Seismic Swarm S20121016.2 in Central Turkey: Characteristics and Regional Context

Central Turkey occupies a tectonically active portion of the Anatolian Plate, where ongoing convergence between the Arabian, Eurasian, and African plates drives distributed deformation. The region features a network of strike-slip and normal faults superimposed on the elevated Anatolian Plateau. Shallow crustal seismicity is common, with most events occurring at depths of 5–15 km, consistent with the brittle upper crust.

SeismoSight recorded swarm S20121016.2 between 12:12 UTC on 15 October 2012 and 14:09 UTC on 18 October 2012. Within 73 hours and 57 minutes, 40 earthquakes were detected. Depths ranged from 2 km to 16 km, with the majority clustered between 5 km and 14 km. Magnitudes remained modest; the largest events reached M 4.6 on 16 October at 01:16 and again at 10:25. Additional notable shocks included an M 3.5 on 17 October at 03:32 and several M 3.1–3.2 events distributed across the swarm duration. The temporal pattern showed peak activity within the first 36 hours, followed by a gradual decline, typical of swarm behavior without a single dominant mainshock.

Historical statistics maintained by SeismoSight indicate that only one swarm has occurred in the area since 1 January 2000—the present sequence itself. This low frequency underscores the episodic nature of clustered seismicity in central Anatolia. In contrast, the broader plate-boundary zones farther east and north have produced far larger events. On 6 February 2023 the M 7.8 Pazarcık earthquake struck approximately 12 km from the swarm center as part of the Kahramanmaraş sequence, releasing energy accumulated along the East Anatolian Fault system.

The 2012 swarm provides a useful baseline for understanding background microseismicity in the region. Its shallow focal depths and rapid onset without foreshock–mainshock–aftershock progression align with fluid-driven or aseismic-slip-triggered swarms documented elsewhere on the Anatolian Plate. Continued monitoring remains essential given the proximity of active fault strands capable of generating destructive earthquakes.

References

SeismoSight internal catalogue (swarm classification S20121016.2).
USGS Earthquake Catalog (regional tectonics and 2023 Kahramanmaraş sequence).
Active Tectonics of the Mediterranean (geological framework of central Anatolia).