# A Numerical Model for Simulating Ground Motions for the Korean Peninsula
## 2 Ground Motions Collected for Developing the Ground Motion Simulation Model  
To develop a numerical model for simulating ground motions in the Korean Peninsula, the ground motions recorded at 111 seismic stations during the 2017 Pohang earthquake were collected from the National Earthquake Comprehensive Information System (NECIS) of Korea Meteorological Administration (KMA). Figure 1 shows the distribution of 111 stations out of 157 stations in Korea, which provided ground motion records with a high signal-to-noise ratio (SNR). To exclude ground motions with signal distortion due to noise, we only collected recordings with a signal-to-noise ratio (SNR) greater than 2.0. Each station provided three components (North-South, East-West, and Vertical) of ground motions. Thus, the total number of recorded ground motions is 333 (=\(3\times 111\)). All collected ground motions were recorded with a sampling rate of 0.01 s (100 samples per second), and the NECIS provided these records after applying a high cut anti-aliasing filter to remove the noise with a frequency greater than 40 Hz. In this study, low-frequency noise was also removed by using the 0.1 Hz (corresponding period 10 s) low-cut filter, and baseline correction was done using a technique  
Figure 1: The 2017 Pohang earthquake and seismic recording stations with ray path lines. proposed by [PERSON] and [PERSON] [13]. Table 1 summarizes the information on the 2017 Pohang earthquake. Figure 2 shows the East-West (E-W) direction component of ground acceleration (\(\ddot{u}_{g}\)), velocity (\(\ddot{u}_{g}\)), and displacement (\(u_{g}\)) at station BUS2. Figure 2a-c show raw record data for ground acceleration, velocity, and displacement. Figure 2d-f show the records after applying a low-pass filter, whereas Figure 2g-i show ground motions after applying base line correction. Figure 2j-l show ground motions after applying a low-cut filter, as well as base correction. It can be observed that ground motions are properly adjusted by using both a low-cut filter and base correction. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Event Name** & **Local Date-Time** & **Longitude** & **Latitude** & **Focal** & **Magnitude** \\  & **(East)** & **(North)** & **Depth (km)** & **\(M_{L}\)** \\ \hline the 2017 Pohang earthquake & 14:29 15 November, 2017 & 129.37 & 36.11 & 9 & 5.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Information on the 2017 Pohang earthquake (National Earthquake Comprehensive Information System (NECIS)). Figure 2: Original and adjusted ground motions at station BUS2: (**a**) Original data-acceleration, (**b**) Original data-velocity, (**c**) Original data-displacement, (**d**) Low cut filter-acceleration, (**e**) Low cut filter-velocity, (**f**) Low cut filter-displacement, (**g**) Baseline-acceleration, (**h**) Baseline-velocity, (**i**) Baseline-displacement, (**j**) Signal processing-acceleration, (**k**) Signal processing-velocity, (**l**) Signal processing-displacement. The site amplification effect was also removed from the ground motion records because a ground motion model has been developed for hard rock conditions without considering site effects. In general, site effects are considered in numerical models by applying a site amplification factor to the ground motions generated for hard rock site conditions. In this study, the site amplification effect was removed from the recorded ground motions by using a horizontal-to-vertical spectral ratio (HVSR) technique, which has been widely used for site amplification factor calculation [14; 15; 16; 17]. The site amplification factor, \(AMP(f)\), can be calculated from Equation (1). \[AMP(f)=\frac{\sqrt{PSA_{EW}(f)\times PSA_{NS}(f)}}{PSA_{V}(f)} \tag{1}\]  
where \(PSA_{EW}(f)\), \(PSA_{NS}(f)\), and \(PSA_{V}(f)\) are the 5% damped pseudo spectral acceleration (PSA) from the East-West, North-South, and Vertical components of ground motions, respectively.