An unusual "experimental explosion" designation appeared on the US government's earthquake monitoring website, sparking questions about a mysterious seismic event off the coast of Florida.
The US Geological Survey (USGS) detected a 3.9 magnitude seismic event east of Ponce Inlet, south of Daytona Beach, at 3:04 p.m. ET on Thursday. The event was recorded at a depth of 0 feet, suggesting the source was at or very near the surface, a characteristic more consistent with an explosion than a typical tectonic earthquake.
A USGS spokesperson told the Daily Mail that the "recorded ground motions from this event are more typical of an explosion than a naturally occurring earthquake." The spokesperson added that "the Navy has conducted Full Ship Shock Trials (FSST) in this region in the past."
These trials involve controlled underwater detonations to test the resilience of new or upgraded warships, such as aircraft carriers or combat ships, against battle-like explosions, including those from mines or torpedoes. The Navy has conducted these tests for decades, having discovered that nearby explosions can disable critical ship systems without causing significant physical damage.
In 2021, a similar event was recorded in the same location when the US Navy conducted a test explosion near its new aircraft carrier, the USS Gerald R. Ford. This type of test is known as a "shock trial."
While military testing is the likely cause for the "experimental explosion" reading, the alert caused alarm among the public. Meteorologist Nic Merianos with CBS Miami commented on X that he had "never seen this before."
These tests utilize large explosive charges, sometimes tens of thousands of pounds in past instances, to simulate battlefield conditions. The Navy states that these are planned, permitted tests with environmental considerations for marine life, and no damage or injuries are expected or reported.