Location:

Period:

2 Oct 2007 18:02:51 - 15 Oct 2007 04:22:24 (12 days 10 hours 19 minutes)

Volcanoes in 100km radius:

Dutton(96km)

Earthquakes:

292

4 swarms found nearby.

2007

PS20071002.1(12.8km)

2 Oct

2 hours

5 earthquakes

S20071026.1(5.5km)

25 Oct

2 days 13 hours

46 earthquakes

2009

S20090502.1(6.2km)

2 May

1 day 8 hours

54 earthquakes

2020

S20200805.1(22.6km)

4 Aug

1 day 16 hours

45 earthquakes

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Seismic Swarm S20071002.1 Near King Cove, Alaska: Geological Context and Event Analysis

The seismic swarm designated S20071002.1 occurred approximately 101 km south-southeast of King Cove on the Alaska Peninsula. It began at 18:02 UTC on 2 October 2007 and concluded at 04:22 UTC on 15 October 2007, spanning 298 hours and 19 minutes. During this period, 292 earthquakes were recorded. This sequence represents the sole swarm documented in the region since 1 January 2000.

The Alaska Peninsula lies within the tectonically active Pacific Ring of Fire. It is situated above the convergent boundary where the Pacific Plate subducts northwestward beneath the North American Plate at rates of approximately 6–7 cm per year. This subduction drives the Aleutian megathrust and produces frequent intermediate-depth seismicity along the Wadati-Benioff zone. The study area is underlain by Mesozoic to Cenozoic volcanic and sedimentary rocks of the Aleutian arc, with crustal thickness averaging 30–35 km. Regional fault systems, including strike-slip structures accommodating oblique convergence, contribute to distributed seismicity.

Earthquake depths in the swarm predominantly ranged between 10 km and 45 km, consistent with events occurring within the subducting slab and overlying crust. Magnitudes of the first 100 events varied from 2.3 to 4.6, with the largest shock (M 4.6) recorded at 21:59 UTC on 2 October at 29 km depth. The initial 24 hours featured the highest rate of activity, including multiple events above M 4.0 clustered near 25 km depth. Subsequent events showed a gradual decline in both frequency and maximum magnitude, with many occurring at depths of 16–26 km. Shallow events (depths <15 km) were infrequent and typically below M 3.0 after the first day.

The swarm exhibited classic characteristics of a non-mainshock-aftershock sequence, lacking a single dominant event followed by a clear decay curve. Instead, activity remained elevated for nearly two weeks before returning to background levels. No surface rupture or significant ground deformation was associated with the sequence, aligning with the moderate magnitudes involved.

Historically, the Alaska Peninsula experiences recurrent seismic swarms linked to fluid migration or stress transfer within the subduction interface. The 2007 swarm fits this pattern and remains the only such episode catalogued in the area since 2000. Updated monitoring by regional seismic networks continues to track background seismicity, confirming that post-2007 rates have remained typical for the arc without recurrence of swarm-type activity.

This event underscores the persistent seismic hazard along the Aleutian subduction zone. Continued instrumentation and real-time analysis are essential for distinguishing swarm behavior from potential foreshock sequences preceding larger megathrust ruptures.

References

USGS Earthquake Catalog
Alaska Earthquake Center regional reports
SeismoSight internal swarm classification S20071002.1