## 2 Materials and Methods
### Establish Evaluation Index System  
For the evaluation of susceptibility, the construction of the index system is quite an important step. Generally speaking, the commonly used indicators for the evaluation of landslide susceptibility are topography, elevation, slope, the density of gullies, relief of the terrain, etc. ; geomorphology: geomorphological units, micro-geomorphological patterns, overall terrain, etc. ; stratigraphic lithology: lithological characteristics, the thickness of rock layers, type of rock genesis, etc. ; geological structure: faults, folds, joints and fissures, etc. ; earthquake: intensity, dynamic peak acceleration, historical seismic activity, etc. ; geology: stability of regional crust, depth of bedrock, lithology of main bearing layers, bearing capacity, engineering geological zoning of geotechnical bodies, etc. [37; 38]. It is almost impossible in practice to build a model that encompasses all geo-environment-ental factors to evaluate susceptibility [34; 35]. This is because the parameters included in certain factors are sometimes difficult to obtain, and with many evaluation parameters, there may be intricate synergies or interactions between the parameters. Therefore, it is the key to evaluation factors to select the stable and quantifiable participation factors that play a leading role in evaluation objectives. In terms of the geological background of the investigation area, the topography, stratigraphic lithology, geological structure, hydrogeology and other geological environmental conditions in the study area are very complex, but when combined, it can be found that the entire geological background is mainly determined and controlled by the tectonic pattern of the Minjiang River Fracture Zone-Xueshan Fracture Zone-HuYa Fracture Zone. For example, although the whole area is covered with gullies, the gullies around Huanglong, Xiaohe and Baiyang are obviously denser and more deeply cut, thus causing numerous geological hazards, while the distribution of outcrops of stratigraphic lithology and the distribution of tectonic patterns are also somewhat related. Therefore, from this level, it is possible to select geological formations, engineering geological rock groups and gully density factors. For example, in the case of landslides with a large number of creep-slip-slip mechanisms, the main controlling condition is the slope of the terrain, which is why the development of landslides is well correlated with the slope of the terrain in the statistical analysis of the gestation conditions. Based on this, the factors that influence the occurrence of geological hazards under heavy rainfall conditions through the analysis of the incubation conditions are, in summary, the following factors: slope, plane curvature, slope structure, human engineering activities and river geological process [39; 40]. Table 5 shows that the following factors can be preliminarily selected for landslide susceptibility evaluation (1:50,000) in the study area. For the initially selected vulnerability evaluation factors, these factors are not independent of each other but are correlated with each other to a certain extent. If they are not processed, the influence weights between the indicator factors may be superimposed, which in turn may lead to inaccurate evaluation results. Therefore, to ensure the mutual independence of the indicator factors and to meet the accuracy of the input parameters of the model, it is necessary to screen each of the selected indicator factors. To sum up, the correlation analysis of all the preliminary selected indicator factors in the ArcGIS spatial analysis tool was applied to measure the correlation degree between the indicators by calculating the correlation coefficient R. The value of R takes the range [\(-\)1, 1], and the closer R is to 1, the higher the correlation between the two indicators as shown in Table 6.