## 3 Physical Model Experiment  
We established the soil-rock interface slope model in the laboratory to simulate the rainfall-induced landslide process (Figure 4). In total, 24 electrodes were randomly distributed on the slope. The flow rate was maintained at approximately 15 mL/s. Rainfall was applied for 5 min intervals, after which it was suspended to allow for measurements until the slope was completely damaged. The original data were inverted to obtain a series of resistivity profiles. We used the DC method to repeatedly detect the resistivity of the underground medium in the landslide body, thereby obtaining the changes in resistivity values at different locations and times. A comprehensive analysis was then performed on the resistivity value changes and their time-lag characteristics in the landslide body.  
The three main elements of a landslide are the landslide bed, the sliding surface, and the landslide body. Generally, the landslide bed does not slide and can maintain its original structure without deformation, resulting in relatively high resistivity values. The sliding surface is formed by the crumpling and grinding of nearby soil and rock, with a thickness ranging from a few centimeters to several meters. The resistivity value of the sliding surface  
Figure 3: The inversion images of different arrays under different soil resistivities.  
is generally much lower than that of the landslide bed. The resistivity value of the landslide body is determined by its condition. If the landslide body is relatively fragmented, contains more soil, and has high water content, it will exhibit relatively low resistivity values; if it consists of large broken blocks with less clay content and poor water content, it will exhibit high resistivity values.  
The results are shown in Figure 5. The initial resistivity is depicted in Figure 5a, indicating higher overall resistivity values in the absence of rain. After 40 min, an arc-shaped feature suspected to be the sliding face is evident (Figure 5b). Experimental findings demonstrate that the resistivity interface closely aligns with the actual position of the sliding face. Figure 5c shows a low-resistivity band with the left and right sides divided into two separate electrical bodies. At this point, a 2 mm-wide crack emerges between the 10 th and 11 th electrodes, signaling the onset of landslides. Then, the sliding mass has experienced significant displacement and deformation, with the widest part of the crack expanding to 2.5 cm, as shown in Figure 5d. The landslide event concluded after 128 min.  
This experiment displays the area damaged by the landslide aligning with the discontinuous section of the resistivity profile during slope stability, which becomes increasingly pronounced under rainfall. These areas may represent weak points in the slope vulnerable to damage. The suspected sliding surface indicated on the resistivity profile before slope failure matches the actual slide face during failure, showcasing the remarkable accuracy of the DC method in predicting slide faces. During the formation of tensile cracks at the rear edge of the landslide, they manifest as low-resistance strips vertically. Over time with rainfall, this area expands horizontally from the soil-rock interface to the surface. Once the low-resistivity band reaches the surface and separates the left and right sides into independent electrical bodies, early warning signals should be raised.  
Figure 4: Physical slope model diagram. (**a**) Model schematic map; (**b**) Experimental setup.  
Figure 5: Resistivity results of physical model experiment. (**a**) T = 0 min; (**b**) T = 40 min; (**c**) T = 80 min; (**d**) T = 120 min.