An elastic wave generated by an impulse such as an earthquake or an explosion. Seismic waves may travel either along or near the earth's surface ("Rayleigh" and "Love" waves) or through the earth's interior ("P" and "S" waves).

Waves of Destruction

Earthquakes are said to radiate destruction much like bomb blasts in that seismic waves burst from the underground hypocenter (the point within the earth where an earthquake rupture starts; also known as the focus).

Surface waves consist of heaving waves produced by P and S waves. The P wave is the fastest wave which is generated by the fault rupture and it compresses and stretches the rock area. The S wave is slower but often the more destructive wave as it shakes rock from side to side.

• P waves, which compress and stretch rock, deliver the quake's initial thrust.
• Slower and often more destructive S waves follow, slithering side to side.
• S waves tear buildings off foundations and can churn wet soils into a mixture that acts like quicksand, causing buildings to tilt.
• At ground level, P and S waves produce surface waves that can flatten bridges, crack windows, or simply pass unnoticed.
• Eventually the waves weaken as they roll away from the hypocenter; but the seismic echoes of powerful quakes can resonate across and around the globe

A "Rayleigh wave" is a seismic surface wave causing the ground to shake in an elliptical motion, with no transverse, or perpendicular, motion.

A "Love wave" is a surface wave having a horizontal motion that is transverse (or perpendicular) to the direction the wave is traveling.