Location:

Period:

28 Dec 2008 13:31:36 - 29 Dec 2008 01:44:24 (12 hours 12 minutes)

Volcanoes in 100km radius:

Sinarka(68km), Raikoke(80km), Ekarma(82km), Sarychev Peak(86km), Kharimkotan(95km)

Earthquakes:

10 swarms found nearby.

2003

PS20031231.1(140.0km)

30 Dec

1 day 20 hours

8 earthquakes

2004

PS20041218.1(154.5km)

18 Dec

2 hours

7 earthquakes

2006

PS20061108.1(102.1km)

8 Nov

18 hours

7 earthquakes

PS20061115.1(153.4km)

15 Nov

2 days 17 hours

53 earthquakes

PS20061115.2(154.8km)

15 Nov

1 day 19 hours

15 earthquakes

PS20061120.1(123.2km)

19 Nov

1 day 1 hours

7 earthquakes

2007

PS20070113.1(166.2km)

13 Jan

19 hours

16 earthquakes

2012

PS20121015.1(10.6km)

14 Oct

20 hours

5 earthquakes

2018

PS20181011.1(174.5km)

10 Oct

15 hours

9 earthquakes

2025

PS20250804.1(192.5km)

3 Aug

22 hours

5 earthquakes

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Seismic Swarm PS20081229.1: Activity in the Southern Kuril Subduction Zone

The seismic swarm designated PS20081229.1 occurred approximately 296 km south-southwest of Severo-Kuril’sk, Russia, within the Kuril-Kamchatka subduction zone. This region forms part of the Pacific Ring of Fire, where the Pacific Plate subducts northwestward beneath the Okhotsk Plate at rates of 8–9 cm per year. The resulting megathrust interface generates frequent intermediate-depth earthquakes, typically between 30 and 50 km, consistent with the recorded depths of this swarm.

The sequence began at 13:31 UTC on 28 December 2008 and concluded at 01:44 UTC on 29 December 2008, spanning 12 hours and 12 minutes. Five earthquakes were detected:

28 December 2008, 13:31:36 UTC, magnitude 5.4, depth 37 km
28 December 2008, 18:03:38 UTC, magnitude 5.0, depth 39 km
28 December 2008, 21:40:16 UTC, magnitude 5.4, depth 42 km
28 December 2008, 22:39:45 UTC, magnitude 5.0, depth 46 km
29 December 2008, 01:44:24 UTC, magnitude 4.9, depth 43 km

These events clustered tightly in both space and time, characteristic of swarm behavior rather than a mainshock-aftershock sequence. No larger triggering event was identified, and activity ceased abruptly after the final shock.

The Kuril arc has a long history of clustered seismicity driven by slab dehydration and stress transfer along the subduction interface. Since 1 January 2000, seven swarms have been documented in the broader region, occurring in 2003 (1 swarm), 2004 (1 swarm), 2006 (4 swarms), and 2007 (1 swarm). Such episodes reflect episodic strain release within the downgoing slab and overlying crust, often without producing significant surface deformation or tsunami threats when magnitudes remain below 6.0.

Monitoring networks operated by regional seismic agencies continue to track microseismicity in this sector, providing data essential for understanding subduction dynamics and long-term seismic hazard assessment along the island arc.

References SeismoSight internal swarm classification records USGS Earthquake Hazards Program regional tectonics overview Global CMT catalog for Kuril-Kamchatka focal mechanisms