What are earthquakes?

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What are earthquakes?
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Words to know

• Earthquake
• Focus
• Epicenter
• Seismic Wave

a vibration of the earth (affects large area)
the point where the earthquake starts
the point on the earths surface directly above
the focus
energy sent out from an earthquake
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Facts

• Most earthquakes occur along faults (where two
  plates touch) when potential energy is changed to
  kinetic energy.
• There are more than 3,000,000 earthquakes every
  year.
• 8,000 a day 1 every 11 seconds (According to
  the United States Geological Survey)
• Most of these are NOT felt by humans.

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Earthquakes to know

• 1906 San Francisco
• 60 times more energy than the 89 quake
• 1989 San Francisco (Loma Prieta)

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Notes

• There are 2 types of Seismic Waves
• 1.) Body Waves
• Primary Waves (p-waves)
• Faster
• Travel through solid and liquid rock
• Travels as a longitudinal wave
• Secondary Waves (s-waves)
• Slower
• Travel through solid rock (not outer core)
• Travels as a transverse wave

travel through earths body (interior)
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Notes

• 2.) Surface waves
• usually responsible for shaking the ground
• Sideways Wave
• Shakes the ground from side to side like a snake
• Up-and-Down Wave
• Can open and close cracks in the earth

travel through the earths surface (crust)
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How are earthquakes detected?
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Words to know

• Seismograph
• Seismogram

a device that is used to measure earthquakes
the paper with the zigzag lines (created by a
seismograph)
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How are earthquakes measured?
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Notes

• There are 2 scales used to measure earthquakes
• 1.) Richter Scale
• very accurate because it uses a seismograph to
  measure the ground motion
• tells magnitude of earthquake on a scale from 1
  10 (10 is largest magnitude)
• 2.) Mercalli Scale
• inaccurate because scale is based on eye
  witnessed destruction from earthquake
• scale in roman numerals from I XII