Controlled-Source Audio-frequency Magnetotelluric Two-dimensional Modeling For Arbitrary Anisotropy Structures

Controlled-source audio frequency magnetotellurics method(CSAMT)is widely used as a powerful geophysical tool in geothermal resource exploration,mineral prospecting and environmental geophysics.Compared with the magnetotelluric method,the advantage of the controlled-source audio frequency magnetotelluric method is that the artificial source is used to substitute the natural field source,thus the characteristics of the weak electromagnetic field strength of the natural field source is avoided.In the actual production work,we usually adjust the strength of the artificial source according to the requirement of production standard.In the research of theoretical algorithm,the current research on the controlled-source magnetotelluric focused generally on isotropic subjects.With the requirement of practical research and the development of theoretical studies,the anisotropic investigation in CSAMT method has become a hot research topic in the field of electromagnetics.Based on the classical Maxwell equations,the CSAMT 2D anisotropic forward problem have been solved by the finite-element method based on the dual equation concerning the electric field and magnetic field that is parallel to the structure strike.We have designed many one-dimensional and two-dimensional isotropic models to perform numerical simulation,then we compared the numerical results with the calculated results of the open isotropic one dimensional marine controlled-source electromagnetic and two dimensional magnetotelluric forward code,respectively.The comparison results verify the correctness of the forward code in calculating the electromagnetic responses for the isotropic model.The two-dimensional anisotropic models have been designed to simulate,we compared the numerical results with the forward results of Pek's two dimensional magnetotelluric anisotropic forward code.The correctness and applicability of the forward code in calculating electromagnetic responses for the anisotropic model is proved.Based on the CSAMT two-dimensional anisotropic forward program developed in this paper,we have studied the effects of field source,model conductivity,Euler rotation angle and the relationship between the different Euler rotation Angles.The results show that the final forward response is affected by various factors.