# Geo-Proxy-Based Site Classification for Regional Zonation of Seismic Site Effects in South Korea
## 4 Seismic Zonation with Site Response Parameters and Geo-Proxies in Incheon  
The proposed geo-proxy-based site classification system was applied to the extended area of Incheon, which is the target region of a seismic hazard assessment based on the quantification of the geotechnical earthquake engineering characteristics. Figure 2 shows the administrative areas of Incheon as well as the site classification information based on the geo-proxies of surface terrain slope and surface elevation. A comparison with site classification precise zoning information through the geotechnical-DB-based development of geo-spatial grid information was performed. Figure 9: Geo-proxy-based empirical classification for each site classification subdivision according to \(f_{0}\) (\(T_{G}\)) in Seoul: (**a**) surface terrain slope; (**b**) surface elevation. Firstly, to determine the amplification characteristics and cross-check with proxy-based criteria, depending on the site classification system based on the site response parameters, the seismic zonation was performed first for Incheon near Seoul using the geo-spatial grid information, which was reproduced by spatially interpolating the borehole datasets. The ground motion for seismic design can be determined by performing site classification and then calculating site coefficients using the site classification system that includes \(H\), \(V_{S30}\) and \(T_{G}\) as classification criteria (Table 1). Figure 10 presents the site classification based on \(H\), \(V_{S30}\) and \(T_{G}\), which were derived by the individual or combined utilization of the spatial geotechnical layer information and the representative \(V_{S}\)[4] for each geotechnical layer predicted for Incheon in this study. The study area has a maximum bedrock depth of approximately 48 m, while bedrock over 20 m depth is mainly distributed in plains near the coast (Figure 10a). \(V_{S30}\) is distributed from approximately 320 to 500 m/s in the areas including plains near the coast, where residential and industrial facilities are concentrated (Figure 10b). In addition, the site period is distributed from approximately 0.2 to 0.5 s in most of the plains near the coast (Figure 10c). By considering the earthquake vulnerability based on the structure resonance possibility using the site-period distribution information, it is possible to predict the earthquake vulnerability of facilities between two and five stories high in plains dense with residential and industrial facilities. This is based on the natural period of 0.1 s according to each building floor [2,33] but major sites in Incheon show approximately 0.2-0.5 s site periods. Considering that the study area contains not only residential but also industrial and commercial areas, it is likely that seismic performance assessments and seismic reinforcement are required for a large number of buildings and structures. Incheon, a representative coastal metropolitan city in South Korea, has a diverse site classification distribution, in which the amplification of earthquake ground motion is expected in plains near rivers, where residential and commercial facilities are concentrated and industrial facilities are located. In other words, where areas with site classifications C (C1-C4) and D (D1-D4), which are more vulnerable in terms of geotechnical earthquake engineering, are distributed. In some regions, site classification E is distributed if classification according to the site period is applied. Although a considerable area corresponds to site classification C, where the magnitude of ground motion is amplified to relatively small values, such site distribution requires more comprehensive and systematic precision zonation of the study area. It can also be seen that the same site can have somewhat different site classification depending on \(H\), \(V_{S30}\) and \(T_{G}\), which are the geotechnical earthquake engineering parameters.