3D magnetotelluric forward modeling using an edge-based finite element method with a variant semi-unstructured conformal hexahedral mesh

This research presents the implementation of a semi-structured hexahedral mesh for the edge-based finite element method, which is utilized in solving 3D magnetotelluric (MT) modeling. The semi-unstructured conformal hexahedral mesh comprises an unstructured quadrilateral mesh for the horizontal directions and an automatically generated non-uniform mesh for the vertical direction. The edge-based finite element approach, utilizing this mesh pattern, has been developed. We present, compare, and discuss the accuracy, efficiency, and flexibility of our MT forward modeling codes for various 3D models. Numerical experiments indicate that our approach provides good accuracy when local mesh refinement is applied around sites and within the focus zone, yielding superior results compared to the conventional edge-based finite element method with a standard structured hexahedral mesh. The reliability of the developed codes was confirmed through comparisons with analytical solutions, benchmark COMMEMI3D, and topographic models. Furthermore, our developed codes, which incorporate a semi-unstructured conformal hexahedral mesh, exhibit valuable features, such as managing topographic and complex zones, and refining the local mesh for a 3D domain over a structured hexahedral mesh. However, they require fewer mesh data points, such as nodes and elements, within the mesh.