'Swarm' of Quakes Shake SoCal Thursday Morning: Did You Feel Them?

RIALTO, CA— A magnitude 4.3 earthquake struck with an epicenter in Muscoy, in San Bernardino County, on Thursday, according to the United States Geological Survey. Initial indicators showed the quake at 4.5 magnitude, but it was quickly downgraded as multiple other quakes struck close by in Rialto.

The temblor was reported at 9:30 a.m.

The quake rattled nearby residents in Los Angeles, Orange and Riverside Counties, as far south as Chula Vista and far west as Oxnard, according to initial reports.

Seismologist Gabrielle Tepp of Cal Tech Seismology Lab discussed the quakes that struck Thursday morning.

"An early warning alert went out with a magnitude 4.5, based upon a small amount of information, and as more data comes in, our automated systems will do a more robust measurement of magnitude," Seismologist Gabrielle Tepp of Cal Tech Seismology Lab said.

USGS has asked all who felt it to chime in on its Did You Feel It report.

No injuries were reported as a result of today's quake.

The quake was preceded by five events since Monday, the largest immediately before, with a magnitude 3.0, according to Cal Tech. It was also followed by other small quakes in neighboring Rialto, including a 3.1 magnitude earthquake. Thursday's activity originated from the Fontana Seismicity Lineation, around Fontana, which is near the San Jacinto Fault Line. The fault runs at an angle toward the San Andreas Fault Line. There was no immediate concern about larger magnitude quakes in that area, according to Cal Tech seismologists.

Aftershocks from this series of quakes were likely, seismologists said, and the chance of a larger quake striking this area was about 5%.

Other seismic activity in the region:

This region has experienced 26 seismic events of magnitude 4.0 or more since CalTech began keeping records in 1932, they tell us. The largest quake occurred on Sept. 12, 1970. The most recent earthquake in the area, a 4.2 magnitude temblor, occurred on Jan. 25, 2024.

This week's 8.8 quake in Russia and the tsunami warnings that followed did not affect current seismic activity in southern California, according to Tepp.

"It will take more time and analysis to know for sure; however, generally when an earthquake occurs across the globe, it doesn't typically affect us here," she said.

This is a developing report and additional information will be added as it is received.

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