Seismic Swarm SVS20220302.1: Analysis of Activity Southeast of West Yellowstone

The seismic swarm designated SVS20220302.1 occurred approximately 66 km southeast of West Yellowstone, Montana, within the tectonically active zone influenced by the Yellowstone volcanic system. This region lies along the eastern margin of the Basin and Range Province and is shaped by the Yellowstone hotspot, which has driven volcanism for millions of years. The underlying geology features rhyolitic caldera structures, fault networks, and hydrothermal systems that contribute to frequent low-magnitude seismicity.

The swarm initiated at 01:25 on 2 March 2022 and concluded at 00:23 on 4 March 2022, spanning 46 hours and 57 minutes. During this interval, 33 earthquakes were recorded. Event magnitudes ranged from 0.5 to 2.2, with the largest shock measuring 2.2 at a depth of 6 km. Most events clustered between 4 km and 6 km depth, consistent with shallow crustal processes typical of the area. Activity showed an initial peak in the early hours of 2 March, followed by intermittent smaller events through 3 March and a final minor tremor early on 4 March.

Depth distribution remained stable, with events at 3–7 km indicating brittle failure in the upper crust rather than deeper magmatic movement. The temporal pattern exhibited classic swarm characteristics: a rapid onset, lack of a single dominant mainshock, and gradual decay without aftershock sequences typical of tectonic mainshock-aftershock sequences.

Since 1 January 2000, 27 swarms have been documented in this locale. Yearly counts include five in 2002, one in 2004, two in 2006, two in 2008, three in 2009, one in 2010, one in 2011, three in 2013, one in 2015, one in 2016, one in 2018, one in 2019, four in 2020, and one in 2021. These recurrent swarms reflect ongoing stress adjustments along regional faults and fluid migration within the hydrothermal network.

The Yellowstone area experiences hundreds of earthquakes annually, the majority below magnitude 2.0. Such swarms are common and rarely signal imminent volcanic unrest, as the caldera’s magmatic system resides at depths greater than 5 km where current activity does not indicate significant pressurization. Monitoring by regional networks confirms that similar episodes have occurred without leading to eruptive activity.

References

• U.S. Geological Survey Earthquake Hazards Program, Yellowstone Region Seismicity Reports (2022 updates)
• Montana Bureau of Mines and Geology, Intermountain Seismic Belt Catalog
• Yellowstone Volcano Observatory, Annual Seismic Summaries (2000–2022)