# A Combined Method for Preparation of Landslide Susceptibility Map in Izmir (Turkije)
## 3 Materials and Methods
### Geo-Environmental Factors: Definition and Statistical Analysis  
Conditions that disturb the balance when the rock mass is stable can be defined as geo-environmental factors. Understanding the role of predetermined conditions for landslides is critical to determining the susceptibility of landslide formation [83; 84; 85]. For this reason, the correct selection of geo-environmental factors is of great importance in the accuracy of the final LSM being prepared [86]. We can categorize geo-environmental factors into four groups according to their source: geomorphological, geological, hydrological and human. The first three factors relate to causes that are independent of any external effects and occur in completely natural ways. Human factors, on the other hand, are non-natural activities that can disturb stability via the application of surcharge loading on slopes that would otherwise remain stable in nature, for example, via excavation, construction or engineering of the structure in ways that disrupt its stability. In the preparation of the LSM for this study, slope angle, slope aspect, elevation and curvature were taken as geomorphological factors; lithology and density of discontinuity factors as geological factors; stream power index and distance from stream as hydrological factors; and land use as a human factor were used (Table 1). Geo-environmental factors and associated percentages of landslides are given in Figures 4 and 5. Figure 3: Landslide inventory map of the study area. \begin{table}
\begin{tabular}{l l l l l l} \hline \hline  & **Group** & **Data Source** & **Scale/Resolution** & **Factor** & **Data Type** \\ \hline \multirow{6}{*}{**Sampling**} & \multirow{6}{*}{Geomorphological factors} & \multirow{6}{*}{ASTER GDEM [87]} & \multirow{6}{*}{30\({}^{\text{\text{\text{\textaster}}}}\)30 m} & Slope angle & Numerical \\ \cline{3-5}  & & & & Slope aspect & Categorical \\ \cline{3-5}  & & & & Elevation & Numerical \\ \cline{3-5}  & & & & Slope curvature & Categorical \\ \cline{3-5}  & & & & SPI & Categorical \\ \cline{3-5}  & & & & Distance from stream & Numerical \\ \cline{3-5}  & & & & Lithology & Categorical \\ \cline{3-5}  & & & & Density of discontinuity & Categorical \\ \cline{3-5}  & & & & & Categorical \\ \hline Human factor & Satellite images & 30\({}^{\text{\text{\textaster}}}\)30 m & Land use & Categorical \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Geo-environmental factors used in LSM mapping. Figure 4: Geo-environmental factors and associated percentages of landslides for evaluation of landslide susceptibility. A 1/25,000 scale geological map of GDMRE, a 1/25,000 scale topographical map, ASTER GDEM data [87], aerial photographs and Google Earth satellite images [88] were used in this study. Lithology and density-of-discontinuity maps were produced from a geological map and ASTER GDEM data [87]. Elevation, slope angle, slope aspect, elevation and slope curvature maps were prepared using ASTER GDEM data (Table 1). SPI and distance-from-stream maps were produced using a topographical map. A land use map was prepared using satellite images. Landslide data from Avsar [81] and GDMRE [82] was used to prepare the landslide inventory map, updated with aerial photographs and Google Earth satellite images [88]. All geo-environmental factor maps were exported to the raster data at 25 \(\times\) 25 m resolution and the LSMs were produced using this data (Table 1). **Slope angle:** This can be defined as the angle made by morphological structures. The slope angle is relevant because the potential for landslide formation increases as the angle increases. This is because as the inclination angle increases, the weight of the rock mass in the direction of the slope increases and eventually the shear stress overcomes the forces  
Figure 5: Geo-environmental factors: (**a**) slope, (**b**) slope aspect, (**c**) lithology, (**d**) slope curvature, (**e**) elevation, (**f**) density of discontinuity, (**g**) SPI, (**h**) land use, (**i**) distance from stream.