Earthquakes how measureimpact

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Earthquakes how measureimpact

  1. 1. Earthquakes: How do we measure their impact?<br />8SCIENCE: Wed. April 6/Thurs. April 7<br />
  2. 2. Review: Forces and Faults<br />What are 3 types of forces responsible for earthquakes?<br />Compression<br />Tension<br />Shear <br />What faults are associated with each type of force? Describe.<br />Compression – reverse fault<br />Tension – normal fault<br />Shear – strike – slip fault<br />Reverse<br />
  3. 3. Energy and Seismic Waves<br />Seismic waves<br />Created by the earthquake<br />When rocks move and break along a fault, energy is released and this creates damage<br />Energy is released from the focus, located under the surface of the Earth<br />This energy travels away from the focus as seismic waves<br />
  4. 4. Seismic Waves<br />Primary waves (P – waves)<br />Make rocks vibrate back and forth<br />Fastest waves at about 6km/second<br />Secondary waves (S – waves) <br />Shake rocks from side to side <br />Half the speed of P waves about 3 km/second<br />Energy that reaches the surface is in the form of waves called surface waves<br />Cause the most damage but are the slowest<br />
  5. 5. Surface Waves<br />The point on the Earth’s surface directly above an earthquake’s focus is the epicenter<br />Surface wavestravel outward from the epicenter and move up, down and side to side<br />Can cause buildings to move in different directions and fall apart <br />
  6. 6. How do we measure the strength of an earthquake?<br />Scientists (seismologists) use the different speeds of the seismic waves to find the distance to the epicenter of the earthquake<br />A seismograph measures the energy released, or magnitude of the earthquakes<br />Which types of waves arrive first to a station? <br />1)Primary2)Secondary3)Surface <br />
  7. 7. How do we measure the strength of an earthquake?<br />Earthquake magnitude is usually measured using the Richter scale <br />1.0 – 9.0<br />Each 1 step increase = 10 x strongerEx: From 6.0 to 8.0 = 100x<br />

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