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• Earthquakes


  Occur where there is seismic activity, in linear patterns, on transform or constructive plate boundaries
• Earthquake locations


  • Mid Atlantic ridge
  • San Andreas fault
• Earthquake hazards at different plate boundaries

  • Conservative: Frequency
  • Magnitude
  • Depth - shallow
  • Distribution

  Divergent/constructive: Frequency

  • Magnitude
  • Depth - less than 30km
  • Distribution - earthquakes are common, but restricted to a narrow zone close to the the ridge

  Convergent/destructive (subduction): Frequency - earthquakes near the upper side of the subducting place, greatest near the surface and around the area where large subduction earthquakes happen

  • Magnitude - larger earthquakes take place at the subduction zone
  • Depth - increasingly deep on the landward side of the subduction zone - extents to at least 400km
  • Distribution - get deeper with distance from the trench

  Convergent/destructive (collision): Frequency

  • Magnitude
  • Depth - significant concentration of both shallow and deep (greater than 70km) earthquakes
  • Distribution

  Intraplate locations: related to the build up of stress due to continental rifting or the transfer of stress from other regions
• Body waves


  Primary waves (P) - travel by compression and expansion and pass through rocks gases liquids

  Secondary waves (S) - transverse waves making them a series of oscillations at right angles to the direction of movement, travel through solids but not liquids or gases
• Epicentre


  Point on surface above the focus where the earthquake started
• Focus


  Where the seismic shock waves start from
• Seismic waves


  A wave of energy that travels trough the earths body, creates a vibration
• Frequency


  How often a certain magnitude is reached within a location, 20,000 earthquakes across the globe per year
• Earthquake


  Series of vibrations that are seismic shock waves that originate from the focus

  Foreshocks - small intilal tremors

  Aftershocks - small tremors after the large shock
• Cause of earthquakes


  Movement of oceanic crust as it subducts into the subduction zone

  Where there is hotter fluid mantle, the slab distorts and cracks eventually causing an earthquake

  More plate movement = larger earthquakes

  Pressure between moving plates increases stress on rocks which deform and eventually give way and snap, releasing energy = the earthquake

  Size depends on size of slab subducting and rate of movement

  On mid ocean ridges earthquakes are small as the crust is very hot and brittle
• Primary earthquake hazards


  • Ground shaking

  Surface faulting
• Secondary earthquake hazards


  • Ground failure and soil liquefaction

  Landslides and rockfalls

  Debris flow and mudflow

  Tsunamis

  Soil salinisation

  Radioactive material released

  Gas pipes rupture
• Earthquake impacts


  • Loss of life

  Loss of livelihood building destruction

  Interruption of water supplies

  Breakage of sewage disposal systems

  Loss of public utilities eg gas and electric

  Floods and collapsed dams

  Released hazardous material

  Fires

  Spread of chronic illness
• Earthquake prediction methods


  • Small scale ground surface changes

  Small scale uplift or subsidence

  Ground tilt

  Changes in rock stress

  Micro- earthquake activity

  Anomalies in the earth's magnetic field

  Changes in radon gas concentration

  Changes in electrical resistivity of rocks

  Distortion of fences, roads, and buildings

  Changing levels of water in boreholes

  Satellites to examine position of points of earth
• Parkfield in California, on the San Andreas fault, is an intensively studied earthquake site with many monitoring instruments
• The 1994 Northridge earthquake was not predicted and occurred on a fault that scientists did not know existed
• Earthquake preparedness strategies


  • Awareness and education in earthquake prone areas

  Drop, cover, hold on

  Earthquake warning systems

  Tsunami warning system

  Evacuation training and plans
• Earthquake-resistant building design


  • Single storey buildings as less people at risk

  Soft storey at bottom on raised pillows which collapse to cushion the impact in the earthquakes
• Richter scale


  Measures the magnitude of an earthquake, logarithmic
• Mercalli scale


  Intensity scale based on ground movement and common place observations
• Earthquakes are hard to fully predict as they have no exact pattern, preparation is the best way to reduce risk
• Factors affecting earthquake damage globally


  • Strength and depth of earthquake and number of aftershocks

  Population density

  Type of buildings

  Time of day

  Distance from the epicentre

  Type of rocks and sediments

  Secondary hazards

  Economic development
• Human activities that can trigger or alter earthquakes


  • Underground disposal of liquid waste

  Underground nuclear testing

  Fracking and mining

  Increased crustal loading
• Significant earthquakes


  • Good Friday earthquake, Alaska 1964 - Magnitude 8.5, over 130 deaths, $500 million damage, triggered tsunamis

  Kobe earthquake, Japan 1995 - Magnitude 7.2, 5000 deaths, buildings built to withstand earthquakes, local preparedness
• Volcanoes


  Found at plate boundaries, in linear patterns, not found at transform faults as there is no magma rising, found at convergent and divergent boundaries
• Volcano locations


  • None in Australia, Pacific ring of fire
• Shield volcanoes (Hawaiian)


  • Hot runny lava, gentle slopes, divergent plate boundaries, less pressure
• Composite volcanoes (Plinian)


  • Cone shaped, thick lava, convergent plate boundaries, explosive as under high pressure, made from ash and lava
• Hotspots


  Not related to plate boundaries, hot magma plumes from the mantle rise
• Magnitude 7.2


  5000 deaths
• Places on known earthquake zones


  • Buildings built to withstand earthquakes
  • Local people have been prepared for the earthquake
• Volcanoes


  Describe and explain the relationship of volcanoes to the world's plate boundaries
• Where volcanoes are found


  • At plate boundaries
  • In linear patterns
  • None in Australia
  • Exceptions such as Hawaii
  • Pacific ring of fire
  • Not found at transform faults as there is no magma rising
  • Found at a convergent boundary
  • Found at divergent boundaries
• Shield volcanoes: Hawaiian


  • Hot runny lava
  • Gentle slopes
  • Divergent plate boundaries
  • Less pressure
• Composite volcano: Plinian


  • Cone shaped
  • Thick lava
  • Convergent plate boundaries
  • Continental-oceanic
  • Oceanic-oceanic
  • Explosive as its under high pressure
  • Made from ash and lava
• Hotspots


  • Not related to plate boundaries
  • Hot magma plumes from the mantle rise
  • Burn through weaker parts of the crust
  • Creates volcanoes or islands
  • Plume stays in same place as plate moves = chain of islands Hawaii
• Products of a volcanic eruption


  • Nuées ardentes (glowing clouds)
  • Lava flow
  • Mud flow
  • Lahar
  • Pyroclastic flow
  • Ash fall out
  • Ballistic clouds
  • Acid rain
  • Glacier bursts
  • Volcanic landslides
• Primary hazards of a volcanic eruption


  • Pyroclastic flows
  • Volcanic bombs
  • Lava flows
  • Ash fallout
  • Volcanic gases
  • Earthquakes
  • Ecosystems damaged
  • People killed
  • Homes destroyed
• Secondary hazards of a volcanic eruption


  • Atmospheric ash fallout
  • Landslides
  • Tsunamis
  • Acid rainfall
  • Lahars
  • Fires
  • Mudflows
  • Homelessness
• Impacts of volcanoes


  • Destruction of settlements
  • Loss of life
  • Loss of farmland and forests
  • Destruction of infrastructure (roads, airstrips, port facilities)
  • Disruption of communications
  • Food shortages