Earthquakes and Volcanoes

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Earthquakes and Volcanoes
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Key Terms

• focus
• epicenter
• P waves
• S waves
• surface waves

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Key Terms

• seismology
• Richter scale
• vent

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Objectives

• Identify the causes of earthquakes
• Distinguish between S waves, P waves, and surface
  waves
• Describe how earthquakes are measured and rated

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Objectives

• Explain how and where volcanoes occur
• Describe the different types of common volcanoes

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What are earthqukes

• Occur mostly at the boundaries of tectonic
  plates
• California, Japan
• As plates move, rocks along the edges experience
  great pressure

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What are earthquakes?

• Eventually, the stress becomes so great it breaks
  the rocks along a fault line
• Energy is released as seismic waves
• The exact point where the rocks first break the
  focus

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What are earthquakes?

• The point on the surface immediately above the
  focus is the epicenter (damage is usually
  greatest here)

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Energy is transferred through waves

• Earthquakes generate three kinds of waves
• Longitudinal waves originate from the focus (P
  waves, or primary waves)
• reach recording stations first--they move fastest.

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Energy is transferred through waves

• Compression wave in the Earths crust
• Second wave is a transverse wave (more slowly)
  called S waves
• Both of these spread out in all directions

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Three kinds of waves

• Surface waves (like ocean waves), only at the
  surface
• these do the damage--low frequency, long
  wavelength, circular motion--bad news for
  buildings.

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Did you catch those definitions?

• focus the area along a fault at which slippage
  first occurs, initiating an earthquake
• epicenter the point on Earths surface directly
  above the focus

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Definitions

• P waves primary waves the longitudinal waves
  generated by an earthquake
• S waves secondary waves the transverse waves
  generated by an earthquake

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More definitions

• surface waves seismic waves that travel along
  Earths surface
• seismology the study of earthquakes and related
  phenomena

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Seismograph measures quakes

• Three seismograph stations are necessary to
  locate the epicenter and focus of an earthquake.
• Waves change speed and direction when the density
  of the medium changes

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Investigating Earths interior

• Thats where we get the model of Earths interior!

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Richter scale

• Each step on the Richter scale is a 30-fold
  increase of the energy released
• Kind of the same idea as the Decibel scale.

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Vocanoes

• Wherever MAGMA reaches the Earths surface
  (vents)
• Shield volcano mild sloping hill from buildup
  of lava--mild eruptions (magma rich in iron and
  magnesium--very fluid)

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Volcanoes

• Composite volcano Magma rich in silica
  (thicker)gasses are trapped eruptions alternate
  between flows and explosive activity. Layers of
  cinder and ash. Steeper slopes.

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Composite volcanoes

• Mt. Fuji
• Mt. St. Helens
• Mt. Rainier
• Mt. Hood
• Mt. Shasta

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Cinder cones

• smallest and most abundant.
• large amounts of trapped gas
• erupt for a short time
• steep sides

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Volcanoes

• Volcanoes occur at
• convergent plate boundaries
• divergent plate boundaries
• hot spots (mantle plumes)