2013年芦山M_S7.0地震前甘孜台地电阻率变化分析  

Analysis on Apparent Resistivity Variations of Ganzi Station before 2013 Lushan M_S7.0 Earthquake

作　　者：解滔[1] 卢军[1] 任越霞[2] 赵民渊 

机构地区：[1]中国地震台网中心,北京100045 [2]四川省地震局,成都610041 [3]甘孜地震台,甘孜626700

出　　处：《震灾防御技术》2013年第4期377-388,共12页Technology for Earthquake Disaster Prevention

基　　金：国家科技支撑计划专题(2012BAK19B02-03);国家自然科学基金(41204057)共同资助

摘　　要：甘孜台地电阻率N30°E测道观测资料自2011年7月开始出现趋势上升变化,N60°W测道地电阻率则从2012年出现趋势上升变化。2011年测区原317国道实施扩建工程,N30°E测道测量电极分别向供电极方向移动10m。采用甘孜台电测深曲线以水平层状模型反演了测区的电性结构,理论计算表明,测量电极的移动将会引起N30°E测道4Ω·m的上升变化,扣除这部分变化后,甘孜台两测道观测值于2012年同步上升。以水平层状模型计算了甘孜台两测道各层介质的影响系数,两测道浅层两层介质影响系数均为负,能合理地解释甘孜台地电阻率在雨季降水量增加时观测值上升、旱季降水量减少时观测值下降这一"夏高冬低"的年变现象。建立三维有限元模型计算了317国道拓宽部分对观测的影响,计算结果表明,拓宽部分仅能引起N60°W测道约0.15Ω·m的下降变化和N30°E测道约0.1Ω·m的上升变化,其对观测的影响非常小。同时2013年1月甘孜台两测道年变低值显著高于2008年以来各年的年变低值,在芦山地震前呈同步的上升变化,但是与汶川地震前的下降变化相反,因此甘孜台自2012年的趋势上升变化是不是芦山地震的前兆异常还难以确定。Apparent resistivity data of N30°E monitoring direction observed at Ganzi station began to increase since July 2011.And data of N60°W direction also increased since 2012.In 2011 the potential electrodes of N30°E direction moved 10m towards the current electrodes due to the expansion construction of national road No.317.By using a horizontal layered model our analysis indicates that the potential electrodes shift can cause 4 Ω· m raise to measurement of N30° E direction.Therefore,apparent resistivity of the two directions increased in the same time of 2012 after offset the effect from electrodes shift.Sensitive coefficients of two directions were also obtained using the model.Sensitive coefficients of shallow layers were minus for the two directions and the unexpected annual variations of Ganzi station were well explained.In order to quantitatively analyze effects on observation from the national road,we constructed an finite element model based on the electric structure.Analysis results also suggested that,the national road expansion construction can only cause 0.15 Ω· m decrease on N60°W monitoring direction and 0.1 Ω·m increase on N30°E direction.Additionally,the valley values of annual variation of 2013 were distinctively higher than other years from 2008,meaning that there existed abnormal rise of apparent resistivity of the two directions at Ganzi station before the Lushan earthquake.However,the rise was contrary to the decline variation before Wenchuan earthquake.Therefore,it was still unconfirmed that whether or not the rise variation was related to Lushan earthquake.

关 键 词：芦山地震 甘孜台 地电阻率 趋势上升 年变化 

分 类 号：P315.72[天文地球—地震学]