What to Know
- Several aftershocks of magnitude-4.0 and greater were reported after Thursday's 7.0 earthquake off the coast of Northern California.
- The strongest was a magnitude-4.7 reported about two minutes after the main shock.
- In San Francisco, about 270 miles away, residents said the quake produced a rolling motion for several seconds.
- Millions of Californians were under a tsunami warning following the earthquake.
- The northwest corner of California is the most seismically active part of the state because it’s where three tectonic plates meet.
Dozens of offshore aftershocks followed a magnitude-7.0 earthquake off the coast of Northern California that led to a brief tsunami warning.
By Friday morning, nine of the nearly 200 aftershocks reported by the USGS measured magnitude-4.0 or and greater. The strongest aftershock was a magnitude-4.7 about two minutes after the main shock, which struck at 10:44 a.m. Thursday and caused shaking along the California coast and some inland areas.
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Click here to see an updated USGS map of recent earthquakes.
There have been no reports of significant damage, but residents and business owners in the region report damaged windows and ruptured water pipes. The shaking knocked items off store shelves.
About 5 million people were under a brief tsunami warning that extended from Oregon to the Bay Area. The warning expired after seismologists determined the undersea quake in California's most seismically active region was unlikely to produce a water surge and significant coastal flooding.
The earthquake was centered west of Ferndale, a small city in coastal Humboldt County, about 130 miles from the Oregon border. In San Francisco, about 270 miles away, residents said the quake produced a rolling motion for several seconds.
Weak to light shaking was reported in Half Moon Bay, Redwood City, Sunnyvale, San Francisco and other parts of the Bay Area, Santa Cruz, Eureka, Sacramento, Livermore and other areas.
"An earthquake this size doesn't happen very frequently, but frequently enough that we need to be ready for them," said USGS seismologist Robert DeGroot.
The region with an active seismic history was struck by a magnitude-6.4 quake in 2022 that left thousands of people without power and water. The northwest corner of California is the most seismically active part of the state because it’s where three tectonic plates meet, seismologist Lucy Jones said.
The quake was a strike-slip type of earthquake that shifts more horizontally than vertically. That makes a strike-slip quake less likely to cause a tsunami.
Some earthquakes are followed by a larger earthquake, in which case the first quake would then be called a foreshock. For example, the magnitude-9.1 Japan earthquake and tsunami in 2011 was preceded by a magnitude-7.3 foreshock two days earlier.
Aftershocks can continue for days, weeks, months and years. The USGS provides an aftershocks forecast.
