Transcript The Earth’s structure - Bishopston Comprehensive School

The Earth’s structure
The Structure of the Earth
A thin crust –
6-40 km thick
Layer we live on
A mantle (treacle) –
properties of a solid
but it can also flow
2900 km
A core – made of
molten nickel and iron.
Outer part (2000km)
is liquid and inner
part (1300km) is solid
How do we know this? These facts have all been
discovered by examining seismic waves (earthquakes)
Earth’s Surface
• Earth’s lithosphere = crust + upper part of mantle
• It’s cracked into pieces called tectonic plates
• Tectonic plates are like big rafts that float across
the liquid mantle
• Map: Edges of plates
As plates move so
do continents
• Plates move
1cm/year
Earthquakes
• An earthquake is the shaking and vibration of
the crust due to movement of the Earth's
tectonic plates
• Vibrations are caused by rocks suddenly
fracturing and moving
• Fracturing releases loads of energy which
makes the ground vibrate
Vibrations
• These vibrations travel away from the focus
(start) of the earthquake
• Earthquakes are caused when tension is
released from inside the crust.
• This happens because plates do not move
smoothly - sometimes they get stuck.
• When this happens a great deal of pressure
builds up.
• When this pressure is eventually released, an
earthquake tends to occur.
• The point inside the Earth's crust where
the pressure is released is called the focus.
• The point above the focus, on the Earth's
surface is called the epicentre.
Earthquakes cause great damage
Earthquakes on land
• Often the ground can be seen moving
• Buildings collapse
• Mountains can break up
Earthquakes under the Sea
• Ground movements
under the sea form
big waves
• The waves get even
bigger as they get
closer to the coast
• Tsunami
Vibrations
• Vibrations (waves) are picked up by
machines called seismometers
Seismometers
• Measure the strength of the waves
3 main types of seismic waves
• Seismographs show there are 3 main
types of seismic waves
• P-waves (Primary)
• S-waves (Secondary)
• L-waves (Large surface)
P-waves
• Primary waves
• Fastest waves therefore 1st to be
recorded
• Longitudinal waves (push-pull)
• Travel through liquids and solids
S-waves
• Secondary waves
• Slower than p-waves
• Transverse waves (shake and shear
waves)
• Only travel through solid materials
L-waves
• Large surface waves
• Transverse waves (push-pull)
• Only travel along surface of Earth’s
crust
• Most damaging seismic waves
P-waves
P and Swaves
P, S and Lwaves