Abstract
“Chuseki-so” are deposits that formed after the last glacial maximum and are distributed under alluvial plains. The detailed distribution and stratigraphy of these Chuseki-so deposits have been revealed mainly by borehole surveys. Borehole databases created from soil surveys on plains in the study of Chuseki-so and the examination of sedimentary cores reveal the latest Pleistocene to Holocene subsurface geology. Although three-dimensional geological models of these shallow subsurface geological distributions have been constructed using the borehole databases for several alluvial plains, most such models are surface models and have problems handling subsurface aspects such as the identification of stratigraphic boundaries. In this study, we constructed “voxel-based” three-dimensional geological models using a borehole database for the Tokyo Bay area. The shallow subsurface geology of the Tokyo Bay area consists of the buried topography of the Pliocene Edogawa and Tokyo formations created by the last glacial maximum, and thick incised-valley fills. The borehole database is composed of various soil parameters in addition to lithology and the N-value, a standard penetration test of logs. We constructed two types of models: a lithologic model based on grain size analysis and an N-value model. The three-dimensional models agree well with previous studies of sedimentary facies distributions and buried topography, and show the spatial distributions of subsurface shallow-marine deposits under the Tokyo Bay area.
