The latest long-term forecast by the government’s Earthquake Research Committee says there is a high probability that a killer earthquake on a scale of magnitude 7 to 8 will occur within the next 30 years along the Japan Trench off the Pacific coast of northeastern Honshu — with the chance of such a quake taking place in certain areas along the trench as high as 90 percent. The committee warned people against assuming there won’t be a big quake anytime soon after the magnitude 9 Great East Japan Earthquake hit off the coast of Miyagi Prefecture eight years ago, causing a tsunami that killed more than 18,000 people along the Tohoku coast.
Indeed, these forecasts only show long-term estimates based on past patterns of big earthquakes hitting certain areas at certain intervals. Despite the latest seismology data, much remains unknown. It is impossible to predict when and where an earthquake, or of what intensity, will occur. We are reminded of that whenever big temblors hit our quake-prone country, including the ones that hit Osaka Prefecture and Hokkaido last year as well as the Kumamoto earthquakes in 2016.
People cannot be neglectful about big temblors in areas where the likelihood of a quake is deemed low. What we can do in the face of the forecasts is beef up our preparedness against severe earthquakes to contain the damage.
Quakes on the scale of magnitude 7 to 8 are known to have repeatedly struck in areas along the Japan Trench, which stretches from Aomori to Ibaraki prefectures off the Pacific coast. These include a magnitude 7.4 temblor off Miyagi Prefecture in 1978 that left 28 people dead and more than 1,300 injured. In the forecast updated for the first time since the one following the Great East Japan Earthquake, the committee said the probability of a mega-quake of around magnitude 9 taking place in the same area as the 2011 quake in the next 30 years is close to zero — based on the assumption that such a quake will be repeated in the area at an interval of 550 to 600 years. At the same time, the panel did not rule out a mega-quake of that scale hitting other areas along the trench, although its possible magnitude or probability is not known due to lack of data.
According to the forecast, there is a better than 90 percent chance that an earthquake in the magnitude 7 to 7.5 class will hit off the eastern coast of Aomori Prefecture and the northern coastal area of Iwate Prefecture within 30 years, while the chance of such a quake originating off Miyagi Prefecture was predicted at 90 percent. These quakes, which would be far smaller than the March 2011 quake in seismic intensity, could still bring extensive damage to coastal areas.
These forecasts should not be taken to mean that anti-disaster efforts in areas along the Japan Trench should focus on places where the probability of a big quake is high. The nation needs to be on guard against severe quakes hitting anytime and anywhere in the archipelago, including temblors occurring along active faults, which are said to number more than 2,000 across the country. We cannot identify when and where quakes will hit or stop them from occurring even if we do. But we can take precautionary steps to mitigate the damage.
From the anti-disaster perspective, damage from an earthquake will be determined not only by its sheer intensity but ground and other conditions of the area hit by the temblor as well as quake-resistant features of houses and buildings. Making houses and other buildings more resistant to quakes, as well as making coastal communities more resilient against tsunami, are among initiatives that can minimize the damage. Many local governments across the country have created hazard maps showing the extent and scope of possible damage if their area is hit by natural disasters, including typhoons or flooding, which wreak havoc on people’s lives almost every year. This information can be utilized to beef up our efforts to defend against the disasters.
Big quakes catch people off guard, which is inevitable given that it’s impossible to predict when and where they will hit. But when they do strike, whether the people have been prepared — such as in confirming their routes or means of evacuation, keeping sufficient stockpiles of emergency food and other goods, and removing sources of potential hazards — will make a difference in reducing the damage.