The quake occurred about 100 miles off the coast of Eureka, near the Oregon border, around 6:50 a.m. local time. There were no immediate reports of injuries or damage.
The depth of the quake was about 6.2 miles, according to the U.S. Geological Survey, which issued no tsunami warnings in connection with the temblor.
The morning jolt was followed by a quake. The magnitude 5.0 quake was about 108 miles just west of Ferndale. The quake occurred at 8:32 a.m.
So far, there have been no reports of damage in the communities of Fortuna or Ferndale, Fortuna Police Lt. Matthew Eberhardt told the Los Angeles Times. Patrol officers, he said, will be looking for any damage.
“The radio is quiet,” he said.
Eberhardt said he felt the quake while getting ready for his shift Thursday morning.
“It kind of felt like a rolling,” he said.
The quake off Eureka was felt from southern Oregon south into the Bay Area. It was also felt inland in the Sacramento Valley, the USGS said.
As of 8 a.m., nearly 2,000 people reported feeling the quake with light shaking, according to the USGS “Did You Feel It?” map.
Soon after the quake, Bay Area residents took to social media to report the shaking. Some residents said they were rattled from their sleep.
Bay Area Rapid Transit trains ran 10 minutes slower and at reduced speeds in San Francisco due to “seismic activity.”
The north coast of California is one of the state’s most seismically active areas, regularly producing major earthquakes. There had been other smaller quakes in the area in recent days.
A 6.5 quake hit the area in January 2010, snapping power lines, toppling chimneys, knocking down traffic signals, shattering windows and prompting the evacuation of at least one apartment building.
But a 6.9 earthquake in the same area, which like Thursday’s temblor was centered in the ocean, did little damage.
The north coast sits along the Mendocino Triple Junction, where the Pacific, North American and Juan de Fuca tectonic plates collide.
Seismologist Lucy Jones said the earthquake was on the Pacific-Gorda plate on the end of the San Andreas Fault.
In 2005, a magnitude 7.2 quake struck off the north coast.
Generally, seismologists say a major quake like this will be followed by numerous smaller aftershocks.
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