The effect of base-rock characteristics on the stochastic dynamic response of dam-reservoir-foundation systems subjected to different earthquake input mechanisms is investigated by using the Lagrangian approach in this paper. The effects of compressible wave propagation and surface sloshing motion are included in a finite element formulation of the fluid elements. A concrete gravity dam is chosen as a numerical example. The Pacoima Dam record of the San Fernando earthquake in 1971 is selected as a ground motion. Three different earthquake input mechanisms are used to consider the effect of base-rock characteristics in the analyses: the standard rigid-base input, the massless-foundation input and the deconvolved-base-rock input models. The means of the maximum values of the displacements, stresses and hydrodynamic pressures obtained from the three input model are compared with each other. (c) 2005 Elsevier Ltd. All rights reserved.