Seismic Swarm S20080203.1 Near Mammoth, Wyoming: Geological Context and Event Analysis

On February 3, 2008, a seismic swarm designated S20080203.1 occurred 23 km SSW of Mammoth, Wyoming. The sequence began at 01:00 and concluded at 22:04, registering 47 earthquakes over 21 hours and 4 minutes. Magnitudes ranged from -0.1 to 2.1, with the largest event recorded at 07:42. Depths varied between 1 km and 7 km, predominantly clustering around 2–6 km. Most activity concentrated between 07:00 and 10:00, featuring frequent low-magnitude events that reflect typical swarm behavior rather than a mainshock-aftershock pattern.

This swarm exemplifies patterns common in volcanically active regions. Events remained small and shallow, consistent with fluid migration or minor stress adjustments within the crust. No damage or felt reports were associated with the sequence, underscoring its microseismic character.

The location lies within the broader Yellowstone volcanic system, where the underlying hotspot drives ongoing geological processes. Yellowstone National Park and surrounding areas experience frequent small earthquakes due to the interaction of magmatic fluids, hydrothermal systems, and regional tectonic stresses. Historical records indicate that earthquake swarms have been a persistent feature, often linked to the movement of groundwater or gases through fractured rock.

Since January 1, 2000, 35 swarms have been documented in the region. Annual counts show variability: 10 in 2000, 5 in 2001, 6 in 2002, 1 in 2003, 2 in 2004, 1 in 2005, 5 in 2006, 3 in 2007, and 2 in 2008. These episodes highlight the dynamic nature of the subsurface environment shaped by millions of years of volcanic activity.

Geologically, the area sits atop a large caldera system formed by massive eruptions over the past 2 million years. The most recent caldera-forming event occurred approximately 631,000 years ago. Ongoing uplift and subsidence, monitored through geodetic methods, correlate with seismic swarms, suggesting pressure changes from magma or hydrothermal reservoirs at depth. Depths observed in this swarm align with the brittle-ductile transition zone influenced by elevated temperatures from the hotspot.

Seismic monitoring in this region supports hazard assessment and scientific understanding of volcanic unrest. Swarms like S20080203.1 contribute data on how energy releases in clusters without progressing to larger events.

References

SeismoSight internal swarm classification database.
United States Geological Survey, Yellowstone Volcano Observatory reports on regional seismicity.
Smith, R. B., et al., "Yellowstone hotspot: The magmatic evolution of the Yellowstone volcanic system," Geological Society of America publications.