earth interior
DESCRIPTION
earthTRANSCRIPT
![Page 1: Earth Interior](https://reader033.vdocuments.us/reader033/viewer/2022042721/577cc0331a28aba7118f3a7b/html5/thumbnails/1.jpg)
…what has seismology taught us about the earth’s interior?
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travel of seismic waves through Earth - information about interior
The Earth's Interior
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if Earth was a homogeneous planet, seismic waves would travel in straight line
Seismic Wave Transmission
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increase in velocity with depth would cause seismic waves to follow curved paths
Seismic Wave Transmission
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Refraction - gradual/continuous increases in rock density with depth cause seismic waves to refract (bend) toward surface (follow curved paths)
Seismic Wave Transmission
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Seismic Wave Transmission
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Seismic Wave Transmission
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farther seismic waves travel from earthquake, deeper they penetrate the Earth
Seismic Wave Transmission
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Reflection -abrupt changes in rock properties cause some energy to be reflected back toward surface
Seismic Wave Transmission
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Seismic Wave Transmission
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S-waves not transmitted through liquids
Seismic Wave Transmission
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The Earth's Interior
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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
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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
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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
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lithosphere rigid outer layer of
Earth (crust and upper mantle)
asthenosphere zone within mantle
plastic and capable of flow
Layers of the Earth
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low-velocity zone - boundary between lithosphere and asthenosphere marked by seismic discontinuity (between 100-250 km depth)
Layers of the Earth
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The Earth's Interior
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Layers of the Earth
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… what else has the application of geophysics taught us about our earth?
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Earth’s Internal
Heat
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heat flow - flow of heat from earth interior to atmosphere (varies with location)
Internal Heat
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Internal Heat
geothermal gradient - increase in T with depth (about 25˚C/km near surface on continents, but varies with location)
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Internal Heat
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Earth’s Gravity Field
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force of attraction between masses
proportional to the mass
Gravity
F = Gm1 ⋅m2
R2
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1. elevation2. density of rocks beneath surface
force of gravity on Earth varies with
Gravity
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Gravity
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Gravity
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Gravity
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Gravity
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Gravity
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gravitational balance of masses [lithosphere ‘floating’ on the plastic mantle]
thick crust floats higher low density crust floats higher
Isostacy
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Isostacy
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Isostacy
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Earth’s Magnetic
Field
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The Earth's Magnetic Field
Earth has a dipolar (N and S) magnetic field similar to that of a bar magnet
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apparently produced by electrical currents in liquid Fe-Ni outer core
The Earth's Magnetic Field
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compass needle or magnetic mineral will point toward the N magnetic pole
The Earth's Magnetic Field
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Inclination - deviation from horizontal
The Earth's Magnetic Field
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declination - difference in apparent angle between magnetic and geographic pole
The Earth's Magnetic Field
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magnetic minerals in orientation of Earth's magnetic field (analogous to a compass)
Rock Magnetism
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Rock Magnetism
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study of different ages of rocks indicates that N magnetic pole has switched from N to S geographic location many times in past
Paleomagnetism
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horizontal and vertical angle of rock magnetism indicates location with respect to Earth's magnetic field
Paleomagnetism
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The Earth's Magnetic Field
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The Earth's Magnetic Field
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The Earth's Magnetic Field
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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’
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in 1912, Alfred Wegener proposed that: continents had
move Africa and South
America had been once joined
Continental Drift
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shape or ‘fit’ of continents (geography) best fit
obtained with continental slope
Evidence for Continental Drift
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fossil similarities in ancient rocksEvidence for Continental Drift
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Evidence for Continental Drift
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similarities in paleoclimate [glaciations]Evidence for Continental Drift
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Evidence for Continental Drift
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similarities in ancient rock types & agesEvidence for Continental Drift
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The Supercontinent Pangea
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Break-up of Pangea
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Break-up of Pangea
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Break-up of Pangea
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Break-up of Pangea
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Break-up of Pangea
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Break-up of Pangea