Lecture11 earthquakes
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Transcript of Lecture11 earthquakes
Earthquakes
Global Seismicity
Continental Drift Animationbased 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 stress4. Tension (stretching)5. Compression (shortening)6. Shear (twisting or tearing)
Strain
= how rocks respond to stress
2 types4. folding (bending)5. faulting (breaking)
depends on rock composition, pressure, and rock characteristics (brittle vs. ductile)
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
Types of folds
synclineanticline 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 faultFault scarp = steep cliffs that make up the
edge of a displaced block
3 Types of Faults
1. Normal• tension
2. Reverse• compression
3. 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 epicenterFocus = center of fault motionEpicenter = surface directly above focus
Seismometer
Seismogram
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
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
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
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 1018J
For comparison, the average U.S. electric power consumption rate is 3 x 1012J/sec