Chapter 11 Earthquakes


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Chapter 11 Earthquakes

  1. 1. Chapter 11 Earthquakes
  2. 2. When rocks break they move along faults.
  3. 3. Applied forces cause rocks to undergo elastic deformation.
  4. 4. When elastic limits are passed, rocks break.
  5. 5. Rock on one side of a fault can move up, down, or sideways in relation to rock on the other side of the fault.
  6. 6. Faults occur because forces inside the Earth cause earth’s plates to move placing stress on or near the plate edge
  7. 7. Rocks will bend, compress, stretch, and possibly break.
  8. 8. Earthquake: vibrations produced by breaking rock
  9. 9. Rocks break, move along the fault, and return to original shapes.
  10. 10. Rock on one side of a fault can move over, under, or past each other along fault lines.
  11. 11. Three types of forces act on rocks: tension, compression, and shear.
  12. 12. Tension forces; normal fault: caused by rock above the fault moving downward in relation to the rock below the fault.
  13. 14. Reverse fault: compression forces squeeze rock above the fault up and over the rock below the fault.
  14. 16. Created by shear forces; strikeslip fault: rocks on either side of the fault move past each other without much upward or downward motion.
  15. 18. Section 2:
  16. 19. Seismic – waves generated by an earthquake can move the ground forward and backward, up and down, and side to side.
  17. 20. Focus: an earthquake’s point of energy release
  18. 21. Primary waves (P waves): cause particles in rocks to move back and forth in the same direction that the wave is traveling.
  19. 22. Secondary waves (S waves) – cause particles in rock to move at right angles to the direction of wave travel.
  20. 23. Surface waves – move rock particles in a backward, rolling motion and a sideways swaying motion.
  21. 24. The point on the Earth’s surface directly above the earthquake focus is called the epicenter.
  22. 25. The different speeds of seismic waves allow scientists to determine the epicenter.
  23. 26. Primary waves move the fastest. Secondary waves follow Surface waves move slowest and arrive at the seismograph station last.
  24. 27. Seismograph: measures seismic waves.
  25. 28. Consists of a rotating drum of paper and a pendulum with an attached pen.
  26. 29. The paper record of a seismic event is called a seismogram.
  27. 30. Earth’s structure consists of an inner, mostly iron, solid core surrounded by a mostly iron liquid outer core surrounded by the mantle.
  28. 31. The curst is Earth’s outer layer, about 5 to 60 km thick.
  29. 32. A seismic wave’s speed and direction change as the wave moves through different layers with various densities.
  30. 33. Density generally increases with depth as pressures increase.
  31. 34. Shadow zones do not receive seismic waves because the waves are bent or stopped by materials of different density.
  32. 35. Changes in seismic wave speed allowed detection of boundaries between Earth’s layers.
  33. 36. Although earthquakes are natural geologic events, they kill many people and cause a lot of damage
  34. 37. Seismologists <ul><li>scientists who study earthquakes </li></ul>
  35. 38. Magnitude <ul><li>measure of energy released by an earthquake </li></ul><ul><li>determined by the Richter scale and based on the height of the lines on a seismogram </li></ul>
  36. 40. The Richter Scale has no upper limit
  37. 41. Most earthquakes have magnitudes too low to be felt by humans – 3.0 to 4.9 on the Richter Scale
  38. 42. The modified Mercalli intensity scale describes earthquake intensity based on structural and geologic damage
  39. 43. Liquefaction <ul><li>shaking from an earthquake can make wet soil act like a liquid </li></ul>
  40. 45. Ocean waves caused by earthquake are called tsunamis
  41. 46. <ul><li>caused when a sudden movement of the ocean floor pushes against the water </li></ul><ul><li>can travel thousands of kilometers in all directions </li></ul>
  42. 47. Earthquakes cannot be reliably predicted
  43. 48. <ul><li>Knowing how and where to plan for earthquakes can help prevent death and damage </li></ul><ul><li>Buildings can be constructed to withstand seismic vibrations </li></ul>
  44. 49. <ul><li>Flexible, circular moorings are being placed under buildings </li></ul><ul><li>made of alternating layers of rubber and steel </li></ul>
  45. 50. The rubber acts like a cushion to absorb earthquake waves
  46. 51. Homes can be protected by careful placement of heavy objects and securing gas appliances
  47. 52. During an earthquake, crawl under a sturdy table or desk <ul><li>outdoors, stay away from buildings and power lines </li></ul>
  48. 53. After an earthquake, check for water or gas line damage leave IMMEDIATELY if a gas smell is present