Seismic Swarm S20200517.1: Analysis of Activity Near Mina, Nevada

A notable earthquake swarm, designated S20200517.1 by internal classification, occurred 36 km southeast of Mina, Nevada. The sequence began at 16:08 on 16 May 2020 and concluded at 18:00 on 27 May 2020, spanning 265 hours and 52 minutes. During this period, 418 earthquakes were recorded, with the majority exhibiting magnitudes between 1.0 and 3.7 and focal depths ranging from 0 to 14 km.

Analysis of the first 100 events reveals a pattern typical of swarm activity, characterized by numerous small-magnitude tremors without a dominant mainshock. The initial event registered magnitude 1.9 at a depth of 0 km. Subsequent events included several above magnitude 3.0, such as a 3.2 at 16:32 on 16 May, another 3.2 at 23:49 the same day, a 3.5 at 06:11 on 17 May, and a peak of 3.7 at 11:22 on 17 May. Depths remained predominantly shallow, with many events at or near 0–5 km, though some reached 11–14 km. Activity showed clustering in time, with elevated rates during evening and early morning hours on 16–17 May, gradually declining thereafter. This distribution indicates fluid migration or stress redistribution along local faults rather than a single rupture.

The region lies within the western Basin and Range province of Nevada, an area defined by extensional tectonics driven by the interaction between the Pacific and North American plates. Mina sits near the Walker Lane belt, a northwest-trending zone of right-lateral shear accommodating approximately 20% of the relative plate motion. This tectonic setting produces frequent normal and strike-slip faulting, contributing to elevated seismic hazard. The crust here consists of Tertiary volcanic and sedimentary rocks overlying older metamorphic basement, with active faults including segments of the Mina deflection and related structures.

Historical records indicate recurrent swarm behavior in this locale. Since 2000, five swarms have been documented in the immediate area, occurring in 2003 (two swarms), 2013 (one swarm), and 2020 (two swarms). Such sequences often reflect episodic strain release along distributed fault networks rather than large, isolated events.

The 2020 swarm aligns with broader patterns observed across the Walker Lane, where low-magnitude, prolonged activity is common due to the region's fragmented fault system. No significant damage or felt reports beyond local scales were associated with this sequence, consistent with the modest magnitudes involved.

References

• USGS Earthquake Catalog (earthquake.usgs.gov)
• Nevada Seismological Laboratory historical data
• Basin and Range Province tectonic summaries from USGS Professional Papers