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Earthquakes Chapter 6

Earthquakes Chapter 6. Elastic Rebound Theory. Rocks on either side of a fault move slowly When locked, stress builds…until fault ruptures Rocks fracture and slip to new position releasing vibrations - create seismic waves. Relaxed Stressed Released. What are faults.

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Earthquakes Chapter 6

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  1. Earthquakes Chapter 6

  2. Elastic Rebound Theory • Rocks on either side of a fault move slowly • When locked, stress builds…until fault ruptures • Rocks fracture and slip to new position releasing vibrations - create seismic waves

  3. Relaxed Stressed Released

  4. What are faults • A fault is a crack in the Earth's crust along which movement has occurred. • Occur at plate boundaries or within a plate • Consists of a hanging wall (HW) and a foot wall (FW)

  5. 3 types of faults • Normal: • at divergent boundaries, HW moves down, FW moves up

  6. Reverse (or thrust fault): • at convergent boundaries: HW moves up, FW moves down

  7. Strike-slip faults: • At transform boundaries; movement is horizontal

  8. San Andreas Fault Strike-slip fault From shuttle (above) From air (at right)

  9. More San Andreas

  10. Earthquake Vocab Focus: area along fault where slippage 1st occurs Epicenter: point on surface directly above the focus

  11. Major EQ Zones – 1. Ring of Fire

  12. 2. Mid-Ocean Ridges

  13. 3. Eurasian-Melanesian Mts Boundary of Eurasian-Indian-African plates

  14. 4. Fault Zones • Faults along plate boundaries – San Andreas strike-slip fault • Faults within plates – in middle of US - 1812 New Madrid, Missouri EQ • New England, too? • Nov. 2006 NH – 1.2

  15. Recording EQs • Seismograph: instrument used to record EQs • Seismogram: printout from a seismograph

  16. Types of Seismic Waves • Primary “P” • Secondary “S” • Surface Waves • Rayleigh “R” • Love “L” http://www.rsuw.daleh.id.au/html/seismic_waves.html

  17. Primary “P” waves • “push-pull” waves • Fastest seismic waves; 1st to be recorded • Compression waves (like sound) • Cause movement in the same direction as the wave motion • Rocks vibrate backwards and forwards, • P waves can travel through liquids and solids

  18. Secondary “S” waves • Shake or shear waves • Second to be recorded • Slower and more destructive than P waves • Rocks are moved from side to side as the wave passes, moving at right angles to the direction of wave motion • Transverse waves, like water waves • Move through solid only

  19. Surface, “L” waves • L for “Love” waves • Slowest of the three EQ wave types • L waves take the longer surface route around the earth • Have a rolling motion, side to side • Cause great damage • Behaves most like waves in a pond or on the sea

  20. Other surface waves • Rayleigh waves • Rolls along the ground, moving ground up and down • Animation: http://www.edcenter.sdsu.edu/ssc/3d/rayleighwave/rayleighwavetest2.mov

  21. Power and ground type • The type of rock will determine how fast the wave travels, and will thus affect amplitude of the waves • Animation: http://www.edcenter.sdsu.edu/ssc/3d/seismicpropagation2d/seismicpropagation-sm.mov

  22. Using Seismic Waves to determine Earth’s Interior • P waves travel through solids, liquids and gases • S waves travel through solids only • Outer core must be liquid (no S waves pass)

  23. Earthquakes, Tsunami and animals • http://www.teachersdomain.org/asset/nat08_vid_waves/

  24. Homework • Read and take notes – pp 104-105 • Answer questions #1-4, pg 102 and #3-5, pg 105

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