USGS: Mysterious 'Non-Earthquake Event' prompted report of 4.0 magnitude shaking off L.A. coast

Intensity map.
USUS Community Intensity Map Photo credit USGS

LOS ANGELES COUNTY (KNX) — Federal seismologists clarified reports of a magnitude-4.0 earthquake striking near Catalina Island off the coast of Los Angeles Friday morning, calling it a "non-earthquake event" that triggered a false alert.

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The Shake Alert early warning system employed by the Geological Survey detected the false tremor, the scientific agency said late Friday morning, noting that no public alerts were distributed because of the error.

"This is a bit of a first time for us because these events happen so rarely," the USGS said on Twitter. "Apologies for any confusion from our previous tweets."

The agency said its app development team was working to make improvements to the system based off what they learned from this event.

Asked whether a source of energy triggered that large-tremor warning, the USGS said it was "looking into it."

The earthquake had reportedly rumbled at approximately 9:48 a.m. Its epicenter is believed to be about 18 miles southwest of the island city of Avalon and 44 miles south of San Pedro, according to the United States Geological Survey. The earthquake struck at a depth of roughly 5 miles, USGS experts had said.

There were no reports of any damages or injuries.

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