What happened
A research team led by Fumiaki Tomita at Tohoku University found that the Japan Trench is locked and building seismic stress again, similar to conditions before the March 11, 2011 earthquake and tsunami.
The 2011 magnitude 9.0 quake ruptured a large section of the undersea fault where the Pacific Plate slides beneath Japan. It devastated Japan’s northeast coast, caused approximately 20,000 deaths and disappearances, and triggered the Fukushima Daiichi nuclear disaster.
The tsunami crossed the Pacific and caused about $100 million in damage across dozens of US ports and harbors. Crescent City, California suffered the worst effects, with all docks in its small-boat basin heavily damaged or destroyed, 16 boats sunk, and an estimated $28 million in local damage. Dustin Douglas Weber, a 25-year-old photographing the wave near the Klamath River, was swept out to sea and killed.
Tomita’s team studied ancient tsunami deposits in coastal lowlands and used GPS-style instruments to measure seafloor and land movement for 14 years after the 2011 disaster. They found that post-earthquake plate sliding largely stopped by 2021, meaning the fault has relocked and is storing energy again only a decade after the last giant event.
Historical sand layers suggest magnitude 9.0 earthquakes along this trench section typically recur every 500 to 900 years, with the previous similar event occurring in 869. However, the researchers warned in the journal Science that a relocked megathrust can rupture earlier than the centuries-long average, citing the July 2025 magnitude 8.8 earthquake on Russia’s Kamchatka Peninsula as a comparable example.
If a similar-strength earthquake occurs again, scientists say it could send another tsunami across the ocean, endangering the US West Coast and Pacific territories.