Lecture11 earthquakes
- 1. Earthquakes
- 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
- 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