Can You Check Liquefaction Risk Before Buying? Ground, Reclaimed Land and Quake Insurance
Written by：SUMIMOTO Inc.Editorial Policy
When searching for property in Japan, the ground beneath the building tends to come last, after price, distance to the station and building age. Yet in an earthquake, the same seismic intensity can cause very different damage depending on the ground, and on reclaimed land or former riverbeds in particular, liquefaction can become an issue.
This article walks through how to check liquefaction risk yourself before signing, what such checks can and cannot tell you, and how to think about earthquake insurance as protection after purchase.
What is liquefaction, and where is it more likely?
Liquefaction occurs when loose, sandy ground with a shallow water table is shaken hard: the sand grains separate and the ground temporarily behaves like a liquid. It can tilt or sink buildings, push water and sand up through the surface, and damage utilities.
It is generally considered more likely on reclaimed land, former riverbeds, filled-in wetlands or ponds, and low ground between sand dunes. But this is a tendency only; conditions differ plot by plot even within one neighbourhood, so an area name alone should not decide whether it is safe.
Figures worth keeping in mind
- New seismic standards take effect (June)
- 1981
- Rules for timber foundations and joints clarified
- 2000
- Earthquake insurance sum insured (share of fire insurance)
- 30–50%
For older buildings, it is common to check whether a seismic assessment exists
Foundations are expected to match the strength of the ground
Typical caps: about JPY 50 million for buildings, JPY 10 million for contents
Where can you check liquefaction risk?
No single document settles liquefaction risk. In practice, the basic approach is to layer several sources and read how the land was formed.
Main ways to check liquefaction risk
| Method | What it tells you | Caveats |
|---|---|---|
| Municipal liquefaction map | Liquefaction hazard zones published by the city or ward | Not every municipality publishes one; the year and assumed quake differ by document |
| Landform classification (e.g. GSI) | Reclaimed land, former riverbeds, fill, valley floors | Shows tendencies from landforms, not whether damage will occur |
| Ground data (boring logs) | Soil layers and water table at survey points published by public bodies | Even a nearby point may not match the plot itself |
| Old maps and past topographic maps | Whether the site was once a river, pond or sea | Takes some practice to read; an expert can make it more reliable |
Once you have a shortlist, check each address against these sources. For newly built homes, it is also practical to ask the seller to show the ground survey results and any ground improvement work in writing.
Does the pre-contract briefing cover liquefaction?
Under the Real Estate Brokerage Act, a licensed agent must explain important matters before the contract is concluded. The location on the flood hazard map has become a required item, but liquefaction hazard generally is not, so the information may not come up unless you ask.
Laws on building safety
- Building Standards Act, Art. 20
- Buildings are required to have a structure that is safe against their own weight and external forces such as earthquakes.
- Enforcement Order of the Building Standards Act, Art. 38
- Foundations must transmit building loads safely to the ground and be safe against ground settlement and deformation.
Laws on pre-contract explanation
- Real Estate Brokerage Act, Art. 35
- Before a contract is concluded, a licensed agent is required to explain important matters in writing.
How should you think about protection after buying?
Ground conditions cannot be changed after purchase, so the basic approach is to decide before signing whether to accept the risk knowingly or avoid it. If you accept it, earthquake insurance is the usual form of protection: it is added to a fire insurance policy, and building tilt or settlement caused by liquefaction is assessed according to the degree of damage.
Common oversights and fixes
✕Relying on a "low hazard" label on one map and missing that the plot sits on a former riverbed or fill.
→Layer landform classification and old maps on top of the liquefaction map to confirm how the land was formed.
✕Signing for a new home without seeing the ground survey results.
→Get the ground survey report and the ground improvement details in writing, and keep them.
✕Assuming liquefaction damage is covered by fire insurance.
→Damage caused by earthquakes is generally excluded from fire insurance. Check earthquake insurance conditions and coverage before signing.
✕Looking only at the building's seismic performance and not at the ground under it.
→Check seismic performance and ground together, and take expert advice where needed.
Ground checklist before you commit
- I checked the zone on the municipal liquefaction map
- I checked the landform classification for reclaimed land, former riverbeds or fill
- I checked old maps to see whether the site was once a river, pond or sea
- For a new home, I confirmed the ground survey report and any ground improvement in writing
- I kept my questions to the agent and their answers in writing or email
- I obtained a quote for earthquake insurance coverage and premiums
Frequently asked questions
- Q. Should I avoid reclaimed land altogether?
- A. Risk varies with the ground improvement and reclamation method even on reclaimed land. It is common to judge from the documents and ground survey results rather than avoid it across the board.
- Q. What if my municipality has no liquefaction map?
- A. Combine landform classification, old maps and public ground data. If you are unsure, you can consult a ground engineering specialist.
- Q. Am I safe if ground improvement was done?
- A. Effectiveness depends on the measures and the assumed earthquake size, so do not rely on a single word like "improved"; read the details of the report.
- Q. Will insurance pay if liquefaction tilts my house?
- A. Earthquake insurance has a mechanism for assessing tilt and settlement caused by liquefaction, but payment is a proportion based on the degree of damage. Please check your policy in advance.
In the SUMIMOTO Hub app, a 24-hour AI advisor can use a property's location to walk you through how to read ground and hazard maps and which documents to check, in multiple languages. Before any final decision, please also confirm with a real estate company and ground or building specialists.
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References & Sources
This article provides general information as of its publication date and is not individual legal, tax or investment advice. It was written with the help of generative AI.Editorial Policy
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