New Report Warns Tokyo Megaquake Would Be a National-Scale Disaster

In newly released damage estimates for a potential major earthquake directly beneath the Greater Tokyo Area, a working group of the Central Disaster Management Council highlighted the impact of social changes over the past decade.

The number of households in the capital region has grown, and the population has become more diverse, with increases in elderly residents and foreign nationals. At the same time, greater dependence on mobile devices has heightened the risk of communication outages and the rapid spread of misinformation.

'A Disaster on a National Scale'

The report emphasizes not only the limits of structural disaster-prevention measures but also the importance of individuals viewing disaster preparedness as a personal responsibility.

At a press conference on December 19, Hitoshi Ieda, Senior Professor at the National Graduate Institute for Policy Studies (GRIPS) and deputy head of the working group, explained why an earthquake striking the Tokyo metropolitan area would constitute a disaster on a national scale.

"Population density is a critical factor," he noted. "A magnitude 7 earthquake can occur anywhere, but the damage is far greater where large numbers of people are concentrated."

Changes in Housing

Over the past decade, disaster-prevention measures have made steady progress. The proportion of earthquake-resistant housing increased from 79% (estimated in fiscal 2008) to 90% (estimated in fiscal 2023). In addition, about 82% of the roughly 2,500 hectares of "highly dangerous densely built-up urban areas" identified in fiscal 2011 have been eliminated. As a result, total building damage from collapse and fire has been reduced by around 40%.

However, due to population growth and higher at-home rates following the COVID-19 pandemic, the estimated number of fatalities has declined by only about 20%.

*The riverbank near Seiseki-sakuragaoka Station is bustling with families and children on weekends — May 7, Tama City, Tokyo. (©Sankei by Rei Yamamoto)*

Changing Demographics

The projected number of evacuees has also fallen, decreasing by roughly 40% as building damage has been reduced. Even so, the estimate of 4.8 million evacuees is striking when compared with more than 50,000 in the 2024 Noto Peninsula earthquake and 184,000 in the 2016 Kumamoto earthquake.

Social diversity has continued to increase. The number of dual-income households with children under the age of six is now 1.27 times higher than it was a decade ago. Combined with the rise in single-person elderly households and foreign residents, this growing diversity makes it more difficult to follow the basic disaster response of staying where one is. This is especially true for the estimated 8.4 million people who would be unable to return home.

Disasters and Panic: Foreigners in the Equation of Japan's Response

Another major factor is smartphone ownership, which now exceeds 90% of households. While smartphones are indispensable for gathering information and confirming safety, misinformation and rumors spread through social media can hinder rescue and recovery efforts and trigger serious social anxiety.

A Culture of Preparedness

Looking ahead to the next decade, the working group highlighted two figures that point to shortcomings in individual preparedness. One is a furniture-anchoring rate of 35.9%, which helps prevent injuries caused by falling objects during strong shaking.

The other is a 30.5% adoption rate for seismic circuit breakers, which reduce the risk of electrical fires after earthquakes. Professor Ieda stressed that "it is essential to make disaster risk reduction part of the nation's culture, with every individual living in the Tokyo metropolitan area playing a role."