Major earthquake zone newly found off Tohoku

The Yomiuri Shimbun

At least three magnitude-9 level earthquakes may have occurred at intervals of 1,000 to 1,200 years in the Pacific Ocean along coastal prefectures from Aomori to Iwate, a Hokkaido University researcher concluded in study published in Kagaku (Science) magazine on Thursday.

So far, the area has not been considered a potential zone for major earthquakes.

The discovery was made by Kazuomi Hirakawa, a specially approved visiting professor at the university specializing in physical geography.

Hirakawa examined samples of tsunami deposits collected at the Shimokita Peninsula in Aomori Prefecture and other areas after the Great East Japan Earthquake on March 11.

He also analyzed data tracing tsunami over the past 3,500 years along the Pacific coast of Hokkaido and the Tohoku region.

Based on his findings, Hirakawa believes major earthquakes centered near the Shimokita Peninsula and the Rikuchu region further south occurred three times at intervals of 1,000 to 1,200 years. The first one is believed to have occurred 3,000 years ago, with another around the beginning of the first century, and the last occurring in the 12th or 13th century.

Currently, there are two known earthquake regions along the Pacific coastal area from Hokkaido to the Tohoku region.

One is the area where the March 11 quake was centered. The other is in the area from Nemuro to Erimomisaki cape in Hokkaido, where major magnitude-8 level quakes have occurred every 500 years.

Until Hirakawa's findings, there was no information about the region between the two areas.