山峰对电性源地面瞬变电磁响应的影响及校正方法  

Correction of the influence of mountains on grounded-source transient electromagnetic responses

作　　者：周钟航 张莹莹 ZHOU Zhong-Hang;ZHANG Ying-Ying(School of Geology and Mining Engineering,Xinjiang University,Urumqi 830047,China)

机构地区：[1]新疆大学地质与矿业工程学院,新疆乌鲁木齐830047

出　　处：《物探与化探》2023年第5期1236-1249,共14页Geophysical and Geochemical Exploration

基　　金：新疆维吾尔自治区天池博士计划项目。

摘　　要：在山区进行应用电性源瞬变电磁法勘探易受复杂地形影响,瞬变电磁响应会产生畸变,给数据解释造成困难。为此,基于三维非结构时间域有限元算法,开展了地形效应影响规律和校正方法的研究。首先,利用非结构四面体网格对山峰地形进行精细刻画,计算多种带地形模型响应,分析地形效应的影响规律;然后,基于电磁场线性叠加原理提出地形效应校正方法,根据实际高程数据建立山峰地电模型,通过三维正演计算出山峰模型响应,将山峰模型响应减去平坦大地模型响应得到地形响应,再从总响应中剔除地形响应,获得地形校正后的瞬变电磁响应。研究表明:山峰地形对瞬变电磁响应的影响主要集中在早期,随着时间推移,影响逐渐减弱;地形效应主要集中于山体附近,影响强度取决于测点距山顶的距离;影响范围与响应幅值与山体规模成正比;相对高阻山体的地形影响强度更大。通过设计多种带地形简单规则异常体模型进行仿真,发现经过校正的瞬变电磁响应与直接正演的响应吻合较好,在一定程度上能够有效消除地形效应。对地形效应影响和校正方法的研究,可为复杂地形地区瞬变电磁数据处理解释提供参考。The grounded-source transient electromagnetic(TEM)method,which enjoys the advantages of high topographic adaptability and large exploration depths,is suitable for deep resource exploration in mountainous areas.However,the TEM responses can be dis-torted due to topographic effects,causing great difficulties in data interpretation.This study investigated the influence patterns and cor-rection method of topographic effects based on the three-dimensional unstructured time-domain finite element method.First,this study conducted the fine-scale description of mountains using unstructured tetrahedral grids,calculated the response of various topographic models,and analyzed the influence patterns of topographic effects.Then,it proposed a correction method for topographic effects based on the principle of the linear superposition principle of electromagnetic fields,established a geoelectric model of mountains according to the actual elevation data,and calculated the model responses through three-dimensional forward modeling.Subsequently,this study de-termined the topographic responses by subtracting the flat Earth model responses from the mountain model responses and then obtained the corrected TEM responses by removing the topographic responses from the total responses.The results are as follows:(1)The influ-ence of mountains on the TEM responses is concentrated in the early stage and weakens gradually with time;(2)The topographic effects are concentrated near mountains,and their intensity depends on the distance of survey points from mountain peaks;(3)The in-fluencing range and response amplitude of mountains are proportional to the mountain scale.In other words,a larger mountain scale corresponds to a larger influencing range and higher response amplitude;(4)Mountains with relatively high resistivity show more in-tense topographic influence.As shown by multiple models with simple and regular topographic anomalies,the corrected TEM respon-ses,which match well with the responses from direct forward modeling,can effectively

关 键 词：电性源瞬变电磁法 山峰 地形效应 地形校正方法 三维正演 

分 类 号：P631.3[天文地球—地质矿产勘探]