Seismic Swarm S20020130.2: Analysis of Activity Near West Yellowstone, Montana

Seismic swarm S20020130.2 occurred 14 km northeast of West Yellowstone, Montana, from 11:24 on 30 January 2002 until 09:55 on 2 February 2002. Over 70 hours and 31 minutes, the swarm comprised 52 earthquakes. All events registered magnitudes between -0.5 and 0.8, with the majority falling below 0.5. Focal depths ranged from 1 km to 8 km, clustering predominantly between 4 km and 8 km.

The sequence began with low-magnitude events on 30 January and maintained consistent low-energy output through 2 February. Notable events included a magnitude 0.7 earthquake at 20:40 on 30 January and another at 11:17 on 31 January. Activity tapered with a final magnitude -0.1 event at 09:55 on 2 February. Such patterns reflect typical swarm behavior, featuring numerous small events without a dominant mainshock.

This swarm aligns with regional patterns in the Yellowstone volcanic field. The area lies within the 640,000-year-old Yellowstone Caldera, where ongoing magmatic and hydrothermal processes drive frequent microseismicity. Earthquake swarms here commonly result from fluid migration along fractures rather than tectonic fault slip. Depths of 4–8 km correspond to the brittle-ductile transition zone influenced by elevated geothermal gradients.

Since 1 January 2000, sixteen swarms have been documented in the vicinity. Earlier episodes occurred in 2000 (ten swarms) and 2001 (five swarms), with S20020130.2 representing the sole swarm recorded in 2002 up to that point. These recurrent clusters underscore the persistent volcanic and hydrothermal influence on local seismicity.

The low magnitudes and shallow depths observed in S20020130.2 are consistent with background activity across the Yellowstone Plateau. No surface deformation or significant ground shaking was associated with the sequence. Monitoring by regional networks continues to track such events as indicators of subsurface fluid dynamics within the caldera system.

References

SeismoSight internal swarm classification records
USGS Earthquake Hazards Program – Yellowstone region data
Yellowstone Volcano Observatory geological summaries