# Geo-Proxy-Based Site Classification for Regional Zonation of Seismic Site Effects in South Korea
## 1 Introduction
Such maps are available for only a few regions, predominantly for seismically active urban areas of the world. [PERSON] et al. [15] compared topographically based maps with existing \(V_{S30}\) site-condition maps, currently used for ShakeMap and other applications, that are based primarily on geological maps. These analyses are then repeated for \(V_{S30}\) data aggregated in stable continental regions. The topographic slope can be used as a reliable proxy for \(V_{S30}\) in the absence of geologically and geotechnically based site-condition maps through correlations between \(V_{S30}\) measurements and topographic gradients [17]. In South Korea, borehole datasets, which include spatial information, geotechnical layer information and standard penetration test (SPT) information, were evenly distributed on a two-dimensional coordinate plan. In order to estimate the site-specific site effects, empirical correlations among geotechnical layers, SPT-\(N\) value and \(V_{S}\) have been proposed using the borehole datasets in partial metropolitan areas based on appropriate statistical regressions. Accordingly, a seismic zonation map with site response parameters, according to the Korean seismic codes, was developed by considering correlations between the spatially interpolated borehole information [18]. The site effects, resulting in the amplification of earthquake ground motion, are strongly influenced not only by the subsurface soil conditions and structure but also by the surface topography. Yet, over the last several decades, most studies of site-specific seismic responses in South Korea have focused primarily on the seismic amplification associated with geological and soil conditions. Thus, site classification with a digital elevation models (DEM)-based or a geographic coverage datasets-based proxy should be established based on empirical correlations with site response parameters to evaluate regional-scale seismic zonation and to develop an earthquake alert system. In this study, to identify the amplification characteristics in South Korea, depending on the geo-spatial condition (elevation, slope, etc. ), the dual framework for a site classification system with site response parameters and geo-proxies was proposed (Figure 1). First, borehole datasets, DEM and a geographic coverage map were constructed as the geotechnical database (DB). Second, the geo-spatial grid information was estimated based on the optimized geostatistical interpolation method. In particular, the geostatistical optimization of the interpolation method and clustering estimation was developed as a computational framework to construct the appropriate seismic zonation using a geo-spatial DB, which was composed of multi-variable geo-data [18]. Accordingly, the typical geotechnical layer information, which was categorized into fill, alluvial soil and weathered layer, was constructed as a spatial distribution map separated into 100 m mesh areas. In addition, a DEM layer was constructed with the same mesh areas and coordinate system of the geotechnical layer. Third, three site response parameters (depth to bedrock, \(V_{S30}\) and site period) were computed using the thickness of the geotechnical layer with a representative \(V_{S}\) for each layer, based on the conventional criteria for seismic site classification. To establish the site classification criteria with correlations between site response parameters and geo-proxies, the authors first correlated \(V_{S30}\) with topographic elevation and slope data at each grid square in Seoul areas. Thus elevation- and slope-based site classification was determined using the constructed DEM in the Incheon area. Finally, the three-dimensional spatial distribution map and seismic zonation with administrative sub-units were visualized to validate the suitability of the site classification criteria and to provide a site-specific decision-making platform related by site-effect and induced seismic hazard.