The development of excess pore pressure (pw) and consequent reduction in effective stress leads to the softening of a liquefiable soil deposit that can alter ground motions in terms of amplitude, frequency content, and duration. To assess these effects in a 1D medium to loose sand model, two analyses were made: (1) A BIOT hydraulic and mechanical computation of a saturated soil deposit and (2) a mechanical computation of a dry soil with equivalent behavior. The results regarding the profile of maximum accelerations and shear strains, the surface accelerations and their corresponding response spectra ratio are analyzed. The mean values of the normalized response spectra ratio between the wet and dry surface acceleration show a deamplification of high frequencies (i.e. f > 1.0Hz) and an amplification of low ones that tend to increase with the liquefaction zone size. Coupling of pw and soil deformation is therefore of great importance to accurately model the ground motion response. On the contrary, while peak acceleration predictions could be conservative, the amplification on the low frequencies could be largely underestimated which would be highly prejudicial for tall buildings.