UNIT 3: DYNAMIC EARTH Chapter 10: Earthquakes

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UNIT 3 DYNAMIC EARTHChapter 10 Earthquakes

• C/S 10.1 How and Where Earthquakes Occur
• C/S 10.2 Locating and Measuring Earthquakes
• C/S 10.3 Earthquake Hazards
• C/S 10.4 Studying Earths Interior

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C/S 10.1 How and Where Earthquakes Occur

• Causes of Earthquakes
• Earthquake-The shaking of Earth's crust caused by
  a release of energy.
• The cause of most major earthquakes is strain
  that builds up along faults.
• Fault-A break in the lithosphere along which
  plate movement occurs.
• Focus-The point at which first movement occurs
  during an earthquake.
• Epicenter-The point on the earth's surface
  directly above the focus.

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C/S 10.1 How and Where Earthquakes Occur (cont)

• Body Waves
• The energy from an earthquake is released in the
  form of waves.
• Body Waves-Waves that travel from the focus to
  through the body of the earth.
• P waves-Compression waves that squeeze and
  stretch rock material. They can travel through
  any material (water, magma, rock and air).
• S waves-Shear waves that cause material to move
  at right angles to the direction of wave travel.
  They can travel through solids but not liquids or
  gases.

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C/S 10.1 How and Where Earthquakes Occur (cont)

• Surface Waves
• Earthquake waves that travel on the surface.
• Appear when P and S waves reach the surface.
• Cause the most damage. Why?
• Two Types Love and Rayleigh. Love waves move
  side to side. Rayleigh move in elliptical
  patterns.
• Animations of earthquake waves
• Examine P and S waves
• Savage Earth Restless Planet

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C/S 10.2 Locating and Measuring Earthquakes

• Seismograph
• Detects and records waves produced by
  earthquakes.
• Seismogram-A record sheet placed on a drum. The
  drum turns slowly and any movement is recorded on
  the paper. See page 217.
• Interpreting a Seismogram
• P waves arrive first, then S waves.
• The farther the station is from the earthquake,
  the larger the separation between P S waves
  lines. Why? See page 218.

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C/S 10.2 Locating and Measuring Earthquakes
(cont)

• Locating the Epicenter
• We can triangulate the epicenter by using three
  different seismic stations. See page 219.
• Measuring an Earthquakes Magnitude
• Magnitude-A measure of the amount of energy
  released in an earthquake.
• The Richter Scale was developed in 1935. It
  measures the amount of energy released by an
  earthquake.
• An increase of one whole number is equal to a
  31-fold increase in energy. Ex. Mag. 6
  earthquake is 31 times more powerful than a Mag.
  5 earthquake.
• Build Your Own Seismograph

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C/S 10.3 Earthquake Hazards

• Damage from Earthquakes
• Damage is not only caused by the shaking from the
  earthquake, but also by foundation failure, fire
  and tsunamis.
• Liquefaction-Occurs when loose soil temporarily
  takes on some of the properties of a liquid.
  This causes buildings and roads to collapse.
• Aftershocks-Series of small earthquakes that
  follow the initial quake.
• Fire can cause substantial damage. It is usually
  triggered by ruptured gas lines.
• Tsunamis-A huge ocean wave triggered by an
  earthquake. Can travel long distances at speeds
  up to 750 kph.

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C/S 10.3 Earthquake Hazards (cont)

• Preventing Earthquake Damage
• Earthquake prone cities have special building
  codes to help prevent building collapse.
• Monitoring equipment helps to continue learning
  what structures hold up the best during an
  earthquake.
• Earthquake Risk
• Areas near plate boundaries are not the only
  areas at risk.
• New Madrid, MO is located near several faults
  buried under large amounts of sediments.
• Predicting Earthquakes
• Seismic Gaps-Areas where stress may be building
  up along a fault.
• Scientists can predict at risk areas, but not
  specific locations or times.

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C/S 10.4 Studying Earths Interior

• The Shadow Zone
• Changes in the speed and direction of P and S
  waves indicate changes in the composition and
  state of the earth's interior.
• A shadow zone is created by these changes.
  Remember that S waves cannot travel through
  liquids. See page 228.
• The Moho
• Boundary between the crust and the mantle.
• Where the dense rock of the mantle meets the less
  dense rock of the crust.
• Located about 32 km under continents and 5-10 km
  under the oceans. Why?

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C/S 10.4 Studying Earths Interior (cont)

• Transition Zone
• Region in the middle of the mantle where the
  densities of the upper and lower mantle vary.
• This change is due to changes in pressure as
  depth increases.