Effects of Variable‐Thickness Marine Sediment Layer on the Seismic Response of the Seabed: An Analytical Solution

ABSTRACT The seismic response of the seabed is the basis of assessments of the safety of marine engineering structures and seismic geological disasters. However, traditional theoretical analyses often overlook the spatial variations in the thickness of sedimentary layers, which are precisely the geological conditions commonly faced by offshore engineering. To fill this research gap, in this paper, a dynamic interaction model including seawater, a variable‐thickness sedimentary layer and underlying bedrock for the oblique incidence of P waves and SV waves is established, and the analytical solution of its steady state seismic response is derived. A parameter analysis of the system revealed that the spatial variation in the thickness of the sedimentary layer significantly amplifies the spatial heterogeneity of the seabed response. Even within a small range of inclines, this difference is particularly prominent near the natural frequency of the system. In addition, the influence of the inclination angle at the interface between the sedimentary layers and bedrock on the displacement response presents a complex dual effect; that is, it may play a significant amplifying or suppressing role at different frequencies, incident angles and spatial positions. This study reveals the controlling role of the variable thickness effect on the seismic response of the seabed. The analytical model provided can offer a more precise theoretical basis for the seismic design of offshore engineering projects under complex seabed conditions.