When the rupture of the rock occurs the release of energy causes seismic waves to be produced. Just as wind energy causes waves in water to move across a lake or ocean, seismic waves move through the layers of the Earth. These seismic waves are what produces the destruction that can accompany an earthquake by heaving, shaking, and cracking the ground as they pass through an area. The seismic waves spread out in all directions from the focus.

Compression waves are one type of seismic wave. They are the first to arrive at the surface of the Earth. Because of this they are given another name, P or Primary waves.

P waves are the fastest of the seismic waves. They travel at incredible speeds, 14,000 m.p.h at the surface to over 25,000 m.p.h. through the core of the Earth. P waves are even able to pass all the way through the entire Earth.

When P waves strike an object they push and pull the object , like a train engine bumping into a railroad car which then bumps into another and so on all the way through the whole length of the train. This jackhammer movement is the first sign that an earthquake is occurring.

As a wave passes through a house, the house is pushed and pulled. If the house is not strong enough it might collapse.

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