Seismic Swarm S20100930.1 Near Beatty, Nevada: Geological Context and Event Analysis

A notable seismic swarm designated S20100930.1 occurred approximately 61 km west-northwest of Beatty, Nevada, beginning at 10:37 on 29 September 2010 and concluding at 00:45 on 24 October 2010. Over 590 hours and 7 minutes, the sequence produced 754 earthquakes. This activity unfolded in the Basin and Range province of southern Nevada, a region characterized by active extensional tectonics driven by normal faulting.

The local geology features Quaternary alluvial deposits overlying Paleozoic carbonate and siliciclastic rocks, with prominent north-south trending normal faults associated with the Walker Lane deformation zone. These structures accommodate right-lateral shear and east-west extension at rates of several millimeters per year. Beatty lies near the southern end of the Nevada National Security Site, where historical underground nuclear testing has provided detailed subsurface velocity models that aid in precise earthquake location. The area's seismicity reflects ongoing Basin and Range extension superimposed on older Mesozoic thrust faults.

Analysis of the first 100 events reveals a typical swarm pattern dominated by low-magnitude earthquakes. The sequence initiated with a magnitude 1.3 event at 7 km depth. Within the first day, activity intensified, including a magnitude 4.3 shock at 6 km depth followed closely by events of 3.5, 3.2, and 3.4. Depths for these early events clustered between 0 and 14 km, with the majority between 6 and 12 km, consistent with brittle failure in the upper crust. Magnitudes remained predominantly below 2.0 after the initial peak, though several events reached 2.5–2.9. The distribution shows no single dominant mainshock-aftershock decay but rather sustained, clustered energy release.

Historical records indicate that seismic swarms have been infrequent in this precise locale since 2000. Only two prior swarms are documented: one in 2004 and another in 2005. This 2010 sequence therefore represents the third such episode in the instrumental era, highlighting episodic swarm behavior possibly linked to fluid migration or aseismic slip transients along local faults.

The swarm's characteristics align with regional patterns observed elsewhere in the Great Basin, where swarms often occur without clear surface rupture and contribute to long-term strain accommodation. No damage or felt reports beyond minor shaking were associated with the largest events, reflecting both the moderate magnitudes and the remote location.

References

• United States Geological Survey Earthquake Catalog
• Nevada Seismological Laboratory regional fault database
• SeismoSight internal swarm classification records