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# Earthquakes

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### Transcript

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