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10 a diversion, earthquakes and tsunamis

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An earthquake occurred off the coast of Japan on Thursday night. It was one of the largest earthquakes since measurements began, measuring a 6 on the Richter scale. Earthquakes are caused by a buildup of strain in the earth's crust until the elastic limit is reached, releasing energy in seismic waves. When tectonic plates converge under the sea, it can cause both earthquakes and tsunamis as the sudden movement of the seafloor displaces large volumes of water.

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Earthquakes and Tsunamis
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.
Earthquakes One of the largest earthquakes since we’ve been measuring them (6 th strongest).
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.
Faults
Faults
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.
What Causes an Earthquake?
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.
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.
Tectonic Plates
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.
Plate Boundaries
Convergent Plate Boundaries When plates run into one another, the more dense plate is forced underneath the less dense plate, a process called subduction.
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.
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.
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.
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.
Earthquake Damage Ground movement Fire Landslides Liquefaction Tsunamis
Earthquakes and Tsunamis Sudden movement of the sea floor will displace a large volume of water.
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).
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!
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.
Tsunami Occurrences
Indonesia, December 2004 9.1 magnitude earthquake occurred only 8 miles deep. Rupture was 1200 km long with 15 m of vertical displacement.
Indonesia, December 2004
Indonesia, December 2004
Magnitude 8.9. Strong enough quake to affect our axis of rotation (a day on earth is now a little shorter). Japan, March 2011

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10 a diversion, 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.
  • 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.
  • 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.
  • 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.
  • 25. Indonesia, December 2004 9.1 magnitude earthquake occurred only 8 miles deep. Rupture was 1200 km long with 15 m of vertical displacement.
  • 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