A magnitude 4.8 earthquake struck near Petrolia on Friday afternoon, according to the U.S. Geological Survey. The tremor hit at 7:41 p.m. UTC, or 6:41 p.m. local time, originating at a depth of 6 miles with its epicenter positioned approximately 53 miles west of Petrolia.
Ground Shaking and Regional Impact Reports
The USGS categorized the event as a Green Alert, indicating a low likelihood of casualties and structural damage. By Friday evening, the agency had gathered 246 online responses through its “Did You Feel It?” tracking system. Respondents characterized the motion as weak to light shaking.
According to USGS data, residents across multiple California communities felt the ground move. Reports came in from cities including San Francisco, Garberville, Myers Flat, and Bayside.
Did you know?
Earthquakes between 2.5 and 5.4 magnitude are often felt by people, but they rarely cause significant damage, according to data from Michigan Tech cited by the USGS.
Regional Seismicity and Building Vulnerability
This tremor follows two smaller earthquakes measuring 2.6 magnitude in the same general region over the previous week. A 2.6 magnitude quake struck near Ferndale on Aug. 25, followed by another 2.6 magnitude event near Petrolia on Aug. 28.
While most structures in Humboldt County are built to withstand seismic activity, vulnerable architecture remains present. The predominant building types susceptible to damage during stronger shaking include unreinforced brick masonry and reinforced masonry construction, according to the USGS.
Earthquake Safety and USGS Guidelines
Federal officials recommend immediate protective action when shaking begins. According to the Department of Homeland Security, individuals indoors should drop to their hands and knees, take cover under a sturdy table, and hold on until the movement stops. Drivers should safely pull over, set parking brakes, and stay inside vehicles.
Frequently Asked Questions
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What does a Green Alert mean for an earthquake?
A Green Alert from the USGS indicates a low likelihood of casualties and structural damage.
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How do I report shaking?
Residents who felt the tremor can submit their observations via the official USGS Felt Report form.
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What are common secondary hazards?
Recent earthquakes in this region have occasionally triggered secondary hazards such as landslides and liquefaction.
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