Shoichi Hachinohe

Land Subsidence Detected by Persistent Scatterer Interferometry Using ALOS/PALSAR Data from the Nakagawa Lowland in the Central Kanto Plain, Japan

The Nakagawa lowland is located in the central part of the Kanto Plain; the largest plain in Japan. During the 1960s, major land subsidence occurred, exceeding 10 cm/year, as a result of over pumping of shallow and deep groundwaters in this area. In recent times, following the regulation of pumping by national and local governments, the amount of land subsidence in this area has decreased sharply. However, in the Nakagawa lowland, subsidence exceeding 1 cm/year is still ongoing in some areas, and is more pronounced during dry years in which the amount of groundwater use increases. In this study, we examined the local characteristics of land subsidence through persistent scatterer interferometry using ALOS/PALSAR data obtained from April 2006 to April 2011. On the basis of this analysis, we confirmed that subsidence was concentrated along the western margin of an incised buried valley, in which average displacement rates exceed 10 mm/year. The characteristics of this subsidence zone are suggestive of a geological structure that is buried beneath the alluvial plains, which is affected by groundwater pumping that targets the basal gravel layers of buried valley-fills. In addition, we detected a patched zone of around 0.3 km2 in the study area, in which average displacement rates exceed 15 mm/year. We estimated that this zone was formed by consolidation settlement of soft ground as a result of residential landfill.