Seismic Swarm S20030223.3 near Furnace Creek, California

Seismic swarm S20030223.3 occurred in the northern Death Valley region of eastern California, centered approximately 36 km northwest of Furnace Creek. The sequence began at 18:27 UTC on 22 February 2003 and concluded at 08:58 UTC on 25 February 2003, spanning 62 hours and 30 minutes. During this interval, 42 earthquakes were recorded, with magnitudes ranging from -0.2 to 2.1 and focal depths between 4 km and 13 km.

The events exhibited typical swarm characteristics, lacking a dominant mainshock followed by decaying aftershocks. Instead, activity occurred in temporal clusters, with the largest event (magnitude 2.1) recorded early in the sequence at a depth of 13 km. Subsequent events remained below magnitude 2.0, and many fell below magnitude 1.0, reflecting low-energy release distributed across numerous small ruptures. Depths clustered predominantly between 5 km and 8 km, consistent with shallow crustal faulting in the area.

The swarm location lies within the Death Valley fault system, specifically near the northern segments of the Furnace Creek Fault. This right-lateral strike-slip structure forms part of the broader Eastern California Shear Zone, which accommodates a portion of the Pacific-North America plate boundary deformation. The region experiences active extension and shear, producing both normal and strike-slip faulting. Historical seismicity includes moderate events along nearby faults, such as the 1872 Owens Valley earthquake sequence to the north, which demonstrated the capacity for larger ruptures in the Walker Lane belt.

Geological mapping indicates that Quaternary alluvium and playa deposits overlie Paleozoic and Mesozoic bedrock in the Furnace Creek area, with fault scarps preserving evidence of Holocene activity. Updated regional strain models from geodetic data confirm ongoing dextral shear rates of several millimeters per year across the Death Valley fault zone, supporting the occurrence of distributed microseismicity such as swarm S20030223.3.

Analysis of the provided event parameters shows no systematic migration of hypocenters, suggesting localized fluid or stress triggering rather than a propagating rupture front. Such swarms contribute to the cumulative strain release in the region without producing significant surface rupture at these magnitude levels.

References

USGS Earthquake Catalog (event parameters and locations)
California Geological Survey, Regional Fault Maps
USGS Open-File Reports on Death Valley tectonics