SAN DIEGO – U.S. Geological Survey says a “non-earthquake event” triggered a false report of a quake off the coast of Catalina Island Friday morning.

The USGS website initially reported that a quake occurred 18 miles southwest of Avalon, a town on the southern end of the island, at 9:48 a.m. But the event was later deleted, and now officials say they’re adjusting their system to account for a false trigger.

“This is a bit of a first time for us because these events happen so rarely,” USGS ShakeAlert tweeted shortly after 11 a.m.

No public alerts were issued, USGS said, because it did not reach the early warning system’s threshold of a magnitude 4.5.

“The #ShakeAlert team is now making improvements based what we learned from this event,” a second tweet said.

ShakeAlert coordinator Robert de Groot described the trigger as a “noise glitch,” but said it wasn’t yet clear if the glitch was purely technical or if something in the external world made the “noise.”

Four of the agency’s seismometer stations have to get the same reading before triggering an earthquake report, de Groot told FOX 5 by phone. There are hundreds of monitoring stations scattered around Southern California, and confirming that multiple monitors got the same reading helps prevent an anomaly from triggering ShakeAlert.

In this case, four separate stations all registered whatever caused the false alarm. Additionally, some people reported shaking on the agency’s “Did You Feel It?” map for the area.

De Groot and his team will now work to determine what prompted the reading.

“Earth does weird stuff all the time,” he told FOX 5, calling the incident a “learning opportunity” for ShakeAlert that warrants weeks of investigation and tweaking to the system.

The false report came just over 12 hours after a 4.6 magnitude earthquake near Ensenada rattled San Diego.