# Groundwater Detection Using the Pseudo-3D Resistivity Method: A History of Case Studies
## 3 Case Studies
### Groundwater Exploration Cases  
#### 3.2.1 Groundwater Survey in Zixing City with Geophysical Methods  
The Zixing groundwater detection survey area is located in the northeastern part of Zixing City, the southern part of Hunan Province, the intersection of Hunan, Guangdong and Jiangxi provinces, and the Dongjiang Lake Scenic Area (Figure 2). According to previous geological surveys, the exposed strata in the study area is the Middle Devonian Tiaomajian Formation (D2t), which is distributed in the southwest corner of the work area, and belongs to the sediment and clastic deposits of continental facies transitioning to coastal facies. The lithology is a gray-white medium-fine-grained quartz sandstone and a gravel-bearing quartz sandstone. The main outcrop in the working area is a compressive fault, which runs through the entire working area and goes north to northeast. Near the fault zone, silicification and alteration are serious, and the zone is locally altered into quartzite. According to regional information, the layer thickness is 78-300 m.  
The combined profiling method, resistivity sounding method, and CSAMT are limited by geology and other factors, and the exploration effect is poor. The pseudo-3D resistivity method is added to identify the distribution of relevant faults in the survey areas of Hejiashan and Zhoumensi. Among them, the HJS-03 survey line of Hejiashan is selected to compare the results of the pseudo-3D resistivity method and those of the resistivity sounding method (in Figure 6). In Figure 7, there is a low-resistance anomaly tilting towards the large measuring point between No. 250-400 measuring points, and the dip angle is about 50 degrees. It is speculated that the low-resistivity anomaly and the F1 fault have caused rock fragmentation, water content increase, and NW trend factors, such as the presence of rivers. It is speculated that the low-resistance anomalies with an elevation of less than 300 m between the measuring points 560-850 are the combined reaction of Quaternary alluvial layers, streams, NW-trending rivers, and fractured zones. From the perspective of water exploration, due to the presence of the NNE-trending F1 fault and the NW-trending fracture zone near the HJS-03 line, it is speculated that the surrounding area of this survey line is a favorable area for water exploration. As a result, follow-up data analysis should be carried out in combination with other results to verify the speculation. Combined with the geophysical prospecting in the Zixing groundwater survey, it is found that the F1 fault has a relatively obvious display in the survey area. The inclination angle is about 50-70 degrees. The F1 fault has an obvious abnormal response in profile  
Figure 6: Geophysical prospecting arrays in Hejiashan survey area. (**a**) Pseudo-3D arrays. (**b**) The combined profiling method, resistivity sounding method, and CSAMT arrays (the black cross-shaped measuring points are the combined profiling and resistivity sounding points, and the red circles are the CSAMT measuring points). Figure 7: The resistivity sounding and pseudo-3D resistivity inversion results of the HJS-03 survey profile. (**a**) Resistivity sounding result. (**b**) Pseudo-3D resistivity result (the red lines represent fault and the pink lines segment layer the resistivity). HJS-03 and profile HJS-05 in the Hejiashan survey area, and the F1 fault has a relatively obvious abnormal response in profile ZMS-01 in the Zhoumensi survey area. In addition, near the No. 2100 measuring point of profile K1 and the No. 350 measuring point of profile K2 in the Hejiashan survey area, it is speculated that there is a fault with better water content. Profile K4 is mainly located in the river valley, and it is speculated that there are structures in multiple directions. Therefore, the results of this exploration line need to be focused on the superposition effect of structures in multiple directions. The water content between the No. 700-1400 measuring points is relatively strong, and there are relatively complete granites.