Chapter 10: Earthquakes

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Chapter 10 Earthquakes

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

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10.1 How and Where Earthquakes Occur

• Causes of Earthquakes
• 1. Earthquake-The shaking of Earth's crust
  caused by a release of energy.
• 2. The cause of most major earthquakes is strain
  that builds up along faults.

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10.1 How and Where Earthquakes Occur

• 3. Fault-A break in the lithosphere along which
  plate movement occurs.
• 4. Focus-The point at which first movement
  occurs during an earthquake.
• 5. Epicenter-The point on the earth's surface
  directly above the focus.

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10.1 How and Where Earthquakes Occur

• Body Waves
• 1. The energy from an earthquake is released
  in the form of waves.
• 2. Body Waves- Waves that travel from the
  focus to through the body of the earth.

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10.1 How and Where Earthquakes Occur

• 3. P waves-Compression waves that squeeze and
  stretch rock material. They can travel through
  any material (water, magma, rock and air).
• 4. 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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10.1 How and Where Earthquakes Occur

• C. Surface Waves
• 1. Earthquake waves that travel on the surface.
• 2. Appear when P and S waves reach the surface.
• 3. Cause the most damage. Why?
• 4. Two Types Love and Rayleigh. Love waves
  move side to side. Rayleigh move in elliptical
  patterns.

Because they are on the surface

• Animations of earthquake waves
• Examine P and S waves
• Savage Earth Restless Planet

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10.2 Locating Measuring Earthquakes

• Seismograph
• 1. Detects and records waves produced by
  earthquakes.
• 2. Seismogram-A record sheet placed on a drum.
  The drum turns slowly and any movement is
  recorded on the paper. See page 217.

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10.2 Locating Measuring Earthquakes

• B. Interpreting a Seismogram
• 1. P waves arrive first, then S waves.
• 2. The farther the station is from the
  earthquake, the larger the separation between P
  S waves lines. Why?

More time to get ahead. It is like a race
between two people at different speeds.
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10.2 Locating Measuring Earthquakes

• C. Locating the Epicenter
• We can triangulate the epicenter by using three
  different seismic stations. See page 219.

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10.2 Locating Measuring Earthquakes

• D. 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.

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10.2 Locating Measuring Earthquakes

• 3. 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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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.

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10.3 Earthquake Hazards

• 3. Aftershocks-Series of small earthquakes that
  follow the initial quake.
• 4. Fire can cause substantial damage. It is
  usually triggered by ruptured gas lines.
• 5. Tsunamis-A huge ocean wave triggered by an
  earthquake. Can travel long distances at speeds
  up to 750 kph.

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10.3 Earthquake Hazards

• 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.

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10.3 Earthquake Hazards

• C. 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.

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10.3 Earthquake Hazards

• D. 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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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.

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10.4 Studying Earths Interior

• B. 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?

The crust is thinner in the ocean.
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10.4 Studying Earths Interior

• 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.