3D edge-based and nodal finite element modeling of magnetotelluric in general anisotropic media

As a passive-source geophysical exploration technology, the magnetotelluric (MT) method has been widely used in various domains such as oil, gas, and solid minerals by several researchers .Extensive actual MT real data have shown the existence of electrical anisotropy in the Earths interior.Therefore, MT anisotropy is currently a subject of significant interest, to which end several studies have been conducted. At present,most modeling based on the electric (magnetic) field governing equations has the problem of converge slowly at low frequencies for iterative solvers.Because, a considerable null space arises from curl-curl operators at low frequencies, which leads to high ill-conditioning of the stiffness matrix and unstable spurious modes.And for large-scale EM modeling problem, direct solvers may not meet the memory requirements. So, the low frequency convergence problem needs to be solved. A popular static divergence correction technique has been applied to address these limitations, but some complex calculations have been added. In this study, we present an FEM based on A- potentials for 3D MT forward modeling in general anisotropic media. Edge-based FEM was used to discretize the magnetic vector and nodal FEM was used to discretize the electric scalar potential . To the best of our knowledge, this method has not been used in previous studies. We designed 1-D and 3-D models to verify the correctness of our modeling code.