自适应有限元法的大地电磁二维各向异性正反演

发布时间：2018-03-19 15:01

本文选题：大地电磁法　切入点：二维反演　出处：《石油地球物理勘探》2016年04期 　论文类型：期刊论文

【摘要】：电性各向异性广泛存在于地壳和上地幔范围内,对观测电磁场有不可忽视的影响。大地电磁法能够探测大范围深部电性结构并反映其各向异性特征,但目前关于该方法各向异性二维正反演的研究还有待加深。利用基于非结构网格的自适应有限元法求解对角各向异性情况下大地电磁正演控制方程,既有利于起伏地形和复杂地质构造的建模,又便于模拟包含多种尺寸结构的地电模型;网格的自动细化可避免人为网格划分导致的计算误差并可提高计算效率。反演算法则采取了经典模型空间Occam策略,使得模型的搜索过程非常稳定,能在较少迭代次数内获得合理的反演结果。对经典四层层状模型和二维各向异性块体模型进行了正演模拟试算,并分别与一维准解析解、二维有限差分数值解结果进行对比,验证了正演算法的准确性;最后对一复杂海底起伏各向异性模型进行了反演试算,反演结果准确反映了各向异性异常体的存在,并成功地还原了真实模型的主要电性特征。
[Abstract]:The electrical anisotropy exists widely in the crust and upper mantle and has an important influence on the observation of electromagnetic field. The magnetotelluric method can detect the electrical structure in a wide range of depth and reflect its anisotropic characteristics. However, the research on anisotropic two-dimensional forward and inverse modeling of this method needs to be deepened. An adaptive finite element method based on unstructured meshes is used to solve the magnetotelluric forward control equations under diagonal anisotropy. It is not only beneficial to the modeling of undulating terrain and complex geological structure, but also convenient to simulate the geoelectric model with various sizes. The automatic mesh thinning can avoid the error caused by artificial mesh generation and improve the computational efficiency. The inversion algorithm adopts the classical model space Occam strategy, which makes the search process of the model very stable. Reasonable inversion results can be obtained in fewer iterations. The forward simulation of the classical four layer model and the two dimensional anisotropic block model is carried out, and the results are compared with the results of one dimensional quasi analytical solution and two dimensional finite difference numerical solution, respectively. The accuracy of the forward algorithm is verified, and the inversion of a complex seafloor undulating anisotropic model is carried out. The inversion results accurately reflect the existence of anisotropic anomaly and successfully restore the main electrical characteristics of the real model.
【作者单位】：中国地质大学地球物理与空间信息学院地球内部多尺度成像湖北省重点实验室;中国海洋大学海洋地球科学学院;
【基金】：国家自然科学基金项目(41274077,41474055) 湖北省自然科学基金项目(2015CFA019)联合资助
【分类号】：P631.325

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