EARTHQUAKES

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EARTHQUAKES

• Section 21.2

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What is an earthquake?

• WHAT IS AN EARTHQUAKE?
• An earthquake is a movement of Earths crust
  caused by a release of energy  

• WHAT CAUSES AN EARTHQUAKE?
• Eruption of a volcano
• Collapse of a cavern or building
• Major cause stress between two plates

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Where do EQs occur in the world?
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They occur along Plate Boundaries
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Where do EQs occur in the U.S.?
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What Causes Earthquakes?

• Friction builds up between two plates
• The stress causes the plates to deform or
  stretch
• Eventually, the stress becomes great enough that
  it overcomes friction and the plates move
• The plates snap back into their original shape
  and begin building up friction again

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Damage from a 1906 EQ
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What is the Focus of an EQ?

• Point on the fault (or plates) where movement
  first occurs
• Where an earthquake starts
• 3 types
• Shallow (0-70km)
• Intermediate (71-300km)
• Deep (301km and higher)

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Epicenter

• Point on the Earths surface directly above the
  focus
• What is reported as the location of an earthquake

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Earthquake waves

• P-waves primary waves travel through solids,
  liquids, and gases back and forth motion
• P waves are ______________ waves.

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Earthquake waves

• S-waves secondary waves travel through solids
  only side to side motion (snake)
• S waves are ___________ waves

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Earthquake waves

• L-waves surface waves
• Combination of up and down and back and forth
  motion
• Cause the most damage due to their rolling action
  and long wavelengths

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EARTHQUAKE!
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EQ wave Diagram
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Locating an earthquake

• Seismograph an instrument that detects and
  records earthquake waves
• P-waves always arrive first, then S-waves, then
  L-waves

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Determining distance to the epicenter

• P and S Waves Graph pg.767 Under Graphing
  Skills
• As distance increases, the travel time for
  seismic waves increases also.

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Locating an Epicenter

• To locate the exact location of an epicenter, you
  must have points from three separate seismograph
  locations around the world

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Earthquake Magnitude

• Richter Scale
• Developed by Charles Richter in the 1940s
• Measures the amount of energy released by the
  earthquake itself
• Scale from 1-10 (weakest - strongest)
• Each number is 32 times stronger than the next
  lower number (Ex 6 is 32 times stronger than
  a 5 and 1024 times stronger than a 4)

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Earthquake Prediction

• We cannot predict earthquakes other than giving
  periods of time in which we think they will
  occur.
• Earthquakes are most common along sliding plate
  boundaries, but they can occur in other places.
• http//earthquake.usgs.gov/learn/kids/