# Geo-Proxy-Based Site Classification for Regional Zonation of Seismic Site Effects in South Korea
## 1 Introduction  
The near-surface seismic motion and earthquake-induced damage experienced during an earthquake can vary significantly, even for sites located at the same distance from the epicenter. This is due to the source effects and propagation path through the bedrock as well as the seismic response due to site-specific geotechnical dynamic characteristics, such as the shear wave velocity (\(V_{S}\)) in the sub-soil layers. The site-specific site effects indicate the seismic ground motion expressed by the acceleration or velocity of each period (or frequency) [1] and directly affect the dynamic response characteristics of near-surface structures. To predict the site-specific properties and seismic hazards caused by earthquakes, the site classification system has been proposed in almost all current seismic design standards. And to determine the ground motion in a more systematic way by considering site effects, the system is useful for seismic design and seismic performance assessment. This site classification system can be used not only for the engineering purpose of seismic design but also as a fundamental indicator for prompt response or an earthquake early warning framework to minimize seismic damage. In other words, as seismic site effects can occur in a significantly diverse manner depending on the regional geotechnical and geological conditions, it is necessary to improve and rationalize the geotechnical classification system that reflects regional geotechnical and topographical characteristics. In particular, unlike overseas regions with major earthquakes, the Korean peninsula, which is part of a region that experiences medium- or small-scale earthquakes, has insufficient records of strong earthquake ground motion. Thus, related studies have been conducted to quantitatively assess the site effects through seismic response analysis that has used geotechnical dynamic properties, including the \(V_{S}\) distribution, or derived a site-specific site classification system based on such assessment [2; 3; 4; 5; 6]. Nevertheless, there are a few studies on differential and efficient site-specific seismic response assessments and the site classification system derivation for a regional-scale level rather than a local site level. Such broad area information can be useful for promptly identifying geotechnical and geological characteristics at a site of interest. And the zonation information provides available engineering indicator information when simultaneous damages occur in a broad area near the epicenter, such as during the Gyeongju earthquake (M\({}_{\text{L}}\) 5.8, 2016) and Pohang earthquake (M\({}_{\text{L}}\) 5.4, 2017). Recognition of the importance of ground-motion amplification from regolith has led to the development of systematic approaches to mapping seismic site conditions [7; 8; 9; 10] as well as quantifying both amplitude- and frequency-dependent site amplification [11]. A now standardized approach for mapping seismic site conditions is measuring or mapping \(V_{S30}\). Real-time earthquake alert systems, such as the Prompt Assessment of Global Earthquakes for Response (PAGER) [12; 13; 14], seek to rapidly evaluate potential ground shaking in the source region and subsequently provide an estimate of the population exposure to potentially fatal levels of shaking in any region of the world. Consequently, knowledge of local seismic site conditions is an important factor in estimating the ground motion amplification potential. [PERSON] and [PERSON] [15] also presented a method for mapping uniform global seismic site conditions, or the average shear velocity to \(V_{S30}\), from the Shuttle Radar Topography Mission (SRTM), a 30 arcsec (approximately 1 km resolution at the equator) digital elevation model [16]. In many seismically active regions of the world, information about surficial geology and shear wave velocity (\(V_{S}\)) either does not exist, varies dramatically in quality, varies spatially, or is not easily accessible.