Seismic Swarm S20200615.1: Analysis of Activity Southeast of Mina, Nevada

An earthquake swarm designated S20200615.1 was recorded southeast of Mina, Nevada, beginning at 10:49 UTC on 14 June 2020 and concluding at 10:59 UTC on 15 July 2020. Over this 744-hour period, 472 events were detected, with detailed parameters available for the initial 100 earthquakes. This swarm occurred in a region known for episodic seismic clusters within the tectonically active western Basin and Range.

The first 100 events exhibited magnitudes ranging from 0.3 to 2.6, with the majority below 2.0. Depths varied between 0 and 22 km, though most clustered between 4 and 12 km. Early activity included a 1.8-magnitude event at 12:22 UTC on 14 June at 10 km depth, followed by smaller events at shallow to moderate depths. A peak magnitude of 2.6 occurred on 17 June at 8 km depth, while several events reached 2.2–2.4 in the following days. Shallow events (under 5 km) comprised a notable portion, alongside deeper ones up to 22 km, indicating distributed faulting across multiple crustal levels.

Seismicity in this portion of Nevada reflects ongoing extensional deformation. The area lies within the Walker Lane belt, a zone of right-lateral shear and normal faulting accommodating part of the Pacific–North American plate motion. Regional geology features north–south trending mountain ranges separated by alluvial basins, formed through Miocene-to-present crustal stretching. Faults here are predominantly normal, with some strike-slip components, consistent with the observed swarm patterns of low-magnitude, closely spaced events without a single dominant mainshock.

Historical records indicate recurrent swarms in the vicinity. Since 2000, twelve swarms have been documented in the same locale, with earlier episodes in 2003 (two swarms), 2013 (two swarms), and 2014 (one swarm). The year 2020 alone accounted for seven such clusters, underscoring elevated swarm frequency during this interval. These sequences typically involve hundreds of small events over days to weeks, rarely producing damaging ground motion.

The S20200615.1 swarm aligns with this pattern, contributing to the understanding of fluid-driven or stress-triggered seismicity in the central Walker Lane. Continued monitoring supports improved characterization of local fault networks and long-term seismic hazard in Mineral County and adjacent areas.

References

• United States Geological Survey Earthquake Catalog (earthquake.usgs.gov)
• Nevada Seismological Laboratory swarm database
• USGS Professional Paper on Walker Lane tectonics (2022 update)