## 2 Materials and Methods
### Data Preparation and Analysis
#### 2.3.2 Landslide Causal Factors
Plan curvature  
The variation range of plan curvature in the study area was \(-\)13.0 \(\sim\) 10.5 (Figure 2d); it was divided into outward slope [\(-\)13, \(-\)1.5), straight slope [\(-\)1.5,1.5), and inward slope [1.5,10.5], and their information values were \(-\)0.566, 0.035, and \(-\)0.795, respectively (Table 1). 6. Profile curvature  
The variation range of profile curvature in the study area was \(-\)18 \(\sim\) 18 (Figure 2e); according to the profile curvature, the slope pattern can be divided into convex [\(-\)18,\(-\)1.5), flat [\(-\)1.5,1.5), and concave [1.5,18], and the information values were \(-\)0.907, 0.041, and \(-\)0.737, respectively (Table 1). 7. SPI  
Stream power index can quantitatively describe the relationship between water erosion and land performance [33]. It is usually considered as one of the factors affecting slope stability. The calculation formula is as follows:  
\[SPI=A_{S}\tan\beta \tag{12}\]  
where \(A_{s}\) is the catchment area of the basin and \(\beta\) is the slope. The SPI can be divided into four categories (Figure 2f): [0,2), [2,4), [4,8), [8, \(+\infty\)); their information values were 0.262, \(-\)0.020, \(-\)0.327, and \(-\)0.436, respectively (Table 1). TWI  
Topographic wetness index can quantitatively simulate the dry and wet conditions of topography and soil moisture in the watershed [33]. The calculation formula is as follows:  
\[TWI=\text{In}\left(\frac{\alpha}{tan\beta}\right) \tag{13}\]  
where \(\alpha\) is the upstream convergence area and \(\beta\) is the slope. The TWI can be divided into four categories (Figure 2g): [0,4.5), [4.5,6.5), [6.5,8), and [8, +\(\infty\)); their information values were 0.047, -0.158, 0.069, and -0.292, respectively (Table 1). 9. TRI  
Terrain roughness index (TRI) is an index reflecting the change of surface fluctuation. TRI ranges from 1 to 3.9, and the main range is 1 to 1.2, which accounts for about 70% of the total area of the study area. The continuous factors classified method was applied to classify TRI into four categories (Figure 2h): [1,1.2), [1.2,1.4), [1.4,1.6), and [1.6,3.9]; their information values were 0.338, -1.167, -2.291, and -6.780, respectively (Table 1). 10. Lithology  
Lithology is the material basis for the development of a landslide. According to the lithological characteristics of outcropping strata in the study area, they can be divided into seven categories (Table 2), and their spatial distribution is shown in Figure 2i. Nearly 60% of the landslides in the study area developed in category B, and its information value was 0.849 (Table 1). 11. Bedding structure  
According to \"Technical Requirements for Investigation and Evaluation of Collapse, Landslide, Debris Flow\" from the China Geological Survey [34], slope structure can be classified into eight categories (Figure 2j; Table 3), and the statistical results of the information value of each slope structure type are shown in Table 1.  
12. Distance to faults  
Usually, there are many cracks near the structure, and the rock mass is broken, which provides a material basis for a landslide and is also the area where a landslide is more developed. Distance to faults can be divided four categories (Figure 2k): [0,450), [450,900), [900,1750), and [1750, 4900]; their information values were 0.575, 0.532, -0.611, and -4.311, respectively (Table 1). 13. Distance to rivers  
The study area is situated on both sides of the Three Gorges Reservoir, and the river system is the Yangtze River and its main tributaries. The influence intensity is expressed by the distance to rivers. The distance to rivers was divided into six categories (Figure 2l): [0,150), [150,300), [300,650), [650,950), [950,1550), and [1550,5300]. Statistical results showed that the development of landslides in the study area was significantly affected by rivers; 62% of landslides are within 300 m of the Yangtze River, and the farther away from rivers, the fewer landslides developed.