Seismic Swarm S20140217.1: Analysis of Earthquake Activity Near Mammoth, Wyoming

Seismic swarm S20140217.1 was recorded 25 km SSW of Mammoth, Wyoming, beginning at 21:07 on 16 February 2014 and concluding at 05:02 on 20 February 2014. Over 79 hours and 54 minutes, the swarm comprised 52 earthquakes. This event forms part of ongoing monitoring within the Yellowstone volcanic region, where swarms frequently occur due to interactions between magmatic fluids, hydrothermal systems, and regional tectonics.

The Yellowstone Plateau lies at the active terminus of the Snake River Plain hotspot track. The underlying Yellowstone caldera, formed by massive eruptions approximately 2.1 million, 1.3 million, and 640,000 years ago, continues to exhibit uplift, subsidence, and seismicity driven by a crustal magma reservoir and shallow hydrothermal circulation. Earthquake swarms in this setting typically reflect fluid migration rather than tectonic fault slip, with events clustered in time and space at depths of 2–10 km.

Historical records indicate 48 swarms in the broader region since 1 January 2000. Annual counts include nine in 2000, five in 2001, six in 2002, one in 2003, one in 2004, five in 2006, two in 2007, six in 2008, three in 2009, one in 2010, one in 2011, six in 2013, and two in 2014. These episodes underscore the persistent, episodic nature of seismicity tied to the volcanic system.

Within swarm S20140217.1, event magnitudes ranged from –9.9 to 2.8, with the largest shock (magnitude 2.8) occurring at 11:08 on 18 February at 6 km depth. Depths predominantly fell between 2 km and 10 km. Early activity on 16 February featured magnitudes of 0.7–1.4 at depths of 6–8 km. Subsequent peaks included multiple events near magnitude 2.0 on 17–19 February, often at 5–8 km depth. Negative or zero magnitude readings likely represent microseismicity below reliable detection thresholds or instrumental artifacts common in dense swarm sequences.

The temporal distribution showed the highest rate on 17 February, with 24 events, followed by a decline toward the swarm’s termination. Depths remained stable within the shallow crustal volume, consistent with fluid-driven triggering rather than progressive rupture along a single fault plane. No events exceeded magnitude 3.0, aligning with the typical character of Yellowstone swarms that rarely produce felt shaking beyond the immediate vicinity.

Such swarms provide insight into the dynamic state of the volcanic system. Fluid pressure changes within fractured rock can induce rapid sequences of small earthquakes without significant ground deformation. Continuous seismic networks operated by the U.S. Geological Survey and academic partners allow real-time tracking of swarm evolution, supporting hazard assessment for the Yellowstone region.

References

USGS Earthquake Hazards Program, Yellowstone Volcano Observatory reports (2014).
SeismoSight internal swarm classification database.
Yellowstone National Park geologic summary, National Park Service.