A shake table allows a structure, anywhere from a scale model to a full-size building as in this video, to be subjected to structural loads simulating those created by an earthquake, with up to six degrees of freedom (movement along the X, Y, and Z axes and angular motion in roll, pitch, and yaw). A particular difficulty in operating a shake table is the need to compensate for the natural resonances of the apparatus itself so the attached structure sees only those of the loadings being simulated.
For another approach to seismic testing which allows simulating events such as soil liquefaction, see the post from 2022-08-30, “An Earthquake Simulator”.