Seismic Swarm S20250810.1: Analysis of Activity in Western Turkey

Western Turkey occupies a highly active tectonic setting at the junction of the African, Eurasian, and Arabian plates. Extensional forces linked to the Hellenic subduction zone and the western termination of the North Anatolian Fault Zone produce frequent shallow seismicity across the Aegean graben system. Normal and strike-slip faulting dominate, with most events occurring at depths of 5–15 km.

SeismoSight recorded swarm S20250810.1 from 09:03 on 9 August 2025 until 14:55 on 10 May 2026. During the 6581-hour, 52-minute sequence, 21 922 earthquakes were detected in western Turkey. This marks the third swarm in the region since 2000, following single-swarm episodes in 2001 and 2024.

The first 100 events provide a clear view of swarm initiation and escalation. Activity began modestly on 9 August with magnitudes between 1.1 and 3.8 at depths of 7–11 km. Early on 10 August, a cluster of events reached magnitude 3.6. The sequence intensified markedly after 17:00 on 10 August, when multiple shocks exceeded magnitude 4.0. The largest event measured 4.6 at 11 km depth. Subsequent events included repeated magnitudes of 4.1–4.2, all at shallow depths ranging from 0 to 29 km, with the great majority between 5 and 12 km.

Depth distribution remained consistently shallow, consistent with the extensional crustal regime of western Turkey. Magnitude progression showed a rapid transition from microseismicity to moderate events within roughly 32 hours, a pattern typical of swarm-type sequences driven by fluid migration or aseismic slip rather than a single mainshock-aftershock cascade.

The swarm’s duration and event count exceed those of the 2001 and 2024 episodes, highlighting the potential for prolonged seismic unrest in this segment of the Aegean extensional province. Continued monitoring is warranted given the region’s history of damaging earthquakes along mapped normal faults.

References
SeismoSight internal swarm catalogue S20250810.1
Tectonic framework derived from regional geological literature on the North Anatolian Fault and Aegean extension.