An earthquake swarm designated S20000324.1 occurred 8 km south of Kanosh, Utah, between 23:00 on 23 March 2000 and 19:56 on 24 March 2000. The sequence lasted 20 hours and 55 minutes and included 29 events. Swarms of this type feature closely spaced earthquakes without a dominant mainshock, often linked to fluid migration or minor fault adjustments within active tectonic zones.
The events ranged in magnitude from 0.8 to 3.0, with the largest reaching 3.0 at 01:04 on 24 March. Depths varied between surface levels and 12 km, clustering primarily between 2 km and 10 km. Early activity on 23 March included several events below magnitude 2.0, followed by a gradual increase in both frequency and size overnight. Peak energy release occurred between 01:00 and 02:00 on 24 March, featuring multiple shocks above magnitude 2.0. Activity then declined steadily through the morning and afternoon, concluding with three small events after 19:00.
This swarm took place in the Basin and Range Province of central Utah, where east-west extension drives normal faulting along north-south trending structures. The Kanosh area lies near the transition between the Pavant Range and Sevier Valley, regions influenced by both Sevier-age thrust faults and younger extensional features. Historical seismicity in Millard County includes scattered moderate events tied to these faults, consistent with the low-to-moderate strain rates observed across the province.
Depth distribution in the swarm suggests activation of shallow crustal faults, typical for the region’s brittle upper crust. Such sequences provide data on local stress conditions and can help refine models of fault connectivity in central Utah’s extensional setting.
References
Utah Geological Survey – Earthquake Information
USGS Earthquake Catalog – Utah Region
SeismoSight Internal Swarm Classification Records