Location:

Period:

11 Dec 2025 02:17:54 - 14 Dec 2025 10:02:58 (3 days 7 hours 45 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

6 swarms found nearby.

2025

S20251206.1(9.0km)

6 Dec

21 days 22 hours

2086 earthquakes

S20251206.2(29.4km)

6 Dec

21 days 20 hours

833 earthquakes

S20251207.1(15.0km)

6 Dec

1 day 18 hours

52 earthquakes

2026

S20260101.1(15.3km)

1 Jan

5 days 17 hours

167 earthquakes

S20260115.3(4.4km)

15 Jan

1 day 9 hours

34 earthquakes

S20260125.2(5.9km)

24 Jan

6 days 20 hours

137 earthquakes

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Seismic Swarm S20251212.1 Near Yakutat, Alaska: Geological Context and Event Analysis

Seismic swarm S20251212.1 was recorded 114 km north of Yakutat, Alaska, beginning at 02:17 on 11 December 2025 and concluding at 10:02 on 14 December 2025. Over 79 hours and 45 minutes, the swarm produced 62 earthquakes, with magnitudes ranging from 1.5 to 3.1 and focal depths primarily between 0 and 14 km. The largest event reached magnitude 3.1 at 17:21 on 11 December at a depth of 9 km.

The sequence exhibited typical swarm characteristics, featuring numerous events of similar magnitude without a dominant mainshock. Activity clustered in two main phases: an initial period on 11 December with 24 events, including several above magnitude 2.0, and a secondary peak on 13 December with 20 events, highlighted by a magnitude 2.7 earthquake at 10:26. Depths remained shallow throughout, consistent with crustal faulting in the region.

Yakutat lies within the tectonically complex transition zone between the Pacific and North American plates. The Yakutat terrane, a buoyant oceanic plateau, is colliding with and partially subducting beneath the North American margin. This process drives rapid uplift of the St. Elias Mountains and generates frequent seismicity along major structures such as the Fairweather Fault and the Transition Fault. The area experiences both strike-slip and thrust faulting, with historical events including the 1899 Yakutat Bay earthquakes of magnitudes 8.0 and 8.1.

Since 1 January 2000, three seismic swarms have been documented in the broader region, with the first occurring in 2025. Swarm S20251212.1 aligns with background tectonic loading rather than magmatic processes, given the absence of volcanic centers nearby. Depths under 15 km indicate activity within the upper crust, where the Yakutat Block interacts with overriding continental rocks.

This event underscores the ongoing seismic hazard in southeastern Alaska. Continued monitoring by regional networks provides essential data for understanding strain accumulation along the plate boundary.

References

USGS Earthquake Hazards Program
Alaska Earthquake Center, University of Alaska Fairbanks
SeismoSight internal swarm classification records