A powerful 7.0-magnitude earthquake struck Northern California Thursday morning, causing shaking as far south as the Bay Area and prompting a brief tsunami warning for coastal regions.

The quake, dubbed the 2024 Offshore Cape Mendocino earthquake, hit at 10:44 a.m. and was centered about 10 miles southwest of Scotia in Humboldt County.

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It followed two smaller tremors the day before, at magnitudes 4.2 and 4.4.

A tsunami warning was issued across Northern California, urging coastal residents to evacuate immediately to higher ground. However, within an hour, federal officials downgraded the warning, stating that no significant tsunami waves were expected. Although the tsunami did not materialize, authorities at all levels stressed that there was significant initial concern, and it was not a false alarm.

Dozens of aftershocks have hit Northern California following the magnitude 7.0 quake that struck off the Cape Mendocino coast on Thursday morning. At least eight of the aftershocks have measured at 4.0 or above on the Richter scale, with the biggest of those hitting 4.7 two minutes after the initial quake. the U.S. Geological Survey says aftershocks can continue for weeks.

Scientists anticipate aftershocks in the coming days to weeks. Previous earthquakes occurring at the Mendocino Triple Junction (where Thursday's 7.0-magnitude quake occurred) have set off aftershocks at a strength that has gotten close to the original earthquake’s magnitude, but not higher, according to seismologist Lucy Jones.

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Preliminary data suggests the fault that triggered the powerful earthquake ruptured from west to east, Jones said, adding that this style and location of faulting, Jones explained, means there is a chance an aftershock could occur on the San Andreas Fault. Read more here about the aftershock risk.

Less than an hour after being issued, the tsunami warning from the U.S. National Tsunami Warning Center, which is run by the National Oceanic & Atmospheric Administration, was canceled. Temblor CEO and Stanford Geophysics lecturer Ross Stein gave ABC7 News an explanation for the change. He said the earthquake initially appeared to be a 6.0-magnitude shallow earthquake, the kind that involves “a lot of vertical motion of the seafloor, which tends to produce more tsunamis.”

It didn’t take long, however, for scientists to realize it was a much larger 7.0-magnitude earthquake and a different type of earthquake that is unlikely to produce a large tsunami, he said.

It was “a very typical, garden-variety event on this northern extension of the San Andreas Fault, which we call the Mendocino Fault Zone. In that respect it doesn’t move the sea floor up and down very much,” said Stein.

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After the earthquake hit, some damage was seen in Ferndale, Calif., 260 miles north of San Francisco, at Valley Grocery and the Victorian Inn.

In response to the earthquake and tsunami warning, SFMTA said that it coordinated closely with the Department of Emergency Management “to ensure we were prepared to keep our workers and riders safe. Following emergency guidance, we closed downtown stations, and rerouted vehicles away from coastal zones.”

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“We are following all protocols for assessing any damage and debriefing from the Emergency Operations Center,” said Erika Kato, an SFMTA spokesperson.

Kato also said that Muni issued switchbacks on the N and L trains at Sunset Boulevard. “Due to the timing of the announcement, some trains had already reached the outer terminals. Additionally, because of the length of the disruption, only two to three trains were affected on those routes.”

At Fort Mason in San Francisco, Diana Kowalsky was at work at the Radhaus beer hall when she and other staff got the warning to evacuate. “Most people ran up the hill for safety,” she said. The evacuation order meant Radhaus had to shut off ovens and fryers. A large party was waiting to be seated once the order lifted. “We are barely ready for this,” Kowalsky said with a laugh.

Still, she said, the evacuation order would likely mean a slower day than usual.

The earthquake magnitude scale is logarithmic, so each whole number increase reflects a tenfold increase in amplitude—meaning a 7.0 quake is 10 times bigger than a 6.0.

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Here’s a breakdown of the earthquake magnitude scale and its potential impact, according to Michigan Technological University:

2.5 or less: Usually not felt, but can be recorded by seismographs. Estimated occurrences: Millions per year.

2.5 to 5.4: Often felt, but typically causes only minor damage. Estimated occurrences: 500,000 per year.

5.5 to 6.0: May cause slight damage to buildings and structures. Estimated occurrences: 350 per year.

6.1 to 6.9: Can cause significant damage in highly populated areas. Estimated occurrences: 100 per year.

7.0 to 7.9: Major earthquake with potential for serious damage. Estimated occurrences: 10-15 per year.

8.0 or greater: Great earthquake capable of completely destroying communities near the epicenter. Estimated occurrences: One every 1-2 years.

“We don’t expect large (aftershocks) to occur at great distances from this event and the most common aftershock sequence would be a series of smaller earthquakes within several, perhaps tens of miles or something from the original earthquake,” said Stephen De Long of the U.S. Geological Survey. “And there’s a lower probability for something farther away.”

Justin Schorr, a rescue captain with the San Francisco Fire Department, said that Thursday’s tsunami warning, later canceled, was the highest level of alert for tsunami events.

“The scientists were so concerned that they skipped over the other two levels of alert and they went straight to the highest one,” he said

Gov. Gavin Newsom says that the state usually issues tsunami warnings anytime there’s an earthquake of a 5.0 magnitude or greater near the coast. Early damage assessments are being made, he told reporters during a Thursday press conference. He said he approved a state emergency declaration to provide additional resources in the area.

The magnitude 7.0 earthquake is believed to have occurred along the seismically active Mendocino Fault, which sits in an area where three tectonic plates converge, sometimes called the Mendocino Triple Junction. The area has experienced four magnitude 6 or greater quakes over the past decade, the most recent being on Dec 20, 2022, a temblor that triggered rockslides and caused minor home damage in Humboldt County, according to the U.S. Geological Survey. The earthquake was the strongest in the area since 1992, when the 7.2 magnitude Cape Mendocino Earthquake struck.

“Aftershocks are possible. Be ready for more shaking and be ready to take protective action,” said Robert deGroot of the US Geological Survey, on a press call. Aftershocks are unlikely to take place far from the epicenter, Stephen DeLong of USGS said.

Justin Schorr, a rescue captain with the San Francisco Fire Department, said residents shouldn’t view Thursday’s alerts and evacuation warnings as a false alarm. “This was an actual threat,” Schorr said.

Following the NWS alert, teams of law enforcement officers from police, National Park Service and other agencies took to the coastline with loudspeakers, telling people to get out of the water.

About 30 minutes after the earthquake, San Francisco officials began receiving word of an anticipated arrival time of a tsunami wave coming at 12:10, Schorr said.

“We also want to remind people that that’s always an estimate,” he said. “Don’t wait and say, ‘I can make it uphill in 10 minutes.’”

Schorr said it’s unclear yet how many people evacuated from the coastal areas, but said overall the reactions were mixed. Some people did as they were told, while others were seen headed toward the coastline to watch.

“There’s nothing to see in a tsunami event,” Schorr said. “By the time you can see it or hear it, it’s too late.”

Thursday’s earthquake was “well above” established seismic thresholds that could cause a tsunami, according to Amy Palmer, a spokesperson for the Governor’s Office of Emergency Services, speaking on the widespread tsunami warning that was later canceled.

The local governments that issued alerts and the residents that complied “did the right thing” even though the warnings are disruptive, Palmer said.

“The challenge in all emergency communications is getting the right information to people at the right time,” she said. “But we can’t take chances or roll the dice that a tsunami may not hit when there is a tsunami warning in place.” Palmer said her office took cues from the National Tsunami Center under the National Oceanic and Atmospheric Administration, including issuing guidance and working with local government partners shortly after getting a tsunami warning from the federal agency.

The California Department of Conservation’s tsunami map website experienced outages Thursday morning after the warnings across the California coast. The warning was later canceled, but the department’s website, displaying an “HTTP Error 503,” was overwhelmed by heavy traffic from residents searching for tsunami maps. While the site was briefly restored, it went down again shortly after. Meanwhile, alternative emergency sites, including SF72 and the Office of Emergency Services’ MyHazards site, remained operational, though with slower load times.

California is sending immediate assistance to Humboldt and Del Norte Counties to help with emergency operations, according to a post on X from Senate President Pro Tem Mike McGuire, D-Geyserville. “There are reports of some homes that have come off of foundations in the greater Eel River Valley region of Humboldt. Approx 10k customers are currently without power.”

Several minutes after the tsunami alert was lifted, a few people returned to Ocean Beach near Judah Street. Most were unaware the warning had been lifted and one couple was unaware it had even been issued. “You’re kidding,” said a man who did not want to give his name said. At 12:10, well after the warning was canceled, a San Francisco Fire Department pickup truck was still warning people “Get off the beach. When it hits you won’t be any help down here.”

Andre Sea, a 43 year old teacher, lives within a block of the beach and came to see the tsunami. “My house is right there,” he said, pointing. “So if it hits, I’m going to drown anyway.” Jamie Guajardo, a disabled veteran and South Lake Tahoe resident, was at an appointment at the Veterans Administration when he heard the alert. He headed to the beach. “To be honest, I wanted to be present if anyone needed help,” he said, holding a cane in his right hand. “I was in the Marine Corps for years and it’s what we do.”

A cargo ship stacked high with colorful containers could be seen heading to sea as the tsunami warning approached. But shortly after it was lifted, the ship reversed course and appear to be returning to the Golden Gate and the bay.

Pacific Gas & Electric’s website said some customers near the coast and Humboldt Redwoods State Park had lost power. The quake’s epicenter was off the coast near Eureka, the biggest city in Humboldt County.

There were no reports of injuries or major damage in Humboldt County before noon, according to Rex Bohn, a county supervisor. Bohn said the Providence hospitals in Fortuna and Eureka also did not report any major issues.

A series of aftershocks continued to shake Northern California following the 7.0-magnitude earthquake that struck earlier Thursday. The U.S. Geological Survey reported multiple tremors in quick succession, ranging in magnitude from 3.1 to 4.4. The first aftershock, a magnitude 3.1 quake, occurred just minutes after the initial tremor, with several others following closely behind. These aftershocks were centered near Petrolia, Ferndale and Scotia all within roughly 60 miles of the quake’s epicenter in Humboldt County. Experts have warned that aftershock activity could continue for several days, with the risk of further seismic events in the coming week.

The 300 people of unincorporated Petrolia, part of the “Lost Coast” region of high Northern California, took a stiff hit from the quake, knocking down trees and emptying shelves at one of the main stores in town.

“There are some trees that fell down in the street, and everything shook — stuff came off our shelves,” said Dolly Pawar, who works at the Ruth Store downtown. “But I think we’re OK here. This is a very remote area, not many people around. Not much here to fall down.”

BART resumes normal train service with systemwide major delays: The agency said service had resuming after previously holding trains outside the Transbay Tube.

The agency is going back to normal service after the tsunami warning was canceled. Previously, the F Market and 25 Treasure Island routes were temporary suspended. Some buses on the western side of San Francisco were requiring riders to get off early.

All evacuation orders in Berkeley have been lifted, police say, as the tsunami warning was canceled.

The agency said the F Market and 25 Treasure Island routes are temporarily suspended. It is also “switching back” all routes on the west side of San Francisco, which requires all riders to exit and the train or bus to go in the opposite direction. “Likely” affected lines include the 5, 7, 18, 31, 38, 38R, 48, and 58.

The ShakeAlert advance earthquake warning system was activated Thursday morning and sent alerts to cell phones as far north as Lincoln City, Ore. and as far south as Salinas, according to the U.S. Geological Survey.

USGS officials said that how much advance notice people got depended on their distance from the earthquake but preliminary reports suggest those 20 to 30 miles from the epicenter got about a second of warming time.

“It performed as designed,” said Robert DeGroot, operations team lead for the USGS Shakealert system.

Both the San Francisco Bay Ferry and Golden Gate Ferry said they were operating normally prior to the tsunami warning being canceled. The S.F. Bay Ferry runs between San Francisco and the East Bay, while the Golden Gate Ferry connects the Ferry Building to Marin County.

Christine Goule, Director of the USGS Earthquake Science Center, confirmed there was a 7.0 magnitude earthquake that hit just offshore Petrolia California. A second earthquake that alerted residents near Cobb, California was “overestimated,” Goule said. “It was a much smaller event, and reassessed as a 2.5 (magnitude).”

“There were a flurry of much smaller aftershocks, that’s what we have so far, that’s what we know, and we’re monitoring the situation,” Goule said.

The aftershock risk is expected to continue for a week. With such quakes, the trend is “that the aftershocks will decrease in intensity, so how large they are and how often they happen,” Goule said.

The USGS predicts the risk of aftershocks in a forecast: https://earthquake.usgs.gov/earthquakes/eventpage/nc75095651/oaf/overview. “For the next week we can expect 6% chance or so of a magnitude 6.0 or larger. For (magnitude) 5 and above the probability is closer to 40%,” Goule explained.

The US Geological Survey said in a conference call that a tsunami warning is expected to be canceled at noon. No significant tsunami waves are expected from this event. The only tsunami wave detected was off Marina Cove, and it was just 10 cm in height. No other tsunami waves have been detected at any offshore buoy sites. This was a strike-slip fault, as opposed to a subduction fault, so it’s less likely to cause tsunamis.

The Bay Area Rapid Transit system is experiencing significant delays in all directions due to an earthquake. According to an official alert from BART, service to and from San Francisco through the Transbay Tube has been temporarily halted. “Please seek alternate means of transportation,” the agency said. The delay is affecting the entire system, and passengers are encouraged to monitor updates from BART for further information. Travelers should plan for possible extended delays.

“We are activating our Emergency Operations Center in response to the Tsunami Warning,” SF mayor London Breed tweeted. “Please move off the coast and at least one block inland. Public safety personnel are deploying to the coast to warn people to move inland.”

The city of Berkeley ordered the evacuation of a massive swath of the city following Thursday’s earthquake. At 11:30 a.m., city officials ordered people to evacuate all areas west of Seventh Street, including Interstate 80. “LEAVE NOW,” the alert said.

A Marin County tsunami warning via phone call says to expect a tsunami at noon p.m.

Phones across the Bay Area buzzed on Thursday with a tsunami warning from the National Weather Service that read, “A series of powerful waves and strong currents may impact coasts near you. You are in danger. Get away from coastal waters. Move to high ground or inland now. Keep away from the coast until local officials say it is safe to return.”

Humboldt County deputies are sounding their high-low sirens warning residents to evacuate the coastline due to expected tsunami.

Vallejo schools said people can pick up kids if they want. (Correction: a prior post said Pacifica schools were evacuating.)

Evan Sernoffsky, SFPD spokesperson: Police are on alert, urging everybody to follow the warnings of the U.S. tsunami system. Anybody near the coast should seek higher ground

People are asked to stay east of 7th Street. Nixle: https://nixle.us/FZ3E9

The Northern California coast has a long history with tsunamis, but some of the worst have been caused by earthquakes in Alaska. In 1964, a 9.2 magnitude earthquake near the Aleutian Islands caused a tsunami with surges 21 feet high that killed 12 people and caused major destruction in Crescent City, which is about 114 miles north of Ferndale in Del Norte County.

Ferndale is close to what’s called the triple junction of three tectonic plates, the North American Plate, the Pacific Plate and the Juan de Fuca Plate. They meet where the San Andreas Fault meets two other faults including the Cascadian Subduction Zone, a 700-mile fault that extends from Northern California to British Columbia.

In December 2022, a 6.4-magnitude earthquake with an epicenter off the coast of Ferndale rattled the area in the middle of the night and caused injuries but no tsunami.

The National Tsunami Warning Center issued a tsunami warning Thursday morning following a preliminary 7.3 earthquake in the waters off Eureka that is expected to have waves reach San Francisco by 12:10 p.m.

It is unclear how large the waves might be, scientists are still examining the potential strength. Residents are being warned to stay away from beaches and coastlines.

The tremor came on the heels of two smaller tremors in the same area on Wednesday, which registered magnitudes of 4.2 and 4.4, though those did not trigger alerts.

A 5.8-magnitude quake followed three minutes later and 150 miles away near Cobb, just north of Santa Rosa.

While there were no immediate reports of widespread damage, the earthquake revived memories of previous seismic events, including the 6.0 magnitude earthquake that struck Napa County in 2014, which caused extensive damage to buildings and infrastructure, buckling roads and cracking foundations.

BART Transbay tube service was halted.

The San Francisco Zoo & Gardens has temporarily closed in response to a tsunami warning issued for the area by the National Weather Service. In a statement shared on its official Twitter account, the zoo announced, “Guests have been evacuated, animals secured and staff have moved to higher ground.”

Tsunami sirens went off on the coast, including in Bonny Doon in Santa Cruz County.