## 4 Results Interpretation and Drilling Verification  
### Results Interpretation  
According to the input format requirements of the Res2 Dinv software, the original data of the designed G4 section that was obtained from the high-density electrical method are spliced and sorted into an independent data file. The least square method based on the smooth constraint was used for inversion, and the results in Figure 2a were obtained after terrain correction. The resistivity of the whole section is low above the altitude of \(-\)50 m, generally less than 2000 \(\Omega\cdot\)m. Combined with the survey results of surface geological mapping, it is inferred that most of them belong to Quaternary, and the low resistivity characteristics are relatively continuous. Based on the results of Table 1, it can be inferred that it is middle Pleistocene series Mawangdui formation reticular clay, and the underlying layer is a Quaternary Holocene gravel layer before 1920 measure points and after 2450 measure points when near the surface. \begin{table}
\begin{tabular}{c c c c c} \hline
**Stratigraphic Code** & **Rock** & **Number** & \begin{tabular}{c} **Average** \\ **Resistivity/R\({}_{av}\) (\(\Omega\cdot\)m)** \\ \end{tabular} & \begin{tabular}{c} **Range/** \\ **(\(\Omega\cdot\)m)** \\ \end{tabular} \\ \hline Qb-E & pre-Quaternary bedrock & 32 & 998.3 & 212.3–5998.8 \\ \hline Qp\({}_{1}cd\) & \begin{tabular}{c} lower Pleistocene series Changde \\ formation conglomerate \\ \end{tabular} & 22 & 223.1 & 128.3–889.5 \\ \hline Qp\({}_{2}mv\) & \begin{tabular}{c} middle Pleistocene series Mawangdui \\ formation reticular clay \\ \end{tabular} & 33 & 23.1 & 100.5–2122.9 \\ \hline Q\({}_{l}\) & \begin{tabular}{c} Quaternary Holocene series gravel \\ layer, silty clay \\ \end{tabular} & 27 & 298.3 & 12.5–588.7 \\ \hline O\({}_{1}bs\) & \begin{tabular}{c} Ordovician Baishuixi formation \\ silty shale \\ \end{tabular} & 36 & 1000.3 & 621.9–1768.5 \\ \hline \(\in_{3-4}t\) & \begin{tabular}{c} Cambrian Tanxi formation \\ dolomitic limestone \\ \end{tabular} & 31 & 2788.5 & 1189.3–5998.8 \\ \hline \(\in_{2-3}w\) & \
\begin{tabular}{c} Cambrian Wunidtang formation \\ micritic argillaceous limestone \\ \end{tabular} & 33 & 1757.3 & 1121.1–2678.3 \\ \hline \(\in_{1-2}n\) &
\begin{tabular}{c} Cambrian Niutitang formation \\ Carbonaceous shale and mudstone \\ \end{tabular} & 35 & 798.2 & 339.1–1233.5 \\ \hline \end{tabular}
\end{table} 
Table 1: Resistivity characteristics of different strata in the study area. \begin{table}
\begin{tabular}{c c c} \hline
**Stratigraphic Code** & **Rock** & **Transverse Wave Velocity/V\({}_{tw}\) (m\(\cdot\)s\({}^{-1}\))** \\ \hline Qb-E & pre-Quaternary bedrock & \textgreater{}800 \\ Qp\({}_{1}cd\) & lower Pleistocene series Changde formation conglomerate & 300–700 \\ Qp\({}_{2}mv\) & middle Pleistocene series Mawangdui formation reticular clay & \textless{}300 \\ Q\({}_{l}\) & Quaternary Holocene series gravel layer, silty clay & 300–800 \\ O\({}_{1}bs\) & Ordovician Baishuixi formation silty shale & 700–900 \\ \(\in_{3-4}t\) & Cambrian Tanxi formation dolomitic limestone & \textgreater{}1300 \\ \(\in_{2-3}w\) & Cambrian Wunidtang formation micritic argillaceous limestone & \textgreater{}1100 \\ \(\in_{1-2}n\) & Cambrian Niutitang formation Carbonaceous shale and mudstone & \textgreater{}900 \\ \hline \end{tabular}
\end{table} 
Table 2: S-wave velocity range of different strata in the study area. Figure 2b shows the data processing results of the controlled-source audio-frequency magnetotelluric method. Stratum stratification is obvious and can be divided into three layers. The first layer is a low resistivity layer with an altitude above \(-100\) m, and the resistivity is generally less than \(2000\)\(\Omega\cdot\)m. The second layer is a medium resistivity resistance layer over \(-550\) m above sea level, but it presents two depressions similar to a faulted basin. The first is located between \(1650\) and \(2120\) measure points and the other between \(2320\) and \(2920\) measure points.