Location:

Period:

23 Oct 2011 10:52:05 - 31 Dec 2011 20:10:57 (69 days 9 hours 18 minutes)

Volcanoes in 100km radius:

Nemrut Dagi(87km), Tenduruk Dagi(90km)

Earthquakes:

2474

9 swarms found nearby.

2011

PS20111023.1(7.6km)

23 Oct

1 day 4 hours

10 earthquakes

S20111023.2(29.7km)

23 Oct

14 days 17 hours

739 earthquakes

S20111027.2(14.9km)

26 Oct

2 days 14 hours

99 earthquakes

S20111029.1(24.9km)

28 Oct

8 days 13 hours

155 earthquakes

S20111030.1(10.4km)

29 Oct

2 days 2 hours

46 earthquakes

S20111105.1(3.0km)

4 Nov

24 days 12 hours

631 earthquakes

S20111119.2(8.7km)

18 Nov

3 days 5 hours

70 earthquakes

S20111130.1(25.1km)

29 Nov

10 days 23 hours

95 earthquakes

2012

S20120801.1(16.5km)

31 Jul

1 day 6 hours

29 earthquakes

AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20111023.1: Analysis of Activity Northwest of Van, Turkey

The seismic swarm S20111023.1 occurred in eastern Turkey, approximately 31 km northwest of Van, between 10:52 on 23 October 2011 and 20:10 on 31 December 2011. Over 166 hours and 18 minutes, the sequence produced 2474 earthquakes, highlighting the intense seismic productivity of the region during this period.

Eastern Anatolia lies within a complex tectonic setting shaped by the ongoing collision between the Arabian and Eurasian plates. This convergence drives crustal shortening and uplift along the Bitlis-Zagros suture zone, resulting in frequent moderate-to-large earthquakes. The Van area specifically sits near active strike-slip and thrust faults that accommodate the regional deformation. Historical records document recurrent seismicity, with notable events underscoring the area's long-term hazard.

The swarm began with a series of events on 23 October 2011. The initial recorded earthquake reached magnitude 4.8 at a depth of 7 km. Subsequent shocks included magnitudes of 4.4, 4.7, and additional events clustered between 2.4 and 4.8 within the first hours. Depths remained predominantly shallow, typically between 2 km and 10 km, though occasional events extended to 20–27 km. Magnitudes in the first 100 events showed a clear pattern: frequent events in the 2.5–3.5 range interspersed with stronger shocks reaching 4.0–4.9. Notable peaks included a magnitude 4.8 at 12:42, another 4.8 at 19:06, and a magnitude 4.9 at 18:53, all at depths of 5–12 km.

Analysis of these early events reveals a high rate of occurrence, with many events separated by minutes. Shallow depths dominated, suggesting activity concentrated in the upper crust where brittle failure is favored. The sequence displayed typical swarm characteristics, lacking a single dominant mainshock but featuring multiple comparable-magnitude events. By late 23 October, activity had already produced dozens of felt shocks, consistent with the swarm's overall productivity of nearly 2500 events through December.

Geological context indicates that such swarms often occur along pre-existing fault networks activated by regional stress. In the Van vicinity, the interplay of strike-slip and reverse faulting facilitates clustered seismicity. The 2011 swarm aligns with this pattern, occurring in a zone of known Quaternary faulting and elevated strain accumulation.

Since 1 January 2000, only one swarm has been recorded in the region, making S20111023.1 a singular episode in the modern instrumental record. This rarity emphasizes the exceptional nature of the 2011 activity.

References:

United States Geological Survey Earthquake Catalog
Turkish Disaster and Emergency Management Presidency (AFAD) seismic reports
Journal of Geophysical Research: Solid Earth articles on Eastern Anatolian tectonics