大地电磁三维宏观电各向异性识别及定量解释

Magnetotelluric (MT) is one of the important tools for investigating the geologic process of the orogenic belt and subduction zone. As the considerable evidence for the lithospheric tectonic deformation, the electrical anisotropy can provide the necessary restraint for the geodynamic model. Large high-quality MT data has been acquired from several continental-scale lithospheric exploration programs. This offers the good foundation for researching the lithospheric electrical anisotropy, but raises the imperious demand for the meticulous interpretation. Based on the MT forward responses of typical anisotropy models, we propose to analysis and summarize the response parameters and their combinations for discerning the electrical anisotropy. By 1D anisotropic inversion and 3D isotropic inversion, we propose to delineate the distribution of the 3D anisotropy body. Furthermore, we propose to seek the method for constructing the 3D model with the anisotropy and isotropy to obtain the optimal mixture model. We aim to identify and interpret the electrical anisotropy in 3D media from MT data, which will provide the 3D dynamic information of electrical structures for researching the geodynamic evolution.

大地电磁方法是研究造山带、俯冲带等活动地质构造过程的重要工具之一。宏观电各向异性信息作为推断岩石圈构造变形过程的重要证据，能够为地球动力学演化模型提供必要的约束。现今全球多国陆续实施了大陆尺度的岩石圈电性结构探测计划，并已采集大量优质的长周期大地电磁数据，为研究岩石圈电各向异性提供了良好的基础条件，但对大地电磁三维精细化解释的迫切需求也日渐明显。基于此，本项目拟从典型各向异性地电模型的大地电磁正演响应出发，系统地分析和总结可识别电各向异性存在性的响应参数及其组合；通过较成熟的一维各向异性反演和三维各向同性反演，详尽展开圈定三维电各向异性空间分布范围的方法研究；并探索构造三维各向异性与各向同性混合地电模型的手段，以获得可靠的精细化最优混合模型。本项目以期实现识别与定量解释三维介质中的大地电磁宏观电各向异性，为研究地球动力学演化问题提供来自电性结构的三维“动态”信息。

如何识别和定量解释大地电磁响应中的宏观电各向异性信息是国内外研究的热点和难点。本研究基于典型二维和三维各向异性地电模型的大地电磁正演响应，分析和归纳了电各向异性对相位张量和感应矢量以及维数性分析的影响规律，结合一维各向异性反演以及二维和三维各向同性反演对电各向异性的响应特征，提出了一套识别大地电磁响应中电各向异性信息的技术方案，并将其应用到了美国西北部卡斯卡迪亚俯冲带和琼北第四纪火山区岩石圈电各向异性的研究中。本研究为深化地球内部电性结构的认识提供了一种有效手段，为研究岩石圈构造演化提供了一种新的视角。