Groundwater resources survey of tongchuan city using the audio magnetotelluric method

音频大地电磁法在铜川市地下水资源调查中的应用

The development of Tongchuan City,Shaanxi Province,located in the northwestern region of China,is restricted by water resources.The direct current resistivity and induced polarization sounding methods are typically applied in finding urban groundwater.These methods,however,are not effective due to their complicated topography and geological conditions.The application practice shows that the audio magnetotelluric(AMT)method has a large depth of exploration,high work effi ciency,and high lateral resolution.To investigate the distribution of groundwater resources,we deployed three audio-frequency magnetotelluric profiles in the city area.The impedance tensor information of AMT data is obtained using SSMT2000.AMT data dimension analysis reveals that the two-dimensional structural features of the observation area are obvious.The main structure of the observation area is about 45°northeast,as indicated by structural trend analysis.A shallow two-dimensional electrical profile of 1 km in Tongchuan City is obtained by two-dimensional nonlinear conjugate gradient inversion.Finally,combined with regional geological information,the geological structure characteristics reflected by the electrical profile were obtained along with the detailed characteristics of water-rich structures in the area.The infl uence of the structure on the groundwater distribution was analyzed,and the water-rich areas were identifi ed.This work contributes to the prospective development of Tongchuan City.

铜川市位于我国西北地区的陕西省,其发展受水资源制约。直流电法和激电法常常被用于城市地下水调查。然而西北地区特有的地形、地质条件限制了它们的应用。音频大地电磁法具勘探深度大,工作效率高和横向分辨率高等优势。为调查铜川市地下水资源分布情况,部署了3条音频大地电磁剖面。首先利用SSMT2000软件获得了测区AMT数据的阻抗张量信息。然后进行了AMT数据维性分析与电性主轴分析,结果表明观测区二维构造特征明显,主构造走向为北-东45°左右。最后采用二维非线性共轭梯度反演方法,获得了铜川市1km以浅二维电性剖面。结合区域地质资料,分析了电性剖面所反映的地质构造特征并详细分析了区内富水构造类型及特征,讨论了区内构造对地下水分布的影响并划分了富水区域,为铜川市城市发展及水资源开发及利用提供了重要的科学依据。