The Asahi Shimbun reported Sunday that the study, by Nagoya University’s Disaster Mitigation Research Center, showed that of the nation’s 128 million residents, 21.8 million lived on land less than 16 feet above sea level, most of which extends along coastal areas.
This equates to 17 percent of the population on 3.3 percent of Japan's total land mass that is at risk, according to the study.
Tokyo had the largest number of residents living in a potentially tsunami vulnerable area, with 3.43 million, followed by Osaka Prefecture with 3.06 million, Aichi Prefecture with 1.74 million and Chiba Prefecture with 1.44 million.
The study says the expected height of a tsunami and the scope of damage would depend on the topography of each area and how prepared local communities were for dealing with a disaster with countermeasures such as a seawall, researchers say.
But Nobuo Fukuwa, professor of environmental and safety management at the center who led the study, said authorities should compile response measures by taking into account various dangers facing lowlands.
“Low-lying lands are at risk not only for tsunami, but also for tidal waves, the strong tremors of a quake and liquefaction,” Fukuwa said.
Around seven percent of the population lived in lowlands less than 16 feet above sea level in the prefectures of Iwate, Miyagi and Fukushima, when a massive tsunami struck after the 9.0-magnitude earthquake on March 11, 2011.
Despite the lesser population density, the tsunami caused a large number of deaths in the region. More than 15,000 reportedly died as a result of the tsunami.
Fukuwa conducted the study with Kumiko Wakita and other researchers. Their findings are based on the maps showing the elevation in each of the 250-square meter segments compiled by the Geospatial Information Authority of Japan and the 2005 national census.