Country reacts with calm concern over heightened chance of major disaster

TOKYO — Japan is on alert for the heightened possibility of a huge earthquake that could cause immense loss of life and property across a wide stretch of the central and western parts of the country.

For the first time, the Japan Meteorological Agency on Thursday issued a special bulletin and advisory saying that the odds of such a catastrophe occurring increased after a magnitude 7.1 quake struck off Miyazaki prefecture on the southern island of Kyushu earlier in the day, generating several small tsunami.

Situated on the “Pacific Ring of Fire” — an arc of volcanoes and fault lines encircling the Pacific Basin — Japan is one of the most earthquake-prone nations in the world. Experts have warned for decades that it is just a matter of time before a massive Nankai Trough earthquake occurs.

Here are five things to know about it and what might come next:

What is the Nankai Trough?

A trough is a long hollow in the seabed, like a trench. The Nankai Trough runs along the seafloor off Shizuoka prefecture, southwest of Tokyo, to Miyazaki prefecture on Kyushu. It is the meeting point of the Philippine Sea Plate and the Eurasian Plate, which are two of about 10 rock-hard tectonic plates that cover the Earth’s surface.

The Philippine Sea Plate is consistently sinking beneath the Eurasian Plate at a rate of several centimeters per year, creating strain along the plates’ boundaries in the process. When too much pressure accumulates, the Eurasian Plate bounces up and causes an earthquake.

Throughout history, the Nankai Trough has repeatedly caused earthquakes about once every 100 to 150 years. The last series of them was observed about 80 years ago, and experts have been warning that the next one has a 70% chance of occurring within 30 years.

Such an earthquake could shake much of central and western Japan, simultaneously or in succession, at a magnitude of up to 9, and lead to a tsunami of more than 30 meters in height. This could result in 242,000 deaths, according to a 2023 government document.

How important is the area to Japan’s economy?

A major Nankai Trough earthquake could severely shake or flood an area that covers about a third of the nation and where about half the nation’s population of more than 120 million people lives, according to a government report in 2013.

Any megaquake is expected to extensively damage areas where manufacturing industries such as cars, steel, petrochemicals, and electronics are concentrated. The industries form part of global supply chains, so the impact of economic damage is likely to spread nationwide and overseas. Aichi prefecture is home to headquarters, factories and suppliers to Toyota Motor.

A 2019 report by Japan’s Cabinet Office said that in its base case scenario, economic damage in affected areas could amount to 100 trillion yen ($679 billion), while the impact on production of goods and services could result in damage of 24.8 trillion yen.

What is the government saying?

The epicenter of Thursday’s temblor was located where the much-feared Nankai Trough earthquake is expected to occur. An expert panel under the Japan Meteorological Agency judged that the possibility of a large-scale earthquake has become “multiple times higher than usual” and issued a Nankai Trough Earthquake Extra Information bulletin and accompanying advisory for the first time.

The agency urged people to stay alert for a week, as there have been cases in the past in which large earthquakes occurred consecutively in the same area within seven days. While under the advisory there is no call to evacuate, residents in potentially affected areas should be ready to do so immediately if necessary.

People are urged to stay prepared by keeping emergency packs with certain provisions and goods close by, checking evacuation sites, and taking disaster prevention measures such as stabilizing furniture and stockpiling food, water and other necessities.

Authorities are also warning people to be careful about disinformation on social media.

How are people reacting? Has there been any disruption?

As of Friday morning, Thursday’s quake, despite its size, had resulted in little widespread damage. Eight people were injured and three houses in Kyushu had collapsed, according to the Ministry of Land, Infrastructure, Transport and Tourism.

Japanese people, who are taught from childhood how to act in earthquakes and natural disasters, have reacted with a mix of concern and traditional calm. The government advisory comes at a prime summer vacation time in Japan and ahead of a three-day weekend. Many people pay annual visits to their hometowns and visit ancestral graves.

A monitor at Tokyo Station announces that Tokaido Shinkansen trains will be run at reduced speeds after the issuance of a Nankai Trough earthquake advisory. (Photo by Mayumi Tsumita)

In response to the advisory, the Tokaido Shinkansen high-speed train line is currently running slower than usual between stations in Shizuoka and Aichi prefectures, areas which are expected to be hit by the highest intensity ground shaking in the event of a large Nankai Trough earthquake. The operator has reported delays, which could be amplified from Saturday as it plans to increase the number of trains to cope with the larger number of travelers. Some limited express trains have also been canceled. Flights have been largely unaffected.

Prime Minister Fumio Kishida canceled plans to visit Kazakhstan, Uzbekistan, and Mongolia from Friday to stay home and oversee the situation. He had been scheduled to attend a summit with Central Asian nations in Kazakhstan.

Where can people go for English-language information and updates on the situation?

Japanese media options are numerous but unfortunately there is not really a one-stop clearing house for information in English. Still, it can be found.

The JMA website contains basic information about the Nankai Trough earthquake. It can be accessed on the agency’s homepage by clicking the “Services” button at the top, where a link called “Monitoring of Earthquakes, Tsunamis and Volcanic Activity” can be found.

Japanese morning newspaper front pages on Aug. 9, the day after a magnitude 7.1 temblor off Miyazaki prefecture triggered an advisory over a possible megaquake along the Nankai Trough. (Photo by Suzu Takahashi)

The Cabinet Office generally recommends downloading smartphone applications such as “Safety tips,” “Japan Official Travel App” and “NHK WORLD-JAPAN” operated by public broadcaster NHK.

Details are in a multilingual leaflet, which can be found on the Cabinet Office’s website for disaster management.