Magnitude 6.4 earthquake strikes northern California

Followed by at least two aftershocks of 4.6 and 3.1 magnitude

A 6.4-magnitude earthquake has struck in northern California, plunging more than half of the hardest-hit county into darkness, causing road and building damage and leaving two people injured.

The strong earthquake was reported at 2.34am local time on Tuesday. It had a depth of 10 miles and was centred 7.5 miles southwest of Ferndale, Humboldt County – 130 miles north of San Francisco and close to the Pacific coast, according to the US Geological Survey (USGS).

The epicenter was just offshore, and followed by at least two aftershocks of 4.6 magnitude and 3.1 magnitude. The United States’ National Oceanic and Atmospheric Administration (NOAA) said that there is no current tsunami threat.

Power went out across more than half of Humboldt County as a result of the quake, with 52.7 percent of the area’s 99,000 customers in darkness at 3.10am, according to Poweroutage.us, which tracks utility service.

The region is part of California’s lightly populated far north coast, home to redwood forests, mountains, a port and a state university. Long before the state legalized marijuana, Humboldt was part of the three-county Emerald Triangle where clandestine cannabis production was legendary.

Two injuries were reported but both people were expected to recover, county sheriff’s information specialist Samantha Karges said in an email to The Associated Press.

One woman posted on Twitter that power had gone out in the Ferndale area and that her home had been left “a mess” from the tremor.

“That was a big one. Power is now out in #ferndaleca. House is a mess. #earthquake,” she tweeted along with a video showing the destruction inside her home.

A resident in nearby Sacramento said that he was alerted to the earthquake by the USGS’s Shake Alert app and noticed the blinds in his home shaking.

“The ⁦@USGS_ShakeAlert⁩ app alarm went off, warning me to expect shaking here in Sacramento from #earthquake in Eureka. I didn’t feel it my blinds did,” he said.

California state Senator Mike McGuire tweeted that he was in contact with power company PG&E and emergency management, while the state is standing by to assist people in need.

“We’re in contact with Emergency Management officials in Humboldt along with PG&E,” he said.

A road closure on California State Route 211 at Fernbridge, a 1,320-foot-long (402.3 m) concrete arch bridge that spans the Eel River near Fortuna, California (AP)

“The #earthquake was significant…6.1-6.3 magnitude. Aftershocks continue. No tsunami threat at this time. The State stands ready to provide any and all assistance needed.”

The USGS activated its Shake Alert system for those living in affected areas.

“The quake was large enough to trigger the delivery of #ShakeAlert-powered alerts to cell phones by the @fema Wireless Emergency Alert System,” the agency tweeted.

“We hope everyone is safe and if you felt shaking or got an alert you took a protective action like Drop, Cover, and Hold On.”

The earthquake comes just three days after the San Francisco Bay Area was struck by a magnitude 3.6 earthquake. That quake was felt early on Saturday morning in the East Bay area just northeast of El Cerrito, near Oakland.

California is susceptible to experiencing many earthquakes, in part due to the fact that the San Andreas Fault runs through the state.

The fault, a boundary between the Pacific Plate and the North American Plate which extends around 1,200km through California, is one of the most active fault zones in the world.

Besides California, other parts of the US have also experienced significant earthquakes in recent weeks.

Last week, Texas was rocked by its fourth-strongest earthquake in state history, when a magnitude 5.4 earthquake struck Midland in the western part of the state on Friday evening. A minor aftershock also followed that earthquake, but no significant damage or injuries were reported.

It marked the second moderate earthquake to hit the area in as many months after a magnitude 5.3 earthquake struck 95 miles west of Midland on 16 November.

AP contributed to this report