Location:

Period:

26 Aug 2007 12:03:32 - 28 Aug 2007 21:55:02 (2 days 9 hours 51 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

2 swarms found nearby.

2007

S20070816.1(23.4km)

15 Aug

5 days 1 hours

191 earthquakes

2017

PS20170509.1(78.4km)

8 May

17 hours

5 earthquakes

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Seismic Swarm S20070827.1 Near Adak, Alaska

Seismic swarm S20070827.1 occurred 187 km SSW of Adak, Alaska, from 12:03 on 26 August 2007 to 21:55 on 28 August 2007. Over 57 hours and 51 minutes, the swarm produced 38 earthquakes. Depths ranged primarily between 8 km and 25 km, with the majority clustered around 10 km. Magnitudes varied from 1.9 to 3.4, indicating moderate low-level activity without a dominant mainshock.

The sequence began with events at greater depths, including a 2.9 magnitude quake at 25 km, followed by shallower activity. Multiple 3.1 magnitude events occurred early in the swarm, alongside several 2.9s. Later stages showed consistent 10 km depths with magnitudes mostly between 2.0 and 2.8. The final recorded event reached 2.0 magnitude at 9 km depth. This pattern reflects typical swarm behavior driven by fluid migration or stress adjustments along faults rather than a single large rupture.

Adak lies within the Aleutian Islands, part of the circum-Pacific Ring of Fire. The region forms through subduction of the Pacific Plate beneath the North American Plate at rates of approximately 6–7 cm per year. This tectonic setting generates frequent earthquakes and volcanic activity along the Aleutian arc. Historical records document major events, including the 1957 magnitude 8.6 Andreanof Islands earthquake and the 1965 magnitude 8.7 Rat Islands earthquake, both occurring nearby and underscoring the area's high seismic hazard.

Earthquake swarms in subduction zones often precede or accompany volcanic unrest or afterslip. Data from this swarm show no escalation to larger events, consistent with background seismicity in the central Aleutians. Since 2000, only this single swarm has been classified in the region, highlighting its relative rarity compared to isolated earthquakes.

The Aleutian subduction zone remains one of the most active seismic areas globally. Ongoing monitoring by regional networks supports improved understanding of swarm dynamics and long-term hazard assessment.

References

USGS Earthquake Catalog
Alaska Earthquake Center reports
Global Volcanism Program, Smithsonian Institution