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# 10 a diversion, earthquakes and tsunamis

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### 10 a diversion, earthquakes and tsunamis

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