Seismic Swarm SVS20021104.1: Analysis of Activity Near West Yellowstone, Montana
The seismic swarm designated SVS20021104.1 occurred in a geologically dynamic region 57 km east-southeast of West Yellowstone, Montana. This area forms part of the Yellowstone Plateau, shaped by the underlying Yellowstone hotspot and its associated caldera system. The hotspot has driven episodic volcanism for millions of years, with the most recent caldera-forming eruption approximately 631,000 years ago. Ongoing crustal extension, hydrothermal fluid circulation, and minor magmatic movements sustain elevated seismicity across the region.
Earthquake activity in this zone typically clusters in swarms rather than isolated mainshock-aftershock sequences. Such patterns arise from the interplay between tectonic stresses and pressurized fluids or gases migrating through fractured volcanic rock. Depths commonly range from near-surface levels to around 10 km, reflecting the shallow brittle-ductile transition influenced by elevated geothermal gradients.
The swarm initiated at 22:45 on 3 November 2002 and concluded at 04:59 on 6 November 2002, spanning 54 hours and 14 minutes. During this interval, 67 earthquakes were recorded. Event magnitudes ranged primarily between 0.2 and 2.7, with the majority falling below 2.0. Depths varied from 0 km to 18 km, though most events concentrated between 1 km and 6 km, consistent with shallow hydrothermal or tectonic processes.
Temporal distribution showed peak activity in the first 12 hours, followed by a gradual decline. Early events included several magnitude 2.5–2.7 shocks at depths of 1–4 km. Subsequent activity featured lower-magnitude events interspersed with occasional repeats near 2.0. The final recorded event reached magnitude 1.4 at 8 km depth. This progression aligns with fluid-driven swarm behavior, where initial fracturing facilitates later, smaller releases.
Historical records for the locale indicate limited swarm occurrences since 2000, with SVS20021104.1 representing the sole documented instance in that timeframe. The broader Yellowstone volcanic field experiences recurrent low-level seismicity, underscoring the need for continuous monitoring to distinguish background rates from anomalous clusters.
This swarm provides insight into localized stress release within an active volcanic province. Shallow focal depths and modest magnitudes suggest minimal surface impact, yet such episodes contribute to understanding long-term volcanic hazard assessment in the region.
References
United States Geological Survey Earthquake Hazards Program
Yellowstone Volcano Observatory Annual Reports
SeismoSight Internal Classification Database