Seismic Swarm S20220123.1 Near Mina, Nevada: Geological Context and Event Analysis
Seismic swarm S20220123.1 occurred 26 km southwest of Mina, Nevada, in Mineral County. The sequence began at 22:40 UTC on 22 January 2022 and concluded at 15:39 UTC on 29 January 2022, spanning 160 hours and 59 minutes. During this interval, 114 earthquakes were recorded. The first 100 events exhibited magnitudes predominantly between −0.3 and 4.3, with the largest shock registering 4.3 at a depth of 11 km. Depths across the sequence ranged from 0 km to 16 km, indicating activity within the shallow to mid-crustal levels typical of the region.
The swarm initiated with a 4.3 magnitude event followed rapidly by smaller aftershocks. Subsequent events showed a rapid decay in magnitude, with the majority falling below 2.0. Temporal distribution revealed the highest rates of seismicity within the first 48 hours, after which activity declined steadily while persisting at low levels until the swarm’s termination. Negative and zero magnitudes were common in later stages, reflecting the dense station coverage that permitted detection of microearthquakes.
Regional Geological Setting
Mina lies within the Walker Lane belt of western Nevada, a zone of distributed right-lateral shear accommodating approximately 20 % of the Pacific–North America plate motion. The belt forms a transition between the Sierra Nevada microplate and the extensional Basin and Range province. Local faulting is dominated by northwest-striking dextral and normal faults that have developed since the Miocene. The crust in this area averages 30–35 km thick and experiences elevated heat flow, conditions that favor swarm-type seismicity rather than mainshock–aftershock sequences.
Historical deformation is recorded in Quaternary fault scarps and offset volcanic units. The region has hosted multiple earthquake swarms since 2000, with documented episodes in 2006, 2012, 2014, 2015 (two swarms), 2016 (five swarms), 2018, 2020 (eight swarms), and 2021 (two swarms). These recurrent swarms are attributed to fluid migration and aseismic slip on critically stressed faults within the transtensional regime.
Seismicity Patterns and Interpretation
Analysis of the first 100 events indicates a classic swarm signature: an abrupt onset, lack of a single dominant mainshock, and a gradual decline in rate without a clear Omori-law aftershock decay. Magnitudes clustered below 2.0 after the initial 4.3 event, consistent with swarm behavior observed elsewhere in the Walker Lane. Focal depths concentrated between 7 km and 11 km suggest nucleation near the brittle–ductile transition, where small stress perturbations from fluids or aseismic creep can trigger numerous small ruptures.
The 2022 swarm fits the established pattern of elevated swarm frequency in the Mina area during the past two decades. No surface rupture or significant damage was reported, aligning with the modest energy release and shallow focal depths.
Implications for Seismic Hazard
Although individual events remained small, swarm activity highlights the potential for larger triggered earthquakes on nearby mapped faults. Continued monitoring by regional seismic networks provides essential data for refining hazard models in this transtensional corridor. Updated catalogs through 2022 confirm that swarm recurrence in the Mina vicinity remains higher than the long-term average for the central Walker Lane.
References
- U.S. Geological Survey Earthquake Catalog (ANSS Comprehensive Catalog)
- Nevada Seismological Laboratory swarm database
- Faulds, J.E., and Henry, C.D. (2008). Tectonic influences on the spatial and temporal evolution of the Walker Lane. Geological Society of America Special Paper 439.