大回线源内三维地形对电磁响应影响研究  

Effect of topographic relief inside the large loop source on EM response

作　　者：饶丽婷 武欣 党博[1] 党瑞荣[1] RAO LiTing;WU Xin;DANG Bo;DANG RuiRong(School of Electronic Engineering,Xi’an Shiyou University,Xi’an 710065,China;Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]西安石油大学电子工程学院,西安710065 [2]中国科学院矿产资源研究重点实验室,中国科学院地质与地球物理研究所,北京100029

出　　处：《地球物理学进展》2021年第5期2090-2101,共12页Progress in Geophysics

基　　金：国家自然科学基金项目(42004064,41874158,51974250);陕西省教育厅专项科研计划项目(19JK0669);陕西省创新人才推进计划(2020KJXX-018);陕西省高校科协青年人才托举计划项目(20210702)联合资助。

摘　　要：我国地质地形条件复杂多样,地形效应研究与影响校正是电磁勘探数据处理与解释中的重要问题,忽略地形影响将造成数据解释的较大误差.为了避免复杂的地形效应,实际勘探中尽量将发射源与接收点布置在地形平缓处,但源内仍然可能存在水坑、空洞等小型地形对电磁响应造成一定影响.本文基于有限元法实现了频域、时间域电磁法三维数值模拟,构建了大回线源内含凹陷地形的多种勘探场景,分析了地形尺寸、填充介质变化对电磁响应的影响规律.文中通过与均匀半空间解析解、前人的块状高导体模型的数值结果对比,验证了基于有限元法的频域、时域电磁法三维正演的正确性和精度.在矩形回线源内构造了不同尺寸的凹陷区域,将凹陷区域填充空气、雨水介质模拟空洞和水坑,以均匀半空间响应为参考,定量考察了空洞、水坑对电磁响应的影响程度.研究表明,回线源内地形对电磁响应的影响主要反映在较高频段和时间域早期,水坑对电磁响应的影响显著高于空洞,在实际勘探中,应尽量避开水坑,而存在较小空洞时,可忽略地形效应.The geological and topographic conditions in China are complex and various. Terrain effect is an important problem in processing and interpretation of electromagnetic prospecting data for mountain region. Ignoring the topographic effect will cause relatively large errors in data interpretation. It is hard to separate the coupling effect of various parameters of terrain and source when considering the situation of ground electromagnetic method in topographic relief mountainous regions. In order to avoid the complex influence of terrain effect, the transmitting source and receiving device would be arranged at the flat terrain as far as possible in the real exploration. However, there may still be small undulate terrain, such as puddles, cavities, inside the large source, which have a certain impact on the electromagnetic responses. Therefore, this paper constructs a variety of prospecting scenarios with topographic relief inside the large loop source, without considering the deformation of the source. We realize the three-dimensional numerical simulation of electromagnetic method in frequency and time domain based on the finite element method. The effects of electromagnetic responses are investigated by changing the related parameters of terrain size and filling medium. Through the comparison with analytical solutions and other numerical techniques, the correctness of the three-dimensional forward modeling based on the finite element method is verified. We construct the models with different sizes of depressions inside the rectangular loop source and fill the depressions with air or rainwater to simulate cavity or puddle. The electromagnetic responses with and without cavity or puddle are compared and analyzed to illustrate the effect of topographic relief. The results show that the effect of topographic relief inside the loop source is mainly reflected at higher frequency or early time on electromagnetic response. The puddle has more significant impact on electromagnetic response than the cavity. The loop source s

关 键 词：大回线源 电磁法 地形效应 数值模拟 

分 类 号：P631[天文地球—地质矿产勘探]