二维电各向异性对大地电磁数据维性分析的影响  

Influence of two-dimensional electrical anisotropy on dimensionality analysis of magnetotelluric data

作　　者：孙浩 刘营[1] 王正 姬肖杰 赵伟 陈超[1] SUN Hao;LIU Ying;WANG Zheng;JI XiaoJie;ZHAO Wei;CHEN Chao(Hubei Subsurface Multi-Scale Imaging Key Laboratory,School of Geophysics and Geomatics,China University of Geosciences,Wuhan 430074,China;Guangzhou Traffic Design and Research Institute Co.,Ltd,Guangzhou 510599,China)

机构地区：[1]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,武汉430074 [2]广州市交通设计研究院有限公司,广州510599

出　　处：《地球物理学报》2024年第12期4794-4805,共12页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(42430307,41904079);中央高校基本科研业务费专项资金资助项目(CUG2106338)资助.

摘　　要：大地电磁方法是探测岩石圈电性结构的主要方法之一.大地电磁数据的维性分析可以推断地电结构性质进而确定适合的建模方法(1D、2D或3D).然而,当地下介质为电各向异性时,对维性分析的影响研究相对较少.本文基于含电各向异性体的二维理论模型,利用常用的维性分析方法WAL准则、相位张量和感应矢量,研究了电各向异性对大地电磁数据维性分析的影响;根据模型的真实维度信息及维性分析结果,进行了各向同性反演计算,探讨了电各向异性对反演的影响.研究结果显示,方位各向异性和电各向异性结构复杂度是影响大地电磁维性分析的重要因素,方位各向异性会造成明显的“假三维性”.基于模型真实维性的二维各向同性反演表明,TE+TM数据集联合反演结果在电各向异性块体区域出现高低阻交错的电性结构;TE、TM数据集单独反演结果呈现的差异性与电各向异性分布特征紧密相关,TM数据集反演结果更加合理,方位各向异性响应的TE数据集反演出现“T”字形低阻异常.根据维性分析结果的三维各向同性反演表明,倾子数据集反演可以有效识别方位角的变化,而阻抗数据集反演容易受到电各向异性畸变的影响.研究表明,识别并考虑电各向异性影响的大地电磁维性分析新方法将是今后的一个研究重点,有助于提高实测数据的解释精度.The magnetotelluric(MT)method is one of the main methods for imaging the electrical resistivity structure of the whole lithosphere.Dimensionality analysis of MT data can infer the properties of the subsurface geoelectric structure and is fundamental in determining the most suitable modeling method(1D,2D or 3D).However,when the subsurface exhibits electrical anisotropy,its effect on dimensionality analysis is relatively less studied and more unknown.Here,based on two-dimensional theoretical models with electrical anisotropy,we used WAL criterion,phase tensor and induction vector to study the effect of anisotropy on dimensionality analysis of MT data.According to the real dimensional information of our models and the results of dimensionality analyses,isotropic inversions were subsequently carried out to study the influence of electrical anisotropy on the inversions.Our research shows that the azimuthal anisotropy and the structural complexity of electrical anisotropy are important factors that influence the dimensionality analysis.Azimuthal anisotropy can result in apparent“false three-dimensionality”.According to two-dimensional isotropic inversions,joint inversions of TE+TM modes show an electrical structure interleaved by high and low resistivity anomalies in the true anisotropic body region.The differences in the separate inversions of the TE and TM modes are closely related to the distribution of electrical anisotropy.The inversion results of the TM dataset are more reasonable,while inversions of the TE dataset from the responses of azimuth anisotropy models show a“T”-shaped low-resistivity anomaly.According to the 3D inversions indicated by dimensional analysis,inversion of the tipper can effectively identify the change of azimuth angle,while the impedance is susceptible to the distortion of electrical anisotropy.Our study suggests that dimensionality analysis of MT data with identifying and considering electrical anisotropy will be a key research point in future,which can help to improve the interpr

关 键 词：大地电磁 维性分析 电阻率 各向异性 反演 

分 类 号：P319[天文地球—固体地球物理学] P631[天文地球—地球物理学]