Seismic Swarm SVS20200910.1 Near West Yellowstone, Montana

Seismic swarm SVS20200910.1 was recorded 61 km southeast of West Yellowstone, Montana, within the Yellowstone volcanic region. The sequence began at 00:20 on 10 September 2020 and concluded at 23:22 on 12 September 2020, spanning 71 hours and registering 117 earthquakes.

Analysis of the first 100 events reveals predominantly low-magnitude activity. Magnitudes ranged from 0.0 to 2.8, with the majority between 1.0 and 2.0. Depths clustered between 0 and 5 km, though several events occurred at greater or negative depths indicative of measurement variation. The strongest events reached 2.8 on 10 September at depths of 1 km and 0 km. Early activity showed clusters around 10:50–11:50 and 12:00–13:00, with repeated magnitudes near 2.0–2.6. Later events maintained similar shallow characteristics through the morning of 11 September.

This swarm aligns with the broader seismic patterns of the Yellowstone area, situated on the eastern edge of the Yellowstone Caldera. The caldera formed approximately 631,000 years ago during the most recent supereruption and remains one of the largest active volcanic systems on Earth. Ongoing crustal deformation, hydrothermal fluid movement, and regional tectonic stresses contribute to frequent earthquake swarms. Swarms in this setting typically involve numerous small events without a single dominant mainshock, often linked to fluid migration rather than magmatic intrusion.

Historical records indicate repeated swarm activity in the region. Since 2000, thirty swarms have been documented, with notable occurrences in 2002 (five swarms), 2006 and 2008 (three each), 2009, 2013, and 2018 (three each). Additional swarms took place in 2004, 2010, 2011, 2014–2017, and 2019. These episodes underscore the persistent seismicity driven by the underlying volcanic and hydrothermal systems.

The 2020 swarm remained modest in scale and energy release. No damage or felt reports beyond instrumental detection were associated with the sequence. Continued monitoring by regional seismic networks supports ongoing assessment of activity levels in this geologically dynamic zone.

References

• U.S. Geological Survey, Yellowstone Volcano Observatory reports (2020–2024 updates)
• Montana Bureau of Mines and Geology seismic catalogs
• SeismoSight internal swarm classification SVS20200910.1