Magnetotelluric Forward In Anisotropic Medium And NLCG Inversion Research

Magnetotelluric (MT) as an important geophysical exploration method, is widely used in actual productions. But in nature, anisotropic rocks are widespread. So it has high practical value on doing MT forward and inversion researching. After more than half a century development, it has gained fruitful achievements in MT forward and inversion researching, but most of the research is based on the theory of isotropic medium, magnetotelluric study in anisotropic medium is relatively few.The first part of this paper mainly studies the magnetotelluric forward modeling using finite element method, first of all, on the basis of isotropic medium, deduce the rectangular-triangle finite element format with Linear interpolation and quadratic interpolation. Realized2D MT high precision forward. Then on the basis of this study above, analyzes the truncated boundary effects in the finite element method simulation. The research shows that the truncated boundary has some effects on the computation when use the finite element method to model two-dimensional magnetotelluric. Truncated boundary results in large error. Through a lot of calculation, this paper summarizes a standard reference about boundary choice when use finite element method to calculate magnetotelluric response. The standard reference is related to the skin depth of minimum frequency participated in the calculation. Finally, considering anisotropic conductivity, deduce electrical conductivity tensor matrix in a simplify mode and analyze finite element format in anisotropic medium with this situation. Numerically simulate two-dimensional electromagnetic response in anisotropic medium. Through the study, find that MT response in the anisotropic medium is different from that in isotropic medium.The second part of this paper study magnetotelluric inversion. Firstly introduce briefly the magnetotelluric nonlinear conjugate gradient inversion. Then calculate and analyse the distributionin in the space with source at observing sites using reciprocity theory. Secondly study the effective profile length in magnetotelluric inversion. Through analysing forward results and inversion results, look for the effective cross section of length in the inversion calculation. Research has shown that the effective sectional length and the skin depth with the lowest frequency of inversion are relative. Finally we study the inversion of anisotropic media and analyse the results with different situation. Studies show that it is always to make false abnormal or serious distortion in the inversion results which is based on isotropic medium theory.Through the magnetotelluric inversion and forward, we can provide reference and help for field magnetotelluric data processing and interpretation, thus can apply magnetotelluric sounding results more effectively.At last, summarize the study contents and principles in the paper. Give the deficiency of the paper and proposes for the following study.