Efficient geo-electromagnetic modeling techniques for complex geological structures: A karst MT example

In the field of geo-electromagnetic modeling, the unstructured tetrahedral mesh technique holds great potential for realistically simulating various complex geological structures. However, its practical application is limited by the difficulty in building complex geological models and performing tetrahedral meshing. To solve these problems, we propose a novel workflow for geological modeling and tetrahedral meshing, specifically tailored for electromagnetic modeling. Additionally, we have developed a batch code interface that utilizes MATLAB and COMSOL software to reduce manual operations, efficiently construct geophysical models featuring complex geological interfaces and irregular three-dimensional (3D) structures. We will illustrate the workflow using a magnetotelluric (MT) example in a karst geological context. Firstly, we use Non-Uniform Rational B-Splines (NURBS) modeling, point cloud contour extraction, Boolean operations, and geometric operations to reconstruct complex geological structures and load geophysical exploration devices. Secondly, we devise a specialized mesh sequence to achieve local refinement and generate high-quality unstructured tetrahedral meshes. Finally, we have successfully conducted the first MT forward modeling of such fine geological structures, such as topographies, karst caves and tunnels. This study presents a novel approach to complex geophysical modeling with a straightforward, and open-source workflow, which can significantly enhance modeling efficiency.