The Sındırgı region of western Anatolia, located within the extensional tectonic regime of Türkiye, experienced two moderate earthquakes in 2025, occurring on 10 August (Mw 6.1) and 27 October (Mw 6.1). In this study, high-rate (1 Hz) Global Navigation Satellite System (GNSS) observations were analysed to estimate earthquake magnitudes using peak ground displacement (PGD) measurements. GNSS data from 10 stations for the August event and 12 stations for the October event were processed using the PRIDE PPP-AR software to derive displacement time series. Earthquake magnitudes were estimated from PGD values using empirical relationships proposed in previous studies. Overall, the GNSS-based magnitude estimates show good agreement with values reported in seismic catalogues, ranging between Mw ≈ 5.5 and 6.1, with one of the evaluated empirical PGD–Mw relationships providing the closest agreement (Mw = 6.07 ± 0.3 and Mw = 6.13 ± 0.2, respectively). In addition, a strong consistency was observed between GNSS-derived PGD onset times and S-wave arrival times recorded at seismometer stations, particularly within 10–50 km of the epicentre, demonstrating the capability of GNSS observations to reliably capture both coseismic displacement and seismic-wave propagation characteristics. Furthermore, the observed consistency between co-located low-cost and geodetic-grade GNSS receivers highlights the potential of low-cost GNSS systems for reliable coseismic deformation monitoring and for the development of dense GNSS observation networks.

This study presents a new high-resolution GNSS-derived velocity field and the first internally consistent, segment-resolved block model for the Havran–Balıkesir Fault Zone (HBFZ) in western Anatolia. Inversion of the GNSS velocity field was performed using a dense network of 77 sites within a 3D elastic half-space framework to estimate fault slip rates and interseismic coupling. The results reveal that the HBFZ behaves as a kinematically heterogeneous fault system, with deformation systematically partitioned along strike. Block-modeling results indicate pronounced along-strike variations in interseismic coupling and slip-deficit accumulation. While the westernmost Havran segment is weakly coupled and accommodates limited accumulation, the Turplu and Gökçeyazı segments emerge as major strain-accumulation zones with high and laterally continuous slip-deficit rates. In particular, the Gökçeyazı segment exhibits slip-deficit rates of ~4–6 mm/yr and nearly two millennia of seismic quiescence, implying the potential for a future large-magnitude earthquake (Mw ~7.1–7.3). The strong agreement between GNSS-derived deformation patterns and independent geological and paleoseismological constraints suggests that this segment is currently in an advanced stage of the seismic cycle. These findings highlight the importance of segment-scale geodetic observations for seismic hazard assessment in northwestern Anatolia.

The radiation balance of our planet affect climate system that showing signs of breaking down due to the rising temperatures, melting of ice and water flows to the oceans from glaciers. In the last decade, GNSS Meteorology and Reflectometry methods are increasingly used for global climate change studies that provides important parameters such as water vapor in the troposphere and ice/sea level measured based on reflected signals. The main purpose of the study is retrieving meteorological and physical parameters of the Earth's surface in the Antarctica to contribute monitoring climate change. For this purpose, dual antenna and single antenna GNSS stations were specially designed within the scope of TUBITAK research project 118Y322 to produce output by combining an ultrasonic sensor to detect real-time ice/sea level. These two GNSS stations including meteorological station were installed on Horseshoe Island during 4th National Antarctic Science Expedition of Turkey (TAE-4). It is believed that these stations will contribute to monitor global climate change by providing important information about troposphere and physical characteristics of Earth surface. In this study, the processes and objectives from the design works of the stations to their installation in Antarctica are explained.  

GNSS-derived strain-rate analysis, geodetic earthquake recurrence modeling, and seismic potential estimations were integrated to investigate segment-scale deformation behavior along the central North Anatolian Fault Zone (NAFZ) using a high-resolution geodetic velocity field. The obtained strain rates reveal that deformation within the central NAFZ is distributed across a geometrically complex and kinematically heterogeneous fault network rather than being restricted to the main fault strand alone. While the main fault accommodates the majority of regional deformation, significant strain accumulation is also observed along major splay fault systems, including the Merzifon–Esençay, Ezinepazarı, Sungurlu, Eldivan, and Ekinveren faults. The derived strain patterns further indicate the coexistence of localized transtensional and transpressional deformation regimes controlled by fault geometry, segment boundaries, and structural discontinuities. Geodetically derived earthquake recurrence periods display pronounced spatial variability, with shorter recurrence periods concentrated along the main fault strand and comparatively longer earthquake cycles characterizing structurally complex splay systems. Among the investigated structures, the eastern and central segments of the Merzifon–Esençay Fault (MEF) exhibit relatively elevated strain accumulation and seismic potential. In particular, the estimated potential earthquake magnitudes reaching Mw 7.3–7.5, together with paleoseismological evidence indicating that the most recent major surface-rupturing event along the Esençay segment occurred approximately 3700 years ago, suggest that this fault system may represent a candidate seismic gap within the central NAFZ. Overall, the results demonstrate that deformation within the central NAFZ is strongly partitioned among interacting fault segments and highlight the importance of segment-scale geodetic analyses for improving seismic hazard assessments in complex strike-slip fault systems.

Atmospheric water vapor plays a critical role in the climate system, governing energy balance, climate variability and precipitation processes. Accurate monitoring of precipitable water vapor (PWV) is therefore essential for both meteorological and climate-related studies. The Global Navigation Satellite System (GNSS) provides an effective and continuous tool for PWV estimation through the calculation of zenith tropospheric wet delay (ZWD). Given the scarcity of continuous ground-based observations in Antarctica, the TUR1 and TUR2 permanent GNSS stations, established on Horseshoe Island during the Turkish Antarctic Expedition-4 (TAE-4) under the TÜBİTAK Polar Research Project (No. 118Y322), provide a valuable infrastructure for continuous atmospheric water vapor monitoring, which constitutes the primary contribution of this study. The conversion of ZWD to PWV requires an accurate estimation of the weighted mean temperature (Tm), which is typically derived from empirical models. However, globally applied Tm models may not adequately represent the regional atmospheric variability of high-latitude environments, where the vertical atmospheric structure and water vapor distribution differ substantially from mid-latitude conditions. This limitation is especially pronounced in Antarctica, which serves as a natural laboratory for climate change research while remaining one of the most observationally constrained regions on Earth due to sparse meteorological infrastructure and logistical challenges. In this study, a locally derived Tm parameterization (HRS) was obtained from radiosonde profiles at near sea-level stations within the 66°S–70°S latitude belt and evaluated against both the existing regional Antarctic Tm model (ANT) and the globally applied GPT2, GPT3 and Bevis models, using radiosonde observations as an independent reference. The HRS parameterization reproduced the radiosonde-derived Tm values with an RMSE of 2.90 K, clearly outperforming the global models (4.20–4.51 K) and showing close agreement with the existing regional Antarctic Tm model (r = 0.987), independently confirming the transferability of the regional approach to the Horseshoe Island region. The GNSS-derived PWV based on the regional Tm parameterization was then evaluated against ERA5 reanalysis data as an independent reference. The estimates showed strong agreement, with a correlation of 0.95, an RMSE of 1.65 mm and a mean bias of +1.22 mm, the seasonal agreement being strongest in austral summer (RMSE ≈ 1.24 mm) and weakest in austral winter (RMSE ≈ 1.92 mm), consistent with the lower water vapor content and stronger surface temperature inversions that characterize the cold season. The close agreement between the two independent TUR1 and TUR2 stations further supports the repeatability of GNSS-based PWV retrieval under coastal Antarctic conditions, highlighting the observational value of these stations for atmospheric water vapor monitoring in Antarctica, where continuous observations remain limited.

Postseismic deformation provides fundamental insights into earthquake-cycle processes, lithospheric rheology, and stress redistribution following large earthquakes. Although the 2020 Mw 7.0 Samos earthquake has been extensively investigated in terms of coseismic deformation and early postseismic behavior, the long-term evolution of deformation following the event remains poorly constrained. This study characterizes the long-term spatiotemporal evolution of postseismic deformation associated with the 2020 Mw 7.0 Samos earthquake using combined campaign and continuous GNSS observations. A total of 18 GNSS stations were analyzed over an approximately 4.5-year period following the earthquake. Pre-earthquake GNSS velocities were incorporated as prior constraints, while postseismic deformation was modeled using linear, logarithmic, exponential, and combined logarithmic–exponential functions. The preferred model for each station component was identified using the corrected Akaike Information Criterion (AICc), and model-selection robustness was evaluated through 1000 Monte Carlo observation–perturbation simulations. The results reveal a spatially heterogeneous postseismic deformation field with station-dependent temporal behavior. Among the nonlinear solutions passing the Monte Carlo and goodness-of-fit criteria, the seven single-process LOG and EXP solutions yielded characteristic relaxation times ranging from 182.6 to 730.5 days, with a median of 438.3 days. The two LOGEXP solutions additionally contained a logarithmic timescale of 109.6 days and exponential timescales of 292.2–438.3 days. These findings demonstrate that campaign GNSS observations, when integrated with continuous GNSS data and an objective statistical framework, can provide meaningful constraints on the long-term evolution of postseismic deformation despite sparse temporal sampling. More broadly, the results emphasize the strongly time-dependent nature of postseismic deformation and the critical role of observation timing in capturing its spatiotemporal evolution.