Tectonic Hazards

• Plate tectonic theory


  Earth's crust split into several tectonic plates
• Distribution of earthquakes


  • Found in belts along all plate margins
  • Some found away from margins due to human activity such as fracking
• Distribution of volcanoes


  • Found in belts along constructive and destructive plate margins (Ring of Fire)
  • Found at hotspots (Hawaii)
• Types of crust


  • Oceanic
  • Continental
• Oceanic crust

  0.5-10km thick, denser, tiny crystals, very hard rock, more easily eroded, very old (3-4 billion years old)
• Continental crust

  25-100km thick, less dense, bigger crystals, doesn't sink
• Processes at constructive margins

  1. Plates move away from each other

  2. Magma rises to fill the gap and cools to form new crust

  3. Volcanoes and earthquakes occur
• Processes at destructive margins

  1. Plates move towards each other

  2. Denser oceanic plate is subducted

  3. Creates magma

  4. Volcanoes and earthquakes occur

  5. Ground is folded to form mountains
• Processes at conservative margins


  1. Plates move past each other side by side

  2. Earthquakes occur
• Plates move, driven by convection in the mantle and under gravity
• Ridge push


  • Magma rises as the plates move apart
  • Magma cools to form new plate material
  • As it cools it becomes denser and sinks down away from the ridge, causing the tectonic plates to move away from each other
• Slab pull


  • The denser plate sinks back into the mantle under the influence of gravity
  • This pulls the rest of the plate going behind it
• Convection currents in the mantle cause magma to rise and sink, building pressure and carrying plates with it
• Reasons people live near tectonic hazards include poverty, low frequency of events, geothermal energy, and agriculture
• Measures to reduce effects of tectonic hazards

  • Monitoring (ground deformation, water pressure changes, satellite imagery)
  • Predicting (based on past events, smaller earthquakes)
  • Planning (seismic maps, planning restrictions, building regulations, earthquake kits, evacuation plans, drills)
  • Protecting (earthquake resistant buildings, tsunami walls)
• Reasons for living in areas of tectonic risk include family ties, fertile soil from volcanic ash, geothermal energy, and mineral resources