Effects of seawater of Tokyo Bay on short-period strong ground motion

The effects of the seawater of Tokyo Bay on strong ground motions are investigated in a short-period range of less than about 2.0 sec for engineering importance. A recent study based on observed accelerograms revealed that considerable short-period surface waves were included in strong ground motions in the reclaimed zone of Tokyo, and that those surface waves were mainly Love waves. However, it was not clarified whether short-period Rayleigh waves were present. The present study is aimed at assessing the excitation of short-period Rayleigh waves on land and at exploring the effects of the shallow (approximately 25 m) water layer of Tokyo Bay on Rayleigh waves in the reclaimed zone of Tokyo. We use a theoretical approach in which a 2D P-SV-wave field is calculated for a multilayered structural model. The model is composed of a sea zone and a land zone, and includes a water layer and soft-surface layers. To examine the effects of seawater, we use models without and with a water layer. As a result, it is concluded that in the reclaimed zone of Tokyo, stripping the water layer off of a typical model for shallow Tokyo Bay has little influence on the short-period ground motions around the theoretical predominant period of the ground of about 1.0 sec. It is not essential to incorporate the water layer in modeling shallow Tokyo Bay for short-period, ground-motion simulations.