Location:

Period:

17 Nov 2002 19:35:10 - 20 Nov 2002 20:40:57 (3 days 1 hour 5 minutes)

Volcanoes in 100km radius:

Buzzard Creek(65km)

Earthquakes:

12 swarms found nearby.

2002

S20021023.1(2.9km)

23 Oct

12 days 6 hours

727 earthquakes

S20021024.1(1.1km)

23 Oct

10 days 5 hours

183 earthquakes

S20021023.2(22.0km)

23 Oct

1 day 18 hours

37 earthquakes

S20021105.2(2.6km)

4 Nov

16 days 23 hours

418 earthquakes

S20021108.2(4.0km)

8 Nov

1 day 9 hours

133 earthquakes

S20021110.1(27.8km)

9 Nov

1 day 17 hours

53 earthquakes

S20021227.1(16.5km)

26 Dec

7 days 19 hours

98 earthquakes

2003

S20030107.1(29.4km)

6 Jan

4 days 21 hours

72 earthquakes

S20030307.1(13.3km)

6 Mar

26 days 8 hours

396 earthquakes

S20030403.1(25.3km)

2 Apr

23 days 4 hours

248 earthquakes

S20030714.1(28.7km)

13 Jul

20 days 18 hours

166 earthquakes

S20030807.1(24.5km)

7 Aug

6 days 18 hours

95 earthquakes

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Seismic Swarm S20021118.1: Analysis of Earthquake Activity Near Cantwell, Alaska

Seismic swarm S20021118.1 occurred approximately 33 km east-northeast of Cantwell, Alaska, within the tectonically active Alaska Range. The sequence began at 19:35 on 17 November 2002 and concluded at 20:40 on 20 November 2002, spanning 73 hours and 5 minutes. During this period, 69 earthquakes were recorded, with magnitudes ranging from 0.4 to 2.9 and focal depths between 1 km and 14 km. All events remained shallow, consistent with activity along regional fault structures.

The swarm exhibited typical characteristics of clustered seismicity without a dominant mainshock. Events occurred in irregular bursts, with the largest recorded at magnitude 2.9 at 20:40 on 20 November. Earlier peaks included magnitudes 2.8 on 18 November and 2.5 on both 18 and 19 November. Depths averaged around 6 km, suggesting brittle failure in the upper crust. No damage or felt reports were associated with these low-magnitude events.

Regional Geological Setting

The swarm location lies within the Alaska Range, part of the broader Pacific-North American plate boundary. This region experiences ongoing deformation due to oblique convergence, with the Pacific plate subducting beneath the North American plate at rates of approximately 5–6 cm per year. The Denali Fault, a major right-lateral strike-slip system, dominates local tectonics and passes near Cantwell. The 3 November 2002 magnitude 7.9 Denali earthquake, which nucleated nearby, produced extensive surface rupture along this fault and likely influenced subsequent seismic patterns through stress redistribution.

Historical seismicity in the area reflects both subduction-related and intraplate activity. The Denali Fault has generated multiple large events over the Holocene, including prehistoric ruptures documented through paleoseismic trenching. Post-2002 monitoring by the Alaska Earthquake Center has confirmed elevated background rates near the fault trace, underscoring the persistent seismic hazard.

Swarm Context and Regional History

Since 1 January 2000, six seismic swarms have been documented in the broader region, with this event representing the earliest. Such swarms often occur in volcanic or faulted terrains and may reflect fluid migration or aseismic slip transients rather than classic aftershock decay. Depths and magnitudes recorded here align with shallow crustal processes along the Denali system.

References

Alaska Earthquake Center, University of Alaska Fairbanks – Regional seismicity catalogs and Denali Fault studies.
USGS Earthquake Hazards Program – Tectonic framework of south-central Alaska and 2002 Denali event reports.
Freymueller et al. (various publications) – GPS-derived plate motion and fault slip rates in the Alaska Range.