Seismic Swarm S20150118.1: Analysis of Activity Near Indian Springs, Nevada

An earthquake swarm designated S20150118.1 was recorded 24 km north of Indian Springs, Nevada, between 02:26 UTC on 17 January 2015 and 19:13 UTC on 18 January 2015. The sequence lasted 40 hours and 47 minutes and comprised 28 events. Magnitudes ranged from -0.2 to 2.1, with the majority below 1.5 and only three events exceeding magnitude 1.7. Focal depths remained shallow, between 0 km and 13 km, consistent with upper-crustal faulting in the region. The temporal distribution showed two main clusters on 17 January, one in the early morning hours and another in the afternoon, followed by a sharp decline in activity on 18 January. The largest event, magnitude 2.1 at 13:38 UTC on 17 January, occurred at 5 km depth and was not followed by a classic aftershock sequence, confirming the swarm character. Several events registered negative or zero magnitudes, typical of microseismicity detected by dense local networks. Southern Nevada lies within the Basin and Range Province, where east-west extension is accommodated by north-striking normal faults. The Indian Springs area sits near the transition between the Walker Lane belt and the stable Colorado Plateau margin. Historical seismicity includes scattered moderate events and occasional swarms linked to fluid migration along pre-existing fractures. Depths observed in S20150118.1 align with the seismogenic zone documented across the province, generally limited to the upper 15 km. No surface rupture or damage was reported, as expected for events of this size. Such swarms are common in the western Great Basin and often reflect transient increases in pore-fluid pressure rather than mainshock-aftershock triggering. Continued monitoring by regional networks remains essential for distinguishing background activity from potential precursors to larger tectonic events. References USGS Earthquake Hazards Program catalog Nevada Seismological Laboratory annual reports Basin and Range Province tectonic summaries (USGS Professional Papers)