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Lecture11 earthquakes

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Transcript

  • 1. Earthquakes
  • 2.  
  • 3. Global Seismicity
  • 4. Continental Drift Animation based on paleomaps from University of Texas Arlington
  • 5. Plate tectonics: predicting the future
  • 6. Plate tectonics in the future: 50 my
    • Australia will straddle the equator
    • E. Africa will form new continent
    • Antarctica will swing off the south pole
    • Mediterranean will close off
    • Atlantic Ocean will grow
    • Pacific Ocean will shrink
  • 7. Global Seismicity
  • 8. Rocks are stressed too…
    • Rock stress: from tectonic forces, gravity, and weight of rocks above
    • Types of stress
    • Tension (stretching)
    • Compression (shortening)
    • Shear (twisting or tearing)
  • 9. Strain
    • = how rocks respond to stress
    • 2 types
    • folding (bending)
    • faulting (breaking)
    depends on rock composition, pressure, and rock characteristics (brittle vs. ductile)
  • 10. Types of folds
    • Anticline
      • simple upfold
      • layers slope down from axis
      • younger on outside
    • Syncline
      • simple downfold
      • layers slope up from axis
      • younger on inside
    younger older younger older
  • 11. Types of folds syncline anticline overturned anticline
  • 12. Types of Faults Tension Compression Shear Stretching Shortening Twisting
  • 13. Faulting
    • = rocks on either side of a fracture are displaced relative to each other
    • Earthquake: caused by sudden release of energy along a fault
  • 14. Anatomy of a fault
    • Fault scarp = steep cliffs that make up the edge of a displaced block
  • 15. 3 Types of Faults
    • Normal
      • tension
    • Reverse
      • compression
    • Strike-slip (transcurrent)
      • shearing
      • lateral displacement
  • 16. 3 Types of Faults
  • 17. 3 Types of Faults Divergent Plate Boundaries
  • 18. 3 Types of Faults Convergent Plate Boundaries
  • 19. 3 Types of Faults Transform Plate Boundaries
  • 20. Earthquakes
    • = vibration in the Earth
    • produced by shockwaves from sudden movements along faults
    Seismic = pertaining to earthquakes
  • 21. Focus vs epicenter
    • Focus = center of fault motion
    • Epicenter = surface directly above focus
  • 22. Seismometer
  • 23. Seismogram
  • 24. Richter Scale Scale is exponential For every increase of 1 in the Richter scale, the wave amplitude increases x10 Exponential decay Exponential growth y = y 0 e -kx y = e kx
  • 25. a = 10 M Where M is Richter magnitude, and a is wave amplitude M = log 10 (a) Which is the same as Richter Scale Scale is exponential For every increase of 1 in the Richter scale, the wave amplitude increases x10
  • 26. But wave amplitude is not the same as energy released . (see pg 408 in Strahler) E = 10 (4.8+1.5M) = 10 4.8 ·10 1.5M Where M is Richter magnitude, and E is energy released So for every increase of 1 in the Richter magnitude, energy increases x 32 Richter Scale
  • 27. How much energy is released?
    • For example, the earthquake that caused the Indian Ocean tsunamis on Boxing Day 2004 (12/26/04) measured 9 on the Richter scale
    • How much energy was released by this quake?
      • E = 10 (4.8 + 1.5M)
  • 28. The Boxing Day Quake
    • How much energy was released by this quake?
    • E = 10 (4.8 + 1.5M)
    • = 10 (4.8 + 1.5(9))
    • = 10 (4.8 + 13.5)
    • = 10 (18.3) = 1.99 x 10 18 J
    For comparison, the average U.S. electric power consumption rate is 3 x 10 12 J/sec