Location:

Period:

26 Oct 2011 19:47:52 - 29 Oct 2011 10:38:23 (2 days 14 hours 50 minutes)

Volcanoes in 100km radius:

Nemrut Dagi(88km)

Earthquakes:

8 swarms found nearby.

2011

PS20111023.1(10.7km)

23 Oct

1 day 4 hours

10 earthquakes

S20111023.1(14.9km)

23 Oct

69 days 9 hours

2474 earthquakes

S20111029.1(27.6km)

28 Oct

8 days 13 hours

155 earthquakes

S20111030.1(20.1km)

29 Oct

2 days 2 hours

46 earthquakes

S20111105.1(17.5km)

4 Nov

24 days 12 hours

631 earthquakes

S20111119.2(17.6km)

18 Nov

3 days 5 hours

70 earthquakes

S20111130.1(10.5km)

29 Nov

10 days 23 hours

95 earthquakes

2012

S20120801.1(20.1km)

31 Jul

1 day 6 hours

29 earthquakes

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Seismic Swarm S20111027.2 in Eastern Turkey: Analysis and Geological Context

Eastern Turkey lies within a tectonically complex zone shaped by the ongoing convergence of the Arabian and Eurasian plates. This collision, part of the broader Alpine-Himalayan belt, produces significant crustal deformation accommodated primarily along the East Anatolian Fault Zone and associated strike-slip structures. The region experiences frequent seismic activity, with shallow crustal earthquakes reflecting the compressional regime and localized extension in pull-apart basins.

The swarm designated S20111027.2 occurred in this setting from 19:47 on 26 October 2011 to 10:38 on 29 October 2011, spanning 62 hours and 50 minutes. A total of 99 earthquakes were recorded, with magnitudes ranging from 2.2 to 4.3 and focal depths predominantly between 2 and 21 km. These events clustered in time and space, exhibiting the characteristic swarm behavior of numerous small-to-moderate shocks without a single dominant mainshock.

Inspection of the sequence reveals several notable features. Early activity on 26 October included events of magnitude 2.9 at depths of 5–7 km, followed by a magnitude 3.7 shock at 2 km depth shortly after midnight on 27 October. Peak productivity occurred on 27–28 October, with multiple magnitude 3.3–3.5 events at shallow depths (2–7 km) and isolated deeper events reaching 20–21 km. The largest recorded shocks reached magnitude 4.3 on 28 October at 5 km depth and again on 29 October at 5 km depth. The sequence concluded with a magnitude 3.1 event at 21 km on 29 October.

Such swarms provide insight into fluid migration or stress redistribution along fault networks in Eastern Turkey. The shallow depth distribution aligns with the brittle upper crust in this area, where historical seismicity is concentrated above 20 km. The absence of larger events within the swarm itself distinguishes it from typical aftershock sequences following major regional earthquakes.

Since 1 January 2000, only two swarms have been identified in the instrumental record for the region, with S20111027.2 representing the first. This low frequency underscores the episodic nature of swarm activity amid the dominant background of isolated tectonic events and occasional large mainshock-aftershock sequences.

References

USGS Earthquake Catalog
EMSC Earthquake Database
SeismoSight internal swarm classification records