Lecture11 earthquakes
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Transcript of Lecture11 earthquakes
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Earthquakes
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Global Seismicity
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Continental Drift Animationbased on paleomaps from University of Texas Arlington
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Plate tectonics: predicting the future
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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
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Global Seismicity
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Rocks are stressed too…
Rock stress: from tectonic forces, gravity, and weight of rocks above
Types of stress4. Tension (stretching)5. Compression (shortening)6. Shear (twisting or tearing)
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Strain
= how rocks respond to stress
2 types4. folding (bending)5. faulting (breaking)
depends on rock composition, pressure, and rock characteristics (brittle vs. ductile)
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Types of folds1. Anticline
• simple upfold• layers slope down from
axis• younger on outside
2. Syncline• simple downfold• layers slope up from
axis• younger on inside
younger
older
younger
older
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Types of folds
synclineanticline overturned
anticline
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Types of Faults
Tension
Compression
Shear
Stretching
Shortening
Twisting
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Faulting
= rocks on either side of a fracture are displaced relative to each other
Earthquake: caused by sudden release of energy along a fault
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Anatomy of a faultFault scarp = steep cliffs that make up the
edge of a displaced block
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3 Types of Faults
1. Normal• tension
2. Reverse• compression
3. Strike-slip (transcurrent)• shearing• lateral displacement
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3 Types of Faults
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3 Types of Faults
Divergent Plate Boundaries
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3 Types of Faults
Convergent Plate Boundaries
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3 Types of Faults
Transform Plate Boundaries
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Earthquakes
= vibration in the Earth• produced by shockwaves from sudden
movements along faults
Seismic= pertaining to earthquakes
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Focus vs epicenterFocus = center of fault motionEpicenter = surface directly above focus
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Seismometer
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Seismogram
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Richter ScaleScale is exponentialFor every increase of 1 in the Richter scale, the wave amplitude increases x10
Exponential decay
Exponential growth
y = y0e-kx y = ekx
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a = 10M
Where M is Richter magnitude, and a is wave amplitude
M = log10(a)Which is the same as
Richter ScaleScale is exponentialFor every increase of 1 in the Richter scale, the wave amplitude increases x10
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But wave amplitude is not the same as energy released. (see pg 408 in Strahler)
E = 10(4.8+1.5M) = 104.8 ·101.5M
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
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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)
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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 1018J
For comparison, the average U.S. electric power consumption rate is 3 x 1012J/sec