It is very difficult to predict the timing, location and size of an earthquake because they happen over long periods of time. Each earthquake involves different forces and geological structures which alter the depth and intensity. For example, earthquakes in subduction zones are deeper than earthquakes that happen at a transform boundary.Seismic waves are produced from vibrations as energy is released from an earthquake. Scientists use seismic waves to determine the thickness of earth's layers and their composition. Seismology is the study of earthquakes and seismic waves and is used to classify and describe earthquakes.
SURFACE WAVES
Seismic waves can either travel underground as body waves, or ripple along earth's surface. These waves are called surface waves or L-waves (love waves). Although surface waves arrive the slowest, they end up causing the most damage as it moves the ground from side to side in a rolling action.
PRIMARY WAVES
Primary waves (P-waves) or Compressional waves are a type of body wave that travel at 6 km/s though earth's crust and over 14 km/s deep underground. They can travel through both liquids, solids just like a sound wave would. They are the first to arrive because it travels through the earth and it's layers, unlike surface waves. P-waves cause particles move in the same direction that the wave is moving, which is the direction that the energy is traveling. It causes the ground to compress and stretch.
SECONDARY WAVES
Secondary waves are another type of body wave. They are also called Shear waves or S-waves. This wave is the second to arrive, after primary waves, at 3.5 km/s. These waves cause more structural damage than P-waves because the ground motion is perpendicular to the direction of wave movement and the waves are larger. In the outer core, S-waves aren't present because the completely liquid layer offers no resistance to the waves.
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