Earthquake hits Northern California, triggers brief tsunami warning
A magnitude 7 earthquake struck along the San Andreas fault, triggered a now-discontinued tsunami warning from Oregon to San Francisco.
(This article has been updated to correct the location of the fault where the earthquake occurred.)
SAN FRANCISCO ‒ A magnitude 7.0 earthquake struck near the town of Petrolia on Thursday at 10:44 a.m. local time, generating a now discontinued tsunami warning that stretched from southern Oregon to San Francisco.
The quake occurred on the sparsely populated northern coast of California in a seismically complex area known as the Mendocino Triple Junction. It is where three tectonic plates meet and the Northwest’s Cascadia subduction zone and California’s San Andreas Fault system meet. The quake itself occurred on the Mendocino fault zone.
In Arcata, California, just under 60 miles from Petrolia, 25-year-old Jared Mitchell was having an early lunch in his apartment when he felt a “jolt,” he told USA TODAY.
“It wasn’t that big of a violent shake,” said Mitchell, an assistant manager at Los Bagels, a bagel shop in town. “But my apartment was swaying back and forth for a bit. It was kind of scary, like I was on a raft in the middle of the sea.”
By 12:30 p.m., less than two hours after the initial quake, the area had experienced 13 different aftershocks, ranging from 5.1 to 3.1, according to the U.S. Geological Survey. By 2:30 p.m., the USGS had reported at least 39 aftershocks of at least a 2.5 magnitude in the region, including Petrolia and Ferndale.
The National Tsunami Warning Center canceled its warning at 11:54 a.m. local time and said no tsunami observations were available to report. “No destructive tsunami has been recorded,” the center said. However, it advised the public not to reoccupy hazard zones until local emergency officials indicate it is safe to do so.
USGS initially estimated more than 150,000 people might have been exposed to earthquake shaking, between just north of Fort Bragg to Eureka. One USA TODAY reporter in San Francisco did not feel its impacts, but another resident right on the San Francisco Bay said it was the longest earthquake she’d ever felt.
Traci Grant, 53, a public relations specialist, said she was on the phone with a friend when she felt her San Francisco apartment of 20 years “swaying.”
“I felt my whole apartment was moving in slow motion,” said Grant, adding that the older building she lives in the Marina District is retrofitted. “For a moment I thought I should get my purse and my cat and get out.”
Grant said she felt it for nearly 30 seconds, “which was long enough to me.” She said nothing fell down in her apartment.
“It just kept going and going,” Grant said. “It was scary and a bit exciting at the same time. … It was more of a roll than just shake, shake, shake.”
See where the epicenter was
The Earth’s crust is made up of many tectonic plates that move slowly over the Earth’s surface. Thursday’s earthquake hit in an area that’s extremely complex, seismically speaking, said Stephen DeLong, a supervisory research geologist with the U.S. Geological Survey.
It’s near the Mendocino Triple Junction, a tectonic boundary where three plates meet: the Pacific, North American and Juan de Fuca. The Triple Junction is also the point that the Northwest’s northern Cascadia subduction zone and the southern San Andreas Fault system meet.
Thursday’s earthquakes are occurring in the Mendocino fracture zone, said Justin Rubinstein, a geophysicist with the U.S. Geological Survey in Menlo Park.
Large earthquakes also occurred near the junction in northern California in previous Decembers, according to the geological survey. There were two, a 6.1 and 6.0, near Petrolia in 2021 and a 6.4 near Ferndale in 2022.
More aftershocks expected
The USGS released an aftershock forecast on Thursday.
There is a greater than 99% probability of one or more magnitude 3.0 earthquakes in the area over the next day, a 74% chance of a magnitude 4.0 or larger, 22% chance of a magnitude 5.0 and larger and a 3% chance of magnitude 6.0 or larger.
Approximately 10,000 Pacific Gas and Electric customers in Humboldt county were without electric power on Thursday as the utility assessed its gas and electric systems. “Once it is safe to do so, PG&E will begin inspections by ground and air of its electric and gas infrastructure,” said spokesperson Megan McFarland.
Between 1850 and 2004, 51 credible tsunamis were recorded in San Francisco Bay, according to 2004 research led by Lori Dengler, a professor emeritus at Cal Poly Humboldt. Only two of those generated damage, the 1960 Chile earthquake and the 1964 Alaska earthquake, which generated waves of almost 4 feet at the Presidio, the authors reported.
Previous tsunami warning canceled
Previously, a tsunami warning advised a tsunami could arrive along the coast starting near Fort Bragg at 11:10 a.m. local time and move along the coast in northern California and southern Oregon, arriving in San Francisco at 12:10. Residents within the zone – stretching from Davenport, California, northwest of Santa Cruz, to the Douglas Lane county line in Oregon – were urged to move off the water and beach and evacuate inland beyond tsunami hazard zones.
“Move out of the water, off the beach, and away from harbors, marinas, breakwaters, bays and inlets,” the tsunami warning center advised. “Repeated coastal flooding is possible as waves arrive onshore, move inland, and drain back into the ocean.”
Just how big is a 7.0 quake?
Magnitude is a measurement of the strength of an earthquake. Officially it’s called the moment magnitude scale. It’s a logarithmic scale, meaning each number is 10 times as strong as the one before it. So a 5.0 earthquake is ten times stronger than a 4.0.
The magnitude and effect of an earthquake, according to Michigan Technological University:
Below 2.5: Generally not felt.2.5 to 5.4: Minor or no damage.5.5 to 6.0: Slight damage to buildings.6.1 to 6.9: Serious damage.7.0 to 7.9: Major earthquake. Serious damage.8.0 or greater: Massive damage, can destroy communities.
Preliminary data from the U.S. Geological Survey indicates a 32% chance of estimated economic losses of $1 million-$10 million, and a 32% chance of economic losses of $10 million-$100 million, with the chances of losses greater than that estimated at 15%.
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