Seismic Swarm S20130630.1 Near West Yellowstone, Montana

Seismic swarm S20130630.1 occurred 18 km northeast of West Yellowstone, Montana, within the tectonically active Yellowstone volcanic region. The sequence began at 16:51 on 29 June 2013 and concluded at 09:46 on 3 July 2013, spanning 88 hours and 55 minutes. During this interval, 79 earthquakes were recorded.

Earthquake swarms in this area commonly arise from fluid migration along fractures, hydrothermal pressurization, and minor crustal adjustments linked to the underlying Yellowstone hotspot. Depths ranged primarily between 5 and 13 km, consistent with brittle failure in the upper crust above deeper magmatic and hydrothermal systems. Magnitudes remained modest, with the largest event reaching 3.0 on 1 July 2013 at 13 km depth. Most events clustered between 0.5 and 2.0, typical of swarm behavior where energy releases gradually rather than through a single mainshock-aftershock pattern.

The temporal distribution showed peak activity on 30 June and 1 July, with multiple events exceeding magnitude 2.0 occurring within short windows. Shallower events near 1–5 km depth interspersed with deeper ones, suggesting distributed fracturing rather than a single fault plane. Such patterns align with historical observations of swarm dynamics driven by volatile release from the caldera’s extensive geothermal network.

Yellowstone lies at the northeastern terminus of the Snake River Plain volcanic track, formed by the North American plate overriding a mantle plume. The modern caldera, approximately 45 by 75 km, formed during the most recent supereruption 631,000 years ago. Ongoing uplift and subsidence cycles, monitored by GPS and InSAR, reflect magma recharge and hydrothermal fluid movement that frequently trigger seismicity. The region experiences hundreds of earthquakes annually, the majority in swarms lasting hours to weeks.

Since 2000, 47 swarms have been documented in the broader area, with notable years including 2000 (9 swarms), 2008 (7 swarms), and 2002 and 2006 (5 swarms each). These recurrent episodes underscore the persistent influence of magmatic and hydrothermal processes beneath the plateau. Swarm S20130630.1 fits within this established pattern, contributing to long-term monitoring records that help distinguish background unrest from potential precursory signals.

No surface deformation or significant changes in geothermal features were associated with this particular sequence, reinforcing its classification as a typical hydrothermal swarm. Continued instrumentation by regional seismic networks supports refined models of stress transfer and fluid pathways in the crust.

References

USGS Earthquake Hazards Program – Yellowstone seismicity reports
Yellowstone Volcano Observatory annual summaries
Smith RB, Jordan M, et al. (2009) Geodynamics of the Yellowstone hotspot and mantle plume. Journal of Volcanology and Geothermal Research