ABSTRACT
ABSTRACT: The fluidisation and subsidence of gently sloped farming fields took place in Tanno area of Kitami city in Hokkaido, Japan, during 2003 Tokachi-oki Earthquake, which occurred at 4:50 am on September 26, 2003. The area of 35 metres wide and 150 metres long subsided and the water channel located at the downstream area was filled with erupted subsurface soils for a length of about 1 km. The subsided farming field corresponded to the area that had been used as a paddy field, however had been reclaimed with the deposits of local volcanic soil. The subsurface layer consisting of loosely dumped deposits of volcanic soil was found to have been liquefied and erupted onto the surface, which caused subsidence during the earthquake. Multiple series of Swedish weight sounding tests were conducted and the soil profiles at several cross sections were estimated. Based on the soil profiles estimated from the field sounding tests, the subsurface liquefiable soil layer was detected. The progressive sequence of fluidisation and flow of subsurface soil and associated ground subsidence is discussed.
