Interseismic Slip Rates of the Sındırgı Fault Forecast Extensional Kinematics During the 2025 M6+ Earthquakes

We investigated the geometry and the kinematics of the Sındırgı fault, which was activated during the two M6+ earthquakes (10.08.2025 and 27.10.2025) and their aftershocks. We analyzed all available seismographs from KOERI (Kandilli Observatory and Earthquake Research Institute) and AFAD (Disaster and Emergency Management Authority) to identify fault geometry, earthquake locations, and focal mechanisms. We analyzed P-wave initial polarities and arrival times of a total of 43 M4+ earthquakes including two mainshocks (waveforms from KOERI and AFAD). Fault plane solutions as well as the accurate hypocenter locations indicate that the majority of the mainshocks and the aftershocks activated a south dipping fault. The results indicate an average strike of 110 ± 5.6°, a dip of 61.6 ± 4.4°, and rake a rake -124.6 ± 2.3°. Additionally, we investigated inter-seismic slip rates using 2D dislocation model analyzing the GNSS velocity field. We transformed the most recent velocity field into Anatolian-fixed reference frame. We decomposed GNSS velocities into fault-parallel and fault-perpendicular components and applied 2D arctan curve fitting to simultaneously determine the slip rates and the fault locking depths. Bootstrap error analysis was performed (1σ) to assess error bounds. The lateral motion is nearly negligibly small; however, fault-perpendicular velocities indicate the extension along the Sındırgı fault at 2.34 ± 0.69 mm/y slip rate. Inter-seismic slip rates suggest a rake of -95.2°, a nearly pure normal fault, which is consistent with average mainshock-aftershock rakes. In this context, GNSS-derived interseismic slip rates are capable of forecasting the extensional kinematics of the Sındırgı fault that generated two predominantly normal-faulting M 6+ earthquakes in 2025.