2013年甘肃岷县漳县M_s6.6地震前地壳形变特征研究

Crustal Deformation before the Minxian-Zhangxian M_s6.6 Earthquake in Gansu

基于2013年岷县漳县M6.6地震震源区及其邻区1999年以来的GPS观测资料,通过应变率动态特征分析、多期次GPS剖面分析和基线变形速率的分析讨论了地震的震前变形特征。GPS速度场和块体应变率表明,汶川地震的发生导致了柴达木地块运动与变形状态发生明显调整,但由于西秦岭北缘等深大断裂的存在,岷-秦地块对其响应不明显;GPS连续应变率显示,在汶川地震引起的区域地壳变形调整过程中岷县漳县地震震源区附近的应变积累速率有减缓的迹象;GPS剖面显示,平行于岷县漳县主破裂带的运动分量对汶川地震响应显著,汶川震后表现为剪切变形速率的增强,而垂直于主破裂带的运动分量则对汶川地震响应不明显;震中周边GPS基线变形速率表明,基线伸缩变化率总体呈现NW向拉张、NE向压缩状态,且拉张量明显小于压缩量。上述地壳变形动态特征表明西秦岭北缘断裂及其附近地区的应变积累水平和断层闭锁程度可能处于较高水平,在岷县漳县地震前该区表现出局部"硬化"迹象。

Using GPS observation data since 1999 in the Lintan-Tanchang fault and the surrounding regions,the deformation characteristics of the region before the Minxian-Zhangxian MS6.6 earthquake are obtained through analysis of the GPS profile,the block strain rate,and the baseline time series.The results from the block strain rate show that the strain accumulation level of the northern margin of the western Qinling fault zone and its nearby faults were promoted by the Wenchuan MS8.0 earthquake.The response of the Wenchuan earthquake on the Lintan-Tanchang fault is obvious in the southern block and not obvious in the northern block,indicating that there is a strong earthquake risk in the boundary area between the two blocks.The results of the GPS profile across the LintanTanchang fault show that the parallel component response of the Wenchuan earthquake is obvious;however,the vertical component is not obvious.This indicates that there might be a higher level of compressive strain and degree of fault locking in the area.In general,the GPS observation results show that the pre-earthquake deformation characteristics are consistent with the coseismic rupture characteristics of the Minxian-Zhangxian earthquake.