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Understanding Earthquakes: Causes, Waves, and Impacts

Explore the causes, types of waves, and impacts of earthquakes. Learn about seismic activity, measuring earthquakes, and historical examples. Discover how seismographs work, locate epicenters, and understand earthquake prediction. Dive into Earth's layers and shadow zones.

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Understanding Earthquakes: Causes, Waves, and Impacts

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  1. Chapter 3: ObjectivesEarthquakes Result from Stress • Define earthquake, list problems caused by earthquakes, and discuss several causes of earthquakes • Definefocusand epicenter and identify the significance of the depth of the focus • Name and describe the kinds of waves produced by earthquakes

  2. VocabularyEarthquakes Result from Stress • Earthquake • Elastic-rebound theory • Focus • Epicenter • P waves • S waves • L waves

  3. What is an earthquake? • An earthquake is a shaking of Earth’s crust caused by a release of energy • Earthquakes are the result of the movement of Earth’s tectonic plates

  4. Causes of earthquakes Earthquakes can occur for many reasons. • Volcanic eruptions • Collapsing caverns • Meteor impacts • Stress that builds up between tectonic plates. This is the main cause of earthquakes.

  5. Elastic-rebound theory

  6. Depth of earthquakes

  7. Earthquake waves

  8. P waves • Primary waves • Compressional waves • These are the first waves of energy released from an earthquake • P waves can travel through liquids and solids

  9. S waves • Secondary waves • Shear waves • These are the second waves of energy released from an earthquake • S waves can travel through solids, but not liquids

  10. P and S waves in a slinky

  11. Ground waves • Occur on the surface of the ground • Ground waves are the slowest-moving earthquake waves • There are two kinds of ground waves: • Love waves • Rayleigh waves

  12. Ground waves Rayleigh waves Love waves

  13. Earthquake waves

  14. Chapter 3: ObjectivesLocating an Earthquake • Describe how a seismograph works • Discuss the relationship between the arrival time of the P and S waves at a seismograph station and the distance of the station from the earthquake epicenter • Explain how to locate an earthquake epicenter

  15. VocabularyLocating an Earthquake • Seismogram • Seismograph • Time-travel graph

  16. Seismometers

  17. Seismometers

  18. Seismogram

  19. Time-travel graph

  20. Locating the epicenter

  21. Chapter 3: ObjectivesMeasuring an Earthquake • Identify the scales used to describe earthquake magnitude • Name two major causes of building collapse during earthquakes • Identify several kinds of data that are being studied for earthquake prediction

  22. Vocabulary Measuring an Earthquake • Seismic moment • Richter scale

  23. Earthquake magnitude

  24. Earthquake magnitude and energy

  25. Earthquake damage: USA

  26. Earthquake damage: Los Angeles

  27. Earthquake risk and prediction Earthquake prediction includes • The time an earthquake will happen • The location of the earthquake • The magnitude of the earthquake Methods such as animal behavior, radon emission studies, changes in magnetic fields, and changes in electrical conductivity have been used, but the results are mixed

  28. Earthquake damageLoma Prieta 1989

  29. Earthquake damageLoma Prieta 1989

  30. Earthquake damageLoma Prieta 1989

  31. Earthquake damageNorthridge 1994

  32. Earthquake damageNorthridge 1994

  33. Earthquake “proof” structures?

  34. Earthquake “proof” structures?

  35. Earthquake “proof” structures?

  36. Earthquake retrofit on freeways

  37. Chapter 3: ObjectivesEarthquake Waves inside Earth • Explain changes in P and S wave velocities inside Earth • Locate the Mohorovičić discontinuity and explain how it was discovered • Describe the shadow zone and explain its significance

  38. Vocabulary Earthquake Waves inside Earth • Shadow zone • Mohorovičić discontinuity

  39. The seismic shadow zone • When an earthquake occurs, seismic waves radiate out spherically from the earthquake's focus. • The P waves are bent by the liquid outer core of the Earth and are not detected between 104° and 140° from the epicenter • The S waves cannot pass through the liquid outer core are not detected more than 104° from the epicenter.

  40. The shadow zone

  41. Chapter 3: ObjectivesExamples of Earthquakes • Identify movement along a subduction boundary as the cause of the 1964 Alaskan earthquake • Discuss earthquake activity along the San Andreas fault system • Explain the cause and significance of midplate earthquakes such as the 1811-1812 New Madrid earthquakes

  42. San Francisco 1906 • Occurred at 5:12 am on April 18, 1906 • Epicenter: 3 km west of San Francisco • Focus: 8 km deep • Magnitude 7.8 • The shaking lasted 60 seconds • 700 - 3000 fatalities

  43. San Francisco 1906

  44. San Francisco 1906

  45. San Francisco 1906

  46. San Francisco 1906

  47. Alaska 1964 • Occurred at 5:36 pm on March 27, 1964 • Epicenter: 120 km east of Anchorage • Focus: 25 km deep • Magnitude 9.2 • The shaking lasted 4 ½ minutes • 139 fatalities

  48. Alaska 1964

  49. Alaska 1964

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