A comparative study of seismic responses of land and sea sites based on centrifuge model testing

Earthquake ground motion records often show that soil sites typically exhibit nonlinear amplification characteristics during strong seismic motions. The surface ground motion amplification effects are typically affected by site conditions and topographic features; however, the ground motion and site response of sea-based soil sites have not been extensively investigated due in part to the scarcity of available strong seismic records from few geotechnical observation arrays in the sea areas. In the present study physical centrifuge models are explored to simulate the ground motion response of land-based and sea-based soil sites and site response analysis is conducted to assess the free-field response of both deposits to earthquake motion. Both sites exhibit multiple modes of vibration; the first-order mode dominates in both the land-based and the sea-based soil sites with strongest amplification effect. The second-order mode occurs in both sites and the amplification effect is far more modest than the first-order mode. The amplification effects in the sea-based site are somewhat weaker than those in the land-based site. The third-order mode is found only in the response of sea-based site and the distribution of the amplification factor across the depth appears more complex without a clear pattern than in the lower order modes.