Which type of seismic wave compresses and expands the ground?

The correct answer is P wave. P waves, or primary waves, are the fastest type of seismic waves and are classified as compressional waves. They move through the Earth's interior by compressing and expanding the material they pass through, similar to how a slinky works when pushed and pulled. As they travel, they create areas of high pressure where particles are pushed together and areas of low pressure where particles are pulled apart. This back-and-forth motion results in the characteristic compressive nature of P waves, allowing them to travel through solids, liquids, and gases. This behavior distinguishes them from the other types of seismic waves, which do not compress and expand the ground in the same manner.