We

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Weve looked at plate tectonics...

• Now lets look at a possible outcome

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Earthquakes
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What are Earthquakes?

• The shaking or trembling caused by the sudden
  release of energy
• Usually associated with sudden movements of
  tectonic plates
• Continuing adjustment of position results in
  aftershocks

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• The point within the Earth where faulting begins
  is the focus, or hypocenter
• The point directly above the focus on the surface
  of the earth is the epicenter

http//www.earthquakecountry.info/roots/basics.htm
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Wadati-Benioff zone

• A dipping flat zone of earthquakes that is
  produced by the interaction of a downgoing
  oceanic crustal plate with a continental plate.

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Seismographs

• The instrument used to record and measure
  vibrations caused by the breakage of rock along a
  fault zone.
• http//www.youtube.com/watch?vDX5VXGmdnAgfeature
  related
• http//www.youtube.com/watch?v83GOKn7kWXMfeature
  related

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Using Waves

• The shock waves spreading out from an earthquake
  are called seismic waves.
• There are two general types of seismic waves
  body waves and surface waves.
• Surface waves travel just beneath the Earth's
  surface.
• Body waves travel through the Earth's interior.
• There are two types of body waves, P waves and S
  waves.
• S waves have much higher amplitude than P waves,
  travel more slowly, carry more destructive force,
  but cannot travel through the Earth's liquid
  core, while P waves can.
• P waves arrive first, and then S waves (followed
  by L and R waves).
• Because we know the average speeds for the waves,
  after an earthquake, the difference in arrival
  times at a seismograph station can be used to
  calculate the distance from the seismograph to
  the epicenter.

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• http//www.youtube.com/watch?vyOGoKCK17a4

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How is an Earthquakes Epicenter Located?

• Three seismograph stations are needed to locate
  the epicenter of an earthquake
• A circle where the radius equals the distance to
  the epicenter is drawn
• The intersection of the circles locates the
  epicenter

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Measuring the Strength of Earthquakes

• The Richter scale measures total amount of energy
  released by an earthquake
• Measurements on the Richter Scale increase by
  factors of 10.
• An earthquake of magnitude 6 is 10 times stronger
  than one of magnitude 5 and 100 times stronger
  than one of magnitude 4

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Earthquakes Occurrence

• 80 of all earthquakes occur in the
  circum-Pacific belt
• 15 occur in the Mediterranean-Asiatic belt
• 5 occur in the interiors of plates and on
  spreading ridge centers
• More than 150,000 quakes strong enough to be felt
  are recorded each year

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Destructive Effects of Earthquakes

• Ground Shaking
• Damage increases in poorly consolidated rocks
• Best place to be is on solid bedrock

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• http//www.youtube.com/watch?vCtBXTvtFaCUfeature
  fvwrel

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Earthquake Damage
Mexico City 1985
Alaska 2002
Indonesia 2005
New Zealand 1987
San Francisco 1989
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Effects

• Landslides
• Fires (from damaged electrical or gas lines)
• Soil liquefaction (sand temporarily transforms
  from a solid to a liquid, causing
  buildings/bridges to tilt or sink)
• Tsunamis
• Flooding
• Injury, disease, loss of life
• Property damage (higher insurance rates)

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Can Earthquakes be Predicted?

• Clues that an Earthquake may happen
• changes in elevation or tilting of land surface,
• fluctuations in groundwater levels and/or
  magnetic fields,
• electrical resistance of the ground,
• opening of gaps or fissures

We know where they can happen, and we can produce
risk assessments, but we cant warn
public. Geologist can say its coming soon. But
soon could be next week or in 123 years!!!
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Earthquake Prediction Programs

• laboratory and field studies of rocks before,
  during, and after earthquakes
• monitor activity along major faults
• produce risk assessments

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• Predicting earthquakes