From the London Mail [caution, tabloid]:
An unusual ‘experimental explosion’ entry appeared on the government’s earthquake tracking website, sparking questions about the mysterious event. The US Geological Survey detected a 3.9 magnitude earthquake east of Ponce Inlet, just south of Daytona Beach, at 3.04pm ET on Thursday.
The event was listed with a depth of 0 feet, indicating the seismic source was at or very near the surface, a characteristic more consistent with an explosion than a typical tectonic earthquake. Meteorologist Nic Merianos with CBS Miami said on X that he has ‘never seen this before.’