Dynamic Response of the Seawater-Layered Seabed System Subjected to Rayleigh Waves

[Purposes] The study on Rayleigh wave propagation characteristics at the interface between seawater and layered seabed as well as the dynamic response of free field by the virtue of a coupled finite element and theoretical method is currently insufficent. [Methods] Both the overlying sedimentary layer and the fluid layer were discretized into (one-dimensional, two-node, linear elements) according to standard finite-element techniques. The relation between the node displacement and node force on the surface of the underlying half-space was integrated into the global stiffness matrix. The dispersion characteristic equation of Rayleigh wave in the wavenumber-phase velocity (k-c) domain was solved by transforming it into a quadratic eigenvalue problem. The multiple modes and dynamic response of the free field as well as the overlying fluid layer were obtained. [Findings] The results show that a thicker seawater layer or sedimentary layer will result in a slower phase velocity under the fundamental mode and a more obvious decreasing rate with the increase of frequency, while both horizontal and vertical displacements at the bottom of seawater are relatively larger. The hydrodynamic pressure increases first and then decreases with increasing frequency, and finally decays to zero. Furthermore, with same frequencies the displacements under high order modes are relatively large.