The US Geological Survey detected a 3.9 magnitude earthquake east of Flagler Beach, Florida, on Tuesday, listed on its site as an "experimental explosion." It is the second such event recorded off the northeast Florida coast in less than two weeks.
The quake was listed with a depth of zero feet, indicating the seismic source was at or very near the surface, a characteristic more consistent with an explosion than a typical tectonic shake.
The location is about 20 miles from where a similar event was recorded on July 16 east of Ponce Inlet, an area where the US Navy is known to conduct Full Ship Shock Trials. The trials test how new or upgraded warships, including aircraft carriers and combat vessels, withstand battle-like explosions near mines or torpedoes.
A Navy spokesman said after the July 16 event that the future USS Ted Stevens had completed the first of two planned trials, part of the certification process for its DDG 51 Flight III destroyer program.
In 2021, a test explosion occurred near the new aircraft carrier USS Gerald R Ford, also off Ponce Inlet.
Public reaction
One X user wrote: "What the hell is going on? This is the second 3.9 magnitude 'experimental explosion' earthquake off northeast Florida in the last two weeks. Same spot, same magnitude." Another user pointed out that no explanation had been attached to the USGS listing.
How the tests are tracked
The USGS records experimental explosions because its network of highly sensitive seismographs detects the ground vibrations they produce. Seismologists then analyze the signals to distinguish human-made blasts from natural earthquakes. Such events are typically linked to controlled military exercises, including underwater ship shock trials, as well as scientific seismic research and industrial mining operations.
Navy tests use large explosive charges, in past cases tens of thousands of pounds, to simulate battle conditions such as nearby mines or torpedoes and gauge warship resilience. No damage or injuries have been reported, as the tests are planned and permitted with environmental considerations for marine life.
The Navy has conducted these trials for decades after finding that nearby explosions can disable critical ship systems without causing major physical damage. Recent tests have included the littoral combat ships USS Jackson and USS Milwaukee in 2016, the USS Mesa Verde in 2008, the USS Wasp in 1990 and the USS Mobile Bay in 1987. The last aircraft carrier to undergo the trial was the USS Theodore Roosevelt in 1987.
The Navy and USGS have been contacted for comment.
