6.8 Quake Shakes Northern California Coast; No Tsunami Threat

11:45 a.m. Monday Update: The U.S. Geological Survey has revised its assessment of last night's quake off the Humboldt County coast, now rating it as a magnitude-6.8 event. About 26 aftershocks have been recorded since the quake, which hit at 10:18 p.m. last night.

Original post, 12:10 a.m. Monday: The U.S. Geological Survey says a magnitude-6.9 earthquake struck at 10:18 p.m. Sunday night off the Humboldt County coast, about 250 miles northwest of San Francisco.

The Associated Press and Los Angeles Times both quote local officials as saying there were no early reports of damage or injuries. The California Office of Emergency Services reported, via Twitter, that as of 11:30 p.m. it had no reports of trouble from the coast.

The West Coast and Alaska Tsunami Warning Center said there is no danger of a tsunami from the quake.

The quake was centered about 40 miles west of Eureka, the largest town in Humboldt County, and was about 7.5 miles under the seafloor. The initial quake was followed by 10 aftershocks by midnight Sunday, the largest a magnitude-4.6 shake recorded at 10:51 p.m. The USGS "Did You Feel It?" public report page included a smattering of reports from as far away as the Bay Area, the northern Sierra Nevada and the Willamette Valley in Oregon. More than 2,000 reports came from communities around Humboldt Bay.

The offshore region is the site of the Mendocino Triple Junction, where the Gorda, Pacific and North American tectonic plates meet just north of the terminus of the San Andreas Fault.

In April 1992, a 7.2-magnitude quake, followed by 6.5 and 6.7 shocks, violently shook the coast 30 miles southwest of Eureka, causing more than 100 injuries and severe damage in several towns, including Ferndale and Petrolia.

In November 1980, a 7.2-magnitude quake centered just off the coast caused widespread damage around Eureka, including the partial collapse of a freeway overpass south of Eureka.