Seismic Swarm S20030103.1: Analysis Near Arvin, California

The earthquake swarm designated S20030103.1 occurred 18 km northeast of Arvin in Kern County, California. It began at 03:17 on 2 January 2003 and concluded at 21:04 on 15 January 2003, spanning 329 hours and 46 minutes. During this interval, 222 earthquakes were recorded. This swarm took place in the southern San Joaquin Valley near the transition to the Tehachapi Mountains. The region lies within a tectonically active zone influenced by the intersection of the San Andreas Fault system and the Garlock Fault. These structures accommodate lateral motion between the Pacific and North American plates, producing frequent small-magnitude events. Historical records indicate recurrent low-level seismicity in the area, consistent with the swarm's occurrence following a prior episode in 2001. Examination of the first 100 events reveals predominantly shallow hypocenters, with depths clustered between 0 and 7 km and a few reaching 11 km. Magnitudes ranged from 0.8 to 3.6, with the largest events (3.6 and 3.5) occurring early on 2 January at depths of 3 km and 2 km. Most activity remained below magnitude 2.5, producing a typical swarm pattern of numerous small shocks without a single dominant mainshock. Event frequency peaked within the first 48 hours, then gradually declined while maintaining shallow focal depths. The swarm's characteristics align with fluid-driven or stress-triggered sequences common in this part of California. No damage or injuries were associated with the activity, reflecting the modest energy release.

References

USGS Earthquake Catalog California Geological Survey Fault Database SeismoSight internal classification records