Photo/Illutration A home in Suzu, Ishikawa Prefecture, damaged in the Jan. 1 Noto Peninsula earthquake remains unremoved on Dec. 4. The district head said the house was vacant before the quake. (Yota Kosaki)

At least 1.45 million vacant wooden homes are located in areas vulnerable to severe shaking in long-expected mega-earthquakes, creating a potential hazard for rescue and recovery operations, an Asahi Shimbun analysis found.

These homes are in 856 municipalities across 28 of the nation’s 47 prefectures, where intensities of lower 6 or higher on Japan’s seismic scale of 7 are expected during a Nankai Trough quake or Tokyo inland earthquake.

A quarter of the buildings show signs of decay or structural damage.

The Jan. 1 Noto Peninsula earthquake highlighted a serious problem with abandoned homes. Many of these vacant buildings collapsed during the shaking, obstructing rescue efforts and delaying recovery.

The analysis drew on data from the internal affairs ministry’s housing and land statistical survey as of October 2023 and the Cabinet Office’s projected seismic intensity data.

In the Noto Peninsula earthquake, Ishikawa Prefecture reported damage to about 99,000 homes as of Dec. 17.

In the hardest-hit cities of Wajima and Suzu, vacant wooden houses accounted for about 22 percent of all homes, far exceeding the national average of 4.5 percent.

The collapsed homes blocked roads, and in many cases, unclear ownership prevented their removal.

The analysis focused on 658 municipalities of the 856 nationwide projected to experience seismic intensities of 6 to 7. Towns and villages with populations under 15,000 were omitted due to a lack of housing data.

Among the 42.3 million homes in these municipalities from Kita-Kanto to Kyushu, 1.445 million wooden homes, or around 3 percent of the total, were vacant with no specific use. They did not include rental properties and vacation homes.

Of the vacant buildings, 90 percent were detached houses.

Around 364,000 of the buildings were showing signs of decay or structural damage, such as cracks in the walls or foundations.

A separate 2019 survey by the infrastructure ministry found that nearly 80 percent of vacant homes were built before 1981 under the old seismic standards that do not meet the current criteria for withstanding quake intensities of upper 6 to 7.

Poor ventilation, particularly in wooden homes, accelerates structural decay, as moisture and mold can quickly weaken pillars and other key components.

By prefecture, Osaka had the most vacant homes with about 127,000, followed by Aichi with 98,000, Tokyo with 87,000, Chiba with 86,000, and Hyogo with 83,000.

“The Noto Peninsula earthquake highlighted the disaster risks posed by vacant homes, but few owners seem fully aware of the dangers,” said Nobuo Fukuwa, professor emeritus of earthquake engineering at Nagoya University.

“As the number of vacant homes is expected to rise, policies to encourage reuse or removal, such as implementing vacancy taxes or strengthening taxation measures, will be critical,” he said.

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