Three-dimensional arbitrarily anisotropic modeling for time-domain airborne electromagnetic surveys
Huang Wei1,3, Ben Fang1,3, Yin Chang-Chun2, Meng Qing-Min1, Li Wen-Jie1, Liao Gui-Xiang1, Wu Shan1, and Xi Yong-Zai1
1. Institute of Geophysical and Geochemical Exploration, Chinese Academy of Geological Science, Langfang 065000, China.
2. College of Geo-exploration Sciences and Technology, Jilin University, Changchun 130021, China.
3. Laboratory of geophysical Electromagnetic Probing Technologies, Ministry of land and Resources, Langfang 065000, China.
Abstract Electrically anisotropic strata are abundant in nature, so their study can help our data interpretation and our understanding of the processes of geodynamics. However, current data processing generally assumes isotropic conditions when surveying anisotropic structures, which may cause discrepancies between reality and electromagnetic data interpretation. Moreover, the anisotropic interpretation of the time-domain airborne electromagnetic (TDAEM) method is still confined to one dimensional (1D) cases, and the corresponding three-dimensional (3D) numerical simulations are still in development. In this study, we expanded the 3D TDAEM modeling of arbitrarily anisotropic media. First, through coordinate rotation of isotropic conductivity, we obtained the conductivity tensor of an arbitrary anisotropic rock. Next, we incorporated this into Maxwell’s equations, using a regular hexahedral grid of vector finite elements to subdivide the solution area. A direct solver software package provided the solution for the sparse linear equations that resulted. Analytical solutions were used to verify the accuracy and feasibility of the algorithm. The proven model was then applied to analyze the effects of arbitrary anisotropy in 3D TDAEM via the distribution of responses and amplitude changes, which revealed that different anisotropy situations strongly affected the responses of TDAEM.
This paper is financially supported by National Nonprofit institute Research Grant of IGGE (Nos. AS2017J06, AS2017Y04, and AS2016J10), Survey on coastal area for airborne magnetic method of UNV in Jiangsu (No. DD20160151-03), Key National Research Project of China (No. 2017YFC0601900), Key Program of National Natural Science Foundation of China (No. 41530320), Natural Science Foundation (No. 41274121), and China Natural Science Foundation for Young Scientists (No. 41404093).
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