Please view the main text area of the page by skipping the main menu.

As I See It: People must understand Nankai Trough quake update system's shortcomings


A major earthquake is expected to strike sometime along the Nankai Trough, a submarine trench running off the Japanese archipelago from around Shizuoka Prefecture in Honshu to the seas east of Kyushu. And for the past 40-some years, the central government has sought to estimate when the next such quake will hit the Tokai region and establish disaster-prevention measures accordingly. Not anymore.

The government has essentially thrown up its hands and declared that the temblors are "scientifically difficult to predict." Instead, it will track phenomena that could be precursors to a quake, and send out updates on whether the chances of a major shake "are greater than normal."

All this has a direct impact on whether people live or die, but how are they to respond to such vague quake updates that may be off the mark? The government ought to reveal its thinking on this problem soon, and I would also like to think about how each of us should respond.

The Japan Meteorological Agency (JMA) launched the "Nankai Trough earthquake-related information" service in November last year, and releases updates based on expert evaluations of conditions. When the government was still attempting to predict the next Nankai Trough, it had planned to issue "warning declarations" and halt transport and certain economic activity when deemed necessary. Now, it posts updates that are less accurate than the now abandoned predictions. The areas affected go beyond the Tokai region to encompass all of western Japan. What's more, the new information service has also done away with specifying a potential quake's epicenter location, timing, and scale.

After the new information system was launched, I surveyed the governments of Metropolitan Tokyo, 13 prefectures and 139 municipalities projected to be hit by major tsunami in the event of a Nankai Trough temblor. Ninety-one of the municipalities, or over 60 percent, said that they were considering issuing official announcements such as evacuation advisories and evacuation preparation notices if the JMA update pointed to a potential quake. However, there were a striking number of municipal governments who said they could not decide exactly how they would respond to such news. The updates only say whether there is "a relatively higher chance of an earthquake compared to normal conditions," making it hard for local governments to evaluate the true gravity of the situation.

"The national and prefectural governments have just shoved everything into our laps."

"The whole thing just feels rushed and shoddy."

I heard a lot of remarks like these when interviewing municipal officials about the new JMA quake information system. Some 20 municipalities also wrote on the survey forms that they wanted the central government to establish specific criteria for when to initiate an evacuation. Their confusion is to be expected. The national government is committed to releasing guidelines on this issue, but local bodies are still waiting, and a date has yet to be set for the guidelines' final formulation. If a JMA update warning of a quake risk comes out before then, chaos seems the likely result.

I learned from the survey that some 60,000 people in 33 municipalities are in danger of being caught in a tsunami even if they tried to evacuate immediately after a major Nankai temblor. In areas where a tsunami is projected to hit so soon after a quake, preparations need to be made to help get people to safety. Fifty-seven of the municipalities polled said they were considering opening evacuation centers when a JMA quake update pointed to a possible temblor. If the government takes a long time to draw up general response guidelines, then at the very least perhaps it ought to set out examples of what to do in specific situations where people's lives are on the line.

The term "phenomena that could be (earthquake) precursors" in the new JMA updates refers specifically to temblors or shifts in the Earth's crust in the projected quake zone. However, even if there were 100 times more possible precursor events than normal, that would only boost the quake risk from, say, around 0.02 percent to 2 percent -- hardly significant enough to say that the chances of a major quake "have risen." That is why the JMA has elected to use the term "relatively higher ... compared to normal conditions." How people are to respond to this depends on a multiplicity of factors, from the special characteristics of particular regions to the health conditions of individuals.

There are "strain meters" in 27 locations in the Tokai region, checking for changes in the Earth's crust and other phenomena. Interpreting the observations, however, is difficult. Under the previous system, if the strain meters detected major shifts in three or more locations, the prime minister had been supposed to issue an official warning stating there was a "risk of a Tokai earthquake within the next few hours to two to three days." However, this standard also ended when the JMA did away with quake predictions.

It is possible that, sometime in the future, the official response to the quake risk will be determined by how many strain meters register a serious abnormality. However, if these standards are overly specific, they would likely be confused with the more precise quake predictions of the previous system. Furthermore, if municipalities count too much on the new JMA updates, it would become impossible to respond to unexpected shifts leading to major quakes before a new update was issued.

There are yet more problems that need to be overcome. Updates stating that the quake risk is "not rising" are effectively declarations that conditions are safe, and therefore the information underpinning them must be concrete. However, we do not have the scientific expertise to make that guarantee. A prolonged suspension of economic activity due to a potentially imminent quake would have a serious impact. There is also criticism that the updates just invite confusion. However, it cannot be denied that the strain meter system is picking up signals of an impending quake. This is information on which people's lives are riding, so not revealing the information is not an option.

Will the next Nankai Trough quake be a magnitude-8 class temblor along its eastern or southern stretches? Or linked quakes in both regions? Will it be a magnitude-9 monster? We will not know until it happens. The JMA update system has lapses as well, and so no update hinting at the next Nankai temblor may come before it actually hits. That being the case, every agency and individual affected must truly understand the updates' lack of certainty, and discuss how to respond based on this knowledge.

When an ominous update is released, there are measures that can be taken short of outright evacuation. We could ask, for example, that the government warn people to secure their furniture, and confirm the locations of their closest evacuation centers and the routes to them. Hospitals and care facilities projected to be flooded by a tsunami could also move patients' beds to higher floors. Those living in two-story structures vulnerable to quakes could move their sleeping quarters from the first to the second floor.

The fact is that the new JMA quake update system is not widely understood. However, every person and region needs to look at their own circumstances and think about what preparations they can make. To spark that society-wide conversation, the government should better publicize the update system and its shortcomings. (By Tomohiro Ikeda, Osaka Science & Environment News Department)

Also in The Mainichi

The Mainichi on social media