Download Seismic Waves

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. 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.