Seismic Swarm Analysis: Indian Springs, Nevada – December 2023

A seismic swarm designated S20231228.1 occurred approximately 29 km west-northwest of Indian Springs, Nevada. The sequence began at 15:43 UTC on 27 December 2023 and concluded at 01:28 UTC on 31 December 2023, spanning 81 hours and 44 minutes. During this interval, 69 earthquakes were recorded.

The events exhibited low magnitudes, with the largest reaching 1.6. Most events registered between 0.1 and 0.5 in magnitude, and focal depths clustered near 3 km, although a few reached 4 km or, in one instance, 11 km. Activity peaked during the first 24 hours, with subsequent events occurring at diminishing frequency. The spatial distribution remained tightly confined, consistent with swarm behavior rather than a mainshock-aftershock sequence.

This region lies within the Basin and Range Province of southern Nevada, where crustal extension produces active normal faulting. The tectonic regime features north-south trending mountain ranges separated by sediment-filled valleys, with deformation accommodated along range-bounding faults. Southern Nevada experiences persistent low-level seismicity driven by this ongoing extension, which occurs at rates of several millimeters per year.

Seismic swarms have been documented repeatedly in the area. Since 1 January 2000, 22 swarms have been identified, distributed across the years 2000 (3), 2002 (2), 2005 (1), 2006 (1), 2007 (1), 2008 (1), 2009 (3), 2010 (1), 2014 (1), 2015 (2), 2016 (3), 2019 (1), and 2022 (2). These episodes typically involve dozens of small-magnitude events occurring over hours to days, without a dominant mainshock.

The December 2023 swarm fits this established pattern. Its short duration, modest energy release, and shallow depths align with fluid-related triggering mechanisms commonly inferred for Nevada swarms, although definitive causative processes require further geophysical investigation. No damage or felt reports were associated with the sequence.

Continued monitoring of the Indian Springs area remains important given the broader tectonic setting. The historical recurrence of swarms indicates that similar episodes are a normal component of regional seismicity.

References
SeismoSight internal swarm catalog (S20231228.1 parameters and historical statistics).
U.S. Geological Survey Earthquake Hazards Program – Basin and Range Province tectonics summaries.