1. The Earth’s structure

2. 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)

3. 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 cm/year

4. 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

5. 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.

6. 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.

7. Earthquakes cause great damage
Earthquakes on land
Often the ground can be seen moving
Buildings collapse
Mountains can break up

8. 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

9. Vibrations
Vibrations (waves) are picked up by machines called seismometers

10. Seismometers
Measure the strength of the waves

11. 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)

12. P-waves Primary waves Fastest waves therefore 1st to be recorded
Longitudinal waves (push-pull)
Travel through liquids and solids

13. S-waves Secondary waves Slower than p-waves
Transverse waves (shake and shear waves)
Only travel through solid materials

14. L-waves Large surface waves Transverse waves (push-pull)
Only travel along surface of Earth’s crust
Most damaging seismic waves

15. P-waves
P and S-waves
P, S and L-waves