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earthquakes

earthquakes. The Way Tectonic Plates Move. Learning Targets:. Understand the anatomy of an earthquake – Elastic Rebound Theory Know the types of seismic waves 2 types of Body Waves 2 types of Surface Waves Understand the impacts of tsunamis. Earthquakes.

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earthquakes

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  1. earthquakes The Way Tectonic Plates Move

  2. Learning Targets: • Understand the anatomy of an earthquake – Elastic Rebound Theory • Know the types of seismic waves • 2 types of Body Waves • 2 types of Surface Waves • Understand the impacts of tsunamis

  3. Earthquakes • Earthquake: a sudden release of energy into the earth’s crust • Almost constant small earthquakes • 18 per year with 7 or greater magnitude • 1 per year with 8 or greater magnitude

  4. Elastic Rebound Theory • When stresses build, rocks bend elastically

  5. Elastic Rebound Theory • When stresses persist, energycontinues to build in the rocks.

  6. Elastic Rebound Theory • When the stresses are greater than internal strength of rocks, the rocks snap or fracture.

  7. Elastic Rebound Theory • Although the rocks return to their original shape the stresses cause the rocks to move to a new position.

  8. Elastic Rebound Theory • This movement releases the energy that was stored in the rocks, which creates an earthquake

  9. Focus and Epicenter • Focus: place where rocks first move • Can be anywhere from surface to 200 miles below ground • Most earthquakes are shallow (6-10 mi) • Why can’t earthquakes happen any deeper? • High temperatures makes rocks plastic; no stress builds up

  10. Focus and Epicenter • Epicenter: spot on surface above the focus • Most shaking happens at epicenter • Most damage may happen elsewhere • 95% of epicenters are along plate boundaries • This is how plate boundaries are drawn

  11. Earthquake Zones • Pacific Ring of Fire • ~80% of all earthquakes • Mediterranean-Asiatic Belt • ~15% of all earthquakes • Other plate boundaries and intraplate • ~5%

  12. Transform Plate Boundaries - Shear Stress • Shallow earthquakes = more damage • A lot of the energy goes to the surface • Examples: • San Andres, California • Dead Sea, Jordan • Chaman, Pakistan • North Anatolian, Turkey • Queen Charlotte, Alaska

  13. Convergent Plate Boundaries -Compression Stress • Deep earthquakes • Very powerful • Volcanic activity • Examples: • Himalayas • Aleutian Islands • Andes • Marianas and Mariana trench • Cascades

  14. Divergent Plate Boundaries Tension Stress • Weak, shallow earthquakes • New crust is thin • Stress is released frequently • Examples: • Mid-Atlantic ridge • Red Sea rift • East Africa rift • East Pacific rise

  15. Seismic Waves • Earthquake energy travels in seismic waves • Study of seismic waves: seismology • Body Waves: seismic waves that travel through the interior of the Earth • Surface Waves: seismic waves that travel on Earth’s surface

  16. Body Waves – P- & S- Waves 1. P-waves • P = primary • Fastest & first wave to be detected • Can travel through solids, liquids, gases • Compression waves • A lot of power but not much damage done

  17. Body Waves – P- & S- Waves • S-waves • S = secondary • Slower & secondwave to be detected • Motion produces Shear stress • Only move through solidsbecause liquids and gases have no shear strength • S-shaped

  18. Surface Waves • Cause most damage • Surface waves travel along the ground outward from an earthquake’s epicenter. • Slowestof all seismic waves.

  19. Surface Waves – Love & Rayleigh Waves • Love waves • Side-to-side motion • Like a snake

  20. Surface Waves – Love& RayleighWaves • Rayleigh waves • Rolling motion • Like ocean waves

  21. Tsunamis • Caused by underwater earthquakes • Water is very heavy. One cubic yard of water weighs almost one ton (2000 lbs)

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