Magnitude Estimation of the 2025 Sındırgı Earthquakes Using High-Rate GNSS-Derived Peak Ground Displacement (PGD): Insights from Low-Cost and Geodetic Receivers

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.