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Chapter 7 Lesson 2 Earthquakes

Chapter 7 Lesson 2 Earthquakes. What is an Earthquake?. A sudden trembling of the ground caused by movement happening in the crust . Where Do Earthquakes Happen?. Most earthquakes happen at the edges of plates, where plates meet

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Chapter 7 Lesson 2 Earthquakes

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  1. Chapter 7 Lesson 2Earthquakes

  2. What is an Earthquake? • A sudden trembling of the ground caused by movement happening in the crust

  3. Where Do Earthquakes Happen? • Most earthquakes happen at the edges of plates, where plates meet • About 80 percent of all earthquakes happen along the edge of the Pacific Plate • Along the edges, plates can collide, they may pull apart, or they may slide past each other • These motions can cause the rocks to bend and stretch until they break • As a result, faults form at or below the surface of the crust

  4. Tectonic Plates

  5. Earthquake Locations

  6. What is a Fault? • Fault- huge cracks in the Earth’s crust

  7. Three Kinds of Faults • 1. Normal Fault • Produced at divergent boundaries • Rocks above the fault surface move down • http://earthquake.usgs.gov/learn/animations/animation.php?flash_title=Normal+Fault&flash_file=normalfault&flash_width=220&flash_height=320

  8. Three Kinds of Faults • 2. Reverse Fault • Produced at convergent boundaries • Rocks above the fault move upward • http://earthquake.usgs.gov/learn/animations/animation.php?flash_title=Thrust+Fault+and+Reverse+Fault&flash_file=thrustfault&flash_width=220&flash_height=320

  9. Three Kinds of Faults • 3. Strike Slip Fault • Produced at transform boundaries • Rocks slide past each other in different directions • http://earthquake.usgs.gov/learn/animations/animation.php?flash_title=Strike-Slip+Fault&flash_file=strikeslip&flash_width=240&flash_height=310

  10. How Earthquakes Start • Earthquakes start the moment rocks begin to scrape past each other along a fault.

  11. How Earthquakes Start • Focus • The point where the earthquake starts, where rocks begin to slide past each other • It is usually below the surface • The sudden movement causes vibrations to spread out from the focus • These vibrations travel through the crust in the form of waves

  12. How Earthquakes Start • Seismic Waves • A vibration that spreads out away from a focus when an earthquake starts • They soon reach the Earth’s surface at a point directly above the focus

  13. How Earthquakes Start • Epicenter • The point on the Earth’s surface directly above the focus of an earthquake • People can first feel the ground shaking at the epicenter

  14. How Earthquakes Start • Epicenter • This shaking is what causes most earthquake damage • Damage is usually greatest at the epicenter because it is so close to the focus • As waves travel away from the focus they get weaker

  15. Aftershocks • After the first shaking, it may be quiet, and then there are aftershocks • This is the shaking of the Earth’s crust after the initial shaking of an earthquake

  16. Earthquake Waves • There are different kinds of seismic waves which travel differently and at different speeds.

  17. Earthquake Waves • Primary Waves, or P Waves • Accordion-like motion shaking • Rock material squeezes together and spreads apart repeatedly • This motion produces seismic waves that move in the same direction that the rock is shaking • They are the fastest seismic wave- the first to reach any faraway location • http://www.youtube.com/watch?v=2rYjlVPU9U4&feature=player_embedded

  18. Earthquake Waves • Secondary Waves, or S waves • Shaking like a ruler held off the edge of a desk and “twanged” • This motion in rocks creates seismic waves that move in a perpendicular direction from the vibration • These waves travel slower than primary waves • They are second to arrive at any given faraway location. • http://www.youtube.com/watch?v=en4HptC0mQ4&feature=player_embedded

  19. Earthquake Waves • Surface Waves • This shaking causes Earths surface to heave up and down like an ocean wave, or sway from side to side • Tears apart structures built on the surface

  20. Earthquake Waves • Seismographs • Scientists study and identify waves using a seismograph • A sensitive device that detects the shaking of the Earth’s crust during an earthquake • http://www.youtube.com/watch?feature=player_embedded&v=DX5VXGmdnAg

  21. Seismograph

  22. Seismogram

  23. Tsunamis • If the focus of the earthquake is beneath the sea floor, the seismic waves can travel through the ocean, producing huge ocean waves called tsunamis • http://www.youtube.com/watch?v=yexLVVeWHb8

  24. See Mrs. Balducci’s Website…. • …..For more information on earthquakes such as earthquake current events and earthquake simulations. • Look under Chapter 7 Restless Earth LINKS http://earthquake.usgs.gov/learn/kids/

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