Seismic Swarm SVS20180411.1: Analysis of Activity Near West Yellowstone, Montana

On April 11, 2018, at 02:42 UTC, a seismic swarm designated SVS20180411.1 began approximately 60 km east-southeast of West Yellowstone, Montana. The sequence concluded at 03:02 on April 12, registering 114 earthquakes over 24 hours and 20 minutes. This event occurred within the tectonically active Yellowstone region, where crustal stresses arise from the underlying volcanic system.

The Yellowstone area lies above a continental hotspot, characterized by a large magma reservoir beneath the Yellowstone Caldera. Seismic activity in this zone frequently manifests as swarms rather than isolated mainshock-aftershock sequences, driven by fluid migration, hydrothermal processes, and minor crustal adjustments. Depths of recorded events typically range from 1 to 12 km, consistent with shallow brittle failure in the upper crust influenced by elevated geothermal gradients.

Analysis of the first 100 events reveals predominantly low-magnitude earthquakes. Magnitudes spanned from -0.1 to 2.3, with the majority falling between 0.5 and 1.8. Depths clustered around 2 to 8 km, indicating activity within the seismogenic layer above deeper magmatic influences. Temporal distribution showed an initial intense phase on April 11 morning, followed by continued but diminishing activity through the afternoon and evening. Notable peaks included multiple events exceeding magnitude 2.0 between 16:00 and 21:00 on April 11.

Historical records indicate 20 swarms have occurred in the region since January 1, 2000. These episodes cluster in specific years: five in 2002, one in 2004, two in 2006, one in 2008, four in 2009, one each in 2010 and 2011, three in 2013, and one each in 2015 and 2016. Such recurrence underscores the persistent, swarm-dominated seismicity pattern tied to the Yellowstone volcanic field.

This swarm aligns with established patterns of low-magnitude, shallow activity that rarely poses significant hazard but contributes to ongoing monitoring of the broader volcanic system. Continuous seismic networks provide essential data for distinguishing swarm behavior from potential precursors to larger events.

References

SeismoSight internal swarm classification data for SVS20180411.1 and associated historical statistics.