Seismic Swarm S20240803.1 Near Salton City, California

SeismoSight recorded seismic swarm S20240803.1 beginning at 14:41 on 2 August 2024 and concluding at 13:49 on 5 August 2024. The sequence occurred 11 km southwest of Salton City, California, and comprised 54 earthquakes over 71 hours and 7 minutes.

The swarm exhibited a typical clustered pattern with events concentrated in the first 48 hours. Magnitudes ranged from 0.4 to 3.4, with the largest shock (M3.4) occurring at 18:39 on 2 August at a depth of 3 km. A secondary peak of M3.2 was noted at 08:29 on 4 August, also at 3 km depth. Depths remained shallow throughout, predominantly between 3 km and 5 km, consistent with activity in the upper crust.

Event frequency declined steadily after the initial burst, with only isolated events recorded on 5 August. The distribution shows no clear migration of hypocenters, indicating a localized source volume.

The Salton Trough lies at the southern termination of the San Andreas Fault system, where the Pacific–North American plate boundary transitions into a zone of oblique extension and right-lateral shear. This setting produces frequent earthquake swarms driven by fluid migration and geothermal processes rather than mainshock–aftershock sequences. The Imperial and Brawley fault zones, together with associated cross-faults, accommodate much of the regional strain and host recurrent swarms.

Since 1 January 2000, nine swarms have been documented in the immediate area, occurring in 2006, 2008, 2009 (two episodes), 2015, 2018, 2020, 2021, and 2022. These episodes illustrate the persistent seismic character of the region, with swarm activity often linked to the high heat flow and hydrothermal circulation beneath the Salton Sea geothermal field.

The August 2024 swarm aligns with this established pattern. Its modest maximum magnitude and shallow focal depths are characteristic of fluid-driven sequences previously observed in the Brawley Seismic Zone. No damage or felt reports beyond the immediate vicinity were associated with the largest events.

Continued monitoring remains essential given the proximity to critical infrastructure and the potential for larger triggered events along the San Andreas and Imperial faults.

References:
USGS Earthquake Catalog (earthquake.usgs.gov)
California Geological Survey regional fault maps
SCEC Community Fault Model documentation