Earthquakes and Volcanoes

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Layers of The Earth


Tectonic Plates


  • The Earth's surface is made up of a series of large plates (like pieces of a giant jigsaw puzzle).
  • These plates are in constant motion travelling at a few centimetres per year.
  • Convection currents beneath the plates move the plates in different directions.
  • The source of heat driving the convection currents is radioactive decay which is happening deep in the Earth.

Three Ways that Plates Move

  • destructive plate boundary - two plates move together
  • constructive plate boundary - two plates move apart
  • conservative plate boundary - two plates move side by side

Earthquake Key Terms

  • Earthquake - violent shaking of surface cause by sudden release in tension
  • Epicentre - Point on Earth's surface directly above surface where earthquake is felt
  • Seismic Wave Energy - Energy released as a shock through crust
  • Focus - Point inside crust where built up pressure is released
  • Faults - Large cracks in crust
  • Magnitude - Unit of measurement for how much energy is release by an earthquake
  • Richter Scale - Scale used to measure magnitude of earthquake
  • Tsunami - a giant wave or series of large waves in the ocean 
  • Liquefaction - process in an earthquake when the movement of energy waves causes the ground to act like a liquid
  • Intensity - a measure of the effect of an earthquake
  • Aftershock - smaller earthquakes that occur after main quake
  • Foreshock - Smaller earthquakes that occur prior to earthquake

Responding to Earthquakes

  • Predict - tiltmeters (change in gradient of volcanoes)
  • Protect - sit under a table or inside a cupboard
  • Prevent - redesign buildings to be earthquake proof.

San Andreas Fault Line

Earthquakes occur quite often along the San Andreas Fault Line because the two plates - North American Plate and the Pacific Plate are of the conservative type of plate boundary which means that they moev side by side to create a lot of friction. Moreover, they move at different speeds; the Pacific Plate moves at 3cm/yr while the North American Plate moves at 1.4cm/yr. Eventually, the friction causes a lot of pressure to


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