Seismic Swarm S20120213.1: Analysis of Activity Near Goldfield, Nevada

Seismic swarm S20120213.1 occurred 42 km east-southeast of Goldfield, Nevada, beginning at 10:16 UTC on 12 February 2012 and concluding at 08:57 UTC on 20 February 2012. Over 190 hours and 41 minutes, the sequence produced 107 earthquakes. The first 100 events exhibited magnitudes predominantly between 0.2 and 1.9, with the largest reaching 1.9 on 15 February at a depth of 6 km. Depths ranged from surface levels to 23 km, indicating activity across multiple crustal layers typical of the region’s extensional regime.

The swarm’s temporal distribution showed an initial cluster of low-magnitude events on 12–13 February, followed by sporadic larger events mid-sequence. Notable activity included a 1.5-magnitude event at 16 km depth on 16 February and two 1.8-magnitude shocks on 16–17 February at depths of 16–17 km. Many events occurred at depths of 12–20 km, consistent with brittle failure in the mid-crust, while shallower events (0–7 km) suggest possible fluid involvement or fault reactivation near the surface.

The Goldfield area lies within the Basin and Range Province, characterized by north-south trending normal faults and ongoing crustal extension driven by Pacific-North American plate interaction. This tectonic setting produces frequent small-magnitude seismicity, with swarms often linked to fluid migration along fault networks rather than mainshock-aftershock sequences. Historical records indicate sparse swarm activity since 2000, with the prior event occurring in 2010, underscoring the episodic nature of such clusters in this part of western Nevada.

Geological context includes proximity to the Walker Lane shear zone, where right-lateral strike-slip motion accommodates a portion of the plate boundary strain. Quaternary fault scarps and volcanic rocks in the region reflect long-term extension rates of approximately 1 cm per year. Updated seismic monitoring by regional networks confirms that events in this magnitude range rarely cause surface damage but contribute to understanding strain accumulation on nearby structures such as the Goldfield Hills fault system.

The 2012 swarm’s characteristics align with typical background seismicity in the area, where low-magnitude events dominate and depths commonly exceed 10 km. No significant surface rupture or felt reports above intensity III were associated with the sequence, consistent with its modest energy release.

References

• USGS Earthquake Catalog (earthquake.usgs.gov)
• Nevada Bureau of Mines and Geology seismic reports
• SeismoSight internal swarm classification data