Adaptive Finite Element Numerical Simulation Of2D MT With The Topography

Magnetotelluric sounding (MT) is a frequency domain electromagnetic sounding method, which is usually used for the research of deep geological structure through observing the natural electromagnetic field with a wide frequency range. Magnetotelluric method is usually carried out on the topographic regions, the effect of complex terrain to the measured field data is very large, which will bring great difficulties to the processing and interpretation of the data, so, the numerical modeling of the MT data with terrain is necessary.For many numerical modeling techniques, finite element method is applied widely, when the traditional finite element method is used to simulate the model, the mesh is generally artificially set, the rectangular unit and the triangular unit based on rectangular unit are usually used in two-dimensional simulation, if the geological structure is relatively simple and the model is regular, the result of simulation is good, but the geological structure is usually complex and the model is irregular, if we still use the regular grid, the numerical simulation will produce large errors, which will reflect in the simulation results.In order to solve the above problems, this paper uses adaptive finite element method to simulate the effect of topography on magnetotelluric data. A posteriori error estimator-dual error estimate weighting method is used to control the adaptive refinement and encryption. Through simulating the horst, graben, ridge, valley and combination of terrain, we summarized the effect laws of topography on the magnetotelluric response curves:the effect of raised terrain on magnetorelluric two polarization modes is larger than the canyon; the TM polarization mode is more influenced by topography than the TE polarization mode; the apparent resistivity of TM polarization mode will get smaller and smaller as the frequency increasing; the impedance phase of TM mode, the apparent resistivity and impedance phase of TE mode will increase with frequency increasing.