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Location:
58 km SE of West Yellowstone, Montana
Period:
17 Sep 2009 18:01:15 - 18 Sep 2009 13:05:12 (19 hours 3 minutes)
Volcanoes in 100km radius:
None
Earthquakes:
25
32 swarms found nearby.
2002
8 Oct
3 days 11 hours
120 earthquakes
3 Nov
2 days 6 hours
67 earthquakes
3 Nov
1 day 2 hours
25 earthquakes
10 Nov
15 hours
30 earthquakes
5 Dec
1 day 6 hours
39 earthquakes
2004
31 Aug
1 day 10 hours
27 earthquakes
2006
18 Mar
12 hours
28 earthquakes
5 Apr
16 hours
77 earthquakes
2008
23 Nov
1 day 15 hours
66 earthquakes
27 Dec
8 days 7 hours
823 earthquakes
2009
14 Sep
2 days 16 hours
39 earthquakes
14 Oct
3 days 23 hours
138 earthquakes
2010
12 Jun
22 hours
28 earthquakes
2011
14 Apr
7 hours
24 earthquakes
2013
6 Jan
1 day 14 hours
54 earthquakes
15 Apr
17 hours
30 earthquakes
23 Jun
5 hours
29 earthquakes
2015
4 Sep
4 hours
24 earthquakes
2016
24 Nov
1 day 13 hours
60 earthquakes
2018
11 Apr
1 day 0 hours
114 earthquakes
31 Dec
4 hours
57 earthquakes
2019
29 Aug
14 hours
43 earthquakes
2020
12 Feb
11 hours
36 earthquakes
10 Sep
2 days 23 hours
117 earthquakes
1 Dec
2 days 8 hours
114 earthquakes
6 Dec
1 day 7 hours
37 earthquakes
2021
15 Jul
7 days 4 hours
820 earthquakes
2022
12 Feb
7 hours
25 earthquakes
2 Mar
1 day 22 hours
33 earthquakes
2023
29 Mar
2 days 6 hours
110 earthquakes
16 Apr
1 day 20 hours
38 earthquakes
24 Apr
6 hours
31 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm SVS20090918.1: Activity Southeast of West Yellowstone

A seismic swarm designated SVS20090918.1 occurred 58 km southeast of West Yellowstone, Montana, between 18:01 on 17 September 2009 and 13:05 on 18 September 2009. In 19 hours and 3 minutes, 25 earthquakes were recorded. Magnitudes ranged from -0.1 to 1.8, with the majority below 1.0 and depths concentrated between 4 and 6 km. The sequence began with a magnitude 0.0 event at 8 km depth, followed by a 1.8 event at 6 km within the first five minutes. Subsequent activity included multiple events of 1.2–1.5 at depths of 5–6 km during the evening of 17 September, tapering to smaller shocks through the night and concluding with a magnitude 0.1 event at 5 km depth on 18 September.

This swarm fits the established pattern of earthquake clusters in the Yellowstone region. Since 1 January 2000, eleven swarms have been identified in the area. Earlier episodes occurred in 2002 (five swarms), 2004 (one swarm), 2006 (two swarms), 2008 (two swarms), and 2009 (one swarm prior to SVS20090918.1). Such sequences typically involve low-magnitude events clustered in time and space, often linked to fluid migration within the crust rather than magmatic intrusion.

The swarm location lies on the southwestern margin of the Yellowstone Caldera, part of the larger Yellowstone Plateau volcanic field. The caldera formed during the most recent super-eruption approximately 631,000 years ago, following earlier events at 1.3 million and 2.1 million years ago. Ongoing crustal deformation, hydrothermal circulation, and basaltic magma at depths greater than 10 km sustain elevated seismicity. Earthquakes in this zone commonly occur at 2–10 km depth, consistent with the 2–8 km range observed in SVS20090918.1.

Seismic monitoring by the Yellowstone Volcano Observatory indicates that swarms of this scale occur several times per year and rarely precede significant volcanic unrest. The 2009 activity remained within background levels for the region, where annual earthquake counts frequently exceed 1,000 events, most below magnitude 2.0.

References

  • U.S. Geological Survey Earthquake Hazards Program catalog
  • Yellowstone Volcano Observatory annual reports (2009–2023)
  • Intermountain Seismic Belt historical seismicity summaries