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Earthquakes

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  • 1. Earthquakes
  • 2. Elastic Limit
    • The point of how far an object can bend.
      • Ex: Rubber band; Wooden Stick
    • Rocks have an elastic limit .
      • When pass their elastic limit, rocks break.
  • 3.  
  • 4. Faults
    • When rocks break, they move along surfaces called faults .
    • Rocks can move up, down, or sideways along a fault.
      • Normal, Reverse, Strike-slip faults.
    • Forces within Earth (CONVECTION) cause plates to move -> Puts stress on rocks.
  • 5. Earthquake Distribution-I Fig. 4-7
  • 6. How Earthquakes Occur
    • Rocks move past each other along faults (B/c of tectonic plate movement).
    • Rough surfaces of rock catch against each other.
    • Plates continue to move despite stuck rocks.
    • Rocks become stressed beyond their elastic limit , they break, move along the fault, and return to their original shape.
  • 7.
    • To relieve stress, rocks will bend, compress, or stretch.
    • If rocks break, the resulting vibration is an earthquake .
    • Locations of earthquakes outline the tectonic plates .
  • 8. Seismic Waves
    • Seismic waves are the energy released when rocks break along faults.
    • “ Focus” = the point at which this energy is first released.
    • Seismic waves are produced and travel outward from the earthquake focus .
  • 9.  
  • 10. Types of Seismic Waves
    • Primary Waves (P-waves)
      • Cause particles in rocks to move back & forth in same direction .
      •  Ex: Stretched Spring
    • Secondary Waves (S-waves)
    •  Cause particles in rocks to move at right angles to the direction of the wave travel .
    • Surface Waves
    •  Move rock particles in a backward, rolling, side-to-side, swaying motion .
    •  Most damaging type of seismic waves.
  • 11. Epicenter
    • Earthquake epicenter = the point on the Earth’s surface directly above the earthquake’s focus .
    • Speeds of seismic waves allows us to determine how far away earthquake epicenter is .
      • Measured with Seismograph .
  • 12. Measuring Earthquakes-I http://quake.usgs.gov/recent/helicorders/Examples/M5.6_example.html http://earthquake.usgs.gov/image_glossary/seismograph.html
  • 13. Measuring Earthquakes
    • Richter Scale
      • Used to measure the strength of an earthquake .
      • Based on the height of the lines on the seismograph.
      • Scale has no upper limit, but 9.5 is estimated maximum.
  • 14. Measuring Earthquakes
    • Mercalli intensity scale
      • Used to measure the intensity of an earthquake based on the amount of damage caused by the earthquake.
      • Scale has 12 levels.