at depth that can account for the reason of this devastating earthquake. Tectonically, it is obvious that the India-Eurasia plate collision serves as the most important dynamic setting of major earthquakes in southwestern China. The Eastern Himalayan Syntaxis is moving rapidly in NNE direction into the Tibetan plateau, forcing deep material to flow toward east. Due to the obstruction of the NE trending Longmen Shan tectonic zone in the northwestern margin of the Sichuan basin, the partial flow turns to southeast. Longmen Shan is a conspicuous boundary of topography and crust structure, across which the elevation difference is as large as 3500±500 m, with crustal thickness 60±5 km in its west and 40±2 km in its east, respectively. Thus it must experience intense deformation and stress accumulation, though very slow without appreciable manifestation. Based on available data, it is inferred that material of lower crust and covering strata of upper mantle is flowing eastward along two deep slide surfaces, of which one is the layer of low-velocity and low-resistivity (20~25 km depth), and the other is the top of mantle asthenosphere. Hindered by rigid matter beneath the Sichuan basin, the flow of lower crust and covering strata of upper mantle material turns overthrusting at high angles at the Longmen Shan. On the other hand, three thrust faults visible west of the Longmen Shan extend downward to depth 20 km, where they converge into one active zone. Thus the Longmen Shan tectonic zone is a place where occurs the coupling between slippage on faults of shallow subsurface and material flow of lower crust and covering strata of upper mantle. Under the intense exchange of matter and energy, the source medium ruptures suddenly at a large scale to release a huge amount of elastic strain, resulting in the Wenchuan Ms8.0 earthquake.