Seismic Swarm S20250425.1: Analysis of Activity North of Simav, Turkey

An earthquake swarm designated S20250425.1 was recorded 20 km north of Simav in Kütahya Province, western Turkey. The sequence began at 14:22 on 24 April 2025 and concluded at 18:14 on 11 May 2025, spanning 411 hours and 52 minutes. During this period, 818 earthquakes were detected.

Analysis of the first 100 events reveals predominantly low-magnitude activity. Magnitudes ranged from 0.8 to 4.6, with the majority below 2.5. Depths clustered between 5 km and 14 km, consistent with shallow crustal seismicity. Notable events include a magnitude 4.6 quake at 07:20 on 25 April at 10 km depth and several magnitude 2.8 shocks. Temporal distribution shows clustering in the initial 48 hours, followed by a gradual decline, with events distributed across daytime and nighttime hours without strong diurnal patterns.

Western Anatolia, where Simav is situated, forms part of an extensional tectonic regime driven by the westward extrusion of the Anatolian Plate and back-arc spreading in the Aegean region. This setting produces normal faulting along graben structures, including the Simav Graben and associated segments of the Simav Fault Zone. The crust here experiences ongoing extension at rates of approximately 20–30 mm per year, leading to frequent small-to-moderate earthquakes and occasional swarms. Geothermal activity and Quaternary volcanism further characterize the area, reflecting thinned lithosphere.

Historical records since 2000 indicate nine prior swarms in the immediate region, occurring in 2009 (one swarm), 2011 (four swarms), 2012 (three swarms), and 2025 (one swarm). These episodes underscore the recurrent nature of clustered seismicity along local fault networks.

The 2025 swarm aligns with established patterns of swarm-type activity in western Turkey, where fluid migration or aseismic slip may trigger successive events without a single dominant mainshock. Depths and magnitudes observed match typical values for the extensional domain, providing additional data on strain accumulation in the Simav area.

References

SeismoSight internal classification data for swarm parameters and event lists.
Geological background drawn from peer-reviewed studies on Aegean extension and Anatolian tectonics (e.g., publications in Tectonophysics and Journal of Geophysical Research).