汶川M_s8.0地震孕育发生的机制与动力学问题  

The mechanism and dynamics of the generation and occurrence for Wenchuan M_S 8.0 earthquake

作　　者：李延兴[1] 张静华[1] 周伟[1] 胡新康[1] 郭良迁[1] 张中伏[1] 

机构地区：[1]中国地震局第一监测中心,天津300180

出　　处：《地球物理学报》2009年第2期519-530,共12页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(40474036;40474039);国家重点基础研究发展规划项目(2007CB411702)资助

摘　　要：2008年5月12日四川省汶川县发生了M_S8.0强烈地震.发震断层是龙门山断裂带的映秀—北川断裂.分析震前的UPS速度场发现,从巴颜喀拉块体西部到龙门山断裂带沿大约N103°E方向的缩短速率为13.0mm/a,龙门山断裂带的右旋走滑速率1.1mm/a,断裂带处于闭锁状态.四川盆地沿大约N103°E方向有少量的压缩变形,而沿SW方向有少量的拉张变形.同震位移场显示,这次地震可能是巴颜喀拉块体SE向逆冲与四川盆地NW向俯冲同时发生的.应变场分析发现,震前震中区的主压与主张应变率分别为—30.840×10^(-9)/a与13.956×10^(-9)/a,主压应变轴N105.4°E与震源机制解得到的主压应力轴的方向N103°E一致.由本文提出的应力-应变机制得到的断层滑动方向和走向与地表破裂调查和震源机制解得到的结果一致.印度、太平洋和菲律宾海板块与欧洲板块的相互作用是龙门山断裂带积累弹性应变能和孕育汶川地震的长期作用力.苏门达腊大地震使青藏高原和华南块体的相互作用加强,促进了汶川地震的发生.On 12 May 2008, an Ms8.0 earthquake occurred in Wenchuan, Sichuan Province. The seismogenic fault is Yingxiu- Beichuan fault of the Longmenshan fault zone. Analysis of GPS velocity field before the earthquake discovers that the shortening velocity along the direction of about N107.5°E from west Bayan Har to the Longmenshan faults is 13.5 mm/a, the clockwise slipping velocity of the Longmenshan faults is 1. 1 mm/a, the faults are locked. Sichuan Basin shows a little compressing deformation along the direction of about N107° E, and a little expanding deformation along the direction of SW. Co-earthquake displacement field shows that the earthquake may be caused by thrust of Bayan Har block along direction of SE and the downthrust of Sichuan Basin along the direction at NW occurred simultaneously. Analysis of the strain field discovers that the principal compressive and the principal tensile strain rates in the epicenter area are -30. 840 × 10^-9/a and 13. 956× 10^-9/a respectively before earthquake, and the principal compressive strain axis is in a direction of N105.4°E which is consistent with the average direction at N107.5°E of the principal compressive stress axis from focal mechanism result. The earthquake fault trend and slipping direction obtained by the mechanism proposed in the paper are also consistent with the results of the focal mechanism. The interactions of the Indian, the Philippine Sea and the Pacific plates with the Eurasian plate are long term acting force of accumulating elastic strain energy and generating Wenchuan great earthquake. Sumatra-Andaman great earthquake of Dec. 2004 makes the interactions of Tibetan plateau and South China block to strengthen, which promoted occurrence of Wenchuan earthquake.

关 键 词：速度场分析 应变场分析 发生机制 动力学 汶川地震 

分 类 号：P541[天文地球—构造地质学]