# Assessment of Internal and External Factors Causing Slow-Moving Landslides
## 3 Results and Discussion
### Analysis of Rainfall Effects
#### 3.3.1 Effects of Rainfalls
The width and length of the slow-moving landslide area showed significant definitional correlations with rainfall intensity at the time of slow-moving landslide occurrence, with correlation coefficients of 0.590 and 0.602, respectively (Table 6). It was analyzed that \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Cls.**} & \multirow{2}{*}{**Len.**} & \multirow{2}{*}{**Dep.**} & \multirow{2}{*}{**Rf.**} & \multirow{2}{*}{**C.Rf.D.**} & \multirow{2}{*}{**C.Rf.**} & \multirow{2}{*}{**Mx.H.Rf.**} & \multicolumn{4}{c}{**Rf.I.**} & \multicolumn{4}{c}{**A.Rf.**} \\ \cline{5-12}  & & & & & & & & **3 Days** & **5 Days** & **7 Days** & **15 Days** \\ \hline Wid. & 0.625 * & 0.086 & \(-\)0.067 & 0.533 * & \(-\)0.312 & 0.355 & 0.590 * & 0.020 & 0.207 & 0.131 & \(-\)0.049 \\ Len. & & 0.401 & 0.274 & 0.517 * & \(-\)0.097 & 0.335 & 0.602 * & 0.306 & 0.524 & 0.440 & 0.180 \\ Dep. & & & 0.765 ** & 0.041 & 0.318 & 0.699 ** & 0.077 & 0.696 ** & 0.738 ** & 0.821 ** & 0.445 \\ Rf. & & & & 0.295 & 0.498 & 0.688 ** & \(-\)0.204 & 0.785 ** & 0.910 ** & 0.937 ** & 0.811 ** \\ C.Rf.D. & & & & & 0.747 ** & 0.313 & \(-\)0.345 & 0.046 & \(-\)0.062 & 0.016 & 0.435 \\ C.Rf. & & & & & & 0.400 & \(-\)0.035 & 0.554 * & 0.267 & 0.258 & 0.524 ** \\ Mx.H.Rf. & & & & & & 0.71 & 0.427 & 0.713 ** & 0.763 ** & 0.710 ** \\ Rf.I. & & & & & & & \(-\)0.184 & \(-\)0.031 & \(-\)0.094 & \(-\)0.186 \\
3 days & & & & & & & & 0.864 ** & 0.847 ** & 0.463 \\
5 days & & & & & & & & 0.978 ** & 0.748 ** \\
7 days & & & & & & & & & 0.726 ** \\ \hline \hline \end{tabular} Note: Cls. = classification, Wid. = width of the slow-moving landslide area, Len. = length of slow-moving landslide area, Dep. = depth of slow-moving landslide area, Ref. = rainfall, C.Rf.D. = continuous rainfall, C.Rf. = continuous rainfall, Mx.H.Rf. = maximum hourly rainfall, Rf.I. = rainfall, and A.Rf. = antecedent rainfall. Values indicate Pearson’s correlation coefficient (two-tailed). * \(p<0.05\) and ** \(p<0.01\).  
\end{table} 
Table 6: Results of the correlation analysis of the scale of occurrence of slow-moving landslides and rainfall factors. the larger the rainfall intensity, the larger the size of the slow-moving landslide. It was reported that slow-moving landslides occurred relatively more when the 15-day antecedent rainfall ranged from 301-400 mm [39]. However, this study did not show a significant result with the slow-moving landslide area size. Meanwhile, the depth of the slow-moving landslide area was significantly correlated with the three-day, five-day, and seven-day antecedent rainfalls, with correlation coefficients of 0.696, 0.738, and 0.821, respectively (Table 6). It has been reported that among the rainfall factors affecting slow-moving landslides, seven-day antecedent rainfall has a significant effect [16]. The more the antecedent rainfall, the deeper the water infiltrates into the ground in the direction of gravity. Furthermore, it was found that the slow-moving landslide phenomenon occurs deeper in the soil layer containing a large amount of clayey soil subjected to earth pressure and water pressure than in other layers, accelerating the chemical weathering of rocks and soil [40].