Measuring Earthquakes

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Measuring Earthquakes
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Focus and Epicenter

• Earthquakes start at one point in the lithosphere
  called the focus.
• The point directly above the focus on the Earths
  surface is called the epicenter.

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Seismic Waves

• Earthquakes release wave vibrations that travel
  through solid material.
• Seismic waves carry the energy of an earthquake
  away from the focus, through Earths interior,
  and across the surface.

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Seismic Waves
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Types of Seismic Waves

• There are 3 types of seismic waves.
• P waves
• S waves
• Surface waves

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P Waves

• P waves are primary waves and are the first to
  get to the surface.
• They act like an accordion and travel through
  solids and liquids.

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S Waves

• S waves are secondary waves.
• They vibrate from side and side and up and down,
  shaking the ground.
• They cannot move through liquids.

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Surface Waves

• At the surface, S and P waves transform into
  surface waves.
• These waves move slow and make the ground roll.

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Detecting Seismic Waves

• Seismographs are used to record how waves move
  through Earth.
• The higher the wave,
• the stronger the earthquake.
• Used to use mechanical seismographs, but now we
  use electronic seismographs.

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Measuring Earthquakes

• 20 measures for rating earthquakes.
• Magnitude measures
• the strength of
• earthquakes based on
• seismic waves
• and fault movement.

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Mercalli Scale

• Rates earthquakes on a scale from 1-12 based on
  how they affect people, buildings, and land
  surface.
• The rating changes
• based on the location.

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Richter Scale

• Richter scale rates the size of the seismic waves
  using a mechanical seismograph.
• Works well for small,
• nearby earthquakes
• only.

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Moment Magnitude Scale

• The scale we use today.
• Estimates the total energy released by an
  earthquake.
• Can be used to rate earthquakes of all sizes,
  near or far.

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Moment Magnitude Scale

• The rating is based on the size of seismic wave
  and the movement on fault lines. (1 10)
• Below 5.0 is a small earthquake
• Above 5.0 can create destruction.

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Locating the Epicenter

• Seismic waves travel at different speeds.
• Scientists measure the difference between the
  arrival of the P wave from the S wave to figure
  out where the epicenter is.

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