Japan Geoscience Union Meeting 2023

Presentation information

[E] Oral

S (Solid Earth Sciences ) » S-EM Earth's Electromagnetism

[S-EM14] Electric, magnetic and electromagnetic survey technologies and scientific achievements

Tue. May 23, 2023 3:30 PM - 4:45 PM 103 (International Conference Hall, Makuhari Messe)

convener:Kiyoshi Baba(Earthquake Research Institute, The University of Tokyo), Tada-nori Goto(Graduate School of Science, University of Hyogo), Yuguo Li(Ocean University of China), Wiebke Heise(GNS Science, PO Box 30368, Lower Hutt, New Zealand), Chairperson:Yuguo Li(Ocean University of China), Keiichi Ishizu(University of Hyogo)

4:00 PM - 4:15 PM

[SEM14-08] An efficient multigrid technique for 3D electromagnetic modeling in general anisotropic conductivity media

*Jian Li1,2, Jianxin Liu1,2, Yasuo Ogawa3, Rongwen Guo1,2, Yongfei Wang1, Gangqiang Yang1 (1.Central South University, School of Geosciences and Info-Physics, Changsha, China, 2.Central South University, Hunan Key Laboratory of Nonferrous Resources and Geological Hazards Exploration, Changsha, China, 3.Tokyo Institute of Technology, Volcanic Fluid Research Center, Tokyo, Japan)


Keywords:Magnetotelluric, Numerical modeling, Multigrid solver, Anisotropic

The magnetotelluric (MT) is the main method to study the electrical structure of the subsurface employing natural alternating electromagnetic fields, which has the characteristics of large penetration depth and high resolution, and is widely used in hydrocarbon exploration, geothermal investigations, ore-deposit surveys and deep structure mapping. In recent years, a large body of literature has focused on conductivity anisotropy on the earth.
MT forward modeling is an effective tool for analyzing the electromagnetic field in anisotropic conductivity media. However, the modeling of full anisotropy has not been well solved, as the boundary problem of electromagnetic fields is much more complex than that of isotropic media. As a result, the effect of conductivity anisotropy is often neglected when interpreting electromagnetic data. In order to provide a reasonable interpretation of MT data in anisotropic media, it is necessary to investigate effective modeling techniques for electromagnetic fields and to invoke the technique several times during the 3D inversion. In addition, the condition number of the coefficient matrix is worsened by the difference in conductivity and a large number of grids, which non-linearly increases the computation time of traditional iterative solvers. The Multigrid (MG) algorithm is widely used for solving electromagnetic equations due to its efficiency. However, the existing isotropic MG algorithm cannot be used directly for solving the electromagnetic field in anisotropic media.
In this paper, the original discrete grid is coarsened several times in the MG scheme. Then the linear equations are constructed under different degrees of coarsened grids. The smoothing algorithm is invoked multiple times to solve the equations, significantly improving computational efficiency.