9th Grade Chapter 8 Lesson 2


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9th Grade Chapter 8 Lesson 2

  1. 1. 9 th Grade Chapter 8 Lesson 2 Pgs. 203-212 For student Use Only
  2. 2. Earthquakes <ul><li>Earthquake: </li></ul><ul><ul><li>Any vibration (trembling or shaking) of the earth’s crust </li></ul></ul><ul><ul><li>Tremors: weak earthquake </li></ul></ul><ul><li>Vibrations move through the ground like ocean waves </li></ul><ul><li>Earthquakes result from a sudden break in the rocks </li></ul>
  3. 3. Earthquakes <ul><li>Earthquakes: </li></ul><ul><ul><li>Even the largest earthquakes only last one minute, but can cause massive damage </li></ul></ul><ul><ul><ul><li>Buildings, bridges, overpasses can collapse and rocks and earth can be moved </li></ul></ul></ul><ul><ul><ul><li>Aftershocks: smaller earthquakes or tremors accompany earthquakes </li></ul></ul></ul>
  4. 4. Earthquakes <ul><li>Seismology: Study of earthquakes </li></ul><ul><ul><li>Earthquakes follow the same natural laws </li></ul></ul><ul><ul><li>Tectonic Plates are the primary cause of the earthquakes (sudden movement of rock along a fault) </li></ul></ul><ul><ul><li>Faulting: involves vertical or horizontal movement of the plates </li></ul></ul>
  5. 5. Earthquakes <ul><li>Earthquakes: </li></ul><ul><ul><li>The rocks grind together because they are jagged </li></ul></ul><ul><ul><li>The rocks get stuck </li></ul></ul><ul><ul><li>The rocks slip and release massive amounts of energy </li></ul></ul><ul><ul><li>Elastic Rebound Theory: rocks spring back to a position of little or no strain </li></ul></ul>
  6. 6. Earthquakes <ul><li>In an earthquake: </li></ul><ul><ul><li>Rocks on one side of fault can be higher than on the other side of the fault </li></ul></ul><ul><ul><ul><li>This is called a fault scarp </li></ul></ul></ul><ul><ul><ul><li>This happens along a strike-slip fault </li></ul></ul></ul><ul><ul><ul><li>Slickenslides are smooth fault scarps </li></ul></ul></ul><ul><ul><ul><ul><li>San Andres Fault is a strike-slip fault </li></ul></ul></ul></ul>
  7. 7. Earthquakes <ul><li>Earthquakes begin below the ground, but appear on the surface </li></ul><ul><ul><li>Focus: the point below the earth where the earthquake begins </li></ul></ul><ul><ul><li>Epicenter: point directly above the focus on the earth’s surface </li></ul></ul>
  8. 8. Earthquakes <ul><li>Shallow Focus Earthquakes: </li></ul><ul><ul><li>85% of earthquakes originate 5-40 mi. below the surface </li></ul></ul><ul><li>Intermediate Focus Earthquakes: </li></ul><ul><ul><li>12% of earthquakes occur at depths of 40-200 mi. </li></ul></ul><ul><li>Deep Focus Earthquakes: </li></ul><ul><ul><li>3% of earthquakes occur at depths of below 200 mi. </li></ul></ul>
  9. 9. Earthquakes <ul><li>Earthquake Waves: </li></ul><ul><ul><li>P waves: primary waves, push and pull motion (up and down) </li></ul></ul><ul><ul><li>S waves: secondary waves, side to side motion </li></ul></ul><ul><ul><li>Surface Waves: These are a combination of P and S waves and act like ocean waves </li></ul></ul>
  10. 10. Earthquake <ul><li>Waves are measured by a seismograph </li></ul><ul><ul><li>Seismograph measures P and S waves </li></ul></ul><ul><ul><ul><li>P waves travel fastest </li></ul></ul></ul><ul><ul><ul><li>S waves arrive next </li></ul></ul></ul><ul><ul><ul><li>Surface waves come last </li></ul></ul></ul><ul><ul><li>Seismographs can be used to detect where earthquakes are but there must be three points (This is called triangulation) </li></ul></ul>
  11. 11. Earthquakes <ul><li>Earthquake Zones: </li></ul><ul><ul><li>Earthquakes occur everywhere, however, most occur in narrow areas </li></ul></ul><ul><ul><li>Circum-Pacific belt: </li></ul></ul><ul><ul><ul><li>80% of earthquakes </li></ul></ul></ul><ul><ul><li>Mediterranean-Trans-Asiatic belt: </li></ul></ul><ul><ul><ul><li>15% of earthquakes </li></ul></ul></ul><ul><ul><li>Mid-ocean ridges: </li></ul></ul><ul><ul><ul><li>5% of all earthquakes </li></ul></ul></ul>
  12. 12. Earthquakes <ul><li>Earthquake Ratings: </li></ul><ul><ul><li>Mercalli Scale: </li></ul></ul><ul><ul><ul><li>Based on how it affects structures </li></ul></ul></ul><ul><ul><ul><li>Does not measure energy </li></ul></ul></ul><ul><ul><ul><li>Rates 1-12 </li></ul></ul></ul><ul><ul><li>Richter Scale </li></ul></ul><ul><ul><ul><li>Measures power of Earthquake </li></ul></ul></ul><ul><ul><ul><li>Scale from 1-10 </li></ul></ul></ul><ul><ul><ul><li>Each step is 250 times more powerful </li></ul></ul></ul>
  13. 13. Earthquakes <ul><li>Earthquake Waves Teach Us: </li></ul><ul><ul><li>Waves travel differently from different substances </li></ul></ul><ul><ul><li>They use this information as they study the structure of the Earth </li></ul></ul><ul><ul><li>Use artificial waves to find oil, use waves to spy on nuclear testing </li></ul></ul>
  14. 14. Earthquakes <ul><li>Earthquake Damage: </li></ul><ul><ul><li>Most deaths come from falling buildings </li></ul></ul><ul><ul><li>Engineers design building codes to help reduce damage </li></ul></ul><ul><ul><li>Build on solid bedrock vs. sand </li></ul></ul><ul><ul><ul><li>Sand is very unstable </li></ul></ul></ul>