Magnitude 4.3 earthquake in San Bernardino County sends shaking across Southern California

Karen Garcia and Hannah Fry, Los Angeles Times on Jul 31, 2025

By clicking submit, I authorize Arcamax and its affiliates to: (1) use, sell, and share my information for marketing purposes, including cross-context behavioral advertising, as described in our Privacy Policy , (2) add to information that I provide with other information like interests inferred from web page views, or data lawfully obtained from data brokers, such as past purchase or location data, or publicly available data, (3) contact me or enable others to contact me by email or other means with offers for different types of goods and services, and (4) retain my information while I am engaging with marketing messages that I receive and for a reasonable amount of time thereafter. I understand I can opt out at any time through an email that I receive, or by clicking here

LOS ANGELES — A magnitude 4.3 earthquake rumbled through Muscoy in San Bernardino County on Thursday morning, triggering shaking across the Inland Empire region, Los Angeles and Orange counties, according to the U.S. Geological Survey.

The earthquake occurred at 9:32 a.m. at a depth of about 3.3 miles and was followed by a magnitude 3.1 quake about four minutes later in Rialto, according to USGS.

The Rialto Fire Department reported that a series of small earthquakes shook the northwest portion of the city Thursday morning. The first foreshock in the region, a magnitude 3.0, struck about 8:34 a.m., followed by a magnitude 2.8 about eight minutes later. Two smaller temblors occurred over about 13 minutes before the magnitude 4.3 hit, according to USGS.

There were no immediate reports of damage.

“There’s no reportable damage but it’s still pretty early,” said Chris Jensen, the department’s interim fire chief. There hadn’t been any medical calls related to the earthquake but Jensen said the agency will continue to monitor the situation.

Data shows the quake was felt over a wide swath of Southern California, from Los Angeles to San Diego and as far east as Ventura County. Residents who felt the earthquake closest to the epicenter and sent information to the USGS’ Did You Feel It? website reported experiencing the equivalent of Intensity 4 shaking on the Modified Mercalli Intensity Scale, which is light shaking too weak to cause any damage.

Areas farther away from the epicenter, from Simi Valley to San Diego, reported Intensity 2 to Intensity 3 shaking, or weak shaking that wouldn’t cause damage.

Seismologist Lucy Jones said the earthquakes were a small swarm in the Fontana Trend, a series of earthquakes that run along a northeast geographic line under the sediments of the San Bernardino Valley. Scientists suspect there’s a fault in that area, but they can’t map it because it’s covered by sediment, she said.

“It’s a place that has lots of little earthquakes and they do often come in little clusters, like this one,” she said.

Since 1990 there have been roughly 130 magnitude 3.0 earthquakes and eight magnitude 4.0 along the Fontana Trend, Jones said.

In the past 10 days, there have been three earthquakes of magnitude 3.0 or greater centered nearby. An average of 25 earthquakes with magnitudes between 4.0 and 5.0 occur per year in California and Nevada, according to a recent three-year data sample.

The temblor comes days after a powerful earthquake struck off Russia’s sparsely populated east coast, sending waves slamming into buildings in Siberia and northeastern Japan. At magnitude 8.8, the earthquake ranks as the sixth-most powerful ever recorded.