Earthquakes Chapter 19
Earthquakes <ul><li>Natural vibrations of ground caused by movement along fractures in Earth’s crust or by volcanic erupti...
Stress and Strain <ul><li>Stress- forces per unit area exceed the strength of the rocks involved </li></ul><ul><ul><li>Com...
Faults- fracture of Earth’s crust <ul><li>Reverse- Horizontal compression, Causes shortening, Foot wall goes down </li></ul>
Faults- Con’t <ul><li>Normal- Horizontal tension, Causes extension, Foot wall goes up </li></ul>
Faults- Con’t <ul><li>Strike-Slip- Horizontal Shear, causes offset </li></ul>
 
Waves <ul><li>Primary- P- Pressure Wave </li></ul><ul><li>Secondary- S- Side-to-side wave </li></ul><ul><li>Surface Wave- ...
Location of Earthquakes <ul><li>Focus- point where an earthquake originates </li></ul><ul><li>Epicenter- Place on Earth's ...
Seismic Waves <ul><li>Seismology- Study of Earthquake waves </li></ul><ul><li>Seismograph- instrument for recording earthq...
Waves <ul><li>P wave- arrives 1 st </li></ul><ul><li>S wave- arrives 2nd </li></ul><ul><li>L wave- last and largest </li><...
Clues to Earth’s Interior <ul><li>Seismic waves change speed and direction when they encounter different materials </li></...
Clues to Earth’s Interior- Con’t <ul><li>S-waves cannot travel through liquids so they can’t pass through the core (never ...
 
Measuring and Locating EQ <ul><li>Magnitude- amount of energy released </li></ul><ul><ul><li>Richter Scale- size of larges...
Measuring and Locating EQ- Con’t <ul><li>Moment Magnitude Scale- uses size of fault rupture, amount of movement and rock’s...
Measuring and Locating EQ-Con’t <ul><li>Locating EQ- time and location unknown </li></ul><ul><ul><li>Distance determined b...
Seismic Belts <ul><li>Earthquakes not random </li></ul><ul><ul><li>Ring of Fire- Edge of Pacific Plate- 80% of all Earthqu...
 
Earthquakes and Society <ul><li>Earthquake Hazards </li></ul><ul><ul><li>Structural  failure </li></ul></ul><ul><ul><ul><l...
Earthquakes and Society- Con’t <ul><li>Tsunami- ocean waves created by EQ </li></ul><ul><ul><li>Travels fast and are low (...
Earthquake Risk <ul><li>Here we have a 3% risk over 50 years </li></ul><ul><li>Hot Spot in US: </li></ul><ul><ul><li>CA </...
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Earthquakes Lecture

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Earthquakes Lecture

  1. 1. Earthquakes Chapter 19
  2. 2. Earthquakes <ul><li>Natural vibrations of ground caused by movement along fractures in Earth’s crust or by volcanic eruptions </li></ul>
  3. 3. Stress and Strain <ul><li>Stress- forces per unit area exceed the strength of the rocks involved </li></ul><ul><ul><li>Compression-Decreases Volume </li></ul></ul><ul><ul><li>Tension- Pulls material apart </li></ul></ul><ul><ul><li>Shear- Causes Twisting </li></ul></ul><ul><li>Strain- Deformation of materials caused by stress </li></ul>
  4. 4. Faults- fracture of Earth’s crust <ul><li>Reverse- Horizontal compression, Causes shortening, Foot wall goes down </li></ul>
  5. 5. Faults- Con’t <ul><li>Normal- Horizontal tension, Causes extension, Foot wall goes up </li></ul>
  6. 6. Faults- Con’t <ul><li>Strike-Slip- Horizontal Shear, causes offset </li></ul>
  7. 8. Waves <ul><li>Primary- P- Pressure Wave </li></ul><ul><li>Secondary- S- Side-to-side wave </li></ul><ul><li>Surface Wave- L-Wave </li></ul><ul><li>Page 498 </li></ul>
  8. 9. Location of Earthquakes <ul><li>Focus- point where an earthquake originates </li></ul><ul><li>Epicenter- Place on Earth's surface where EQ occurred </li></ul>
  9. 10. Seismic Waves <ul><li>Seismology- Study of Earthquake waves </li></ul><ul><li>Seismograph- instrument for recording earthquake waves </li></ul>
  10. 11. Waves <ul><li>P wave- arrives 1 st </li></ul><ul><li>S wave- arrives 2nd </li></ul><ul><li>L wave- last and largest </li></ul>
  11. 12. Clues to Earth’s Interior <ul><li>Seismic waves change speed and direction when they encounter different materials </li></ul><ul><ul><li>P and S waves travel fairly straight through the mantle </li></ul></ul><ul><ul><li>P waves strike the core and are bent (11,000 Km from focus) </li></ul></ul><ul><ul><ul><li>Re-emerge at 16,000 km from focus, after shadow </li></ul></ul></ul>
  12. 13. Clues to Earth’s Interior- Con’t <ul><li>S-waves cannot travel through liquids so they can’t pass through the core (never beyond shadow) </li></ul><ul><li>P waves speed up through solids </li></ul>
  13. 15. Measuring and Locating EQ <ul><li>Magnitude- amount of energy released </li></ul><ul><ul><li>Richter Scale- size of largest seismic waves released by quake </li></ul></ul><ul><ul><ul><li>Each # increase is a 10 fold increase in energy </li></ul></ul></ul><ul><ul><ul><li>Each increase in amplitude (height of wave) is a 32 time increase in energy </li></ul></ul></ul>
  14. 16. Measuring and Locating EQ- Con’t <ul><li>Moment Magnitude Scale- uses size of fault rupture, amount of movement and rock’s stiffness </li></ul><ul><li>Modified Mercalli Scale- uses damage to buildings at location of worst damage </li></ul><ul><ul><li>Uses I-XII Roman Numerals- Called Intensity </li></ul></ul><ul><ul><li>Measures Surface Waves </li></ul></ul><ul><li>Depth of Focus- Deeper EQ usually less intense </li></ul>
  15. 17. Measuring and Locating EQ-Con’t <ul><li>Locating EQ- time and location unknown </li></ul><ul><ul><li>Distance determined by time between P wave and S wave--- AT 3 STATIONS </li></ul></ul><ul><ul><li>Time calculated using same P-S interval </li></ul></ul>
  16. 18. Seismic Belts <ul><li>Earthquakes not random </li></ul><ul><ul><li>Ring of Fire- Edge of Pacific Plate- 80% of all Earthquakes </li></ul></ul><ul><ul><li>Mediterranean- Asian Belt- 15% of EQ </li></ul></ul>
  17. 20. Earthquakes and Society <ul><li>Earthquake Hazards </li></ul><ul><ul><li>Structural failure </li></ul></ul><ul><ul><ul><li>Ground floor fails -> Upper Floors Fail -> Pan caking </li></ul></ul></ul><ul><ul><ul><li>Height- 5-15 stories causes vibrations which are similar to natural sway; Shorter and taller buildings are different </li></ul></ul></ul><ul><ul><li>Land/Soil Fracture </li></ul></ul><ul><ul><ul><li>Landslides- Common in saturated areas </li></ul></ul></ul><ul><ul><ul><li>Soft ground conducts waves well -> more damage </li></ul></ul></ul><ul><ul><li>Fault Scarps- vertical offsets -> waterfalls, road problems </li></ul></ul>
  18. 21. Earthquakes and Society- Con’t <ul><li>Tsunami- ocean waves created by EQ </li></ul><ul><ul><li>Travels fast and are low (less than 4 feet high) in open ocean, but pile up hundreds of feet tall near shore </li></ul></ul><ul><ul><li>Ocean recedes dramatically before tsunami </li></ul></ul>
  19. 22. Earthquake Risk <ul><li>Here we have a 3% risk over 50 years </li></ul><ul><li>Hot Spot in US: </li></ul><ul><ul><li>CA </li></ul></ul><ul><ul><li>Rocky Mountains </li></ul></ul><ul><ul><li>WA, OR </li></ul></ul><ul><ul><li>MO </li></ul></ul>
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