TOKYO -- The Sept. 6 deadly earthquake that hit the eastern Iburi region in the northernmost prefecture of Hokkaido triggered soil liquefaction at more than 2,900 spots among 15 municipalities, a team of researchers at the National Research Institute for Earth Science and Disaster Resilience (NIED) has concluded.
Liquefaction occurred in many places as the area was spread out over soft soil susceptible to tremors. In particular, developed land was heavily damaged.
Principal researcher Shigeki Senna and other members from the NIED identified sites presumed to have suffered from liquefaction, prompting sand and water to spew out from the ground. In this process, the team used aerial photographs and other materials showing the land's surface taken by the Geospatial Information Authority of Japan and land survey and planning companies.
NIED members also conducted field research and confirmed 2,933 locations had been hit with liquefaction as of Dec. 5.
In particular, municipalities near the epicenter suffered the most from liquefaction. These included the town of Atsuma, with 919 spots observed, the town of Abira with 512 sites and the town of Mukawa with 387 places. However, the research team presumes that there are more liquefied sites within Atsuma, as some spots have been covered up due to massive landslides.
Furthermore, 370 sites were identified to have been damaged by liquefaction in the prefectural capital of Sapporo, 58 places in the city of Ishikari and four spots in the city of Otaru -- one of which lies in an area about 80 kilometers northwest from the epicenter.
Liquefaction occurred frequently around the Ishikari Lowland plains. Its likely cause was the temblor measuring at least a lower 5 on the 7-point Japanese seismic intensity scale there that shook the soft sedimentary soil stretching out deep under the ground. In general, liquefaction tends to be triggered by a quake registering a lower 5 or greater on that scale.
Most of the liquefied land was developed for installing solar panels and other facilities. A golf course in Ishikari sank due to liquefaction and cracks in the ground. A residential area in Sapporo's Kiyota Ward that suffered severe damage had been built on land developed by filling up a valley.
The places identified to have suffered liquefaction will be reflected in an online hazard map at the Japan Seismic Hazard Information Station website. Users can search earthquake susceptibility and other information on a map compiled by NIED.
(Japanese original by Tomohiro Ikeda, Science & Environment News Department)