Location:

Period:

6 Dec 2025 20:53:31 - 28 Dec 2025 16:56:03 (21 days 20 hours 2 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

833

M 7.0+:

M 7.0; 2025 Hubbard Glacier Earthquake; (6 Dec 2025) (7km from the swarm center)

5 swarms found nearby.

2025

S20251206.1(23.7km)

6 Dec

21 days 22 hours

2086 earthquakes

S20251208.3(9.5km)

7 Dec

2 days 11 hours

139 earthquakes

S20251212.1(29.4km)

11 Dec

3 days 7 hours

62 earthquakes

2026

S20260115.3(25.9km)

15 Jan

1 day 9 hours

34 earthquakes

S20260125.2(27.3km)

24 Jan

6 days 20 hours

137 earthquakes

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Seismic Swarm S20251206.2 Near Yakutat, Alaska: Geological Context and Event Analysis

A significant seismic swarm, designated S20251206.2, occurred 116 km north of Yakutat, Alaska. The swarm initiated at 20:53 on 6 December 2025 and concluded at 16:56 on 28 December 2025, spanning 524 hours and 2 minutes. During this period, 833 earthquakes were recorded. The swarm coincided with the M 7.0 Hubbard Glacier Earthquake on 6 December 2025, located just 7 km from the swarm center.

Yakutat lies within a tectonically complex region where the Yakutat terrane collides with the North American Plate. This interaction drives ongoing deformation along the Fairweather Fault system and contributes to the broader subduction dynamics of the Pacific Plate beneath Alaska. The area's geology features accreted oceanic crust and sedimentary basins that amplify seismic activity. Shallow crustal faults in this zone frequently host earthquake swarms due to fluid migration and stress transfer from larger events.

Alaska's seismic history reflects its position at an active plate boundary. Major historical earthquakes include the 1964 Great Alaska Earthquake (M 9.2) and numerous events along the Queen Charlotte-Fairweather fault system. Since 2000, only one prior swarm has been documented in the immediate region, occurring earlier in 2025. The Hubbard Glacier area has experienced recurrent moderate seismicity linked to glacial unloading and tectonic strain accumulation.

Analysis of the first 100 events reveals predominantly shallow focal depths between 0 and 10 km, with the majority clustered at 5 km. Magnitudes ranged from 2.2 to 4.4, with several events exceeding M 4.0 in the initial hours, including multiple M 4.4 shocks on 6 December. Activity showed a rapid onset followed by a gradual decline in both frequency and magnitude, consistent with swarm behavior rather than a classic mainshock-aftershock sequence. Depths remained consistently crustal, indicating activation of near-surface faults.

The swarm's timing immediately following the M 7.0 Hubbard Glacier mainshock suggests it represents triggered seismicity along adjacent structures. Such sequences are common in Alaska's convergent margin, where dynamic and static stress changes can induce prolonged earthquake clusters.

This event underscores the persistent seismic hazard in the Yakutat region, where plate boundary forces continue to shape the landscape through both tectonic and glacio-seismic processes.

References

United States Geological Survey Earthquake Hazards Program
Alaska Earthquake Center Annual Reports
SeismoSight Internal Swarm Classification Database