# Geo-Proxy-Based Site Classification for Regional Zonation of Seismic Site Effects in South Korea
## 2 Site Classification System with Seismic Response Parameters
### Site Class Based on the Seismic Response Parameters in South Korea  
The amplification of ground motion due to the site-specific seismic response varies significantly depending on the geotechnical characteristics of the target region. Such differences are presented as a site classification system for seismic design and performance assessment. The site classification system currently used in South Korea is based on the regional characteristics of the western part of the United States, which are very different from those of the Korean peninsula. Recently, related studies [2; 3; 19; 20] have been conducted to improve and modify the site classification system for the appropriate local site response characteristics in South Korea. The site geotechnical classification in South Korea (Ministry of Construction and Transportation) [21] directly used the 1997 NEHRP (National Earthquake Hazards Reduction Program) regulation and 1997 UBC (Uniform Building Code), which were enacted based on the site classification method according to \(V_{S30}\) proposed by [PERSON] [11], through a review of the 1989 Loma Prieta earthquake records [3]. This site classification method has also been empirically verified for the 1984 Northridge earthquake in the western part of the United States [22]. Table 1 summarizes the current site classification system for earthquake zones I (\(Z\) = 0.11) and II (\(Z\) = 0.07) in South Korea, which are localized for possible earthquakes with a 500-year return period. The site coefficients, \(Fa\) and \(Fo\), are the relative ground motion ratios of the ground surface exposed to bedrock (bedrock outcrop) to the ground surface that is not exposed to bedrock but covered with soil. They can be determined using the response spectrum (\(RS\)) of each structure period (\(T\)) of the ground motion [2,3,23]. The seismic design regulations in the western part of the United States have been derived from a combined analysis of actual earthquake damage records and additional numerical analysis [2,3]. In the seismic design process in South Korea, the design ground motion from the quantitative application of the site effects can be overestimated or underestimated depending on the local geotechnical characteristics. Accordingly, a site classification system in which the classification criteria, classification steps and site coefficients are quantitatively improved, considering the geotechnical characteristics in South Korea, was developed. In particular, the developed site classification system presents the site period (\(T_{G}\)), which is a comprehensive geotechnical earthquake engineering indicator, as an additional classification criterion. [PERSON] [2,4] and [PERSON] and [PERSON] [18,24] conducted seismic response analysis for various site conditions in South Korea, analyzed the results and recalculated domestic site coefficients to systematically reflect the site-specific seismic response characteristics in South Korea. In addition, their studies suggested various improvement measures for the domestic geotechnical classification system and the subdivision of the geotechnical classification. Furthermore, to confirm the possibility of site classification using only the geometrical conditions of the ground from a more intuitive and practical perspective, their studies suggested that the bedrock depth (\(H\)) and site period (\(T_{G}\)) generally have a correlation of \(T_{G}\) = 0.01\(H\), when their units are not considered. In particular, in this study, the site classification system (Table 1) of [PERSON] [2], which is based on various site response parameters, was introduced as a technique that considers the geotechnical characteristics in South Korea. This classification system is used as a basis for developing an efficient empirical site classification system for broad areas in the Korean peninsula. As shown in Table 1, site classification can be performed using the site period and the short-term site coefficient (\(Fa\)) as well as the long-term site coefficient (\(Fv\)) can be determined accordingly.