Exploration Geophysics Exploration Geophysics Society
Journal of the Australian Society of Exploration Geophysicists
RESEARCH ARTICLE

Divergence correction schemes in finite difference method for 3D tensor CSAMT in axial anisotropic media

Kunpeng Wang 1 Handong Tan 1 2 3 Zhiyong Zhang 1 Zhiqiang Li 1 Meng Cao 1
+ Author Affiliations
- Author Affiliations

1 School of Geophysics and Information Technology, China University of Geosciences (Beijing), Beijing 100083, China.

2 Key Laboratory of Geo-detection (China University of Geosciences), Ministry of Education, Beijing 100083, China.

3 Corresponding author. Email: thd@cugb.edu.cn

Exploration Geophysics 48(4) 363-373 https://doi.org/10.1071/EG15074
Submitted: 6 August 2015  Accepted: 18 April 2016   Published: 12 May 2016

Abstract

Resistivity anisotropy and full-tensor controlled-source audio-frequency magnetotellurics (CSAMT) have gradually become hot research topics. However, much of the current anisotropy research for tensor CSAMT only focuses on the one-dimensional (1D) solution. As the subsurface is rarely 1D, it is necessary to study three-dimensional (3D) model response. The staggered-grid finite difference method is an effective simulation method for 3D electromagnetic forward modelling. Previous studies have suggested using the divergence correction to constrain the iterative process when using a staggered-grid finite difference model so as to accelerate the 3D forward speed and enhance the computational accuracy. However, the traditional divergence correction method was developed assuming an isotropic medium. This paper improves the traditional isotropic divergence correction method and derivation process to meet the tensor CSAMT requirements for anisotropy using the volume integral of the divergence equation. This method is more intuitive, enabling a simple derivation of a discrete equation and then calculation of coefficients related to the anisotropic divergence correction equation. We validate the result of our 3D computational results by comparing them to the results computed using an anisotropic, controlled-source 2.5D program. The 3D resistivity anisotropy model allows us to evaluate the consequences of using the divergence correction at different frequencies and for two orthogonal finite length sources. Our results show that the divergence correction plays an important role in 3D tensor CSAMT resistivity anisotropy research and offers a solid foundation for inversion of CSAMT data collected over an anisotropic body.

Key words: divergence correction, finite difference, resistivity anisotropy, tensor CSAMT.


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