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Earthquakes and earthquake (or seismic) waves

Earthquakes and earthquake (or seismic) waves. EARTHQUAKE: Vibrations caused by the sudden release of energy stored in the rocks. SEISMIC WAVES or EARTHQUAKE WAVES : Energy that moves through the earth because of an earthquake. Surface waves. Travel along the surface of the earth.

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Earthquakes and earthquake (or seismic) waves

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  1. Earthquakes and earthquake (or seismic) waves

  2. EARTHQUAKE: Vibrations caused by the sudden release of energy stored in the rocks SEISMIC WAVES or EARTHQUAKE WAVES : Energy that moves through the earth because of an earthquake

  3. Surface waves Travel along the surface of the earth There are two broad groups of seismic waves Body waves Can travel through the interior of the earth

  4. Body waves are used to study the internal structure of the earth Two different types of body waves PRIMARY or COMPRESSIONAL waves (P-waves) SECONDARY or SHEAR waves (S-waves)

  5. http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm Compressional Wave (P-Wave) Animation Deformation propagates. Particle motion consists of alternating compression and dilation. Particle motion is parallel to the direction of propagation (longitudinal). Material returns to its original shape after wave passes.

  6. http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm Shear Wave (S-Wave) Animation Deformation propagates. Particle motion consists of alternating transverse motion. Particle motion is perpendicular to the direction of propagation (transverse). Transverse particle motion shown here is vertical but can be in any direction. However, Earth’s layers tend to cause mostly vertical (SV; in the vertical plane) or horizontal (SH) shear motions. Material returns to its original shape after wave passes.

  7. P-waves are faster than S-waves • Both P-and S- waves travel faster through denser material • Only P-waves can travel through liquids • P- waves travel faster through solids than through liquids

  8. Two types of surface waves Rayleigh waves (“vertical” surface waves) Love waves (“horizontal” surface waves)

  9. http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm • Rayleigh waves • Make the surface go up and down like ripples

  10. http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm • Love waves • Make the ground move sideways like a moving snake

  11. Now work with your partner(s) to answer the 1st question on your assignment

  12. Size of earthquakes

  13. MODIFIED MERCALLI SCALE • Defines the INTENSITY of an earthquake by the amount of damagecaused

  14. Characteristics: • Depends on subjective assessment of the damage and not any measurement with an instrument • Does not provide an accurate measurement of the strength of the earthquake (Why?) • Useful for planners and building officials

  15. Moment magnitude (M) Use the colors near the stars to determine Perceived shaking, potential damage and instrumental intensity for both earthquakes Complete the table below (work by yourself or with a partner)

  16. The instrument used to record an earthquake Seismograph The actual record of an earthquake Seismogram

  17. Amplitude Seismograms record the AMPLITUDE (height of the peaks) of the seismic waves against TIME along the horizontal axis

  18. RICHTER MAGNITUDE SCALESpecifies the amplitude of the largest ground motion generated by the earthquake at a seismograph station located 100 km from the epicenter

  19. What is the maximum amplitude recorded on this seismogram?

  20. What is the maximum amplitude recorded on this seismogram?

  21. Characteristics of Richter Scale • The amplitude can be measured directly from a seismogram (more quantitative) • The scale is logarithmic • An increase of one magnitude on the Richter scale means approximately 30- fold increase in energy released

  22. Now work with your partner(s) to answer the 4th. question on your assignment

  23. MOMENT MAGNITUDE SCALEProvides more accurate measure of the total energy released during earthquakes than the Richter scale. Seismic moment = (amount of slip) x (the area of rupture) x (rock strength)

  24. Bigger earthquakes: • Cause more slip • Break more rocks (bigger rupture area) • Happen in stronger rocks (why?) Now answer question #5 on your assignment with your partner(s)

  25. Ground motion is caused by a combination of all types of earthquake waves Ground motion from March 3, 2011 magnitude 8.9 earthquake in Japan

  26. City of Salinas, after the October 17, 1989, Loma Prieta Earthquake Effects of earthquakes http://pubs.usgs.gov/dds/dds-29/web_pages/salinas.html

  27. http://www.earthinstitute.columbia.edu/news/story11_16_01.htmlhttp://www.earthinstitute.columbia.edu/news/story11_16_01.html

  28. SURFACE WAVES • Not much used in studying the interior of the earth • Slower than body waves • Most destructive of the earthquake waves

  29. Effects of earthquakes • Ground shakes, buildings collapse, structural damage, death and destruction… • Fire • Landslides • Tsunamis (do NOT call them tidal waves)

  30. 2004 Indonesian tsunami http://staff.aist.go.jp/kenji.satake/animation.html

  31. Tsunami generation

  32. Earthquake prediction • Monitoring faults for small tremors and foreshocks • Radon emissions • Measuring ground tilts • Animal behavior • Studying historic earthquake patterns

  33. http://www.usgs.gov/hazards/images/maps/earthquake_lores.jpg

  34. Next you will get to work on the rest of your assignment on plate boundaries with a partner

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