# Geo-Proxy-Based Site Classification for Regional Zonation of Seismic Site Effects in South Korea
## 3 Development of Site Classification with Geo-Proxies Using Geotechnical Database in Seoul
### Framework for Site Classification Based on Geo-Proxy in South Korea  
The geo-proxy-based empirical site classification system was derived from Seoul, South Korea. Seoul includes various geographical features, such as mountains, hills, plains and landfills, as well as geological features, such as various types of bedrock surface geology and alluvium. Considering the representative and inclusive nature of Seoul, the geo-proxy-based site classification system proposed in this study is considered to be sufficiently applicable to the whole of South Korea. In this study, the slope and elevation information of the surface terrain, which may correspond to the major terrain factors related to the geotechnical characteristics, were firstly regarded as topographical indicators and defined as geo-proxies. Studies that evaluate regional seismic response and derive information using proxies from a terrain or geological perspective have been mainly conducted for overseas regions with strong earthquakes [15; 17; 28; 29; 30]. In South Korea, such studies have been conducted at an extremely limited level [31; 32] and approaches with verification based on a comprehensive geotechnical DB have not been performed. Table 3 is an empirical site classification system derived by setting \(V_{S30}\) and the terrain slope as proxies for overseas sites [15]. According to the tectonic characteristics, the target areas were classified into active tectonics, where tectonic activities such as earthquakes are active and stable continent regions inside the plate. Figure 4: Correlation between the site period (\(T_{G}\)) and \(V_{S30}\) based on the spatial calculation site response information of Seoul. Figure 5: Correlation between the fundamental frequency (\(f_{0}\)) and \(V_{S30}\) based on the spatial calculation site response information of Seoul. To establish a discriminative site classification system that considers differences in the regional, seismic and geotechnical characteristics, this study derived the surface terrain slope and elevation, which are geo-proxies. And the geo-proxy-based correlations for calculated geo-spatial grid locations in Seoul was utilized as statistical datasets based on site classification according to established site-specific seismic response. The terrain slope and elevation datasets derived for geo-spatial grid squares in Seoul with a 100 m interval were classified as B, C, D, or E according to the calculated site classification criteria (Table 1), i.e., \(V_{S30}\) and site period (\(T_{G}\)) and their normal probability density functions were identified, as shown in Figures 6 and 7. In the division of each probabilistic site classification that can be identified from Figures 6 and 7, the site period (\(T_{G}\)) was better than \(V_{S30}\). The tendency for such a relative classification possibility is particularly pronounced in site classifications C and D. This is because the site conditions are concentrated at approximately 360 m/s, which is the criterion of \(V_{S30}\) for site classifications C and D in South Korea. This probabilistic tendency of the site class with \(V_{S30}\) has been suggested by [PERSON] et al. [32] based on the geotechnical DB of major inland sites in South Korea. For this reason, this study aimed to develop a geo-proxy-based site classification system based on a site classification system according to site period, which can more accurately reflect the geotechnical characteristics in South Korea, instead of the conventional classification criteria \(V_{S30}\). Additionally, the fundamental frequency (\(f_{0}\)), which corresponds to the reciprocal of the site period, was introduced instead of the site period to match the increasing and decreasing tendency of \(V_{S30}\) for each site class.