相位张量分析约束下的大地电磁测深阻抗张量分解方法研究  

Study of Magnetotelluric Impedance Tensor Decomposition Under the Constraint of Analysis of Phase Tensor

作　　者：谢成良[1,2] 魏文博[1,2,3] 金胜[1,2] 叶高峰[1,2] 景建恩[1,2] 张乐天[1,2] 董浩[1,2] 张帆[1,2] 王辉[1,2] 姚硕[1,2] 

机构地区：[1]中国地质大学(北京)地球物理与信息技术学院,北京100083 [2]中国地质大学(北京)地下信息探测技术与仪器教育部重点实验室,北京100083 [3]地质过程与矿产资源国家重点实验室,北京100083

出　　处：《地球物理学进展》2013年第3期1208-1218,共11页Progress in Geophysics

基　　金：国家深部探测技术与实验研究专项SinoProbe-01-01和SinoProbe-01-02;国家自然科学基金委青年科学基金项目(40904025);中央高校基本科研业务费(2011YXL058)资助

摘　　要：由于浅部、局部不均匀三维异常体的影响,大地电磁测深(Magnetotelluric,MT)观测数据往往需要进行畸变校正.本文针对相位张量不受局部电场畸变影响的特点,研究相位张量分析约束下的大地电磁测深(MT)阻抗张量GB(Groom-Bailey)分解方法.分析由相位张量得到的相关参数,结合初步电性结构维性判断及二维或近似二维电性结构条件下电性主轴方向等信息,设计较合理的GB阻抗张量分解初始模型,提高GB算法的稳定性及可靠性.同时,在传统GB分解求解模型的基础上,将各向异性参数引入目标函数,并采用共轭梯度法进行模型的最优化求解.理论数据计算结果表明,MT阻抗张量GB分解方法的计算结果,依赖于初始模型中电性主轴角、阻抗张量值等参数的选择,相位张量分析约束下的GB分解方法能有效改善算法的稳定性和计算结果的可靠性.此外,研究表明,在合理的初始模型选择下,较之传统的GB分解方法,尽管各向异性参数仍旧无法求出,但带各向异性参数的GB分解方法在计算效率和结果可靠性方面均具有一定的优势.选择实际大地电磁测深点数据进行方法验证,取得了理想的电性分析结果.The observational data of Magnetotelluric （MT） sounding is necessary to be corrected of distortion because of the effect of small, shallow, local inhomogeneous 3D body. The purpose of this research is to get more reliable regional geo-electric strike and MT sounding data under the assumption that the regional conductivitystructure is 2D. We extended Groom-Bailey （GB） decomposition method under the constraints of phase tensor which was independent of local distortion from ＇galvanic effects. Subsurface conductivity information such as regional strike could be obtained from analysis of phase tensor, and which was considered as constraints to get better initial model for GB decomposition in order to improve the stability and reliability. In addition, different with traditional algorithm, we took anisotropy factor into the objective function and solved the optimization problem with Conjugate Gradient （CG） strategy. We added different Gaussian noise into synthetic data to test the sensitivity of each item in the initial model. The results showed that the reliability of GB decomposition of MT impedance tensor was strongly dependent on initial value of strike and impedance tensor. And the GB decomposition under the constraints of phase tensor was demonstrated to improve validity a lot. Moreover, the study showed GB algorithm with anisotropy factor performed well than the traditional way in terms of accuracy and computational cost, although there was no way to calculate the anisotropy parameters without any assumption. We compared decomposition results of our method with the classic muhisite, multi-frequency way with real MT data from north-west china. And the results showed our study could get reliable conductivity analysis information. Further study into getting anisotropy parameters under special constraints is necessary. On the other hand, research of multisite, multi-frequency decomposition with the constraints from phase tensor should he further studied in relation to the too complicated statistical re

关 键 词：大地电磁测深 阻抗张量分解 相位张量 GB分解 

分 类 号：P318[天文地球—固体地球物理学]