Location:

Period:

3 Nov 2002 22:30:49 - 19 Dec 2002 12:02:48 (45 days 13 hours 31 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

1332

5 swarms found nearby.

2002

PS20021103.1(21.7km)

3 Nov

6 hours

10 earthquakes

S20021104.8(24.6km)

3 Nov

9 days 21 hours

287 earthquakes

S20021106.1(29.1km)

5 Nov

23 days 19 hours

352 earthquakes

S20021220.1(21.2km)

19 Dec

17 days 21 hours

205 earthquakes

2005

S20050830.1(23.7km)

30 Aug

1 day 4 hours

33 earthquakes

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Seismic Swarm S20021104.3: Analysis of Activity Near Mentasta Lake, Alaska

The seismic swarm designated S20021104.3 was recorded in a remote area of eastern Alaska, centered 42 km west-northwest of Mentasta Lake. Activity commenced at 22:30 on 3 November 2002 and concluded at 12:02 on 19 December 2002. Over a duration of 1093 hours and 31 minutes, a total of 1332 earthquakes were registered. This event represents the sole swarm documented in the region since 1 January 2000.

Examination of the first 100 events reveals predominantly shallow hypocenters, with depths ranging from 0 km to 17 km. The sequence initiated with a magnitude 5.4 earthquake at 0 km depth, followed by multiple events exceeding magnitude 4.0 in the initial hours. Magnitudes across these events spanned 1.7 to 5.4, with the majority falling between 2.5 and 4.2. Temporal clustering was evident, particularly in the first 24 hours, where 23 events of magnitude 3.0 or greater occurred. Depths remained concentrated in the upper 5 km for most shocks, indicating shallow crustal processes.

The Mentasta Lake region occupies a tectonically active zone within the eastern Alaska Range. This area is influenced by the interaction between the Pacific and North American plates, producing both subduction-related and strike-slip seismicity. The Denali Fault, a major right-lateral strike-slip structure extending over 2000 km, traverses nearby and accommodates significant lateral motion. Regional geology features Paleozoic to Mesozoic metamorphic and sedimentary rocks intruded by Tertiary granitic bodies, with Quaternary glacial deposits mantling much of the surface. Ongoing deformation along the fault system contributes to elevated seismic hazard.

Historical records indicate recurrent moderate to large earthquakes in this portion of Alaska. The 2002 Denali Fault earthquake sequence, which included a magnitude 7.9 mainshock on 3 November, generated widespread aftershock activity across the broader region. Such events underscore the persistent strain accumulation and release along the fault network.

The S20021104.3 swarm provides insight into localized stress adjustments within this dynamic setting. Shallow event depths and rapid onset align with patterns observed in fault-related sequences, where fluid migration or aseismic slip may trigger clustered seismicity. Continued monitoring of the Denali Fault system remains essential for assessing future activity.

References

USGS Earthquake Hazards Program regional reports on Alaskan tectonics.
Alaska Earthquake Center historical seismicity summaries.
Geological Society of America publications on Denali Fault geology.