AVALON, Calif. (CNS) — The U.S. Geological Survey reported a 4.0-magnitude earthquake Friday off the coast of Catalina Island, but later determined that the quake never actually happened.

The USGS initially reported the temblor at 9:48 a.m., saying it occurred 18 miles southwest of Avalon. More than a dozen people responded on the agency’s “Did You Feel It?” page, saying they felt the temblor.

Problem is, there was no quake. About an hour after the original report, the USGS’ ShakeAlert system reported that it had actually “detected a non-earthquake event which triggered our system.” The agency noted that such occurrences are rare.

“The ShakeAlert team is now making improvements based on what we learned from this event,” according to USGS ShakeAlert.