Seismic Swarm S20080126.1: Analysis of Activity Near West Yellowstone, Montana
On 25 January 2008 at 23:30 UTC, a seismic swarm designated S20080126.1 began approximately 25 km east-southeast of West Yellowstone, Montana. The sequence concluded at 11:48 on 26 January 2008, encompassing 33 earthquakes over roughly 12 hours and 17 minutes. Magnitudes ranged from 0.6 to 2.4, with the largest event recorded at 01:43 on 26 January. Focal depths varied between 2 km and 11 km, indicating shallow crustal activity typical of the region.
The swarm exhibited a rapid onset followed by a gradual decline in event rate. Early events clustered around magnitudes 1.0–1.7 at depths of 4–9 km. Mid-sequence activity included the peak magnitude of 2.4 at 7 km depth, accompanied by several events near 1.5–1.7. Later stages featured lower-magnitude occurrences, predominantly between 0.8 and 1.5, at similar shallow depths. This temporal pattern reflects classic swarm behavior driven by fluid migration or stress adjustments rather than a single mainshock-aftershock sequence.
The location lies within the Yellowstone volcanic plateau, an area shaped by multiple caldera-forming eruptions over the past 2.1 million years. The most recent major event, approximately 631,000 years ago, formed the current Yellowstone Caldera. Ongoing magmatic and hydrothermal processes sustain elevated seismicity, with small earthquakes frequently occurring due to movement of fluids within fractured rock and minor adjustments along regional faults.
Historical records document 31 swarms in the broader area since 1 January 2000. Annual counts include seven each in 2000, 2002, and 2006; three each in 2001 and 2003; two in 2007; and one each in 2004 and 2008. Such recurrent swarms underscore the dynamic nature of the Yellowstone system, where earthquake clusters often last hours to weeks without leading to larger tectonic events.
Seismic monitoring in this zone benefits from dense station coverage operated by the U.S. Geological Survey and university partners. Data from S20080126.1 align with established patterns of low-magnitude, shallow activity that rarely exceeds magnitude 3.0 in swarm episodes. No surface deformation or significant changes in geothermal features were associated with this particular sequence.
Continued observation remains essential for distinguishing background volcanic seismicity from any precursory signals. The 2008 swarm contributed to the long-term dataset used to refine models of crustal stress and fluid dynamics beneath the Yellowstone region.
References
- U.S. Geological Survey, Yellowstone Volcano Observatory reports on regional seismicity.
- University of Utah Seismograph Stations, historical earthquake catalog for the Intermountain West.
- SeismoSight internal swarm classification database for event parameters of S20080126.1.