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Earthquakes

Earthquakes

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Earthquakes

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  1. Earthquakes

  2. A. Earthquake Effects and Building Design • Shaking • usually affects a large area • Surface Faulting • limited to the fault zone • this hazard is more easily avoided • Philosophy of building design • Building must sustain little or no damage during minor Earthquakes • There must be no damage to life during the rare major Earthquake

  3. An apartment building in San Francisco's Marina District was thrown from its foundation and crushed a car in the 1989 earthquake. The Marina District was the scene of voracious fires caused by broken gas lines.Photo by Vince Maggiora

  4. What Controls the Level of Shaking? • Magnitude • More energy released • Distance • Shaking decays with distance • Local soils • Amplify the shaking usgs

  5. Is there such a thing as “Earthquake Weather”??? No! usgs

  6. Earthquake Effects - Ground Shaking Northridge, CA 1994

  7. Earthquake Effects -Ground Shaking Northridge, CA 1994 usgs

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

  9. Earthquake Effects - Ground Shaking Kobe, Japan 1995 usgs

  10. Earthquake Effects - Ground Shaking Kobe, Japan 1995 usgs

  11. Earthquake Effects - Surface Faulting Landers, CA 1992 usgs

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

  13. Fig. 16.17b

  14. In the Santa Cruz mountains, the 1989 earthquake caused deep cracks. "I can't stop shaking," said one resident. "I guess I'm surviving, but I'm scared."Photo by Deanne Fitzmaurice

  15. 03CO, p.35

  16. Fig. 3-1, p.36

  17. Fig. 3-3, p.37

  18. Fig. 3-5, p.37

  19. In the Santa Cruz mountains, the 1989 earthquake caused deep cracks. "I can't stop shaking," said one resident. "I guess I'm surviving, but I'm scared."Photo by Deanne Fitzmaurice

  20. B. The Origin of Earthquakes • 1. Earthquakes are the abrupt releases of stress in the form of seismic waves • 2. Fault breakage is the immediate cause of Earthquakes • a. First recognized in 1906 when the San Andreas ruptured along a 270 mile section

  21. Fig. 3.12

  22. Magnitude and Intensity Intensity • How Strong Earthquake Feels to Observer Magnitude • Related to Energy Release • Determined from Seismic Records • Rough correlation between the two for shallow earthquakes www.uwgb.edu/.../EarthSC202PowerPoint/Faults%20and%20Earthq...

  23. Intensity How Strong Earthquake Feels to Observer Depends On: • Distance to Quake • Geology • Type of Building • Observer! Varies from Place to Place Modified Mercalli Intensity Scale • a. measure of the severity of ground motion at a particular location • Describes damage to structures. • Ranges from I (felt by only a few) to XII (total destruction). • Intensity of an earthquake depends on: • Distance to epicenter • Building materials and design • Type of ground material - soil, rock, etc. www.uwgb.edu/.../EarthSC202PowerPoint/Faults%20and%20Earthq...

  24. Fig. 3-21, p.46

  25. Intensity and Geology in San Francisco, 1906 www.uwgb.edu/.../EarthSC202PowerPoint/Faults%20and%20Earthq...

  26. Intensity and Bedrock Depth in San Francisco, 1906 www.uwgb.edu/.../EarthSC202PowerPoint/Faults%20and%20Earthq...

  27. Fig. 3-22, p.46

  28. Magnitude - Determined from Seismic Records Richter Scale: measure of the amplitude of ground motion at a distance from the focus Related to Energy Release Exponential log scale: Each number on the Richter Scale is ten times greater in wave amplitude. No Upper or Lower Bounds Largest Quakes about Mag. 8.7 Magnitude - a measure of energy released a. Richter Scale - b. Magnitude-Energy Relation 4 - 1 5 - 30 6 - 900: 1 Megaton = about 7 7 - 27,000 8 - 810,000 www.uwgb.edu/.../EarthSC202PowerPoint/Faults%20and%20Earthq...

  29. Seismic - Moment Magnitude A Seismograph Measures Ground Motion at One Instant But -- • A Really Great Earthquake Lasts Minutes • Releases Energy over Hundreds of Kilometers • Need to Sum Energy of Entire Record • Modifies Richter Scale, doesn't replace it • Adds about 1 Mag. To 8+ Quakes www.uwgb.edu/.../EarthSC202PowerPoint/Faults%20and%20Earthq...

  30. Magnitude and Energy www.uwgb.edu/.../EarthSC202PowerPoint/Faults%20and%20Earthq...

  31. Magnitude and Energy www.uwgb.edu/.../EarthSC202PowerPoint/Faults%20and%20Earthq...

  32. Earthquake Magnitude M5 M6 M7

  33. Fig. 3-28, p.50

  34. Moment Magnitude Scale • Works accurately • More reliable • It measure the amount of strain energy released by movement of the fault • Seismic moment (Mo) relies on the • Amount of movement along the fault • That is the Mo equals • the shear strength of the rocks times the rupture area of the fault times the average displacement (slip) on the fault Seismic Moment is incorporated into the new earthquake magnitude scale by Hiroo Kanamori the moment magnitude scale (Mw) where: Mw = 2/3 log10 (Mo)-6 The moment magnitude scale is used for big Earthquakes

  35. Why technically there is no earthquake larger than M 9.5? Because rocks can at most store elastic energy equivalent to M9.5before they snap!

  36. Idealized diagram showing the procedure for calculating the Richter magnitude of an earthquake.

  37. First seismograph developed by Chinese ~ 2000 years ago. • Consists of 8 metal balls around large sphere • Pendulum inside sphere swung back and forth knocking one of the balls off its stand. • This indicated the direction that the earthquake vibration came from.

  38. Fig. 3.16 Abbott, 2005

  39. Types of seismic waves • Body waves • P-waves • Primary, pressure, compressional waves • “push-pull” wave • Travel fastest of the seismic waves • Travel through solids and liquids • S-waves • Secondary, shaking, shear, side-to-side • Travel through solids only • Push material at right angles to their path of travel

  40. Surface waves • Often referred to as L-waves or long waves. • Complex motion. Up-and-down and side-to-side. • Slowest. • Causes damage to structures during an earthquake.