Seismic Swarm Activity near Hawthorne, Nevada: The April 2017 Event

The region 30 km south-southwest of Hawthorne, Nevada, lies within the tectonically active Walker Lane belt of western Nevada. This zone accommodates a significant portion of the Pacific-North American plate motion through a combination of normal faulting and right-lateral strike-slip deformation. The area forms part of the broader Basin and Range province, where crustal extension has produced numerous north-trending mountain ranges and intervening valleys bounded by active faults. Seismicity here is common, with most events occurring at shallow to moderate depths consistent with the brittle upper crust. On 15 April 2017, a seismic swarm designated S20170415.1 was recorded in this setting. The sequence began at 03:10 UTC and concluded at 15:25 UTC, lasting just over 12 hours. During this interval, 83 earthquakes were detected. Magnitudes remained modest, with the largest event reaching 2.9; the majority clustered between 0.5 and 1.6. Focal depths were predominantly between 5 and 9 km, although a few events extended to 25 km. The swarm displayed a typical pattern of clustered, low-magnitude activity without a single dominant mainshock. Key events illustrate the temporal evolution. An early 1.2-magnitude shock occurred at 04:20, followed by a gradual increase in rate. The peak activity took place between 10:36 and 11:51, when multiple events above magnitude 1.5 were recorded in rapid succession, including the 2.9-magnitude earthquake at 10:36. Later activity included a 2.7-magnitude event at 13:45 before the sequence tapered off by mid-afternoon. Depths remained consistent with the regional seismogenic zone throughout. Historical records indicate that swarm behavior is recurrent in this locale. Since 2000, 22 swarms have been identified in the immediate area. Notable years include 2011 (seven swarms), 2006 (three), 2015 (three), and 2016 (three). Earlier episodes occurred in 2001, 2004, and 2013. The 2017 sequence was one of two recorded that year. Such swarms are characteristic of fluid-driven or aseismic-slip-triggered processes along the distributed fault network of the Walker Lane. The April 2017 swarm provides a clear example of the low-to-moderate seismicity that defines the Hawthorne region. Continued monitoring of these episodic clusters contributes to improved understanding of strain accommodation and fault interaction within this tectonically complex corridor. References
SeismoSight internal swarm classification records, 2017.
Walker Lane tectonic framework, USGS Earthquake Hazards Program regional summaries.
Basin and Range province seismicity characteristics, Nevada Seismological Laboratory publications.