Observations from permanent GNSS stations are actively used for the research and monitoring of geodynamic processes. Today, with the use of modern scientific programs and IGS products, it is possible to determine GNSS station coordinates and velocities at the level of a few millimeters. However, the scientific community constantly faces the question of increasing the accuracy of coordinate definitions to obtain more reliable data in the study of geodynamic phenomena. One of the main sources of errors is systematic measurement errors. To date, the procedure for their removal is still incomplete and imperfect. Also, during the processing of long-term GNSS measurements, it was found that the coordinate time series, after the removal of trend effects, are also characterized by seasonal variations, mainly of annual and semi-annual periods. We estimated the daily coordinate time series of 10 permanent GNSS stations in the central-eastern part of Europe from 2001 to 2019 and calculated the seasonal variation coefficients for these stations. The average value of the coefficients for the annual cycle for the N, E, and H components is −0.7, −0.2, and −0.7 mm, and for the semi-annual cycle the average value is 0.3, 0.4, and −0.5 mm. The obtained coefficients are less than 1 mm, which is why it can be argued that there is no seasonal component in the coordinate time series or that it is so small that it is a problematic task to calculate it. This practical absence of a seasonal component in long-term time series of GNSS coordinates, in our opinion, is partly compensated by the use of modern models of mapping functions (such as VMF3) for zenith tropospheric delays instead of the empirical GMF. To test the obtained results, we calculated the coefficients of seasonal variations for the sub-network of GNSS stations included in the category of the best EPN stations—C0 and C1. The values of the coefficients for the stations of this network are also less than 1 mm, which confirms the previous statement about the absence of a seasonal component in the long-term time series of coordinates. We also checked the presence of seasonal changes in the time series using the well-known decomposition procedure, which showed that the seasonal component is not observed because the content does not exceed 10% for additive decomposition and 20% for multiplicative decomposition.

The purpose of research is to identify horizontal deformation of the Ukraine territory, using only proven and suitable for geodynamic interpretation GNSS stations. The initial data are observations from 30 GNSS stations for 2017 to 2020. Methodology. The methodology includes the analysis of modern Earth's crust deformations of Ukraine. As a result, for the first time the impact of the coordinates time series created by two different methods: Precise Point Positioning (PPP) and the classical differential method, on determining deformation processes was analysed. It was established that nowadays for the tasks of monitoring, including geodynamic, it is necessary to use the Precise Point Positioning (PPP) method, because the accuracy of determined velocities of the GNSS stations by this method was higher than in the classical differential method. Results. A map of horizontal Earth's crust deformations on the territory of Ukraine was created according to the coordinates time series of GNSS stations. The extension areas of Shepetivka-Starokostiantyniv Khmelnytsky region, Boryspil- Pryluky-Pereyaslav-Khmelnitsky Kyiv and Chernihiv region, as well as a compression area of the Earth's crust in Nizhyn - Stepovi Khutory - Kozelets of Chernihiv region was identified. Additionally, a map of horizontal displacements of the GNSS-stations was created, where the diverse of these displacements was observed, which is likely to be caused by the presence of modern subvertical and sub-horizontal faults and fault areas. For better interpretation of the obtained results, it is necessary to involve geological and geophysical data of tectonic activity of the Ukraine territory.

This study examines the use of GNSS (Global Navigation Satellite Systems) for earthquake detection, utilising the GipsyX software to analyze ground displacements. GNSS technology provides real-time, high-precision measurements of the Earth’s crust, which are crucial for detecting the subtle shifts that indicate seismic activity. We investigated three seismic events from 2023 and 2024, assessing how the earthquake magnitude and the distance from the epicenter impacted the GNSS station coordinate time series. Stations located closer to the epicenters showed more pronounced displacements, especially in events with higher magnitudes. For smaller earthquakes, shifts were observed mainly in the vertical (Up) direction, while larger tremors caused noticeable changes in both horizontal and vertical coordinates. The results reveal that even moderate seismic activity can be detected when stations are positioned within a certain range from the epicenter. These findings underscore the reliability of GNSS-based systems in monitoring seismic shifts and highlight the value of distance and magnitude in determining the extent of ground displacements. By enhancing real-time monitoring, this approach improves early warning systems, offering critical insights for earthquake preparedness and risk mitigation. Keywords: GNSS, earthquake detection, seismic monitoring, high-frequency GNSS data, GipsyX.

The article presents the results of a study of the spatial dynamics of the Earth’s crust in the area of the Rivne Nuclear Power Plant based on long-term observations using global navigation satellite systems (GNSS). The main objective of the work is to quantify the horizontal and vertical velocities of the Earth’s surface displacement within the potentially sensitive zone to geodynamic impacts. To achieve this goal, we used the Precise Point Positioning (PPP) methodology implemented in the GipsyX software environment, which provides absolute positioning with millimeter accuracy without the need to involve local reference stations. The processing of daily RINEX files covered a six-year observation period (2019-2025). Coordinate time series were generated for six permanent GNSS stations spatially located in the immediate vicinity of the Rivne NPP. The displacement rates in the topocentric coordinates (E, N, U) of ITRF2014 were calculated. The obtained results indicate a predominantly northeast direction of horizontal displacements with an average velocity of about 22 mm/year, and also record vertical subsidence in the range of -1.6 to -3.7 mm/year. The spatial visualization of the displacement vectors made it possible to identify local anomalies and assess possible impacts of both natural and man-made nature. The presented study is of practical importance for ensuring long-term geodynamic monitoring of critical infrastructure facilities. The results obtained can be integrated into the system of engineering and geodetic monitoring of the stability of the Rivne NPP site, as well as used to develop recommendations for improving the safety of nuclear power facilities in Ukraine.

To investigate and remove the network effect to the national GNSS network the results obtained from three GNSS networks which are tied to ITRF2008 using minimal constraints were compared. The first network is the EUREF Permanent Network (EPN), the second is EPN subnetwork processed by WUT LAC (WUT), the third is exactly Ukraine reference network (URN). The position differences between these networks - EPN and URN (WUT and URN) can reach 9.1 (6.6) mm for X, 4 (3.8) mm for Y and 11.7 (12.2) mm for Z. To obtain consistent station positions and velocities without network effect two weekly solutions were combined. The results demonstrate that the network effect on the local solution (Ukraine reference network) can be eliminated. This approach is valid because the same data analysis strategy was applied during both network processing.