An integrated geophysical approach for ground water prospecting in plateau slope zone: a case study from Shuangnuo Village, Fuyuan, Yunnan Province

The direction of drilling wells in the plateau slope area is toward finding local favorable water-rich blocks, which are relative groundwater accumulation areas under the control of structure, lithology, and landform. These areas often have obvious geological boundary conditions (such as the presence of a water resisting layer in the vertical direction, the development of a fault fracture zone in the plane), and their corresponding physical boundary often has a relatively low or high resistivity to the surrounding rock. In this paper, the comprehensive geophysical method is used to study the application of water prospecting in the plateau slope of Shuangnuo village, Fuyuan, Yunnan Province. First, according to the hydrogeological conditions (the development of a fault fracture zone and clastic rock is unknown), the plane distribution range and vertical development of the low-resistivity abnormal fault fracture zone are determined using the electrical resistivity tomography (less than 100 m) and audio magnetotelluric methods (100–500 m). Vertically, the development depth and thickness of the clastic rock aquifuge (P₁l) are determined using the audio frequency magnetotelluric method, which provides a basis for the maximum depth of the borehole layout. The combination of the electrical resistivity tomography and audio frequency magnetotelluric methods can delineate the favorable water-rich block in the study area well and verify that the study area has the prerequisite to become a water prospecting target. To determine the best location of the borehole layout, a combination of the composite profiling, microtremor horizontal-to-vertical spectral ratio (HVSR), apparent resistivity sounding, and K-reflection coefficient methods are carried out in the favorable water-rich block, which delineated by the electrical resistivity tomography and audio frequency magnetotelluric methods. The optimal borehole layout location is determined through the synchronous low resistivity anomaly of the composite profiling method, and the synchronous low resistivity anomaly is determined as a karst fracture zone (qualitative determination) in combination with the HVSR high-value anomaly of the microtremor method. The development depth of the karst fracture zone is finally determined by using the apparent resistivity sounding and K curves. This study reveals that the depth of the drilled hole is 243.5 m, and the water inflow is 144.3 m³/ day, successfully solving the serious water shortage problem in the local area. The case study results show that the combination of geophysical prospecting methods, namely, the electrical resistivity tomography, audio frequency magnetotelluric, composite profiling, microtremor, apparent resistivity sounding, and k-reflection coefficient methods, is effective for water exploration in the plateau slope zone.