Input motion of an actual embedded foundation subjected to spatially variable seismic ground motions can be simulated by using the spatial averaging procedure of free-field ground motions considering random (spatially incoherent component) and deterministic(time delay along the propagation path) effects. The simulation results are discussed by the records of earthquake observations and the data of excitation experiment. The conclusions are summed up as follows: (1) The horizontal-translational component and torsional component calculated from the realistic spatial-correlation model of ground motions at the site, almost agreed with the actual records of thirteen earthquake events. (2) The amplitude characteristics of translational component estimated from the spatially variable motions shows the reduction of 20 percent at the frequency of 8Hz in comparison to the characteristics due to uniform S-wave vertical incidence.