Seismic Swarm S20140122.1: Analysis of Activity Near West Yellowstone, Montana

Seismic swarm S20140122.1 occurred approximately 25 km east-northeast of West Yellowstone, Montana, within the Yellowstone volcanic region. The sequence began at 06:00 on 21 January 2014 and concluded at 07:24 on 23 January 2014, spanning 49 hours and 24 minutes. During this period, 46 earthquakes were recorded, with magnitudes ranging from -0.2 to 2.4 and focal depths primarily between 4 and 11 km.

The Yellowstone area lies above a large silicic magmatic system associated with the Yellowstone Caldera. This setting produces frequent earthquake swarms driven by fluid migration, hydrothermal pressurization, and minor crustal deformation rather than direct magma intrusion in most cases. Earthquake activity in the region reflects the interplay between the underlying hotspot, extensive fault networks, and active geothermal features. Depths observed in swarm S20140122.1 align with typical shallow crustal seismicity linked to these hydrothermal processes.

Events clustered around 7–8 km depth, with the largest shock (magnitude 2.4) occurring early in the sequence at 8 km. Subsequent activity showed a mix of microearthquakes and events between magnitude 1.0 and 2.0. The temporal pattern featured an initial burst on 21 January, sustained lower-level seismicity through 22 January, and a final event on 23 January. Such sequences commonly exhibit rapid onset and decay without a single dominant mainshock, consistent with swarm behavior in volcanic-hydrothermal environments.

Since 1 January 2000, 56 swarms have been documented in the broader region. Yearly counts include 10 swarms in 2000, 5 in 2001, 6 in 2002, 3 in 2003, 2 in 2004, 1 in 2005, 5 in 2006, 3 in 2007, 7 in 2008, 5 in 2009, 1 in 2010, 1 in 2011, and 7 in 2013. This distribution indicates persistent seismic unrest, with swarm frequency varying annually but remaining a characteristic feature of the Yellowstone system.

Swarm S20140122.1 fits within this established pattern of episodic, low-magnitude activity. No surface deformation or significant changes in hydrothermal discharge were associated with this particular sequence based on available monitoring records. Continued seismic monitoring remains essential for distinguishing routine swarm behavior from any signals that might indicate evolving magmatic or hydrothermal conditions.

References

SeismoSight internal swarm classification data.
USGS Volcano Hazards Program – Yellowstone seismic monitoring summaries.
USGS Earthquake Hazards Program – regional fault and seismicity reports.