基于大地电磁法的水文地质结构及参数推断

Identification of hydrogeological structure and inference of hydraulic parameters based on the magnetotelluric method

大地电磁法已被广泛用于矿产资源勘探和工程勘查,但该方法在水文地质参数定量方面的成果文献尚不多见。以科尔沁沙丘—草甸相间地区巨厚第四系沉积层为研究对象,通过EH-4大地电磁法的测试结合地质钻探试验数据,划定出研究区埋深105 m范围内砂黏土层在空间上的分布;经检验大地电磁法探测总体误差在5.1%~7.2%,其精度足以满足水文地质勘察的需求。然后利用研究区已有的土壤传递函数(Pedo-transfer functions,PTFs)模型对测区埋深105 m范围内的饱和导水系数进行了估算,进而首次利用大地电磁法所得数据建立了视电阻率与饱和导水系数的拟合模型。利用该模型推断出研究区埋深200 m范围内含水层的富水性,刻画出饱和导水系数的空间分布,为研究区提供了更加丰富的水文地质信息,同时也极大地提升了水文地球物理方法在水力参数预测方面的尺度。

The magnetotelluric method has been widely used in the exploration of mineral resources and engineering survey for several years.However,this method is seldom employed in hydrogeological investigation.In this paper,we regard the thick Quaternary sediments in a sand dune-and-meadow interlaced region of Horqin as the research area,and analyze the application of the EH-4 exploration to the thick quaternary phreatic aquifer through the EH-4 magnetotelluric method system.By using the EH-4 data and particle size analyses we delineate the spatial distribution of the sandy clay layer in a depth of 105 m in the study area.We carry out a test on the results of the geophysical prospecting by using three peripheral borehole data,which show that the total error of the geophysical prospecting is between 5.1%and 7.2%.The results indicate that EH-4 has a good application effect on hydrogeological exploration in the thick Quaternary phreatic aquifer.To calculate the soil saturated hydraulic conductivity in the range of 105 m we use the existing Pedo-transfer function model in the study area,and obtain a fitting model of the saturated hydraulic conductivity and the apparent resistivity from the EH-4 magnetotelluric method in the saturated fresh water.The model results reveal the distribution of water yield property and saturated hydraulic conductivity with the depth range of 200 m in the study area.The quantitative interpretation of the EH-4 magnetotelluric method in hydrogeologic field is realized,which may provide more abundant information of the study area.At the same time,the scale of the hydro-geophysical method in hydraulic parameter prediction is greatly improved.