Seismic Swarm S20190611.1: Analysis of Activity near Goldfield, Nevada

The seismic swarm designated S20190611.1 occurred approximately 54 km east-southeast of Goldfield in Esmeralda County, Nevada. It began at 07:24 UTC on 11 June 2019 and concluded at 01:59 UTC on 13 June 2019, spanning 42 hours and 35 minutes. During this interval, 29 earthquakes were recorded, with magnitudes ranging from -0.3 to 4.1 and focal depths predominantly between 13 km and 24 km.

The sequence initiated with a magnitude 4.1 event at 15 km depth, followed shortly by a magnitude 2.8 shock at the same depth. Subsequent activity consisted largely of microearthquakes below magnitude 1.0, interspersed with occasional events up to magnitude 2.9. Depths clustered around 15–20 km, consistent with brittle failure in the upper crust. The largest events occurred early in the swarm, with activity gradually diminishing over the following day.

This region lies within the Basin and Range Province of western Nevada, where ongoing east-west crustal extension produces normal faulting along north- to northwest-striking structures. The swarm location sits near the transition between the central Nevada seismic belt and the Walker Lane shear zone, a zone of distributed right-lateral shear that accommodates roughly 20 percent of Pacific–North American plate motion. Historical seismicity in Esmeralda County reflects this tectonic setting, with events typically occurring on Quaternary faults that cut Tertiary volcanic and sedimentary rocks.

Goldfield itself developed during a major early-twentieth-century mining boom hosted in hydrothermally altered volcanic rocks. Regional fault systems, including strands of the Goldfield fault zone and nearby structures associated with the Mina deflection, have been mapped as active or potentially active. Paleoseismic studies indicate recurrence intervals for moderate-to-large earthquakes on the order of several thousand years, although smaller events and swarms occur more frequently.

Since 2000, four prior swarms have been documented in the immediate area: one each in 2008, 2010, 2012, and 2014. Each involved a limited number of events and lacked significant damage or surface rupture. The 2019 swarm follows this pattern, exhibiting a rapid onset, a modest mainshock, and a swift decay in rate without migration suggestive of fluid-driven processes.

Depth distribution and magnitude statistics indicate failure within the seismogenic crust under ambient tectonic stress, without clear evidence of triggering by magmatic intrusion. Such swarms are common in the Walker Lane and serve as indicators of strain accumulation along secondary faults.

References

• U.S. Geological Survey Earthquake Catalog (earthquake.usgs.gov)
• Nevada Seismological Laboratory, University of Nevada, Reno
• USGS Quaternary Fault and Fold Database of the United States
• Faulds, J.E., and Henry, C.D. (2008), Tectonic influences on the spatial and temporal evolution of the Walker Lane, Geological Society of America Special Paper 442