## 2 Materials and Methods
### Data Preparation and Analysis
#### 2.3.2 Landslide Causal Factors  
The occurrence of a landslide is caused by the combination of the basic geological conditions of the slope and the external environmental factors. The former are factors that play a controlling role in the occurrence of a landslide, including topography and geological structures, among other factors. The latter are triggering factors for the occurrence of a landslide, such as hydrogeological environment, earthquake, and human engineering activities, among others [28]. According to the field survey and preliminary research results in TGRA [29; 30; 31], 14 causal factors were initially selected as the factors for landslide susceptibility modelling, including altitude, slope, aspect, curvature, plan curvature, profile curvature, stream power index (SPI), topographic wetness index (TWI), terrain roughness index (TRI), lithology, bedding structure, distance to faults, distance to rivers, and distance to gully. The factors were prepared using a digital elevation model (DEM) with a spatial resolution of 25 m, and geological and geomorphology maps, which were collected from the Chongqing Natural Resources Bureau. In this study, ArcGIS 10.2 ([[http://www.esrichina.com.cn/](http://www.esrichina.com.cn/)]([http://www.esrichina.com.cn/](http://www.esrichina.com.cn/))) was applied to process geodata, and slope and aspect was obtained by Three Dimensions spatial analysis function; SPI and TWI were calculated by hydrological analysis function and the Raster calculator, respectively. TRI was also calculated using the Raster calculator, and distance to rivers, distance to gully, and distance to faults were calculated using the Euclidean distance method. The continuous causal factors, such as altitude, should be discretized before modelling. The discretization method of continuous landslide causal factors proposed by [PERSON] et al [32] was utilized in this study. 1. Altitude  
The altitude range of the study area is 145-1800 m (Figure 1), which is divided into four levels by the discretization method of continuous causal factors: [145, 300], [300, 450], [450, 750], [750, 1800]. As shown in Table 1, landslides in this study area mainly developed within the altitude from 145 to 300 m, its information value is the highest of 1.752. In the area where the altitude is higher than 750 m, there has been no landslide occurrence, and its information value is \(-\infty\). 2. Slope  
The slope of the study area varied greatly, mainly from 0\({}^{\circ}\) to 75\({}^{\circ}\) (Figure 2a), the slope is divided into six levels: [0,6\({}^{\circ}\)), [6\({}^{\circ}\),15\({}^{\circ}\)), [15\({}^{\circ}\),24\({}^{\circ}\)), [24\({}^{\circ}\),33\({}^{\circ}\)), [33\({}^{\circ}\),51\({}^{\circ}\)) and [51\({}^{\circ}\),75\({}^{\circ}\)]. Nearly 55\(\%\) of the landslides were located in the [6\({}^{\circ}\),15\({}^{\circ}\)) and [15\({}^{\circ}\),24\({}^{\circ}\)) areas, and their information values were 1.102 and 0.572, respectively. When the slope becomes steep, landslides do not easily occur in this area, with the information value in the [51\({}^{\circ}\),75\({}^{\circ}\)] area being \(-\)6.306 (Table 1). 3. Aspect  
In this study area, aspect can be divided into eight categories (Figure 2b). According to the statistical data, the probability of landslide occurrence on the southeast slope was the largest (Table 1). Its information value was 0.297. 4. Curvature  
The curvature of the study area ranged from \(-\)24 to 27 (Figure 2c), and it was divided into four categories: [\(-\)24,\(-\)1), [\(-\)1,3), [3,7), and [7,27], their information value being \(-\)2.849, 3.668, 2.561, and \(-\)0.032, respectively. It can be seen from the calculation results that the information values of the curvatures [1,3) and [3,7) were relatively larger (Table 1), having a promoting effect on the development of a landslide. 5.