二维局部异常体与起伏地形复杂电磁场的畸变矩阵性质研究  

The study of electromagnetic distortion matrix's property with local abnormal body and topography

作　　者：刘子杰 胡艳芳 汤井田[2,3,4] 原源 邹明亮[1] 董湘龙 LIU Zijie;HU Yanfang;TANG Jingtian;YUAN Yuan;ZOU Mingliang;DONG Xianglong(Research Institute No.230,CNNC,Changsha 410011,China;Hunan Key Laboratory of Nonferrous Resources and Geological Hazards Exploration,Changsha 410083,China;Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring(Central South University),Ministry of Education,Changsha 410083,China;School of Geosciences and Info-Physics,Central South University,South Lushan Road,Changsha 410083,China;East China University of Technology,School of Geophysics and Measurent-contral Technology,Nanchang 330013,China)

机构地区：[1]核工业二三〇研究所,长沙410011 [2]有色资源与地质灾害探查湖南省重点实验室,长沙410083 [3]有色金属成矿预测与地质环境监测教育部重点实验室(中南大学),长沙410083 [4]中南大学地球科学与信息物理学院,长沙410083 [5]东华理工大学地球物理与测控技术学院,南昌330013

出　　处：《物探化探计算技术》2020年第1期64-75,共12页Computing Techniques For Geophysical and Geochemical Exploration

基　　金：中国核工业地质局铀矿地质项目(201719-3);湖南省自然科学基金(2017JJ3002)。

摘　　要：在大地电磁(MT/AMT)中,当浅地表存在小尺度的局部异常体时,在其附近的测点会产生电磁场畸变,导致观测阻抗和区域阻抗之间产生较大的偏差,进而给反演带来困难。阻抗张量分解可以用来减小局部异常体所导致的畸变影响,进而获得更为符合实际情况的区域构造信息,因此对局部异常体和起伏地形所造成的畸变规律的研究,对大地电磁数据处理具有非常重要的意义。这里利用基于非结构化网格的大地电磁正演程序进行正演模拟计算,设计了一个二层介质模型,将其计算结果作为区域电磁场响应信息,同时将存在局部异常体和地形起伏时的计算结果作为观测数据,进而求解电磁场畸变矩阵。通过设置具有电性参数差异的局部异常体以及起伏地形模型,研究其对电磁场所导致的畸变影响。研究结果表明,对于类似模型在研究的频率范围内,具有电阻率差异的局部异常体和地形起伏将会导致电场数据产生较严重的畸变,而磁场在该频段几乎不受畸变影响;在高频段电场畸变矩阵不能简单地认为是实数,其虚部数值较大,畸变矩阵性质更为复杂,且与频率相关。When a small local abnormal body near the surface in the magnetotelluric(MT/AMT),the sites near the body will produce electromagnetic field distortion,and cause the deviation between observation impedance and regional impedance,thus bring greater difficulties for data processing and interpretation.The essence of various the decomposition of MT impedance tensor is to reduce the local distortion caused by abnormal body and obtain the more in line with the regional structure information,so it is significant of the research on the influence of the local abnormal body distortion for data processing in the magnetotelluric.In this paper we design a two layer medium model which is computed by finite-element modeling using unstructured grids.The regional response is the calculation of model without the local abnormal body,and the observation response is the model with the local abnormal body,thus calculate the electromagnetic distortion matrix.We assess the influence of the distortion for the electromagnetic field by setting the local abnormal body with different electrical parameters and the topography.The results show that the local abnormal body with the difference of resistivity and topography will cause a greater galvanic distortion.The magnetic distortion with negligible in the frequency band are studied.The matrix of galvanic distortion becomes complex and frequency-dependant in a lower frequency.

关 键 词：大地电磁(MT/AMT) 局部异常体 起伏地形 畸变矩阵 

分 类 号：P631.2[天文地球—地质矿产勘探]