# A Fully Automatic DEXP Method for Gravity Data and Its Application on a Potash Salt Deposit
## 4 Application on Real Gravity Data  
The survey area for the potash salt deposit is situated on the eastern edge of the Sakhon Nakhon basin within the Korat Plateau in Laos. This region has garnered significant attention from explorers and researchers due to its abundant potash resources, as depicted in Figure 9. To validate the proposed method, we applied it to the residual gravity anomaly obtained from real ground relative-gravity survey data. The survey area covered approximately 291 km\({}^{2}\) and was measured at a scale of 1:50,000. The grid distance between measurement points was set at 0.5 \(\times\) 0.5 km, and the measurements were  
Figure 8: The imaging result of the combined model with different step terrain (1–8 km). Figure 7: The estimated depths shown in Figure 6 (the green symbol is the difference between the real depth and the estimated depth) and their calculated error ratio. conducted using CG-5 gravipmeters (Scintrex Ltd., Concord, ON, Canada). To ensure accuracy, corrections were applied to the data, including tide correction, drift correction, latitude correction, height correction, mass correction, and terrain correction (the correction radius is 2 km). These corrections yielded the Bouguer gravity anomaly, with an accuracy of 0.042 \(\times\) 10\({}^{-5}\) m/s\({}^{2}\). All the processes followed the technological standard outlined in \"The Standard of 1: 50,000-scale Areal Gravity Prospecting, it is published by Ministry of Natural Resources of the People's Republic of China\". To facilitate a more meaningful comparison, Profile I refers to a specific cross-sectional profile that was selected for analysis. The profile traversed Well Jx4 and Well Jx5, which are boreholes drilled in the survey area. By comparing the imaging results obtained from the improved DEXP method with the geological information derived from the borehole data, we aim to determine whether the imaging depth of the potash salt layer corresponds to the known geological layers. Furthermore, we possess additional information regarding Well Jx4 and Well Jx5, both of which have been logged to identify potash layers. In Well Jx4, the rich potash layer is situated at a depth ranging from 132.5 m to 140 m. Following this, the potash salt layer extends from 140 m to 149 m. Consequently, the target rock exhibits a thickness of 16.5 m (132.5 m to 149 m). Well Jx5 features a rich potash salt layer ranging from 183 m to 187 m, succeeded by a potash salt layer spanning from 187 m to 254 m. Beyond that, there exists a layer consisting of potash salt and rock salt, extending from 254 m to 270 m. As a result, the target rock in Well Jx5 showcases significant thickness, amounting to 87 m (183 m to 270 m) (as illustrated in Figure 10). Within this survey area, the density of the potash salt deposit varies from 1.97 \(\times\) 10\({}^{3}\) kg/m\({}^{3}\) to 1.99 \(\times\) 10\({}^{3}\) kg/m\({}^{3}\), which is lower than the density of gypsum and rock salt, ranging from 2 \(\times\) 10\({}^{3}\) kg/m\({}^{3}\) to 2.2 \(\times\) 10\({}^{3}\) kg/m\({}^{3}\). The potash layer,  
Figure 9: The location and geological map of the study area (revised by [PERSON], 2015 [39]). exhibiting thickness ranging from a few meters to 80 m, is commonly found adjacent to the gypsum layer. Consequently, our objective is to analyze and interpret the low-density rock formations in order to accurately identify the potash layer. The topography in the study area exhibits undulating characteristics, although it is not highly pronounced, with an elevation range of approximately 40 m (as depicted in Figure 11a). Figure 11b presents the residual gravity anomaly, which displays a high anomaly superimposed on the background of a relatively low anomaly. In the northern part of the study area, several higher-value anomalies are observed, forming localized traps amidst the overall high background anomaly. Furthermore, there exists a large-scale high-gravity anomaly between Songmengnu and Nongpang, which may be associated with the explosion of the old stratum.