Preparing for a landslide induced tsunami hitting the US East Coast

We should have an alert system

Nicholas Phillips

Stephan Grilli, former chair of ocean engineering,
in the University of Rhode Island’s College of Engineering (URI photo)

On Jan. 27, an earthquake measuring 3.8 in magnitude shook parts of New England. Its epicenter was near Portsmouth, New Hampshire, though the tremor was felt in Maine, Massachusetts, and Rhode Island. 

While the eastern United States doesn’t sit along major tectonic plate fault lines like the West Coast, earthquakes can still happen here. The last tremor along the Eastern Seaboard was less than a year ago, on April 5, when a 4.8 magnitude earthquake was felt in New Jersey.

These earthquakes weren’t large enough to trigger a tsunami, which typically requires a more significant seismic event, such as a magnitude 7 earthquake. 

Nevertheless, Stephan Grilli, the former chair of ocean engineering, in the University of Rhode Island’s College of Engineering, points out that just because the East Coast doesn’t regularly see earthquakes that size doesn’t mean it eliminates the risk for one.

In fact, the East Coast is regularly hit by miniscule tsunamis – about 20 a year – many of which go unnoticed, said Grilli. While earthquakes are commonly associated with tsunamis, Grilli explains that seismic activity can cause tsunamis, along with underwater landslides. 

EDITOR'S NOTE: Last Monday, Progressive Charlestown ran THIS ARTICLE after earthquake rumblings from a small earthquake off the coast of Maine rattled Charlestown. In that article, I noted that the greatest credible earthquake threats to Charlestown comes from the event come from tsunami-generating landslides and deep ocean quakes that are being studied by URI professor Dr. Stephan Grilli, subject of this URI article. DISCLOSURE: Dr. Grilli was my nephew Chris O'Reilly's mentor from Chris's undergraduate years through his Ph.D. in marine engineering. - Will Collette

Sediment from the Hudson River or Chesapeake Bay can accumulate offshore. If that sediment is nudged off the eastern part of the continental shelf into the abyss of the Atlantic Ocean, it has the potential to trigger a tsunami.

“There is no warning system in place for landslide-induced tsunamis right now,” said Grilli. “This is one very, very dangerous potential source of tsunamis on the East Coast.”

Grilli and a colleague who’s an emergency manager in Massachusetts is funded by the National Tsunami Hazard Mitigation Program. The program splits the U.S. into several regions, with the East Coast being one. The program focuses on researching the potential impacts of a major tsunami and how to mitigate the risks in the 14 states from Florida to Maine most vulnerable to such an event, which includes Rhode Island.

Grilli and his colleague are not tasked with predicting tsunamis and where they’ll happen. It’s impossible to predict when one will form. Instead, their job deals with assessing outcomes and readiness, such as inundation and the potential economic impact and how cities along the Eastern Seaboard can improve preparedness.

“Every year, the West Coast could face up to $200 million in damages if a major tsunami were to hit. On the East Coast it’s $160 million,” said Grilli.

A major earthquake, like the one off the coast of Puerto Rico in 2020, that registered as a 6.4 magnitude could generate a tsunami that reaches New England in about seven hours.

“In the deep ocean, a tsunami moves at about the speed of a jetliner but only grows about a foot high,” said Grilli. “When it gets to the shelf, it slows down, but as a result, it grows in height.”

Most cities on the East Coast have an emergency plan for more common natural disasters like nor’easters or hurricanes. Though less frequent, major tsunamis could have far more devastating consequences. Grilli notes that the rarity of tsunamis on the East Coast only helps underscore the importance of planning and preparing.

As part of the National Tsunami Hazard Mitigation Program Grilli has examined strategies implemented on the West Coast to help cities prepare for the worst-case scenario. Some strategies included establishing alert systems, creating designated evacuation routes and areas, reinforcing critical infrastructure like power plants, and even relocating vulnerable buildings. 

“In Oregon, they realized that their main high school was in an exposed place right in a tsunami zone. They did crowdfunding and got $100 million to move the school to the top of a hill,” said Grilli.

For those on the East Coast, Grilli advises taking simple yet effective precautions, such as reviewing flood maps to assess potential risks, creating an emergency plan, and ensuring that evacuation routes lead to higher ground.