A magnitude 7.0 earthquake off the coast of Northern California prompted a rare tsunami warning for coastal areas along the California-Oregon state line, including San Francisco Bay.
According to the United States Geological Survey, a severe 7.0 earthquake struck roughly 60 miles offshore of Ferndale, California, at 10:44 a.m. PT.
The FOX Forecast Center reports that the 7.0 earthquake is the strongest in the region since at least 2005, when it registered a magnitude of 7.2.
The big earthquake triggered a tsunami warning from Davenport to 10 miles south of Florence, Oregon. The warning affected more than 4.6 million people and was set to expire shortly before 11 a.m.
A tsunami warning indicates that a tsunami with major inundation is possible or has already occurred.
A tsunami is a sequence of lengthy waves induced by large ocean disruptions, such as earthquakes along tectonic plate boundaries.
Pat Abbott, a geologist at San Diego State University, says that even a little tsunami wave can do significant 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
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The major earthquake caused trembling in Napa Valley and the surrounding areas of San Francisco.
Officials in West Berkeley issued tsunami evacuation orders for the area west of 7th Street.
Emergency management in San Francisco informed citizens, “You are in danger.” Stay away from coastal waterways.
BART temporarily shuttered the Transbay Tube following the earthquake. Trains resumed running about 11 a.m. PT.
Abbott stressed the need for the NWS to issue the tsunami warning soon.
“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 expects further 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.”
These aftershocks should lessen in severity and frequency over time. Geologists said that several dozen aftershocks had already occurred, with the strongest measuring 4.7 barely two minutes after the main quake. Scientists have measured the vast majority of aftershocks below magnitude 4.0.
There is a slight probability that aftershocks will be stronger than the main 7.0 earthquake.
The USGS first reported a magnitude 5.8 quake at Cobb, California, three minutes after the 7.0 quake, but later corrected its data to reduce the magnitude to 4.1.