Photo/IllutrationPolice train for emergency rescue operations in the event of the Nankai Trough earthquake in November 2017. (Asahi Shimbun file photo)

A powerful earthquake striking the Nankai Trough off the southeastern coast of Japan could cause 1,240 trillion yen ($11.3 trillion) in economic damage over 20 years, a group of engineers said June 7.

The Japan Society of Civil Engineers, an academic society whose members include scholars, commercial civil engineering businesses and infrastructure operators, said the damage could be reduced by about 40 percent by further quake-proofing buildings, improving roads and other means within the next 15 years or so.

Seismologists and other experts have said the probability of a huge Nankai Trough earthquake striking is 70 to 80 percent within the next 30 years.

The trough is a shallow seabed depression extending along the Pacific coast from Shizuoka Prefecture to Kyushu.

Such an earthquake is expected to spawn a tsunami that would devastate much of the southeastern coast of the Japanese archipelago, from the Kanto to Kyushu regions.

The government has estimated the Nankai Trough earthquake would cause a direct loss of 169.5 trillion yen, such as destroyed buildings, and could lead to 50.8 trillion yen in economic damage in the year after it hits.

But the government has not made a long-term estimate of the damage.

The academic society’s estimates were part of a study by its investigation committee into the long-term effects in the worst-case scenarios for three possible disasters: the Nankai Trough earthquake, a powerful earthquake striking directly beneath the capital, and major flooding in Tokyo, Nagoya and Osaka.

The committee’s estimates on the duration of the economic damage were based largely on data from the 1995 Great Hanshin Earthquake that destroyed much of Kobe, one of the busiest port cities and an economic hub in western Japan.

According to the committee’s calculations, a full-scale Nankai Trough earthquake would cause a loss of 1,048 trillion yen from damaged factories and roads and a loss of 192 trillion yen from damaged ports to Japan’s economy over 20 years.

For a powerful earthquake striking directly under Tokyo, the committee estimated that the economic damage would be 731 trillion yen over 20 years.

The Japanese government’s general budget for fiscal 2018 is 97.7 trillion yen.

The academic society said counter-disaster measures, if thoroughly implemented, could reduce the economic damage by 509 trillion yen for the Nankai Trough earthquake and 247 trillion yen for the Tokyo earthquake.

It also maintained that investing in counter-disaster measures, such as strengthening quake-resistance of buildings and erecting higher seawalls, would benefit the economy by easing a drop in tax revenue over the 20 years after such disasters.