At least seven magnitude 9 earthquakes have occurred along the Pacific coast from Hokkaido to Tohoku over the past 3,500 years, generating huge tsunami that inundated the coastline, a new study by a Hokkaido University professor says.
Kazuomi Hirakawa, professor of natural geography at the university, drew the conclusion after analyzing deposits believed linked to tsunami at more than 400 sites from Nemuro in Hokkaido to Kesennuma, Miyagi Prefecture, in Tohoku's Sanriku region.
Deposits of seabed gravel and fossilized marine life washed ashore by each of the seven massive tsunami except the one on March 11 turned out to be identical in age at nearly all of the survey locations, Hirakawa said Wednesday.
The analysis covers a much wider area than any previous surveys.