Seismic Swarm S20020120.1: Analysis of Activity Near Indian Springs, Nevada
A seismic swarm designated S20020120.1 was recorded northwest of Indian Springs, Nevada, beginning at 15:06 on 19 January 2002 and concluding at 08:19 on 27 January 2002. The sequence lasted 185 hours and 13 minutes, during which 99 earthquakes were detected. The epicentral area lies approximately 45 km northwest of Indian Springs within the Basin and Range Province, a region defined by active extensional tectonics and numerous normal faults.
Earthquake magnitudes in the swarm ranged from -0.3 to 2.6, with the majority of events below magnitude 1.0. Depths clustered between 0 and 8 km, indicating shallow crustal sources typical of the area. The largest event, magnitude 2.6, occurred early in the sequence on 19 January at 15:06:38 UTC at a depth of 7 km. Subsequent activity showed intermittent bursts, including a magnitude 2.5 event on 24 January at 19:49:35 UTC at 6 km depth. Many events registered near or below magnitude 0.0, reflecting the sensitivity of the monitoring network.
The Indian Springs region forms part of the southern Nevada seismic belt, influenced by the Walker Lane shear zone and proximity to the Nevada National Security Site. Historical seismicity here stems from ongoing crustal extension along range-bounding faults. The area has experienced both natural earthquakes and induced events linked to underground nuclear testing conducted through 1992. Post-testing monitoring has documented persistent low-level activity and occasional swarms along reactivated structures.
Since 1 January 2000, four swarms have occurred in the vicinity, with three in 2000 and one in 2002. Swarm S20020120.1 fits this pattern of clustered, low-magnitude seismicity without a clear mainshock-aftershock sequence. Such episodes are common in the Basin and Range and often reflect fluid migration or aseismic slip triggering brittle failure at shallow depths.
This swarm underscores the value of continuous seismic surveillance for distinguishing natural from anthropogenic signals in a region with complex tectonic and historical nuclear legacies. Ongoing monitoring supports hazard assessment for nearby communities and infrastructure.
References
- USGS Earthquake Catalog (earthquake.usgs.gov)
- Nevada Seismological Laboratory historical records
- SeismoSight internal swarm classification data