龙滩库区库水加卸载过程深部电阻率变化与水库地震  

The deep resistivity variation during water loading and unloading and induced earthquake in the Longtan reservoir,Guangxi

作　　者：詹艳[1] 王立凤[1] 肖骑彬[1] 莫青云 高鹏飞 张远韩 韦永福 

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 [3]广西天峨县地震局,广西天峨547300

出　　处：《地球物理学报》2012年第8期2625-2635,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);中国地震局监测预报司"水库诱发地震"项目共同资助

摘　　要：广西龙滩库区于2009年度至2010年2个年度库水加卸载及渗透过程中,在交比屯、坪上、中良坪和向阳4个地点进行了5期次大地电磁定点测量,观测频段为320Hz～1000s.结合区域深部电性结构探测研究成果分析.结果显示,4个测点位于不同的岩性和深部电性结构区域,4个测点上观测的5期次视电阻率值发生变化的频段不同,位于库区中游的坪上、中良坪和向阳3个测点上5期次测量的视电阻率数值在频率1Hz以下频段在高水位时段测量值小、在低水位时段测量值大,位于库首区域的交比屯测点在最高水位时段视电阻率数值最小,说明库水在加卸载及渗透过程中对地下介质有明显影响,库区上游库水渗透影响深度可达7km左右,在坝首区域可达10km.龙滩水库区4个地震丛集区中的3个地震丛集区的震源区位于具有低阻特性的二迭系下统和石炭系地层的下部,以岩溶水体诱发地震为主;位于坝首地震丛集区的震源区位于上宽下窄似"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.电磁探测结果说明库水渗透对龙滩水库区地震孕育和发生起着重要、直接的作用.Longtan reservoir is located in the northwest of Guangxi province in South China.The reservoir began to store water since 2006.As the reservoir water level rose,earthquakes frequently happened,and the distribution of these earthquakes is mainly concentrated in four clustering areas.In order to understand the relationship between reservoir earthquakes and reservoir water level change,five times of magnetotelluric measurements were carried out during loading and unloading of the Longtan reservoir from 2009 to 2010.The surveys were conducted at 4 sites（Jiaobitun,Pingshang,Zhongliangping,and Xiangyang） with a frequency band of 320 Hz^1000 s and the Jiaobitun and Pingshang sites were located in an earthquake clustering area.Moreover along the two NW-trending Profiles,32 MT sites had measured and the two MT profiles across the four reservoir earthquake clusters.Combining the regional deep electrical structure and the five measured apparent resistivity values at four sites during loading and unlaoding of the reservoir,the result suggests that the four sites are located in different lithology and deep electrical structure areas.The apparent resistivity values are the smallest at the low frequency band less than 1 Hz in Pingshang,Zhongliangping and Xiangyang which are located in the middle of reservoir and at 0.1 Hz at Jiaobitun which is located in the vicinity of the dam when the water level of the reservoir was the highest during loading and unloading of the reservoir.This demonstrates that reservoir water infiltration during loading and unloading can change the electrical property of rock at a certain depth.The depth of the water infiltration is about 7 km in middle reservoir areas and 10 km in the vicinity of the dam in Longtan reservoir.Among the sources of 4 reservoir earthquake clustering areas,three are located in the lower portion of the Permian and Carboniferous strata with low resistivity,attributed to the induced events associated with water in karsts.The seismic event with the maximum magnitude occurred w

关 键 词：龙滩水库 库水加卸载 视电阻率值 渗透 水库地震 

分 类 号：P542[天文地球—构造地质学] P631[天文地球—地质学]