# Compatible Ground Motion Models for South Korea Using Moderate Earthquakes
## 3 Results  
### Comparisons with Site-to-Source Distance  
For plotting purposes, the median of the measured and inferred V\({}_{530}\) = 610 m/s was used as input to GMMs that required a V\({}_{530}\) value. For brevity, a series of acceleration plots against distance will be made for the major events, 2016 Gyeongju and 2017 Pohang, for NGA-West GMMs. An example showing the dependent events will also be shown as well as NGA-West2 and NGA-East GMMs for the major events. These are made to help the reader familiarize the environment and dataset available. An example of the data comparison is shown in Figure 1. The figure plots NGA-West GMMs for PSA(T = 0.2 s) against processed SA(T = 0.2 s) data for both the 2016 M\({}_{\rm W}\) 5.5 Gyeongju earthquake and the 2017 M\({}_{\rm W}\) 5.5 Pohang earthquake. With respect to the 2016 Gyeongju event, the data appear to plot somewhat below the NGA-West GMMs on average but do relatively well in the 100 to 200 km range. Although originally not intended for distances past 200 km, the data appear to be bound by all 5 NGA-West GMMs. With respect to the 2017 Pohang event, the GMMs appear to predict relatively well at the 100 to 200 km distances, with some slight overprediction scattered across the available distance range. Figure 1: Comparison of processed ground motion data from the (**a**) 2016 M\({}_{\rm W}\) 5.5 Gyeongju earthquake and the (**b**) 2017 M\({}_{\rm W}\) 5.5 Pohang earthquake with NGA-West GMMs. The comparison is made for spectral acceleration and pseudo spectral acceleration at T = 0.2 s.  
For comparison, Figure 2 is similar to Figure 1 except for PSA(T = 1.0 s) against processed SA(T = 1.0 s) data. The figure shows the GMMs to be relatively more linear with respect to log-log space, with an overall overprediction of accelerations, especially for the 2017 Pohang event. Interestingly, the variability in these GMMs is wider at T = 0.2 s than at T = 1.0 s for distances greater than 200 km. Figure 3 is a plot of spectral accelerations at T = 0.02 s. Interestingly, the plot shows similar patterns as seen in Figure 1, with visual inspection suggesting that the NGA-West GMMs tend to overestimate accelerations on the Korean peninsula, at least for-moderate sized earthquakes. Figure 4 plots PSA(T = 10.0 s) against processed SA(T = 10.0 s) data. The absolute values of the data are quite small and perhaps insignificant but are kept here for completeness and comparison. Such small values will have an impact on the residuals. What is  
Figure 3: Comparison of processed ground motion data from the (**a**) 2016 \(M_{\mathrm{W}}\) 5.5 Gyeongju earthquake and the (**b**) 2017 \(M_{\mathrm{W}}\) 5.5 Pohang earthquake with NGA-West GMMs. The comparison is made for spectral acceleration and pseudo spectral acceleration at T = 0.02 s.  
Figure 2: Comparison of processed ground motion data from the (**a**) 2016 \(M_{\mathrm{W}}\) 5.5 Gyeongju earthquake and the (**b**) 2017 \(M_{\mathrm{W}}\) 5.5 Pohang earthquake with NGA-West GMMs. The comparison is made for spectral acceleration and pseudo spectral acceleration at T = 1.0 s.  
noticeable is that the 2017 Pohang earthquake does not seem to show significant signs of attenuation with distance relative to the 2016 Gyeongju earthquake. Interestingly, the scatter in NGA-West GMMs at T = 10.0 s is significant, with about two orders of magnitude in difference at the longer distances considered. A similar plot is made for dependent events in Figure 5. Figure 5a shows the results for an M\({}_{\rm W}\) 5.1 foreshock to the 2016 Gyeongju earthquake. The recordings seem to show similar levels of ground shaking to the M\({}_{\rm W}\) 5.5 main shock and plot quite closely, from a visual sense, to NGA-West GMMs in the 100 to 200 km range. Figure 5b shows the results for an M\({}_{\rm W}\) 4.7 aftershock to the 2017 Pohang earthquake. Unlike the foreshock in the figure, the NGA-West GMMs tend to overestimate ground shaking on average.