Seismic Swarm SVS20230425.1: Analysis of Activity Near West Yellowstone, Montana

A seismic swarm designated SVS20230425.1 occurred 44 km east-southeast of West Yellowstone, Montana, within the Yellowstone volcanic region. The sequence began at 22:57 UTC on 24 April 2023 and concluded at 05:08 UTC on 25 April 2023, spanning 6 hours and 10 minutes. During this interval, 31 earthquakes were recorded.

Event parameters indicate shallow focal depths predominantly between 0 and 4 km. Magnitudes ranged from 0.6 to 1.9, with the strongest events reaching 1.9 at depths of 1–2 km. Activity clustered intensely between 00:49 and 01:18 UTC on 25 April, when multiple events above magnitude 1.4 occurred in rapid succession. Later phases showed lower rates, tapering to isolated events by 05:08 UTC.

This swarm aligns with the established pattern of seismicity in the Yellowstone Plateau. The area sits within the eastern margin of the 640,000-year-old Yellowstone Caldera, where the North American plate overrides a mantle hotspot. Resulting crustal extension and hydrothermal fluid migration produce frequent small-magnitude earthquakes. Swarms, defined as clusters without a dominant mainshock, are characteristic and typically reflect fluid-driven processes rather than magmatic intrusion.

Regional monitoring since 2000 has documented 53 swarms in the vicinity. Annual counts include one each in 2000, 2001, 2004, 2010, 2011, 2014, 2015, 2016, and 2017; six each in 2002 and 2021; four each in 2006, 2009, 2020, and 2022; three each in 2008 and 2018; five each in 2013 and 2020; and two in 2023. These episodes underscore persistent, low-level tectonic and hydrothermal adjustment along the Intermountain Seismic Belt.

No surface deformation or volcanic unrest accompanied the April 2023 swarm. Such sequences remain common background activity monitored continuously by the U.S. Geological Survey and Yellowstone Volcano Observatory.

References

U.S. Geological Survey Earthquake Hazards Program – Yellowstone region seismicity reports
Yellowstone Volcano Observatory monthly and annual summaries (2000–2023)
SeismoSight internal swarm classification SVS20230425.1