What If a Direct-Hit Earthquake with a Seismic Intensity of 6 or Higher Struck “Tokyo, Nagoya, and Osaka”? Estimated Damage and Countermeasures

Major earthquakes with a seismic intensity of 6 or higher and a magnitude (M) of 7 or higher have been occurring frequently. However, in earthquakes in Aomori and Yamanashi, while about 800 buildings were damaged and nearly 40 people were injured, there were no fatalities.

The epicenter of the Aomori earthquake was off the coast of Iwate Prefecture, while that of the Yamanashi earthquake was in the Fuji Five Lakes region in eastern Yamanashi. What would happen if a major earthquake with a seismic intensity of 6 or higher and a magnitude (M) of 7 or higher struck a major metropolitan area such as Tokyo, Nagoya, or Osaka? If, as with the earthquake that occurred in June, the epicenter were located far from where people live, the damage might be minimal. But…

[Part 1] Major Earthquakes Occurring Frequently Across the Country… Experts Explain! What Would Happen If One Struck a Major Metropolitan Area?

Underground shopping arcades could be flooded in as little as 15 minutes

Let’s look at the damage projections for an earthquake directly beneath the southern part of Tokyo’s 23 wards—with the epicenter in that area—as published by the Central Disaster Prevention Council last December. The greatest damage is expected during winter evenings, when open flames are frequently used in restaurants and other establishments.With wind speeds of 8 m/s, the death toll would be approximately 18,000 (including about 5,300 deaths from building collapses and about 12,000 from fires). The number of injured would reach approximately 98,000.

“In areas like the old downtown districts with narrow streets, debris from collapsed buildings will litter the ground, preventing fire trucks and ambulances from passing even if a fire breaks out, which will cause the damage to escalate. Liquefaction is also a serious concern in reclaimed land areas. The ground becomes unstable, and in the worst-case scenario, entire buildings could collapse.
In low-lying areas, caution is also needed regarding levee breaches. During periods when water levels rise due to typhoons or other factors, rivers can overflow, causing massive amounts of water to rush into urban areas all at once. Research has shown that underground shopping districts can be submerged in as little as 15 minutes. After a major earthquake, please exit underground areas immediately.”

There are also types of damage unique to urban areas.

“Due to blocked roads and damaged bridges, public transportation in the city center will come to a near standstill. Large numbers of people unable to return home will flood the streets. In narrow areas, population density will become extremely high, potentially leading to a domino effect where people are crushed to death one after another.Residents of high-rise apartment buildings will be forced to use the stairs since elevators will stop working.
Due to the disruption of communication networks, smartphones and computers will also become unusable. As it becomes difficult to obtain information—leaving people unaware of the extent of the damage or the safety of their families—people overcome by anxiety may trigger mass panic.Hospitals should be able to operate for about three days after a major earthquake using emergency power. However, if the power outage persists, critically ill inpatients will be exposed to life-threatening risks.”

What preparations should people living in urban areas make to minimize damage as much as possible?

“It’s important to understand the characteristics of where you live—such as whether it’s on reclaimed land or near a river—and to familiarize yourself with evacuation routes. Please also prepare a hand-crank radio in case your smartphone becomes unusable.”

According to the government’s Headquarters for the Promotion of Earthquake Research, there is about a 70 percent chance that a magnitude 7-class direct-hit earthquake will occur in central Tokyo within the next 30 years. Major earthquakes do not occur only in rural areas. The threat is looming over urban areas as well.

From the July 31, 2026 issue of *FRIDAY*