seismicity

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  • Created by: Sharon
  • Created on: 30-12-15 15:26
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  • Seismicity
    • Earthquakes
      • When energy stored in elastically strained rocks suddenly released.
      • causes waves of energy sent through the earth.
      • Causes
        • rocks subject to forces tend to bend. when they bend they deform. Forces "stress&strain"
        • Tensional - Stretches
        • Compressional - squash
        • Shear - slippage
      • How
        • elastic energy sends out vibrations "seismic waves"
        • Focus - point where fault rupture starts
        • Epicenter - point on surface directly above focus.
        • P waves, primary travel with velocity depending on elasticity or rock. move compressing and expanding material
        • S waves, secondary velocity depending on rigidity and density of material. 0 in liquid,
        • Surface waves parallel to earth surface up/down/side2side
    • Measuring
      • Seismometers - instrument records vibrations resulting in a graph called "seismogram"
        • moves with vibrations part of it is stationary.. pen attached to large mass suspended by spring spring and mass move less than paper (attached to earth)
    • Size
      • Richter scale - max ground shaking one area of epicenter (ENERGY)(SEISMOGRAPH)
      • Better to measure energy released.
      • Mercalli scale - intensity and ground shaking & building damage over large area, (EFFECT)(OBSERVATION
      • amplitude of largest recorded wave at specific distance from earth.
    • During
      • Ground shaking - depends on intensity and bedrock underlying.(wood/steel flexible)(Concrete brittle)
      • Ground rupture - along fault zone moves during quake, structures across collapse
      • Fire - secondary effect, power lines knocked/ natural gas. if water supply broken no extinguish.
      • Landslides - mountainous regions mass-wasting events of lose debris.
      • Liquefaction - occurs in water when completely surrounds all grains and eliminates contact = flows like fluid (requires shaking)
      • Aftershocks - further earthquakes after main event.cause further damage
      • Tsunami - giant ocean waves, disturbance of water by any means. larger cause=greater distance

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