Seismic Swarm S20110706.1: Western Turkey, July 2011

Western Turkey occupies a highly active tectonic setting shaped by the convergence of the African, Arabian, and Eurasian plates. The region experiences extensional deformation linked to the Aegean back-arc system and strike-slip motion along the North Anatolian Fault, producing frequent shallow crustal earthquakes. Depths typically range from 2 to 16 km, consistent with brittle failure in the upper crust.

Swarm S20110706.1 began at 02:23 on 5 July 2011 and concluded at 11:56 on 9 July 2011, spanning 105 hours and 32 minutes. During this interval, 63 events were recorded, with magnitudes between 1.9 and 3.8. The largest shocks reached 3.8 and occurred at shallow depths of 2–5 km. Most activity clustered between 5 and 10 km depth, indicating a compact source volume.

Event timing shows distinct pulses. On 5 July, activity intensified in the afternoon with multiple events near magnitude 2.7–3.0. Peak energy release occurred on 6 July, including three magnitude-3.8 events at depths of 2–5 km. Subsequent days exhibited lower rates but maintained similar magnitude and depth ranges. The final event on 9 July measured 3.1 at 2 km depth.

This swarm fits the established pattern in Western Turkey, where short-lived clusters of small-to-moderate events occur without a single dominant mainshock. Historical records since 2000 document only three such swarms in the region, with one in 2009 and two in 2011. The 2011 episodes highlight recurring swarm behavior in the same tectonic corridor.

Shallow focal depths across the sequence suggest fluid involvement or aseismic slip triggering successive failures along distributed faults. No damage or felt reports exceeding moderate intensity were associated with these low-magnitude events.

References

SeismoSight internal swarm classification S20110706.1
USGS Earthquake Catalog (Western Turkey tectonics)
Peer-reviewed literature on Aegean extensional province (2010–2023 updates)