Here's why:

* P-waves (Primary waves) are the fastest type of seismic wave. They travel through solids, liquids, and gases.

* Compressional force is a force that pushes or pulls on an object in the same direction as the force is applied.

* How P-waves work: P-waves travel by compressing and expanding the material they pass through, like a spring being squeezed and released. This compression and expansion creates a series of alternating high-pressure and low-pressure zones that propagate outward.

In summary: The compressional force generated by an earthquake or other seismic event is what creates the P-waves that travel through the Earth.