Seismic Swarm S20060613.1: Earthquake Activity near West Yellowstone, Montana

Seismic swarm S20060613.1 was recorded 18 km east-southeast of West Yellowstone, Montana, beginning at 20:41 on 12 June 2006 and concluding at 11:04 on 14 June 2006. Over 38 hours and 22 minutes, the sequence comprised 45 earthquakes. Magnitudes ranged from -0.1 to 2.5, with the largest event occurring on 13 June at 08:05. Focal depths clustered between 6 km and 12 km, predominantly around 9–11 km, consistent with shallow crustal processes in the area.

The swarm unfolded with low-level activity on 12 June, featuring events of 0.5–0.8 magnitude. Activity intensified on 13 June, including multiple shocks above magnitude 1.0 and the peak magnitude 2.5 event. Later phases on 14 June showed diminishing frequency, ending with a magnitude 1.3 event. Depths remained stable throughout, suggesting a localized source volume without significant migration.

This portion of Montana lies adjacent to the Yellowstone Plateau, part of the active Yellowstone volcanic field. The area overlies a partially molten crustal magma reservoir that drives regional deformation and seismicity. Earthquake swarms here commonly arise from fluid migration, hydrothermal pressurization, or minor slip along pre-existing faults rather than magmatic intrusion. Historical patterns indicate swarms recur frequently within the broader caldera and its margins, reflecting ongoing volcanic and tectonic adjustment since the last major caldera-forming eruption approximately 631,000 years ago.

Since 1 January 2000, thirty swarms have been documented in the region. Annual counts include ten in 2000, five in 2001, eight in 2002, three in 2003, two in 2004, one in 2005, and one in 2006. These episodes underscore persistent low-magnitude unrest typical of the Yellowstone system.

References

USGS Earthquake Catalog
Yellowstone Volcano Observatory Annual Reports
Montana Bureau of Mines and Geology Seismicity Summaries