广西龙滩库区深部孕震结构大地电磁探测研究  

Electromagnetic survey of the seismogenic structures beneath the Longtan reservoir in Guangxi Province

作　　者：詹艳[1] 王立凤[1] 王继军[1] 肖骑彬[1] 莫青云 

机构地区：[1]地震动力学国家重点实验室(中国地震局地质研究所),北京100029 [2]广西地震局龙滩台网中心,广西天峨547300

出　　处：《地球物理学报》2012年第4期1400-1410,共11页Chinese Journal of Geophysics

基　　金："十一五"国家科技支撑计划项目(2008BAC38B033);中国地震局地质研究所基本科研业务专项(IGCEA1013;DFIGCEA0608215)和中国地震局监测预报司"水库诱发地震"项目共同资助

摘　　要：在广西龙滩库区布置2条北北西-南东东向大地电磁探测剖面进行了32个测点的观测,观测频段为320Hz～1000s.对2条剖面上测量和计算得到的各种电磁参数、深部电性结构图像以及库区地质构造、岩性和水域分布等进行分析研究.结果显示库区发育的6条断裂在电性上表现为不同程度的电性差异边界,其中拉浪—达良断裂和拉色—辉马断裂为库区主要断裂带.库区深部电性结构总体表现为纵向上自地表到20km深度呈现高—低—高的波浪起伏的三层结构,横向上呈明显的高低电阻块状组合样式.龙滩库区4个地震丛集区的震源都位于高、低电阻接触带附近,其中3个地震丛集区的震源位于低阻特性的石炭系地层的下部,为岩溶水体诱发地震;发生最大震级的地震丛集区的震源位于上宽下窄似"铆钉状"的高阻体下部,推测是因水库蓄水后水体压力增大和库水渗透作用下在聚集高变形能的脆性高电阻体内部发生的地震.A magnetotelluric（MT） survey was carried out at 32 sites along two NNW-SEE trending profiles across the Longtan reservoir in Guangxi Province,with a measurement frequency band 320 Hz～1000 s.From the acquired MT data,electromagnetic parameters and images of deep electric structure beneath the study area were obtained,allowing us to conduct an integrated analysis of the seismotectonics in combination with geological structure,lithology and water system distribution of this region.The result indicates that there are 6 faults in the reservoir area,which can be identified by difference of electric property,among which the Lalang-Daliang and Lase-Huima faults are the primary fractures.The electric structure below the reservoir can be described by a three-layer model which is characterized by high-low-high values from the surface to depth 20m in vertical direction.In horizontal direction,the structure exhibits a pattern of combined blocks with high and low resistivity values.The sources of 4 earthquake clustering areas all lie nearby the boundary between high and low resistivity zones,of which the 3 sources are located in the lower portion of the Carboniferous stratum with low resistivity,attributed to induced events associated with water in karsts.The seismic event with the maximum magnitude occurred within the lower high-resistivity body,of which the width tapers downward.It is speculated that the earthquakes in this reservoir can be attributed to strain accumulation in the high-resistivity body due to the increase of water pressure after water storage and the water permeation.

关 键 词：广西龙滩水库 深部电性结构 水库地震 

分 类 号：P631[天文地球—地质矿产勘探] P541[天文地球—地质学]