Tectonics EQ 1

  • Created by: Yespacito
  • Created on: 03-01-20 14:42
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  • Tectonics EQ1
    • Distribution of Hazards
      • Earthquakes
        • OFZ - Belt of activity in mid ocean ridges eg. Atlantic belt
        • CFZ - belt from Spain, thru Alps, to Himilayas
        • Pacific Ring of Fire - ring of activity surrounding Pacific Plate eg. Japan, San andreas fault etc.
        • Intra - plate Earthquakes - old fault lines reactivate so small amount of shaking occurs
        • Can cause tsunamis if underwater eg. Japan 2011
      • Volcanoes
        • Mid Atlantic Ridge - Volcanic belt down middle of Atlantic between North Pole and Spain latitude - Formed Iceland
        • Belt from Japan to Malaysia
        • Hotspots in mantle melt thru crust so mantle plumes come out of Earth - cool and harden so volcano forms. Plate moves away so island chains form eg Hawaii
      • Boundaries
        • Cont. - cont. convergent: forced together, build pressure and can cause earthquakes. Forms fold mountains.
        • Destructive: dense oceanic subducts under cont. so dead plankton destroyed in mantle. CO2 formed and enters cont. cracks so magma bubbles out of composite volcanoes. Gas build up makes explosive eruptions.
        • Conservative: plates move side to side, either same direction at different speeds or in opposite directions. No subduction or gaps in crust so no eruptions. Edges can get caught and a locked fault is formed, so pressure builds to form an earthquake.
        • Constructive: plates move apart due to convection currents, and the pressure on the mantle due to crust is released and magma emerges from the gap created so eruptions occur but are weak. Slab pull creates friction so earthquakes occur, but are weak.
    • Theoretical Frameworks
      • Earth structure
        • Inner core: solid due to pressure above, made of nickel and iron, 6000km deep, radiation creates heat here.
        • Outer core: liquid, 2900 - 5000km deep, iron and nickel.
        • Mantle: liquid at bottom, has temperature gradient, convection cells operate here.
          • Radiation from core heats mantle, becomes less dense, so rises. When it reaches crust, it pulls them as it falls due to temperature decreasing so density decreases.
      • Evidence for tectonic theory
        • Paleomagnetism: Magnetic reversals either side of a sea floor ridge are symmetrical, so suggests it emerged from the ridge. Minerals attracting towards opposite poles creates stripes.
          • Shows that tectonic activity is occurring.
          • Can only be used on ocean seafloors, so not universal
        • Wegener's Contintental Drift theory: proposed that continents drifted apart from one large super-continent. If true, then supports plate tectonics as driving force.
          • Fossils of same species run in bands across continents, but some seem to jump across oceans
            • Scientific and reliable
          • Some continents seem to fit together eg. South America and Africa.
            • Intuitive and makes sense
            • Could be coincidental - needs other evidence as well.
      • Subduction
        • Benioff Zone: zone of seismic activity which corresponds to the subduction zone at a plate boundary. Useful in determining earthquake magnitude because hypocentres can be plotted.
    • Physical Processes
      • Earthquakes
        • Primary
          • Crustal fracturing: Fissures in the ground formed by an earthquake.
          • Ground shaking: energy released shakes ground and buildings, leading to deaths due to buildings collapsing on people.
        • Secondary
          • Landslides: large land fragments (eg. rock) falls down a slope and can pick up rock on the way.
          • Liquefaction: Water saturated  material loses strength, shaking causes it to behave like a liquid. Land near rivers can slide across a liquefied layer - lateral spreading.
          • Tsunami: seabed jolts up and part of the water column is displaced. Waves move away from this point. Long wavelength and short amplitude at sea. When it reaches land, the wavelength decreases but amplitude increases. Many waves arrive as a wave train, not just one.
        • Seismic waves
          • P waves arrive first, are compression based and low power.
          • S waves arrive second, vibrate at right angles to energy transfer, and can't travel through liquids. They are more powerful.
          • L waves arrive last, travel through the crust, and are the most powerful wave type.
      • Volcanoes
        • Primary
          • Pyroclastic flows: molten magma in vents froth and bubbles burst, ejecting hot material. Most deadly hazard from volcanoes.
          • Tephra: rock and other particles ejected into the air. Vary in size, and larger material can cause collapse of building roofs. Dust can affect air travel like it did in E15, Iceland
          • Lava flows: depending on the viscosity of lava, can pose a great threat. Depends on amount of SiO2 in lava.
          • Volcanic gases: water vapour, silicon dioxide (SiO2), carbon monoxide in air. Dangerous because they are odourless and colourless. Can kill many over time.
        • Secondary
          • Lahars: heavy rainfall mobilises old tephra along with fine silt into a mudflow.
          • Jokulhaups: heat from lava melts glaciers which causes flooding. Can cause landform changes.


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