6.4 magnitude earthquake shakes Northern California

By Aditi Sangal, Elise Hammond and Leinz Vales, CNN

Updated 7:05 p.m. ET, December 20, 2022
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12:03 p.m. ET, December 20, 2022

About 72% of Humboldt County is without power

More than 72% of customers are without power in Humboldt County, California, following a 6.4 magnitude earthquake earlier Tuesday.

According to poweroutage.us, 71,763 customers have been without power as of 8:39 a.m. PT. This is significantly increase from 55,176 customers who had lost power as of 3:15 a.m. PT. 

12:00 p.m. ET, December 20, 2022

More than 3 dozen smaller quakes struck the area after Tuesday's main temblor, USGS says

From CNN's Jason Hanna, Caroll Alvarado and Stella Chan

Damaged storefronts are seen in Fortuna, California, on December 20.
Damaged storefronts are seen in Fortuna, California, on December 20. (KRCR)

After the 6.4 magnitude earthquake struck Northern California’s Eureka area early Tuesday, more than three dozen smaller quakes impacted the territory afterward, the US Geological Survey reported.

Some were as powerful as a 4.6 magnitude earthquake.

The main quake also produced at least some shaking from coastal Oregon to south of San Jose, California, public reports collected by the survey show. It poses no tsunami threat, the National Oceanic and Atmospheric Administration said.

Tuesday’s temblor comes a year after a 6.2 magnitude quake struck just off Humboldt County’s Cape Mendocino on Dec. 20, 2021, and caused minor damage to buildings in the area.

11:27 a.m. ET, December 20, 2022

Here's what you need to know about Ferndale, one of the cities near the earthquake's epicenter

Damage is seen inside a house after an earthquake was detected near Ferndale on December 20.
Damage is seen inside a house after an earthquake was detected near Ferndale on December 20. (Courtesy Caroline Titus)

The epicenter of Tuesday's quake was in the Pacific about 9 miles from the city of Ferndale, the US Geological Survey said.

Ferndale is a city of about 1,400 people in Humboldt County, known for its Victorian homes and storefronts.

The dairy town near Eureka is considered a gateway to California’s Lost Coast and deems itself a "destination for a fun family vacation, rugged outdoor adventure or romantic weekend getaway" on its website.

Ferndale has been in or near the site of earthquakes in the last few years. A 6.2-magnitude tremor shook the town in December 2021.

10:13 a.m. ET, December 20, 2022

At least 2 injured in Northern California earthquake, sheriff's officials say

From CNN's Stella Chan

At least two people were injured after a magnitude 6.4 quake rattled Northern California early Tuesday, according to the Humboldt County Sheriff’s Office. 

The sheriff's office is still collecting information from local dispatch centers, sheriff's spokesperson Samantha Karges told CNN.

12:09 p.m. ET, December 20, 2022

Damage assessment is still ongoing, authorities say

From CNN's Stella Chan

Earthquake damage is seen outside a building in Rio Dell, California, on December 20.
Earthquake damage is seen outside a building in Rio Dell, California, on December 20. (Kent Porter/The Press Democrat/AP)

The California Governor’s office of Emergency Services (Cal OES) shared an update, saying the damage assessment work continues after a 6.4 magnitude earthquake struck Humboldt County.

“Cal OES is coordinating with local and tribal governments to assess the impacts of the Earthquake and supporting with resources, mutual aid and damage assessment. State Agency response including Cal OES, Cal Fire, Cal Trans, Cal CGS, CHP in support of local efforts,” it said.

The quake was centered in the Pacific just off the coast, about 7.5 miles from Ferndale in Humboldt County, the US Geological Survey said. That’s about a 20-mile drive southwest of Eureka and a 280-mile drive northwest of Sacramento.

9:26 a.m. ET, December 20, 2022

Here's how to stay safe after an earthquake strikes 

From CNN's Scottie Andrew

Here's a list of safety steps to take after an earthquake happens, according to the Department of Homeland SecurityEarthquake Country Alliance and Red Cross.

Wait out the aftershocks: Quakes of smaller magnitude nearly always follow the most severe shocks of an earthquake sequence, so be aware in the hours following the initial earthquake.

Get out: If you’re in a damaged building, get outside and move far away to avoid falling debris.

If you’re stuck, close your mouth: You could inhale fumes or debris, so it’s best to send a text, bang on a nearby object or whistle so rescuers can locate you.

Monitor the news: The government will likely alert the public with emergency instructions via TV, social media and radio, so look to your devices for updates.

Avoid making phone calls: Call volume has exceeded the capacity of mobile carriers’ networks after earthquakes in the past, so some calls were blocked to allow others. It’s best not to call unless it’s an emergency, so text or instant message instead.

9:28 a.m. ET, December 20, 2022

Authorities warn residents to be ready for aftershocks as damage assessment continues

From CNN's Stella Chan

The Humboldt County Sheriff’s Office warned residents to be prepared for aftershocks following the 6.4 magnitude quake that jolted the county at 2:34 a.m. PT Tuesday. 

“Due to a large earthquake, widespread damages to roads and homes are reported throughout Humboldt County. Be prepared for aftershocks. Check gas and water lines for damages or leaks. Exercise caution if traveling,” the sheriff's office tweeted

The earthquake damaged a bridge that connects to Ferndale with a population of 1,387.

“State Route 211 at Fernbridge, Humboldt County is CLOSED. The bridge is closed while we conduct safety inspections due to possible seismic damage,” Caltrans District 1 tweeted.

Smaller quakes continue to rattle the area, according to the US Geological Survey

8:58 a.m. ET, December 20, 2022

Here's how earthquakes are measured

From CNN's Emily Smith

Earthquakes are measured using seismographs, which monitor the seismic waves that travel through the Earth after an earthquake strikes.

Scientists used the Richter Scale for many years but now largely follow the Modified Mercalli Intensity (MMI) Scale, which the US Geological Survey says is a more accurate measure of size.

The Richter scale measures magnitude, whereas the MMI scale measures intensity.

Here's how each range of magnitude would feel according to the US Geological Survey, which follows the MMI scale:

8:41 a.m. ET, December 20, 2022

Bridge in Ferndale cracked due to 6.4 magnitude earthquake in California's Humboldt County

From CNN’s Rebekah Riess

California Highway Patrol (CHP) and local law enforcement are responding to a bridge in Ferndale, California, where Tuesday morning’s 6.4 magnitude earthquake caused cracks to the structure, according to CHP and Ferndale Police.

The bridge cracked in four places, there is debris in the roadway, and law enforcement are on scene to facilitate a road closure, according to CHP’s incident information page.

If the crack in the bridge “gets any bigger” the roadway may slide, CHP said, according to the Humboldt County Sheriff's Office.