Location:

Period:

8 Nov 2002 17:34:52 - 10 Nov 2002 03:10:20 (1 day 9 hours 35 minutes)

Volcanoes in 100km radius:

Buzzard Creek(61km)

Earthquakes:

133

10 swarms found nearby.

2002

S20021023.1(6.8km)

23 Oct

12 days 6 hours

727 earthquakes

S20021024.1(4.5km)

23 Oct

10 days 5 hours

183 earthquakes

S20021023.2(24.1km)

23 Oct

1 day 18 hours

37 earthquakes

S20021105.2(6.6km)

4 Nov

16 days 23 hours

418 earthquakes

S20021110.1(28.9km)

9 Nov

1 day 17 hours

53 earthquakes

S20021118.1(4.0km)

17 Nov

3 days 1 hours

69 earthquakes

S20021227.1(18.3km)

26 Dec

7 days 19 hours

98 earthquakes

2003

S20030307.1(15.8km)

6 Mar

26 days 8 hours

396 earthquakes

S20030403.1(28.3km)

2 Apr

23 days 4 hours

248 earthquakes

S20030807.1(26.4km)

7 Aug

6 days 18 hours

95 earthquakes

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Seismic Swarm S20021108.2: Analysis of Activity Near Cantwell, Alaska

Seismic swarm S20021108.2 was recorded 36 km ENE of Cantwell, Alaska, beginning at 17:34 on 8 November 2002 and concluding at 03:10 on 10 November 2002. Over 33 hours and 35 minutes, the sequence produced 133 earthquakes. This event represents the earliest swarm documented in the region since systematic recording began in 2000.

The sequence initiated with a magnitude 5.1 earthquake at a depth of 6 km. Subsequent events were predominantly of low magnitude, with the first 100 shocks showing a rapid decay in size after the initial event. Magnitudes ranged from 0.5 to 5.1, while focal depths remained shallow, concentrated between 0 and 10 km. The majority of events clustered within the first 12 hours, indicating a high initial rate of activity that gradually diminished.

Insight from the first 100 events reveals a classic swarm pattern characterized by the absence of a single dominant mainshock-aftershock decay. Instead, multiple events of similar magnitude occurred in close succession, particularly in the 1.0–2.6 range. Depths showed consistent shallow distribution, with many events at 1 km or less, suggesting activation within the upper crust. Temporal clustering was pronounced during the evening of 8 November, with intervals between events often under five minutes in the initial phase.

The Cantwell area lies within the central Alaska Range, where active faulting is driven by ongoing convergence between the Pacific and North American plates. The Denali Fault system dominates regional tectonics, accommodating right-lateral strike-slip motion. Shallow seismicity in this zone frequently occurs along subsidiary structures associated with the main fault trace. Historical records indicate that four swarms have occurred in the broader region since 2000, underscoring episodic swarm behavior superimposed on background tectonic activity.

This swarm provides valuable data on short-term crustal stress release in a tectonically active corridor. The shallow depths and rapid succession of events are consistent with fluid involvement or localized stress transfer along minor faults, common in the Alaska Range. Continued monitoring of such sequences contributes to improved understanding of seismic hazards in central Alaska.

References

Alaska Earthquake Center, University of Alaska Fairbanks
U.S. Geological Survey Earthquake Hazards Program
SeismoSight internal swarm classification records