大地电磁资料精细处理和二维反演解释技术研究(一)——阻抗张量分解与构造维性分析

Refined techniques for data processing and two-dimensional inversion in magnetotelluric Ⅰ:Tensor decomposition and dimensionality analysis

本文对大地电磁观测阻抗实施一种数学变换——"共轭阻抗变换",发现转换后的观测阻抗和区域阻抗之间存在特定的关系,这种特定关系不受电场局部畸变的影响,而且同样不需要关于地下区域结构维性的假设,在区域结构是三维的情况下也是成立的.对转换后的观测阻抗采用已有的Swift旋转方法即可求得区域主轴方位角,然后采用最优化方法求取区域阻抗相位、振幅以及畸变因子.同时根据转换后的观测阻抗重新定义了不受电场局部畸变影响的构造维性参数.采用合成理论数据验证了新算法的正确性,和Swift、Bahr、GB、相位张量、WAL方法进行了对比分析,并将新方法应用于实测资料的解释,发展了一套消除局部畸变和进行构造维性分析的MT精细资料处理技术.进一步的工作是将新算法推广到多点多频,并采用最优化技术分解,发展一种稳定性好、多测点多频点的阻抗张量分解技术.

The special relationship between the observed and regional impedance tensors can he derived from a mathematical transformation called conjugate impedance transformation of the magnetotellnric impedance tensor. This relationship is independent of galvanic distortion. No assumption about the dimensionality of the underlying regional conductivity structure is required and this representation is applicable to 3-D regional conductivity structure. Through the transformation of the observed impedance tensor, firstly the regional strike angle can be determined using conventional Swift method. Secondly, the phases, amplitude of regional impedance tensor and distortion parameters are obtained by optimization method. New dimensionality parameters of the geoelectric structure which are free of galvanic distortion are defined based on the transformation of the observed impedance tensors. Synthetic data are used to check the validity of new methods and for comparative analysis of Swift, Bahr, GB, phase tensor, WAL, and new approach. Finally, the new methods are applied to the field data and a set of refined processing techniques for magnetotelluric data including removing local distortion and dimensionality analysis are developed. The future work is to extend this new strategy to multisite, multi-frequency decomposition by using optimization method and develop a more stable multisite, multi-frequency tensor decomposition for magnetotelluric data processing.