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.

It wasn’t immediately clear why the ShakeAlert system was activated, or 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.

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.

“We’re in the process of figuring out what happened,” said Robert de Groot, an operations team leader for the U.S. Geological Survey’s ShakeAlert system.

There have been other times when earthquake early warnings have misfired.

In 2023, a scheduled drill of the MyShake app at 10:19 a.m. rang instead at 3:19 a.m., which occurred 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 that actually occurred was 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.