An earthquake is caused by a sudden slip on a fault An earthquake is caused by a sudden slip on a fault. Stresses in the earth's outer layer push the sides of the fault together. Stress builds up and the rocks slips suddenly, releasing energy in waves that travel through the earth's crust and cause the shaking that we feel during an earthquake.  

Earthquakes occur on faults Earthquakes occur on faults. When an earthquake occurs on one of these faults, the rock on one side of the fault slips with respect to the other. Plate interaction cause rocks to fail (give way to the stresses on them). This releases energy that causes vibrations to be sent out from the site of the earthquake in the form of waves.  

Seismic Waves When an earthquake occurs, it releases energy in the form of waves that radiate from the earthquake source in all directions. The different types of energy waves shake the ground in different ways and also travel through the earth at different speeds.

The P waves, also called primary or compressional waves are the fastest wave, traveling 5.5 km/second (3.3 miles/second or 12,000 miles/hour). They and are the first to arrive at a given location and can travel through solid and liquid layers of the earth. They alternately compresses and expands material in the same direction it is traveling. They travel similar to the way an earthworm travels in a push-pull linear motion. Because they travel in a linear motion, there is little displacement of Earth's materials. P-waves are the least damaging of all seismic waves.

The S waves, also called secondary or sheer waves is slower than the P wave, maximum speed is 3 km/second. S waves shake the ground up and down and back and forth perpendicular to the direction it is traveling. Because S waves do not travel in a linear motion these are the most destructive. S waves can only pass through solids, and not through the liquid outer core of the Earth's interior. This is why we can't predict an earthquake.

The Energy of a Tsunami The sudden vertical rise of the seabed by several meters during the earthquake displaced massive volumes of water, resulting in a tsunami that struck the coasts of the Indian Ocean.