天然电场选频法的响应特性分析与应用  

Analysis and application of the responses of the frequency selection method of telluric electricity field

作　　者：杨天春[1] 胡峰铭 于熙 付国红[1] 李俊 杨追 YANG Tian-Chun;HU Feng-Ming;YU Xi;FU Guo-Hong;LI Jun;YANG Zhui(School of Earth Sciences and Spatial Information Engineering,Hunan University of Science and Technology,Xiangtan 411201,China;Nuclear Geological Survey of Hunan,Changsha 410007,China;Hunan Puqi Geologic Exploration Equipment Institute,Changsha 410000,China)

机构地区：[1]湖南科技大学地球科学与空间信息工程学院,湖南湘潭411201 [2]湖南省核地质调查所,湖南长沙410007 [3]湖南普奇地质勘探设备研究院,湖南长沙410000

出　　处：《物探与化探》2023年第4期1010-1017,共8页Geophysical and Geochemical Exploration

基　　金：国家自然科学基金项目(42074219)。

摘　　要：静态效应是频率域电磁法应用中不可避免的一种物理现象,通常通过校正方法进行压制或消除。本文提出一种直接利用天然电磁法的静态效应进行浅部电性异常体勘探的新思路,利用天然电场选频法(FSM)能够测量天然交变电磁场在地表所产生的几个不同频率的水平电场分量来研究地下介质的电性变化。首先采用二维有限单元法对FSM开展正演模拟,模拟结果表明:当近地表存在低阻异常体时,地表沿测线方向的水平电场分量曲线与FSM实测曲线形态相同,在低阻体的上方出现十分明显的低电位异常;当计算的频率点增多时,电场分量剖面曲线及其拟断面图会出现静态偏移现象,发现FSM异常实质上主要是静态效应所致。FSM实践应用成果及钻井验证结果表明,当有地下水存在时,FSM实测的剖面曲线及拟断面图会出现明显的静态效应现象,且与CSAMT的勘探成果一致。通过理论与实践可知,直接利用天然电磁场的电场分量开展浅部电性异常体的勘探具有可行性,今后也可利用频率域电磁法的静态效应现象开展浅层地质勘探。As an inevitable physical phenomenon in the application of frequency-domain electromagnetics,the static shift effect is gen-erally suppressed or eliminated by correction.This study proposed a new approach of directly utilizing the static shift effect of natural e-lectromagnetic methods to explore shallow electrical anomalies.The frequency selection method of telluric electricity field(FSM)is to study the variations in electrical properties of subsurface media by measuring several horizontal electric field components with different frequencies generated on the surface by the natural alternating electromagnetic field.In this study,the forward modeling of FSM data was conducted using the two-dimensional finite element method.The modeling results are shown as follows:(1)In the case of low-re-sistivity anomalies near the surface,the curves of horizontal electric field components along the survey line on the surface showed the same morphologies as the FSM-derived curves,with significant low-potential anomalies above the low-resistivity anomalies;(2)As the calculated frequencies increased,both the profile curves and the pseudosection map of electric field components exhibited a static shift effect,indicating that the FSM-derived anomalies were mainly caused by the static shift effect.Both the FSM application results and the drilling verification results showed that with the presence of groundwater,the FSM-derived profile curves and pseudosection map exhibi-ted a significant static shift effect,which was consistent with the CSAMT exploration results.As indicated by theoretical and practical research,it is feasible to directly use the components of the telluric electricity field for the exploration of shallow electrical anomalies.Moreover,shallow geological exploration can be conducted by utilizing the static shift effect of the frequency domain electromagnetics.

关 键 词：地球物理勘探 静态效应法 可控源音频大地电磁测深 有限单元法 天然电场选频法 地下水 

分 类 号：P631.1[天文地球—地质矿产勘探] P641.7[天文地球—地质学]