the interior of earth.pptx

8/18/2019 The Interior of Earth.pptx

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The Internal Structure

of the Earth


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• This drilling ship samples sediment and rock from thedeep ocean floor. It can only sample materials well

within the upper crust of the earth, however, barelyscratching the surface of the earth's interior


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Deepest hole drilled in the earths continent is in the !ola "eninsula, #ussia, at adepth of $%km

!ola Superdeep hole, #ussia & $%,%% metres ()*,%+* ft


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How do we know that?•Geophysics

–Seismology, mainly•By studying arrival times of seismic waves , we can determine the velocity

structure of the earth. It is consistent with a radial organization, except forthe crust, which varies from place to place. he text discusses howseismology has !een used to pro!e the interior of the earth.

•Seismic waves come in several flavors. "mong the important ones here are# $#rimary, compressional% and S $Secondary, shear% waves. &nly solids can

transmit S'waves. Solids and li(uids transmit # waves. )e know the earthhas a li(uid outer core and a solid inner core !ecause it transmits #'waves !ut not S'waves* the solid inner core is from #'wave to S'wave conversions.

•he velocity of a seismic wave depends on the density and elastic propertiesof the medium through which it travels. +elocities can vary sharply $easy todetect, usually at a compositional interface% or gradually $hard to detect,often due to phase changes or a gradual changes in composition%.


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How do we know that? -eophysics

-ravity !y using very sensitive measuring scales, geophysicists

measure the strength of gravity, usually for exploration or missile'

lo!!ing. hese measurements have shown that most areas have

nearly the same mass !elow them $roots under mountains and holes

under !asins%.


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How do we know that?

Magnetics :

arth, has a magnetic field.

It is a dipole, kind of parallel to the

spin axis.


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Magnetics :

/easurements on orientation of

magnetic field frozen into volcanic

rocks indicates that the earth0s

magnetic field flips from time totime, which we understand even

less.


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How do we know that? -eophysics

/oment of Inertia

– he rate at which the earth wo!!les on its axis can !e used to

estimate its moment of inertia. he values found indicate that the core

must !e very dense.


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•Meteorites :

• "nalysis of meteorites and various rock samples suggests that the earth

has a !ulk composition similar to car!onaceous chondrites, one of the

more commonly found types of meteorites, except that most of the light

elements $car!on, hydrogen% have !oiled off. 1ar!onaceous chondrites

also have composition similar to the sun $!ased on ratios of heavy

elements%.


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How do we know that? vidences

• Heat flow can !e measured, and indicates that the continents have

rather high heat flow, trenches and ocean floor have very low heat

flow, and mid'ocean ridges have high heat flow rates that are rather

spotty.

• Speculation and xtrapolation are the main tools in most discussions

of earth2s interior.


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• Evidence from Seismic Waves

• Seismic Waves – - vibration that moves through the Earth.

• Body waves –

Seismic waves that travel through the Earthsinterior, spreading outward from a disturbance inall directions.


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• (-- seismic wavemoving from a

slower/velocitylayer to a higher/ velocity layer isrefracted up.

• (0 The reverseoccurs when a

wave passes from ahigher/velocity to aslower/velocity

layer.


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• (-This illustrates the curvedpath of seismic waves

between an e1plosion and arecording seismograph van.The curved path is caused byincreasing seismic velocity with depth in uniform rock.

• (0 This illustratesincreasing seismic velocity with depth in uniform rock.The waves curve out in alldirections from adisturbance.


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Types of Seismic waves

2ocus

2ault

Epicenter


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Types of Seismic waves

• " waves (0ody 3aves Arepush-pull waves that push

(compress) and pull

(expand) in the direction

that the waves travel.

• Travel through solids,liquids, and gases

• Have the greatest velocity

of all seismic waves


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Types ofSeismic waves

• S waves ha!e particlesat right angles to the

direction that they travel.

• Travel only through solids

• lower velocity than " waves


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Seismic waves

• The velocity of #oth - and "-waves is determined #y

the density and rigidity of the material.

• $aves travel faster in denser more rigid material. $aves are reflected at #oundaries where elastic

properties differ.

%f the reflected waves reach the surface, they can #e

measured #y a seismograph. $ave refraction can also #e used to determine

properties of the interior of the &arth. $aves are refracted (#ent) when they pass from a layer with

higher density to a layer with lower density.


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Seismograms


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Seismographs

" ti f S i i 3 Th h E th I t i


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"ropagation of Seismic 3aves Through Earths Interior

4ongitudinal waves travel through bothsolids and li5uids.

Transverse waves travel throughsolids only.

'ig


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'ig. .


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6rust * Thin, roc!y outer layer

* +aries in thic!ness* Crust has P-wave velocities


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6rust * Thin, roc!y outer layer

8ceanic crust

- averages thic!ness 9 !m.- 2ade up of roc!s rich in and silica.

- Average density density around 6.0 g5cc

- 8ceanic crust is elastic-#rittle all the way through.

- :ounger (0 million years or less) than the continental crust

h


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7ohorovicic Discontinuity

ontact #etween rust ; 2antle (The 2oho)

This is an area of increased velocity of seismic wavesas the material is denser in the mantle (due to higher

proportion of ferromagnesium materials and the crust is

higher in silicates).

h l


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The 7antle

* Mantle has P-wave velocities >8 km/sec

* 2870 !m "#ic! between the crustand the core omposition of theuppermost mantle is the igneous roc!

peridotite (changes at greater depths).

* eismic wave velocities increase at

depths of a#out /00 !m and 00 !m.* 8** km is the boundary between the

upper mantle and the lower mantle.

* 9o earth5uakes occur in the lowermantle.

h i h h


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The 4ithosphere

• Lithosphere is solid and includes the crust and the rigid,

outermost part of the mantle.

h h h


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The -sthenosphere

* sthenosphere has fast #'waves and slow, attenuated S'waves,

indicating partial melting or plastic state.

* It is located below the lithosphere (the crust and uppermantle, between about $** and %:* kilometers deep.

Mechanical Layershi i ! d ! i f d i l ! i d i i h i l i f i


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his is !ased on our o!servation of density structures, la!oratory experiments determining mechanical properties of certainrocks at various pressure'temperature conditions, and on estimates of the variation of temperature with depth•Lithosphere is solid and includes the crust and the rigid, outermost part of the mantle. –Crust has P-wave velocities


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• http;;terravir.com;DepthSeverance.html

• http;;wikiislam.net;wiki;Earth

the interior of earth.pptx

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