Second apparent experimental explosion recorded off Florida coast

A seismic event registered off Florida’s Atlantic coast on Tuesday, nearly two weeks after a similar reading rattled the same stretch of ocean, according to the U.S. Geological Survey.

The USGS recorded Tuesday’s event east of Flagler Beach at a magnitude of 3.9, with a depth listed at zero feet — a characteristic more consistent with a surface-level detonation than a typical tectonic earthquake, though the agency has not yet issued a formal classification of the event.

The reading closely resembles a July 16 event roughly 91 miles east-northeast of Ponce Inlet, which USGS did formally classify as an experimental explosion. The agency said at the time that the recorded ground motions were more typical of an explosion than a naturally occurring earthquake and noted a history of Navy testing in the same waters. The Navy later confirmed that event was tied to the future USS Ted Stevens (DDG 128), a guided-missile destroyer undergoing Full Ship Shock Trials as part of its certification under the DDG 51 Flight III program. A Navy spokesperson said the ship had completed the first of two scheduled test events for Full Ship Shock Trials, which validate a warship’s ability to withstand combat conditions using live ordnance. Afterward, the Navy said another test would occur in about two weeks, consistent with the timing of Tuesday’s event. The Navy has not yet issued a statement on Tuesday’s reading specifically. 

Full Ship Shock Trials involve detonating large underwater explosive charges near a vessel to simulate the shock of nearby mines or torpedoes, testing whether a ship’s systems and crew can withstand combat-like conditions without significant damage. The Navy has relied on the trials for decades, after finding that shockwaves from nearby blasts can disable a ship’s systems even without inflicting visible structural damage. The Navy’s tests in the region date back years — the July 16 reading was at least the ninth event the USGS has classified as an experimental explosion in the area since 2016.

No damage or injuries have been reported from Tuesday’s event. Officials have described the earlier tests as planned, permitted exercises with environmental safeguards for marine life.

Similar shock trials have been conducted on aircraft carriers, destroyers and littoral combat ships going back decades, including the USS Gerald R. Ford in 2021, the USS Jackson and USS Milwaukee in 2016, and the USS Theodore Roosevelt in 1987 — the last carrier to undergo the test before the Ford.