Seismic Swarm S20111105.1 in Eastern Turkey: Analysis and Geological Context

Eastern Turkey lies within one of the most seismically active zones on Earth, part of the broader Alpine-Himalayan orogenic belt. The region experiences intense tectonic deformation due to the northward convergence of the Arabian Plate with the Eurasian Plate at rates of approximately 15–20 mm per year. This interaction drives strike-slip motion along major structures such as the East Anatolian Fault Zone and distributed shortening across the Anatolian Plateau, resulting in frequent shallow crustal earthquakes.

The area’s geological history reflects prolonged continental collision that began in the Miocene and continues today. Thrust faulting, folding, and basin development characterize the landscape, with volcanic activity also present from earlier subduction phases. Instrumental records since 2000 document six earthquake swarms in Eastern Turkey, with the first occurring in 2011. These swarms highlight episodic seismic energy release distinct from classic mainshock-aftershock sequences.

SeismoSight internal classification identifies swarm S20111105.1 as beginning at 16:29 on 4 November 2011 and concluding at 05:07 on 29 November 2011. Over 588 hours and 38 minutes, the swarm produced 631 earthquakes. Analysis of the first 100 events reveals predominantly low-to-moderate magnitudes between 2.0 and 4.0, with the majority falling in the 2.4–2.9 range. Depths were consistently shallow, concentrated between 2 km and 20 km, indicating activity within the brittle upper crust.

Temporal patterns show an initial cluster on 4–5 November featuring events up to magnitude 3.2, followed by a gradual increase in both frequency and peak magnitudes by 6 November, including a magnitude 4.0 event at 20:56. Depths remained variable yet shallow throughout, with many events at 2–10 km suggesting fluid involvement or stress migration along minor faults. The swarm exhibited no single dominant mainshock, consistent with swarm behavior driven by distributed crustal weakening.

Such sequences in Eastern Turkey often relate to local fault networks accommodating regional strain. The shallow focus of recorded events aligns with the region’s known seismogenic thickness of roughly 15–20 km. Continued monitoring of similar swarms contributes to refined hazard models for nearby population centers.

References

SeismoSight internal swarm classification records.
General tectonic framework from peer-reviewed studies on Arabian-Eurasian plate interaction.