| 东昆仑大地震的深部构造背景 |
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| 引用本文：李秋生,彭苏萍,高锐,管烨,范景义.2004.东昆仑大地震的深部构造背景[J].地球学报,25(1):11-16. |
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| 基金项目:国家重点基础研究发展规划项目(编号:G1998040800) |
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| 中文摘要:本文以深地震测深剖面资料揭示的地壳结构形态为切入点 ,探讨东昆仑 8.1级大地震的深部构造背景。沱沱河—小柴旦长 5 0 0km的剖面范围内发现两处大的莫霍面错断 ,分别位于东昆仑 柴达木结合带之下和金沙江断裂之下。青藏高原北部的地壳厚度 6 1～ 75km :莫霍面具有一致南倾 ,逐步加深的产状及弱反射性特征 ;下地壳明显增厚 ,但速度未见明显降低 ;上地壳发育逆冲、走滑断裂 ;地壳中部存在低速层。北邻的柴达木盆地地壳相对刚性 ,厚 5 2± 2km。东昆仑及邻区的壳幔结构有利于强地震孕育。在印度板块向北推挤和柴达木地块的向南插入的区域挤压应力场中 ,青藏高原北部较弱的下地壳缩短增厚 ,变形过程中的蠕滑引起地壳浅部的应力放大。但NE向主压应力的作用不是大地震形成的唯一要素 ,与青藏高原北部各地体侧向运动有关。侧向运动速率和幅度的差异使应力在各地体的边界断裂积累并使其复活。而低速层对形成孕育大地震需要的“立交桥式”的局部应力环境是必不可少的条件。 |
| 中文关键词:深地震测深剖面 地壳结构 地震 青藏高原 东昆仑 |
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| Deep Tectonic Background of the 8.1 Ms Earthquake in the East Kunlun |
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| Abstract:This paper has discussed the deep background of East Kunlun Ms 8.1 earthquake through the crust structure derived from the deep seismic sounding profile. Along a 500 km profile from Tuotuohe to Xiaochaidan, there exist two large Moho offsets under the transitional belt from East Kunlun Mountains to Qaidam basin and under Jinshajiang suture respectively. The crustal thickness is 61 to 75 km beneath the northern Tibet plateau. Moho with weak reflectivity remains continuously dipping southward and gets dee pened. The low crust has been thickened with no obvious decrease of velocity. In the upper crust, thrust and slide faults are developed, and the lower velocity layer appears between the upper and the lower crust. The Qaidam basin has a thickness of 52±2 km, being more rigid than the northern Tibet plateau. The special structure of the crust and the upper mantle beneath the East Kunlun Mountain and its surrounding areas is favorable for the formation of violent (great) earthquakes. In the regional stress field where the India plate pushes northward and the Qaidam block underthrusts southward, the relatively weak low crust beneath the northern Tibet plateau has been shortened and thickened. The creep slide movement in the process of deformation has enlarged the stress in the shallow part of the crust. Nevertheless, the formation of a great earthquake is related not only to the northeastern main compresso stress but also to the lateral movement of the blocks in the northern Tibet plateau. The differences in velocity and magnitude of the lateral movement between various terrenes of northern Tibet have resulted in the stress accumulation along the boundaries of the blocks and reactivated boundary faults. The existence of the low velocity layer is the prerequisite for the formation of such local stress setting as 'viaduct' which is the favorable site for violent (great) earthquake. |
| keywords:deep seismic sounding crust structure earthquake Tibetan Plateau East Kunlun |
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