|MadSci Network: Earth Sciences|
Dear Anna, Broadly speaking, there are two types of earthquake waves, namely body waves and surface waves. Body waves are waves that travel through the Earth’s interior. Surface waves are waves that travel close to the Earth’s surface, like waves on a lake. There are two types of body waves, namely P-waves and S-waves. They are as follows: P-waves. P-waves are sometimes called pressure waves, and sometimes they are called longitudinal waves. P-waves are transmitted through the Earth’s interior with a backwards and forwards motion along the line of travel, by alternating compression and dilatation. A jack hammer creates P-waves. They are capable of passing through any type of material they encounter, including the liquid of the Earth’s outer core, although they will be bent and deflected when they pass across the boundaries separating layers of different densities. S-waves. S-waves are also called transverse waves. They travel with a side-to-side or up and down motion, or a combination of the two, in which the particles in the medium through which the wave is passing move at right angles to the direction in which the wave is travelling. A good analogy is the wave motion that occurs when you shake a rope or a curtain cord which is fixed at one end. S-waves will not travel through liquid, so they are stopped when they reach the Earth’s liquid outer core. There are also two types of surface waves, namely Love waves and Rayleigh waves. They are as follows: Love waves. Also called L-waves, these are rather like horizontal S- waves, but with the difference that the amplitude of the wave diminishes rapidly with increasing depth, so that they can only travel long distances close to the Earth’s surface. Rayleigh waves. Rayleigh waves are similar to ocean waves, in that the motion of each particle in the medium through which the wave travels describes an ellipse as the wave passes, and the amplitude of the wave decreases with increasing depth. Therefore, Rayleigh waves also travel long distances only near to the Earth’s surface. I hope this answers your question. Best wishes, David Scarboro
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