L05_11-13_Sept_Earth_Interior(1)

Slinky s waves in a slinky consider a solid iron bar

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Unformatted text preview: = 7870 3 m € 7 Meteorite evidence of planetary differen>a>on into metallic core, silicate mantle, rocky crust planetesimal with ‘ordinary chondrite’ composi>on molten silicate solid silicate 8 Internal Structure of Earth: Inference from seismic waves: The way the Earth ‘rings’ aier an earthquake tells us about its interior structure 9 10 There are two primary types of seismic waves that travel through the Earth: P- waves (pressure, or compression waves): these travel in liquids AND solids S- waves (shear waves) these travel in solids ONLY 11 P- waves in a slinky S- waves in a slinky Consider a solid iron bar… And an iden>cal bar cut up into slices… 14 Both will transmit compressional stress (P- waves) 15 Only the solid bar will transmit shear stress (S- waves) (The sliced- up bar is like a liquid in that it cannot transmit shear stress) 16 Expected travel paths of S- waves for a solid Earth with density increasing towards the center 17 Observed paths of S- waves. The presence of an ‘S- wave shadow zone’ indicates that a liquid layer exists inside of the Earth (since S- waves do not travel through liquids) 18 There is also a P- wave shadow zone, indica>ng that refrac>on of seismic waves occurs due to a density transi>on refrac>on of ocean waves Refrac>on of light 19 Seismologists also use P- and S- wave travel >mes to gain insight into more subtle features of Earth composi>on and structure 20 21 High temperature, high pressure experiments reproduce the condi>ons deep inside of the Earth and help to iden>fy minerals with densi>es, mel>ng points, and seismic wave veloci>es...
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