Seismic swarm S20260322.1 was recorded 15 km northeast of Milford, Utah, commencing at 11:33 on 21 March 2026 and concluding at 12:30 on 2 April 2026. Over 288 hours and 56 minutes, the swarm produced 175 earthquakes. Analysis of the first 100 events reveals predominantly shallow focal depths between 0 and 3 km, with the majority occurring at 2 km. Magnitudes ranged from -0.6 to 2.2, with most events below 1.5 and only a few reaching or exceeding 2.0. The sequence began with events of magnitude 1.5 and 0.9 within the first 20 minutes, followed by a cluster of low-magnitude activity throughout 21–22 March. Peak magnitudes appeared on 22 March with events of 1.9, 2.2, and 1.2 in quick succession. Subsequent days showed sustained low-level seismicity, including negative-magnitude detections on 22 March, indicative of microfracturing. Depths remained consistently shallow, suggesting activity within the upper crustal layers.
The region lies in the Basin and Range Province of western Utah, where extensional tectonics drive normal faulting and episodic seismic swarms. Milford sits near the Mineral Mountains and the Roosevelt Hot Springs geothermal field, areas influenced by Quaternary volcanism and hydrothermal circulation. These geological conditions facilitate swarm-type seismicity, often linked to fluid migration along faults rather than mainshock-aftershock sequences. Depths of 1–3 km align with the brittle upper crust overlying ductile zones influenced by heat flow.
Historical data indicate 18 swarms in the area since 1 January 2000. Yearly counts show variability: four swarms in 2020, one in 2021, one in 2022, two in 2023, seven in 2024, two in 2025, and one in 2026. This pattern reflects ongoing tectonic and possibly geothermal influences, with swarm frequency increasing notably in 2024.
The current swarm fits the established regional character, featuring numerous small events at shallow depths without a dominant mainshock. Such activity poses minimal surface hazard but provides valuable data on crustal stress and fluid dynamics in this extensional setting.
SeismoSight internal swarm classification records.