# Compatible Ground Motion Models for South Korea Using Moderate Earthquakes
## 2 Materials and Methods
### GMMs Considered  
PEER separated ground motion work into generational and geographical segments. The first set of GMMs was released under the program Next Generation of Ground Attenuation Models for the Western United States (NGA West). This initial set was based on a comprehensive and extensive earthquake ground motion database and consisted of 5 GMMs for active shallow crustal regions. The program concluded in 2008 and produced GMMs, named by their developers as Abrahamson and Silva, Boore and Atkins, Campbell and Bozorgnia, Chiou and Youngs, and Idriss, which will be abbreviated to AS08, BA08, CB08, CY08, and I08, respectively, herein [1; 2; 3; 4; 5]. These NGA West GMMs estimated the natural log of the pseudo spectral accelerations (PSAs) using the geometric mean of a period and azimuth-decoupled version of the Rot50 intensity measure (GMRotI50) [41] as well as their associated uncertainties. Studies show that the differences between Rot50 and GMRotI50 were similar in short periods, with a maximum difference of about 7% in longer periods [40]. The subsequent NGA program was aptly named NGA-West2, which utilized an expanded database as well as a better understanding and quantification of earthquake and wave propagation phenomena. This set of 5 GMMs was again applied to active shallow crustal regions and named by their developers as [PERSON], [PERSON], and [PERSON]; Boore, \begin{table}
\begin{tabular}{c c c} \hline \hline Time Window & At the beginnings (s) & Event time \(-\)10 \\  & At the end (s) & Event time +200 \\ \hline \multirow{2}{*}{Cosine Taper} & At the beginning (\%) & 5 \\  & At the end (\%) & 5 \\ \hline \multirow{2}{*}{High-Pass Filter} & Low-Pass (Hz) & 0.1, 4 th order \\  & High-Pass (Hz) & 49.9, 5 th order \\ \hline \multirow{2}{*}{Post-Cosine Taper} & At the beginning (\%) & 5 \\  & At the end (\%) & 5 \\ \hline \multirow{2}{*}{Baseline Correction} & Fitting Domain & Velocity \\  & Polynomial Order & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Ground motion processing and baseline correction program. [PERSON], [PERSON], and [PERSON]; [PERSON] and [PERSON]; [PERSON]; and [PERSON]. These are abbreviated as ASK14, BSSA14, CB14, CY14, and II4, respectively, herein [6; 7; 8; 9; 10]. However, the NGA-West2 GMMs estimated the natural log of the PSA from the aforementioned Rot50. The final NGA GMM project was NGA-East. This project focused on developing GMMs for Central and Eastern North America (CENA), a relatively stable region with low seismicity [42]. Like NGA-West2, NGA-East estimated the natural log of the PSA using Rot50. Although NGA-East offers multiple GMMs, only two by [PERSON], [PERSON], [PERSON], and [PERSON] and [PERSON], [PERSON], [PERSON], and Tavakoli, abbreviated as DASG15 and PZCT18, respectively, are considered in this study [11; 12]. Both were selected for consideration because they seemed to have survived the test of time, with one having been updated. We use the newer version herein [12]. Additionally, some of the proposed NGA-East GMMs are slight modifications to an NGA-West or NGA-West2 counterpart, some require parameters that are unobtainable at this point, and at least one did not offer a quantifiable relationship within the document. It should be noted that DASG15 offers 4 versions of their GMM. These four versions are binary combinations of a corner frequency (1 or 2) and stress parameter (constant or variable) used in their simulation technique [11]. Interestingly, DASG15 did not seem to offer practical guidance on which version to use; therefore, all four will be initially considered herein as DASG15-ICC, DASG15-1 CV, DASG15-2 CC, and DASG15-2 CV. PZCT18 also has two versions, and the one designated for CENA is considered herein. The NGA GMM models considered in this study are detailed in Table 4.  
With respect to the NGA-West and NGA-West2 GMMs, there are several input parameters, which are very difficult to obtain or are not typically used in seismology or earthquake engineering analyses.