Which type of seismic wave causes the ground to move up and down?

The movement of the ground up and down is primarily associated with Rayleigh waves, which are a type of surface wave. These waves cause both vertical and horizontal ground movement, leading to the characteristic rolling motion often felt during an earthquake.

While P waves (primary waves) do compress and expand materials in the direction of travel, their motion is more about pushing and pulling rather than creating an up-and-down movement. S waves (secondary waves) move in a shearing manner but primarily produce side-to-side motion, and surface waves encompass both Rayleigh waves and Love waves, with Rayleigh being the specific type that contributes significantly to the vertical displacement in the ground during an earthquake. Thus, Rayleigh waves would be the precise choice for describing the up-and-down motion of the ground.