Seismic Swarm S20170102.1 Near Hawthorne, Nevada: Geological Context and Event Analysis

The seismic swarm designated S20170102.1 occurred 23 km northeast of Hawthorne, Nevada, in Mineral County. It began at 02:11 on 2 January 2017 and concluded at 12:42 on 3 January 2017, spanning 34 hours and 31 minutes. During this interval, 31 earthquakes were recorded, with magnitudes ranging from -0.2 to 3.8 and focal depths between 4 km and 12 km.

Hawthorne lies within the Basin and Range Province of western Nevada, a region defined by extensional tectonics and active normal faulting. The area forms part of the Walker Lane belt, a northwest-trending zone of right-lateral shear that accommodates approximately 15–25 % of the relative motion between the Pacific and North American plates. This tectonic setting produces frequent small-magnitude earthquakes and occasional seismic swarms along distributed faults.

The largest event of the swarm reached magnitude 3.8 at 10 km depth on 2 January at 02:11:09 UTC. Subsequent activity consisted predominantly of microearthquakes below magnitude 1.0, with only a few events exceeding magnitude 1.0. Depths remained shallow throughout, consistent with brittle failure in the upper crust of the Basin and Range. No mainshock-aftershock sequence was observed; instead, the energy release was distributed across numerous events of similar size, a hallmark of swarm behavior.

The sequence began with the magnitude-3.8 shock followed rapidly by events of magnitude 1.8 and 0.6 within the first five minutes. Activity continued at low levels for the remainder of 2 January, with isolated events of magnitude 1.0–1.3 occurring through the afternoon and evening. On 3 January, seismicity tapered off, ending with a final magnitude-0.7 event at 7 km depth.

Historical records maintained by SeismoSight indicate that 13 swarms have occurred in the same region since 1 January 2000. Prior swarms were documented in 2011 (1 swarm), 2014 (3 swarms), 2015 (3 swarms), and 2016 (6 swarms). This pattern underscores the recurrent nature of swarm activity along local fault networks in the Walker Lane.

Seismic swarms in this setting are commonly linked to fluid migration or aseismic slip transients that trigger distributed failure without a dominant mainshock. The 2017 swarm’s shallow depths and lack of a clear magnitude progression align with such mechanisms observed elsewhere in the western Great Basin.

References

SeismoSight internal swarm classification database
USGS Earthquake Hazards Program – Basin and Range tectonics overview
Nevada Seismological Laboratory – Walker Lane seismic belt summary