GIS-based study on liquefaction-induced soil subsidence in the Urayasu area due to the 2011 off the Pacific Coast of Tohoku Earthquake

Soil liquefaction is one of the geotechnical related effects of earthquakes especially in cities built on young alluvial deposits and reclaimed land. Geotechnical problems associated with liquefaction in these areas include ground subsidence. Therefore, a detailed study on the occurrence and extent of ground subsidence after severe liquefaction following an earthquake is essential in such an area. Urayasu City in the Tokyo Bay area, Japan was selected as the study area. This area is young reclaimed land where severe liquefaction occurred following the 2011 off the Pacific Coast of Tohoku Earthquake (M=9.0). Twenty three borehole locations were selected for the study of liquefaction potential and a geostatistical method of interpolation was applied to attain a spatial variation of liquefaction potential within the area. The ground subsidence was estimated by using airborne LiDAR (Light Detection And Ranging) images before (2006) and after (2011) the earthquake, giving the spatial distribution of soil subsidence. The liquefaction potential and ground subsidence were determined using a PL distribution map and ground subsidence map, respectively. By studying these maps, the relationship between liquefaction potential and ground subsidence was developed. The relationship shows that high ground subsidence is observed in the area with high liquefaction potential.