In order to understand the response of strong motion at the ground landfill in Tokyo Bay area, we conducted a seismic response analysis of a wide area. The area is a reclaimed land in Tokyo Bay, and it was modeled by three-dimensional FEM over 100m depth 8km north-south east-west 10km. Alluvium was expressed by the non-linear model. In the results of the displacement distribution and acceleration distribution, we found that there is a strong correlation with the alluvium base contour and buried valley.
A simple seismic isolation system by leveraging buoyancy has been devised for spread foundation structures. Through dynamic centrifuge tests, it is shown experimentally that a sliding isolation effect arises during seismic loading if a buoyant force of appropriate magnitude is applied to the base of the foundation. It is confirmed that seismic isolation performance tends to improve as the buoyancy-to-weight ratio increases. Performance when the buoyancy-to-weight ratio is 90% or more is particularly good, and the maximum response acceleration of a structure can be reduced to below 100 cm/s<sup>2</sup> against a sinusoidal wave with a maximum acceleration of 500 cm/s<sup>2</sup>.