Geography (Earthquake)

• Earthquakes


  • Caused by the movement of plates
  • Earth's surface, or crust, is made up of large pieces of land and sea masses called plates
  • Plates are not stationary but move very slowly relative to each other
  • Plates may move towards, move away from, or slide past each other
• Plate movements


  1. Convergent

  2. Divergent

  3. Transform
• When two plates push against or slide past each other

  Friction from the movement causes stress within crustal rocks
• Pressure from the stress builds up over time


  When pressure is released, the Earth's crust vibrates
• Earthquake shockwaves


  • P-waves (primary waves)
  • S-waves (secondary waves)
  • Travel through the Earth's crust to the surface
  • Begin at the focus
  • Radiate outwards from the focus and reach the epicentre first
  • Epicentre is the point on the Earth's surface directly above the focus
  • Intensity of the shockwaves is highest at the epicentre and decreases further from the epicentre
• After the main earthquake shock


  A region may experience aftershocks
• Aftershocks


  Vibrations of the Earth's crust following the main shock of the earthquake
• Aftershocks may continue for hours or days, causing further damage
• Damage from aftershocks includes collapsing buildings, leaking gas pipes, explosions and fires
• Seaquakes


  Earthquakes originating from under the ocean floor
• Seaquakes may produce tsunamis, which are huge ocean waves capable of causing great damage to coastal areas
• Example of a tsunami

  • Indian Ocean Tsunami in 2004, which devastated coastal communities of countries like India, Sri Lanka and Indonesia
• Richter Scale


  Used to measure the magnitude, or strength, of an earthquake
• Richter Scale magnitudes and effects

  • <2.0: Not felt
  • 2.0-2.9: Generally recorded but not felt
  • 3.0-3.9: Often felt, but rarely causes damage
  • 4.0-4.9: Noticeable shaking of indoor items
  • 5.0-5.9: Some damage to property
  • 6.0-6.9: Much damage to buildings
  • 7.0-7.9: Severe damage to buildings and infrastructure
  • 8.0-8.9: Devastating; most buildings collapse
• Seismographs


  Instruments that record earthquake waves and produce a trace of ground motion
• Seismologists use seismographs to record earthquake waves
• Seismic waves are measured using a device called a seismograph.
• The Richter scale is used to measure the magnitude of earthquakes.
• The Richter scale is used to measure the intensity of an earthquake based on its energy release.