Inclination of houses induced by liquefaction in the 2018 Hokkaido Iburi-tobu earthquake, Japan

BackgroundOn September 6th, 2018, at 3:07 local time, a strong earthquake of magnitude Mw=6.6 struck the east Iburi region in Hokkaido, Japan. Many serious damages such as landslide, liquefaction and collapse of houses occurred from this earthquake. Liquefaction caused road deformation and inclination of houses in Sapporo city, Hokkaido. In order to understand the damage caused by the earthquake, and find a solution to mitigate the liquefaction-induced damage in Sapporo city, a preliminary investigation of the 2018 Hokkaido Iburi-tobu earthquake was conducted from 18 to 20 September 2018.ResultsThe damages to the houses at Satozuka town and Utsukushigaoka town in Sapporo city are focused on. The damage at Satozuka was so enormous that the residents could not continue to live in their houses. Although the inclination of houses can be seen by visual inspection at Satozuka, there were few houses where the inclination can be judged visually at Utsukushigaoka. Therefore we did a field survey of inclined houses by using a digital angle meter at Utsukushigaoka.ConclusionsThe inclination of 57 houses at Utsukushigaoka was measured, and the maximum value and direction of inclination are shown on the map. The houses located at the reclaimed land of the former river and former valley plain were inclined. Therefore, the old terrain greatly affected to the inclination of houses. These liquefaction-induced damage occurred in the same area where liquefaction occurred during the 2003 Tokachi-oki earthquake.