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# Earthquakes

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### Earthquakes

1. 1. Earthquakes
2. 2. Elastic Limit <ul><li>The point of how far an object can bend. </li></ul><ul><ul><li>Ex: Rubber band; Wooden Stick </li></ul></ul><ul><li>Rocks have an elastic limit . </li></ul><ul><ul><li>When pass their elastic limit, rocks break. </li></ul></ul>
3. 4. Faults <ul><li>When rocks break, they move along surfaces called faults . </li></ul><ul><li>Rocks can move up, down, or sideways along a fault. </li></ul><ul><ul><li>Normal, Reverse, Strike-slip faults. </li></ul></ul><ul><li>Forces within Earth (CONVECTION) cause plates to move -> Puts stress on rocks. </li></ul>
4. 5. Earthquake Distribution-I Fig. 4-7
5. 6. How Earthquakes Occur <ul><li>Rocks move past each other along faults (B/c of tectonic plate movement). </li></ul><ul><li>Rough surfaces of rock catch against each other. </li></ul><ul><li>Plates continue to move despite stuck rocks. </li></ul><ul><li>Rocks become stressed beyond their elastic limit , they break, move along the fault, and return to their original shape. </li></ul>
6. 7. <ul><li>To relieve stress, rocks will bend, compress, or stretch. </li></ul><ul><li>If rocks break, the resulting vibration is an earthquake . </li></ul><ul><li>Locations of earthquakes outline the tectonic plates . </li></ul>
7. 8. Seismic Waves <ul><li>Seismic waves are the energy released when rocks break along faults. </li></ul><ul><li>“ Focus” = the point at which this energy is first released. </li></ul><ul><li>Seismic waves are produced and travel outward from the earthquake focus . </li></ul>
8. 10. Types of Seismic Waves <ul><li>Primary Waves (P-waves) </li></ul><ul><ul><li>Cause particles in rocks to move back & forth in same direction . </li></ul></ul><ul><ul><li> Ex: Stretched Spring </li></ul></ul><ul><li>Secondary Waves (S-waves) </li></ul><ul><li> Cause particles in rocks to move at right angles to the direction of the wave travel . </li></ul><ul><li>Surface Waves </li></ul><ul><li> Move rock particles in a backward, rolling, side-to-side, swaying motion . </li></ul><ul><li> Most damaging type of seismic waves. </li></ul>
9. 11. Epicenter <ul><li>Earthquake epicenter = the point on the Earth’s surface directly above the earthquake’s focus . </li></ul><ul><li>Speeds of seismic waves allows us to determine how far away earthquake epicenter is . </li></ul><ul><ul><li>Measured with Seismograph . </li></ul></ul>
10. 12. Measuring Earthquakes-I http://quake.usgs.gov/recent/helicorders/Examples/M5.6_example.html http://earthquake.usgs.gov/image_glossary/seismograph.html
11. 13. Measuring Earthquakes <ul><li>Richter Scale </li></ul><ul><ul><li>Used to measure the strength of an earthquake . </li></ul></ul><ul><ul><li>Based on the height of the lines on the seismograph. </li></ul></ul><ul><ul><li>Scale has no upper limit, but 9.5 is estimated maximum. </li></ul></ul>
12. 14. Measuring Earthquakes <ul><li>Mercalli intensity scale </li></ul><ul><ul><li>Used to measure the intensity of an earthquake based on the amount of damage caused by the earthquake. </li></ul></ul><ul><ul><li>Scale has 12 levels. </li></ul></ul>