Seismic Swarm Analysis: Mina, Nevada Region – January 2021 Event

A seismic swarm designated S20210101.1 occurred 26 km south of Mina, Nevada, on 1 January 2021. The sequence began at 05:58 UTC and concluded at 22:36 UTC, encompassing 24 earthquakes over 16 hours and 37 minutes. Magnitudes ranged from 0.6 to 2.4, with most events clustered between 0 and 13 km depth. Notable events included a magnitude 2.4 earthquake at 21:00:49 UTC at 2 km depth and a magnitude 2.2 event at 19:21:06 UTC at 4 km depth. Shallower events predominated early in the swarm, while deeper activity appeared later, indicating possible migration along fault structures.

This swarm fits the established pattern of episodic seismic activity in the Mina area. Historical records document 17 swarms since 1 January 2000, distributed across specific years: one in 2000, two in 2003, two in 2013, one in 2014, and eleven in 2020. The 2021 event continues this trend of clustered, low-magnitude sequences rather than isolated mainshock-aftershock patterns.

The Mina region occupies the western Basin and Range Province within the Walker Lane belt of western Nevada. This tectonic domain accommodates approximately 20 percent of the relative motion between the Pacific and North American plates through a combination of dextral strike-slip and normal faulting. Active faults, including segments of the Mina deflection and related structures in the Excelsior and Pilot Mountains, host recurrent microseismicity. The area features Quaternary alluvial fans and basin-fill sediments overlying Mesozoic basement rocks intruded by Tertiary volcanic units, creating a heterogeneous crust prone to distributed deformation.

Seismicity in this portion of the Walker Lane typically manifests as swarms linked to fluid migration or aseismic slip transients on normal and strike-slip faults. Depths recorded in the 2021 swarm align with the brittle-ductile transition zone observed regionally, generally between 0 and 15 km. No surface rupture or significant ground deformation has been associated with these events, consistent with their modest energy release.

Long-term monitoring indicates that swarm frequency in the Mina area has increased in recent decades, potentially reflecting improved detection capabilities alongside ongoing tectonic strain accumulation. The 2020–2021 cluster represents the highest recent activity level, underscoring the persistent seismic hazard in this sparsely populated but structurally complex zone.

References
USGS Earthquake Catalog (earthquake.usgs.gov)
Nevada Seismological Laboratory regional reports
Walker Lane tectonic summaries from the Nevada Bureau of Mines and Geology