Impacts of coastal effects on the distortion of magnetotelluric data
YANG Fu-Qiang1,2(), LIAO Hai-Zhi1, WANG Zheng3(), MO Ya-Jun1, LI Ye-Fei1, LIU Ying2
1. Geophysical Survey Institute of Guangxi Zhuang Autonomous Region, Liuzhou 545005, China 2. Hubei Subsurface Multi-Scale Imaging Key Laboratory, School of Geophysics and Geomatics, China University of Geosciences(Wuhan), Wuhan 430074, China 3. Jiangxi Survey and Design Research Institute of Co., Ltd., Nanchang Key Laboratory of Hydrogeology and High-quality Groundwater Resources Exploitation and Utilization, Nanchang 330095, China
Magnetotelluric (MT) data collected from offshore areas are generally distorted due to coastal effects, posing challenges in obtaining true subterranean electrical structures. Based on the model of half-space with seawater, 2D electrical isotropy and anisotropy models, and 3D electrical isotropy model, this study analyzed the distortion patterns of MT responses under coastal effects through forward modeling. Moreover, it conducted 2D and 3D inversions of MT data with or without seawater constraints. Key findings are as follows: (1) The initial frequency points of distortion in MT apparent resistivity curves are closely correlated to the distances from survey points to seawater; (2) Compared to MT responses free from coastal effects, the high-frequency sections exhibit increased amplitudes in real induction vectors only at survey points in offshore areas and higher phase tensor ellipticity, whereas the low-frequency sections display expanded influence areas subjected to coastal effects; (3) Excluding seawater constraints, the inversion results show false anomalies in offshore areas and poor reconstruction effects on subsurface anomalies. Considering seawater constraints, the constrained inversion can effectively suppress the distortion caused by coastal effects. Overall, this study will provide a significant reference for the collection, processing, and interpretation of MT data from offshore areas.
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YANG Fu-Qiang, LIAO Hai-Zhi, WANG Zheng, MO Ya-Jun, LI Ye-Fei, LIU Ying. Impacts of coastal effects on the distortion of magnetotelluric data. Geophysical and Geochemical Exploration, 2024, 48(5): 1284-1293.
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