Seismic Swarm S20100117.1: Analysis of Activity Near West Yellowstone, Montana

Seismic swarm S20100117.1 occurred 17 km southeast of West Yellowstone, Montana, within the tectonically active Yellowstone volcanic region. The swarm initiated at 22:20 on 16 January 2010 and concluded at 06:59 on 5 February 2010, spanning 464 hours and 39 minutes. During this interval, 2268 earthquakes were recorded, characteristic of swarm behavior where events cluster in time and space without a single dominant mainshock.

The Yellowstone area lies at the northeastern edge of the Basin and Range Province and above the Yellowstone hotspot, a mantle plume driving crustal extension and magmatism. The region encompasses the Yellowstone Caldera, formed by massive rhyolitic eruptions approximately 2.1 million, 1.3 million, and 0.63 million years ago. Ongoing hydrothermal activity and ground deformation reflect persistent magmatic and fluid processes beneath the surface. Earthquake swarms here commonly arise from fluid migration along faults or pressure changes in the hydrothermal system rather than direct magmatic intrusion.

Analysis of the first 100 events reveals predominantly shallow focal depths between 6 km and 12 km, with magnitudes ranging from negative values to a peak of 2.7. Most events registered below magnitude 2.0, consistent with microseismicity typical of fluid-driven swarms. Early activity included a magnitude 2.1 event at 20:38 on 17 January followed by a magnitude 2.6 at 21:04, indicating rapid energy release in the initial phase. Depths clustered tightly around 10 km, suggesting a concentrated source volume within the brittle upper crust overlying the deeper magmatic system.

Historical records document 48 swarms in the area since 1 January 2000. Annual counts varied as follows: nine in 2000, five in 2001, seven in 2002, three in 2003, two in 2004, one in 2005, six in 2006, three in 2007, seven in 2008, and five in 2009. This pattern underscores the recurrent nature of swarm activity driven by the dynamic geological setting.

Such swarms contribute to understanding stress transfer and fluid pathways in volcanic environments. Monitoring by regional seismic networks continues to track similar episodes, providing data on the interplay between tectonics, magmatism, and hydrothermal circulation in one of North America's most geologically dynamic landscapes.

References

USGS Earthquake Hazards Program
Yellowstone Volcano Observatory Annual Reports
SeismoSight internal swarm classification database