Rotational and vertical components of ground motion are almost always ignored in design or in the  assessment of structures despite the fact that vertical motion can be twice as much as the horizontal  motion and may exceed 2g level, and rotational excitation may reach few degrees in the proximity of fault  rupture.The proposed multi-component response spectrum reflects  kinematic characteristics of the ground motion that are not identifiable by the conventional spectrum  itself, at least for the near-fault region where high intensity vertical shaking and rotational excitation are likely to occur.