Application of 2D inversion of magnetotelluric data bearing terrain information based on an unstructured mesh
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摘要: 本文对基于自适应非结构三角形网格的带地形MT数据二维Occam反演进行应用研究。自适应非结构三角形网格能够准确地模拟起伏地形和复杂地质构造,正演网格由有限元解的后验误差估计指导自动细化,保证了模型响应的准确性,反演网格在反演目标区域采用精细网格剖分,在模型边界区域采用粗网格剖分,在满足反演精度的前提下减少了不必要的反演参数。基于快速Occam正则化反演方法,采用伴随方程法推导灵敏度矩阵并结合加权平方法计算模型粗糙度。通过对陆地起伏地形模型和起伏海底模型反演试算,验证了算法的精确性和适用性,能够对陆地及海底起伏地形下的多尺度结构进行成像。然后,将该方法应用于克拉玛依后山区域的实测数据反演处理中,反演得到的电阻率结构与地质资料以及采用非线性共轭梯度反演所得结果相吻合。Abstract: This paper focuses on the application of the 2D inversion of magnetotelluric data that bear terrain information based on an unstructured adaptive triangular mesh. An adaptive unstructured triangular grid can be used to accurately simulate undulating terrain and complex geological structures. The adaptive unstructured triangular grids for magnetotelluric forward modeling are automatically refined using the a posteriori error estimation with the finite element solution, which ensures the accuracy of the model response. As for adaptive unstructured triangular grids for magnetotelluric inversion, fine mesh generation is adopted for the inversion target areas, while coarse grid generation is utilized for the boundary areas of the model, thus reducing unnecessary inversion parameters on the premise of satisfying the inversion accuracy. According to the inversion of an undulating-terrain model of land and an undulating-seabed model, the accuracy and applicability of the algorithm are verified and the algorithm can be used to image the multi-scale structures under the undulating terrain of land and seabed. Then, the method was applied to the inversion of the measured data of the Houshan area in Karamay. As a result, the resistivity structure obtained through the inversion was consistent with the geological data and the results obtained through the nonlinear conjugate gradient inversion.
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Key words:
- unstructured mesh /
- MT /
- 2D inversion /
- terrain /
- Karamay
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