Earthquakes

• Plate boundaries are where tectonic plates meet

  
• There are 4 types of plate boundaries

  • destructive
  • Collision
  • constructive
  • Conservative
• destructive boundaries:

  • where an oceanic and continental plate meet
  • the denser oceanic plate is forced down and subducts beneath the continental plate into the mantle
  • there it gets destroyed
  • can create volcanos or ocean trenches (deep sections of the ocean floor where the oceanic plate goes down)
  • example: pacific plate forced under eurasian plate along east coast of japan
• collision plate boundaries:

  • both plates are continental and move towards eachother
  • both plates are forced upwards and fold up to create fold mountains
  • example: Eurasian and Indian plate collide to form the Himalayas
• constructive boundaries:

  • two plates move away from each other
  • magma rises form the mantle in the gap created and cools
  • this creates new crust
  • example: Eurasian plate and North American plate form the Mid-Atlantic ridge
• Conservative boundaries:

  • when two plates are moving sideways past each other or in the same direction but at different speeds
  • crust isn’t created or destroyed
  • Often they might get stuck and this generates a lot of pressure —> earthquake (when pressure is released)
  • Example: pacific plate and North American plate on USA west coast
• earthquakes can occur at all 4 types of plate boundaries
• constructive boundaries — tensions builds along cracks within plates as they move away from each other, which can trigger an earthquake
• earthquake

  1. plates send out shock waves which are the earthquakes
  2. the focus is the name of the place where the pressure is released from
  3. near the focus the waves are stronger and cause more damage
  4. the epicentre is the point on the earth surface directly above the focus
• earthquakes are measures using

  • moment magnitude scale (energy released)
  • mercalli scale (measures the effects)
  • Richter scale (no longer used)
• 2 types of earthquakes:

  1. shallow focus

  • 0-70km below earth surface surface
  • Cause a lot of damage as shock waves travels less far to the surface so is stronger when it reaches

  1. Deep focus

  • 70-700km below earths surface
  • Usually due to crust that has been subducted into the mantle
  • Less damage as waves have to travel through more rock — reduces power
• Hotspots are places where the magma rises up through the crust