地面瞬变电磁勘探中源外地形的影响  

Effect of Topographic Relief Outside the Large Loop Source in Transient Electromagnetic Exploration

作　　者：饶丽婷 武欣 党博[1] 党瑞荣[1] 李勇 RAO Li-ting;WU Xin;DANG Bo;DANG Rui-rong;LI Yong(School of Electronic Engineering,Xi'an Shiyou University,Xi'an 710065,Shaanxi,China;Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;Beijing Zhongke Diyuan Technology Co.,Ltd.,Beijing 100190,China)

机构地区：[1]西安石油大学电子工程学院,陕西西安710065 [2]中国科学院地质与地球物理研究所中国科学院矿产资源研究重点实验室,北京100029 [3]北京中科地垣科技有限公司,北京100190

出　　处：《地球科学与环境学报》2022年第2期338-351,共14页Journal of Earth Sciences and Environment

基　　金：国家自然科学基金项目(42074121,42004064,41874158);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项目(2020KJXX-018);陕西省高校科协青年人才托举计划项目(20210702)。

摘　　要：起伏地形为中国矿产资源的发现和勘查造成了极大困难,为了避免复杂的地形效应,在地面瞬变电磁勘探中尽量将发射源与接收点布置在地形平缓处,但源外起伏地形的影响仍然存在。目前,对地形影响的分析大多从测道曲线图或者视电阻率断面图进行定性判断,较少从整个观测时间段内量化评估地形影响的程度。基于有限元法实现了带地形条件下矩形回线源的瞬变电磁三维正演,在源外构造了山脊、山谷地形,将地形与发射源的距离、大地电导率、异常体电导率作为变化参数,给出了整个观测时间段内在不同接收点处地形造成的相对误差分布,从而分析了源外地形对电磁响应的影响规律。结果表明:源外地形对电磁响应的影响主要集中在某个时间段内,随着与发射源距离增大,地形作用减弱,受影响区域也推移到较晚期时间段上;随着大地电导率增大,地形主要影响区域会推移到较晚期时间上,但受影响程度基本一致;相同几何尺寸的山谷地形比山脊地形对电磁响应的影响更大;地形、异常体对电磁响应的影响可以分离,如果异常体产生的二次场比较强,地形效应的影响相对较小,可以忽略地形影响。研究结果为地面瞬变电磁勘探中地形效应的识别与后期处理解释提供了理论依据。The topographic relief has caused great difficulties for the discovery and exploration of mineral resources in China. The calculation and interpretation of transient electromagnetic(TEM) data are often based on flat terrain. The topography can change the distribution of TEM response, which results in some error in recognition of underground targets. To avoid the complex influence of topographic effect, the transmitting source and observation point are normally laid on the flat terrain as possible, but the topography outside the source still impacts on TEM response. In recent years, most of the studies of topographic effect are based on the response curve or apparent resistivity section, while quantitatively evaluations of the degree by topography in the whole observation period are relatively few. The vector finite element method was adopted to perform the three-dimensional forward TEM problems with topography. The model containing topography of ridge and valley were constructed, and the distance between the topography and source, the conductivity of the earth and the anomaly were taken as variable parameters. The effects of topographic relief were investigated through the comparisons of different models. The results show that the topographic effects on EM response mainly reflect in a certain time period, and the topographic effect becomes weaker, the affected area on EM response moves to a later time period as the distance between the topography and source increases;with the increase of earth conductivity, the main affected area of topography on EM response moves to a later time period, but the degree of impact remains the same basically;the influence of valley topography on EM response is greater than that of ridge topography with the same geometric size;the influence of topography and anomaly on EM response can be separated;if the secondary field generated by anomaly is strong enough, the influence of topographic effect can be ignored. The research conclusions provide theoretical basis for the identification a

关 键 词：瞬变电磁法 大回线源 地形 三维正演 有限元法 异常体 电导率 数值模拟 

分 类 号：P631[天文地球—地质矿产勘探]