1. State Key Laboratory of Nuclear Resources and Environment, East China University of Technology, Nanchang, Jiangxi 330013, China; 2. Engineering Research Center for Seismic Disaster Prevention and Engineering Geological Disaster Detection of Jiangxi Province, Nanchang, Jiangxi 330013, China; 3. Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring(Central South University), Ministry of Education, Changsha, Hunan 410083, China
Abstract：In order to improve the solving accuracy of wide-field electromagnetic method forward modeling, an adaptive finite element technique of a posterior error estimation strategy based on normal continuity of current density is used to realize three-dimensional(3D) wide-field electromagnetic method forward modeling. Firstly, based on Maxwell's equations, the electric field equations satisfied by the controlled field source are derived. The vector finite element technique with unstructured tetrahedral meshes is used to discretize the electric field equations, which results in large and sparse complex linear equations. Then, a posterior error estimation strategy based on normal continuity of current density is designed and incorporated into large and sparse complex linear finite element equations, and a high-precision 3D wide-field electromagnetic method forward calculation is achieved. Finally, an optimized Brent-Dekker root-finding algorithm is used to improve the stability of wide-field apparent resistivity, and the correctness of the adaptive algorithm is verified by using a layered media model. At the same time, typical terrain and spherical geo-electric models are designed to analyze the response characteristics of the wide-field electromagnetic method. The results show that the adaptive finite element method can reduce the low efficiency caused by artificial mesh design and improve the accuracy of forward modeling by mesh refinement in key regions. In addition, compared with CSAMT (controlled source audiofrequency magnetotellurics), the wide-field electromagnetic method has a larger exploration depth and range and is less affected by non-plane waves under the same transmit/receive distance.
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