民乐-山丹地震的区域构造变形背景与中短期前兆

Regional Tectonic Background and Medium-and Short-Term Auspice of the Minle-Shandan Earthquakes

利用青藏块体北缘地区 2 0 0 1～ 2 0 0 3年GPS水平运动资料和 1988～ 2 0 0 3年跨断层短水准流动观测资料 ,借助改进的负位错模型及断层形变应变强度比 -时变曲线 ,研究了与 2 0 0 3年 10月 2 5日民乐 -山丹MS6 1,MS5 8地震孕育有关的区域构造变形背景与中短期前兆异常。分析表明 ,在昆仑山MS8 1大震引起的大区域形变调整 -短期松弛 -开始恢复的背景下 ,民乐-山丹地震震源位于可能反映应变能积累加速的块体边界压性锁定段之间的剪应力强度增强段北侧 ;距震中最近的石灰窑口跨断层短水准流动场地在震前 3个月呈现显著应变强度比异常 ,而震前 10余天至数月内整个监测区异常个数、震前

Using the data of horizontal movement during 2001～2003 observed by GPS and mobile short-leveling observation crossing faults from 1988 to 2003 in the northern margin of the Qinghai-Xizang block, aided by improved negative dislocation model and time-curve for strain intensity ratio of fault deformation, the regional tectonic background and medium- and short-term auspice abnormity related to the Minle-Shandan M_S=6.1 and M_S=5.8 earthquakes occurred on October 25,2003 are given. The analysis shows that, under the background of large-range deformation adjustment——short time relaxation——recovery caused by the Kunlun Mountain M_S=8.1 earthquake, the earthquakes located on northern side of enhanced segment of shear stress intensity which lay between two compressive locked segments reflecting acceleration of strain energy; Moreover, the Shihuiyaokou site (near epicenter) of mobile short-leveling observation crossing fault, revealed remarkable abnormity of strain intensity ratio in 3 months before those earthquakes, and the number of abnormity of entire monitoring area from 10 odd days to several months and locally enhanced and centralized abnormity region close to the epicenter in 3 months before those earthquakes foreshowed them.