Lecture 25-26 Earth's Structure(1)

L about 1 of the earths volume is the crust about 04

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Unformatted text preview: and P- waves approximately 8 kms- 1 Seismogram for an Earthquake about 30 km away 21 l༆  Of course, all this tells 22 you is that the Earthquake was 30 km away but that could be in any direcHon from where the seismometer is. l༆  In order to locate the origin of an actual Earthquake you need to have at least 3 seismometers surrounding the source, and then you can triangulate it’s posiHon. •  hop://www.youtube.com/watch?v=n- FMpNBfna8 l༆  P and S waves were first discovered by Richard Oldham in 1900. l༆  He used this discovery and some basic knowledge of physics to deduce that the Earth had a solid and dense core. l༆  How? l༆  Well, if the Earth were perfectly homogeneous then the P and S waves generated by Earthquakes would propagate in straight lines through the Earth. 24 l༆  But, as you have likely learned by now, nothing is that simple! l༆  Oldham observed was that S- waves did not make it through the Earth. Indeed, there was something called an S- wave shadow, from 105º to 180º if you divide the Earth into a hemisphere. Deduced wave velociHes –...
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