Did your phone light up this morning with an earthquake alert? Good news: There was no quake.
The ShakeAlert early warning system that notifies people about earthquakes as they are occurring alerted more than 600,000 people across Northern California of a magnitude 5.9 earthquake Thursday morning in Nevada. But the ground didn’t shake.
The ShakeAlert message said there was a quake at 8:06 a.m. located near Dayton, Nevada, about 15 miles east of Lake Tahoe. Within minutes, however, the notification was deleted, and the initial event report was taken off the USGS website.
Steven Sobieszćzyk, a spokesman for the USGS, said that it was a false alarm.
“There was no 5.9 earthquake near Carson City, Nevada this morning” he said. “We are currently looking into why the warning was issued, and we will provide more information when we learn more.”
Before the report was removed, the USGS ‘Did You Feel It’ survey logged only three respondents saying they had felt a quake — all of them more than 100 miles from the reported epicenter.
ShakeAlert uses buried sensors to send earthquake notifications to millions of mobile phone users, including through the app MyShake. The sensors measure the fastest, earliest ground movement from earthquakes, called P waves, which occur a few seconds before heavier shaking begins. The goal is to give an early warning before strong shaking hits, so that people can duck under tables and take other precautions.
Sobieszćzyk noted the ShakeAlert system is automated and that, while usually accurate, it has given the incorrect magnitude for an earthquake a few times.
Christie 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 very excited and then we felt nothing. We are waiting to hear from the ShakeAlert folks to find out what went wrong. They have a very low false alarm rate, so this is unusual.”
Rowe said that since the ShakeAlert system went live in October 2019, there have been 160 correct alerts, three false alerts before this one and 14 missed quakes.
“It’s a very reliable system,” she said. “False alarms are rare.”
In May 2021, the ShakeAlert system reported a 6.0 earthquake near Truckee, on the west side of Lake Tahoe. It was later determined that a smaller quake occurred, one with a 4.7 magnitude. USGS scientists said the overestimation was due to the fact that the quake occurred on the edge of the array of ShakeAlert seismic sensors, and that the problem was fixed when new sensors were added in Nevada and software was updated.
Had there been a real 5.9 earthquake Thursday morning 15 miles east of Lake Tahoe in rural Nevada, Bay Area residents might have felt some mild shaking, particularly people living on softer soils, such as areas in the East Bay near the Delta, Rowe said.
Nearly a year ago, on Dec. 9, 2024, there was a real 5.7 earthquake near Yerington, Nevada, about 15 miles southeast of the location of Thursday’s false alarm, she said.
That quake, called the Parker Butte Earthquake, was located in a desert area on the Walker River Paiute Indian Reservation. Some residents of the Bay Area and the Central Valley from Chico to Fresno reported feeling light shaking from that quake, the USGS documented.
Rowe said she doesn’t know why the false alert occurred. She noted it came not from a person, but from an “autodetect” — the automated process by which an earthquake’s location, magnitude and intensity is computed by specialized algorithms and sensors without direct human input.
Alerts were sent as far north as Redding, as far south as Fresno and across the Bay Area, said Bob deGroot, a ShakeAlert coordinator with the USGS in Pasadena. People in Truckee also reported receiving notifications. The rough estimate for the number of cell phones affected is at least 600,000, deGroot said.
The My Shake app was developed by the UC Berkeley Seismological Lab. Transmitting the data from the USGS ShakeAlert system, it is run by UC Berkeley in partnership with the California Office of Emergency Services.
In a social media post Thursday after the false alarm, My Shake administrators said, “This incident is both unprecedented and rare. Fortunately, there was no danger this morning, but this serves as a reminder that earthquake preparedness is essential.”
