# Compatible Ground Motion Models for South Korea Using Moderate Earthquakes
## 4 Discussion and Conclusions  
To ascertain which, if any, of the PEER NGA GMMs would be applicable to the Korean peninsula, collections of earthquake and ground motion data were compiled and processed. This resulted in data from five diverse earthquakes of moderate magnitude around the Korean peninsula from 2016. There were three main shocks, one of which may be a potentially induced or triggered event, with another being offshore, one foreshock, and one aftershock. Plots of distance against spectral acceleration at T = 0.02, 0.2, 1.0, and 10.0 s showed appreciable scatter at distances less than 100 km but would monotonically increase or decrease, representing underestimation and overestimation, respectively, at distances farther than 200 km, the typical limit of the NGA-West/West2 GMMs considered. NGA-East GMMs also showed similar patterns with distance but did not exhibit the considerable monotonic increase or decrease, as shown in the NGA-West/West2 GMMs. Tabulating the relative residuals across all earthquake events showed that the NGA-East GMMs performed well except at T = 0.02 s. The results also suggested the NGA-West/West2 GMMs I08/I14 also performed comparatively well across the board. In terms of rankings, the NGA-East GMMs DASG15 and PCZT18 did relatively well and would be recommended for earthquake- and seismic-related studies in the Korean peninsula. Surprisingly, the I08 and I14 GMMs did well overall, with the only major setback being at an evaluation of SA(T = 10.0 s). For long periods, both GMMs by CB08 and BSSA14 can perform well; however, the earthquake magnitudes considered herein are not conducive to long periods of strong ground motion. Therefore, it is better to consider DASG15 or PCZT18 instead. An interesting outcome of this study is the consideration of aftershocks. AS08, ASK14, and CY08 integrate aftershocks into their GMMs, and the results suggest AS08 performs well for such earthquake types, better than ASK14, surprisingly. There were many challenges with this investigation, with most revolving around a lack of information. An important one was the lack of geological and seismological data available for ground motion recording sites and past earthquakes. Much of the missing information used to compensate for missing parameters was inferred or taken from specific studies, such as the V\({}_{\text{S30}}\) dataset. However, this investigation did not consider earthquakes without an M\({}_{\text{W}}\), which restricted the availably of data. Hopefully, the authorities will attempt to integrate a system for estimating and publicizing M\({}_{\text{W}}\) estimates. Estimating the magnitude was out of scope for this study. Another issue was the confusion with ground motion recordings and a lack of appropriate technical support. Much of the time was spent searching for ground motion data, which ended up being KIGAM instead of KMA. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**GMM** & **2016 M\({}_{\text{W}}\) 5.5** & **2017 Mw 5.5 P** & **Mw 5.1 F** & **M\({}_{\text{W}}\) 4.7 A** & **M\({}_{\text{W}}\) 4.5** & **Sum** \\ \hline AS08 & 1.00 & 1.12 & 1.14 & 1.21 & 1.77 & 6.24 \\ BA08 & 2.41 & 1.65 & 3.18 & 1.59 & 2.14 & 10.97 \\ CB08 & **0.73** & **0.76** & **0.95** & **0.93** & **1.56** & **4.93** \\ CY08 & 1.15 & 1.42 & 1.35 & 0.95 & 5.14 & 10.01 \\ IQ8 & 4.55 & 5.75 & 3.65 & 3.50 & 8.82 & 26.27 \\ \hline ASK14 & 1.08 & **1.09** & 1.27 & 1.97 & 5.32 & 10.73 \\ BSSA14 & **1.07** & 1.47 & **1.17** & **1.30** & **3.84** & **8.85** \\ CB14 & 1.44 & 1.90 & 1.74 & 2.52 & 7.70 & 15.30 \\ CY14 & 2.39 & 2.46 & 2.56 & 2.25 & 9.12 & 18.78 \\ I14 & 1.78 & 2.40 & 1.57 & 1.89 & 5.15 & 12.79 \\ \hline DASG15 & **0.41** & **0.26** & **0.54** & **0.47** & **1.72** & **3.4** \\ PCZT18 & 1.38 & 1.08 & 1.58 & 0.67 & 3.36 & 8.07 \\ \hline SUM & 19.39 & 21.36 & 20.70 & 19.25 & 55.64 & \\ \hline \end{tabular} \({}^{\text{F}}\) foreshock. \({}^{\text{A}}\) aftershock. \({}^{\text{F}}\) possible induced or triggered earthquake.  
\end{table} 
Table 8: _Score_ for each GMM per earthquake event for SA(T = 10.0 s).