## 5 Results and Discussion
All the observed stations, regardless of the value's magnitude, show visible earthquake-triggered behavior on the vertical component, as seen on Figure 4. The occurrence of the mainshock and the significant foreshock the day before are seen in the daily solutions of the time-series. The height behavior is rather uniform prior to the shocks, where the recovery in the initial state is visible as time goes by; the earthquake caused a vertical displacement of 1 cm, and the station returned to its original height 10 days after the occurrence of the mainshock. Figure 4: Distortion of the CROPOS’s CORS stations after the earthquake. However, the positional displacements are rather permanent; although not of a uniform trend, the shifted values have slight irregularities regarding the new position, displaying the significant impact of the hazardous earthquake: the distortion of the national reference frame. The outlines of inhomogeneous deformation in horizontal displacements of a smaller scale are similar to the corresponding patterns of aftershocks occurring days after the mainshock. Related co-seismic deformations in the wider area of around a 100 km radius are still appearing and making their impact on land deformation. The distortion values are determined within the frame of the observed sequences. As seen from the triggered vertical displacement, the co-seismic deformation seems to gradually disappear, slowly reaching the original state. For long-term displacement determination, the analysis should be conducted after a longer time span. Surprisingly, the strong correlation between the positional distortion and the distance from the epicenter has not been identified, as seen from the distortion shown in Figure 5. Despite the fact that the Sisak (SISA) station situated nearby the epicenter suffered the greatest shift, followed by the closely dispersed stations of NOVI and ZAGR, the stations of NOVS and BJEL, distanced 60 and 75 km away, respectively, were affected significantly more than the stations of SLUN and KARL, which are closer to the epicenter by about 20 km. The irregular impact of the earthquake noticed on the irregular positional displacement of the CROPOS stations implies the existence of several faults over the observed area. The most remote stations of the CROPOS network, PULA and DUBR, recorded the mainshock in the vertical component but didn't record the related positional displacements. The conducted analysis resulted in the map of the distortion of the CROPOS reference stations affected by the earthquake, seen in Figure 6. The blue and red dots are the positions of the reference stations before and after the earthquake, respectively. The distortion scale was chosen based on the most suitable values for the visible interpretation of the displacement. The direction of the positional distortion is not following any seismological pattern. However, from the inset in the Figure 6, it can be seen that the stations' positional co-seismic displacement can be the resultant vector of the tectonic blocks' movements along the activated strike-slip fault system (details of the fault system are described in [33]). The resultant vector shown on an inset of the figure coincides with the direction of the positional shift of the SISA CROPOS station. Other observed CROPOS stations situated  
Figure 5: Horizontal shifts of the CORS stations after the earthquake. along the Pannonian fault have biased movement; the stations south of the epicenter, NOVI and SANM, have displacement toward the north, while the two stations situated on the northern part of the Pannonian fault regarding the epicenter, ZAGR and ZABO, shifted to the southeast, toward the epicenter. The vice versa movement of these stations implies the existence of the suspected Jastrebarsko fault, which would explain the aftershocks occuring in the vicinity of Zagreb after the Petrinja earthquake.