The study srea, Mizushima is occupied by polder and reclaimed land. The ground of this area is composed of the Holocene deposits below the surface. The deposits are mostly 10 to 20m in thickness and composed of 2 units, the B Unit and C&D Unit. The B Unit is composed of muddy sand with 2 to 3m in thickness. This unit is thought to be deposited in the mouth of paleoriver. The C&D Unit is composed of marine mud and sand with 10 to 15m in thickness. This unit is especially soft and will expand ground oscillations during an earthquake.