A new study by Japanese scientists has revealed that tsunamis generated by major earthquakes can cross entire oceans and later rebound back to their origin, creating delayed risks for coastal regions.
The study examined the magnitude 8.8 earthquake near Russia’s Kamchatka Peninsula that struck on July 30 last year. Researchers found that the tsunami waves traveled across the Pacific Ocean to South America, roughly 15,000 kilometers away, before reflecting off the continent and returning toward Japan.
The rebound waves were estimated to have arrived in Japan approximately 48 hours after the earthquake, at a time when tsunami warnings and advisories had already been canceled. Despite the absence of warnings, waves measuring 0.6 meters were observed in Kamisu, Ibaraki Prefecture, and Kuji, Iwate Prefecture.
Initial tsunami warnings were issued along the coasts of Tokyo and 12 other prefectures shortly after the quake. The first waves reached Japan on the same day, and the largest waves, up to 1.4 meters, were recorded by July 31. Authorities lifted all advisories later that evening after determining there was no further risk of damage.
The Meteorological Research Institute simulated the tsunami using a supercomputer and seabed pressure data collected off the Tohoku region. Scientists noted that when South America was removed from the simulation, the rebound tsunami did not appear, confirming that continental reflection played a crucial role.
Tsunami advisories are typically issued when waves exceed 0.2 meters, but officials said no renewed advisory was issued as damage was not expected. However, experts emphasized that delayed tsunami waves have caused destruction in the past.
In 1960, a tsunami caused by a magnitude 9.5 earthquake off Chile reached Japan in about 22 hours, killing or leaving more than 100 people missing.
Researchers urged the public to understand that tsunami threats may persist long after the initial waves. “People must remain alert and prepared, as tsunami can arrive much later than expected,” experts said.
