数值模拟探讨青藏高原东部应力应变场及断裂活动性

Numerical Study of the Crustal Stress, Strain Rate and Fault Activity in the Eastern Tibetan Plateau

青藏高原东部是我国活动构造非常强烈的区域,现今的应力应变状态对活动构造研究有重要参考意义。本文依据地质资料和岩石力学性质构建相应的有限元数值模型,以GPS观测为边界约束,计算得到了青藏高原东部应力应变场,在此基础上探讨了主要断裂的活动特征。结果显示,距离印度板块和欧亚大陆板块碰撞带较近的青藏高原,汇聚速度、最大压应变率和最大压应力均较高,而随着远离碰撞带各个数值相应降低;在青藏高原东部,以喜马拉雅东构造结为旋转中心的一系列弧形断裂滑动速率相对较高,如玉树—鲜水河—小江断裂带,巴塘—金沙江断裂带,嘉黎断裂带等,这些走滑断裂带控制着青藏高原东南缘物质旋转挤出的特征,而其它断裂带滑动速率则相对较低,在块体内部则更低;结果同时表明应变速率分配高的断裂达到屈服的时间短,对应的地震复发周期短。

The seismic activity in the eastern part of the Tibetan Plateau is very strong.The localization of stress and strain rate is very important for the active tectonic study.In this study,based on geological data and rock mechanical properties,the authors constructed a numerical model.With the constraint of GPS observation,the localization of stress and strain rate and the activity of major faults in this area were investigated.The results show that the convergence velocity,the maximum compressive strain rate and the maximum compressive stress are very high around the Indo-Asian collision zone.With decreasing distance from the collision zone,their values decrease accordingly.Around the eastern Himalayan syntaxis,a series of faults form a arcuate structural system.The localization of stress and strain rate along these faults is very high,which indicates that the seismic activity is strong in this area.Faults such as Yushu-Xiangshuihe-Xiaojiang faults,Batang-Jingshajiang faults and Jiali fault control the rotation and extrusion of substances in the southeastern Tibetan Plateau.Along other faults and in the interior of blocks,the localization of stress and strain rate is low.The faults with high strain rate spend short time to reach yield strength,indicating short earthquake recurrence period.