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Lecture22

# Lecture22 - Quote of Day Fools show their anger at once but...

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Quote of Day Fools show their anger at once, but the prudent ignore an insult. (Proverbs 12:16) http://www.bartleby.com/66/66/166.html

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Chapter 12 Earth’s Interior
Probing Earth’s interior ¾ Most of our knowledge of Earth’s interior comes from study of earthquake waves Travel times of P and S waves depend on the elasticity (compressibility K and shear modulus μ ) and density ( ρ ) of the rock P waves travel faster than S-waves as evident from its larger numerator S waves can not propagate through liquids because a liquid’s shear modulus μ is zero. Figure 12.2 numerator denominator

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Probing Earth’s interior ¾ If the density or elastic parameters of rocks did not change with depth in Earth, P- and S-waves would travel “straight” through the Earth. ¾ The isochron surface (i.e., surface of equal time) would be spherical in shape. Figure 12.3 T=1 T=2 T=3
¾ Because stress increases with depth in Earth, the density ( ρ ) and elastic parameters ( K and μ ) of rocks increase ¾ K and μ increase more quickly with depth than density, thus causing an increase in velocity with depth. ¾ Results in curved trajectories for seismic waves Probing Earth’s interior Figure 12.4 s lo w f a t e r

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http://www.dmna.state.ny.us/historic/reghist/wwii /infantry/165thInf/gfx_165thInf/165thInfTank.jpg pavement mud I often think of a moving tank that has one track on pavement and one in sand or mud. Unless the driver forces the tank back onto the pavement, it will “naturally” go into the mud because of the difference in velocity between its two moving tracks.
When seismic waves pass from one material to another, the path of the wave (or wave energy) is partly reflected and partly refracted, similar to the behavior of light in diamonds. Probing Earth’s interior http://www.diamondhunt.co.uk /testimonial/lightreflection.jpg 25 o Reflection Critical reflection Refraction air diamond

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reflection refraction

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Important observations …. 1) Between 105 to 140
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Lecture22 - Quote of Day Fools show their anger at once but...

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