Seismic Swarm SVS20020115.1: Analysis of Activity Near West Yellowstone

Seismic swarm SVS20020115.1 was recorded beginning at 17:08 on 15 January 2002 and concluding at 00:14 on 16 January 2002. The events occurred 31 km east-southeast of West Yellowstone, Montana, with a total of 67 earthquakes registered over 7 hours and 5 minutes. Magnitudes ranged from 0.2 to 2.9, and focal depths varied between 0 and 13 km, with the majority concentrated between 4 and 10 km. The largest event reached magnitude 2.9 at 18:37 on 15 January.

This swarm exhibited typical characteristics of clustered seismicity, featuring numerous low-magnitude events occurring in rapid succession without a dominant mainshock. Depths remained consistently shallow, consistent with activity influenced by crustal fluids or magmatic processes. The sequence began with events around magnitude 1.4–2.7 within the first minutes, followed by sustained smaller tremors that gradually decreased in frequency toward the end of the period.

The location places the swarm within the tectonically active zone adjacent to Yellowstone National Park. This region forms part of the Yellowstone volcanic plateau, underlain by a large magma reservoir that drives regional deformation and seismicity. The Yellowstone Caldera, formed by massive eruptions approximately 2.1 million, 1.3 million, and 640,000 years ago, continues to exhibit uplift, subsidence, and hydrothermal features. Earthquake swarms here often result from movement of magmatic or hydrothermal fluids rather than tectonic fault slip alone.

Since 1 January 2000, ten swarms have been identified in the area under SeismoSight classification, including seven in 2000 and three in 2001. These recurrent episodes highlight the persistent nature of seismic unrest in the volcanic system. Monitoring by agencies such as the U.S. Geological Survey confirms that such swarms are common and rarely lead to larger tectonic events or eruptive activity.

Overall, SVS20020115.1 represents a short-lived but energetic swarm typical of the Yellowstone region's dynamic geology, providing valuable data on subsurface processes at depths indicative of the brittle-ductile transition zone.

References

SeismoSight internal swarm classification records
USGS Volcano Hazards Program – Yellowstone observations
USGS Earthquake Catalog for Montana region