Earthquakes

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  • Earthquakes
    • Seismic waves
      • Primary waves (P waves)
        • body waves
        • travel fastest
          • reach surface first
        • less destructive
        • backwards and forwards
      • Secondary waves (S waves)
        • body waves
        • travel slower
          • 2nd to arrive
        • more destructive
        • sideways
      • Love waves (L waves)
        • surface waves
        • most destructive
        • side-to-side
        • slowest
          • last to arrive
    • Scales
      • Richter scale
        • 1st widely used method
        • amplitude of wave and distance between earthquake and seismometer
      • Moment Magnitude scale
        • range of sizes
        • applicable globally
      • Mercalli scale
        • observations of people who experienced earthquake
        • less accurate
          • exaggerate
          • disagree
          • amount of damage may not reflect strength of earthquake
    • Formation
      • build-up of tectonic strain
        • stores elastic energy in crustal rocks
          • pressure exceeds strength of fault
            • rock fractures
              • sudden release of energy
                • seismic waves radiate away from point of fracture
                  • crust rebounds
                    • ground shaking
    • Secondary impacts
      • liquefaction
        • shaking causes particles in ground to have more energy and less strength so behave like a liquid
          • subsoil cannot support foundations of buildings
            • buildings and roads tilt/ sink
      • landslides
        • occur in mountainous areas
          • travel several miles from source
            • grow in size as they pick up trees, boulders and other materials
    • Case studies
      • New Zealand
        • 2010
          • Primary impacts
            • buildings collapsed
            • roads and railways destroyed
            • no direct fatalities
          • Secondary impacts
            • cars sunk due to liquefaction
            • damaged property and possessions
            • internal migration from south to north
          • 7.1
        • 2011
          • Primary impacts
            • 185 fatalities
          • Secondary impacts
            • houses sunk due to liquefaction
              • ground already weak from 2010
                • cars sunk due to liquefaction
            • economic damage - $20 billion
          • 6.3
      • Loma Prieta, San Francisco 1989
        • Primary impacts
          • 63 fatalities
          • 20 mile section of freeway collapsed
          • 20 metre section of Oakland Bay Bridge collapsed
        • Secondary impacts
          • 1,000 people made homeless
          • severe damage due to liquefaction
          • 30 fires due to burst pipelines
          • economic damage - $10 billion
        • 6.9

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