# Assessment of Internal and External Factors Causing Slow-Moving Landslides
## 3 Results and Discussion
### Overlap Analysis
based on grade using the Shapiro-Wilk test. The combined analysis of skewness, kurtosis, and significance probability revealed that the grade-based area data were not normally distributed (Table 2). Thus, we conducted a non-parametric test to analyze the difference in graded area. The non-parametric test (Kruskal-Wallis test) on the area data revealed that the difference in area based on grade was significant (\(p<0.001\)). ANOVA conducted on the difference between grades using the ranking data of the slow-moving landslide areas based on grade revealed a significant difference between various grades (\(p<0.001\)). In particular, the post hoc analysis showed that Grades 1 and 5 were characterized by low rankings, whereas Grades 2, 3, and 4 and excluded areas (non-hazardous areas) were characterized by high rankings (Table 3). Thus, slow-moving landslides occurred mainly in relatively low landslide hazard areas on the landslide hazard map, particularly in excluded areas (non-hazardous areas). Until recently, slow-moving landslides were treated as a type of landslide in South Korea. Unlike landslides, which are a type of surface failure type of mountain erosion, slow-moving landslides can cause large-scale damage because the soil layer moves slowly over a long period [8; 34]. Predicting and responding to the risk of slow-moving landslides is not possible with a landslide hazard map. Therefore, slow-moving landslides must be treated as a distinctly different phenomenon from landslides. Moreover, there is an urgent need to establish a national SMLHIS (slow-moving landslide hazard map) like the one for landslides. Landslides are downslope movements of rock, soil, or both that occur on curved (rotational slide) or planar (translational slide) rupture surfaces. The material often moves as a coherent or semicoherent mass with slight internal deformation. On the other hand, slow-moving landslides can occur on gentle-to-moderate slopes, generally in fine-grained soils, such as clay or silt, but also in very weathered, clay-bearing bedrock. The mass in a slow-moving landslide moves as a plastic or viscous flow with internal solid deformation [6]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Grade**} & **Mean** & **SD** & \multirow{2}{*}{**Skewness**} & \multirow{2}{*}{**Kurtosis**} & \multicolumn{2}{c}{**Shapiro–Wilk**} \\ \cline{4-7}  & **(m2)** & **(m2)** & & & **Statistics** & \(p\) \\ \hline
1 & 1233.3 & 1729.4 & 1.136 & \(-\)0.283 & 0.738 & 0.001 \\
2 & 6093.3 & 6594.0 & 0.992 & \(-\)0.443 & 0.817 & 0.006 \\
3 & 11,320.0 & 9264.5 & 0.466 & \(-\)1.343 & 0.891 & 0.070 \\
4 & 7666.7 & 7373.7 & 0.926 & \(-\)0.020 & 0.893 & 0.074 \\
5 & 4940.0 & 15,214.7 & 3.749 & 14.283 & 0.367 & \(<\)0.001 \\ Ea \({}^{z}\) & 12,660.0 & 16,929.8 & 1.849 & 3.472 & 0.767 & 0.001 \\ \hline \hline \end{tabular} \({}^{z}\)Ea = excluded area (non-hazard area); SD = standard deviation.  
\end{table} 
Table 2: Normality test results for the slow-moving landslide areas based on grade. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Grade**} & **Area** & \multicolumn{2}{c}{\(p\)} & \multicolumn{4}{c}{**Rank Data of Grade Area**} \\ \cline{3-8}  & **(m2)** & **(Kruskal–Wallis)** & **N** & **Mean y** & **SD** & \(F\) & \(p\) \\ \hline
1 & 18,500 & & 15 & 27.333 \({}^{a}\) & 17.846 & & & \\
2 & 91,400 & & 15 & 49.133 \({}^{b}\) & 21.516 & & & \\
3 & 169,800 & & 15 & 62.167 \({}^{b}\) & 19.566 & & & \\
4 & 115,000 & \(<\)0.001 & 15 & 52.933 \({}^{b}\) & 23.658 & 5.975 & \(<\)0.001 \\
5 & 74,100 & & 15 & 27.867 \({}^{a}\) & 24.365 & & & \\ Ea \({}^{z}\) & 189,900 & & 15 & 53.567 \({}^{b}\) & 29.197 & & & \\ Total & 658,700 & & 90 & 45.500 & 26.000 & & \\ \hline \hline \end{tabular} \({}^{z}\)Ea = exclude area (non-hazard area); [PERSON]’s multiple range test at \(p<0.05\), \({}^{z}\)< b; SD = standard deviation.  
\end{table} 
Table 3: Results of non-parametric tests and analysis of variance (ANOVA) for differences in slow-moving landslide areas based on grade.