Analysis of the December 2004 Earthquake Swarm Near Little Lake, California
The seismic swarm designated S20041202.1 occurred 16 km northeast of Little Lake, California, beginning at 08:13 on 1 December 2004 and concluding at 02:55 on 4 December 2004. Over 66 hours and 41 minutes, the sequence produced 36 earthquakes. Magnitudes ranged from 0.2 to 2.0, with the largest event recorded at 07:40 on 2 December. Depths remained predominantly shallow, between 0 and 6 km, consistent with activity along near-surface fault structures.
This swarm exemplifies a typical cluster of events lacking a dominant mainshock, instead featuring numerous events of comparable size distributed over several days. Such sequences often indicate fluid migration or aseismic slip triggering successive failures within a localized volume. The recorded events clustered tightly in both space and time, with the majority occurring on 2 December.
The Little Lake region lies within the Eastern California Shear Zone, a broad zone of distributed right-lateral shear accommodating a portion of the Pacific–North America plate motion. The area experiences active deformation along northwest-striking faults that link the Garlock Fault system to the Owens Valley and Coso regions. Shallow seismicity is common, reflecting brittle failure in the upper crust above a ductile transition zone influenced by nearby geothermal and volcanic processes in the Coso Volcanic Field.
Historical records indicate persistent swarm activity in this locale. Since 1 January 2000, sixteen swarms have been documented, distributed as follows: four in 2000, four in 2001, two in 2002, and six in 2004. This pattern underscores the region’s tendency toward episodic, clustered seismicity rather than isolated large-magnitude events.
The December 2004 swarm adds to the established record of low-magnitude, shallow activity that characterizes the Eastern California Shear Zone. Continued monitoring of such sequences provides valuable data on fault interaction and strain accumulation in this tectonically complex setting.
References
USGS Earthquake Catalog (historical seismicity data)
California Geological Survey regional fault maps
Southern California Earthquake Data Center swarm documentation