Short answer: liquefaction (液状化, ekijōka) is when loose, water-saturated sand behaves like a liquid during strong shaking, so the ground under a house loses its bearing capacity. The building often survives structurally but ends up tilted, sunk or with broken pipes, and putting it level again is expensive. Japan publishes a national liquefaction tendency map you can check by address in a few minutes, plus older land-history layers that show whether the lot was once a river, a pond or a rice paddy. None of this is in the hazard section an agent must explain before a contract, so you have to check it yourself.
Many low-priced akiya stand on exactly the kind of land that liquefies: former rice paddies converted to housing lots, filled-in ponds, old river channels straightened decades ago, reclaimed coast and sandy dune edges. These were cheap to develop and are still cheap to buy. Liquefaction damage was widespread on reclaimed land around Tokyo Bay after the 2011 Great East Japan Earthquake and in parts of Ishikawa and Niigata prefectures after the January 2024 Noto Peninsula Earthquake, including inland areas far from the epicentre.
The damage pattern is specific, and it changes your budget rather than your safety in most cases:
Since 28 August 2020, an agent selling a house must show you where the property is on the municipality's flood hazard maps (flooding from rivers, inland water and storm surge) as part of the important matters explanation (重要事項説明). Landslide warning zones and tsunami zones designated under their own laws are also explained. Liquefaction is not on that mandatory list. A conscientious agent may mention a local liquefaction map, and the seller must not hide known past damage, but there is no legal duty to tell you that the lot is on a former river channel.
That gap is why this check belongs in your own due diligence, alongside the flood, landslide and tsunami maps. If the house did tilt or have its foundations repaired after an earthquake, that should appear as a disclosure; see kokuchi jiko (告知事項).
The Ministry of Land, Infrastructure, Transport and Tourism (MLIT) and the Geospatial Information Authority (GSI) publish a liquefaction tendency map based on landform classification (地形区分に基づく液状化の発生傾向図). It covers the whole country in a mesh of roughly 250 m × 250 m and shows the relative tendency to liquefy in five levels. It has been available on the national Hazard Map Portal since 17 December 2020 (MLIT press release, Japanese).
How to read it, with the limits the Ministry itself states:
| What the map is | What it is not |
|---|---|
| A relative ranking of how likely each type of landform is to liquefy, based on where liquefaction happened in past earthquakes | A prediction for a specific earthquake, or a statement that a lot will or will not liquefy |
| Good for screening: comparing two or three candidate houses, or spotting a lot that sits on a former channel or reclaimed land | A substitute for a ground investigation at the exact spot. A 250 m mesh can contain both a ridge and a filled pond |
| Nationwide and consistent, so it works in rural areas with no local map | Up to date with recent ground improvement or fill work on an individual lot |
The data behind the layer numbers the levels so that level 1 is the landform most prone to liquefy and level 5 the least; the map legend shows them as colours with short Japanese notes such as 液状化しやすい (liquefies easily) or 液状化しにくい (does not liquefy easily). As a rule of thumb for screening: the two levels at the "liquefies easily" end are a reason to run the next two checks and ask the questions below; the levels at the other end, typically on hill or terrace ground, are usually not where liquefaction risk concentrates, though slope risks then matter more (see our retaining wall and cliff guide).
The single best clue is the history of the ground. The GSI's free web map, 地理院地図 (GSI Maps), has layers that show it directly:
| Layer (Japanese name) | What to look for |
|---|---|
| 治水地形分類図 (flood-control landform classification) | 旧河道 (former river channel), 旧落堀, 湿地, 盛土地 (filled ground) under or next to the lot |
| 土地条件図 (land condition map) | 埋立地 (reclaimed land), 盛土地・埋土地 (filled land), 干拓地 (polder), 砂州・砂丘 (sand bars and dunes) |
| 明治期の低湿地 (Meiji-era wetlands) | Whether the lot was marsh, paddy or water around 1880–1910 |
| 空中写真 (aerial photos, 1945–50 and later) | Whether the lot was a paddy field, pond or river bend before the houses were built |
A house built on a former paddy is extremely common in rural Japan and is not in itself a red flag. A house built on a filled pond, a former river channel or reclaimed land is the combination that most often appears in liquefaction damage reports. Coverage of the classification maps is not complete in every rural area; the aerial photos are available almost everywhere.
While you are on the map, also check MLIT's large-scale fill land map (大規模盛土造成地マップ), which shows housing estates built on large valley fills or side-hill fills. These are a separate earthquake risk (fill sliding), most common in suburban developments from the 1960s–80s.
Many prefectures and cities publish their own liquefaction prediction maps (液状化予測図, 液状化危険度マップ, 液状化しやすさマップ) based on borehole data and a specific scenario earthquake. Where they exist, they are more detailed than the national map. Search for the municipality's name plus 液状化 マップ, or look in the municipality's disaster prevention map (防災マップ). MLIT also publishes a guide for municipalities on liquefaction hazard maps, which lists how local maps are meant to be read.
Local maps often use the PL value (液状化指標値): roughly, PL above 15 is described as high risk, 5–15 as moderate, below 5 as low, in the scenario modelled. Check which earthquake the map assumes and when it was made — some predate the 2011 and 2024 experience.
Checking several houses? An Akiya Check report puts the hazard layers, earthquake shaking probability (J-SHIS), elevation and zoning for the exact lot in one English PDF and flags what needs a follow-up question. Compare 3 does the same for a shortlist, side by side.
Single report $49 · Compare 3 $99 Free 12-point checklistIf you or someone you trust can visit — or during a video walk-through — look for:
A building inspection (建物状況調査) measures floor and wall inclination and checks the foundation for cracks; see home inspection in Japan. It does not investigate the soil.
A soil test at the lot — in housing usually a screw-weight sounding test (SWS試験, formerly called the Swedish sounding test) — tells you how firm the upper layers are. It is routine before building a new house and is usually inexpensive compared with the house price, but it is rarely done before buying an existing akiya. It makes sense when:
For a cheap house you intend to renovate, the map checks above plus a building inspection are usually the proportionate level of diligence. Ask the agent whether the seller has any past ground investigation data (地盤調査報告書) from when the house was built; houses built since about 2000 often have one.
| Japanese | English |
|---|---|
| この土地は過去の地震で液状化や地盤沈下の被害がありましたか。 | Has this land had liquefaction or subsidence damage in past earthquakes? |
| 建物の傾きや基礎の補修、沈下修正の履歴はありますか。 | Has the building been tilted, had foundation repairs or been re-levelled? |
| 新築時の地盤調査報告書や地盤改良の記録はありますか。 | Is there a ground investigation report or record of ground improvement from construction? |
| 市の液状化予測図ではこの場所はどう評価されていますか。 | How is this location rated on the city's liquefaction prediction map? |
| この区画は以前、田・池・川などでしたか。 | Was this lot previously a paddy, pond or river? |
More questions in Japanese and English, ready to copy: questions to ask the agent before buying.
Ordinary fire insurance does not cover earthquake damage, including liquefaction. Earthquake insurance (地震保険), which is sold as an add-on to fire insurance, does cover it, and since the 2011 earthquake the damage assessment includes criteria based on how far a wooden house has tilted or sunk because of liquefaction. Payouts are a fixed percentage of the insured amount by damage grade, and the insured amount is capped at a share of the fire insurance amount — so it softens the cost of re-levelling rather than paying for it in full. See fire and earthquake insurance for akiya.
The national Hazard Map Portal has a liquefaction tendency layer, but it is not part of the flood hazard maps that agents must explain before a contract. You have to switch the layer on yourself under 土地の特徴・成り立ち.
No. Reclaimed coastal land is the best-known case, but liquefaction also occurs inland on former river channels, filled ponds, low-lying paddy land and sandy river plains. The 2024 Noto Peninsula Earthquake caused liquefaction damage well away from the coast in several areas.
Yes, if the price reflects it and you plan for it: earthquake insurance, a check for existing tilt, and an understanding that a rebuild would need ground improvement. Many affordable rural houses stand on paddy-derived land.
It is a screening tool. It ranks landform types by their past tendency to liquefy across a 250 m mesh and does not model a specific earthquake or a specific lot. Use it to decide where to look more closely, not as a guarantee either way.
The report reads the national liquefaction tendency layer for the lot, including the landform classification it is based on (for example a former river channel or reclaimed land), and whether the lot is on mapped large-scale fill. It does not replace a ground investigation, and items that cannot be determined from official data are marked as unknown rather than guessed.
Have a specific listing in mind? Get the official zoning, hazard and transaction data for that exact lot — plus the questions to send the agent — in one report.
Get a $49 risk report Free 12-point checklistThis guide is general information based on public sources cited above. It is not legal, tax, or real-estate brokerage advice. Confirm every item for a specific property with the agent, the municipality, and licensed professionals.