The geographic coincidence of the Chile Ridge slab window and the Patagonia ice fields offers a unique opportunity for assessing the effects of slab window rheology on glacial isostatic adjustment (GIA). Mass loss of these ice fields since the Little Ice Age causes rapid but variable crustal uplift, 12–24 mm/yr around the North Patagonia ice field, increasing to a maximum of 41 mm/yr around the South Patagonia ice field, as determined from newly collected or processed geodetic data. We used these observational constraints in a three-dimensional Maxwell viscoelastic finite element model of GIA response above both the subducting slab and slab window in which the upper-mantle viscosity was parameterized to be uniform with depth. We found that the viscosity of the northern part of the slab window, ~2 × 10¹⁸ Pa·s, is lower than that of the southern part by approximately an order of magnitude. We propose that this along-strike viscosity contrast is due to late Cenozoic ridge subduction beneath the northern part of the slab window, which increases asthenospheric temperature and reduces viscosity

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In the last 300 years the window of time for two consecutive large and destructive intermediate-depth earthquakes in Vrancea (Romania) was between 36 and 102 years. An explanation for the larger window of time might be a release of stress produced by a slow-slip-event (SSE). In a vertical sinking slab slightly attached from the Earth’s crust both large earthquakes and SSE are expected to generate a downward movement in the vertical displacements of GPS data. The building-up of stress in the asperity preventing a steady aseismic sinking was expected to be transmitted upwards to faults in the crust and recorded based on a magnetotelluric phase splitting effect. A large stress build-up has been suggested around a fault in the years 2012–2013, but no large earthquake was recorded. We supposed a large SSE in the year 2013–2014 with a duration of 13 months released the accumulated stress. GPS stations in the epicentral region of Vrancea seismic active region supported our suggestion by showing a downward displacement of vertical data obtained for the year 2014. However, the vertical displacements are small and other possible causes than SSE need to be taken into account.

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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

After a great subduction earthquake, viscoelastic stress relaxation causes prolonged seaward motion of inland areas of the upper plate, as was observed around the turn of the century in the area of the 1960 Mw 9.5 Chile earthquake with Global Navigation Satellite System (GNSS) measurements. However, recent GNSS observations during 2010–2019 indicate a systematic decrease in the velocity of the seaward motion over a region covering the latitudinal range of the southern half of the 1960 rupture. Data from the only long-lived continuous site in this region (COYQ since 1997), situated over 200 km away from the trench, suggest that the decrease in the seaward velocity (or increase in the landward velocity) occurred within a few years prior to 2010. This rapid and regional change cannot be explained by viscoelastic relaxation. We thus propose that the change was caused by a relatively sudden downdip widening of the zone of locking along the megathrust. Using three-dimensional finite element modelling, we find that the observed velocity change cannot be otherwise explained, although the amount of the increase in locking cannot be uniquely determined because of trade-offs between, and uncertainties in, the various parameters involved. For example, the degree of the increase in locking is affected by the value of coseismic slip in 1960 in the southernmost part of the rupture zone. A postseismic deformation model with greater coseismic slip in accordance with the most recent coseismic slip model in the literature better fits COYQ data prior to 2005 and requires greater locking increase afterwards. A model with less coseismic slip requires less locking increase but an additional long-term slow slip event prior to 2005. The rapid surface velocity change and the inferred increase in megathrust locking several decades after a great earthquake present new challenges to the understanding of fault mechanics and subduction zone dynamics.

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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

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