# The Dynamic Crust Regents Earth Science. Seismic Waves and Earth’s Structure How can we tell that the outer core is liquid and the inner core is solid?

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The Dynamic Crust Regents Earth Science

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

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

Seismic Waves and Earth’s Structure P-waves P-waves Travel through solids, liquids and gases S-waves S-waves Travel only through solids

Seismic Waves and Earth’s Structure Scientists infer the properties of Earth's interior through the analysis of seismic wave data. 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. 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. The following diagram shows the results of these thousands of studies.

P and S Waves

Seismic Waves and Earth’s Structure

P and S Waves

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

Inferred Properties of Earth’s Interior

Earth’s Layers - Detail Crust Crust Lithosphere Lithosphere Moho Moho Asthenosphere Asthenosphere Mantle Mantle Asthenosphere (plastic) Asthenosphere (plastic) Stiffer Mantle Stiffer Mantle Outer Core Outer Core Inner Core Inner Core

Earth’s Crust Continental Crust Continental Crust Beneath continents Beneath continents Thicker Thicker Thickest where highest (beneath mountains) Thickest where highest (beneath mountains) Granitic Rocks Granitic Rocks Less Dense Less Dense Oceanic Crust Oceanic Crust Beneath Oceans Thinner Basaltic Rocks Denser

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

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

Inferred Properties of Earth’s Interior

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