Location:

Period:

3 Aug 2025 21:55:09 - 4 Aug 2025 20:29:32 (22 hours 34 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 7.5; 221 km SSE of Severo-Kuril’sk, Russia; (25 Mar 2020) (81km from the swarm center)

7 swarms found nearby.

2004

PS20041218.1(59.4km)

18 Dec

2 hours

7 earthquakes

2008

PS20081229.1(192.5km)

28 Dec

12 hours

5 earthquakes

2012

PS20121015.1(181.9km)

14 Oct

20 hours

5 earthquakes

2018

PS20181011.1(32.5km)

10 Oct

15 hours

9 earthquakes

2025

PS20250730.1(58.6km)

29 Jul

1 day 7 hours

16 earthquakes

PS20250730.2(114.2km)

30 Jul

1 day 7 hours

15 earthquakes

2026

PS20260607.1(116.5km)

7 Jun

9 hours

5 earthquakes

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Seismic Swarm Activity in the Kuril Islands: Analysis of the August 2025 Event

A seismic swarm designated PS20250804.1 occurred in the Kuril Islands, registering five earthquakes between 21:55 on 3 August 2025 and 20:29 on 4 August 2025. The sequence unfolded over 22 hours and 34 minutes in a tectonically active segment of the western Pacific.

The events began with a magnitude 5.1 earthquake at 35 km depth on 3 August. Subsequent activity included a magnitude 6.2 event at 16 km depth early on 4 August, followed by a magnitude 5.0 at 38 km, a magnitude 5.2 at 10 km, and a final magnitude 4.6 at 10 km depth. Depths ranged from shallow crustal levels to intermediate values, consistent with the subduction dynamics of the region.

The Kuril Islands form part of a volcanic island arc situated above the Kuril-Kamchatka subduction zone. Here, the Pacific Plate converges with and descends beneath the Okhotsk Plate at rates exceeding 8 cm per year, generating frequent earthquakes and volcanic activity. This tectonic setting has produced a well-documented history of both isolated large-magnitude events and episodic swarms.

Since 2000, six swarms have been recorded in the area, occurring in 2004, 2008, 2012, 2018, and twice in 2025. These clusters typically involve multiple moderate-magnitude events over short periods without a single dominant mainshock. The 2025 swarm aligns with this pattern, remaining below the threshold of destructive shaking reported in stronger regional events.

A notable prior earthquake was the magnitude 7.5 event of 25 March 2020, located 221 km south-southeast of Severo-Kuril’sk and approximately 81 km from the recent swarm center. Such occurrences underscore the persistent seismic hazard along the arc.

The Kuril-Kamchatka Trench and associated faults continue to accommodate plate motion, sustaining elevated seismicity. Monitoring of swarm characteristics, including temporal clustering and depth distribution, contributes to refined assessments of regional strain release.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Global CMT Catalog (globalcmt.org)
Russian Academy of Sciences Far East Branch seismological reports