Seismic Swarm S20230206.1 in Central Turkey: February 2023 Analysis

Central Turkey occupies a tectonically complex zone at the intersection of the Anatolian, Arabian, and Eurasian plates. The region experiences frequent seismic activity driven by strike-slip faulting along the North Anatolian Fault and East Anatolian Fault systems, as well as distributed deformation within the Anatolian plate interior. These structures accommodate westward extrusion of the Anatolian plate at rates of approximately 20 mm per year, resulting in recurrent moderate earthquakes.

SeismoSight internal classification identifies Swarm S20230206.1 as a distinct sequence that initiated at 02:01 on 6 February 2023 and concluded at 21:58 on 13 February 2023. Over 187 hours and 56 minutes the swarm produced 120 earthquakes. Analysis of the first 100 events reveals a temporal decay typical of swarm sequences, with the largest magnitude recorded at 4.8 and focal depths predominantly between 2 km and 22 km. Early activity on 6 February featured several events above magnitude 4.0 within the first 12 hours, followed by a gradual decline in both frequency and magnitude through 11 February.

The swarm's shallow depth distribution indicates brittle failure within the upper crust, consistent with the regional fault architecture. Magnitudes remained below 5.0 throughout the documented period, distinguishing this sequence from mainshock-aftershock patterns. Historical records maintained by SeismoSight show only five comparable swarms in Central Turkey since 1 January 2000. Prior episodes occurred in 2012 (three events) and 2013 (one event), underscoring the relative rarity of swarm-type behavior in this sector of the plate boundary.

Geological context places the swarm within a zone of distributed shear between major strike-slip faults. Crustal heterogeneity, including ophiolitic mélanges and sedimentary basins, influences rupture propagation and may contribute to the observed clustering. Long-term seismic hazard assessments for Central Turkey incorporate both fault-specific recurrence intervals and background seismicity rates derived from instrumental catalogs spanning the past century.

The February 2023 swarm provides additional data on transient strain release in an area already subject to elevated seismic risk. Continued monitoring of microseismicity remains essential for refining probabilistic hazard models and understanding the interplay between swarm activity and regional tectonics.

References

SeismoSight internal swarm database (S20230206.1 classification and event parameters).
USGS Earthquake Hazards Program – regional tectonics summaries for Anatolia.
Active tectonics literature on Anatolian plate motion and fault systems.