The FEM for modeling 2-D MT with continuous variation of electric parameters within each block

To model arbitrarily shaped two-dimensional topography and structures in field work, triangular element grid was used in the finite element method (FEM). In view of the fact of continuous variation of the subterranean rock-mineral electric parameters, the electromagnetic field and some electric parameters of models are designed to bilinear variation within each triangular element in our numeric modeling method, and which is developed for modeling two-dimensional magnetotelluric (MT) under the field topography condition. The calculation formulae of the auxiliary field, and the definition of apparent resistivity and impedance phase are deduced according to the relationship between the main fields of the three nodes and the linear shape function within each element. By calculating a continuous medium model and two topography models set up by other scholars to test our method, the result of our method shows a high accuracy (the mean square error is less than 1%), and the results of modeling two topography models accord with other scholar's, too. Through modeling a sloping interface abnormity body, we find that our method can model arbitrarily complicated terrain and geoelectric bodies preferably.