Earth Interior

…what has seismology taught us about the earth’s interior?

travel of seismic waves through Earth - information about interior

The Earth's Interior

if Earth was a homogeneous planet, seismic waves would travel in straight line

Seismic Wave Transmission

increase in velocity with depth would cause seismic waves to follow curved paths


Refraction - gradual/continuous increases in rock density with depth cause seismic waves to refract (bend) toward surface (follow curved paths)




farther seismic waves travel from earthquake, deeper they penetrate the Earth


Reflection -abrupt changes in rock properties cause some energy to be reflected back toward surface



S-waves not transmitted through liquids



crust - two types continental

Si-rich Mg-poor granodiorite 30-65 km thick

oceanic Mg-rich Si-poor basalt 5-10 km thick

Mohorovicic discontinuity (MOHO) - abrupt increase in seismic velocities

Layers of the Earth

mantle thickest layer of Earth (≥

80% Earth's volume) increased body wave speed

below Moho indicates high density, mafic rock (Mg-rich Si-poor rocks)

essentially solid, but portions under slow flow

bottom 2900 km deep

Layers of the Earth

core outer core liquid Fe-Ni alloy Earth's magnetic

field caused by circulation of the outer liquid core

inner core solid Fe-Ni alloy

Layers of the Earth

lithosphere rigid outer layer of

Earth (crust and upper mantle)

asthenosphere zone within mantle

plastic and capable of flow

Layers of the Earth

low-velocity zone - boundary between lithosphere and asthenosphere marked by seismic discontinuity (between 100-250 km depth)

Layers of the Earth


Layers of the Earth

… what else has the application of geophysics taught us about our earth?

Earth’s Internal

Heat

heat flow - flow of heat from earth interior to atmosphere (varies with location)

Internal Heat

Internal Heat

geothermal gradient - increase in T with depth (about 25˚C/km near surface on continents, but varies with location)

Internal Heat

Earth’s Gravity Field

force of attraction between masses

proportional to the mass

Gravity

F = Gm1 ⋅m2

R2

1. elevation2. density of rocks beneath surface

force of gravity on Earth varies with

Gravity

Gravity

Gravity

Gravity

Gravity

Gravity

gravitational balance of masses [lithosphere ‘floating’ on the plastic mantle]

thick crust floats higher low density crust floats higher

Isostacy

Isostacy

Isostacy

Earth’s Magnetic

Field

The Earth's Magnetic Field

Earth has a dipolar (N and S) magnetic field similar to that of a bar magnet

apparently produced by electrical currents in liquid Fe-Ni outer core


compass needle or magnetic mineral will point toward the N magnetic pole


Inclination - deviation from horizontal


declination - difference in apparent angle between magnetic and geographic pole


magnetic minerals in orientation of Earth's magnetic field (analogous to a compass)

Rock Magnetism

Rock Magnetism

study of different ages of rocks indicates that N magnetic pole has switched from N to S geographic location many times in past

Paleomagnetism

horizontal and vertical angle of rock magnetism indicates location with respect to Earth's magnetic field

Paleomagnetism




Continental Drift early scientists (including Greeks) postulated that

continents had moved on the planet The Rev. Thomas Dick (Scottish) wrote in 1838:

‘It is not altogether improbable that these continents (Africa & South America) were originally conjoined’

in 1912, Alfred Wegener proposed that: continents had

move Africa and South

America had been once joined

Continental Drift

shape or ‘fit’ of continents (geography) best fit

obtained with continental slope

Evidence for Continental Drift

fossil similarities in ancient rocksEvidence for Continental Drift


similarities in paleoclimate [glaciations]Evidence for Continental Drift


similarities in ancient rock types & agesEvidence for Continental Drift

The Supercontinent Pangea

Break-up of Pangea

Break-up of Pangea

Break-up of Pangea

Break-up of Pangea

Break-up of Pangea

Break-up of Pangea

Earth Interior

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