Geomorphological condition and land history of liquefaction damaged sites in the lower part of the Tone River lowland induced by the 2011 off the Pacific coast of Tohoku Earthquake

Abstract

Extensive liquefaction damage due to the 2011 off the Pacific coast of Tohoku Earthquake was observed in the lower part of the Tone River lowland. Numerous sand boils due to liquefaction were observed in rice paddies and high-water channels along the Tone River. Severe structural damage was also observed due to liquefaction such as settling and tilting of structures and electricity poles, vertical offset between building foundations and subsided surrounding ground, settling and cracking of river dikes and roads, and uplift of sewage manholes. Most of these liquefaction sites in this area were concentrated in former river channels, ponds, and marshes along the Tone River and Kokai River, which had been artificially filled with loose sandy deposits of dredged soil since about 1900 to increase the land area for the production of rice or development of residential land. The occurrence of extensive liquefaction damage in the study area was largely affected by the existence of loose young soil formed by these recent man-made landfills. The filling of these former river channels and ponds had been mostly completed before 1970, and the ground consisting of more recent landfills is more susceptible to liquefaction than that created by the older ones. Each condition also resulted in the amount of uplift displacement of sewage manholes in the study area smaller than in other liquefied areas. Vulnerability to liquefaction is therefore significantly affected by the land history such as landform evolution and artificial modification of the topography and subsurface layer as well as the distribution of microtopography.