This study presents the results of a numerical analysis investigating the influence of the interaction between seismic waves and slopes on seismically induced displacements of existing landslides. Three step‐like slope geometries with dip angles varying from 10° to 45° and two landslide mechanisms were considered; 54 multifrequential dynamic equivalent signals were applied to the models and were derived according to the LEMA_DES approach based on the accelerometric records of the European Strong Motion and COSMOS databases. The simulations were performed using a finite‐difference approach that assumed different viscous rheologies and considered different values for both the dynamic properties and the mechanical parameters. The interaction between seismic waves and landslides was analyzed using frequency ratios defined for characteristic periods associated with the landslide dimensions (i.e., thickness and length) and the seismic input. A regression analysis was also performed to derive correlations between seismically induced displacements and the frequency ratios, the values of the Arias intensity, and the critical accelerations. The obtained results reveal that (a) the seismically induced displacements increase with the seismic amplification induced by the landslide mass; (b) the coupling of a 2D interaction between seismic waves and slope with the 1D resonance of the landslide mass, which is strictly related to the high‐impedance contrasts between the landslide mass and the substratum, significantly affects the seismically induced displacements; and (c) the seismically induced displacements increase more intensely with increasing slope angle for a rototranslational mechanism with respect to a translational one. Moreover, the seismically induced displacements that can be expected from the here‐obtained results can significantly differ from those computed by the sliding‐block stability analyses based on Newmark’s method.