Seismic Swarm S20120601.1 Near Beatty, Nevada: Geological Context and Event Analysis
Seismic swarm S20120601.1 occurred 45 km east-southeast of Beatty, Nevada, in a tectonically active portion of the Basin and Range Province. The swarm began at 08:20 on 31 May 2012 and concluded at 11:15 on 5 June 2012, lasting 122 hours and 54 minutes. During this interval, 101 earthquakes were recorded. This activity aligns with the region's established pattern of episodic swarms driven by extensional faulting along normal faults.
The local geology features Quaternary alluvium overlying Paleozoic carbonates and Tertiary volcanic rocks. Regional extension, at rates of approximately 10 mm per year, accommodates deformation through distributed normal faulting. Proximity to the Nevada National Security Site and the Walker Lane belt contributes to elevated microseismicity. Historical records document 33 swarms in the area since 1 January 2000, with notable clusters in 2000 (5 swarms), 2002 (7), 2008 (7), and 2009 (4). These events typically produce low-magnitude earthquakes at shallow to mid-crustal depths, reflecting fluid migration or stress triggering along pre-existing faults rather than large mainshock-aftershock sequences.
Analysis of the first 100 events reveals predominantly microseismic activity. Magnitudes ranged from -0.9 to 2.7, with the majority below 0.5. The largest event, magnitude 2.7, occurred on 1 June 2012 at 06:54:08 UTC. Depths centered between 7 and 10 km, though outliers extended from 0 to 13 km. Early events on 31 May showed shallow foci (1–8 km), while activity on 1–2 June stabilized around 8–10 km. Later events on 3–4 June included several at 5–7 km, suggesting possible upward migration of seismicity. Temporal clustering was evident, with bursts on 1 June coinciding with the two largest events (magnitudes 2.1 and 2.7). Overall, 78 events registered magnitudes of 0.0 or lower, underscoring the swarm's low-energy character.
Such swarms contribute to long-term strain release in the southern Great Basin without producing surface rupture. Monitoring by regional networks continues to track similar activity, informing hazard assessments for nearby infrastructure.
References
- USGS Earthquake Hazards Program: Nevada seismicity reports (updated through 2023)
- Nevada Seismological Laboratory historical swarm catalog
- SeismoSight internal swarm classification S20120601.1