Earthquakes Lecture

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Transcript

  • 1. Earthquakes Chapter 19
  • 2. Earthquakes
    • Natural vibrations of ground caused by movement along fractures in Earth’s crust or by volcanic eruptions
  • 3. Stress and Strain
    • Stress- forces per unit area exceed the strength of the rocks involved
      • Compression-Decreases Volume
      • Tension- Pulls material apart
      • Shear- Causes Twisting
    • Strain- Deformation of materials caused by stress
  • 4. Faults- fracture of Earth’s crust
    • Reverse- Horizontal compression, Causes shortening, Foot wall goes down
  • 5. Faults- Con’t
    • Normal- Horizontal tension, Causes extension, Foot wall goes up
  • 6. Faults- Con’t
    • Strike-Slip- Horizontal Shear, causes offset
  • 7.  
  • 8. Waves
    • Primary- P- Pressure Wave
    • Secondary- S- Side-to-side wave
    • Surface Wave- L-Wave
    • Page 498
  • 9. Location of Earthquakes
    • Focus- point where an earthquake originates
    • Epicenter- Place on Earth's surface where EQ occurred
  • 10. Seismic Waves
    • Seismology- Study of Earthquake waves
    • Seismograph- instrument for recording earthquake waves
  • 11. Waves
    • P wave- arrives 1 st
    • S wave- arrives 2nd
    • L wave- last and largest
  • 12. Clues to Earth’s Interior
    • Seismic waves change speed and direction when they encounter different materials
      • P and S waves travel fairly straight through the mantle
      • P waves strike the core and are bent (11,000 Km from focus)
        • Re-emerge at 16,000 km from focus, after shadow
  • 13. Clues to Earth’s Interior- Con’t
    • S-waves cannot travel through liquids so they can’t pass through the core (never beyond shadow)
    • P waves speed up through solids
  • 14.  
  • 15. Measuring and Locating EQ
    • Magnitude- amount of energy released
      • Richter Scale- size of largest seismic waves released by quake
        • Each # increase is a 10 fold increase in energy
        • Each increase in amplitude (height of wave) is a 32 time increase in energy
  • 16. Measuring and Locating EQ- Con’t
    • Moment Magnitude Scale- uses size of fault rupture, amount of movement and rock’s stiffness
    • Modified Mercalli Scale- uses damage to buildings at location of worst damage
      • Uses I-XII Roman Numerals- Called Intensity
      • Measures Surface Waves
    • Depth of Focus- Deeper EQ usually less intense
  • 17. Measuring and Locating EQ-Con’t
    • Locating EQ- time and location unknown
      • Distance determined by time between P wave and S wave--- AT 3 STATIONS
      • Time calculated using same P-S interval
  • 18. Seismic Belts
    • Earthquakes not random
      • Ring of Fire- Edge of Pacific Plate- 80% of all Earthquakes
      • Mediterranean- Asian Belt- 15% of EQ
  • 19.  
  • 20. Earthquakes and Society
    • Earthquake Hazards
      • Structural failure
        • Ground floor fails -> Upper Floors Fail -> Pan caking
        • Height- 5-15 stories causes vibrations which are similar to natural sway; Shorter and taller buildings are different
      • Land/Soil Fracture
        • Landslides- Common in saturated areas
        • Soft ground conducts waves well -> more damage
      • Fault Scarps- vertical offsets -> waterfalls, road problems
  • 21. Earthquakes and Society- Con’t
    • Tsunami- ocean waves created by EQ
      • Travels fast and are low (less than 4 feet high) in open ocean, but pile up hundreds of feet tall near shore
      • Ocean recedes dramatically before tsunami
  • 22. Earthquake Risk
    • Here we have a 3% risk over 50 years
    • Hot Spot in US:
      • CA
      • Rocky Mountains
      • WA, OR
      • MO