KS4 Physics. Earth’s Structure. Contents. Earth’s Structure. Earth and earthquakes. Seismic waves. More about plate boundaries. Continental drift. Summary activities. Structure of the Earth. crust. mantle. inner core. outer core. Tectonic plates. .
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The Earth’s crust is made of sections called tectonic plates. Where two plates meet is called a plate boundary.
Convection currents in the mantleplates move these tectonic plates, which can move towards each other, move away from each other and or move past each other.
Two plates can slide past each other, but this doesn’t always happen smoothly. The large friction forces involved mean that strain builds up and the plates move suddenly when the strain gets too much.
This sudden movement of plates is called an earthquakeand it can be very destructive.
Which part of this cross-section of the Earth should each label point to?
An earthquake has occurred in the area shown in this picture.
If the plates moved in the directions indicated by the arrows, what would the location would look like after the earthquake?
During an earthquake there are two types of seismic waves that are released from the epicentre. These are called primary waves (P waves) and secondary waves (Swaves).
Primary or P waves are the faster type of seismic waves. They are longitudinal waves and when they hit the Earth’s surface they make objects and buildings vibrate vertically. P waves can travel through solids and liquids.
Secondary or s-waves are the slower type of seismic waves. They are transverse waves and when they hit the Earth’s surface they make objects and buildings vibrate horizontally. S waves can only travel through solids.
P-waves arrive first and shake buildings vertically.
This causes little damage.
S-waves arrive next and shake buildings horizontally.
This can cause a lot of damage.
S wave shadow - only P waves are detected in this region.
Waves within a layer change direction gradually because there is a gradual change in density.
At a layer boundary there is a big change in direction because there is a big change in density between layers.
The faster type of seismic wave, that is longitudinal and makes buildings vibrate up and down.
The location where the shift in plates occurred producing seismic waves.
The slower type of seismic wave, that is transverse and makes buildings shake from side to side.
Complete this table comparing the properties of the two types of seismic waves.
What happens at a plate boundary where an oceanic plate and a continental plate collide?
The thinner, more dense oceanic plate is driven down into the mantle.
This is known as subduction.
thicker, less dense continental plate
thinner, more dense oceanic plate
melted oceanic plate
What happens at a plate boundary when oceanic plates move apart due to convection currents in the Earth’s mantle?
Magma moves up to the surface, cools and forms new oceanic plate.
This is known as sea-floor spreading.
The force that causes earthquakes.
When an oceanic plate is pushed down into the mantle as it collides with a continental plate.
When two oceanic plates move apart to create new crust.
It is thought that all the continents were once joined together in a huge supercontinentcalled Pangaea.
Over millions of years the continents drifted apart because the tectonic plates they were on moved apart due to convection currents in the Earth’s mantle.
There are a number of pieces of evidence to support the theory of continental drift:
2. The rock strata on separated continents are identical.
3. The fossil records on separated continents are identical.