[S-SS04] Seismological advances in the ocean

[SSS04-P02] Investigation on the Effect of Surface Soft Soil on Seismic Ground Motion Parameter in Bohai Sea, China

*Yi Fang¹、Yanju Peng¹、Xingyuan Zhou¹ (1.National Institute of Natural Hazards, Ministry of Emergency Management of China)

キーワード：Nonlinear analysis, Surface soft soil, Ground motion parameters

The surface soft soil in Bohai presents a significant impact on the ground motion design parameters. The boreholes in the central Bohai are selected as the basis for the seismic response simulation. The site models with surface soft soil and without surface soft soil are constructed respectively, and a series of new soil models are constructed by changing thickness of surface soft soil. The seismic site response analyses are performed by equivalent linear wave propagation analysis (EL) and nonlinear analysis (NL). The influences of the surface soft soil on the ground motion parameters are concluded as follows. The submarine surface soft soil has a significant impact on the peak acceleration of ground motion. The amplification effects of the soft soil layer fade with the increasement of
the input ground motion, and the reduction effects strengthen gradually. In the EL method, the surface soft soil layer has obvious filtering effects on the high-frequency part of the bedrock response spectrum. In the NL method, the filtering effects are much weaker, and the seabed surface response spectrum appears as the input ground motion increases at first and decreases afterwards. The maximum of the seismic effect coefficient decrease, and the characteristic periods of response spectra increase because of the existence of surface soft soil. It is recommended to remove the soft surface layer before building the site model for the determination of the marine engineering ground motion parameters.