seismic hazards

• Plates


  • Do not perfectly fit into each other
  • Do not move in fluid motions
• Plate movement


  1. Plates become stuck due to friction

  2. Convection currents in asthenosphere continue to push

  3. Pressure builds up

  4. Plates eventually give way

  5. Sudden movement causes seismic waves
• Focus


  Point underground where earthquake originates
• Epicentre


  Area above ground directly above the focus
• Seismic hazards occur along all plate boundaries
• The Ring of Fire accounts for 90% of the world's earthquakes
• The Alpine-Himalayan belt accounts for 5-6% of the world's earthquakes
• Richter Scale


  Logarithmic scale measuring strength of seismic waves
• Modified Mercalli Intensity Scale


  Scale measuring rate of destruction caused (originally Mercalli scale developed in 1884)
• The Mercalli scale is subjective and dependent on human development rather than strength of seismic waves
• Earthquake magnitude


  Dependent on depth of focus
• Conservative boundaries have shallowest focuses, destructive boundaries have deeper focuses
• Earthquakes are frequent around the world and occur every day at boundaries
• Hundreds of smaller magnitude earthquakes occur every day, larger earthquakes are less frequent
• Earthquakes follow no pattern and are random, so there is irregularity between events
• Earthquakes are almost impossible to predict
• Shockwaves (seismic waves)


  • Caused by friction building up pressure which is then released as kinetic energy
  • Weaker the further away from the focus as energy is transferred into surroundings
• Tsunamis


  • Caused by displacement of water above jolted oceanic crust
  • Waves travel fast with low amplitude, then slow down and gain height as they approach coast
• Liquefaction


  • Soil becomes saturated and acts like a liquid during earthquake vibrations, causing subsidence
• Landslides and avalanches


  • Caused by movement in soil or snow making it unstable
• Primary seismic hazards


  • Fault lines destroying environment
  • Liquefaction
• Secondary seismic hazards


  • Radioactive/dangerous substances leaked
  • Saltwater flooding freshwater ecosystems
  • Soil salinisation
  • Economic decline
  • High cost of rebuilding
  • Sources of income lost
  • Gas pipes rupturing and starting fires
  • Water supplies contaminated
  • Flooding from tsunamis
  • Political unrest from shortages
  • Borrowing money for aid
  • Lawlessness e.g. looting
• prevention


  The majority of seismic hazards cannot be prevented. (earthquakes and tsunamis will occur regardless) Liquefaction can be prevented through soil stabilisation (gravel columns put in the ground). Avalanches can be prevented through controlled explosions.
• preparedness

  • Earthquake prone areas have extensive awareness strategies and education put in place.
  • Earthquake warning systems and tsunami warning systems after an earthquake.
  • evacuation plans and training
• mitigation

  • search and rescue, immediate emergency aid, evacuation (short term)
  • demolishing older, unsafe buildings
  • tsunami wave breaks and sea walls
• adaptation

  • move away from area at risk
  • capitalise on opportunities such as encouraging tourism
  • insurance if living in places of risk
  • changing lifestyle choices e.g. moving valuable items so they cannot fall
  • building specially designed "earthquake proof" buildings