Seismic Swarm S20041119.1: Analysis of Activity Near Beatty, Nevada

Seismic swarm S20041119.1 occurred approximately 61 km west-northwest of Beatty, Nevada, beginning at 03:37 UTC on 19 November 2004 and concluding at 10:35 UTC on 20 November 2004. Over this 30-hour period, 26 earthquakes were recorded, with magnitudes ranging from 0.6 to 2.7 and focal depths between 7 and 12 km. The sequence featured a gradual increase in event frequency during the initial hours, peaking with several events above magnitude 2.0, before tapering off.

The swarm initiated with a magnitude 1.0 earthquake at 11 km depth. Subsequent activity included a magnitude 2.4 event at 7 km depth at 08:26 UTC and a magnitude 2.7 event at 10 km depth at 09:27 UTC, representing the largest in the sequence. Later events remained below magnitude 2.3, with the final recorded shock measuring magnitude 1.2 at 11 km depth. Depths clustered consistently in the upper to mid-crust, typical of shallow tectonic release in the area.

The region lies within the Basin and Range Province of southwestern Nevada, an area shaped by extensional tectonics since the Miocene epoch. Normal faulting predominates, driven by crustal stretching that accommodates up to 50 percent extension in places. Beatty sits near the transition to the Amargosa Desert, influenced by structures such as the Bare Mountain fault and proximity to the Furnace Creek fault system extending from California. Volcanic history includes Miocene-age ash-flow tuffs and caldera complexes associated with the Timber Mountain-Oasis Valley caldera complex, contributing to fractured rock that facilitates fluid movement and microseismicity.

Historical seismicity in the vicinity includes multiple swarms linked to both tectonic stress accumulation and hydrothermal processes. The area experiences background rates of small events due to its position along the Walker Lane belt, a zone of dextral shear accommodating Pacific-North America plate motion. Updated monitoring by regional networks confirms ongoing low-level activity, with no significant change in long-term rates through recent decades.

Such swarms often arise from transient stress perturbations, including fluid migration along faults or minor magmatic intrusions at depth, rather than mainshock-aftershock sequences. The 2004 events exhibited no clear migration pattern or escalation to a larger mainshock, consistent with aseismic slip or pore-pressure diffusion models observed in similar Basin and Range settings. Depths align with the brittle-ductile transition zone, where small ruptures release accumulated strain without widespread surface rupture.

This activity underscores the persistent seismic hazard in central Nevada, where even modest swarms inform hazard assessments for infrastructure and historical nuclear testing sites nearby. Continued instrumentation supports refined models of fault interactions in this extensional regime.

References

• Nevada Seismological Laboratory regional catalog data.
• USGS Earthquake Hazards Program reports on Basin and Range tectonics.
• Geological Society of America publications on southwestern Nevada volcanic history.