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Earthquakes

Earthquakes. Plate Boundaries. Sketch the 3 type of plate boundaries. Pacific-North American Plate Boundary. Earthquake Study. Seismology – the study of earthquakes (#27) Seismologist – person who studies earthquakes. Where?. Most occur near tectonic plate boundaries. Causes.

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Earthquakes

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  1. Earthquakes

  2. Plate Boundaries Sketch the 3 type of plate boundaries

  3. Pacific-North American Plate Boundary

  4. Earthquake Study • Seismology – the study of earthquakes (#27) • Seismologist – person who studies earthquakes

  5. Where? • Most occur near tectonic plate boundaries

  6. Causes • Deformation – bending, tilting, and breaking of Earth’s crust (#28) • Caused by plates pushing, pulling & sliding • 2 kinds of deformation • Plastic – bends like piece of soft clay • No earthquake • Elastic – stretches like a rubber band • Earthquake

  7. Elastic Rebound • Elastic rebound – sudden return of elastically deformed rock to its undeformed shape • Like a stretched rubber band that breaks and returns to its unstretched shape, now in 2 pieces • Energy released as seismic waves

  8. Strike-slip Transform Normal Divergent Reverse Convergent

  9. Body Waves • Seismic waves – waves of energy that travel through Earth, away from an earthquake in all directions (#29) • Two types of body waves that travel through interior of Earth • P waves • Primary waves (#30) • Pressure waves (#30) • Back and forth motion (#30) • Go through solid, liquid, gas • Fastest wave • S waves • Secondary waves (#31) • Shear waves (#31) • Side to side motion (#31) • Go through solids only • Slower wave, 2nd to arrive

  10. More Waves • Surface waves – waves that move in top few km of the crust • Up, down, circular motion • Back and forth motion • Travel slower than body waves • More destructive

  11. Draw pictures of P and S Waves

  12. Measurement • Seismograph – instrument that records ground vibrations to find location and strength of earthquake • Seismogram – tracing of earthquake motion created by a seismograph • Epicenter – point on Earth’s surface directly above an earthquake (#32) • Focus – point on a fault where earthquake motion first occurs (#33)

  13. Earthquake Location

  14. Finding Epicenter – Step 1 • Scientists use the S-P Time Method • Use a time-distance graph • S and P curves are already calculated • Determine distance away from epicenter for at least 3 seismograms

  15. Finding Epicenter – Step 2

  16. Earthquake Strength • Richter Magnitude Scale – • Created in 1930s by Charles Richter • Magnitude measures strength of earthquake by ground motion adjusted for distance from epicenter • Each unit represents 10x increase in strength • 5.0 is 10x stronger than a 4.0 • 6.0 is 100x stronger than a 4.0

  17. Richter Magnitude Scale

  18. Earthquake Intensity • Intensity – degree to which earthquake is felt and amount of damage caused • Modified Mercalli Intensity Scale • Numerical scale from I to XII • I not felt by people • XII total destruction • Intensity values highest near epicenter

  19. Earthquake Hazards • How likely area is to have a damaging quake in the future

  20. Earthquake Forecasting

  21. Gap Hypothesis • Areas on active faults that haven’t had many earthquakes are likely to be sites for future strong earthquakes. • Known as seismic gaps

  22. Earthquake Preparations • Resistant buildings • Mass damper • Active tendon system • Base isolators • Cross braces • Flexible pipes • Retrofitting • Reinforce columns • Fasten to foundation

  23. What to do in an Earthquake • Before shaking • Put heavy objects down low • Have an emergency meeting place • Store emergency supplies • During shaking • Crouch or lie under a strong table or desk • Outside – lay down away from buildings, trees, power lines • Stop car and stay inside • After shaking • Stay calm and think • Get away from danger areas • Prepare for aftershocks • Follow emergency plan

  24. Earthquake Examples • Normal • Reverse • Strike slip

  25. Normal Fault Example Dixie Valley-Fairview Peaks, Nevada earthquake December 16, 1954

  26. Thrust Fault Example

  27. Thrust Fault Example

  28. Strike-slip Fault Example

  29. Strike-slip Fault Example 1906 San Francisco Earthquake

  30. Earthquake Effects • Ground shaking • Liquefaction – solid earth turns to liquid • Surface faulting • Landslides • Fires • Tsunami

  31. Earthquake Effects - Ground Shaking Loma Prieta, CA 1989 KGO-TV News ABC-7

  32. Earthquake Effects - Ground Shaking Kobe, Japan 1995

  33. Earthquake Effects - Liquefaction Source: National Geophysical Data Center Niigata, Japan 1964

  34. Earthquake Effects - Surface Faulting Landers, CA 1992

  35. Earthquake Effects - Landslides Source: National Geophysical Data Center Turnagain Heights, Alaska,1964 (upper left inset); Santa Cruz Mtns, California , 1989

  36. Earthquake Effects - Fires Loma Prieta, CA 1989 KGO-TV News ABC-7

  37. Earthquake Effects - Tsunamis 1957 Aleutian Tsunami Photograph Credit: Henry Helbush. Source: National Geophysical Data Center

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