New damage estimates for earthquake beneath Tokyo: 18,000 deaths, economic damage exceeding 82 trillion yen-Reduced from 12 years ago but falls short of target

A government working group published a new damage estimate report on the 19th of December on the subject of an earthquake beneath Tokyo (a "Tokyo inland earthquake") that would strike with intense magnitude 7-class shaking. In the worst-case scenario, approximately 400,000 buildings would collapse or be destroyed by fire, approximately 18,000 people would die, and economic damage from factory destruction and the collapse of distribution networks would exceed a total of 82 trillion yen. The catastrophic scale of damage at a "national crisis level" has been revealed.

This revision of damage estimates is the first in 12 years since the previous estimate in 2013. Although the death toll has decreased from the previous estimate of 23,000 due to progress in seismic reinforcement in buildings and fire prevention measures in densely populated wooden residential areas, it failed to meet the target of "halving the death toll in 10 years" set in 2015 in the "Basic Plan for Promotion of Emergency Countermeasures Against a Tokyo Inland Earthquake." The government plans to revise this plan in the future and strengthen efforts to maintain capital functions and reduce damage, with a Disaster Management Agency scheduled to be established during fiscal year 2026 serving as the command center.

Tokyo Metropolitan Southern Inland Earthquake would have serious impact on national life and economic activity

The Central Disaster Management Council's Working Group on Tokyo Inland Earthquake Countermeasures began reviewing damage estimates and examining new disaster prevention measures in December 2023. Damage was estimated for a "Tokyo Metropolitan Southern Inland Earthquake" type, which is expected to occur with a probability of approximately 70% within 30 years and would have an extremely large impact on the capital's core functions.

The report compiled from this review points out that the Tokyo metropolitan area has concentrated core functions—political, administrative, and economic—and if an inland earthquake occurs in the southern metropolitan area, it would have a major impact not only on national life and economic activity throughout the country but also overseas. It states that due to the concentration of population and buildings, many direct deaths from shaking and fires are unavoidable.

The estimated deaths across the metropolis and four prefectures would be at their maximum should a magnitude 7.3 earthquake occur on a winter evening with wind speeds of 8 meters, totaling approximately 18,000 people: approximately 6,000 from building collapse and approximately 12,000 from fires. Of these, the projected death toll in Tokyo is 8000, which accounts for over 40% of the total.

The maximum estimated deaths outside Tokyo are 5,200 in Kanagawa Prefecture, 3,200 in Saitama Prefecture, 1,500 in Chiba Prefecture, and 10 in Ibaraki Prefecture. The maximum number of completely collapsed buildings is approximately 130,000, with approximately 270,000 destroyed by fire, for a total of over 400,000 collapsed and burned buildings.

Over 40,000 disaster-related deaths, 8.4 million people unable to return home, food shortage of 13 million meals

According to estimates, the number of evacuees would gradually increase starting immediately after the earthquake, reaching 4.8 million people two weeks later, and the number of people unable to return home would reach 8.4 million if the earthquake occurred at noon on a weekday. Separately from this, it was estimated that 650,000 to 880,000 people visiting from overseas for tourism or business trips might also be stranded. This time, disaster-related deaths caused by deteriorating health conditions during evacuation were also estimated for the first time, with figures showing a maximum of 16,000 to 41,000 people.

In addition, worst-case damage estimates include power outages affecting approximately 16 million households, approximately 14 million people unable to use the water supply, approximately 2 million people unable to use the sewage system, approximately 16,000 people trapped in elevators, and a food shortage of approximately 13 million meals in the week following the earthquake.

Compared with the previous maximum damage estimates, deaths decreased by approximately 5,000 people, completely collapsed and burned buildings decreased by approximately 210,000 structures, and evacuees decreased by 2.4 million people. Economic damage also decreased by approximately 13 trillion yen. Although the 2015 countermeasures were deemed to have achieved a certain level of effectiveness, they fell short of the targets set in the Basic Plan for Promotion of Emergency Countermeasures Against a Tokyo Inland Earthquake.

Hiroya Masuda, chairperson of the working group (advisor at Nomura Research Institute), stated that "It is important to take (earthquake damage striking the Tokyo metropolitan area) as one's own responsibility and build a system throughout society."

In a "Great Kanto Earthquake Type," nearly 23,000 people would die in the worst case

The Kanto region, including Tokyo, sits on an extremely complex underground structure where the Philippine Sea Plate subducts from the south toward the North American Plate, and the Pacific Plate subducts from the east. For this reason, the mechanisms of expected earthquakes are also diverse.

This time, the working group also produced estimated damage for a "Great Kanto Earthquake type" magnitude 8-class earthquake originating along the Sagami Trough, in addition to a Tokyo Metropolitan Southern Inland Earthquake. Because this would be a trench-type earthquake, major damage from tsunamis is expected, with the scale of incoming tsunamis reaching a maximum of 10 meters in Chiba and Kanagawa Prefectures, and 8 meters in Tokyo's island areas and Shizuoka Prefecture.

In the worst-case scenario of the quake occurring on a winter evening with wind speeds of 8 meters, deaths would approach nearly 23,000 people, including approximately 3,500 from tsunamis, approximately 13,000 from fires, and approximately 6,300 from building collapse, with injured persons reaching approximately 86,000. Disaster-related deaths are also estimated at a maximum of approximately 33,000.

The number of completely collapsed and burned buildings was estimated at approximately 414,000 structures, with approximately 473,000 partially collapsed. Power outages would reach a maximum of approximately 16 million households, affecting about 50% of the total, with complete restoration taking more than one month. Damage to the information and communications sector would also be significant, with a maximum of approximately 7.5 million landline and internet lines affected, making impacts on post-disaster communications and contact unavoidable.

On the other hand, economic damage would be relatively light for companies concentrated in Tokyo, at 60.5 trillion yen, less than the Tokyo Metropolitan Southern type. The breakdown shows approximately 20.3 trillion yen in impacts on economic activity, with a large impact of approximately 40.2 trillion yen on assets across the private, public, and quasi-public sectors combined.

Confusion in disaster areas also due to spread of online misinformation and rumors

Other damages beyond human casualties and economic damage that would strike Tokyo—a giant, overcrowded city—were also compiled. Among these, delays in information dissemination are serious, not only hindering timely and appropriate information transmission but also causing massive spread of misinformation and rumors through social media that would seriously worsen confusion in disaster areas. The report pointed out that countermeasures in these areas are also necessary.

The damage mitigation targets formulated the following year based on the Basic Plan for Emergency Response to the Tokyo Inland Earthquake decided by the Cabinet in March 2014 aimed to roughly halve the maximum damage estimated at that time (approximately 23,000 deaths, approximately 610,000 completely collapsed and burned buildings). However, this time, when results were produced based on the same shaking conditions as the previous estimate, damage estimates only achieved reductions of just over 30% for deaths and approximately 40% for building damage.

Particularly important among future countermeasures are fire prevention measures in densely populated residential areas, which account for two-thirds of the death toll. Although densely populated areas within Tokyo have decreased due to measures such as road widening, there are still many areas where aging houses are concentrated and many narrow roads through which emergency vehicles such as fire trucks cannot pass.

The key to fire prevention measures is "earthquake-activated breakers" that automatically cut off electricity when they detect shaking, but installation rates have struggled to grow and will become a focus of specific future challenges. Although private companies and others are advancing efforts such as establishing backup functions for headquarters and main offices in regional areas and relocating production bases to regional areas, these are still in progress. Effective methods have not been found for countermeasures against misinformation and fake videos through social media.

Major earthquakes can occur anywhere in the country at any time. To minimize damage, it is important for each individual to prepare to protect lives.