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Chapter 15 – Earthquakes - Review Questions

  1. What is the theory that explains earthquakes?
  2. Elastic-rebound theory

  3. How does this theory give an explanation of how an earthquake occurs?
  4. Stress deforms the crust until the stress is released. This is when the crust will snap back to its original shape, except it is now a bit out of place.

  5. What is the relationship between earthquake, stress, and plate tectonics?
  6. Stress between two plates will produce a fault (a break in the Earth’s crust) which then will eventually cause an earthquake to relieve the stress.

  7. Explain the difference between an epicenter and the focus of the earthquake?
  8. The focus is the location on the fault where stress if first released underground. The epicenter is the location on the surface directly above the focus.

  9. What is the significance of the epicenter and focus?
  10. This is where the most damage from the earthquake will be found. It is also good to know where this location is so you are aware that stress is building up at this location. It would be good to monitor these areas in case of further stress build up.

  11. At what type of boundaries are earthquakes related (found)?
  12. Earthquakes are found at any type of boundary, they range from shallow to deep. The depth is dependent upon the type of boundary.

  13. Why are shallow depth earthquakes the most common?
  14. It only takes a very small amount of energy release to produce a shallow earthquake. Plates moving only slightly can produce this amount necessary. Look at the plate tectonics map. Look at how many long plate boundaries there are. The potential exists all along these boundaries.

  15. At what type of boundary do deep earthquakes occur? What is the reason for this?
  16. Subduction boundaries produce deep earthquakes because the crust is being pulled down further causing stress to build up at a deeper depth.

  17. An earthquake is a release in stress. How is this release in stress transmitted through the crust?
  18. In waves of energy (p, s and eventually l waves)

  19. What are the three types of wave motions?
  20. P waves move back and forth; S waves move side to side; and L waves are up and down rolling waves

  21. What type of material can each wave travel through?
  22. P waves travel through all materials; S waves only travel through solids; and L waves only travel on the surface of the crust.

  23. At what velocity does each wave travel (how fast)?
  24. P waves are the fastest, although their velocity does change; S waves are second; L waves are the slowest

  25. What motion does each wave make as it travels?
  26. P waves move back and forth; S waves move side to side; and L waves are up and down rolling waves

  27. How does each wave motion affect the motion of the crust?
  28. P waves move crust parallel to wave movement; S waves move crust perpendicular to wave movement; and L waves move crust perpendicular to wave movement

  29. What is the difference between a seismograph and a seismogram?
  30. A seismogram is the instrument that collects data about earthquake waves, and and the seismograph is the actual print out of the data.

  31. What do scientists use seismographs and seismograms for?
  32. To find the distance to te epicenter from that location; they can also determine the magnitude of the earthquake at that location.

  33. What is the importance of time-travel graph?
  34. It shows the relationship between arrival times of waves and the distance that they traveled in that amount of time. It is used to determine the distance to the epicenter from each location.

  35. What information would you need to acquire in order to determine the location of the epicenter of an earthquake?
  36. You need at least 3 seismogram locations, from the data on the seismograph and a time-travel graph you can determine the s-p interval which will help you identify the distance the epicenter is from that location. Once you have the distance you can use a compass to draw the radius circle for each location. Wherever the 3 circles intersect is the location of the epicenter. Having more than 3 locations will give you a more accurate location.

  37. Why would we want to know the location of the epicenter?
  38. This is where the most damage is, and this is a location where stress builds up.

  39. Explain the difference between the Richter scale and seismic moment.
  40. The Richter scale measure the amount of energy released at the focus in magnitude 1-10, and the seismic moment measures the total amount of stress released by the entire fault also in magnitude 1-10.

  41. Are we able to predict when, where, and at what magnitude an earthquake will occur? Why or why not?
  42. No, because we do not have the technology to know at what particular moment that stress is going to be released at what exact location, and at what magnitude.

  43. How are seismic waves used to determine the composition of the earth’s interior?

By knowing what type of material each wave can travel through, we are able to look at waves received and know what it passed through.

23. What is the shadow zone of an earthquake, and how is one produced?

It is a band around the earth where no seismic waves have been recorded.