Seismic Swarm PS20041118.1: Analysis of Earthquake Activity Near Aydarken, Kyrgyzstan

A seismic swarm designated PS20041118.1 occurred in southern Kyrgyzstan from 17 to 18 November 2004. The sequence began at 07:34 on 17 November and concluded at 02:30 on 18 November, with six earthquakes recorded over 18 hours and 56 minutes. The epicentral area lies 43 km south-southwest of Aydarken in the Osh Region, within the tectonically active Tien Shan mountain belt.

The events displayed a range of magnitudes and focal depths. The first two occurred within seconds of each other on 17 November at 07:34, registering magnitudes 5.1 at 54 km depth and 5.3 at 74 km depth. A larger event followed at 20:58 with magnitude 5.8 at 20 km depth. On 18 November, three additional shocks were recorded: magnitude 4.9 at 10 km depth at 02:09, followed at 02:30 by magnitude 5.0 at 10 km depth and magnitude 5.1 at 60 km depth. Depths varied significantly, indicating activity across both shallow crustal and intermediate levels.

Southern Kyrgyzstan occupies a key segment of the India-Eurasia collision zone. Ongoing convergence at rates of approximately 20 mm per year drives crustal shortening and uplift across the Tien Shan. The region features complex thrust and strike-slip fault systems that accommodate this deformation. Aydarken lies near the southern flank of the range, where north-directed thrusting interacts with regional strike-slip structures. This tectonic setting produces frequent moderate earthquakes and occasional larger events.

Historical records document repeated seismic activity in the broader area. The 1946 Chatkal earthquake (magnitude 7.3) and the 1992 Suusamyr earthquake (magnitude 7.2) both occurred within several hundred kilometres and caused substantial damage. Paleoseismic studies indicate recurrence intervals of several hundred to a few thousand years for magnitude 7+ events on major faults. The 2004 swarm fits within this pattern of distributed moderate seismicity that releases strain without producing surface rupture.

The temporal clustering and magnitude distribution of the swarm suggest a localized stress perturbation, possibly related to fluid migration or minor fault interactions at depth. No damage or casualties were associated with these events, consistent with their moderate sizes and the sparse population density in the immediate epicentral zone.

Seismic monitoring in Kyrgyzstan has improved since 2004 through upgrades to national and international networks. Current catalogues from regional agencies continue to record similar swarms, underscoring the persistent seismic hazard in the Tien Shan.

References

USGS Earthquake Catalog
Central Asian Seismic Network reports
Tectonic summaries from the International Seismological Centre