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EVIDENCE FOR THE INTERNAL STRUCTURE OF EARTH (Seismic wave velocities…
EVIDENCE FOR THE INTERNAL STRUCTURE OF EARTH
Moho discontinuity
Boundary between crust and mantle
Velocity of P and S waves increases due to increasing density of mantle
Meteorites
Made at the same time as the Earth
Made of similar ingredients
Iron or Nickel
Similar density, to overall Earth's density
Mines and boreholes
Thermal gradient
The deeper underground, the hotter it gets
e.g Kola superdeep borehole
12, 000m
Rocks have characteristics of plastic
Seismic wave velocities (speed)
L waves
Surface only
Slowest of waves
S waves
Transverse waves
Only pass through solids
P waves
Compression waves
Pass through solids and liquids
Change directions (refract) when passing through layers of different density
Gravity mapping
Satellites measure strength of gravity throughout the earth
Xenoliths
Rocks emitted from volcanoes come from mantle