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4.2 4.2 Presentation Transcript

  • Earthquakes Release Energy
  • Seismic Waves
    • The vibrations caused by earthquakes
  • Focus and Epicenter
    • Focus - the of an earthquake is the pint underground where the rocks first begin to move.
    • Epicenter - the point of the Earth’s surface directly above the focus.
      • Scientists often name an earthquake after the city that is closest to the epicenter
  • Waves and Energy
      • Earthquakes produce three types of waves
        • Primary Waves
        • Secondary Waves
        • Surface Waves
  • Primary Waves
    • These are the fastest seismic waves
    • Also called P waves
    • Average speed 5km/sec (3mi/sec)
    • Can pass through solids, liquids and gases
  • Secondary waves
    • Also called S- Waves
    • Travel at about ½ the speed of P-waves
    • Start at the same time as P-waves
    • Can travel through solids (rocks) NOT through liquids or gases
  • Surface Waves
    • Seismic waves that move along Earth’s surface, not through it’s interior
    • Make the ground roll or shake from side to side
    • Cause the largest ground movements and the most damage.
    • The slowest type of seismic waves
  • Seismograph
    • An instrument that constantly records ground movements
    Read page 116 (B), using seismographs
  • Locating Earthquakes
    • Scientist must have at least 3 seismic stations
      • Scientist find the difference between the arrival times of the P and S waves at each of the three stations
      • The time difference is used to determine the distance of the epicenter from each station. The greater the difference in time, the farther away the epicenter is.
      • A circle is drawn around each station, with a radius corresponding to the epicenters distance from that station. The point where the 3 circles meet is the epicenter
  •