Seismology - Seismology We can use seismic waves to probe...

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Seismology We can use seismic waves to probe deep into the earth. These are controlled by wave equations so they are of more use than potential functions like gravity for "inversion" to probe the earth's interior. On a Seismograph we see the arrival of a wave triggered by an explosive event elsewhere. Or rather we see the arrival of a sequence of waves. Typically the surface waves arrive last. These have an amplitude inversely proportional to the distance from the source and attenuated by a factor of e for every approximately 5000km. Before these we get P and S waves - compressional and shear (originally Primary and Secondary) typically in a ten minute spread and with periods < 7 seconds. The P and S waves have arrived after travelling through the body of the earth andgh the body of the earth and curve because the speed of waves increase towards the centre: Shear waves cannot propagate through a liquid. Fermat's Principle can be used to estimate the minimum time of passage for a given structure.
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Seismology - Seismology We can use seismic waves to probe...

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