Residents of the Long Beach and Orange County areas reported feeling a shaking around 8:20 a.m. Monday. Laguna Beach officials confirmed they were aware of "an unconfirmed seismic-like event in the area" at that time.
A Caltech seismologist tells Eyewitness News that the USGS also received "Did You Feel It?" reports from residents in the area. But their analysis concludes the shaking was likely a sonic boom from a plane flyover.
"Based on our analysis of the waveforms for the Caltech sensors, it appears to be a sonic boom, likely due to a plane flyover," said Caltech seismologist Jennifer Andrews."We definitely see no earthquake activity in our data."
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NASA describes a sonic boom as "the thunder-like noise a person on the ground hears when an aircraft or other type of aerospace vehicle flies overhead faster than the speed of sound or supersonic."
The source of Monday's boom has not been identified, but such events are typically associated with powerful military aircraft.