# 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
It can be intuitively known through the site classification distribution that the amplification degree is generally intensified in the order of \(T_{G}\), \(H\) and \(V_{S30}\). Figure 10: _Cont._  
According to the proposed geo-proxy-based empirical site classification using slope and elevation (Table 5), the seismic zonation with elevation- and slope-based classification criteria was developed on the three-dimensional topographic coverage (Figure 11). The spatial distribution of site class was then quantitatively compared with site response parameter-based seismic zonation controlling the geo-spatial grid (Figure 10). Figure 11a presents the spatial distribution of elevation-based site class and site class E was spatially categorized focusing on most of the coast and plain regions, excluding the mountainous area in Incheon. In contrast, the spatial distribution of slope-based site class was estimated in accordance with the classification criteria proposed by [PERSON] and [PERSON] (2015) and the proposed geo-proxy-based framework. There are similar spatial trends, except for part of the plain areas. The site classes C4, D1 and D2, which have an average slope of 0.006 m/m, are concentrically distributed in the plain areas. This study determined a lower grade of site class and the corresponding slope-based site classification. This is because the proposed criteria were developed based on borehole datasets characterized from the shallower soil layer in Seoul than San Francisco Bay, where deep soil deposits over 30 m cover a wide area. Thus, the proposed slope-based classification criteria are more appropriate, considering the site-specific geotechnical characteristics in South Korea. The site-specific site effects estimated from the topographic elevation were relatively overestimated and accordingly, are more conservative criteria in seismic design standards. In addition to the topographic effects, the effects of deep sedimentary basins can also greatly modify the level of  
Figure 10: 3D view of spatial distribution of site classes in Incheon based on the proposed site response parameters: (**a**) \(H\); (**b**) \(V_{\text{S30}}\); (**c**) \(T_{\text{G}}\). ground shaking observed at sites located within them and thus, should be considered in combination with shallow seismic site conditions. It is difficult to find the topographic effect depending on the local curvature by using only the elevation-based classification criteria. Thus, in order to identify the detailed site classification in a plain area (an area with an average elevation lower than 9 m) considering the topographic effects, the slope-based site classification is more appropriate for Incheon. The spatial variation due to geological formation and civil engineering projects is remarkable in Incheon. Moreover, it should be possible to fit simple geometric shapes (e.g., ellipses) at the transition of hills and basins by using the average slope of the hills surrounding the basin as a crude predictor of three-dimensional basin geometry. In case of Seoul and Incheon, the average and standard deviation of slope was 0.015 m/m and 0.002 m/m. Thus, the additional geo-proxy-based application for South Korea is essential to propose the quantitative criterion depending on the simple geometric shapes at the transition of hills and basins. It is likely that this approach will only be valid in regions where large contrasts between hill and basin slopes exist. In this study, the spatial distribution of site class with a slope-based proxy was utilized for developing the seismic zonation. Figure 11: _Cont._  
The seismic zonation maps were developed based on the optimized spatial distribution of seismic sites with the appropriate site response parameter and geo-proxy, by computing the average \(T_{G}\) and the proposed geo-proxy for each unit in the study area of Incheon (Figure 12). Among the three site response parameters, \(T_{G}\), which estimated the intensified amplification property, was selected for the Incheon area.