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    Earthquakes Earthquakes Presentation Transcript

    • Earthquakes
    • 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.
    • 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.
    • Earthquake Distribution-I Fig. 4-7
    • 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.
      • 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 .
    • 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 .
    • 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.
    • 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 .
    • Measuring Earthquakes-I http://quake.usgs.gov/recent/helicorders/Examples/M5.6_example.html http://earthquake.usgs.gov/image_glossary/seismograph.html
    • 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.
    • 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.