Seismic Swarm S20240106.1 Near West Yellowstone, Montana

A seismic swarm designated S20240106.1 occurred 16 km east-northeast of West Yellowstone, Montana, beginning at 16:55 on 6 January 2024 and concluding at 03:08 on 7 January 2024. Over 10 hours and 13 minutes, the swarm produced 35 earthquakes. Magnitudes ranged from -0.9 to 2.0, with focal depths between 0 and 7 km. The sequence featured numerous low-magnitude events clustered in the evening of 6 January, including a peak magnitude of 2.0 at 23:24, followed by a final event of magnitude 1.5 at 03:08 on 7 January.

Earthquake swarms consist of closely spaced events without a dominant mainshock-aftershock pattern. In this case, activity concentrated at shallow depths, consistent with fluid migration or stress adjustments in the upper crust. Such swarms provide insight into localized strain release rather than large-scale tectonic rupture.

The swarm location lies within the Yellowstone volcanic field, part of the eastern Snake River Plain-Yellowstone hotspot track. This region overlies a mantle plume that has driven bimodal volcanism for millions of years. The Yellowstone Caldera, formed during the most recent caldera-forming eruption approximately 631,000 years ago, remains geodynamically active. Ongoing deformation, hydrothermal circulation, and seismicity reflect interactions between crustal magma reservoirs, groundwater, and regional extension.

Seismic monitoring since 2000 has recorded 105 swarms in the broader area, underscoring the persistent nature of swarm activity. Yearly totals vary, with elevated counts in 2000 (10 swarms), 2022 (9), and several years registering 7 events each. These episodes typically involve hundreds of small earthquakes and rarely exceed magnitude 3.0, reflecting the distributed stress regime rather than singular fault failure.

Geodetic and seismic data indicate that swarm activity often correlates with uplift or subsidence linked to magma or hydrothermal fluid movement beneath the caldera. Depths recorded in S20240106.1 align with the brittle-ductile transition zone where such processes commonly occur. Continued surveillance by regional networks supports hazard assessment and improves understanding of volcanic-tectonic interactions.

References
United States Geological Survey Earthquake Hazards Program – Yellowstone region seismicity summaries.
Yellowstone Volcano Observatory – Geological background and caldera history updates.
SeismoSight internal swarm classification records for event parameters.