Seismic Swarm S20140211.1: Analysis of February 2014 Activity Near West Yellowstone, Montana

The seismic swarm designated S20140211.1 occurred 26 km east-northeast of West Yellowstone, Montana, within the tectonically active Yellowstone Plateau. This region overlies the Yellowstone hotspot, a mantle plume responsible for the Yellowstone Caldera, which formed through massive rhyolitic eruptions approximately 2.1 million, 1.3 million, and 640,000 years ago. The area features ongoing hydrothermal systems, crustal deformation, and frequent seismicity driven by magmatic fluids, gas release, and fault interactions within the caldera and its margins.

The swarm initiated at 05:27 on 11 February 2014 and concluded at 01:54 on 15 February 2014, spanning 92 hours and 26 minutes. During this period, 69 earthquakes were recorded. Event magnitudes ranged from negative values to a peak of 3.4, with the majority occurring at depths between 2 and 10 km. Notable activity clustered on 11 February, including the largest event of magnitude 3.4 at 23:03:16, followed by numerous smaller aftershocks and concurrent events within minutes. Subsequent days showed sustained but diminishing activity, with isolated events up to magnitude 2.7 on 13 February and 1.9 on 15 February. Depths remained predominantly shallow, consistent with upper-crustal processes.

This swarm exemplifies typical seismicity patterns in the Yellowstone region, where earthquake clusters often result from fluid migration along faults rather than direct magmatic intrusion. Such swarms contribute to monitoring of the volcanic system, which has produced over 1,000 detectable earthquakes annually in recent decades. Historical records indicate 22 swarms in the vicinity since 1 January 2000, distributed across years as follows: six in 2000, one in 2001, two in 2002, one in 2004, one in 2006, one in 2007, four in 2008, three in 2009, two in 2013, and one in 2014. These events underscore the persistent, episodic nature of seismicity linked to the underlying geological dynamics.

The February 2014 swarm aligns with established patterns of swarm behavior in the area, featuring rapid onset, variable magnitudes, and shallow focal depths. No significant surface deformation or hydrothermal changes were associated with this specific sequence based on contemporaneous observations. Continued seismic monitoring remains essential for understanding long-term volcanic and tectonic evolution in this high-hazard zone.

References

SeismoSight internal swarm classification records.
USGS Earthquake Hazards Program historical data for Yellowstone region.
Yellowstone Volcano Observatory geological summaries on caldera formation and seismicity.