Horizontal and vertical motion at surface of a gassy ocean sediment layer induced by obliquely incident SV waves

Free gas is ubiquitous at shallow sediment depths of the continental margins of the worldwide oceans. However, theoretical study of the dynamic behavior of gassy seafloor under the action of earthquake has been rare. In this paper, a theoretical model for the analysis of the horizontal and vertical motion at the surface of a gassy ocean sediment layer induced by SV waves is developed based on the multiphase poroelasticity theory. The marine sediment layer with finite thickness is assumed to between seawater and underlying elastic solid seabed. The pores of sediment are filled by two compressible and viscous fluids (i.e., liquid and gas). The theoretical formulation is derived for the computation of horizontal and vertical motion in forms of displacement amplitudes, displacement ratios and amplification coefficients, which are defined as a function of incident angle, wave frequency, thickness of porous layer and saturation degree of sediment. Numerical results show that even a slight decrease of full saturation of the porous sediment may lead to significant influence on sediment's displacement amplitudes, displacement ratios as well as the amplification coefficients. Apart from saturation degree, this influence also depends on the incident angle, wave frequency and thickness of sediment layer.