Seismic Swarm S20011113.1 Near Bombay Beach, California
A notable earthquake swarm occurred southeast of Bombay Beach, California, from November 13 to 14, 2001. Registered by SeismoSight, the sequence began at 13:43 UTC on November 13 and concluded at 13:03 UTC on November 14, encompassing 99 events over 23 hours and 20 minutes. The epicentral area lies approximately 5 km southeast of Bombay Beach, within the tectonically active Imperial Valley region adjacent to the Salton Sea.
The swarm featured predominantly low-magnitude events, with the largest reaching magnitude 4.1 at a depth of 5 km on November 13 at 20:43 UTC. Other notable shocks included magnitudes of 3.4, 3.2 (multiple occurrences), 3.1 (multiple), and 3.0, clustered mainly in the initial hours. Depths ranged from 0 to 12 km, averaging around 5–6 km, consistent with shallow crustal activity. Event frequency peaked between 16:00 and 22:00 UTC on November 13, with gradual decline thereafter. This pattern reflects typical swarm behavior driven by fluid migration or aseismic slip rather than a single mainshock-aftershock sequence.
Bombay Beach sits along the southern San Andreas Fault and the Brawley Seismic Zone, where the Pacific and North American plates interact through a network of strike-slip and normal faults. The region experiences frequent seismicity due to transtensional tectonics associated with the Salton Trough, an active rift basin. Historical records indicate elevated swarm activity in this locale, influenced by geothermal processes and sediment loading from the Colorado River delta. The 2001 swarm aligns with prior episodes in the area, underscoring the zone's persistent microseismicity.
Geological monitoring in the Imperial Valley benefits from dense seismic networks, enabling detailed characterization of such sequences. Depths under 12 km suggest activity within the brittle upper crust, where fault interactions can trigger clustered events without producing significant surface rupture.
References
USGS Earthquake Catalog California Geological Survey Regional Fault Maps Southern California Seismic Network Reports