四平台地电阻率相反年变有限元数值分析  

Inverse annual variations of apparent resistivity at Siping earthquake station by using finite element method

作　　者：解滔[1] 王洪岐[2] 刘立波[2] 卢军[1] 

机构地区：[1]中国地震台网中心,北京100045 [2]吉林省地震局,长春130022

出　　处：《地球物理学进展》2014年第2期588-594,共7页Progress in Geophysics

基　　金：国家科技支撑计划专题(2012BAK19B02-03);中国地震局震情跟踪青年课题(2013020404)共同资助

摘　　要：本文依据吉林省四平台地质剖面、地下介质电性资料,将四平台地下介质电性分布简化为沿NW走向的二维电性结构,并结合台站电测深资料建立三维有限元模型,以模型浅层介质电阻率变化模拟测区浅层介质电阻率随季节的变化,计算了四平台N50°W和N40°E两测道地电阻率的年变化形态.计算结果表明,N50°W测道地电阻率在浅层介质电阻率升高时上升,在浅层介质电阻率降低时下降;N40°E测道地电阻率在浅层介质电阻率升高时下降,在浅层介质电阻率降低时升高.两测道地电阻率年变化表现出相反的形态,且N50°W测道年变幅度要大于N40°E测道,计算结果在变化形态上符合四平台实际的观测资料,因此认为四平台测区地下介质的非均匀分布是产生两测道地电阻率年变形态相反现象的原因.Geological section and electric property data of Siping earthquake station, Jilin province, China, were collected in our analysis. According to these information the electric structure of medium beneath Siping station could be simplified as a two dimensional electric section along with NW direction, which maintains homogeneity in N40°E direction and the electric properties only changes in NW direction and with depth. Based on this assumption and combined with electrical sounding data of N40°E and N50°W directions observed at Siping station, a three dimensional finite element model was constructed to analyze apparent resistivity annual changes in the station. In the mathematical analysis, the actual resistivity variations of the shallow medium were substituted with resistivity changes of the first and second layers in the model. Analyzed results of the model suggest that apparent resistivity of N50°W direction increases when resistivity of two shallow layers increases, and decreases with deduction of resistivity of shallow layers. However, apparent resistivity of N40°E direction decreases when resistivity of two shallow layers increases, and increases with deduction of resistivity of the two layers. Amplitude of annual variation of N50°W direction is also larger than that of N40°EW direction, and annual variations of two directions play an inverse way. The mathematical results from the model are accord with the observed data, so we conclude that the inhomogeneous distribution of electric medium beneath Siping station causes the inverse annual variations of the two direction observation.

关 键 词：四平地震台 地电阻率 年变 有限元 

分 类 号：P315[天文地球—地震学]