How to read Tokyo’s tsunami risk maps in 2026
Tokyo sits on the Pacific Ring of Fire, where tectonic plates meet beneath the ocean floor. The city’s eastern wards face the Tokyo Bay, and several coastal neighborhoods carry measurable tsunami risk. Understanding how to read official hazard maps provides clarity for anyone evaluating property in these areas.
The Tokyo Metropolitan Government publishes tsunami hazard maps (津波ハザードマップ) for each ward, based on seismic modeling of specific earthquake scenarios. These maps show predicted inundation depths, evacuation routes, and designated safe buildings. Reading them requires understanding the underlying earthquake models, the color-coding system for water depth, and how to check risk for any specific address.
The earthquake scenarios behind Tokyo’s tsunami maps
Tokyo’s tsunami risk maps model two primary earthquake scenarios: the Genroku-type Kanto earthquake (元禄関東地震) and the Nankai Trough megathrust earthquake (南海トラフ巨大地震).
The Genroku-type earthquake refers to a magnitude 8.2 event that struck the Kanto region in 1703. This historical earthquake generated tsunamis that reached Tokyo Bay. Modern modeling by the Japan Meteorological Agency suggests a similar event would produce wave heights of 2-3 meters in parts of Tokyo Bay, arriving within 30-90 minutes of the initial seismic shock.
The Nankai Trough scenario models a magnitude 9.1 megathrust earthquake along the subduction zone extending from Shizuoka to Kyushu. While the epicenter lies far from Tokyo, wave propagation modeling indicates coastal wards would experience inundation. The Tokyo Metropolitan Government updated its damage estimates in 2022, incorporating revised seismic data and liquefaction risk (液状化) in low-lying areas.
Both scenarios account for ground subsidence following the earthquake, which increases the effective inundation depth in areas with weak soil composition. This matters particularly in reclaimed land areas along Tokyo Bay, where liquefaction can cause the ground to sink by 1-2 meters.
Which Tokyo wards face the highest tsunami risk
Seven wards along Tokyo Bay show measurable tsunami inundation risk: Edogawa (江戸川区), Koto (江東区), Chuo (中央区), Minato (港区), Shinagawa (品川区), Ota (大田区), and parts of Sumida (墨田区).
Edogawa faces the highest predicted inundation depths, with some areas near the Arakawa River mouth showing potential depths of 3-4 meters under the Genroku scenario. The ward’s low elevation and proximity to both the river and bay create compound flood risk.
Koto contains extensive reclaimed land in areas like Ariake (有明) and Toyosu (豊洲). The 2022 Tokyo Metropolitan Government assessment indicates these neighborhoods could experience 1-2 meter inundation depths, with arrival times of 60-90 minutes after the earthquake. Liquefaction risk compounds the hazard in areas built on bay fill.
Chuo ward’s waterfront areas, including Tsukishima (月島) and parts of Harumi (晴海), show predicted depths of 1-2 meters. The Sumida River acts as a pathway for tsunami waves to penetrate inland, affecting areas several hundred meters from the bay shore.
Minato ward’s coastal sections near Shibaura (芝浦) and Odaiba (お台場) face inundation risk, though the elevated areas of Azabu (麻布), Roppongi (六本木), and Akasaka (赤坂) sit well above any predicted tsunami reach. The elevation difference within Minato ward creates distinct risk zones separated by less than two kilometers.
Shinagawa and Ota wards show localized risk along their bay-facing edges, particularly in industrial and port areas. Residential neighborhoods in these wards generally sit at higher elevations, though specific address checks remain necessary.
Sumida ward’s risk concentrates along the Sumida River corridor, where tsunami waves can travel upstream and overtop riverbanks in low-lying sections.
The pattern across these wards shows that elevation determines risk more than simple proximity to the bay. Areas above 5 meters elevation face minimal tsunami risk under current modeling scenarios.
How to read the color-coding and depth indicators
Tokyo’s official tsunami hazard maps use a standardized color system to indicate predicted maximum inundation depth. The scale typically ranges from light blue (0.3-0.5 meters) through darker blues and purples (2-5 meters or more).
0.3-0.5 meters (light blue): Water reaches knee to waist height. Walking becomes difficult, and ground-floor spaces flood. This depth appears in areas at the outer edge of the predicted inundation zone.
0.5-1.0 meters (medium blue): Water reaches waist to chest height on adults. Movement on foot becomes dangerous due to current force. Ground-floor residential spaces experience significant damage.
1.0-2.0 meters (dark blue): Water exceeds adult height. Evacuation on foot becomes impossible once water arrives. First-floor residential units become uninhabitable.
2.0-3.0 meters (purple): Water reaches second-floor level in standard buildings. Evacuation to vertical shelters becomes necessary.
3.0+ meters (dark purple/red): Water reaches third-floor level or higher. Only tall buildings provide adequate refuge.
The maps also indicate arrival time through separate notation, typically showing zones where tsunami waves reach within 30 minutes, 60 minutes, or 90 minutes of the earthquake. This timing matters for evacuation planning, as the initial seismic shaking may damage buildings and infrastructure, complicating movement.
Liquefaction zones appear marked with separate hatching or symbols. These areas face compound risk: the earthquake causes soil liquefaction, buildings may tilt or sink, and then tsunami inundation follows. The combination creates higher effective water depth as the ground surface drops.
Using official portals to check address-specific risk
Two primary online resources allow detailed address-level risk checking: the national Disaportal (重ねるハザードマップ) maintained by the Ministry of Land, Infrastructure, Transport and Tourism, and the Tokyo Metropolitan Government’s hazard map portal.
Disaportal address lookup
The Disaportal website (disaportal.gsi.go.jp) provides a unified interface for viewing multiple natural disaster risks across Japan, including tsunami, flood, landslide, and earthquake hazards.
To check a specific Tokyo address:
Enter the address in the search field at the top of the page. The system accepts both Japanese addresses and postal codes. The map zooms to the specified location and displays overlaid hazard layers.
Toggle the tsunami hazard layer using the menu on the left side. The default view shows all hazard types, which can obscure specific risks. Isolating the tsunami layer provides clarity.
The map displays the predicted inundation depth at that specific point using the color scale described above. Click on the map to see exact depth values and the earthquake scenario used for the prediction.
The portal also shows designated evacuation buildings (津波避難ビル) marked with specific symbols. These structures meet seismic and height requirements to serve as vertical evacuation sites during tsunami events.
Tokyo Metropolitan Government portal
The Tokyo Metropolitan Government maintains a separate hazard map portal (tokyo-bousai.metro.tokyo.lg.jp) with more detailed ward-specific information.
This portal provides PDF downloads of official ward hazard maps, which include additional detail beyond the web map interface. Each ward’s PDF shows evacuation routes, assembly points, and the specific elevation contours that determine inundation boundaries.
The portal also publishes the technical reports underlying the hazard predictions, including the seismic modeling assumptions, wave propagation calculations, and liquefaction risk assessments. These documents provide the methodology for readers who want to understand the confidence intervals and limitations of the predictions.
Ward office resources
Individual ward offices publish their own hazard map versions, often with neighborhood-level detail and local language versions. Wards with significant foreign resident populations, such as Minato and Chuo, provide English versions of their tsunami hazard materials.
Physical copies of hazard maps are available at ward offices, local libraries, and community centers. These printed versions often include evacuation drill schedules and contact information for local disaster preparedness programs.
Elevation as the primary determinant of safety
Tokyo’s topography creates natural protection for large sections of the city. The Yamanote uplands (山の手), which include neighborhoods like Azabu (麻布), Shirokane (白金), Hiroo (広尾), Daikanyama (代官山), Aoyama (青山), and Setagaya (世田谷), sit 20-40 meters above sea level. No tsunami scenario currently modeled reaches these elevations.
The distinction between shitamachi (下町, low city) and yamanote (山の手, high city) historically reflected elevation differences that created flood risk. This same topography determines tsunami vulnerability. The shitamachi areas along Tokyo Bay and the Sumida River face measurable risk, while yamanote neighborhoods remain beyond the reach of predicted waves.
Within individual wards, elevation varies significantly. Minato ward exemplifies this pattern: waterfront areas near sea level face inundation risk, while properties in Azabu, Roppongi, and Akasaka sit on hills 20-35 meters above sea level. A property in Motoazabu (元麻布) faces zero tsunami risk, while a property in Shibaura, five kilometers away in the same ward, falls within the predicted inundation zone.
Real estate listings in Japan typically do not include elevation data, making independent verification necessary. The Geospatial Information Authority of Japan provides detailed elevation maps through its web portal, allowing precise elevation checks for any address.
Understanding the relationship between earthquake and tsunami risk
Tsunami hazard maps show only the inundation risk from waves. They do not indicate seismic shaking risk, which affects all of Tokyo regardless of elevation.
The Tokyo Metropolitan Government publishes separate seismic hazard maps showing predicted shaking intensity for various earthquake scenarios. These maps use the Japanese seismic intensity scale (震度), which ranges from 0 to 7. Most earthquake scenarios show intensity 6-lower to 6-upper across central Tokyo, which causes significant structural damage to older buildings.
The compound risk matters for evacuation planning. The earthquake strikes first, potentially damaging buildings and blocking streets with debris. Tsunami waves arrive 30-90 minutes later. Evacuation must occur during this window, through potentially damaged infrastructure, to reach either high ground or a designated tall building.
Properties in tsunami inundation zones require both seismic resistance and elevation. A building that survives the earthquake but sits in the inundation zone requires occupants to evacuate vertically during the post-earthquake period. A building outside the inundation zone but with poor seismic resistance may collapse during the initial shaking.
Designated tsunami evacuation buildings
Tokyo designates specific buildings as tsunami evacuation sites (津波避難ビル). These structures meet three criteria: seismic resistance to withstand the initial earthquake, sufficient height to exceed predicted inundation depth by at least one floor, and accessible stairwells that remain usable after seismic shaking.
The designation requires building owners to keep evacuation floors unlocked during business hours and to participate in regular evacuation drills. Many designated buildings are public facilities like schools and ward offices, but private buildings including apartments and office towers also receive designation.
Hazard maps mark these buildings with specific symbols, typically a triangle or building icon with the Japanese characters for “evacuation building” (避難). The maps indicate which floors provide safety, as lower floors may still experience inundation.
For property buyers in coastal wards, proximity to designated evacuation buildings provides a measurable safety factor. A residence within 200-300 meters of a designated building allows rapid vertical evacuation, assuming post-earthquake conditions permit movement.
Natural disaster risk beyond tsunamis
Tokyo faces multiple natural disaster risks that compound in various combinations depending on location and season.
Typhoon and flood risk affects river-adjacent areas, particularly along the Arakawa, Edogawa, and Tamagawa rivers. Heavy rainfall during typhoon season (typically August through October) can cause river flooding independent of tsunami risk. Some low-lying areas face both tsunami and river flood risk, requiring evaluation of multiple hazard maps.
Landslide risk affects hilly areas in western Tokyo wards, particularly on steep slopes where residential development extends into areas with unstable geology. The Tokyo Metropolitan Government publishes separate landslide hazard maps showing slopes at risk of failure during heavy rain or seismic shaking.
Seismic liquefaction affects areas built on reclaimed land, river sediment, or bay fill. During strong earthquake shaking, saturated sandy soil temporarily behaves like liquid, causing buildings to tilt or sink. Liquefaction zones overlap significantly with tsunami inundation zones in areas like Koto, Edogawa, and parts of Chuo ward.
The combination of risks varies by neighborhood. Coastal reclaimed land faces tsunami, liquefaction, and potentially typhoon surge. River-adjacent lowlands face flood and liquefaction but minimal tsunami risk. Hillside areas face landslide risk but no inundation risk. Understanding the specific combination for any property requires checking multiple hazard map layers.
Historical context: past tsunamis and Tokyo
The 1703 Genroku earthquake generated tsunamis that reached Tokyo Bay with wave heights of 2-3 meters, causing significant damage in coastal settlements. Historical records describe waves traveling up the Sumida River and flooding low-lying areas of Edo (江戸, Tokyo’s historical name).
The 1923 Great Kanto earthquake (関東大震災) produced a tsunami that affected coastal areas of Kanagawa and Chiba prefectures but caused limited impact in Tokyo proper. The earthquake’s epicenter location beneath Sagami Bay directed the largest waves toward the Shonan coast rather than Tokyo Bay.
The 2011 Tohoku earthquake and tsunami devastated coastal areas of northeastern Japan, including Hokkaido to Fukushima prefectures. Tokyo experienced seismic shaking but minimal tsunami impact, as Tokyo Bay’s narrow entrance and shallow depth dampened wave energy. The event prompted nationwide revision of tsunami hazard assessments, including Tokyo’s current maps published in subsequent years.
These historical events inform current modeling. The Genroku earthquake provides the basis for Tokyo’s primary tsunami scenario, while the 2011 Tohoku event demonstrated the destructive potential of megathrust earthquakes along Japan’s Pacific coast.
Reading the maps for property evaluation
For anyone evaluating property in Tokyo’s coastal wards, tsunami hazard maps provide specific, quantifiable risk data.
Properties outside the colored inundation zones face no tsunami risk under current modeling scenarios. This includes the majority of Tokyo’s residential neighborhoods. Properties in Setagaya (世田谷), Shibuya (渋谷), Shinjuku (新宿), Meguro (目黒), and the elevated portions of Minato ward sit beyond the reach of predicted waves.
Properties within the inundation zone require evaluation of the specific depth, arrival time, and building characteristics. A tenth-floor residence in a seismically sound building in Toyosu faces minimal practical risk, as occupants can shelter in place above the predicted water level. A ground-floor unit in the same building faces significant risk and requires evacuation.
The maps show maximum predicted depth, not probability. Current seismic research suggests the Genroku-type earthquake has a recurrence interval of several hundred years, while the Nankai Trough megathrust earthquake has an estimated 70-80% probability within the next 30 years according to recent government assessments. These probabilities factor into long-term risk evaluation.
Properties in liquefaction zones face compound risk that extends beyond tsunami inundation. Even buildings that survive the earthquake and tsunami may experience permanent tilt or foundation damage from liquefaction, affecting long-term habitability and value.
Practical steps for checking any Tokyo address
To evaluate tsunami risk for a specific property:
First, determine the precise address and elevation. Real estate listings in Japan typically provide the address but not elevation. Use the Geospatial Information Authority elevation map to check the ground height above sea level.
Second, access either Disaportal or the Tokyo Metropolitan Government hazard map portal. Enter the address and view the tsunami hazard layer. Note whether the location falls within any colored inundation zone.
Third, if the property falls within an inundation zone, identify the predicted depth and arrival time. Compare the building height and floor level to the predicted depth. Identify the nearest designated evacuation building and the route to reach it.
Fourth, check the liquefaction hazard layer. Properties in both inundation and liquefaction zones face higher compound risk.
Fifth, review the ward’s official hazard map PDF for additional detail, including evacuation routes and assembly points specific to that neighborhood.
This process provides concrete data for evaluating the specific risk profile of any Tokyo property.
The 2026 context and ongoing updates
As of 2026, Tokyo’s tsunami hazard maps reflect seismic modeling completed primarily in 2012-2013 following the Tohoku earthquake, with damage estimates updated in 2022. The Tokyo Metropolitan Government conducts periodic reviews as new seismic research emerges and as understanding of the Nankai Trough earthquake risk evolves.
Recent research has focused on refining the probability and magnitude estimates for the Nankai Trough scenario, which would affect multiple prefectures from Kanto to Kyushu. Updates to these models may result in revised tsunami predictions for Tokyo Bay in future years.
Climate change and sea level rise do not currently factor into Tokyo’s official tsunami hazard maps, which model wave height above current mean sea level. Independent research suggests that sea level rise of 0.5-1.0 meters by the end of the century would increase effective inundation depths in coastal areas, though this remains outside official government projections as of 2026.
The maps represent the best available modeling given current scientific understanding. They provide specific, actionable information for evaluating property risk, planning evacuation routes, and understanding which Tokyo neighborhoods face measurable tsunami exposure.
Which parts of Tokyo remain safe from tsunamis
The majority of Tokyo’s residential area sits beyond the reach of any currently modeled tsunami scenario. The entire western half of the 23 wards, including Setagaya, Suginami (杉並), Nakano (中野), Nerima (練馬), and Itabashi (板橋), faces no tsunami risk due to elevation and distance from the bay.
Within central Tokyo, the elevated neighborhoods of the Yamanote area remain safe. Azabu (麻布), Shirokane (白金), Hiroo (広尾), Aoyama (青山), Akasaka (赤坂), Yotsuya (四谷), and similar areas sit 20-40 meters above sea level. Shibuya, Harajuku (原宿), and Ebisu (恵比寿) similarly sit on elevated ground beyond tsunami reach.
Even within wards that contain inundation zones, large sections remain safe due to topography. Minato ward’s western portions, Shinagawa ward’s inland areas, and Ota ward’s residential neighborhoods all sit above the predicted inundation line.
The pattern holds across Tokyo: elevation determines risk. Properties above 10 meters elevation face minimal risk under current scenarios, while those near sea level in coastal wards face measurable exposure.
Koukyuu represents buyers evaluating properties across Tokyo’s distinguished addresses, including detailed analysis of natural disaster risk profiles. For a confidential conversation about specific properties and neighborhoods, reach our concierge team.
