Over the last two decades the Romanian territory has been covered by a dense permanent Global Navigation Satellite System (GNSS) network, presently including more than one hundred stations established and maintained by several Romanian agencies. We refer to these as continuous GNSS (cGNSS) stations. For the study presented here we exclusively use the data of the Global Positioning System (GPS), which is the oldest and most widely-used element of GNSS. At the beginning of this century, we realized the potential of cGNSS for scientific purposes. Applications include monitoring of crustal deformations associated with the Carpathian orogen and the neighbouring platforms in Romania, in correlation with tectonic processes in South-East Europe (Africa-Europe plate interactions), observation of (vertical) crustal motions to study the surface expression of deep earthquakes in the Eastern Carpathians Bending Zone (Vrancea region). This study presents the results of our analysis of the aggregated cGNSS measurements in Romania. The results cover the period 2000-2020, but focus on the period 2013-2020 when the majority of the stations became operational. We processed the Receiver Independent Exchange Format (RINEX) daily data (sampled at 30-second intervals) of all available stations. For this purpose, we used the GipsyX scientific GPS analysis software, applying the so-called Precise Point Positioning (PPP) strategy. This resulted in time-series of the horizontal and vertical position components of each station in the International Terrestrial Reference Frame 2014 (ITRF14). Subsequently, the time-series were converted to a stable Eurasian tectonic reference plate using the ITRF14 plate rotation model for Eurasia. All data processing in this study is based on this reference frame. The results of this complex, long-term study indicates that the Romanian territory trends to move slightly southward relative to stable Eurasia, at velocity rates of about 1.0 mm/yr in the north and up to 3.0 mm/yr in the south. This may be an indication of plate-stretching due to slab-rollback of the African plate relative to the Eurasian plate. Until now we did not find an obvious correlation between the deep Vrancea earthquakes and (vertical) surface motions. That is probably because the recent earthquakes were too small. @en

A decade of improvements and new development of tools for observation statistics, standard point positioning, clock-jumps and cycle-slip detection and other interruptions over all constellations, frequencies and signals, satellite elevations and azimuths, elevation-specific histograms, satellite ascending/descending times for horizon and user elevation cut-off, pseudo-range multipath and noise, carrier-phase signal-to-noise ratio, data gaps and small data pieces and other useful lists and statistics allow us to analyze in detail the GNSS data collected for one of the main research subjects resulted from the September 2013 unique seismic swarm event that occurred in Romania. Open-source software such as: G-Nut/Anubis (Geodetic Observatory Pecný), RTKLIB, gLAB (European Space Agency) and commercial software like: Leica Spider QC, Leica Geo Office are used for quality control over all available data of the Ph.D. thesis called “An integrated GNSS and seismotectonic study of the NW Galati seismogenic area”. The main purpose of the paper is currently the quantity and quality monitoring of all available GNSS data achieved in 4 years of continuous monitoring along with the solutions obtained from the 4 GPS measuring campaigns (2013-2016), i.e. signals, frequencies and satellite constellations.@en

In this paper we present the results of an analysis of 15 years of continuous GNSS/GPS measurements in Romania. The purpose of this work is threefold: monitoring of crustal changes occurring in the Romanian territory in correlation with tectonic processes in South-East Europe (Africa-Europe plate interaction), observation of crustal movements in order to establish the surface-to-depth relationship of deep earthquakes in the area of the Eastern Carpathians bend zone (Vrancea region) and improving the accuracy of the coordinates of the national seismic network stations. The development of the Romanian GNSS/GPS (Global Navigation Satellite System/Global Positioning System) network started in 2001 when the first permanent station was installed at Lacauti in the Vrancea seismogenic area. Since then the network has grown to 27 stations covering the entire Romanian territory and is still expanding. In our analysis we also include 18 GNSS stations of the GeoPontica network, developed and maintained by the National Research and Development Institute for Marine Geology and Geoecology, with the purpose to monitor geodynamic processes in the Western Black Sea coastal area. It consists of 13 stations in Romania and 5 in Bulgaria. In this paper we provide a comprehensive description of the GPS networks, reflecting the actual capabilities, justifying implementation choices and presenting the results. The GPS data were processed in daily batches with the “precise point positioning” (PPP) strategy using the GIPSY-OASIS software. From the resulting position timeseries the horizontal and vertical motion vectors were calculated relative to a stable Eurasian reference frame. The results of our study show that internally the Romanian territory appears to be quite stable, but the whole country trends to move slightly southward relative to Eurasia at velocity rates of about 2.5 – 3.0 mm/yr, especially the southern part. We speculate that this is a far-field effect of slab roll-back due to the subduction of the African plate under the Eurasian plate at the Aegean trench, way to the south. Until now, we did not observe any long-term signals due to the deep Vrancea earthquakes because the effects on surface motion are probably small, but we will do more detailed studies of some recent (2016) Mw 5.3 seismic events in the Vrancea area.@en