On December 19th, a government panel released its projections of the probability and scale of quakes that might happen along the Chishima Trench.
Massive earthquakes have struck the area at intervals of about 350 years. The last one was 400 years ago.
The panel's members say the probability of such a quake in the next 30 years is 7 to 40 percent.
The head of the panel, University of Tokyo professor Naoshi Hirata, says, "A quake like the March 2011 temblor off northeastern Japan could happen. We want people to remember that a tsunami occurs when a big quake strikes off the coast."
Regional officials are concerned with the projections. Hokkaido prefectural official Hiroki Mori says, "We take the evaluation very seriously. We always have to be prepared for a possible quake."
The Chishima Trench has been the location of numerous quakes
There was one off the Nemuro peninsula in 1973. In 2003, a magnitude 8.0 quake struck just off Tokachi, causing a tsunami of four meters hit the town of Erimo.
The latest analysis by the panel estimates the quake zone to be in areas off Tokachi and Nemuro, and off the islands of Shikotan and Etorofu.
The report also warns that there is a high chance of an imminent mega-quake that will trigger large tsunamis off eastern Hokkaido.
Akio Nakayama is in charge of crisis management at the city of Kushiro, which lies on the Pacific Coast. He says, "We hope to review our current earthquake and tsunami measures and take action."
The latest projection was based on deposits of sand and other materials carried ashore by major tsunamis in the past.
Even before the March 11 quake six years ago, deposits from previous tsunamis were found along the coast of northeastern Japan. But those findings weren't incorporated into disaster preparedness measures. They were included in the latest evaluation.
The panel has been reviewing its estimates of mega-quakes along trenches and troughs. The one concerning the Chishima Trench is the third such review.
In 2013, the panel said there was a 60 to 70 percent chance of a mega-quake between magnitude 8 and 9 hitting the Nankai Trough in the Pacific in the next 30 years.
Expert calls for preparing against all possibilities
Tohoku University professor Fumihiko Imamura stresses the need to eliminate unanticipated risks when preparing for massive earthquakes and tsunamis.
Imamura says various studies show that if a huge quake occurs in the Chishima Trench, there is a strong chance of tsunamis higher than 20 meters, similar to those in March 2011, hitting the shores of Hokkaido. He adds that tsunamis may also hit the shores of northern Tohoku in such a case.
Imamura says the government panel's analysis of the Chishima Trench suggests that the possibility of such disasters hitting Hokkaido is more imminent than previously thought.
He says the government projections are the result of nationwide scientific efforts to eliminate unanticipated risks, taking lessons from the March 2011 disaster.
The government also plans to release predictions on the heights of tsunamis, and the time it'll take for the waves to reach the coasts.
Imamura says he wants municipalities to make full use of such data and make concrete evacuation plans to save lives.
He says not only regional governments but also residents should think intently about specific problems that may arise in disaster situations. These include how effective cars will be during such events, and how to prepare evacuation shelters.