The Dynamic Crust

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The Dynamic Crust

• Regents Earth Science

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Seismic Waves and Earths Structure
How can we tell that the outer core is liquid and
the inner core is solid?
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Seismic Waves and Earths Structure

• Velocity of Seismic Waves
• P-waves travel fastest (2X faster than S-waves)
• S-waves second fastest
• Increases in denser material
• The waves are refracted (bent) as they pass from
  a material of one density to a material of a
  higher or lower density.

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Seismic Waves and Earths Structure

• P-waves
• Travel through solids, liquids and gases

• S-waves
• Travel only through solids

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Seismic Waves and Earths Structure

• Scientists infer the properties of Earth's
  interior through the analysis of seismic wave
  data.
• By studying thousands of seismograms scientists
  have discovered that seismic waves refract,
  reflect, change velocity, and become absorbed by
  various parts of Earth's interior.
• The following diagram shows the results of these
  thousands of studies.

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P and S Waves
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Seismic Waves and Earths Structure
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P and S Waves
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Shadow Zone

• The Shadow Zone is created by the refraction of
  P-waves and the inability of S-waves to travel
  through a liquid.

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Inferred Properties of Earths Interior
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Inferred Properties of Earths Interior
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Earths Layers - Detail

• Crust
• Lithosphere
• Moho
• Asthenosphere
• Mantle
• Asthenosphere (plastic)
• Stiffer Mantle
• Outer Core
• Inner Core

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Earths Crust

• Oceanic Crust
• Beneath Oceans
• Thinner
• Basaltic Rocks
• Denser

• Continental Crust
• Beneath continents
• Thicker
• Thickest where highest (beneath mountains)
• Granitic Rocks
• Less Dense

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MOHO

• Mohorovic Discontinuity
• Interface between lithosphere and asthenosphere
• Below Moho rocks become denser due to increased
  pressure at depth and solid phase

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Asthenosphere

• Plastic portion of the upper mantle
• Rocks are partially molten (plastic)
• Detected due to decrease in velocity of seismic
  waves through this zone
• Widely accepted theory that magma and lava
  originate in the asthenosphere

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Inferred Properties of Earths Interior
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Inferred Properties of Earths Interior