4.3-magnitude earthquake rattles San Bernardino County, widespread shaking across Southern California

A 4.3-magnitude earthquake struck near Muscoy in San Bernardino County at 9:32 a.m. Thursday, sending tremors across the Inland Empire and much of Southern California. According to the U.S. Geological Survey (USGS), this quake was followed within minutes by a magnitude 3.1 aftershock in the Rialto area, and earlier in the morning by quakes measuring 3.0 and 2.8.

Residents across the region—including Riverside, Los Angeles, Eastvale, Ontario, Redondo Beach, Santa Clarita, Garden Grove, and as far south as San Diego—reported feeling the quake. Many described it as a jolt or rolling sensation, especially on upper floors of buildings. "It gave us a pretty good little jolt for a few seconds," said Ryan Beckers, spokesman for the San Bernardino County Fire Department.

Emergency response and damage reports

Early reports indicate no significant injuries or structural damage from the main quake or its aftershocks. The San Bernardino County Fire Department, as well as other local emergency agencies, confirmed that they had not received any immediate calls for assistance related to the event. Online self-reporting through the USGS “Did You Feel It?” survey drew nearly 5,000 responses within 40 minutes, reflecting broad regional awareness and concern.

Seismic context and expert analysis

Seismologists identified the event as part of a small swarm along the so-called Fontana trend, a northeast-striking lineation of left-lateral faults under San Bernardino Valley sediments. According to the USGS, the region has seen more than 130 earthquakes of M3.0 or greater since 1990, with clusters common in these fault zones.

No early warning triggered

Despite the quake’s moderate strength, the U.S. Geological Survey’s ShakeAlert early warning system did not issue a public notification, likely due to the specifics of the quake's magnitude and depth relative to population density.

Officials urge residents to see this event as a reminder about the region’s seismic risk, advising communities to secure heavy furniture at home, keep emergency kits ready, and know local evacuation and shelter-in-place procedures for future events.