The information and video below was provided by USGS and can be found at http://earthquake.usgs.gov/
This video displays 2 major concepts: the first concept, attenuation, as described by USGS is “When you throw a pebble in a pond, it makes waves on the surface that move out from the place where the pebble entered the water. The waves are largest where they are formed and gradually get smaller as they move away. This decrease in size, or amplitude, of the waves is called attenuation. Seismic waves also become attenuated as they move away from the earthquake source”; the second concept is actually a good visual depiction of how the earthquake waves travel and are translated into waveforms for analysis.