## 6 Conclusions  
The devastating Petrinja earthquake, with a magnitude of Mw = 6.2, occurring on 29 December 2020 in the northwest region of Croatia, prompted a comprehensive investigation into its impact on the Croatian positioning reference system, CROPOS, specifically focusing on its 13 GNSS codes stations. This article details the resulting major findings:  
Figure 6: Distortion of the CROPOS’s CORS stations after the earthquake.  
Spatial Heterogeneity of Displacement: The analysis revealed a notable 5 cm horizontal co-seismic displacement to the southeast at the earthquake's epicenter. Also, the stations within a 100 km radius exhibited spatially heterogeneous displacement, with positional shifts ranging between 1 and 2.5 cm and vertical shifts between 2 and 4 cm. This heterogeneity, not linearly correlated with the distance from the epicenter, suggests the influence of varied geological structures and fault zones. For such a strong earthquake in an area with not-so-indented topography, the deformation is expected to impact radially.  
Within the geological and tectonic domain, vertical displacements, particularly those observed in the Sava, Kupa, and Glina river plains, are attributed to the consolidation of superficial deposits induced by earthquake shaking. The positional co-seismic displacement of the stations is likely a result of tectonic block movements along the activated strike-slip fault system.  
Furthermore, regional implications and thrust fault activation were noticed on the remote GNSS stations, including those in the Zagreb area, which indicated the potential relaxation of accumulated strain on the Mt. Medvednica thrust fault system, which had ruptured in early 2020 with a lower-than-expected magnitude.  
Moreover, regarding the co-seismic subsidence patterns, interestingly, not all of the observed stations experienced co-seismic subsidence. Figure 4 illustrates the vertical subsidence and uplift variations, challenging a direct correlation with the distance from the epicenter. Soil composition and infrastructure intricacies contribute to these variations.  
Undoubtedly, the Petrinja earthquake significantly impacted the GNSS CORS stations of the CROPOS reference system; this is especially evident at stations like SISA. This bears implications for geodetic and geophysical applications, potentially affecting the ground displacement, geodetic field measurements, and cadastral surveys in the affected area. To mitigate future disruptions and prevent the introduction of errors into positioning data, meticulous post-processing, correction efforts, careful assessment, maintenance, and redundancy planning are strongly recommended. These measures are vital for ensuring the resilience and accuracy of future geodetic operations in the affected region.  
Conceptualization, O.B.O.; methodology, M.V. and O.B.O.; computation, M.V., S.Y. and O.B.O.; validation, S.Y.; formal analysis, O.B.O., M.V., and S.Y.; writing--original draft preparation, O.B.O.; writing--review and editing, M.V. and S.Y.; visualization, M.V. and O.B.O. All authors have read and agreed to the published version of the manuscript.  
This research was funded within the scientific project \"Application of modern technologies and smart sensors in geomatics\", in 2023, from the University North, Croatia.  
Data Availability Statement: Data used in this research is open and free satellite data obtained from Copernicus portal and GNSS data obtained from State Geodetic Administration for research only.  
We acknowledge [PERSON] from the Croatian Geological Institute for fruitful discussion and geological insight into the matter.  
The authors declare no conflicts of interest.