Magnetotelluric Forward Modeling Based On Software Of COMSOL

Three-dimensional magnetotelluric numerical modeling is a hot topic of geophysicalexploration, which is the premise and foundation of three-dimensional inversions. The studyof three-dimensional forward modeling is in the research stage for its poor convergence, longcompute time. COMSOL MULTIPHYSICS is software of large scale finite element method,and we study itsconditions of simulating and some related questions of magnetotellurics bysimulated one-dimensional, two-dimensional and three-dimensional magnetotelluric responsein the article.It have simulated two-dimensional and three-dimensional forward modeling aboutlayered media contained homogeneous half space, two-layer G, three-layer H and K, andverify it with analyticsolutionuse AC/DC and RF module of COMSOL software in the article.The result showed that the software is feasible to simulate magnetotellurics for its highprecision by satisfying error requirement by apparent resistivity relative error control in1%,and phase relative error control in2%. We have simulated low resistivity geologic body,transverse mixing model of low-high resistance, vertical hybrid model of high-low resistance,hybrid model of rock-ore body in two-dimensional space etc, and the result shows that thesame as reference that it is better for TE mode to response the level of interface than TMmode, and it is better for TM mode to response the vertical interface than TE mode. It havesimulated COMMEMI3D₁model in three-dimensional space and drew apparent resistivityand phase contour map and pseudosection map, verify the feasibility about magnetotelluricresponse of three-dimension space through contrast of other reference.It have studied precision problem for two-dimension simulation of three-dimensionalgeologic body in softwareof COMSOL in the paper. The result shows that two-dimensionalsimulation of three-dimensional geological body precision is control in about3%whengeologic body is8km. According to contrast apparent resistivity and phase curve of differentprofile of the same geologic body to two-dimensional simulation, it shows that the longer thegeological body is in the horizontal direction, the closer to the two-dimension simulation by three-dimensional numerical simulation result.It has simulated and contrasted the static effectmodel in two-dimensional and three-dimensional space respectively in software of COMSOL.The result shows the similar change rule in TM mode of two and three dimension, whichapparent resistivity downward migration above the shallow inhomogeneous bodies, upwardmigration on the boundary and external, and the greatest influence on the boundary for lowresistance body near surface. The static shift effect curve is closer in two and three dimensionforward modeling from center to boundary and apart from it.