Aftershocks Continue After Northern California Earthquake, Tsunami Warning

Aftershocks continued Friday after a strong earthquake that prompted a tsunami warning for parts of the U.S. West Coast Thursday.

"At this time, there have been 59 earthquakes of magnitude three or greater associated with this earthquake sequence," earthquake geologist Wendy Bohon said in a Friday morning social media post. "Aftershocks will continue in the days and weeks ahead, and they will decrease with time."

"The USGS estimates that there could be an aftershock of M5+. A M6 or M7 quake is very unlikely (but low probability is not no probability)," Bohon said in a series of posts Thursday night. "Remember, no one can predict earthquakes. NO ONE."

People in parts of Northern California and Oregon fled to higher ground, zoo animals were evacuated and thousands of power outages were reported after the quake.

ADVERTISEMENT

The tsunami warning stretched down nearly 500 miles of coastline where more than 5 million people live. It was canceled a short time later and there were reports of widespread damage or serious injuries.

The earthquake's epicenter was offshore of Humboldt County, close to the state line with Oregon. Humboldt Sheriff William Honsal said some homes had cracked foundations and broken windows after the temblor but there were no major issues.

Gov. Gavin Newsom said Thursday afternoon that the state was preparing to assist if needed.

(MORE: What To Have In Your Earthquake Emergency Kit And Where To Keep It

Shaking was felt more than 250 miles south in San Francisco, where the Bay Area Rapid Transit District, or BART, suspended traffic in an underwater tunnel between the city and neighboring Oakland.

What Is A Tsunami?

Tsunamis are very long, very fast waves that are created by large displacements of water.

ADVERTISEMENT

"Earthquakes, landslides, eruptions and explosions are common sources for tsunamis," weather.com digital meteorologist Jonathan Belles said. "Tsunamis are most common in the Pacific where the volcanic ring of fire and Pacific plates align to produce multiple different sources of unbuffered tsunamis. But they are possible in any large body of water."

The San Francisco zoo closed due to the tsunami warning. Visitors were evacuated and staff and animals moved to higher ground.

(MORE: What To Have In Your Earthquake Emergency Kit And Where To Keep It)

The warning didn't include any indication of how high a potential wave could have been. Rachel Kennedy, a meteorologist with the National Weather Service office that covers the Bay Area, said it was “a pretty dangerous situation.”

The National Tsunami Warning Center said the tsunami warning spanned from Lane County, Oregon, southward to Davenport, California, including parts of the San Francisco area. Residents in many coastal areas were urged to evacuate.

ADVERTISEMENT

Further analysis of computer models showed that a tsunami was unlikely and the warning was canceled, according to the tsunami center.

"This earthquake moved the ground sideways," Bohon explained in her posts. "Underwater quakes where the ground moves up are the ones that usually generate tsunamis."

How Strong Was The Earthquake And Where Did It Hit?

According to the U.S. Geological Survey, the tremor was given a magnitude of 7.0. The epicenter was about 60 miles southwest of Ferndale, California, and was reportedly about six miles deep. It hit around 10:45 a.m. local time. The USGS said localized damage was possible.

“It was a strong quake, our building shook, we’re fine but I have a mess to clean up right now,” said Julie Kreitzer, owner of Golden Gait Mercantile in Ferndale, California.

ADVERTISEMENT

More than 10,000 power outages were reported in Humboldt County, according to PowerOutage.us.

EARTHQUAKE NorCal Update.jpg
EARTHQUAKE NorCal Update.jpg

Information from The Associated Press was used in this report.

Weather.com staff writer Jan Childs covers breaking news and features related to weather, space, climate change, the environment and everything in between.