Analysis of the 2011 Hawthorne Earthquake Swarm
The 2011 Hawthorne earthquake swarm, classified internally as S20110414.1 by SeismoSight, occurred 18 km south-southwest of Hawthorne, Nevada. It began at 21:23 UTC on 13 April 2011 and concluded at 08:22 UTC on 4 June 2011, spanning 1234 hours and 59 minutes. During this period, 3166 earthquakes were recorded.
The swarm unfolded within the Basin and Range province of western Nevada, specifically along the Walker Lane belt. This structural zone accommodates northwest-directed right-lateral shear between the Pacific and North American plates at rates of approximately 10–12 mm per year. Active normal and strike-slip faults in the region produce frequent seismic activity, with events typically occurring at depths of 0–16 km, consistent with the brittle upper crust in this extensional setting.
Examination of the first 100 events reveals a characteristic swarm pattern dominated by low-magnitude activity. The sequence initiated with a magnitude 2.8 event at 7 km depth, followed rapidly by a magnitude 4.4 shock at 6 km. Subsequent events clustered between magnitudes 0.1 and 4.1, with the majority falling below 2.0. Depths remained shallow, predominantly between 1 and 10 km, though a few reached 16 km. Temporal distribution showed intense activity in the first 24 hours, with dozens of events per hour initially, gradually declining thereafter. No single mainshock dominated; instead, energy released through numerous smaller ruptures along likely fault segments.
Historical records indicate this was not an isolated occurrence. Since 2000, six swarms have affected the Hawthorne area, including one in 2001 and three in 2006. The 2011 sequence represented the second swarm that year, underscoring recurrent strain release in the Walker Lane.
Such swarms typically arise from fluid migration or aseismic slip triggering brittle failure, rather than a single large rupture. The 2011 events posed minimal surface damage risk given their modest magnitudes, yet they highlight ongoing tectonic deformation in this portion of the western United States.
References
- USGS Earthquake Catalog (earthquake.usgs.gov)
- Nevada Bureau of Mines and Geology seismic reports
- SeismoSight internal swarm classification data