Seismic Swarm S20080109.1 Near West Yellowstone, Montana

Seismic swarm S20080109.1 occurred 18 km northeast of West Yellowstone, Montana, from 06:39 on 9 January 2008 to 03:18 on 14 January 2008. Over 116 hours and 39 minutes, 89 earthquakes were recorded. This activity aligns with patterns typical of the Yellowstone volcanic region, where swarms frequently result from hydrothermal fluid migration and crustal stress adjustments within the caldera system.

The Yellowstone Plateau sits atop a large, active volcanic system featuring a shallow magma reservoir and extensive hydrothermal networks. These features drive recurrent seismicity, with earthquakes often clustered in swarms rather than isolated mainshock-aftershock sequences. Depths in the swarm ranged primarily from 2 to 16 km, with most events between 5 and 10 km, consistent with brittle failure in the upper crust above the magma body. Magnitudes spanned from -1.0 to 3.7, the largest occurring at 21:37 on 9 January at 10 km depth. Smaller events, including negative magnitudes, reflect microseismicity detectable only by dense monitoring networks.

Event timing showed peak activity on 9 January, with multiple events above magnitude 2.0 concentrated between 20:25 and 21:43. Subsequent days featured lower rates and smaller sizes, tapering by 14 January. This temporal distribution illustrates classic swarm behavior, where energy release occurs through numerous small events without a dominant mainshock.

Since 2000, 35 swarms have been documented in the region. Annual counts include 10 in 2000, 5 in 2001, 6 in 2002, 3 in 2003, 2 in 2004, 1 in 2005, 5 in 2006, and 3 in 2007. These statistics underscore the persistent nature of swarm activity driven by the underlying volcanic and hydrothermal processes.

Such events contribute to ongoing assessment of volcanic unrest at Yellowstone. Continuous seismic monitoring supports hazard evaluation, as swarms can precede or accompany changes in geyser activity or ground deformation, though most remain minor and pose limited surface risk.

References

SeismoSight internal swarm classification records.
USGS Yellowstone Volcano Observatory geological summaries on regional seismicity and caldera structure.