Study on the influence of the seafloor soft soil layer on seismic ground motion

摘要

In the complex medium system of the sea area, the overlyingseawater and the surface soft soil have a significant impact on theseafloor ground motion, which brings great seismic risk to the safety ofoffshore-engineering structures. In this paper, four sets of typical free-field models are constructed and established, comprising a land model, landmodel with surface soft soil, sea model and sea model with surface softsoil. The dynamic finite-difference method is used to carry outtwo-dimensional seismic response analysis of a typical free field based on theinput forms of P?and SV?waves. By comparing the seismic response analysisresults of four groups of calculation models, the effects of overlyingseawater and soft soil on the peak acceleration and acceleration responsespectrum are studied. The results show that when an SV wave is input, the peakacceleration and response spectrum of the surface of soft soil on thesurface and the seabed surface can be amplified, while the overlying seawater can significantly reduce the ground motion. When the P?wave is used, theeffect of overlying seawater and soft soil on the peak acceleration and responsespectrum of the surface and seabed can be ignored. The peak accelerationdecreases first and then increases from the bottom to the surface, and thedifference of peak acceleration calculated by four free-field models is notobvious. The results show that the overlying seawater and the surface softsoil layer have little effect on the peak acceleration of ground motionbelow the surface.