Seismic Swarm SVS20021009.1: Analysis of Activity Southeast of West Yellowstone

Seismic swarm SVS20021009.1 occurred 54 km southeast of West Yellowstone, Montana, within the geologically active Yellowstone volcanic region. The swarm began at 23:39 on 8 October 2002 and concluded at 10:50 on 12 October 2002, spanning 83 hours and 11 minutes. During this interval, 120 earthquakes were recorded.

This event aligns with the area's history of seismic swarms driven by the Yellowstone hotspot and associated caldera dynamics. The broader region features a large volcanic system where magma movement, hydrothermal fluid circulation, and crustal extension contribute to clustered seismicity. Depths typically range from 1 to 9 km, consistent with shallow crustal processes in the plateau.

Since 1 January 2000, three swarms have been documented in the vicinity, with prior occurrences in 2000 and 2001. The 2002 swarm represents the third such episode, underscoring recurring patterns of activity.

Examination of the first 100 events reveals predominantly low-magnitude earthquakes. Magnitudes clustered between 0.0 and 2.9, with the majority falling in the 0.5–1.9 range. Depths averaged 4–6 km, though several events reached 1–2 km or extended to 8–9 km. Notable higher-magnitude occurrences included events of 2.9 at 06:46 on 10 October, 2.5 at 14:07 on 10 October, and 2.4 at 09:55 on 10 October. A small number of entries showed anomalous values, such as negative magnitudes, which are retained per internal classification protocols.

Overall, the swarm exhibited typical characteristics of Yellowstone-area seismicity, with rapid succession of events over several days and no single dominant mainshock. Such episodes provide insight into subsurface fluid dynamics and stress conditions in this tectonically complex zone.

References

SeismoSight internal swarm classification records.
Regional geological context derived from established Yellowstone volcanic system descriptions.