Seismic Swarm S20111107.2 in Eastern Turkey

Seismic swarm S20111107.2 occurred in eastern Turkey from 19:13 on 6 November 2011 to 13:29 on 10 November 2011. Over this 90-hour period, 79 earthquakes were recorded. Magnitudes ranged from 2.0 to 4.5, with the largest events measuring 4.5 on 7 November at 22:14 and again on 8 November at 19:34. Focal depths remained shallow, predominantly between 2 km and 15 km, consistent with crustal deformation in the region.

The temporal distribution showed initial low-level activity on 6 November, followed by intensified sequences on 7 and 8 November. Multiple events clustered within short intervals, including several magnitude 3.0–3.7 quakes on 7 November and repeated magnitude 2.8–3.3 occurrences on 8 November. Activity gradually declined by 9 and 10 November, ending with a final magnitude 2.8 event at 13:29 on 10 November. Depths varied modestly but stayed within the upper crust, indicating a localized source volume.

Eastern Turkey occupies a tectonically active zone shaped by the ongoing collision between the Arabian and Eurasian plates. This convergence drives strike-slip and thrust faulting along major structures such as the East Anatolian Fault and the Bitlis-Zagros suture zone. The area experiences frequent moderate seismicity, with shallow crustal events common due to the complex interplay of regional fault systems. Historical records document elevated seismic rates, reflecting long-term strain accumulation from plate motion estimated at 2–3 cm per year.

This swarm represents the first of five documented swarm episodes in eastern Turkey since 1 January 2000. The concentration of events within a narrow time window and limited spatial extent distinguishes swarm behavior from typical mainshock-aftershock sequences. Such patterns often reflect fluid migration or aseismic slip triggering successive failures on adjacent fault segments.

Analysis of the provided event parameters reveals a peak rate exceeding 20 events per day during the most active phases. The predominance of magnitudes below 3.0, interspersed with occasional larger shocks up to 4.5, aligns with swarm characteristics observed in other continental collision settings. Depths averaging around 7 km suggest nucleation within the seismogenic layer above the brittle-ductile transition.

Continued monitoring of eastern Turkey remains essential given the region’s tectonic setting and history of destructive earthquakes. Swarm S20111107.2 provides a documented case of clustered microseismicity that can inform models of short-term hazard assessment in similar geological environments.

References

SeismoSight internal classification records for swarm S20111107.2
USGS Earthquake Catalog (regional tectonics summary)
Active Tectonics of the Eastern Mediterranean Region, Journal of Geophysical Research (updated plate-motion data)