Seismic swarm S20240304.1 was recorded 14 km northeast of Milford, Utah, beginning at 02:59 on 4 March 2024 and concluding at 09:18 on 7 March 2024. Over 78 hours and 18 minutes, the sequence produced 47 earthquakes, all of low magnitude and shallow depth.
The events clustered tightly in both time and space, with the majority occurring at depths of 1–2 km. Magnitudes ranged from −0.8 to 1.7, indicating microseismicity typical of fluid-driven swarm behavior rather than mainshock-aftershock sequences. The largest event, magnitude 1.7, occurred at 02:28 on 5 March at 1 km depth. Activity peaked on 4 March with multiple events above magnitude 1.0, followed by a gradual decline through 6 March and only two final events on 7 March.
This swarm occurred within the Basin and Range Province, where crustal extension along normal faults produces distributed seismicity. The Milford area lies near the Mineral Mountains, a region influenced by Miocene volcanism and ongoing geothermal activity. Shallow focal depths are consistent with fluid migration along fracture networks, a common mechanism for swarm generation in this tectonic setting.
Historical records maintained by SeismoSight document ten swarms in the same locale since 1 January 2000. These episodes occurred in 2020 (4 swarms), 2021 (1), 2022 (1), 2023 (2), and 2024 (2). The recurrence pattern suggests episodic release of strain through swarm-type sequences rather than isolated large earthquakes.
The current swarm aligns with prior episodes in duration, magnitude range, and depth distribution, reinforcing the area’s characteristic low-level seismic behavior. No events exceeded magnitude 2.0, and none were reported as felt by residents.
Continued monitoring remains important given the region’s geothermal resources and proximity to infrastructure. Future swarms may follow similar spatiotemporal patterns observed in the 2000–2024 catalog.
SeismoSight internal swarm classification database (S20240304.1 parameters and historical swarm counts).
U.S. Geological Survey Earthquake Hazards Program – regional tectonics of the Basin and Range Province.
Utah Geological Survey – geologic framework of Beaver County and Mineral Mountains.