A government panel recently warned of a “high possibility” that an earthquake on the scale of the 2011 Great East Japan Earthquake will occur off the eastern coast of Hokkaido within the next 30 years.

The Headquarters for Earthquake Research Promotion called for heightened disaster preparations, saying a massive quake along the Chishima trench appears to be “imminent.”

Based on a review of the risk by seismologists, the science ministry’s research arm warns there is a probability of between 7 and 40 percent that an earthquake with a magnitude exceeding 8.8 will occur offshore along the long, narrow, steep-sided depression in the ocean floor extending northeastward from areas off southeastern Hokkaido.

There is debate among experts on whether “imminent” is the proper word for characterizing the risk.

What is important here is for our society as a whole to recognize that the figures indicate a significant risk.

According to reference information on the likelihood of such a big earthquake occurring, an event that will occur at a probability of 7 percent in 30 years is more likely than, for example, your house (in Japan) catching fire or being burglarized during the period.

Since such mega-quakes rarely occur, there is no single established method of calculating the probability of occurrence. And estimates of probabilities often change with advances in seismological knowledge. These factors impose limitations on the reliability of probability assessments for earthquakes. But the estimates made by an organization that puts probability numbers into perspective should nevertheless be taken seriously as an index of the risk.

People and businesses located in areas in Hokkaido and the Tohoku region close to the Chishima trench should quickly take steps to enhance their preparedness for a gigantic quake, including fixing furniture, bolstering the quake-resistance of buildings and making facilities less vulnerable to tsunami.

Local governments in the areas need to do more to raise awareness of the risk among local residents and build facilities as part of preparedness and mitigation efforts.

In this regard, the authorities should work with neighboring Russia on information sharing and joint research into past earthquakes and tsunami in the area.

But the predicted giant earthquake off Hokkaido is not the only one Japan should brace for.

Topping the list of predicted mega quakes that could strike Japan is one that has long anticipated along the Nankai Trough off the Pacific coast stretching from central to western parts of Japan. It has been estimated there is a probability of around 70 percent that a huge quake with a magnitude of 8 to 9 will occur along the trough within 30 years.

The Nankai Trough earthquake could cause enormous damage to densely populated areas in a region dotted with transportation hubs. It is one of the biggest risks facing Japan.

But the danger of such ocean-trench earthquakes should not make us oblivious to the risk posed by inland quakes caused by rapid movement on active faults.

While this type of quake occurs less frequently than trench earthquakes, their probabilities of occurrence tend to be low. But that is no reason to turn a blind eye to the risk.

With regard to the Great Hanshin Earthquake, which devastated the city of Kobe in 1995, a calculation based on data available at that time would have put the probability of such a quake occurring within 30 years at 0.02 to 8 percent. Still, the earth shook violently in the morning of that day.

With respect to the long-anticipated Tokai Earthquake, which is assumed will strike off the Pacific coast of central Japan, a working group of the government’s Central Disaster Management Council this summer acknowledged it is impossible to predict the temblor. It called for a review of emergency measures prescribed by the law based on the assumption that the quake can be predicted.

This policy shift may seem like a regression, but it is actually a realistic step based on the current level of seismology.

To be better prepared for such catastrophic events, Japan needs to understand that major earthquakes can occur anywhere and at any time. It needs to take at least the minimum necessary measures to minimize the damage these events can cause.

Then, based on accurate knowledge about the geographical and geological features of different parts of the nation and the probabilities of major quakes hitting the areas, anti-quake measures best suited for the conditions of each area should be taken.

The best way to minimize damage from large quakes is to eliminate “unexpected” situations one by one through such efforts.

--The Asahi Shimbun, Dec. 29