Lecture11 earthquakes
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Lecture11 earthquakes

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    Lecture11 earthquakes Lecture11 earthquakes Presentation Transcript

    • Earthquakes
    •  
    • Global Seismicity
    • Continental Drift Animation based on paleomaps from University of Texas Arlington
    • Plate tectonics: predicting the future
    • 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
    • Global Seismicity
    • 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)
    • Strain
      • = how rocks respond to stress
      • 2 types
      • folding (bending)
      • faulting (breaking)
      depends on rock composition, pressure, and rock characteristics (brittle vs. ductile)
    • 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
    • Types of folds syncline anticline overturned anticline
    • Types of Faults Tension Compression Shear Stretching Shortening Twisting
    • Faulting
      • = rocks on either side of a fracture are displaced relative to each other
      • Earthquake: caused by sudden release of energy along a fault
    • Anatomy of a fault
      • Fault scarp = steep cliffs that make up the edge of a displaced block
    • 3 Types of Faults
      • Normal
        • tension
      • Reverse
        • compression
      • Strike-slip (transcurrent)
        • shearing
        • lateral displacement
    • 3 Types of Faults
    • 3 Types of Faults Divergent Plate Boundaries
    • 3 Types of Faults Convergent Plate Boundaries
    • 3 Types of Faults Transform Plate Boundaries
    • Earthquakes
      • = vibration in the Earth
      • produced by shockwaves from sudden movements along faults
      Seismic = pertaining to earthquakes
    • Focus vs epicenter
      • Focus = center of fault motion
      • Epicenter = surface directly above focus
    • Seismometer
    • Seismogram
    • 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
    • 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
    • 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
    • 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)
    • 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