考虑IP效应的可控源电磁法电磁响应畸变分析

Analysis of electromagnetic response distortion of CSEM with IP effect

在野外观测的频率域电磁法的电磁场响应,不仅包含电磁感应响应也含有激发极化(IP)响应。为对IP效应引起的电磁场响应畸变进行分析,首先在纯电磁感应有限长导线源Ex、Hy、Hz电磁场响应表达式的基础上引入Cole-Cole模型,其次设置不同的地电模型,分别对含IP效应、纯电磁感应的有限长导线源频率域电磁法进行一维正演。通过理论模拟结果表明,加入IP效应后电磁场响应会产生畸变,随着极化层埋深的增加,响应畸变出现在更低的频率处,同时受IP效应的影响减弱。根据计算的最大相对异常值可知,水平电场Ex对极化层最为灵敏,而水平磁场Hy对深部极化层的反映能力最弱。

The electromagnetic field response includes both the electromagnetic induction response and the introduce polarization(IP)response.In order to study the response distortion of CSEM with IP effect,this paper presents the Ex,Hy,Hz formula of finite length control source frequency electromagnetic.According to different geoelectric model,the 1-D forward with IP is carried out and compared with the 1D forward modeling of CSEM,which only considers the electromagnetic induction.The simulation results show that the electromagnetic field response will be distorted when the IP effect is added.As the thickness-to-depth ratio decreases,the distorted part gradually moves from high frequency to low frequency.At the same time,and the electromagnetic response affected by the IP effect is more and more weak.The difference between the electromagnetic responses of electrical changes is much smaller.According to the calculated maximum relative abnormal values,the Ex is the most sensitive to the polarization body,while the Hy is the weakest in the deep polarization body.