Location:

Period:

6 Mar 2003 16:49:05 - 2 Apr 2003 01:38:40 (26 days 8 hours 49 minutes)

Volcanoes in 100km radius:

Buzzard Creek(66km)

Earthquakes:

396

15 swarms found nearby.

2002

S20021023.1(13.4km)

23 Oct

12 days 6 hours

727 earthquakes

S20021024.1(14.0km)

23 Oct

10 days 5 hours

183 earthquakes

S20021023.2(8.9km)

23 Oct

1 day 18 hours

37 earthquakes

S20021105.2(11.9km)

4 Nov

16 days 23 hours

418 earthquakes

S20021108.2(15.8km)

8 Nov

1 day 9 hours

133 earthquakes

S20021110.1(16.2km)

9 Nov

1 day 17 hours

53 earthquakes

S20021113.1(18.7km)

12 Nov

1 day 14 hours

71 earthquakes

S20021118.1(13.3km)

17 Nov

3 days 1 hours

69 earthquakes

S20021225.1(22.0km)

24 Dec

5 days 15 hours

113 earthquakes

S20021227.1(4.2km)

26 Dec

7 days 19 hours

98 earthquakes

2003

S20030107.1(16.3km)

6 Jan

4 days 21 hours

72 earthquakes

S20030403.1(12.7km)

2 Apr

23 days 4 hours

248 earthquakes

S20030602.2(17.7km)

1 Jun

11 days 13 hours

108 earthquakes

S20030714.1(15.5km)

13 Jul

20 days 18 hours

166 earthquakes

S20030807.1(11.5km)

7 Aug

6 days 18 hours

95 earthquakes

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Seismic Insights into the S20030307.1 Swarm East of Cantwell, Alaska

The S20030307.1 earthquake swarm was recorded 77 km east of Cantwell, Alaska, beginning at 16:49 on 6 March 2003 and concluding at 01:38 on 2 April 2003. Over 632 hours and 49 minutes, the sequence produced 396 events. Analysis of the first 100 events reveals a classic swarm pattern dominated by low-magnitude activity consistent with fluid migration or minor crustal adjustment along regional faults.

Magnitudes in the initial 100 events ranged from 0.7 to 3.0, with the largest shock reaching M3.0 on 7 March at a depth of 2 km. Depths were predominantly shallow (0–14 km), although one outlier occurred at 79 km. Most events clustered between 1–5 km depth, suggesting activity within the upper brittle crust. Temporal distribution showed an initial burst on 6–7 March, followed by sustained low-level seismicity through 12 March, with repeated M2.6–M2.7 events indicating episodic energy release.

The Cantwell region lies within the Alaska Range, where ongoing convergence between the Pacific and North American plates drives deformation along the Denali Fault system. This right-lateral strike-slip fault accommodates much of the plate-boundary strain and has hosted major historical ruptures. The 2002 Denali earthquake (M7.9) occurred nearby, altering local stress fields and potentially priming the crust for subsequent swarm activity. Post-2002 aftershocks and swarms remain common as the fault zone continues to adjust.

Since 1 January 2000, eleven swarms have occurred in the immediate area. Ten took place in 2002, followed by this single 2003 sequence, underscoring elevated seismicity after the Denali mainshock. Such swarms typically lack a dominant mainshock–aftershock decay and instead exhibit prolonged, diffuse energy release, a signature often linked to hydrothermal or magmatic processes at depth.

The S20030307.1 swarm illustrates the persistent seismic hazard in central Alaska. Continued monitoring is essential given the proximity of critical infrastructure and the potential for larger triggered events along the Denali system.

References

SeismoSight internal swarm classification S20030307.1
USGS Earthquake Hazards Program – Alaska tectonics and Denali Fault summary