The California Integrated Seismic Network and the U.S. Geological Survey reported today that a magnitude 6.4 earthquake struck 3 miles offshore in Northern California on December 20, 2022 at 2:34 am local time (December 20 10:34 UTC) at a depth of 11 miles (18 kilometers). The earthquake occurred about 10 miles (15 kilometers) southwest of Ferndale, California.

Ferndale is located in Humboldt County on the Redwood Coast of Northern California, about 60 miles south of the Oregon border and 200 miles north of the San Francisco Bay Area. The earthquake’s strong shaking near the epicenter (described in the ShakeMap for this event) caused widespread damages to roads and homes and power outages, according to the Humboldt County Office of Emergency Services.  Two individuals have died as a result of medical emergencies occurring during and/or just following the earthquake and an estimated 11 individuals have been reported as injured, as of the time of publication. The National Weather Service has ruled out a tsunami risk.

As of 2:30 pm local time on December 20, there have been 14 aftershocks above magnitude 3, the size where they can typically be felt near the epicenter. There have not yet been any aftershocks at magnitude 5 or higher, the size that typically results in damaging shaking. USGS scientists have issued an aftershock forecast which currently indicates a 13% chance of aftershocks of this size or greater within the next week. Smaller aftershocks are likely to continue over the next week, with scientists currently predicting up to 24 magnitude 3 or higher aftershocks. These aftershocks are likely to occur only in the area where the earthquake and aftershocks are already occurring.

This region has a history of abundant seismic activity. In fact, a sequence of overlapping earthquakes of magnitude 6.2 and 5.7 occurred nearby almost exactly a year ago on December 20, 2021. Earthquakes are common in this area because it's close to where the Pacific, North America, and Juan de Fuca plates meet, a spot known as the Mendocino Triple Junction. In the past century, there have been at least 40 other earthquakes of magnitude 6 or larger, including six earthquakes magnitude 7 or larger, within roughly 150 miles of today’s earthquake.

Sources/Usage: Public Domain. View Media Details

“This area is the most seismically active part of California,” said Keith Knudsen, Deputy Director of the USGS Earthquake Science Center. “Long-time residents have likely experienced many local earthquakes and the associated intense shaking.”

By 9 am Pacific time, more than 4500 people had responded on USGS’s “Did You Feel It?” report. More than half of those reports came in within an hour of the earthquake. Respondents in Eureka, the closest city to the epicenter, reported very strong shaking, but people hundreds of miles away in San Jose, CA, Reno, NV, and Klamath Falls, OR also reported weak shaking.

More than 3 million people were alerted to the earthquake just before early Tuesday morning via the ShakeAlert^® Early Warning System, a system created by the USGS and partners to potentially alert people that shaking from an earthquake is on its way. In California, the earthquake early warning system is overseen jointly with the California Governor’s Office of Emergency Services. ShakeAlert^® is a network of sensors that collects and shares real-time information about the magnitude, location and expected shaking from earthquakes on the West Coast to distribution partners who then deliver alerts via cell phones and the internet. Partners can also initiate automatic protective actions such as stopping trains to prevent derailments and closing water valves to protect infrastructure.

“The ShakeAlert Earthquake Early Warning System is an important tool in our risk reduction toolbox which serves over 50 million residents and visitors in California, Oregon and Washington,” said Robert de Groot, a Physical Scientist at the USGS Earthquake Science Center. “The success of ShakeAlert is a direct result of the partnership between the USGS, alert delivery partners, and state agencies like the California Governor's Office of Emergency Services, the Oregon Department of Emergency Management, and the Washington Emergency Management Division.”

Although even earthquake scientists cannot predict where and when future earthquakes will occur, ShakeAlert® provides vital seconds of warning that an earthquake is happening and shaking is imminent. ShakeAlert can save lives and reduce injuries by giving people time to take protective actions, such as moving away from hazardous areas and making sure to drop, cover and hold on.

The USGS is responding to the earthquake in partnership with various groups:   the California Geological Survey, the California Governor’s Office of Emergency Services, and the Advanced National Seismic System’s California Integrated Seismic Network and its university partners at University of California Berkeley and California Institute of Technology.

Visit the USGS earthquake event page for more information. For estimates of casualties and damage, visit the USGS Prompt Assessment of Global Earthquakes for Response (PAGER) website.

If you felt this earthquake, report your experience on the “USGS Did You Feel It?” website for this event.

For information about tsunami watches, warnings or advisories, visit the National Oceanic and Atmospheric Administration (NOAA) tsunami website.

The USGS operates a 24/7 National Earthquake Information Center in Colorado that can be reached for more information at 303-273-8500.

Learn more about the USGS Earthquake Hazards Program.

We will update this story if more information becomes available.

Earthquake Information/Resources

• Earthquake Basics
• USGS Earthquakes Homepage
• Earthquake Frequently Asked Questions (FAQs)
• USGS Roles, Responsibility, and Research
• Did You Feel It?