Location:

Period:

23 Jan 2018 11:50:21 - 25 Jan 2018 13:26:06 (2 days 1 hour 35 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

2 swarms found nearby.

2018

PS20180123.1(74.1km)

23 Jan

1 day 12 hours

9 earthquakes

S20180124.4(24.3km)

23 Jan

2 days 6 hours

50 earthquakes

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Earthquake Swarm S20180124.2 in the Gulf of Alaska

An earthquake swarm designated S20180124.2 was recorded in the Gulf of Alaska, beginning at 11:50 on 23 January 2018 and concluding at 13:26 on 25 January 2018. Over this 49-hour and 35-minute period, 36 earthquakes were registered. The events ranged in magnitude from 3.1 to 4.9, with focal depths predominantly between 3 and 17 km. The sequence featured several events above magnitude 4.0, including a peak magnitude of 4.9 at 16:46 on 24 January 2018.

The swarm initiated with a magnitude 4.0 event at 11:50 on 23 January, followed closely by a magnitude 4.8 shock at 12:19 the same day. Subsequent activity included multiple magnitude 4.0–4.5 events clustered in the evening of 23 January and early hours of 24 January. Activity continued at a moderate rate through 24 January, culminating in the largest event of the swarm before tapering off with smaller shocks on 25 January.

Geologically, the Gulf of Alaska lies at the convergent boundary between the Pacific Plate and the North American Plate. This region forms part of the Pacific Ring of Fire, where the Pacific Plate subducts northwestward beneath Alaska along the Aleutian Trench and associated thrust faults. The resulting compressional tectonics produce frequent seismic activity, including both interplate thrust earthquakes and intraplate events within the overriding plate. Crustal depths in this swarm (mostly 5–12 km) are consistent with shallow seismicity along the continental margin.

The area has a well-documented history of large earthquakes. The 1964 Great Alaska Earthquake (magnitude 9.2) originated near Prince William Sound and remains one of the most powerful recorded events in North American history, generating widespread tsunami damage. Since 2000, seismic monitoring has identified only two swarms in the Gulf of Alaska, with the first occurring in January 2018.

Swarm sequences such as S20180124.2 differ from typical mainshock-aftershock patterns by lacking a single dominant event. Instead, they exhibit clustered energy release over days, often linked to fluid migration or slow slip along faults. Depths remained shallow throughout, suggesting activity within the upper crust rather than deeper subduction interfaces.

References
USGS Earthquake Catalog (earthquake.usgs.gov)
Alaska Earthquake Center (aeic.alaska.edu)
SeismoSight internal swarm classification S20180124.2