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?

The Dynamic CrustThe Dynamic Crust

Regents Earth ScienceRegents Earth Science

Seismic Waves and Earth’s Seismic Waves and Earth’s StructureStructure

How can we tell that the outer core is liquid and the inner core is solid?

Seismic Waves and Earth’s Seismic Waves and Earth’s StructureStructure

Velocity of Seismic WavesVelocity of Seismic WavesP-waves travel fastest P-waves travel fastest (~2X faster than S-(~2X faster than S-

waves)waves)

S-waves second fastestS-waves second fastestIncreases in denser materialIncreases in denser materialThe waves are refracted (bent) as they The waves are refracted (bent) as they

pass from a material of one density to a pass from a material of one density to a material of a higher or lower density.material of a higher or lower density.

Seismic Waves and Earth’s Seismic Waves and Earth’s StructureStructure

P-wavesP-wavesTravel through

solids, liquids and gases

S-wavesS-wavesTravel only through

solids

Seismic Waves and Earth’s Seismic Waves and Earth’s StructureStructure

Scientists infer the properties of Earth's Scientists infer the properties of Earth's interior through the analysis of seismic interior through the analysis of seismic wave data.wave data.

By studying thousands of seismograms By studying thousands of seismograms scientists have discovered that seismic scientists have discovered that seismic waves refract, reflect, change velocity, waves refract, reflect, change velocity, and become absorbed by various parts of and become absorbed by various parts of Earth's interior.Earth's interior.

The following diagram shows the results of The following diagram shows the results of these thousands of studies.these thousands of studies.

P and S WavesP and S Waves

Seismic Waves and Earth’s Seismic Waves and Earth’s StructureStructure

P and S WavesP and S Waves

Shadow ZoneShadow Zone

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

Inferred Properties of Earth’s Inferred Properties of Earth’s InteriorInterior

Inferred Properties of Earth’s Inferred Properties of Earth’s InteriorInterior

Earth’s Layers - DetailEarth’s Layers - Detail CrustCrust LithosphereLithosphere MohoMoho AsthenosphereAsthenosphere MantleMantle

Asthenosphere Asthenosphere (plastic)(plastic)

Stiffer MantleStiffer Mantle Outer CoreOuter Core Inner CoreInner Core

Earth’s CrustEarth’s Crust Continental Continental

CrustCrust Beneath continentsBeneath continents ThickerThicker

Thickest where Thickest where highest (beneath highest (beneath mountains)mountains)

Granitic RocksGranitic Rocks Less DenseLess Dense

Oceanic CrustOceanic Crust Beneath OceansBeneath Oceans ThinnerThinner

Basaltic RocksBasaltic Rocks DenserDenser

MOHOMOHO

Mohorovic DiscontinuityMohorovic DiscontinuityInterface between lithosphere and Interface between lithosphere and

asthenosphereasthenosphereBelow Moho rocks become denser due to Below Moho rocks become denser due to

increased pressure at depth and solid phaseincreased pressure at depth and solid phase

AsthenosphereAsthenosphere

Plastic portion of the upper mantlePlastic portion of the upper mantleRocks are partially molten (plastic)Rocks are partially molten (plastic)Detected due to decrease in velocity of Detected due to decrease in velocity of

seismic waves through this zoneseismic waves through this zoneWidely accepted theory that magma and Widely accepted theory that magma and

lava originate in the lava originate in the asthenosphereasthenosphere

Inferred Properties of Earth’s Inferred Properties of Earth’s InteriorInterior

Inferred Properties of Earth’s Inferred Properties of Earth’s InteriorInterior