## 3 Results
### Regional Analysis of Coordinate Differences
In contrast, the right panel (GAMIT-Bernese) reveals distinct regional differences between the two software solutions, with Gyeongbuk again exhibiting the highest RMS difference  
Figure 5: Regional horizontal root mean square (RMS) differences in coordinate estimates between GAMIT/GLOBK, Bernese, and KGD2002 solutions. RMS values (in mm) are computed from \(\Delta\)N and \(\Delta\)E components for each of the nine provinces including Jeju. Blue bars represent RMS differences between GAMIT and Bernese solutions, red bars show differences between GAMIT and KGD2002, and yellow bars correspond to differences between Bernese and KGD2002. (>13 mm), followed by Chungnam. Jeju consistently shows the lowest RMS values across all comparisons, suggesting stable and consistent positioning at that site. These spatial patterns corroborate the statistical findings and highlight regions where either geophysical complexity or weaker network geometry may be contributing to increased positioning variation. To further investigate the directional patterns of coordinate discrepancies, we analyzed the azimuthal distribution of the \(\Delta\)N, \(\Delta\)E horizontal residuals across the nine administrative regions. The polar histograms presented in Figures 7-9 provide insight into whether these differences are randomly oriented or exhibit systematic directional tendencies. Each residual vector was projected in the local NE plane, and its azimuth angle was computed using atan2(\(\Delta\)N, \(\Delta\)E). The histograms in Figure 7 (GAMIT vs. KGD2002) demonstrate that most regions exhibit near-isotropic distributions, with residual vectors broadly dispersed around the circle. However, subtle directional trends are visible in certain regions. In Gyeongnam, for example, the vectors show a mild concentration toward the northeast (mean azimuth \(\approx\) 52.3\({}^{\circ}\), directional concentration \(\approx\) 0.22), suggesting possible geometric bias related to the regional station layout. In Jeju, despite a small sample size, residuals are notably concentrated around the southeast quadrant (mean azimuth \(\approx\) 124.6\({}^{\circ}\), directional concentration \(\approx\) 0.41), possibly due to its insular position and asymmetric baseline configuration. Despite the extensive number of control points analyzed in this study, notable directional anomalies remain evident in certain regions--particularly in Gyeongbuk and Gyeongnam. These deviations are likely influenced by localized tectonic activity associated with the Yangsan Fault, as well as seismic events such as the 2016 Gyeongju earthquake (Mw 5.8) and the 2017 Pohang earthquake (Mw 5.4), which were among the most damaging earthquakes recorded in Korea. These findings suggest that long-term reliance on a static reference frame based on ITRF2000 may no longer be sufficient to represent the current geokinematic reality of the Korean Peninsula. Over time, the accumulation of unmodeled crustal motion can lead to spatial inconsistencies between observed GNSS positions and the original reference realization--a phenomenon known as datum deformation [31; 32]. Furthermore, this reflects the broader issue of \(c\), wherein a static frame is maintained without adjustment despite ongoing geophysical change, resulting in increased misalignments  
Figure 6: Spatial distribution of horizontal coordinate RMS differences by region. From left to right, the maps display RMS values (in mm) for GAMIT/GLOBK–KGD2002, Bernese–KGD2002, and GAMIT/GLOBK–Bernese comparisons. The color of each province represents the RMS computed from \(\Delta\)N and \(\Delta\)E components. The color bar indicates the magnitude of the RMS values, with warmer colors (yellow to red) denoting larger differences and cooler colors (blue) indicating smaller differences. with the actual crustal dynamics [33]. These results underscore the necessity of periodically evaluating and updating national geodetic datums. In this regard, the Republic of Korea is currently preparing for a national transition to the ITRF2020 reference frame [34].