The 2025 Sındırgı Earthquake Sequence: Linking Fault Geometry, Stress Transfer and Deep Structure

The 10 August 2025 Mw 6.0 Sındırgı earthquake occurred in one of the most tectonically complex regions of Inner Western Anatolia, where Aegean extension interacts with the westward extrusion of the Anatolian microplate. Despite initial reports indicating a NW–SE–oriented normal-faulting mechanism, the spatial distribution of aftershocks and early field observations point to a more intricate rupture behaviour. Rapid field investigations by the General Directorate of Mineral Research and Exploration (MTA) on 11 August 2025 revealed no evidence of surface rupture or localized coseismic deformation along the Sındırgı, Düvertepe or Gelenbe fault zones.

Full-waveform moment tensor inversion of the mainshock and 31 aftershocks yielded robust, well-constrained focal mechanisms. The mainshock exhibits a NW–SE striking oblique-reverse faulting mechanism, with ~90% double-couple content and a centroid depth of approximately 10 km. Aftershock mechanisms display a clear spatial partitioning: reverse and strike-slip components dominate south of the Sındırgı Segment, whereas normal faulting is prevalent to the north. The aftershock sequence further demonstrates a pronounced eastward migration pattern.

Statistical analysis of 6,711 earthquakes recorded between 20 July and 1 September 2025 indicates low regional b-values (0.60–0.70), suggesting elevated differential stress. Following the mainshock, b-values increase toward the eastern portion of the aftershock zone (0.75–0.80), reflecting evolving stress conditions. The Omori p-value (~0.18) indicates an unusually slow decay of aftershocks, consistent with a prolonged period of seismic activation. Stress tensor inversion of 32 focal mechanisms reveals a strike-slip–dominated regime with NE–SW–oriented maximum compression, in agreement with the regional tectonic pattern.

Integration of regional magnetotelluric (MT) profiles shows that the 2025 Sındırgı sequence coincides with deep, low-resistivity zones interpreted as thermally weakened or partially molten lithospheric domains beneath the Simav–İzmir–Balıkesir structural corridor. These MT-based lithospheric anomalies spatially correlate with previous major earthquake sequences, including the 2011 Simav and 2020 Akhisar events, implying a persistent lithospheric control on fault kinematics, stress localization and seismogenesis.

Overall, the 2025 Sındırgı earthquake sequence highlights the combined role of structural complexity and deep lithospheric processes in determining seismic behaviour in Inner Western Anatolia. The integration of seismological, geological and geophysical datasets provides a comprehensive framework for understanding rupture dynamics in this long-lived, active deformation zone.

Keywords :Sındırgı Earthquake Sequence; Moment tensor; Stress tensor inversion; b-value; Aftershock migration; Western Anatolia; Magnetotellurics; Active tectonics.