基于非结构三角网格的海洋CSEM和MT二维联合反演研究

doi:10.11720/wtyht.2021.1384

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Abstract

In this paper, an unstructured triangular grid combined with a fast Occam algorithm is used to carry out a two-dimensional joint inversion study of marine controlled source electromagnetic (CSEM) and magnetotelluric (MT) data. The unstructured triangular grid can accurately simulate undulating terrain and complex geological structures. Fine meshing is used for the inversion target area, and the other area is divided by coarse meshing, which reduces unnecessary calculations under the premise of meeting accuracy. For the purpose of realizing the joint inversion, the CSEM and MT data are assembled to the same inversion data set, and the relevant weight factors of the CSEM and MT data are constructed from the joint inversion data weight formula, which controls the fitting weights of different data. Finally, inversion calculations are performed on different models, and the results show that the joint inversion has a higher degree of recovery of seafloor structures and anomalous bodies than a single inversion, which verifies the reliability of the joint inversion algorithm.

Key words： CSEM MT Occam joint inversion unstructured grid

Received: 29 July 2020 Published: 01 March 2021

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	Zheng-Min AI
	Yi-Xin YE
	Wen-Wu TANG
	Xiao CHEN
	Jia-Ming DU

Cite this article:

Zheng-Min AI,Yi-Xin YE,Wen-Wu TANG, et al. A test study of 2D joint inversion of marine CSEM and MT based on unstructured triangular grid[J]. Geophysical and Geochemical Exploration, 2021, 45(1): 149-158.

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https://www.wutanyuhuatan.com/EN/10.11720/wtyht.2021.1384 OR https://www.wutanyuhuatan.com/EN/Y2021/V45/I1/149

Schematic diagram of the joint inversion process

Two-dimensional model with flat seafloor

Schematic diagram of adaptive forward meshing (taking CSEM mesh as an example)
a—the first optimized mesh containing 1 445 nodes and 2 849 triangular elements; b—the final mesh after the 12th adaptive refinement, containing 43 127 nodes and 86 139 triangular elements; the diagram only shows the abnormal area in the middle part of the model

Inversion mesh division of the initial model

Inversion results of the simple two-dimensional model
a—MT data inversion result; b—CSEM data inversion result; c—CSEM+MT data joint inversion result

Comparison of pseudo-section diagrams of MT observation data (top) and MT forward responses of joint inversion model (bottom)

Amplitude and phase fitting diagram of the CSEM observation data and model response of the joint inversion result with the emission source at y=0

List of time-consuming, RMS misfit, roughness and iteration number of inversion

Joint inversion results with different q value
a—q=2;b—q=0.5;c—q=10;d—q=0.1

The final RMS value of joint inversion with different q value

Two-dimensional complex ocean model

Inversion mesh division of the initial model

Inversion result
a—MT data inversion result; b—CSEM data inversion result; c—CSEM+MT data joint inversion result; d—RMS diagram

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