浅湖区水上瞬变电磁法探测地下构造效果研究

本文应用水上瞬变电磁方法探测承德坝上地区月亮湖水文地质结构。为了解浅湖区深部地层、断裂及导水构造特征,在总结前人开展的水(海)上瞬变电磁勘探经验的基础上,采用晚期道信噪比较高的中心回线(大定源)瞬变电磁装置,对水下岩层垂向结构及隐伏断裂进行了探测。通过采集试验确定了有效的工作参数,在严格数据采集过程、选用合理的数据处理方法基础上取得了较好的应用效果。结果表明:大定源瞬变电磁装置在浅湖区可达到200 m的探测深度,垂向可分辨厚度为21～50 m的玄武岩层,剖面深部地层横向连续性好,不存在导水断裂,湖区下方探测结果受"低阻屏蔽效应"影响存在相对低阻异常,地质解释须结合地质资料综合研判。本次工作可为其他浅水区瞬变电磁勘探提供借鉴。

Application Effects of Transient Electromagnetic Method on Detecting Underground Structure in Shallow Lake Area

This paper introduces the application effects of transient electromagnetic method(TEM)on water to detect the hydrogeological structure of moon-lake in plateau area,Chengde.In order to understand the characteristics of deep formation,faults and water conducting structures in shallow lake area,based on the experience of TEM exploration on water(sea)carried out by predecessors,the vertical structure and concealed fracture of underwater rock stratum were detectedby using the central loop(large fixed source)device characterized by high signal-to-noise ratio of late channel.The effective working parameters are determined by data acquisition test,and reliable application resultsare achieved on the basis of strict data acquisition process and reasonable data processing methods.The results show that the large stationary source transient electromagnetic device can reach a detection depth of 200m in shallow lake area,and the basalt layer with a thickness of 21~50 m can be vertically resolved.The deep strata in the section have good lateral continuity without any water-conducting faults.Affected by the“low resistance shielding effect”,there is a relatively low resistance anomaly in the lower part of the lake.Therefore,geological interpretation must be comprehensively studied and judged in combination with geological data.This paper has summerized the key points of the application process,which can provide reference for exploration in other shallow water areas.