Location:

Period:

5 Oct 2008 16:04:45 - 7 Oct 2008 04:08:14 (1 day 12 hours 3 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

3 swarms found nearby.

2008

PS20081005.2(33.3km)

5 Oct

2 hours

6 earthquakes

2015

PS20151207.1(89.8km)

7 Dec

2 hours

6 earthquakes

2016

PS20161126.1(45.5km)

25 Nov

19 hours

5 earthquakes

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Seismic Swarm S20081005.2: Analysis of the 2008 Kyrgyzstan Event

Seismic swarm S20081005.2 was recorded from 16:04 on 5 October 2008 to 04:08 on 7 October 2008, approximately 125 km east of Kyzyl-Eshme in Kyrgyzstan. Over 36 hours and three minutes, the sequence comprised 54 earthquakes. This event represents the sole swarm documented in the region since 1 January 2000.

The swarm initiated with low-magnitude activity at 16:04:45 on 5 October, rapidly escalating to events of magnitude 4.6 and 4.7 within the first hour. Subsequent shocks included multiple events reaching magnitude 4.7 and 4.8, with the strongest recorded at magnitude 4.8 on 6 October at 09:30:49. Depths clustered predominantly around 35 km, though several shallower events occurred between 6 km and 25 km. Many recordings registered at magnitude 0.0, consistent with the classification criteria for this swarm. Activity tapered after 7 October, concluding at 04:08:14.

Regional Geological Context

Kyrgyzstan lies within the actively deforming Tien Shan orogenic belt of Central Asia. This mountain range formed through ongoing collision between the Indian and Eurasian tectonic plates, producing north-south crustal shortening at rates of approximately 20 mm per year. The resulting compressional regime generates frequent thrust and strike-slip faulting across a network of active structures.

The location of swarm S20081005.2 aligns with the central Tien Shan, where Paleozoic basement rocks are overlain by Cenozoic sedimentary basins. Historical seismicity in the area includes destructive earthquakes such as the 1911 Chon-Kemin event (magnitude 7.7) and the 1992 Suusamyr earthquake (magnitude 7.2), both linked to reactivation of inherited faults under modern plate convergence. Updated assessments from global monitoring networks confirm persistent moderate-magnitude activity throughout the belt, with focal depths commonly between 10 km and 40 km.

Swarm Characteristics and Tectonic Implications

Earthquake swarms differ from mainshock-aftershock sequences by lacking a dominant triggering event and instead reflecting distributed stress release, often along fluid-influenced or creeping fault segments. In this case, the 54 events displayed a relatively narrow depth range and a rapid onset followed by gradual decay, features typical of swarm behavior in compressional settings. The concentration of hypocenters near 35 km suggests activation within the mid-crustal brittle-ductile transition zone of the Tien Shan.

No surface rupture or significant infrastructure damage was associated with this swarm, consistent with its maximum magnitude of 4.8. The sequence provides insight into the background seismicity that accommodates a portion of the regional strain budget between larger, infrequent great earthquakes.

References

Global CMT Catalog (1976–present)
USGS Earthquake Hazards Program regional reports on Central Asia
International Seismological Centre Bulletin data for Kyrgyz events
Geological Survey of Kyrgyzstan tectonic summaries (updated 2023)