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Earthquakes

6.1 Earthquakes and Plate Boundaries. Earthquakes. The rupture and sudden movement of rocks along a fault. A fault is a fracture surface along which rocks can slip. Majority of earthquakes occur in Earth’s crust. Part of the energy released from earthquakes spreads as complex waves.

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Earthquakes

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  1. 6.1 Earthquakes and Plate Boundaries Earthquakes • The rupture and sudden movement of rocks along a fault. • A fault is a fracture surface along which rocks can slip. • Majority of earthquakes occur in Earth’s crust. • Part of the energy released from earthquakes spreads as complex waves.

  2. 6.1 Earthquakes and Plate Boundaries Elastic Strain Energy • Elastic strain is the energy stored as a material changes in shape. • When rocks can no longer change shape—the fault breaks and slips, causing earthquakes.

  3. 6.1 Earthquakes and Plate Boundaries Elastic Strain Energy (cont.)

  4. 6.1 Earthquakes and Plate Boundaries Focus • The focus is the location on the fault where an earthquake begins. • The closer the focus is to the surface, the stronger the shaking will be.

  5. 6.2 Earthquakes and Seismic Waves Epicenter • The point on Earth’s surface directly above the earthquake’s focus.

  6. 6.1 Earthquakes and Plate Boundaries Fault Zones • Plate boundaries are usually made of multiple faults called zones that are 40–200 km wide.

  7. 6.1 Earthquakes and Plate Boundaries Plate Boundaries and Earthquakes • Lithospheric plates interact at different plate boundaries and produce earthquakes. • Earthquake size and depth and fault type depend on the type of plate boundary.

  8. 6.1 Earthquakes and Plate Boundaries Plate Boundaries and Earthquakes (cont.)

  9. 6.1 Earthquakes and Plate Boundaries Earthquakes Away from Plate Boundaries

  10. 6.1 Earthquakes and Plate Boundaries Earthquakes Away from Plate Boundaries (cont.) • New Madris Earthquakes of 1911 • Millions of years ago, a long zone of intense faulting was formed when the crust began to pull apart, but did not break completely. • Today, the crust is being compressed, or squeezed together. (p. 246)

  11. 6.1 Earthquakes and Plate Boundaries Lesson 1 Review Strike-slip faults occur at what type of plate boundary? Aconvergent plate boundary Btransform plate boundary Cdivergent plate boundary Dsubduction plate boundary

  12. 6.1 Earthquakes and Plate Boundaries Lesson 1 Review The focus of an earthquake is ____. A where an earthquake is first felt on the surface of Earth B where an earthquake dissipates Cwhere the fault and a plate meet Dwhere an earthquake begins

  13. 6.1 Earthquakes and Plate Boundaries Lesson 1 Review Which boundary is associated with earthquakes that occur at relatively shallow depths and are small in size? A divergent plate boundary B convergent plate boundary Ctransform plate boundary Dsubduction plate boundary

  14. 6.2 Earthquakes and Seismic Waves seismic wave epicenter primary wave secondary wave

  15. 6.2 Earthquakes and Seismic Waves Seismic Wave • Waves of energy that are produced at the focus of an earthquake. • Waves move outwardfrom the focus in alldirections. • 3 main types of seismic waves.

  16. 6.2 Earthquakes and Seismic Waves 1. Primary Waves (P-waves)

  17. 6.2 Earthquakes and Seismic Waves 2. Secondary Waves (S-waves)

  18. 6.2 Earthquakes and Seismic Waves 3. Surface Waves

  19. 6.1 Earthquakes and Plate Boundaries Earthquake (p.252)

  20. 6.2 Earthquakes and Seismic Waves Lesson 2 Review Surface waves cause rock particles to move with a(n) _____. A side-to-side motion B rolling motion C up-and-down and side-to-side motion D side-to-side and rolling motion

  21. 6.2 Earthquakes and Seismic Waves Lesson 2 Review What is a characteristic of P-waves? A They cause rock particles to vibrate perpendicular to the direction that waves travel. B They cause rock particles to vibrate in the same direction that waves travel. C They only travel through solids. D They are the slowest seismic wave.

  22. 6.2 Earthquakes and Seismic Waves Lesson 2 Review Which type of wave causes the most destruction at Earth’s surface? A P-wave B S-wave C surface wave D combination of P-wave and surface wave

  23. 6.3 Measuring Earthquakes seismograph seismogram

  24. 6.3 Measuring Earthquakes Measuring Earthquakes • Scientists determine size of earthquakes by measuring how much the rock slips along the fault. • They also analyze the heights of the seismic waves, which indicate how much energy is released by an earthquake.

  25. 6.3 Measuring Earthquakes Seismograph • Records size, direction, and the movement time of ground • Records the arrival times of the P- and S-waves

  26. 6.3 Measuring Earthquakes Seismogram • Record of the seismic waves • Used to calculate the size and locations of earthquakes

  27. 6.3 Measuring Earthquakes Reading a Seismogram • Wave heights indicate the amount of ground motion for each type of wave. • Difference between the arrival times of P-waves and S-waves determines the distance of the seismograph from the epicenter. (p.260)

  28. 6.3 Measuring Earthquakes Locating an Epicenter • Triangulation is used to locate the epicenter. • This method is based on the speeds of the seismic waves. • At least three seismographs must record the distances.

  29. 6.3 Measuring Earthquakes 1. Find the arrival time differences.

  30. 6.3 Measuring Earthquakes 2. Find the difference from the epicenter.

  31. 6.3 Measuring Earthquakes 3. Plot the distance on a map. (p. 263)

  32. 6.3 Measuring Earthquakes Measuring Earthquake Size • Magnitude measures the amount of energy released by an earthquake. • Determined by the buildup of elastic strain energy in the crust, at place where rupture occurs • Magnitude scale is based on record of height of ground motion and ranges from 0–9. • Richter Magnitude Scale

  33. 6.3 Measuring Earthquakes Moment Magnitude Scale • Used today because it is a more accurate scale for measuring earthquake size. • Based on the amount of energy released during an earthquake.

  34. 6.3 Measuring Earthquakes Earthquake Intensity • Intensity values vary and depend on the distance from the epicenter and the local geology. • Usually, the maximum intensity is found near the epicenter. (p. 264)

  35. 6.3 Measuring Earthquakes Lesson 3 Review What information should be known in order to determine the epicenter? Aarrival time of P-waves and surface waves at two seismograph stations Barrival time of P- and S-waves at two seismograph stations Carrival time of P- and S-waves at three seismograph stations Darrival time of P-waves and surface waves at three seismograph stations

  36. 6.3 Measuring Earthquakes Lesson 3 Review Triangulation is used to determine an earthquake’s ____. A P-waves B S-waves C epicenter D magnitude

  37. 6.3 Measuring Earthquakes Lesson 3 Review What two factors influence intensity values? A population and distance from the epicenter B distance from the epicenter and distance from the ocean Cpopulation and local geology Dlocal geology and distance from the epicenter

  38. 6.3 Measuring Earthquakes Predicting Earthquakes • At this time, geologists cannot predict earthquakes. • Geologists can, however, determine the seismic risk by locating active faults and where past earthquakes have occurred. • Geologists create seismic risk maps. (p.274)

  39. 6.4 Earthquake Hazards and Safety Avoiding Earthquake Hazards

  40. End of Resources

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