P1.20-P1.22 Earthquakes

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  • Earthquakes
    • Seismic waves
      • generated by earthquakes or explosions
      • P waves
        • primary
        • faster
        • travel through liquids and solids
          • crust, mantle and core
      • S waves
        • secondary
        • transverse
        • only travel through solids
        • slower
      • reflected and refracted by rocks at boundaries between the crust, mantle and core
      • travel on a curved path
        • because the properties of rocks gradually change with the depth
          • so the waves gradually refract upwards on a curved path
        • when there is a sudden change in density waves are refracted sharply and may be reflected
    • Detecting earthquakes
      • 3 seismometers needed to locate epicentre
        • seismometers are devices that detect earthquakes
      • cant predict
        • don't know how big the forces acting on the tectonic plates are
        • don't know the amount of friction on the plates or how strong they are so can't predict when they will break
      • time between arrival of first P wave and first S wave can be used to work out how far away from a seismometer an earthquake occured
  • convection currents in the mantle
    • plates move in relative motion
      • plates don't slide past each other smoothly due to friction
        • friction builds
          • sudden jolt
            • Earthquakes
              • Seismic waves
                • generated by earthquakes or explosions
                • P waves
                  • primary
                  • faster
                  • travel through liquids and solids
                    • crust, mantle and core
                • S waves
                  • secondary
                  • transverse
                  • only travel through solids
                  • slower
                • reflected and refracted by rocks at boundaries between the crust, mantle and core
                • travel on a curved path
                  • because the properties of rocks gradually change with the depth
                    • so the waves gradually refract upwards on a curved path
                  • when there is a sudden change in density waves are refracted sharply and may be reflected
              • Detecting earthquakes
                • 3 seismometers needed to locate epicentre
                  • seismometers are devices that detect earthquakes
                • cant predict
                  • don't know how big the forces acting on the tectonic plates are
                  • don't know the amount of friction on the plates or how strong they are so can't predict when they will break
                • time between arrival of first P wave and first S wave can be used to work out how far away from a seismometer an earthquake occured

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