Seismic Swarm S20030206.1: Analysis of Activity Near West Yellowstone, Montana

Seismic swarm S20030206.1 was recorded 13 km northeast of West Yellowstone, Montana, beginning at 18:16 on 5 February 2003 and concluding at 12:37 on 7 February 2003. Over 42 hours and 20 minutes, 42 earthquakes were detected. Magnitudes ranged from -0.5 to 1.1, with the majority of events clustered between 7 and 10 km depth. The sequence featured low-magnitude activity, including multiple events below magnitude 0.0, consistent with typical swarm behavior in the region.

The swarm initiated with a magnitude 0.1 event at 8 km depth. Subsequent events on 5 February showed depths predominantly at 8–9 km, with occasional shallower occurrences such as a magnitude -0.3 event at 2 km. Activity continued into 6 February, reaching a peak magnitude of 1.1 at 9 km depth. The final event on 7 February registered magnitude 0.0 at 10 km. This pattern reflects a diffuse release of strain without a dominant mainshock.

The West Yellowstone area lies within the Yellowstone Plateau, part of the tectonically active Intermountain Seismic Belt. The region is influenced by the Yellowstone hotspot, which drives ongoing volcanic and hydrothermal processes beneath the Yellowstone caldera. Earthquake swarms here often result from fluid migration, magmatic movement, or regional extension along normal faults. Depths of 7–10 km align with the brittle-ductile transition zone in the crust, where small fractures accommodate stress from deeper volcanic sources.

Historically, the area has experienced recurrent seismic swarms. Since 1 January 2000, 23 swarms have been documented, with annual counts of 10 in 2000, 5 in 2001, 6 in 2002, and 2 in 2003. These events underscore the persistent seismic vitality linked to the underlying volcanic system, which has shaped the landscape through repeated caldera-forming eruptions over the past 2 million years.

Such swarms provide valuable data on subsurface dynamics without indicating imminent volcanic activity. Monitoring by regional networks helps distinguish swarm patterns from tectonic mainshock-aftershock sequences, supporting hazard assessment in this geologically dynamic setting.

References: USGS Earthquake Catalog Yellowstone Volcano Observatory Geological Summaries SeismoSight Internal Swarm Classification Records