Seismic Swarm S20020502.1: Analysis of Activity Near Little Lake, California

Seismic swarm S20020502.1 occurred approximately 20 km south-southwest of Little Lake, California, in the tectonically active Eastern California Shear Zone. This region experiences frequent small-magnitude earthquakes driven by right-lateral strike-slip faulting along structures such as the Little Lake fault zone. The swarm spanned 47 hours and 57 minutes from 23:02 UTC on 1 May 2002 to 22:59 UTC on 3 May 2002, registering a total of 43 events.

The sequence began with a magnitude 3.0 earthquake at 1 km depth, followed rapidly by a magnitude 2.8 event one minute later. Activity continued with predominantly shallow events, the majority occurring at depths of 1–3 km. The largest event reached magnitude 3.8 at 06:00 on 2 May at 1 km depth. Subsequent events included several magnitude 2.0–2.9 shocks distributed through 2 and 3 May, with the final recorded event at magnitude 1.1 on 3 May at 22:59.

Depth distribution remained consistent with crustal seismicity, ranging from 0 to 10 km and clustering near 1–2 km for most events. Magnitudes generally declined after the peak on 2 May, illustrating the typical decay pattern of swarm sequences rather than a mainshock-aftershock progression. No events exceeded magnitude 4.0, consistent with background levels in this portion of the shear zone.

Historical records indicate this was the third swarm in the immediate area since 1 January 2000. Earlier swarms occurred in 2000 and 2001, each comprising a single documented sequence. Such episodic clustering reflects the ongoing strain accumulation and release along regional faults.

The Little Lake area lies at the transition between the Sierra Nevada and Basin and Range provinces, where volcanic and geothermal influences from the nearby Coso Volcanic Field can modulate seismicity. Monitoring by regional networks continues to track these patterns, providing data for improved hazard assessment in this portion of California.

References
SeismoSight internal swarm classification database.
USGS Earthquake Catalog for regional tectonic context.
California Geological Survey fault activity maps.