2003年民乐M_S 6.1级地震前后Pg波速度横向变化特征  

Characteristics of lateral variation of Pg wave velocity before and after the 2003 Minle M_S 6.1 earthquake

作　　者：曾宪伟[1] 冯建刚 吕俊强[1] 

机构地区：[1]宁夏回族自治区地震局,银川750001 [2]甘肃省地震局,兰州730000

出　　处：《地球物理学进展》2014年第4期1601-1608,共8页Progress in Geophysics

基　　金：地震科技星火计划(XH12054Y);青年震情跟踪课题(2012010203)联合资助

摘　　要：本文研究着眼于与民乐地区地震活动有紧密关联的地壳深度(≤20km),利用1987-2008年的Pg波到时数据反演了河西走廊及其周边地区的中、上地壳速度横向变化结果以及速度横向动态变化结果.分析表明:(1)河西走廊过渡带为低速区,北祁连褶皱带为高速区;(2)地震位于低速体南边与高速区相交的部位,且震前6年,震中边侧逐渐出现速度显著升高区;(3)研究区北东-南西的主压应力方向与两个速度升高区呈现出的延伸方向具有很好的一致性,这说明了在主压应力方向上更容易积累应力的合理性;(4)主震的静态应力变化与震后Pg波速度的横向动态变化有较好的对应关系.The paper focused on focal depth less than 20 km closely related with seismic activity in Minle region.And we inversed velocity lateral variation and dynamic variation of upper and middle crust in Hexi corridor and its surrounding areas using arrival time data from 1987 to 2008.The results show that transition zone of Hexi corridor is low velocity region and fold belt of northern Qinlian is high velocity region.Also the earthquake occurred in transition zone of high velocity and low velocity body from south to north. Furthermore,significantly higher areas of velocity had been gradually appearing beside the epicenter since six years before the earthquake.Meanwhile,north-east and south-west direction of principal compressive stress is almost consistent with extension direction of the two velocity higher regions.This shows that it is reasonable to accumulate stress more easily in the direction of principal compressive stress.In addition,there is good corresponding relationship between static stress changes of the main-shock and dynamic variation of Pg wave velocity after the shock.The above analysis shows that, Minle earthquake occurred in the conversion speed zones from high velocity to the low vilocity,and the side of the epicenter region appeared gradually velocity increased significantly before the earthquake 6 years.These results not only reflect the stress accumulation process,but also should reflect the stress concentration.On the other hand,the rock damage test shows that,fluid in the adjacent fluid layer is likely to fluid into the source in a certain period of time before the earthquake,which is led to weakening of the hypocenter body strength and triggering the earthquake.The above opinion is consist with a number of water,electricity and deformation data changes before the MS6.1 earthquake.Therefore,Minle earthquake may be the result of dielectric strength weakening in the focal region at the background of enhanced crustal stress in the same region.

关 键 词：民乐地震 Pg波速度变化 地震层析成像 高速度区 应力场 静态应力 

分 类 号：P315[天文地球—地震学]