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 S-waves P, S and L-waves