Japan.co.jp

An earthquake damage estimate is not a prediction of what will happen. It is a stress test: a structured way to ask what is most likely to fail, what people will need and which investments could reduce the losses before the ground moves.

In July 2026, Chiba City published its first full revision of its earthquake damage assumptions in nine years. The scenario is a magnitude 7.3 “Chiba City direct-beneath earthquake,” with the center of the source placed beneath the city hall area. The city incorporated newer national and prefectural methods, updated social data and roughly 1,000 additional ground-investigation points.

The results contain an apparent contradiction. The modeled area exposed to seismic intensity 6-upper is larger than in the 2017 assessment. Yet expected building collapse and collapse-related deaths are much lower because the building stock has become more earthquake- and fire-resistant. At the same time, modeled fire deaths rise, disaster-related deaths are counted for the first time, water outages persist for weeks, and the peak number of people living away from home now arrives two weeks after the earthquake rather than immediately.

The intensity-6-upper footprint expands from 54% to 67%

The new model places about 185 square kilometers—67% of Chiba City—at seismic intensity 6-upper. The earlier assessment put about 147 square kilometers, or 54%, in that category.

The city says the increase largely reflects a more detailed ground-motion calculation using roughly 1,000 additional geotechnical data points.

The area classified at high liquefaction risk also increases, from about 20 square kilometers, 7.5% of the city, to about 23 square kilometers, 8.3%.

That is particularly relevant on the Tokyo Bay side. Mihama Ward experienced extensive liquefaction during the 2011 Great East Japan Earthquake, despite being far from the main rupture.

Yet building losses fall sharply

Across shaking, liquefaction and fire, the city estimates about 10,380 buildings would be completely destroyed or burned and another 18,910 partially destroyed.

The components are 7,150 buildings completely destroyed by shaking, 200 completely destroyed through liquefaction effects and 3,030 burned.

Hanamigawa has the highest combined total at 2,270 destroyed or burned buildings, followed by Chuo at 2,150, Inage at 2,140 and Wakaba at 2,040.

Compared with the previous assessment, however, total full and partial structural losses fall from 44,230 buildings to 26,260—a 61% reduction. Buildings lost to fire fall from 5,880 to 3,030, a 48% reduction.

Chiba attributes that change to rebuilding and retrofits that improved seismic and fire performance.

Collapse deaths fall. Fire deaths rise.

The new assessment estimates 520 direct deaths: 260 from building collapse and 260 from fire.

Collapse deaths fall 75%, from 1,040 in the earlier model to 260. Fire deaths move in the opposite direction, rising from 120 to 260.

The city cautions, in effect, that this is not simply proof of a sudden deterioration in fire safety. The newer methodology includes fire spread involving multi-unit residential buildings with large resident populations more fully than the earlier model did.

Methodological change and real-world risk change therefore need to be distinguished.

For the first time, Chiba estimates 140 disaster-related deaths

The revised study adds disaster-related mortality as a new category and estimates 140 such deaths.

These are not deaths caused directly by a collapsing wall or fire. They arise from prolonged evacuation, worsening living conditions, interrupted medical care and the physical or psychological strain that follows a disaster.

Recent Japanese disasters have repeatedly shown that toilets, sleep, temperature, food, medication and access to care can become life-or-death issues well after the shaking stops.

Water is the slowest lifeline to recover

The water scenario is one of the assessment’s most consequential findings.

Immediately after the quake, 712,780 of 957,290 people—75% of the service population—are modeled without water. After three days, 642,800 people, 67%, remain without service. After one week the figure is 533,720, or 56%. After two weeks, 362,660 people—38%—still lack water. Even after a month, 125,880 people, 13%, remain affected.

Electricity is modeled very differently. Some 596,460 customer accounts, 95%, lose power immediately, falling to 32% after three days, 4% after one week and zero by two weeks.

City gas disruption begins at 64% of customers, falls to 38% after one week and 3% after two weeks. Fixed-line communications fall from 95% outage immediately to 3% after one week.

The evacuation peak arrives two weeks later

People living away from home number about 87,620 immediately after the quake but rise over time, peaking at 284,660 two weeks later.

At that point, 170,800 people are projected to be in designated shelters and 113,860 elsewhere—staying with relatives or friends, in hotels, vehicles or other arrangements.

One month after the quake, designated-shelter use falls to 76,010, while non-shelter evacuation remains high at 114,010.

The previous assessment placed the peak at 304,210 immediately after the earthquake. The new model incorporates recent evacuation behavior and shifts that peak to the second week.

Operationally, that is a major change. Chiba cannot plan only for a huge first night; it must support a population that becomes displaced gradually as homes lose water, sanitation and other functions.

“Go to the shelter” is no longer the only standard response

One of the city’s central policies is distributed evacuation.

If a home remains structurally safe, staying there may be preferable. Other options include relatives’ homes, hotels, neighborhood facilities and designated vehicle-sleeping locations.

Chiba plans to expand recognition of community meeting halls as local evacuation facilities, increase agreements with private companies for vehicle evacuation sites and develop “last-mile” systems to deliver supplies to vulnerable people who are not in official shelters.

Shelters are being redesigned around TKB

The city’s policy document explicitly uses the TKB concept: toilets, kitchens, beds and baths.

Planned measures include more manhole toilets, use of municipal cooking facilities, agreements with food trucks, simple beds for people requiring special assistance, expanded bathing support and additional evacuation space.

For the projected peak population, the city also wants enough space to meet the national guideline of 3.5 square meters per person, including possible use of universities and private lodging.

The most effective shelter measure may be making homes safer

Chiba’s first prevention pillar is household safety: seismic strengthening, furniture anchoring and earthquake-sensitive circuit breakers.

The 75% decline in modeled collapse deaths since the earlier assessment is evidence that better buildings matter.

The city continues to promote subsidies for wooden-home seismic diagnosis and retrofit, furniture anti-tip programs for older or severely disabled residents and community-level disaster equipment assistance.

Because modeled fire deaths rise, the city also says it will consider expanding deployment of earthquake-sensitive breakers, which cut electricity after strong shaking and can reduce electrical fires during or after restoration of power.

2011 made liquefaction a lived Chiba experience

The Great East Japan Earthquake demonstrated a different kind of urban vulnerability.

Liquefaction struck reclaimed parts of Mihama Ward. Chiba recorded about 44 kilometers of damaged roads across 392 routes, seven damaged bridges, roughly seven kilometers of sewer damage and damage at 75 parks.

Housing certification eventually counted 31 households destroyed, 282 with major partial damage, 414 partially damaged and 54,354 with lesser damage.

Chiba later designated 143 hectares in areas including Makuhari Nishi, Isobe and Masago for liquefaction recovery programs, with groundwater-lowering countermeasures implemented in districts where residents agreed.

That history means the new liquefaction maps are not abstract planning graphics. They describe a hazard the city has already experienced at metropolitan scale.

The history stretches back to 1923

Chiba became a city in 1921. Two years later, the Great Kanto Earthquake damaged homes inside the young municipality.

In the century since, the city expanded across reclaimed coast, dense residential areas, high-rise buildings, industrial zones and complex transport systems.

The earthquake problem therefore expanded as well. It is no longer only a question of wooden homes collapsing. The 2026 assessment adds categories including disaster-related deaths, toilet failure, temporary-stay facilities, support needs among vulnerable residents, medical-function disruption, high-rise behavior and compound-disaster scenarios.

Recovery starts with faster damage certification

Chiba also places faster issuance of disaster victim certificates in its policy package.

Those certificates establish the degree of housing damage and serve as a gateway to assistance, tax relief, loans and other recovery systems. Slow certification means slow household recovery.

The city plans greater use of digital systems, stronger pre-disaster communication about assistance programs and a network capable of visiting vulnerable residents who might otherwise be missed.

Lifeline policy now includes surviving the outage, not only repairing it

The policy package includes rapid road clearance with electric utilities, solar generation and batteries at shelters, coordinated water and sewer recovery, emergency water tanks and manhole toilets, cassette-stove supply, backup power for mobile base stations, emergency public telephones and shelter Wi-Fi.

The common principle is important: resilience is not measured only by the day full service returns. It is also measured by how well people can function during the days and weeks before it does.

This is a scenario, not the maximum possible earthquake

The model assumes a magnitude 7.3 earthquake centered beneath Chiba City Hall.

A real metropolitan earthquake could occur elsewhere, at a different depth or magnitude, at another time of day and under different wind and fire conditions. Damage may therefore be higher or lower in individual districts.

The city’s own hazard-map guidance emphasizes that the numbers are forecasts for one scenario and should not be interpreted as guarantees of actual future damage.

For residents, the hardest number may not be a three-day supply

The water results change the practical meaning of household preparedness.

Three days after the modeled quake, 67% of the water-service population is still without water; after one week, 56%.

Preparedness therefore goes beyond short-term emergency food. Drinking water, sanitation, medication, battery power, communications and a home environment that can support sheltering in place may matter for much longer.

A structurally intact apartment is not truly habitable if the toilet cannot be used, elevators are stopped and medical or care services are inaccessible.

The purpose of the numbers is not fear

The revised assumptions produce a larger severe-shaking map but much lower collapse mortality.

That combination is the most useful message in the entire assessment: better information can make the hazard look worse while better construction can make the outcome better.

Strengthen homes. Anchor furniture. Install earthquake-sensitive breakers. Prepare to live safely at home when possible. Plan more than one evacuation destination. Design city support around water, sanitation and communications that may fail for weeks.

Chiba City’s public explanation sessions begin October 4. The most important story is not simply how large the modeled disaster is. It is which losses have already been reduced over the past nine years—and which ones remain stubbornly difficult to solve.