Residents describe moment magnitude 6.4 quake struck northern California

The tremor, which struck at 2:30 a.m. PST ( Pacific Standard Time ) and was followed by more than three dozen aftershocks, was centred 215 miles (350 km) north of San Francisco offshore of Humboldt County, a largely rural area known for its redwood forests, local seafood, lumber industry and dairy farms.

In the town of Rio Dell, residents described the horror of the moment the quake struck.

"I was lying in bed asleep, like most people, and it just kept shaking and shaking and things were crashing. The TV was coming down, the microwave, everything, like all my little knickknacks were crashing everywhere," said Liz Peavy, a 68-year-old local resident.

"It was too scary to go under a door jamb or anything because it just kept shaking. So, it was safest to say a bed," she added.

Jacqui Macintosh, a 28-year-old Rio Dell resident, was in the process of trying to sell her house and had a viewing booked with a potential buyer on Tuesday. Her house suffered major foundational damage in the quake.

"Now that it's kind of set in, I'm just kind of like, you know, we're alive. We've got almost all our animals... we can't go back to the house. I don't think this house is going to be able to be brought back," she said.

The region also is known for relatively frequent seismic activity, although the latest quake appeared to cause more disruption than others in recent years.

Tuesday's temblor set off one structure fire, which was quickly extinguished, and caused two other buildings to collapse, according to the California Department of Forestry and Fire Protection (CalFire).

The county sheriff's office reported two people injured near the quake's epicentre, where damage to homes and roads was widespread. One of those victims was a child with a head injury and the other was an older person with a broken hip, according to local media reports citing the sheriff's office.

Police closed the main bridge crossing the Eel River into Ferndale, a picturesque town notable for its gingerbread-style Victorian storefronts and homes after four large cracks were discovered in the span. The California Highway Patrol also said the roadway foundation there was at risk of sliding.

The highway patrol reported at least four other roads in Humboldt County closed due to earthquake damage, and a possible gas line rupture under investigation. One section of roadway was reportedly sinking, the agency said.

While earthquakes producing noticeable shaking are routine in California, tremors at a magnitude 6.4 are less commonplace and potentially dangerous, capable of causing substantial damage to buildings, such as a partial collapse or the shifting of structures off their foundations.

Weak shaking from Tuesday's quake, which occurred at a relatively shallow depth of 11.1 miles (17.9 km) was felt as far away as San Francisco, the U.S. Geological Survey reported.

About five earthquakes of magnitudes ranging from 6.0 to 7.0 are recorded annually in California and Nevada, according to recent data cited by the Los Angeles Times.

Some 79,000 homes and businesses were without power in Ferndale and surrounding Humboldt County, according to the electric grid tracking website PowerOutage.us.

PG&E crews were out assessing the utility's gas and electric system for any damage and hazards, which could take several days, company spokesperson Karly Hernandez said.

Reuters