Special Reports

Government Panel Warns: Great Earthquake Possible in Tohoku Region Within 30 Years

Published

5 years ago

March 7, 2019

The government’s Earthquake Research Committee released a new long-term evaluation of the likelihood of future seismic activities in the Tohoku region of Japan, urging the public to stay alert.

There’s a 90% probability that a magnitude 7-class major undersea temblor will take place off Miyagi Prefecture within 30 years, the committee said on February 26.

The report evaluates the risk of earthquakes along the Japan Trench off the Tohoku region, the northern part of Japan’s Honshu main island where the Great East Japan Earthquake and Tsunami hit eight years ago, on March 11, 2011.

Naoshi Hirata, chairman of the committee, noted: “The repercussions of the March 11, 2011, megaquake have remained alarmingly high even today with earthquakes of magnitude 7 to 8 seen arising with very high probability. We want the public to fully keep in mind the risks of strong quakes and tsunami hitting regions facing the trench again.”

The likelihood of a powerful magnitude 8-class earthquake on the open-ended Richter scale in the next three decades off the coast of Aomori Prefecture and elsewhere is also high, the panel warned.

Big earthquakes followed by tsunami have taken place repeatedly since time immemorial along the Japan Trench, the deep-sea chasm running almost parallel to the Pacific coastline of the Tohoku region and veering a little eastward off Boso Peninsula, Chiba Prefecture. This time, in light of the 2011 megaquake, the scale of which was beyond experts’ expectations with magnitude 9.0, the Earthquake Research Committee conducted a thorough review of its conventional seismic assessment.

The committee’s latest assessment took into consideration earthquakes of around magnitude 7.4 focusing off the coast of Miyagi Prefecture, which have taken place at intervals of about every 38 years, as the committee evaluated before. This time, however, it also considered those of magnitude 7.0 to 7.5 closer to the depths of the trench.

This enabled the panel to make the new projection that there can be a probability of about 90% of a major quake measuring magnitude 7.0 or greater hitting the prefecture within the next 30 years.

The likelihood of strong earthquakes of magnitude 7.0 to 7.5 is also very high — at more than 90% — in the areas stretching from waters off eastern Aomori Prefecture to waters off northern Iwate Prefecture. These are areas adjacent to the focus of the 2011 megaquake, where remnants of the fault rupture continue to be an influence, the assessment warns.

The probability of a quake of magnitude 7 or more off the coast of Fukushima Prefecture has been raised to 50% from the earlier anticipated 10%.

The possibility of a magnitude 7.9 earthquake hitting off the eastern coast of Aomori Prefecture and off the northern coast of Iwate Prefecture, which have been subjected to tsunami four to six meters in height in the past, ranges from 5% to 30%, unchanged from the committee’s earlier evaluation. But the likelihood of such a tremor off the coast of Miyagi Prefecture has risen to 20%.

The probability of a conventional type of earthquake off the coast of Miyagi Prefecture, the last of which occurred at the same time as the 2011 megaquake, has diminished to 50%, according to the study. However, the figure can increase, depending on future seismic activities, the committee said.

Analyses of sediment produced by the 2011 earthquake and conveyed ashore led the committee to consider that the likelihood of another megaquake-type temblor, which is believed to jolt the coastal areas of the Tohoku region once every 550 to 600 years on average, is close to zero within the next 30 years. This is unchanged from earlier projections.

(Click here to read this article in its original Japanese.)

Author: The Sankei Shimbun