## 3 Materials and Methods
### Causative Factors
#### 3.1.1 Seismology-Related Causative Factors  
Peak ground acceleration (PGA): slope instability during earthquakes means that the combined force of the ground acceleration and the gravity of the slope exceeds the adhesion and friction strength of the bedrock in a short time. Normally, the impact of an earthquake on a landslide is measured and quantified by recording the absolute maximum amplitude of the ground acceleration [1]. This study divides PGA into 6 levels with a step of 0.2 g; see Figure 3a.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Causative Factors** & **Classes** & **Classification Criteria** \\ \hline \multirow{4}{*}{Seismology} & PGA/(m/s\({}^{2}\)) & 6 & 1. -0.2; 2. 02–0.4; 3. 0.4–0.6; 4. 06–0.8; 5. 08–10; 6. 10–12 \\  & Distance to fault/(km) & 7 & 1. 0–3; 2. 3–6; 3. 6–9; 4. 9–12; 5. 12–15; 6. 15–18; 7. 3-20 \\  & Earthquake intensity & 4 & 1. \(\,\)VIII; 2. 10; 3. 3–4. 4; \\  & Lithology & 6 & 1. sandstone; 2. magmatic rock; 3. phyllite; 4. shale; 5. glutarentize; 6. carbonate rock \\ \hline \multirow{4}{*}{Terrain} & Elevation/(km) & 10 & 1. 0–5; 1. 2–1.5; 3. 1–1.5; 1. 5–2; 4. 2–2.5; 5. 2–5.3; 6. 3–3.5; 7. 3–3.5; 8. 4–4.5; 9. 4–5.5; 10. 5–5 \\  & Slope (\({}^{\circ}\)) & 8 & 1. 0–10; 2. 10–20; 3. 20–30; 4. 30–40; 5. 4–50; 5. 6–50; 7. 6–70; 8. 9–80 \\  & Aspect & 9 & 1.  Flate; 3. 1-3. 1-3. 1-4. 1-5. 5; 5. 5–7. 5/8; 8. 9–70 \\  & Curvature & 8 & 1. 0–3. 2–3. 6–3. 6; 4. 9–12; 5. 1–15. 18–12; 8. 9–21 \\  & Landform & 7 & 1. plain; 2. platform; 3. hill; 4. small undulating mountain; 5. middle undulating mountain; \\  & 6. high undulating mountain; 7. very high undulating mountain \\ \hline \multirow{2}{*}{Land} & Land use & 5 & 1. cultivated land; 2. woodland; 3. grassland; 4. water; 5. urban and rural residents \\  & Soil & 6 & 1. leaked; 2. semliced soil; 3. primary soil; 4. alpine soil; 5. ferraboli; 6. rock \\  & Distance to road/(km) & 10 & 1. 0–0.5; 2. 0–5; 1. 3–1.5; 4. 1–1.5; 1. 5–2. 5–2.5; 6. 2–5.3; 7. 3–3.5; 8. 3–4.9; 4–4.5; 10. 3–4.5 \\ \hline \multirow{2}{*}{Hydrological} & Distance to river/(km) & 11 & 1. 0–0.5; 2. 0–5.3; 1–3. 1–1.5; 4. 1–5. 2–5. 2–5. 2–5. 2–5. 3–3.5; 8. 3–4.9; 4–4. 4–5. 10. 4–5. 11. 5–5 \\  & Topographic wetness index & 9 & 1. 0–6.3; 2. 2–4. 4–3. 4.6; 4–6. 8–5. 8–10; 10–12; 7. 12–14; 8. 1–4. 10. 1–6. 10–19; 16-19; 45 \\  & Annual average rainfall/(mm) & 7 & 1. 5–525; 2. 5–625; 3. 6–725; 4. 7–825; 8. 8–925; 6. 9–205; 7. 1–205 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Causative factors categories of landslide.  
Figure 3: Seismology-related causative factors. (**a**) PGA; (**b**) Distance of fault; (**c**) Earthquake intensity; (**d**) Lithology.  
Distance to fault: fault structure affects the occurrence of geological disasters. Therefore, the distance between the slope and the fault should be considered in slope stability analysis. The internal factor of landslide development and slope instability is that the various weakness planes produced by tectonic movement form different structural combinations with slope or artificial excavation face. This study divides the distance to the fault into 7 levels with a step of 3 km; see Figure 3b.  
Seismic intensity: seismic intensity is the main parameter to measure the degree of seismic damage. It refers to the intensity of ground vibration in a certain area within the seismic range. The intensity of seismic activity is not only directly related to slope stability but also has an important influence on the spatial distribution of seismic landslides. The seismic intensity of the study area was divided into 4 levels; see Figure 3c.  
Lithology: the lithology is a proxy of the shear strength of the materials constituting slopes, thus directly controlling the state of slope stability. Lithology is the basis to determine slope strength, stress distribution, permeability, and deformation characteristics. There are 6 lithology types in the study area; see Figure 3d.