Seismic Swarm S20071214.1: Analysis of Activity Near West Yellowstone, Montana

The seismic swarm designated S20071214.1 occurred approximately 4 km east-southeast of West Yellowstone, Montana, within the tectonically active region surrounding Yellowstone National Park. This swarm began at 05:58 on 14 December 2007 and concluded at 04:26 on 15 December 2007, encompassing a duration of 22 hours and 28 minutes. During this interval, 28 earthquakes were recorded, all of low magnitude and consistent with typical swarm behavior in the area.

Earthquake swarms in this locale arise from the interplay of regional tectonics and the underlying Yellowstone volcanic system. The broader geological setting lies along the Intermountain Seismic Belt, where crustal extension and magmatic processes contribute to elevated seismicity. Depths of the recorded events ranged primarily between 7 km and 11 km, reflecting activity within the brittle upper crust influenced by hydrothermal fluids and stress perturbations from the nearby caldera.

Magnitudes during the swarm remained modest, with the largest event reaching 1.4. The sequence featured numerous events below magnitude 0.5, interspersed with slightly larger shocks up to 1.1. This pattern aligns with fluid-driven swarm dynamics commonly observed in volcanic and geothermal provinces, where events cluster temporally without a dominant mainshock-aftershock progression.

Historical records indicate persistent swarm activity in the region since the start of 2000. A total of 27 such swarms have been documented through the end of 2007, distributed across years as follows: seven in 2000, four in 2001, five in 2002, three in 2003, two in 2004, one in 2005, four in 2006, and one in 2007. These episodes underscore the ongoing seismic restlessness driven by the Yellowstone hotspot and associated fault systems.

The December 2007 swarm exemplifies the low-level, clustered seismicity that characterizes the area without indicating immediate volcanic unrest. Depths and magnitudes remained within background ranges, posing negligible surface impact. Continued monitoring supports understanding of long-term patterns in this dynamic geological environment.

References

United States Geological Survey, Yellowstone Volcano Observatory reports on regional seismicity.
SeismoSight internal swarm classification database for event parameters.