The quake occurred about 100 miles off the coast of Eureka, near the Oregon border, at about 6:50 a.m. There were no immediate reports of injuries or damage.
The quake was about 6.2 miles deep, according to the U.S. Geological Survey, which issued no tsunami warnings in connection with the temblor.
According to USGS mapping, the quake, while strong, did not produce violent shaking on land.
The morning jolt was followed by another quake. A magnitude 5.0 temblor hit at 8:32 a.m. about 108 miles west of Ferndale, which is fewer than 20 miles south of Eureka.
So far, there have been no reports of damage in the communities of Fortuna or Ferndale, Fortuna Police Lt. Matthew Eberhardt told The 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 than a jerking,” 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.
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.
In January 2010, a 6.5 quake hit the area, snapping power lines, toppling chimneys, knocking down traffic signals, shattering windows and prompting the evacuation of at least one apartment building.
But in 2014, a 6.9 earthquake in the same area, which, like Thursday’s temblor, was miles off the coast, 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 early Thursday was on the Pacific-Gorda plate on the end of the San Andreas Fault.
Generally, seismologists say, a major quake like this will be followed by numerous smaller aftershocks.