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Ch. 8 Earthquakes

Ch. 8 Earthquakes. Types of Stress. Tension – stretches rock, they become thin in the middle 2. Compression – pushes rock together, squeezes rock until it folds or breaks 3. Shearing – masses of rock slip, they move past in opposite directions. Earthquakes.

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Ch. 8 Earthquakes

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  1. Ch. 8 Earthquakes

  2. Types of Stress • Tension – stretches rock, they become thin in the middle • 2. Compression – pushes rock together, squeezes rock until it folds or breaks • 3. Shearing – masses of rock slip, they move past in opposite directions

  3. Earthquakes 8.1 What Is an Earthquake?  An earthquake is the shaking & trembling of rock produced by the rapid release of energy  Focus and Epicenter • Focus is the point within Earth where the rock breaks. • Epicenter is the location on the surface directly above the focus.  Faults • Faults are fractures in Earth where movement has occurred.

  4. Kinds of faults • Normal – due to tension, fault is at an angle, at diverging boundaries, hanging wall slips down footwall • Reverse or thrust – due to compression, fault is at an angle, hanging wall slides up and over footwall • Strike-slip or transform – due to shearing, 2 plates slip past each other sideways, at transform boundaries

  5. Focus, Epicenter, and Fault

  6. Slippage Along a Fault

  7. Fault-block mountains – • uplifted block of rock created • between 2 normal faults • Anticlines – upward • fold = ridges • Synclines – downward fold • = valleys

  8. Fault-block mountains in Juniper Canyon and Yosemite

  9. Cause of Earthquakes 8.1 What Is an Earthquake?  Elastic Rebound Hypothesis • Most earthquakes are produced by the rapid release of elastic energy stored in rock that has been subjected to great forces. • When the strength of the rock is exceeded, it suddenly breaks, causing the vibrations of an earthquake.

  10. Elastic Rebound Hypothesis

  11. Earthquake Waves 8.2 Measuring Earthquakes • P waves - Are push-pull waves that push (compress) and pull (expand) in the direction that the waves travel - Travel through solids, liquids, and gases • Have the greatest velocity of all earthquake waves • a.k.a. primary waves http://www.jclahr.com/science/earth_science/tabletop/pslnkmv.html#

  12. Earthquake Waves 8.2 Measuring Earthquakes http://sunshine.chpc.utah.edu/labs/seismic/index.htm • S waves • Seismic waves that travel along Earth’s outer layer • a.k.a. secondary waves - Shake particles at right angles to the direction that they travel or back & forth - Travel only through solids - Slower velocity than P waves http://www.jclahr.com/science/earth_science/tabletop/sslnkmv.html#

  13.  Surface waves are seismic waves that travel along Earth’s outer layer.-Make most severe ground movements. http://jclahr.com/alaska/aeic/waves/index.html http://www.classzone.com/books/earth_science/terc/content/visualizations/es1002/es1002page01.cfm

  14. Seismic Waves

  15. Earthquake Waves 8.2 Measuring Earthquakes  Seismographs are instruments that record earthquake waves. • Seismogramsarethe drawn records

  16. Seismograph

  17. Seismogram

  18. Measuring Earthquakes 8.2 Measuring Earthquakes • Mercalli Scale • Rates damage at a given place • Uses Roman numerals 1-12  Richter Scale • Based on the amplitude of the largest seismic wave • Each unit equates to roughly a 32-fold energy increase • Does not estimate adequately the size of very large earthquakes

  19. Modified Mercalli Scale

  20. Measuring Earthquakes 8.2 Measuring Earthquakes  Moment Magnitude Scale • Derived from the amount of displacement that occurs along the fault zone • • most widely used measurement for earthquakes because it estimates the energy released by earthquakes. • Scale ranges from 0-10+ • Measures very large earthquakes

  21. Earthquake Magnitudes

  22. Some Notable Earthquakes

  23. 2009 Sichuan, China – 70,000 dead, 10 million homeless 1994 - magnitude 6.7 Northridge Earthquake

  24. Port au Prince, Haiti, Jan. 2010

  25. Shaking – landslides, avalances, • building & bridge topples, gas & • water mains break • Liquefaction – loose, soft soil turns into • Liquid mud, buildings fall & sink • 3. Aftershocks – smaller eqs that occur after the larger one • 4. Tsunami – giant wave created by displaced water Earthquake Dangers

  26. Liquefaction http://earthquake.usgs.gov/learn/animations/animation.php?flash_title=Liquefaction+Flash+Animation&flash_file=liquefaction&flash_width=450&flash_height=200 Photo gallery http://www.chiff.com/science/earthquake-pictures.htm Loma Prieta http://www.vibrationdata.com/earthquakes/lomaprieta.htm Earthquake animation http://www.pbs.org/wnet/savageearth/animations/earthquakes/index.html Haiti clip http://www.youtube.com/watch?v=HgQd0K5W0vI

  27. Building design to minimize EQ damage Transamerica Building in San Francisco, CA

  28. Locating an Earthquake 8.2 Measuring Earthquakes  Earthquake Distance • The epicenter is located using the difference in the arrival times between P and S wave recordings, which are related to distance.  Earthquake Direction • Travel-time graphs from three or more seismographs can be used to find the exact location of an earthquake epicenter.  Earthquake Zones • About 95 percent of the major earthquakes occur in a few narrow zones.

  29. Locating an Earthquake

  30. Seismic Vibrations 8.3Destruction from Earthquakes  The damage to buildings and other structures from earthquake waves depends on several factors. These factors include the intensity and duration of the vibrations, the nature of the material on which the structure is built, and the design of the structure.

  31. Earthquake Damage

  32. Seismic Vibrations 8.3Destruction from Earthquakes  Building Design • Factors that determine structural damage - Intensity of the earthquake - Unreinforced stone or brick buildings are the most serious safety threats - Nature of the material upon which the structure rests - The design of the structure

  33. Seismic Vibrations 8.3Destruction from Earthquakes  Liquefaction • Saturated material turns fluid • Underground objects may float to surface

  34. Effects of Subsidence Due to Liquefaction

  35. Tsunamis 8.3Destruction from Earthquakes  Cause of Tsunamis • A tsunami triggered by an earthquake occurs where a slab of the ocean floor is displaced vertically along a fault. • A tsunami also can occur when the vibration of a quake sets an underwater landslide into motion. • Tsunami is the Japanese word for “seismic sea wave.”

  36. Movement of a Tsunami

  37. Tsunamis 8.3Destruction from Earthquakes  Tsunami Warning System • Large earthquakes are reported to Hawaii from Pacific seismic stations. • Although tsunamis travel quickly, there is sufficient time to evacuate all but the area closest to the epicenter.

  38. Other Dangers 8.3 Destruction from Earthquakes  Landslides • With many earthquakes, the greatest damage to structures is from landslides and ground subsidence, or the sinking of the ground triggered by vibrations.  Fire • In the San Francisco earthquake of 1906, most of the destruction was caused by fires that started when gas and electrical lines were cut.

  39. Landslide Damage

  40. Discovering Earth’s Layers ´ ˇ  Moho 8.4 Earth’s Layered Structure • Velocity of seismic waves increases abruptly below 50 km of depth • Separates crust from underlying mantle  Shadow Zone • Absence of P waves from about 105 degrees to 140 degrees around the globe from an earthquake • Can be explained if Earth contains a core composed of materials unlike the overlying mantle

  41. Earth’s Interior Showing P and S Wave Paths

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