Strong Northern California Quake Triggered Brief Tsunami Warning

A magnitude-7.0 earthquake off the coast of Northern California triggered a brief tsunami warning across a swath of the U.S. West Coast. The tsunami threat was declared over less than an hour later even as the area experienced multiple aftershocks.

It was the strongest earthquake to strike the contiguous U.S. since 2019, when a magnitude 7.1 aftershock was detected in eastern California during a larger seismic outbreak.

Thursday’s quake was detected 62 miles (99 kilometers) west-southwest of the city of Ferndale at 10:44 a.m. local time, according to the U.S. Geological Survey. A tsunami warning was briefly in effect for Eureka, more than 250 miles north of San Francisco, as well as from the central Oregon coast to just north of Santa Cruz, California.

Miles Slattery, the city manager for Eureka, about 15 miles north of Ferndale, said police were evacuating areas in the tsunami hazard zone but initial damage from the quake appeared minimal. “We haven’t received a lot of phone calls about damage to structures or to gas lines or anything like that,” he said. “We’re just in a holding pattern right now.”

Thursday’s earthquake occurred along an active plate boundary off of the California coast. Jessica Turner, a geophysicist with the USGS National Earthquake Information Center, said there were four other small earthquakes along that boundary in recent days that were likely too small to be felt by people onshore.

“It doesn’t necessarily mean we knew something bigger was coming,” Turner said. “That’s pretty much background seismicity.”

Shortly after the earthquake, residents in San Francisco received an emergency tsunami alert on their mobile phones warning of a series of powerful waves and powerful currents impacting nearby coasts. “You are in danger,” the alert said. “Move to high ground or inland now.”

Office workers in areas including the San Francisco Embarcadero waterfront district evacuated from their buildings to higher ground.

There haven’t been impacts on operations at San Francisco International Airport or at Oakland Airport. Bay Area Rapid Transit has begun restoring any service outages.

The large earthquake was on the boundary between the Juan de Fuca plate and the Pacific plate, part of the Cascadia Subduction Zone. It was felt from San Jose north to Grants Pass, Oregon, and as far inland as Sacramento, about 80 miles from the coast, according to USGS, The largest aftershock so far is a magnitude 4.2, which was detected around 11:15 a.m. local time.

A 7.0 quake is larger than the one that shook San Francisco on Oct. 17, 1989, when a magnitude 6.9 earthquake knocked out power and killed 63 people throughout the region. The earthquake, called Loma Prieta, collapsed an elevated freeway and part of the Bay Bridge, which links San Francisco to Oakland. The disaster disrupted a World Series baseball game between the region’s San Francisco Giants and Oakland Athletics.

The most damaging San Francisco earthquake occurred on April 18, 1906, when the San Andreas Fault ruptured near the city, leveling buildings and igniting fires that burned for days. Together, the fires and estimated 7.9-magnitude quake are believed to have killed more than 3,000 people, destroyed about 28,000 buildings and left more than half of San Francisco’s population homeless, according to the US Geological Survey.