Analysis of Earthquake Swarm S20021104.1 Near Mammoth, Wyoming

Earthquake swarm S20021104.1 occurred approximately 23 km south of Mammoth, Wyoming, within the Yellowstone volcanic region. The sequence began at 22:40 on 3 November 2002 and concluded at 03:40 on 8 November 2002, spanning roughly 101 hours. During this period, 118 earthquakes were recorded.

Examination of the first 100 events reveals predominantly low-magnitude activity. Magnitudes ranged from negative values to a maximum of 2.1, with the majority below 1.0. Depths were generally shallow, concentrated between 1 km and 12 km, though occasional outliers reached 16 km or registered at or near the surface. Early events on 3 November included a 2.1 magnitude quake at 12 km depth followed shortly by smaller shocks at shallower levels. Subsequent activity through 4–6 November maintained a pattern of frequent micro-earthquakes interspersed with occasional events above magnitude 1.5. No significant escalation in magnitude or depth migration was evident in the initial dataset.

This swarm fits within the broader seismic behavior of the Yellowstone area, where hydrothermal and magmatic processes drive episodic earthquake clusters. The region overlies a large volcanic system featuring the Yellowstone Caldera, formed by massive eruptions over the past 2 million years. Ongoing crustal deformation, fluid migration, and heat flow contribute to swarm-type seismicity rather than isolated mainshock-aftershock sequences.

Historical records indicate 17 swarms in the area since 1 January 2000. Annual counts include 10 swarms in 2000, 5 in 2001, and 2 in 2002 up to the time of S20021104.1. Such recurrent activity underscores the dynamic nature of the subsurface environment.

References

USGS Earthquake Hazards Program – Yellowstone Seismic Data
Wyoming Geological Survey – Regional Volcanic and Seismic Overview
SeismoSight Internal Swarm Classification Records