USGS seismographs have recorded a massive explosion off of the U.S. east coast east of Jacksonville, Florida today, July 28; registering as the equivalent of a 3.9 magnitude earthquake, experts say there is no risk of a tsunami to the East Coast from the blast. The blast occurred at 1:12 pm local time and was likely the work of the U.S. Navy which is conducting “shock trial testing” of a new ship.
On July 16, USGS reported a similar explosion at sea with the identical “earthquake” parameters. USGS confirmed then it was from a near-surface-level detonation event rather than a traditional earthquake which would happen well below the surface. The U.S. Navy confirmed after they were involved in Full Ship Shock Trials of the new USS Ted Stevens, a new guided-missile destroyer getting certified. While the Navy confirmed the July 16 “earthquake” was a result of their testing, they only said that another test would occur before the end of the month. While the Navy hasn’t confirmed that test occurred today, the location and intensity of today’s explosion and the overall timing offered by the Navy before strongly suggests today’s event was that follow-up explosive test.
The Navy said they’re conducting the shock trial testing in accordance with Office of the Chief of Naval Operations Instruction 9072.2, and as mandated by the National Defense Authorization Act of 2016. According to the U.S. Navy, the USS Ted Steven’s shock trials are being conducted off the East Coast of the United States, within a narrow schedule that complies with environmental mitigation requirements, respecting known migration patterns of marine life in the test area. The Navy also has employed extensive protocols throughout FSST to ensure the safety of military and civilian personnel participating in the testing evolution.
The purpose of the FSST is to ensure the ship is properly hardened to withstand battle conditions. In exercises such as these, Navy experts will analyze data captured in and around the ship from these explosions to confirm the ship is capable of dealing with potential battle conditions with real enemy forces at sea.
According to USGS, the explosion centered roughly 106 miles east-northeast of Flagler Beach on the Florida central east coast was picked up by their network of seismographs. The “experimental explosion” was recorded as a 3.9 magnitude earthquake, a significant seismic event for this region. While earthquakes are ongoing around Puerto Rico and the U.S. Virgin Islands, the area of the explosion isn’t known for any seismic activity.
Tsunamis are giant waves caused by earthquakes or volcanic eruptions under the sea. Out in the depths of the ocean, tsunami waves do not dramatically increase in height. But as the waves travel towards land, they build up to higher and higher heights as the depth of the ocean decreases. The speed of tsunami waves depends on ocean depth rather than the distance from the source of the wave. Tsunami waves may travel as fast as jet planes over deep waters, only slowing down when reaching shallow waters. While tsunamis are often referred to as tidal waves, this name is discouraged by oceanographers because tides have little to do with these giant waves.
Tsunamis are giant waves caused by earthquakes or volcanic eruptions under the sea. Out in the depths of the ocean, tsunami waves do not dramatically increase in height. But as the waves travel towards land, they build up to higher and higher heights as the depth of the ocean decreases. The speed of tsunami waves depends on ocean depth rather than the distance from the source of the wave. Tsunami waves may travel as fast as jet planes over deep waters, only slowing down when reaching shallow waters. While tsunamis are often referred to as tidal waves, this name is discouraged by oceanographers because tides have little to do with these giant waves.
A tsunami is a series of waves not simply a single event. The time between wave crests can vary from 5 minutes to an hour. The hazard may persist for many hours or longer after the initial wave. Impacts can vary significantly from one section of coast to the next due to local bathymetry and the shape and elevation of the shoreline. Impacts can also vary depending upon the state of the tide at the time of the maximum tsunami waves.
While the Pacific is better known for tsunamis, tsunami can and does occur in the Atlantic basin too. As with the Pacific basin, earthquakes can trigger a tsunami threat for the U.S. East and Gulf coasts. According to USGS, submarine landslides can be one result of an Atlantic-based quake. An offshore earthquake with a magnitude 4.5 or greater can destabilize the continental shelf, causing massive underwater avalanches. These landslides displace large volumes of water and can generate significant, localized tsunamis. This was the case during the 1929 Grand Banks earthquake near Canada, which caused a destructive localized tsunami. Distant tectonic earthquakes can also create problems; massive earthquakes along faults further away in the Atlantic, such as the Azores-Gibraltar Transform Fault near Portugal or the Puerto Rico Trench in the Caribbean, are capable of generating tsunami waves that travel across the ocean. While the infamous 1755 Lisbon earthquake created a trans-Atlantic tsunami that was recorded on the East Coast, the height of the waves reaching the US mainland was relatively small but different earthquake intensities and locations can trigger very different results.
Because there isn’t much water displaced in these near-surface explosions, while the explosions alone are significant, there’s little risk of any tsunami being generated by them, especially if there’s no related submarine landslide.
