Computer glitch causes USGS to incorrect report 4.0 quake off Southern California

Seismograph with paper in action and earthquake - 3D Rendering
(Petrovich12 /

Scientists say mysterious ‘noise’ triggered a quake announcement


The U.S. Geological Survey said Friday that an unidentified computer “glitch” led the agency to mistakenly tell the public earlier in the day that a magnitude 4.0 earthquake had occurred at an offshore fault not far from Santa Catalina Island.

“There was ‘noise’ somewhere in the Southern California Seismic Network that triggered four seismic stations on land,” said Bob de Groot, a scientist at the USGS office in Pasadena.

“We don’t know if it was something internal, or external, to our system. We’re going to find out.”

The USGS initially posted an advisory saying that the 4.0 quake occurred at 9:48 a.m. at a point roughly between Santa Catalina Island and San Clemente Island. The notice was widely reported by the news media, including the San Diego Union-Tribune.

De Groot posted a correction on Twitter about 15 minutes later. The agency was able to do so before its computers generated a ShakeAlert, an electronic message that’s meant as a cautionary note to emergency responders, government agencies and the public.

“This is the first time that something like this has happened,” de Groot told the Union-Tribune. “We are relieved that it involved a relatively small event and that a ShakeAlert was not generated.”

The incident came less than 24 hours after a 4.6 earthquake occurred off Ensenada, Mexico, producing shaking that was felt in San Diego County.


2:42 p.m. April 15, 2022: This story has been updated to say that the USGS mistakenly reported that a 4.0 quake had occurred off Southern California.