The problem of the determination of the dynamic pressures and the associated forces on a rigid, vertical cantilever wall retaining a semi-in®nite, uniform, fully-saturated poroelastic (with or without hysteretic damping) layer of soil under conditions of plane strain is considered. The rigid wall and the base of the soil layer are both excited by an acceleration harmonically varying with time and spatially invariant. The method of solution is based on the theory of Mei and Foda and considers the total ®eld to be approximated by the superposition of an elastodynamic problem with modi®ed elastic constants and mass density for the whole domain and a diffusion problem for the pore ¯uid pressure con®ned to a boundary layer at the free boundary (top) of the soil layer. Both problems are solved analytically in the frequency domain. Extensive parametric and comparison studies are conducted in order to assess the range of values of the various parameters (frequency, shear modulus, Poisson's ratio, porosity and permeability) for which the accuracy of the present method against the direct one, reported in a companion paper, is satisfactory.