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Finite Element Numerical Simulation Of Two-dimensional Anisotropic Magnetotelluric

Posted on:2013-04-07Degree:MasterType:Thesis
Country:ChinaCandidate:M X YangFull Text:PDF
GTID:2230330377450042Subject:Earth Exploration and Information Technology
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Based on the natural alternating electromagnetic field as the field sources, the magnetotelluric sounding method-a frequency domain sounding method-is usually used to study the crust and upper mantle structure. At present, two-dimensional isotropic MT forward problem has been basically solved. This paper assumes that in the anisotropic medium one of the principal axes is conincident with direction perpendicular to the stratification, the another is parallel to the structural strike. Under these assumptions, this essay mainly study forward modeling numerical simulation algorithms of magnetotelluric sounding in two-dimensional anisotropic media. All the studies can help to the inversion problem in the future.On the basis of the Maxwell equations and the electrical properties of the layered media, combined with magnetotelluric sounding method of internal and external boundary conditions, the paper deduced that the variational equations of the electromagnetic field of two-dimensional anisotropic earth, dividing the entire region into many rectangular elements and interpolating with a double linear interpolation function in each element, then the variation equation is converted into a system of linear algebric equations. In the process of solving linear equations, we used the program that storaging the overall coefficient matrix by variable bandwidth. By solving linear algebraic equations, we can get the main field value of the nodes. By the relationship between the main field value and the rectangular element linear interpolation shape function, we can calculate the auxiliary field value. By these field values, we can calculate the apparent resistivity values and the impedance phase values in the two polarization modes.By comparing the one-dimensional analytical solution and the numerical solution of anisotropic media in the Horizontal layered model, the validity and correctness of the forward program can be verified which shall also explain the anisotropy of the layered media cannot be ignored; By the horizontal distribution, vertical distribution and V-shaped distribution anomalous bodies, it will show that with the angle from zero degree to tilt to ninety degrees, comparing with isotropic conditions the abnormal magnitude will change form bigger than it to less than it; By the Syncline-shaped low resistivity body model, sounding curves of the measured point which is closed to the anomalous body have large differences between isotropic and anisotropic conditions; By the anomalous amplitude variation of anticline-shaped low resistivity body model in different anisotropic coefficient, it is obvious that the bigger the anisotropic coefficient is, the bigger anomalous amplitude is; By analyzing the double V shaped ground model and the M-type electric model validation in the anisotropic conditions the forward results may reflect the subsurface model form; Consolidated statement: even the isotropic and anisotropic conditions have the same average resistivity, the anisotropic effect in the interpretation of the magnetotelluric data shall not be neglected in any way.
Keywords/Search Tags:magnetotelluric sounding method, anisotropic, isotropictwo-dimensional positive modeling, finite element method, rectangular elementmesh, linear interpolation
PDF Full Text Request
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