NEWS BRIEF Florida is home to several disasters: the hurricanes, the sinkholes that swallow homes, and the #Floridaman hashtag. It is not known for earthquakes. So when a magnitude-3.7 temblor struck 100 miles off the coast of Daytona Beach over the weekend, news outlets reported the phenomenon with headlines like this one from FOX4: Earthquakes in Florida?

But not so fast.

The U.S. Geological Survey picked up the rumbling around 4 p.m. Saturday. The shaking didn’t cause any damage––no earthquake has in Florida since 1879––and the Associated Press, local outlets, and Weather.com all quickly noted how peculiar it was. Some outlets even referenced another earthquake that hit in June, with the exact same magnitude, in almost the same spot. Was this the work of a dormant fault shaking to life?

On Monday, The Daytona Beach News-Journal cleared the mystery up:

It appears the “earthquake” detected on Saturday by seismographs as far away as Venezuela and across the United States and Caribbean was triggered by a man-made explosion designed to test the seaworthiness of a new U.S. Navy vessel.  

It was called a shock trial, and this is the second in a series of tests like it since 2008. The first was in June, which explains the other rare “earthquake” reported off the coast of St. Augustine, just north of Daytona. The ship being tested is the USS Jackson, an anti-submarine boat that was commissioned last December. Essentially what happens during the shock trial is the Navy detonates a massive explosion––a magnitude-3.7 earthquake-sized explosion––right next to the ship in order to test the hull. In May, Rear Admiral Brian Antonio described what happens during a shock trial to the United Naval Institute News:

“This is no kidding, things moving, stuff falling off of bulkheads. Some things are going to break.”

The Navy informed the National Oceanic and Atmospheric Administration, but apparently not any news outlets, or the U.S. Geological Survey, which recorded the explosion as an earthquake as far away as Minnesota and Texas.

Here’s a video of another shock trial on the USS Winston S. Churchill.