Research On 1D Magnetotelluric Forward And 1D Parameterized Inversion In Anisotropic Formation

Currently, the inversion of magnetotelluric sounding data is based on the theory of isotropic medium, but as people knowledge constantly deepened, The anisotropic medium of earth gradually aroused people's concern, more and more data show that the crust and upper mantle is the anisotropic medium.The physical property of earth such as elasticity, density conductivity and magnetism are obvious anisotropy, the MT response function is sensitive to the electrical conductivity of different directions, through the surface observation of MT response, and then to MT anisotropy inversion, We can get the conductivity of different directions.Firstly,this paper review the research status of 1D Magnetotelluric forward and 1D Parameterized inversion in anisotropic formation,and then deduce and summarize the theory of forward in anisotropic medium. Different from the 1D isotropic theory, the 1D anisotropic medium produces four impedance tensor response function,namely Z_xx, Z_xy, Z_yx and Z_yy.Due to the conductivity tensor generally have symmetry,Z_xx= Z_yy and Z_xy ? Z_yx.Through calculation the forward of the two layer model,the three layer model and the four layer model,on the other side changing the parameters of the two layer model one by one, namely changing the conductivity tenser element ?₁, ?₂,?₃ and changing anisotropic angle ?_L, ?_D,?_S one by one,We can conclude the result: ?1?the order of magnitude between the auxiliary impedance and the impedance is large,so the auxiliary impedance contains less useful information. ?2?We analyze the parameter sensitivity about the auxiliary impedance and the impedance,the anisotropic angle and thickness are the most sensitive, followed by electrical conductivity;?3? We can conclude that the ?₁ and ?₂ effect the result of forward, ?₃ has not effect;?4?the anisotropic angle aL have effect on the result ,as well as ?_D, ?_S. So the apparent resistivity to the reaction of different direction of resistivity is determined by the resistivity and rotation Angle of model.This paper carries out the full-parameters inversion by using the LMF method,the parameters contain conductivity tenser,three anisotropic angles and thickness. At the same time,Abandoning the auxiliary apparent resistivity,we only fit two main apparent resistivity,and select the right initial model,so the inversion result is ideal. But the full-parameters inversion has more model parameters, the inversion results are greatly influenced by the initial model. If we choose the inappropriate initial model, it can not get reasonable results.The damped least square feasible direction method to some extent inhibited the uncertainty of inversion. By theoretical model inversion computation, the inversion results tally with the actual parameters of the model.