A shake alert went out over the U.S. Geological Survey's early warning system on Dec. 4, warning that a 5.9 earthquake near Carson City in western Nevada could produce heavy shaking in the region. But moments later, the survey announced the alert, which was sent to people as far west as San Francisco, was a false alarm.

Residents across the Pacific Northwest—a region where catastrophic earthquake risk looms as an inescapable reality—depend on ShakeAlert, the country's only public earthquake early warning system, to buy precious seconds before the ground starts to move.

“On December 4, 2025, the ShakeAlert EEW system released an incorrect alert for a magnitude 5.9 earthquake near Reno and Carson City, Nevada,” the statement read. “The event did not occur, and has been deleted from USGS websites and data feeds. The USGS is working to understand the cause of the false alert.”

Several earthquakes, the largest measured at magnitude-3.3, were reported Thursday morning in Ventura County. The earthquakes were centered near Fillmore, about 25 miles northeast of Ventura. Shaking was reported in Fillmore, Moorpark, Ventura and Santa Paula.

A preliminary 4.1 magnitude earthquake struck Sunday afternoon near Glen Ellen in Sonoma County, according to the United States Geological Survey.

The United States Geological Survey put out a false alarm for a 5.9 earthquake east of Dayton, Nevada, on Thursday morning.

A notification about a magnitude-5.9 earthquake in western Nevada near the California border was a false alert, the USGS said.

Aftershocks have been recorded for both earthquakes. On Dec. 8, Japanese authorities warned an even more powerful earthquake could strike within the next week and called on residents from the northernmost island of Hokkaido down to Chiba prefecture, east of Tokyo, to be on high alert.

Two small earthquakes were recorded near Concrete on Monday morning, according to the U.S. Geological Survey. The first earthquake, measured at magnitude 2.6, was recorded at 7:06 a.m. about 4 kilometers west-southwest of Concrete. The USGS reported the quake occurred at a depth of about 5.5 kilometers beneath the surface.