Seismic Swarm S20220613.1: Eastern Turkey Earthquake Sequence

Eastern Turkey occupies a complex tectonic setting at the convergence of the Arabian, Eurasian, and African plates. The region experiences ongoing crustal deformation primarily along the East Anatolian Fault Zone and the Bitlis-Zagros suture, where northward motion of the Arabian Plate produces strike-slip and thrust faulting. This activity has generated a long record of moderate-to-large earthquakes, with historical events such as the 1976 M7.3 Çaldıran earthquake and the 2011 M7.1 Van earthquake highlighting the area's seismic potential. Updated geological assessments confirm that Eastern Turkey remains one of the most active continental collision zones in the Mediterranean region, with frequent small-to-moderate events reflecting distributed strain accommodation.

Between 18:35 on 12 June 2022 and 20:52 on 15 June 2022, SeismoSight recorded swarm S20220613.1, comprising 44 earthquakes over 74 hours and 17 minutes. The sequence began with a magnitude 5.2 event at 10 km depth, followed rapidly by smaller aftershocks clustered at shallow depths between 2 km and 25 km. Notable events included multiple magnitude 3.3–3.4 shocks on 12 and 14 June, with the majority of activity concentrated in the first 36 hours before gradually declining. Depths remained predominantly crustal, consistent with faulting within the upper 25 km of the lithosphere.

Swarm sequences like this one lack a single dominant mainshock and instead display a diffuse pattern of energy release. In Eastern Turkey, such swarms often correlate with stress perturbations along secondary faults or fluid migration within fractured carbonate and volcanic units common to the Anatolian plateau. The 44 events showed a typical swarm signature: an initial energetic pulse, sustained low-magnitude activity, and a tapering rate without aftershock decay following Omori’s law. Depths clustered between 2 km and 12 km for most events, suggesting activation of shallow crustal structures.

Historical records indicate that swarm activity is recurrent in the region. Since 1 January 2000, ten distinct swarms have been documented, with the earliest identified in 2011. These episodes underscore the episodic nature of strain release along the diffuse plate boundary, where small stress changes can trigger clustered seismicity without progressing to a larger mainshock.

The 2022 swarm contributed to the ongoing characterization of background seismicity rates in Eastern Turkey. While individual events remained below damaging thresholds, the sequence illustrates the value of dense monitoring networks in distinguishing swarm behavior from foreshock-mainshock sequences. Continued observation supports improved probabilistic forecasting for the East Anatolian Fault system.

References

SeismoSight internal swarm catalogue S20220613.1
USGS Earthquake Hazards Program regional tectonic summaries (updated 2023)
Turkish Mineral Research and Exploration General Directorate seismic bulletins