Seismic waves result from the release of energy when earth's crust breaks. These breaks are due to the stress of earth's moving tectonic plates. When there is an earthquake (the release of energy from breaking crust) the resulting waves travel through the earth and can be measured with instruments called seismographs. There are two main types of waves, body waves and surface waves.
Body waves travel at a higher frequency than surface waves and therefore, can travel through all of the materials of the earth, solid and liquid. There are two types of body waves: primary waves and secondary waves.
Also called P waves. P waves are the fastest of all seismic waves. They travel in a path that is parallel to the direction of movement of the wave. Click here to see a demonstration.
Also called S waves. S waves only move through solid material. They travel in a path that is vertically perpendicular to the direction of movement of the wave. Click here to see a demonstration.
Surface waves travel at a lower frequency than body waves and therefore have a longer wavelength. The longer wavelength results in more movement (more damage!) on the surface of the earth. There are two types of surface waves: love waves and Rayleigh waves.
Love waves are the fastest of the surface waves and have movement that is horizontally perpendicular to the direction of movement of the wave. Click here to see a demonstration.
Rayleigh waves move across the surface similar to an ocean wave moving across the sea. The rolling and twisting motion causes most of the movement and damage that is felt during earthquakes. Click here to see a demonstration.