The U.S. Geological Survey says the 5.9 magnitude earthquake alert Thursday morning was a false alarm

Did your phone light up this morning with an earthquake alert? The good news: There was no earthquake.

The ShakeAlert early warning system, which notifies people about earthquakes as they happen, alerted more than 600,000 people across Northern California about a 5.9 magnitude earthquake Thursday morning in Nevada. But the ground did not shake.

The ShakeAlert message said an earthquake occurred at 8:06 a.m. near Dayton, Nevada, about 15 miles east of Lake Tahoe. But within minutes, the notice was deleted, and the initial event report was deleted from the USGS website.

Stephen Sobieszczyk, a spokesman for the US Geological Survey, said this was a false alarm.

“There was no 5.9 magnitude earthquake near Carson City, Nevada, this morning,” he said. “We are currently looking into why the warning was issued, and will provide more information as we learn more.”

The ShakeAlert system, which gives early warning of earthquakes, issued an erroneous reading Thursday morning, Dec. 4, 2025, on phones across the Bay Area. The 5.9 magnitude quake did not occur in Nevada, according to USGS officials, who said they were looking into the cause of the system's false alert. (Photo: Julia Sulik, Bay Area News Group)

Before the report was removed, the USGS “Did You Feel It” survey recorded just three participants who said they felt the quake — all more than 100 miles away from the reported epicenter.

ShakeAlert uses buried sensors to send earthquake notifications to millions of mobile phone users, including through the MyShake app. The sensors measure the fastest and earliest ground motion caused by earthquakes, called P waves, which occur a few seconds before intense tremors begin. The goal is to give early warning before strong shaking occurs, so people can duck under tables and take other precautions.

Sobieszczyk noted that the ShakeAlert system is automated, and that while it is usually accurate, it has given an incorrect earthquake magnitude several times.

Christy Rowe, director of the Nevada Seismological Laboratory at the University of Nevada, Reno, said she received an alert on her phone Thursday morning.

“I got the warning too,” she said. “I was so excited and then we didn't feel anything. We're waiting to hear from the ShakeAlert team to find out what went wrong. They have a very low false alarm rate, so this is unusual.”

Since the ShakeAlert system was launched in October 2019, there have been 160 true alerts, three false alerts before this one, and 14 unanswered earthquakes, Rowe said.

“It's a very reliable system,” she said. “False alarms are rare.”

In May 2021, the ShakeAlert system reported a 6.0 magnitude earthquake near Truckee, on the west side of Lake Tahoe. It was later determined that a smaller earthquake had occurred, with a magnitude of 4.7. USGS scientists said the overestimation was due to the fact that the quake occurred at the edge of the ShakeAlert seismic sensor array, and that the problem was resolved when new sensors in Nevada were added and the software was updated.

If there had been an actual 5.9-magnitude earthquake Thursday morning 15 miles east of Lake Tahoe in rural Nevada, some light tremors might have been felt by Bay Area residents, especially people who live in softer soil, such as areas in the East Bay near the Delta, Rowe said.

Nearly a year ago, on Dec. 9, 2024, a real 5.7 magnitude earthquake occurred near Yerington, Nevada, about 15 miles southeast of the site of Thursday's false alarm, she said.

This earthquake, called the Parker Butte earthquake, occurred in a desert area on the Walker River Paiute Indian Reservation. Some residents of the Bay Area and Central Valley from Chico to Fresno reported feeling mild tremors from this earthquake, as documented by the US Geological Survey.

Rowe said she doesn't know why the false alert occurred. She pointed out that the matter did not come from a person, but from “automatic detection” – the automated process through which the location, size and intensity of the earthquake are calculated by specialized algorithms and sensors without direct human intervention.

Alerts have been sent as far north as Redding, as far south as Fresno and across the Bay Area, said Bob DeGroot, ShakeAlert coordinator with the U.S. Geological Survey in Pasadena. People in Truckee also reported receiving notifications. The rough estimate of the number of affected cell phones is at least 600,000, DeGroot said.

The My Shake app was developed by the UC Berkeley Seismic Laboratory. Data is transmitted from the USGS ShakeAlert system, operated by the University of California, Berkeley in partnership with the California Office of Emergency Services.

In a social media post on Thursday after the false alarm, My Shake officials said: “This incident is unprecedented and rare. Fortunately, there was no danger this morning, but this serves as a reminder that earthquake preparedness is essential.”

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