Lecture 25-26 Earth's Structure(1)

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Unformatted text preview: d in the direcHon that the wave is passing l༆  You can (sort of) see why these might not be too damaging to people on the surface 2. Shear/secondary/surface “S” waves l༆  Travel more slowly than P waves and are called “shear waves” because they don’t change the volume of the material they pass through, rather they shear it (move laterally). l༆  Velocity is in the range of 1 to 8 kms- 1 with the lower velocity being for loose sediment and the higher value for near the base of the Earth’s mantle l༆  These are the waves that cause the damage 18 l༆  Surface waves travel across the Earth’s surface l༆  Body waves – those that pass through the Earth l༆  S and P waves are both of these and it’s the surface waves that cause the damage 20 l༆  The speed of seismic waves can be used to locate the centre of Earthquakes and also gives informaHon about the structure of the Earth l༆  Travel Hme of P- wave = (distance from Earthquake)/velocity p- wave l༆  Travel Hme of S- wave = (distance from Earthquake)/velocity s- wave l༆  For Earthquakes in the 50 to 500 km range in typical crust material, the S- wave travels approximately 3.5 kms- 1...
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