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Ch 19 Earthquakes

Ch 19 Earthquakes. Forces within Earth. Stress = total force acting on crustal rocks per unit area . Strain = deformation of materials in response to stress. Fault. = any fracture or system of fractures along which earth moves. = due to crustal rock failure when stress is too great.

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Ch 19 Earthquakes

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  1. Ch 19 Earthquakes

  2. Forces within Earth • Stress = total force acting on crustal rocks per unit area • Strain = deformation of materials in response to stress

  3. Fault • = any fracture or system of fractures along which earth moves. • = due to crustal rock failure when stress is too great

  4. Types of Seismic Waves • = vibrations of ground made from an earthquake • Types: I. Body Waves: • Primary (P) • Secondary (s) II. Surface Waves: • Surface

  5. Earthquake Waves • Primary Waves • Aka – P waves • Squeeze and push rocks in the direction along which the waves are traveling. • Typically L to R • Secondary Waves • Aka – S waves • Slower than p • Second set of waves to be felt. • Moves at right angles to the wave- “jump rope”

  6. Surface Waves • The 3rd type of wave • Slowest of all • Sideways, up and down movement • Usually the most destructive due to the most ground movement

  7. Seismic Waves • Spread from the point of crustal rock failure • Point of wave origin is called FOCUS • Point directly above the FOCUS on the surface is called EPICENTER.

  8. Interesting fact… • The speed and direction of seismic waves can determine the inside composition of the earth!

  9. To review… • Answer book Questions 1-4 on page 533

  10. 19.2 Seismic Waves and Earth’s interior • Seismometer = a sensitive piece of equipment that measures the earth’s vibrations and disturbances • Seismogram = the written record produced by a seismometer. - These can be used to determine the epicenter of an earthquake based on the p and s wave recording times.

  11. Travel time curves

  12. Distance from the epicenter

  13. 19.3 Measuring and Locating Earthquakes • Richter Scale = the numerical rating system that measures the energy (aka -magnitude!) of the wave and the height (aka – amplitude) of it!

  14. Richter Scale

  15. To find the Magnitude: • You must measure the Height of the S wave. • This is called the AMPLITUDE

  16. Nomogram • Then you use your Distance measurement along with your found Amplitude. • The line that connects the two will cross over the amplitude!

  17. Modified Mercalli Scale • Is a scale that measures the DAMAGE done by the intensity of the earthquake.

  18. 19.4 Earthquakes and Society • Earthquake hazards are determined by many factors, can be identified, and then minimized.

  19. I. Structural failures • 1. Weak ground floors -The supporting walls of the ground floor collapse, so the building begins to pancake. • Pancaking – When the bottom floors crumble allowing the upper layers to land on top – layer by layer

  20. 2. Wood or Cement? • Wooden buildings are actually better than cement buildings. The wood can bend a bit, while the cement building will crack apart!

  21. 3. Building Height… • The taller the building, the more likely it will vibrate with the waves and fall!

  22. II. Land and Soil Failure • 1. May trigger landslides in sloped areas • In 1970 in Peru, a 7.8 magnitude quake produced a landslide that buried several towns and killed an estimated 30,000 people

  23. 2. Soil Liquefaction • Sand is really saturated with water and the shaking allows the water to accumulate and cause it to act like a true liquid.

  24. III. Tsunami • Giant wave caused by vertical seafloor motions.

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