Location:

Period:

23 Jan 2018 10:13:45 - 24 Jan 2018 23:17:23 (1 day 13 hours 3 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

3 swarms found nearby.

2018

PS20180123.1(29.7km)

23 Jan

1 day 12 hours

9 earthquakes

S20180124.5(15.1km)

23 Jan

10 days 3 hours

109 earthquakes

S20180124.6(24.7km)

23 Jan

2 days 8 hours

55 earthquakes

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Seismic Swarm S20180124.1: Analysis of Earthquake Activity East-Southeast of Chiniak, Alaska

Seismic swarm S20180124.1 was recorded beginning at 10:13 on 23 January 2018 and concluding at 23:17 on 24 January 2018. The events occurred approximately 250 km east-southeast of Chiniak, Alaska, with a total of 59 earthquakes detected over 37 hours and 3 minutes.

The swarm exhibited a range of magnitudes between 3.0 and 4.4. Initial activity included events of 3.0, 3.7, and 4.3 within the first hour, followed by multiple shocks clustered around magnitudes 3.4–4.2 throughout the afternoon of 23 January. Later peaks featured a 4.4 magnitude event at 17:27 on 23 January and another 4.4 at 17:50 on 24 January. Depths predominantly ranged from 7 km to 25 km, with many events concentrated between 10 km and 23 km, indicating shallow crustal involvement typical of regional tectonics.

Temporal distribution showed sustained activity with clusters of three to five events per hour during peak periods on both days. The sequence maintained consistent energy release without a dominant mainshock-aftershock pattern, characteristic of swarm behavior driven by fluid migration or stress redistribution along faults.

This location lies within the tectonically active Aleutian subduction zone, where the Pacific Plate converges with and subducts beneath the North American Plate at rates of approximately 6–7 cm per year. The regional geology features a complex system of thrust faults and accretionary prisms, contributing to elevated seismicity across the Gulf of Alaska and Kodiak Island margin. Historical records document major events such as the 1964 magnitude 9.2 Great Alaska Earthquake, which originated nearby and caused widespread deformation.

Since 1 January 2000, only two swarms have been documented in the area, with S20180124.1 representing the first recorded instance in 2018. Such infrequent swarm occurrences underscore the episodic nature of seismic energy release in this segment of the subduction interface.

References

USGS Earthquake Hazards Program – Regional Tectonic Setting of South-Central Alaska
Alaska Earthquake Center – Historical Seismicity Summaries
NOAA National Centers for Environmental Information – Subduction Zone Characteristics of the Aleutian Arc