Nonlinear seismic response of seabed with terrain variation and seawater-seabed coupling

Abstract

Understanding the seismic characteristics of submarine sites and conducting seismic response analysis for such locations are crucial for the safety of marine engineering. However, due to a shortage of strong motion records, the ground motion of offshore earthquakes has not yet been fully characterized. The actual seabed conditions are highly intricate, necessitating consideration of factors such as the dynamic coupling effect between seawater and seabed, the strong nonlinearity of seafloor soft sediments, and the diverse nature of natural submarine terrain. In this study, the modified Davidenkov dynamic constitutive model is used to simulate the nonlinear behavior of the soil. The Coupled Acoustic-Structure method is utilized to simulate the interaction between seawater and seabed. Three typical and simplified terrains, namely flat terrain, valley terrain, and hilly terrain, are individually modeled. The measured seafloor ground motions with different frequency components are used as bidirectional seismic excitations input from the bedrock. The amplification factor in terms of CAV is introduced to evaluate the amplification of seismic ground motion characteristics at seabed surface with respect to those at the bedrock surface. The acceleration response spectra in both horizontal and vertical directions, as well as the corresponding vertical-to-horizontal response spectral ratios, at the representative points are obtained, respectively. Several key findings are consistent with the features of the observed offshore and onshore earthquake ground motions. Numerical examples are presented to illustrate the different influence rules of terrain condition, overlying water depth, and seismic intensity on the nonlinear seismic response characteristics.