The seismic waves that move rock particles at right angles to the direction of the wave are called S-waves, or secondary waves.

Here's why:

* S stands for "shear": These waves cause a shearing motion in the rock, like trying to move a deck of cards by sliding one card over another.

* Right angles: The particles oscillate up and down or side to side, perpendicular to the direction the wave travels.

Important Note: S-waves can only travel through solids because they require the rigidity of the material to propagate. They cannot travel through liquids or gases.