Seismic Swarm SVS20180311.1 Near West Yellowstone, Montana

On March 11, 2018, a seismic swarm designated SVS20180311.1 was recorded 30 km east-southeast of West Yellowstone, Montana. The sequence began at 11:16 and concluded at 18:23, encompassing 28 earthquakes over 7 hours and 7 minutes. Magnitudes ranged from 0.1 to 1.8, with focal depths between 2 km and 11 km. The initial events included a magnitude 0.7 quake at 10 km depth at 11:16:22, followed closely by a magnitude 0.8 event at 2 km depth. Subsequent activity featured peaks such as a magnitude 1.8 shock at 7 km depth at 11:35:32 and a magnitude 1.5 event at 5 km depth at 12:23:48. Later events tapered with smaller magnitudes, including multiple 0.7 events around 18:23 at depths of 5–6 km.

This swarm reflects typical patterns of clustered seismicity in the region, where events occur in rapid succession without a dominant mainshock. Depths concentrated between 4 km and 8 km for most events, consistent with shallow crustal processes. The full sequence demonstrated a gradual decline in both frequency and magnitude after the initial two-hour peak.

The area lies within the Yellowstone volcanic field, underlain by a large silicic magma reservoir and influenced by the North American plate's interaction with a mantle hotspot. This setting produces frequent earthquake swarms driven by hydrothermal fluid migration and minor magmatic movements rather than tectonic fault rupture alone. Historical records since 2000 document 54 such swarms in the vicinity, with notable years including 2000 (7 swarms), 2002 (6), 2006 (7), 2008 (7), 2013 (5), and 2014 (6). Earlier swarms in 2001, 2003, 2007, 2009, 2010, 2016, and 2017 further illustrate the recurrent nature of this activity.

Geological studies of the Yellowstone Plateau indicate that swarm events often align with mapped fault zones and hydrothermal areas east of the caldera rim. Depths in the 2–11 km range correspond to the brittle-ductile transition zone where fluids can trigger brittle failure. The 2018 swarm's characteristics align with prior episodes in duration and energy release, underscoring the region's ongoing volcanic and hydrothermal dynamism.

References

USGS Earthquake Hazards Program reports on Yellowstone seismicity.
Yellowstone Volcano Observatory geological summaries (2000–2018).
SeismoSight internal swarm classification data.