Imperial Valley ‘seismic swarm’ rattles San Diego County

by Karen Pearlman | May 11, 2026 4:05 am

Map courtesy United States Geological Survey

East County News Service

May 10, 2026 (Brawley) — A prolific seismic swarm in Imperial Valley reached a peak in the early morning hours of Sunday, May 10, sending some light shaking into San Diego County and triggering mobile alerts for some residents.

The largest event of the sequence so far — a magnitude 4.7 earthquake — struck at 12:10 a.m. on Sunday. This followed a significant magnitude 4.5 quake on Saturday evening.

To date, the U.S. Geological Survey has recorded more than 350 earthquakes in this cluster, located in the highly active Brawley Seismic Zone between the Salton Sea and the U.S.-Mexico border. The USGS said the seismic swarm started at 5:40 p.m. on Friday with several microearthquakes.

The Southern California Seismic Network reported that it had recorded 368 events in the swarm (within a 20 km radius, and counting five days before the largest event). More activity is expected in the next few days.

Quake felt across San Diego County

While the epicenter was nearly 100 miles east of the coast, the midnight quake was widely felt throughout San Diego County. Residents in El Cajon, Santee, Poway, Chula Vista and Vista reported feeling the swaying, with many receiving a ShakeAlert[1] notification on their smartphones seconds before the waves arrived.

The California Governor’s Office of Emergency Services reported that while the shaking was startling, there have been no reports of major infrastructure damage or injuries within San Diego County.

Earthquake experts emphasize that while the sheer number of quakes is impressive, this behavior is typical for the Brawley Seismic Zone. Unlike other fault systems that produce one large “mainshock” followed by smaller aftershocks, this area is known for “swarms” — clusters of earthquakes of similar magnitude that can go on and on for several days.

Geologically, the Brawley zone acts as a “soft connection” or step-over point between the southern San Andreas and the Imperial faults. Despite the frequent activity, seismologists note that these swarms historically do not trigger a much larger, catastrophic earthquake on the San Andreas Fault.

Local needs and preparation

In the city of Brawley, crews spent Sunday addressing minor utility issues and water leaks caused by the repeated rattling. City officials maintained that there is no immediate threat to public safety, though they continue to monitor the situation as the swarm slowly begins to taper off.

Emergency officials suggest that those who felt the shaking use the opportunity to check their home emergency kits and ensure heavy furniture is properly bolted to walls.

Updates on the swarm and recorded magnitudes can be tracked in real-time at earthquake.usgs.gov[2].

Source URL: https://eastcountymagazine.org/imperial-valley-seismic-swarm-rattles-san-diego-county/

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