ShakeAlert sends false alarm about magnitude 5.9 earthquake in California, Nevada
- - ShakeAlert sends false alarm about magnitude 5.9 earthquake in California, Nevada
Rong-Gong Lin IIDecember 4, 2025 at 7:36 PM
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A phone in the San Francisco Bay Area receives a false alarm about a magnitude 5.9 earthquake that was purported to hit near Carson City, Nev., just after 8 a.m. Thursday. No earthquake actually occurred. (Rong-Gong Lin II / Los Angeles Times)
The ShakeAlert computer system that warns about the imminent arrival of shaking from earthquakes sent out a false alarm Thursday morning for a magnitude 5.9 temblor in Carson City, Nev., that did not actually happen.
The ShakeAlert blared on both the MyShake app and the Wireless Emergency Alert system — similar to an Amber Alert — on phones across the region, including in the San Francisco Bay Area, the Sacramento area, and in eastern California, just after 8 a.m.
The problem likely stemmed from an issue with the algorithm used to calculate earthquake early warnings, according to Angie Lux, a project scientist with the UC Berkeley Seismological Laboratory.
It wasn't immediately clear how many phones got the incorrect alerts. The earthquake report was later deleted from the MyShake app — which carries earthquake early warnings from the U.S. Geological Survey's ShakeAlert system — and from the USGS earthquake website.
"We did not detect any earthquakes," said Paul Caruso, a USGS geophysicist, Thursday morning.
Read more:California earthquake early warning system: How to get it now
The ShakeAlert system has previously proved effective in giving seconds of warning ahead of expected shaking coming from significant earthquakes, including from a magnitude 5.2 earthquake in San Diego County in April; earthquakes in El Sereno and the Malibu area last year; and a temblor east of San José in 2022.
This is the first time the ShakeAlert system has issued an early warning for an earthquake that didn't actually happen, Lux said. ShakeAlert has issued 170 alerts for real earthquakes.
Read more:Unshaken: The complete L.A. Times newsletter guide to earthquake readiness and resilience
There have been other times when an earthquake early warning or test message has misfired.
In 2023, a scheduled drill of the MyShake app woke up Californians at 3:19 a.m. because the warning was inadvertently scheduled for 10:19 a.m. Greenwich Mean Time, instead of Pacific time.
And in 2021, phone users across Northern California got a warning of a magnitude 6 earthquake in Truckee, near Lake Tahoe; but the quake was actually a far more modest magnitude 4.7. Scientists said the significant overestimation of the quake's magnitude was in part caused by it being on the edge of the ShakeAlert seismic network sensors, and that researchers worked on reprogramming the computer system to avoid a similar issue in the future.
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This story originally appeared in Los Angeles Times.
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