10   a diversion, earthquakes and tsunamis
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  • 1. Earthquakes and Tsunamis
  • 2. Earthquakes
    • Late Thursday night (our time), an earthquake occurred of the coast of Japan.
    Earthquakes
    • Late Thursday night (our time), an earthquake occurred of the coast of Japan.
  • 3. Earthquakes
    • One of the largest earthquakes since we’ve been measuring them (6 th strongest).
  • 4. What is an Earthquake?
    • Earthquakes are movements of the earth that release pressure.
    • Occur along faults.
    • - planar breaks in rock where there is movement.
    • - occur in all sizes.
  • 5. Faults
  • 6. Faults
  • 7. What Causes an Earthquake?
    • Build up of strain (gradual or sudden) deforms the earth until the elastic limit is reached – then things snap.
    • Elastic Rebound.
    • Energy is released in the form of seismic waves.
  • 8. What Causes an Earthquake?
  • 9. How do we Measure an Earthquake?
    • Most common way is by the Richter Scale.
    • Based on the amplitude of the seismic waves.
    • Scale is logarithmic! Difference in two whole numbers means in increase in vibrations by a factor of 10!
    • - ground that moves 1 inch in a 4.0 earthquake moves 10 inches in a 5.0 quake, and 100 inches in a 6.0 quake.
  • 10. Where Does the Strain Come From?
    • Plate tectonics.
    • Outermost portion of our planet is broken into different pieces called plates.
    • The plates move all the time.
  • 11. Tectonic Plates
  • 12. Plate Boundaries
    • Most of the action occurs at the boundary between two plates.
    • Plates can move away from one another, towards one another, or just slide past one another.
  • 13. Plate Boundaries
  • 14. Convergent Plate Boundaries
    • When plates run into one another, the more dense plate is forced underneath the less dense plate, a process called subduction.
  • 15. Convergent Plate Boundaries
    • When ocean material runs into continental material one gets a trench in the ocean, and a chain of volcanic mountains on the continent.
  • 16. Convergent Plate Boundaries
    • When ocean material runs into continental material one gets a trench in the ocean, and a chain of volcanic mountains on the continent.
  • 17. Convergent Plate Boundaries
    • When ocean material runs into ocean material one gets a trench in the ocean, and a chain of volcanic islands called an island-arc.
  • 18. Convergent Plate Boundaries
    • When ocean material runs into ocean material one gets a trench in the ocean, and a chain of volcanic islands called an island-arc.
  • 19. Earthquake Damage
    • Ground movement
    • Fire
    • Landslides
    • Liquefaction
    • Tsunamis
  • 20. Earthquakes and Tsunamis
    • Sudden movement of the sea floor will displace a large volume of water.
  • 21. Tsunami Speed
    • The speed of the tsunami is controlled by the depth of the water.
    • C (celerity) = √ g x d
    • where g is gravitational acceleration, and d is the depth of the water in which the wave is travelling.
    • Since g is a constant, the speed is mostly a function of water depth (wavelength also plays a role, but we’re neglecting it for now).
  • 22. Tsunami Speed
    • Average depth of the ocean is 4000 m.
    • C (celerity) = √ g x d
    • C = √ 9.8 m/s 2 x 4000 m
    • C = √ 39,200 m 2 /s 2
    • C = 198 m/s
    • 1609 meters in a mile, 3600 seconds in an hour.
    • C = 198 m/s / 1609 m/mile x 3600 s/hr
    • C = 443 miles/hour!
  • 23. Tsunami Speed
    • As the wave approaches the shore its speed decreases.
    • C (celerity) = √ g x d
    • Aside from slowing, other things happen to the wave as it enters shallower water.
  • 24. Tsunami Occurrences
  • 25. Indonesia, December 2004
    • 9.1 magnitude earthquake occurred only 8 miles deep.
    • Rupture was 1200 km long with 15 m of vertical displacement.
  • 26. Indonesia, December 2004
  • 27. Indonesia, December 2004
  • 28.
    • Magnitude 8.9.
    • Strong enough quake to affect our axis of rotation (a day on earth is now a little shorter).
    Japan, March 2011