复杂介质有限元法2.5维可控源音频大地电磁法数值模拟

2.5-D CSAMT MODELING WITH THE FINITE ELEMENT METHOD OVER 2-D COMPLEX EARTH MEDIA

利用有限元 2 .5维可控源音频大地电磁法 (简称CSAMT)数值模拟方法 ,对 10 0Ωm均匀半空间介质中有限长度的电偶极源产生的电场、磁场及视电阻率、相位特征进行了数值模拟 ,研究了场的空间变化规律 .在一个象限中 ,场的特征存在双叶现象 ,当收发距大于 4个趋肤深度时 ,电阻率较接近介质真实的电阻率 ,这些结果为观测系统和收发距的选择提供了依据 .波数域场的特征表明 ,低波数对源的贡献占较大的比例 .有限元法 2 .5维CSAMT数值模拟的优势在于能较准确地获得复杂介质结构的波场特征 .本文结合直立异常体、倾斜异常体及断陷模型对CSAMT电阻率、相位剖面特征及频率曲线特征的可靠性进行了研究 .数值模拟结果直观地给出了异常体的剖面异常形态 .通过对比研究异常体的剖面异常形态和半空间场的特征进一步说明本文方法和软件在模拟复杂介质结构场特征时是可靠的 .这为认识观测数据 。

This paper discusses deeply the characteristics of EM field for 2-D complex earth media. We introduce the characteristics of electric field, magnetic filed and apparent resistivity, and phase produced by a finite electrical dipole source over 100Ωm homogeneous half-space media. From this result we know the field change behavior over the distance from the transmitter to the receiver, and that we should use a proper transmitting-receiving mode. In wave number domain, the EM field shows that the field of low wave number contributes much more than that of high wave number. And then we demonstrate the CSAMT forward modeling apparent resistivity, phase pseudosetions and frequency curves for two-anomaly bodies, two-lean-anomaly bodies and down faulted anomaly. Numerical modeling results show directly the anomaly characteristics. This is very helpful for recognizing field data and data inversion and interpretation.