Three-dimensional marine magnetotelluric modeling in anisotropic media using finite-element method with coupled perfectly matched layer boundary conditions

Abstract Marine Magnetotelluric (MMT) sounding is widely used in marine resource exploration and geophysical research. Its numerical modeling typically involves an open-domain problem, requiring boundary truncation of the simulation area. Compared to traditional boundary conditions, the Perfectly Matched Layer (PML) represents a more efficient and accurate truncation method. However, previous PML theories were limited to scenarios involving variations in a single conductivity and isotropic media, making them inapplicable to complex marine models. In this paper, we further consider the magnetic permeability and propose a PML suitable for variations in both conductivity and permeability. We analyze and study its applicability to anisotropic anomalies and optimize it for low-frequency bands, achieving three-dimensional vector finite element forward modeling with coupled PML boundary conditions. By comparing our results with previous work, we verify that the PML boundary conditions proposed in this paper exhibit high precision and stable performance. Numerical experiments demonstrate that, compared to traditional mesh extension methods, the PML method proposed in this paper reduces the number of mesh elements by over 80% and the calculation time by over 90%, significantly enhancing the efficiency of MMT modeling. The PML proposed in this paper boasts a broader range of applicability and better performance, holding promise for wider applications.