Seismic Swarm SVS20221005.1: Analysis of Activity Near West Yellowstone, Montana

Seismic swarm SVS20221005.1 occurred 34 km east-southeast of West Yellowstone, Montana, within the Yellowstone volcanic region. The sequence began at 02:05 on 5 October 2022 and concluded at 10:19 on 6 October 2022, spanning 32 hours and 14 minutes. During this interval, 32 earthquakes were recorded, with magnitudes ranging from 0.0 to 2.5 and focal depths between 1 km and 11 km.

The swarm initiated with a cluster of low-magnitude events in the first minutes, including multiple shocks below magnitude 1.0 at depths of 4–11 km. Activity intensified around 02:09 with a magnitude 2.2 event at 7 km depth, followed by additional events reaching magnitude 2.5 at 7 km depth by 02:14. Subsequent events maintained a pattern of shallow to mid-crustal depths, with notable activity continuing through the morning and afternoon of 5 October. The sequence tapered with smaller events on 6 October, ending with a magnitude 1.1 shock at 7 km depth.

This swarm reflects typical seismicity patterns in the Yellowstone area, where the underlying Yellowstone hotspot drives ongoing volcanic and hydrothermal processes. The region sits atop a large caldera system formed by massive eruptions over the past 2.1 million years, with the most recent major event approximately 631,000 years ago. Crustal extension and fluid migration associated with the hotspot contribute to frequent earthquake swarms, which often occur without leading to eruptive activity.

Historical records indicate 76 swarms in the area since 1 January 2000. Annual counts include 7 swarms in 2000, 2 in 2001, 6 in 2002, 2 in 2003, 2 in 2004, 5 in 2006, 2 in 2007, 7 in 2008, 2 in 2009, 2 in 2010, 1 in 2011, 4 in 2013, 6 in 2014, 1 in 2017, 5 in 2018, 3 in 2019, 6 in 2020, 6 in 2021, and 7 in 2022. These episodes underscore the persistent seismic character of the Yellowstone Plateau, where swarms serve as indicators of subsurface stress changes linked to magmatic and geothermal systems.

Monitoring by regional seismic networks continues to track such activity to assess potential changes in volcanic hazard. The modest magnitudes observed in SVS20221005.1 align with the majority of Yellowstone seismicity, which rarely exceeds magnitude 3.0 in swarm events.

References

• U.S. Geological Survey, Yellowstone Volcano Observatory reports (2022–2023 updates)
• Montana Bureau of Mines and Geology seismic catalog
• SeismoSight internal swarm classification data