The Ministry of Land, Infrastructure, Transport and Tourism (MLIT) plans to publish embankment and liquefaction risk maps online later this year in an effort to provide more transparency for home owners and buyers.
Over 10 years have passed since the MLIT requested that cities and towns carry out land surveys and make this information public, however 30% of local jurisdictions have yet to do so. Delays have been due to the costs involved in the reporting process along with fears that areas deemed at risk may suffer from a subsequent drop in land values. To speed up the process, the MLIT is stepping in and carrying out the necessary surveying and reporting on behalf of these cities.
Embankments are often created when developers carve housing subdivisions out of hillsides and valleys. Not all embankments pose a risk to residents, although there have been cases in previous disasters where lives and homes have been lost from landslides and liquefaction.
The 1995 Great Hanshin Earthquake saw 34 lives lost due to a landslide in a housing subdivision. The 2004 Chuetsu Earthquake in Niigata saw 109 of the 521 lots in a hillside subdivision condemned due to landslips, with all households given a temporary evacuation order.
In parts of Sendai, the 2011 Tohoku Earthquake caused serious landslips in hillside residential subdivisions. Many of the affected areas were developed in the 1950s and 1960s, while some were created in the 1980s and 1990s.
In 2006 the government requested that all cities and towns across Japan conduct surveys into any embankments over 3,000 sqm in size or with a height difference of over 5 meters and to publish these results on maps. By the end of 2006, over 1,000 embankments nationwide were designated to be at risk of collapse in the event of a major earthquake.
At the end of 2018, only 66% of the various cities, towns and districts across Japan had published the results of these surveys. In Tochigi Prefecture there are no published maps, while Chiba Prefecture’s ratio sits at 9%. In Tokyo, Saitama, and Kanagawa, the ratio is 100%.
For liquefaction risk areas, the MLIT will be stepping in to finish surveying on behalf of 1,350 cities and towns (80% of the total), with the maps to be made public this year.
Before buying, go for a good walk around the neighborhood and be on the lookout for terraced lots and retaining walls that might indicate that the land has been filled in. Satellite images and old aerial photos can also give an idea of the topological features now and in the past. For hazard maps, check with the local city office where the property is located. Some local city offices publish these maps on their websites.
The Asahi Shimbun, April 3, 2019.
The Ministry of Land, Infrastructure, Transport and Tourism.