Photo/IllutrationStaff members of the land ministry hold a drill in Tokyo on May 7 under a scenario in which the Japan Meteorological Agency releases extraordinary information about a possible powerful earthquake in the Nankai Trough. (Asahi Shimbun file photo)

Around 90 percent of municipalities would consider urging residents to evacuate based on signs that a powerful earthquake, including a secondary temblor, could strike the Nankai Trough, an Asahi Shimbun survey showed May 28.

Such widespread evacuations could affect millions of people.

Seismologists have said the probability of an enormous earthquake hitting the Nankai Trough is 70 percent to 80 percent within 30 years. The Nankai Trough is a 700-kilometer-long sea-bottom depression that runs about 100 km off the southern coast from Shizuoka Prefecture to the Shikoku region.

The Asahi Shimbun conducted the survey on 139 municipalities in 14 prefectures, including Tokyo, that are expected to suffer damage from a Nankai Trough quake. Of them, 136 municipalities replied.

The survey asked the respondents if they would consider evacuations based on “extraordinary” seismic information released by the Japan Meteorological Agency (JMA) in three cases.

In one scenario, movement in only the eastern part or the western part of the Nankai Trough triggered a powerful magnitude 8-class earthquake.

In the second case, a magnitude 7-class earthquake hit the trough and could be a precursor of an even stronger quake striking in a different area of the trough.

In the third case, several strain gauges installed in the Tokai region in and around Nagoya showed changes that indicated a major seismic event is imminent.

For the first and second scenarios, 126 municipalities, or around 93 percent, said they would consider evacuations.

For the third case, 119 municipalities, or 88 percent, said they would consider it.

The JMA in November 2017 started operating a system of issuing extraordinary information on the growing possibility of a powerful earthquake, although actual predictions cannot be made.

Regarding what type of information the municipalities would release in calling for evacuations, most cited “information that pushes residents to prepare for evacuations or requires elderly people to start fleeing.”

That was followed by “information that orders residents to evacuate” and “information that advises residents to evacuate.”

However, some municipalities that replied that they would not consider evacuations said they want more concrete data before taking such action.

“Vague information could cause confusion,” said the town of Ikata in Ehime Prefecture.

The town of Osaki in Kagoshima Prefecture said, “We stipulate that we will order an evacuation when a tsunami warning is issued.”

The 119 municipalities that said they would consider evacuations were asked how long their residents could stay displaced from their homes.

Seventy-six municipalities said, “for about three days,” while 40 answered “for about a week.”

Only three replied “from two weeks to about a month.”

Toyohashi city in Aichi Prefecture, which chose “for about three days,” said, “(The evacuation) would have a huge impact on citizens’ lives.”

Fifty-five municipalities, or 40 percent of the 136 respondents, said measures or regulations to decrease damage from natural disasters are necessary in Japanese society.

Given multiple measures and regulations to choose from, all 55 municipalities said facilities used by people requiring nursing or other care should be obliged to evacuate their residents. Fifty-one municipalities also said classes at schools and kindergartens should be suspended.

Thirty municipalities sought suspension of operations of large-scale facilities; 18 municipalities cited suspension of railway operations or closure of airports; and 16 said traffic regulations on vehicles are needed.