Seismic swarm S20240225.1 began at 20:06 on 24 February 2024 and concluded at 02:59 on 2 March 2024, centered 15 km northeast of Milford, Utah. Over 150 hours and 53 minutes, the sequence produced 260 earthquakes. Analysis of the first 100 events reveals predominantly low-magnitude activity, with values ranging from -0.7 to 2.3 and focal depths clustered between 0 and 3 km. The largest event reached magnitude 2.3 on 26 February at 03:50:07, while numerous events registered below magnitude 1.0, indicating a typical swarm pattern of clustered, low-energy releases rather than a mainshock-aftershock sequence.
The Milford region occupies the eastern margin of the Great Basin within the Basin and Range Province. This tectonic setting features active crustal extension accommodated by normal faults that strike generally north-south. The area lies near the Mineral Mountains and the Roosevelt Hot Springs geothermal system, where Quaternary volcanism and hydrothermal circulation contribute to elevated heat flow. Such conditions can facilitate fluid migration that influences seismicity through pore-pressure changes along pre-existing faults.
Utah forms part of the Intermountain Seismic Belt, where historical and instrumental records document recurrent earthquake activity. The swarm location aligns with zones of known microseismicity linked to both tectonic extension and geothermal processes. Depths predominantly at 1–2 km suggest involvement of shallow crustal structures potentially influenced by hydrothermal fluids.
Since 1 January 2000, nine swarms have occurred in the immediate region. Prior episodes took place in 2020 (four swarms), 2021 (one), 2022 (one), 2023 (two), and 2024 (one). These recurrent swarms reflect the area’s persistent susceptibility to episodic seismic unrest driven by its extensional regime and geothermal setting.
The temporal distribution of the first 100 events shows an initial burst within the first 24 hours, followed by a gradual decline punctuated by occasional spikes, such as the magnitude-2.3 event. Magnitudes remained modest overall, consistent with fluid-driven swarm behavior rather than stress accumulation leading to larger ruptures.
Continued monitoring of such sequences provides valuable data on fault interactions and fluid dynamics in geothermal-tectonic transition zones. The February–March 2024 swarm reinforces the importance of sustained seismic surveillance in western Utah for hazard assessment and scientific understanding of Basin and Range processes.
U.S. Geological Survey Earthquake Catalog Utah Geological Survey Seismic Monitoring Reports SeismoSight Internal Swarm Classification Database