Abstract: The study of the seismic performance of marine soft soil sites becomes increasingly necessary with more and more near shore projects development in recent years. Numerical models for Both the nearshore and onshore sites with and without soft soil lenses were established by the commercial finite difference software FLAC3D. Different seismic waves, El Centro Wave and Kobe Wave, were input horizontally into the numerical models for the peak ground acceleration and seismic response spectrum in different soil sites and their differences. The results indicate that, the onshore site without soft soil, near shore without soft soil, onshore site with soft soil have significant difference in the magnitude of peak ground acceleration and the shape of the seismic response spectrum. At the low and medium frequency area, the response spectrum in the soft soil site is obviously higher than that of in other sites. The presence of the soft soil lens will magnify the acceleration. The soft soil lens in marine site has larger magnify effect than onshore site. Compared with other sites, the peak ground acceleration response spectrum of marine soft soil site has a lapse in the response.

Key words: soft soil, offshore site, peak ground acceleration, seismic response spectrum