Earth - Interior Flashcards
(33 cards)
How does wave differ in materisl it is in?
Light waves travel fastest thoruhg vaccums, slower in air and slower in water, whilst sound waves do not travel in vaccums, travelling faster in water than it does in air.
Why are the properties of sound waves different to light?
Sound waves are variations in pressure, the more force taken to compress a material, the faster they travel.
What are the two types of wave?
Compressional
Shear
Comrpessional Waves
Waves where particle motion is same direction in which wave is propagating.
Shear Waves
These are waves changing the medium of which it travels, altering shape but not volume nor density.
Complication of measuring earth interior with waves…
Waves passing through more than one type of material exhibit seperate travel times and wave paths.
Seismic Wave Propogation
The passage of waves of compression/shear through rock and soil mediums.
How fast do seismic waves travel through Felsic, Mafic and Ultramafic rocks?
6, 7 and 8 km/s respectively.
Composotion of the contiental crust.
Low dense granite
Compositon of Ocean
Gabbro and Basalt
Mohorovivic Discontinuity
Boundary between the crust and the mantle
Composition of the Moho discontinuity…
Dense peridotite due to increased velocity of P waves.
Size of ocean, continent and orogenic mountain zone crusts…
7km, 33km and 70km.
Composition of upper mantle…
Ultramafic peridotite present, greater pressure and temperatures induce greater atomic compression.
Size of the lithosphere…
100km but varies geographically, maximising under continents and minimal near spreading centres where new crust forms.
Why does S-wave velocity decrease at base of lithosphere?
1% melting of peridotite minerals. (top of Astheno)
Asthenosphere
The weak ductile layer the lithosphere plates slide.
Why does s-wave velocity suddenly increase 400km below the crust?
Olvine mineral phase change
Where is the second material phase change of olvine?
660km
Transisiton Zone
410-660km where phase changes occur.
Seismic Shadow Zone
This is an area of the Earth surface when direct P and/or S waves are detected.
Rapid s-wave change at core-mantle boundary…
2890km where change from solid silicate rock to liquid iron alloy.
Why does the core and mantle not mix?
Vast density differnece(greater than atmosphere-lithosphere difference)
What is the core made of?
Iron and nickel and lighter elements
