KH+CA+Earthquake+9-28-07



Earthquake finder at http://quake.usgs.gov/recenteqs/Quakes/quakes0.html Sesmic Wave Info at http://www.seismo.unr.edu/ftp/pub/louie/class/100/seismic-waves.html

P waves  S waves
 * [|P waves]** are [|longitudinal] or compressional waves, which means that the ground is alternately compressed and dilated in the direction of propagation. In solids these waves generally travel slightly less than twice as fast as S waves and can travel through any type of material. In air, these pressure waves take the form of sound waves, hence they travel at the [|speed of sound]. Typical speeds are 330 m/s in air, 1450 m/s in water and about 5000 m/s in granite. P waves are sometimes called "primary waves". When generated by an earthquake they are less destructive than the S waves and surface waves that follow them, due to their lesser amplitudes.
 * [|S waves]** are [|transverse] or shear waves, which means that the ground is displaced perpendicularly to the direction of propagation. In the case of horizontally polarized S waves, the ground moves alternately to one side and then the other. S waves can travel only through solids, as fluids (liquids and gases) do not support shear stresses. Their speed is about 60% of that of P waves in a given material. S waves are sometimes called "secondary waves", and are several times larger in amplitude than P waves for earthquake sources.