SAN FRANCISCO – A magnitude 7.0 earthquake off the coast of Northern California prompted a rare tsunami warning for coastal areas near the California-Oregon state line, including San Francisco Bay.

A powerful 7.0 earthquake was recorded around 10:44 a.m. PT about 60 miles offshore of Ferndale, California, according to the U.S. Geological Survey.

The 7.0 quake is the strongest in the region since at least 2005, when a magnitude of 7.2 occurred, according to the FOX Forecast Center.

The major quake promoted a Tsunami Warning from Davenport to 10 miles south of Florence, Oregon. The warning included more than 4.6 million people and was allowed to expire just before 11 a.m.

A Tsunami Warning means that a tsunami with significant inundation is possible or is already occurring.

A tsunami is a series of long waves caused by significant disruptions in the ocean, most commonly earthquakes along tectonic plate boundaries.

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San Diego State University Geologist Pat Abbott said even a small tsunami wave can do serious damage.

"You go to the beach and you see a wave rise up, break, runs up the beach and pulls back," Abbott said. "But that's not the way a tsunami is. A tsunami is not a solitary wave. It's the front of a big sheet of water coming in. So if it's even coming in knee-depth, then you can't stand up and it's going to carry you, you know, 100 feet, 1,000 feet, a quarter of a mile. And it could be beating you up with three branches and things at the same time."

‘You are in danger': Evacuations ordered for coastal areas

Shaking from the major earthquake was felt in Napa Valley and across San Francisco.

Officials in West Berkley issued evacuation orders for the tsunami zone west of 7th Street.

Emergency management in San Francisco warned residents, "You are in danger. Get away from coastal waters."

Bay Area Rapid Transportation (BART) temporarily closed Transbay Tube after the earthquake. Trains began running again before 11 a.m. PT.

Abbott said it was important the NWS issued the Tsunami Warning quickly.

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"It's best to give people time. We don't want to give fake warnings, you know, warning that there's nothing behind this kind of thing. You don't want people to lose faith in the system," he said. "But this one, it needed to go out."

Aftershocks ongoing

The USGS does expect more aftershocks. According to the USGS Aftershock forecast, "there is a more than 99% chance of magnitude 3 and above aftershocks within the next week, and it is most likely that 3 to 280 of these will occur."

Those aftershocks should decrease in intensity and frequency over time. Geologists said several dozen aftershocks have already occurred; the largest measuring a 4.7 just two minutes after the original quake. The vast majority of aftershocks have been measured under magnitude 4.0.

There is a small chance of aftershocks being stronger than the initial 7.0 earthquake.

The USGS originally reported that a magnitude 5.8 quake struck Cobb, California, three minutes after the 7.0 quake but later updated its data to reduce that quake to a magnitude 4.1.