Seismic Swarm S20071026.1 Near King Cove, Alaska

Seismic swarm S20071026.1 was recorded 78 km southeast of King Cove, Alaska, on the Alaska Peninsula. The sequence began at 20:18 on 25 October 2007 and concluded at 09:20 on 28 October 2007, spanning 61 hours and 1 minute. During this interval, 46 earthquakes were registered, with magnitudes ranging from 2.1 to 5.5 and focal depths between 3 km and 43 km.

The swarm exhibited typical characteristics of clustered seismic activity without a single dominant mainshock. The largest event reached magnitude 5.5 at a depth of 43 km on 26 October at 15:23:30 UTC. Subsequent events included several magnitude 3+ earthquakes, such as a 3.5 at 5 km depth later that day and additional events of 3.4, 3.2, 3.1, and 3.0 over the following 48 hours. The majority of events clustered at shallow to mid-crustal depths, consistent with activity along regional fault structures.

This swarm represents the first of two documented swarms in the area since 1 January 2000. Such sequences are not uncommon in tectonically active zones but warrant monitoring due to their potential to precede larger events or indicate fluid migration along faults.

The King Cove region lies within the 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. This megathrust boundary generates frequent earthquakes and volcanic activity across the Aleutian arc. The local geology features a complex assemblage of accreted terranes, volcanic rocks, and sedimentary basins shaped by millions of years of subduction-related deformation. Historical seismicity includes great earthquakes, such as the 1938 M8.2 event and the 1946 M8.6 tsunami-generating quake, both occurring along segments of the same plate boundary.

Ongoing tectonic loading in the region sustains background seismicity, with swarms occasionally linked to stress changes or hydrothermal processes. Updated monitoring by regional networks continues to track microseismicity, providing data for hazard assessment in this remote but strategically important area of the North Pacific.

References

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