Seismic Swarm S20250608.1: Analysis of Earthquake Activity in Western Turkey

Western Turkey occupies a tectonically complex zone at the junction of the Anatolian, Eurasian, and African plates. The region experiences frequent seismic activity driven by north-south crustal extension linked to the rollback of the Hellenic slab and westward extrusion of the Anatolian Plate along the North Anatolian Fault. This setting produces numerous normal and strike-slip faults that accommodate ongoing deformation, resulting in shallow crustal earthquakes typically occurring at depths of 3–15 km.

Swarm S20250608.1 was recorded in this environment, commencing at 16:24 on 7 June 2025 and concluding at 20:04 on 26 June 2025. Over 459 hours and 40 minutes, the sequence comprised 405 earthquakes. The first 100 events displayed magnitudes ranging from 0.8 to 3.6, with the majority falling between 1.0 and 2.3. Depths concentrated between 3 km and 13 km, consistent with the shallow seismogenic zone of western Anatolia.

The sequence began with low-magnitude events near 2.0–2.1 at depths of 5–7 km. Activity intensified on 8 June, featuring repeated events around magnitude 2.0–2.3 at 10–13 km depth. A notable peak occurred on 9 June, including the largest event of the initial 100 at magnitude 3.6 (9 km depth) alongside several events exceeding magnitude 3.0 at similar depths. Subsequent events showed a gradual decline in both frequency and peak magnitude, with depths remaining predominantly shallow.

This pattern aligns with historical swarm behavior in the region. Since 2000, twelve swarms have been documented in western Turkey, occurring in 2009 (one swarm), 2011 (four swarms), 2012 (three swarms), and 2025 (four swarms). Such episodic clusters reflect fluid migration or stress triggering along pre-existing fault networks rather than mainshock-aftershock sequences.

The 2025 swarm underscores the persistent seismic hazard in western Turkey, where even moderate-magnitude events can affect nearby urban centers. Continued monitoring remains essential given the region's high strain rates and documented recurrence of swarm activity.

References
SeismoSight internal swarm classification records.
USGS Earthquake Catalog (historical western Turkey seismicity).
McKenzie, D. (1972). Active tectonics of the Mediterranean region. Geophysical Journal International.
Barka, A. & Reilinger, R. (1997). Active tectonics of the Eastern Mediterranean region. Tectonophysics.