Earthquakes

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Earthquakes
Earthquakes
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What is an Earthquake?

• Is a shaking of the Earths crust caused by a
  release of energy
• Like volcanoes, they are a result of the motions
  of the lithosphere plates.
• But includes a much larger area.

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How does an Earthquake happen?Elastic Rebound
Theory

• They occur when stress along a fault plane
  overcomes the forces of friction.
• When friction is finally overcome, the plates
  move suddenly and release earthquake energy.
• Then rocks along the boundary snap back to their
  original shape.

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Elastic Rebound Theory
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Depth of Earthquakes

• Focus the point on the fault plane at which the
  first movement occurs
• Epicenter the point on the Earths surface
  directly above the focus

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Earthquake waves

• P waves
• primary (compressional waves)
• S waves
• Secondary (Shear)
• Both are body waves because they travel through
  the body of the Earth
• L waves
• Surface waves

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P waves

• The back and forth wave motion alternately
  squeezes and stretches the rock material
• Occur in through ANY material, even air

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S waves

• They are the side to side wave causing particles
  to move at right angles to the direction the
  waves are traveling.
• Occur in solids only, not through liquid or gases.

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L waves

• These are the result of the p and s waves when
  they reach the surface.
• They travel a lot slower than the P and S waves
  (they are move like ripples on the pond)

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Seismographs

• Instrument that detects and records the size of
  Earthquakes
• Measures the P and S waves

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Determine the distance to the Epicenter

• Time Travel Graph the relationship between P
  and S wave travel times and epicenter distance

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Locating an Epicenter

• You need three locations to pinpoint the location
  of the Epicenter.

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Earthquake Magnitude

• Richter scale is designed to measure the
  intensity of the Earthquake.
• It is a measurement of the amount of energy that
  the earthquake releases itself.
• Seismic movement (not as easy to measure as the
  Richter scale)
• This method, though harder, is more accurate as
  far as measuring the total energy involved.

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Charles Richter
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Top Ten US Quakes
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Prince William Sound, Alaska3/28/ 1964 (9.2)
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Andreanof Islands 1957 (9.1)

• Damaged 2 bridges
• Leveled houses
• Left a 4.3 meter crack in the road
• 15 meter tsunami
• Mt. Vesevidof erupted (200 yrs dormant)

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Rat Islands, Alaska2/3/1965 (8.7)

• Created a 10.7 m tsunami
• A crack was noted on an asphalt runway

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Yakutat Bay, Alaska 9/10/1899 (8.6)
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Shumagin Islands, Alaska 11/10/1938 (8.2)

• Created a small tsunami in Hawaii

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New Madrid (Missouri), Arkansas12/16/1811(8.1)
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Yakutat Bay, Alaska 9/10/1899 (8.0)

• Even shellfish and barnacles were found dead
• 10.6 meter tsunami
• Foreshocks even 7.0

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Andreanof Islands, Alaska 5/7/1986 (8.0)

• Moderate damage done to Atka
• Masonry on buildings were destroyed

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New Madrid, Missouri2/7/1812 (8)

• This is one of 6 major Earthquakes that happened
  in this region over a one year period

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Cape Yakataga, Alaska 9/4/1899 (7.9)

• Knocked over tree
• Generated landslides
• Raised beaches

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Fort Tejon, California 1/9/1857 (7.9)

• One fatality
• Damage to buildings
• Major aftershocks felt for 3 days

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Largest Earthquakes in the Cont. US
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Largest Earthquakes in Alaska
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Largest Earthquakes in Hawaii
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California Seismic activity

• What happen 1/17/94?
• Why so much activity?

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Northridge, Ca1/17/1994