新丰江地区地壳P波三维速度结构及活动构造研究

摘要

利用震源位置和速度结构的联合反演得到2007年6月～2014年7月新丰江地区地震序列的震源位置及P波三维速度结构模型,并进一步对比区域活动构造的产状特征及震源机制解等.结果显示,自ES向WN新丰江库区断裂深度有逐渐增大的趋势,与重力场的研究结果一致.库区大坝至东源锡场之间的中-上地壳存在4个大小不等的高速体,其中,锡场下方的高速体Ⅰ体积最大(EW向截面约6km×7km),速度最大,中心速度达6.3km/s.库区大坝下方存在以人字石断裂(F2)、南山-坳头断裂(F4)、河源断裂(F1)、石角-新港-白田断裂(F5)等为中心的强烈构造变形区,1960年至今大坝下方高速体Ⅲ、Ⅳ边缘已发生包括1962年6.1级地震在内的7次ML≥5.0地震,能量释放较为彻底;锡场下方高速体Ⅰ的边缘自2012年以来中小地震活跃,且b值较低,不排除发展为中强震孕震凹凸体的可能.%In this paper,we determined earthquake sequence location in the Xingfengjiang area from June 2007 to July 2014 and 3D P-wave velocity structure by a simultaneous inversion method.On that basis,we studied the occurrence features of active tectonics and the earthquake source mechanism.The results show the reservoir fracture system has the tendency of increase with the gradual depth from southeast to northwest,consistent with the gravitational field research results.There are 4 high velocity zones(HVZ) under the depth of 7-12km crust between the Xinfengjiang Reservoir dam and Dongyuan Xichang district.The max velocity of the biggest HVZ which is under Xichang is 6.3km/s.Under the reservoir dam there is a strong tectonic deformation zone,as the center exit Renzishi fault F2,Nanshan-Aotou faults F4,Heyuan fault F1 and Shijiao-XingangBaitian fault F5.7 earthquakes with ML ≥5.0(including M6.1 in March 1962)occurred at the high gradient zone of the HVZ Ⅲ and HVZ Ⅳ edge which is under the reservoir dam since 1960,relativity energy releasing more thoroughly.Moderate seismic activity occurred at the HVZ Ⅰ edge which is under Xichang since 2012,which is the dangerous zone of M5.0 earthquakes in the future.