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March 31

March 31. Describe Stress vs. Strain Describe Elastic Rebound Describe the different types of faults. Earthquakes. Forces inside Earth When rocks break they move along FAULTS Applied forces cause rocks to undergo elastic deformation (stress)

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March 31

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  1. March 31 • Describe Stress vs. Strain • Describe Elastic Rebound • Describe the different types of faults

  2. Earthquakes Forces inside Earth • When rocks break they move along FAULTS • Applied forces cause rocks to undergo elastic deformation (stress) • When elastic limits are passed, rocks break (strain) • Rock on one side of a fault can move up, down, or sideways in relation to rock on the other side of the fault

  3. Stress vs. Strain • Rubber Band Example • You apply stress to elongate the rubber band • Strain occurs when you apply to much stress and deform the material.

  4. Elastic Rebound • Geologists think that earthquakes are the result of elastic rebound. • In this process, the rocks on each side of a fault are moving slowly. If the fault is locked, the rock deforms, and stress in the rocks increases. • When rocks are stressed past the point at which they can maintain their integrity, they fracture. • The rocks then separate at their weakest point along the fault and rebound, or spring back to their original shape.

  5. Elastic Rebound

  6. Faults • Faults occur because of the forces inside of Earth cause Earth’s plates move placing stress on or near plate edge • Rocks will bend, compress, stretch, and possible break • Earthquake – vibrations produced by breaking rock • Rocks break, move along the fault, return to original shapes • Rock on one side of a fault can move over, under or past each other along fault lines

  7. Faults Cont’d • Three types of forces act on rocks • Tension • Normal fault – pulls material apart • Compression • Reverse Fault – decreases the amount of material • Shear • Strike slip fault – rocks on either side of the fault move past each other without much upward or downward motion

  8. Types of Fault

  9. Types of Fault

  10. Types of Fault http://www.pbs.org/wnet/savageearth/animations/

  11. Features of Earthquakes • Seismic Waves • Waves generated by an earthquake, can move the ground • forward and backward, • up and down • side to side • Focus – an earthquake’s point of energy release

  12. Types of Seismic Waves • 2 Types of Waves • Body Waves • Primary (P): • Secondary (S): • Surface Waves: • Rayleigh • Love

  13. Types of Seismic Waves • Body Waves • Primary (P): cause particles in rocks to move back and forth in the same direction the wave is traveling • Secondary (S): cause particle s in rock to move at right angles to the direction of wave travel

  14. Types of Seismic Waves • Surface Waves • Rayleigh • Back to back motion on the surface • Love • Up and down motion on the surface

  15. Types of Seismic Waves

  16. Anatomy of an Earthquake

  17. Epicenters • Point on the Earth’s surface directly above the earthquake • Speeds of Seismic waves allow scientists to determine epicenter • Primary = fastest • Secondary = follow P • Surface = slowest

  18. Finding the Travel Times of S and P Waves http://www.newyorkscienceteacher.com/sci/files/user-submitted/pswavechart.swf

  19. Seismograph • Measures seismic waves • Consists of rotating drum of paper and a pendulum with an attached pen • The paper record of seismic event is called a seismogram

  20. Horizontal and Vertical Seismographs

  21. Reading Seismograms

  22. Seismic Recordings and Earth’s Interior • Earth’s Internal Structure • Lithosphere, Asthenosphere, Mantle, Core • Seismic Waves • Change Speed and Direction when they move through material of different densities • Density will increase with depth as pressure increase • Shadow Zone • Do receive seismic waves • The waves are bent or stopped by materials of different densities

  23. Shadow Zone

  24. Shadow Zone

  25. People and Earthquakes • Magnitude: the amount of E released during an earthquake • Usually reported using 1 of 3 scales

  26. Richter Scale Richter: based on the size of the largest seismic waves generated by the quake developed by American Charles Richter • each whole number increase represents an increase in seismic wave size, or amplitude, by a factor of 10 • Ex: A 4.0 earthquake has 10 times the seismic waves as a 3.0 earthquake • the difference in E between two numbers on the Richter Scale is 32x • Ex: A 4.0 earthquake has 32 times the E as a 3.0 earthquake • Ex: How much more E is released during a 7.0 earthquake vs a 5.0 earthquake?

  27. Other Magnitude Detectors • Moment Magnitude: based on several factors (not just largest seismic wave): • size of fault rupture • amount of movement along the fault • rocks’ stiffness • Modified Mercalli: based on intensity or damage done to the area • uses structural damage & eye witness accounts to rate earthquakes • uses Roman numerals I to XII to designate degree of intensity (p. 507 table 19-1)

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