Japan Prepares for a Mega-earthquake With 300,000 Deaths and Billions of Dollars in Losses.

The world’s largest seismic belt stretches along the edge of the Pacific Ocean, where around 90% of the planet’s earthquakes occur and 75% of the world’s volcanoes are concentrated. This area experiences 81% of the world’s largest earthquakes and is also home to most of the planet’s supervolcanoes, whose historically massive eruptions (known as VEI=8 eruptions) have caused global devastation and even mass extinctions. For all these reasons, this zone is known as the “Pacific Ring of Fire.”

According to the United States Geological Survey (USGS), Japan has the highest concentration of earthquakes, particularly because it has the densest seismic detection network in the world. However, the USGS also notes that the dubious distinction of being the country with the most earthquakes may be shared with Indonesia.

Mega-Earthquake

A mega-earthquake is an earthquake with a magnitude greater than 8.5. Although systematic measurement of their magnitudes began in the 20th century, earlier ones have been reconstructed based on the extent of the damage they caused.

Although the deadliest earthquake wasn’t a mega-earthquake, on January 23, 1556, an earthquake estimated at magnitude 8.0 struck eastern China, killing around 830,000 people.

The largest mega-earthquake in history occurred on May 22, 1960, off the southern coast of Chile. Known as the Valdivia earthquake or the Great Chilean Earthquake, it was the first (and so far only) time that a seismograph recorded a magnitude of 9.5. It reduced entire cities to rubble in just over ten minutes and redrew the geography of an entire region. However, the impact on lives was relatively low: about 6,000 people in the quake area and nearly 200 more due to the resulting tsunami in Japan and Hawaii.

Managing Risks

The Cabinet Office of the Government of Japan, responsible for disaster risk management in the country, recently updated projections of deaths and losses from an expected mega-earthquake along the Nankai Trough, south of the islands. While the figures are significantly lower than those calculated a decade ago, they are still catastrophic and fall well short of the government’s targets.

These estimates, made by a panel of experts, updated the projections by calculating the quake’s intensity, tsunami height, and potential flood areas using the latest topographical and soil data for the potentially affected regions. Previous estimates (2012–2013) projected 323,000 deaths and 2.39 million completely destroyed buildings.

The government designated 707 cities, towns, and villages in Tokyo and 28 prefectures across the country, including inland areas, as zones that must take action against the mega-earthquake when the government issued its first Nankai Trough mega-earthquake warning in August of last year.

But Will Deaths and Damage Be Lower?

There are numerous factors contributing to the lower projected losses compared to estimates from 10 years ago, among them:

• A declining and aging population
• A greater number of high-rise buildings and vacant homes
• The rate of reinforced houses to withstand earthquakes increased from about 79% in 2008 to nearly 90% in 2023
• The rate of levee and seawall construction rose from 39% in 2014 to 65% in 2021
• The rate of municipalities conducting disaster prevention drills increased from 79% in 2018 to 86% in 2024

However, these changes have introduced new risks, including the need for more evacuation assistance and the isolation of affected areas.

The Minister in charge of National Resilience Creation, Manabu Sakai, emphasized the importance of reviewing disaster mitigation measures in the summer, based on this report.

Although earthquakes—like many other natural hazards—cannot be predicted or avoided, loss of life and property can be significantly reduced. Japan has learned the lesson, which is why it has adopted comprehensive disaster risk management as a national strategic policy.