Seismic Swarm SVS20060710.1: Analysis of Activity Near West Yellowstone, Montana

A notable earthquake swarm, classified internally as SVS20060710.1, occurred 28 km east-southeast of West Yellowstone, Montana. The sequence began at 21:07 on 10 July 2006 and concluded at 03:05 on 11 July 2006, spanning 5 hours and 58 minutes. During this period, 35 earthquakes were recorded, with magnitudes ranging from 0.3 to 2.8 and focal depths between 1 km and 12 km.

The events clustered tightly in both time and space, characteristic of swarm behavior where numerous small quakes occur without a dominant mainshock. Magnitudes peaked at 2.8 at 23:30 on 10 July, while the majority remained below 2.0. Depths averaged around 6–8 km, suggesting activity within the shallow crust influenced by local tectonic and hydrothermal processes.

This swarm fits into a broader pattern of seismicity in the region. Since 1 January 2000, 24 swarms have been documented, distributed across years as follows: 7 in 2000, 3 in 2001, 6 in 2002, 3 in 2003, 1 in 2004, and 4 in 2006. Such recurrent swarms reflect ongoing crustal adjustments in an area of elevated geothermal gradients and fault networks.

The location lies on the western margin of the Yellowstone Plateau, part of the Yellowstone volcanic system. This region overlies a mantle hotspot responsible for the formation of the Snake River Plain and the current Yellowstone Caldera, which last experienced a major eruption approximately 640,000 years ago. Seismicity arises primarily from fluid migration, thermal expansion, and slip along Basin and Range-style normal faults superimposed on the volcanic edifice. Depths of 1–12 km align with the brittle-ductile transition zone where hydrothermal fluids interact with fractured rock.

Historical monitoring indicates that earthquake swarms in the Yellowstone area often correlate with subtle ground deformation and changes in geyser activity, though no significant surface effects were associated with this particular sequence. The predominance of events under magnitude 3.0 is typical, as larger shocks remain infrequent despite the high overall rate of microseismicity.

Continued observation of such swarms contributes to refined models of stress transfer and volcanic-tectonic interactions in the region. Data from this event underscore the value of dense seismic networks in distinguishing swarm activity from isolated tectonic earthquakes.

References

SeismoSight internal swarm classification records.
USGS Earthquake Hazards Program regional seismicity reports for Yellowstone.
Geological Society of America publications on Yellowstone Caldera structure and evolution.