# Data Mining Approaches for Landslide Susceptibility Mapping in Unyeonsan, Seoul, South Korea
## 2 Study Area  
Seoul is the largest city in South Korea and is located in the center of the Korean Peninsula. The total urban area covered by Seoul (approximately 605 km\({}^{2}\)) is less than 1% of the total land area of South Korea. However, Seoul is one of the most heavily populated cities in the world; over 10 million citizens were recorded in 2011. Thus, the city has a dense and complex transportation system. Natural disasters, including landslides, have the potential to cause serious damage in the city [2]. The study area, Umyeonsan, is an urbanized mountain rising 321.6 m above sea level in the southern sub-central area of Seoul (Figure 1). Due to the fact that it is not very high or steep, the mountain is a popular site for Seoul residents and it has a large transient population  
Umyeonsan is comprised of a low mountainous area with a slope of approximately 30\({}^{\circ}\) near the top of the mountain. The area is mainly comprised of gneissic rock formed by geomorphological movement and weathering. The composition of biotic gneiss, which is prone to weathering and fault formation, increases its susceptibility to landslides. The foliation structure of the gneiss is sparsely generated due to multiple flexures. The main soil type distributed in the study area is brown forest soil formed from the base materials of biotite gneiss and granite gneiss, which are metamorphic rocks, and the soil texture is sandy loam to loam, which has good drainage. Deep soils and high organic content brown forest soil is distributed in some valley areas in the study area, where the soil texture is silt loam in silt and sand. Due to the soil textures present, the Umyeonsan area is prone to severe weathering, causing the unstable condition of outcrops.  
Figure 1: Map showing the location of the study area of Umyeonsan: (**a**) South Korea; (**b**) Seoul; and (**c**) Umyeonsan.  
The main forest type in Umyeonsan is temperate deciduous broad-leaved forest. Broad-leaved forest, pine forest, poplar forest, and broad-leaved plantation forest are all present in the study area. The principal species in the forests are similar to those in the central Korean Peninsula: _Quercus Mongolia_, _Robinia pseudoacacia_, _Quercus variabilis_, _ oak trees_ and _Asian black birch_.  
On 27 July 2011, heavy rains occurred in central Korea and a large landslide occurred in Umyeonsan. The heavy rainfall lasted from 26-28 July. The cumulative precipitation in the Seoul metropolitan area was 587.5 mm, which is the largest three-day cumulative precipitation recorded since precipitation monitoring began in Seoul. Based on data from Seocho automatic weather system, the maximum precipitation per hour at the time of the landslide was 85.5 mm [38]. The landslide from the heavy rains affected an area of 73.23 ha. Sixteen people were killed, including 6 residents from the village of Namtaeryeong and 7 residents from the southern area of the southern ring roads; 2 people remained missing, and approximately 400 people were evacuated [39]. The water supply was cut off. Thousands of apartments near Gangnam and Umyeonsan were damaged; and over 20,000 households experienced water problems. Therefore, we chose this landslide to obtain data for our study (Figure 2d,e). The study area was determined by the road and river boundaries in the Umyeonsan area (Figure 2).