3D Magnetotelluric Forward Modelling In Anisotropic Media

The magnetotelluric method is one of the few electromagnetic methods that can detect deep structures of tens of kilometers or more,and has good effect on the crust-mantle boundary and the deeper upper mantle structure.At present,the processing of magnetotelluric data is still mostly based on the conductivity isotropy assumption.In fact,the anisotropy characteristics of the earth's internal media are widespread,so the isotropy assumption determines that its interpretation results are difficult to reflect the true geological structure characteristics.Forward simulation is the premise of actual data processing and inversion interpretation.Therefore,a three-dimensional magneto-electromagnetic anisotropy forward algorithm is developed to study the effects of anisotropic parameters on the magneto-electromagnetic response,inversion and interpretation of the magneto-electromagnetic anisotropy it is important to understand the real geological structure characteristics.This paper derives the variational equation of the quadratic electromagnetic field in any anisotropic medium,and solves it by the unstructured vector finite element method,and compares the calculation results with the one-dimensional analytical solution,and then compares it with the published two-dimensional anisotropic model.And the comparison of the calculation results of the COMMEMI 3D model verifies the correctness of the algorithm.Based on this algorithm,this paper designs a spherical anomaly model,discusses the effect of anisotropic parameters on apparent resistivity in detail,and delves into the common horizontal anisotropy characteristics in actual production.Unlike previous understandings,the rotation phenomenon of morphology does not accurately reflect the size of the anisotropy parameter.The degree of rotation is also related to the size of the horizontal anisotropy coefficient,which further deepens the understanding of the complexity of the anisotropy effect.Inversion software based on isotropic algorithm is used to invert anisotropic media data,and the obtained inversion results are quite different from the real model,which further illustrates the necessity of anisotropic inversion.