## 3 Results
### Electrical Resistivity Tomography Results  
The inversion and interpretation results of G1 and G2 profiles by electrical resistivity tomography method are shown in Figure 5. The interface between the rock and soil layers obtained by inversion is clear and has varying depth. The thickness of the Quaternary cover layer is 5-29 m, and the resistivity value range is 4-100 \(\Omega\).m. The resistivity values in karst areas range from roughly 100 to 350 \(\Omega\).m, and the resistivity values of the limestone formation range from 400 to 800 \(\Omega\).m.  
Four karst abnormal areas are found in two sections, which are grouped in pairs and located at 70-90 m and depth 14-29 m in section 1 and 110-140 m and depth 20-32 m in section 2, respectively. At the same time, the similarity of the karst low-velocity anomaly in the two sections proves that the karst is connected in the south-north direction, and it is inferred that the karst has two potential water conduction channels, which make the groundwater flow northward and control the karst development in Tianmeixin village. TMCT 1 and TMCT 2 are located in the middle of the two sections at 118 m and 143 m of the survey line, which verifies the existence of a karst area in the east of the section (Drilling results will be discussed in Section 3.2).  
The electrical resistivity tomography measurement lines G3-G5 are arranged at the inner streets of Tianmeixin village from north to south. The distance between the G3 and G4 measurement lines is about 28 m, and the distance between the G4 and G5 measurement lines is about 18 m. The interpretation results are shown in Figure 6. The range of resistivity values of layers and karst areas in this area is roughly the same as that of the G1 and G2 profiles, and the highest resistivity value of the limestone layer reaches 1000 \(\Omega\)-m, higher than that of the G2 profile at 800 \(\Omega\)-m, which is considered to be caused by the low water content of rocks far away from the pond. There are many low-resistance abnormal areas in the three sections, among which two are large karst areas, located at 70-95 m and depth 14-29 m in the survey line and 155-170 m and depth 5-32 m in the survey line, respectively. The other low-resistance abnormal areas are small and distributed around the two large karst areas.  
On the whole, the karst area is mainly distributed in the middle and south of the survey line, and there is less karst in the northern region. Among them, the resistivity of the limestone below the X-axis 0-60 m interface is higher than 800 \(\Omega\)-m, and there is no low-resistance abnormal area. It is speculated that as the distance from the southern pond increases, the dissolution effect of groundwater in the area north of 60 m of the survey line weakens, the water content of the limestone layer is low, the karst is not well developed, and the overall resistivity is relatively high. In order to verify this conjecture, four boreholes, TMCT 3-TMCT 6, were designed on both sides of the survey line, and cross-well seismic computed tomography detection was carried out.  
Figure 5: Inversion results and geological interpretation maps of resistivity tomography detection data from sections G1 and G2.