Seismicity characteristics of Sındırgı-Balıkesir in western Türkiye in the context of the 10 August 2025 (Mw=6.1) and 27 October 2025 (Mw=6.1) earthquakes

Two earthquakes with Mw 6.1 occurred in Sındırgı–Balıkesir, western Türkiye, within a few months (10 August 2025 and 27 October 2025). This short time separation provides a valuable opportunity to compare spatiotemporal changes in post-event seismicity and faulting parameters under broadly similar regional conditions, while also allowing potential differences in detection capability and catalogue completeness between the two periods to be handled explicitly.

In this study, a homogenised regional earthquake catalogue is analyzed within an explicit magnitude-of-completeness (Mc) framework to minimize bias arising from temporal variations in detectability when comparing the two post-event periods. Completeness is assessed in a time-dependent manner, and all subsequent analyses are conditioned on the estimated Mc to ensure a like-for-like comparison between the August and October sequences. The aftershock sequences are examined in both space and time, spatiotemporal clustering and migration patterns are evaluated from the mapped aftershock distributions, while temporal decay is characterized using the Omori–Utsu law by estimating and comparing sequence-specific decay parameters. In parallel, b-values are estimated from the Gutenberg–Richter frequency–magnitude distribution and their spatial variations are evaluated to identify potential heterogeneity in the post-event stress state and rupture environment across the source region.

To link seismicity patterns with faulting behaviour, focal-mechanism solutions are used to determine the dominant faulting styles, the principal P- and T-axis orientations, and the regional stress regime associated with each sequence. The joint interpretation of aftershock decay, b-value variability, and mechanism-derived faulting characteristics provides an integrated, catalogue-consistent comparison of post-event behaviour for the August and October 2025 earthquakes, and yields a consolidated description of how seismicity and faulting evolve in the Sındırgı region of western Türkiye following closely spaced moderate–large events.