Ch12_Outline

Ch12_Outline - Chapter 12 Earth's Interior Probing Earth's...

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1 Chapter 12 Earth’s Interior Probing Earth’s interior ± Most of our knowledge of Earth’s interior comes from the study of earthquake waves Travel times of P (compressional) and S (shear) waves through the Earth vary depending on the properties of the materials Variations in the travel times correspond to changes in the materials encountered P and S waves moving through a solid Figure 12.2
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2 Probing Earth’s interior ± The nature of seismic waves Velocity depends on the density and elasticity of the intervening material Within a given layer the speed generally increases with depth due to pressure forming a more compact elastic material Compressional waves (P waves) are able to propagate through liquids as well as solids Probing Earth’s interior ± The nature of seismic waves Shear waves (S waves) cannot travel through liquids In all materials, P waves travel faster than do S waves When seismic waves pass from one material to another, the path of the wave is refracted (bent) Seismic waves and Earth’s structure ± Abrupt changes in seismic-wave velocities that occur at particular depths helped seismologists conclude that Earth must be composed of distinct shells ± Layers are defined by composition Because of density sorting during an early period of partial melting, Earth’s interior is not homogeneous
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3 Seismic waves and Earth’s structure ± Layers are defined by composition Three principal compositional layers Crust – the comparatively thin outer skin that ranges from 3 km (2 miles) at the oceanic ridges to 70 km (40 miles in some mountain belts) Mantle – a solid rocky (silica-rich) shell that extends to a depth of about 2900 km (1800 miles) Seismic waves and Earth’s structure ± Layers are defined by composition Three principal compositional layers Core – an iron-rich sphere having a radius of 3486 km (2161 miles) ± Layers defined by physical properties
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This note was uploaded on 07/17/2008 for the course GS 121 taught by Professor Leavell during the Fall '07 term at Ohio State.

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Ch12_Outline - Chapter 12 Earth's Interior Probing Earth's...

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