含激电信息的人工源频率域电磁法正演研究——大功率人工固定源极低频电磁法激电效应预研究

ABSTRACT Base on Dias-model, this paper study the forward modeling to IP response with MT souece and CSAMT source with the author’s program，that is to provide the theoretical basis for extracting the IP information from the far field, near field and transition field in extremely low frequency electromagnetic sounding with artificial strong fixed source signal. The outline of the paper is as follows. Firstly, review the history of the complex-resistivity-model, and analyses the bases for choosing Dias model; meanwhile, effects and responses of each parameter in Dias model are analyses. Afterward, study the forward modeling to 1D layered model with MT source, numerically simulate the IP effects of classic geoelectric objects; Find the clear anomaly and relationship between the peak value of the amplitude anomaly ratio and phase anomaly difference with and without IP parameters to be considered within a frequency range. On the basis of the modeling of MT, Study the CSAMT modeling with a dipole-source, obtain the anomaly responses and the relationship between anomaly and characters of object. Base on the infinite line source, study the 2D IP effect of geoelectric objects with 2D modeling. Calculate the response with different source distance, object depth and different wall rock resistivity systemically. Finally, conclude the viewpoints and give the discussion of the result, and point out the lack of this research also.

计算层状介质中电磁场的层矩阵法

As an important branch of electrical prospecting method, the artificial source frequency domain electromagnetism method has received more and more attention. But when conducts the fundamental research, people often isolated study some concrete method, so the research results of one method are very difficult to apply to another method directly. This article will possess the artificial source frequency domain EM method to an 1D model simply. It is stratified medium model, with an electric or magnetic source in or outside of it. Then take the horizontal electric dipole source as an example to introduce how to computing the EM field in stratified medium. Because layer matrix is the key of establishing equations, so we call it the layer-matrix method. The key of layer-matrix method is establishing equations by using layer matrixes in wavenumber(kx, ky, z) domain, then obtains the electromagnetic field value of wavenumber domain. After Fourier transform, we can get electromagnetic field of any position in spatial domain. The layer matrix technique theoretically can calculate electromagnetic field of any position for any source, is suitable for many kinds of electromagnetic method. After introduction of the layer matrix method, this article has done some CSAMT, MCSEM and Wireless Electro-Magnetic Method (WEM) modeling with layer matrix method separately. In CSAMT modeling, we get electromagnetic field dissemination characteristics considering wave number of the air, and obtain three-dimensional distribution characteristics of the electromagnetic field. In MCSEM modeling, we get electromagnetic field dissemination characteristics with and without considering the airwave, and obtain three-dimensional distribution characteristics of electromagnetic field. In WEM modeling, we get electromagnetic field’s difference between considering the ionosphere and not considering it, and recognize the ionosphere’s influence of electromagnetic field. With the layer matrix technique, we have got some new understandings of EM dissemination rules of different situations. All analysis results indicate that the layer-matrix technique is credible and effective, and are worthy of further thorough research and development.