Uplift of the Longmen Shan Range and the Wenchuan Earthquake
Uplift of the Longmen Shan Range and the Wenchuan Earthquake
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DOI：
10.18814/epiiugs/2008/v31i3/002
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发表时间：
2008-09
期刊：
影响因子：
3.1
通讯作者：
Zhiqing Xu;S. Ji;Haibing Li;L. Hou
中科院分区：
文献类型：
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作者：
Zhiqing Xu;S. Ji;Haibing Li;L. Hou
2008年5月12日汶川地震发生在龙门山前陆冲断带，震级为S 8级。该事件发生在龙门山山脉长期隆升的背景下，这是青藏高原地壳物质向四川盆地流变性较强的地壳广泛向东挤压的结果。龙门山以西缘茂县-汶川-康定韧性拆离带和东缘映秀-北川-泸定韧性冲断带为约束的前震旦纪结晶杂岩为特征。龙门山隆起是松潘-甘孜地体与扬子地块之间的陆内俯冲作用在前新生代启动的。∼50 Ma以来，印度板块与欧亚板块的碰撞使隆升速率显著增加。汶川地震造成了两条NE向同震大断裂(即∼长275公里的映秀-北川-青川断裂和长100公里的∼安县-冠县断裂)。结合震源解和地震反射剖面的野外研究表明，同震破裂在∼15公里厚的上地壳中是陡峭的闭合逆或右逆斜滑断层。这些断裂在水平挤压体制下的摩擦滑动方向不利，因此它们需要较长的重复间隔来积累构造应力和流体压力，使其达到在特定地点形成强震的临界水平。研究还发现，所有S级大地震都发生在GPS测得的水平运动速度明显较低的断裂带上(<；3 mm/年)。这些断裂构成了不断扩大的青藏高原与强大的四川盆地、阿拉山和鄂尔多斯地块相对的东北前缘，尽管它们的平均复发间隔一般很长，但破坏性很强。
The 12 May 2008 Wenchuan earthquake (M s =8.0) struck on the Longmen Shan foreland thrust zone. The event took place within the context of long-term uplift of the Longmen Shan range as a result of the extensive eastward-extrusion of crustal materials from the Tibetan plateau against the rheologically strong crust of the Sichuan Basin. The Longmen Shan range is characterized by a Pre-Sinian crystalline complex constrained by the Maoxian-Wenchuan-Kangding ductile detachment at the western margin and the Yingxiu-Beichuan-Luding ductile thrust at the eastern margin. The Longmen Shan uplift was initiated by intracontinental subduction between the Songpan-Ganzi terrane and the Yangtze block during the Pre-Cenozoic. The uplift rate was increased considerably by the collision between the Indian and Eurasian plates since ∼50 Ma. The Wenchuan earthquake resulted in two major NE-striking coseismic ruptures (i.e., the ∼275 km long Yingxiu- Beichuan-Qingchuan fault and the ∼100 km long Anxian-Guanxian fault). Field investigations combined with focal solutions and seismic reflection profiles suggest that the coseismic ruptures are steeply dipping close-topure reverse or right reverse oblique slip faults in the ∼15 km thick upper crust. These faults are unfavorably oriented for frictional slip in the horizontally compressional regime, so that they need a long recurrence interval to accumulate the tectonic stress and fluid pressure to critically high levels for the formation of strong earthquakes at a given locality. It is also found that all the large earthquakes (M s >7.0) occurred in the fault zones across which the horizontal movement velocities measured by the GPS are markedly low (<3 mm/yr). The faults, which constitute the northeastern fronts of the enlarging Tibetan plateau against the strong Sichuan Basin, Ala Shan and Ordos blocks, are very destructive, although their average recurrence intervals are generally long.