In this paper the effect of underground cavities on the seismic response under incident plane waves of volume and surface has been studied.The numerical solution is obtained using the boundary element method in the BESOIL /14/ computer code that allows a 2D analysis of propagation both of volume and Rayleigh waves, and any geometry of the cavity and the ground surface.The main parameters that govern the phenomenon of amplification are considered and the criteria for determining their importance are provided. Finally a realistic cavity of irregular shape has been examined for different values of its depth and dimension.