How Do Earthquakes Make Waves

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How Do Earthquakes Make Waves?

• An earthquake starts the moment rocks begin to
  scrape past each other along a fault.
• Focus the point where the earthquake starts.
• Usually below the surface.

• Seismic Waves the waves that travel through the
  crust.
• Epicenter the place at the surface directly
  above the focus.
• Tsunamis huge ocean wages caused by earthquakes
  beneath the sea-floor.

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P waves, S waves

• Primary Waves (P wave) the first to reach any
  faraway location after a earthquake.
• Accordion-like motion
• Secondary Wave (S wave) the second to arrive at
  any given faraway location.
• Twanged ruler held off the edge of the desk.

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Seismograph

• A seismograph shows patterns in the waves that
  arrive.
• By carefully studying the waves, a scientists can
  identify the P waves, S waves, and surface waves.

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Surface waves

• Third kind of shaking causes Earths surface to
  heave up and down like an ocean wave, or sway
  from side to side.
• Surface waves tear apart structures built on the
  surface.

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What Can We Learn from Seismic Waves?

• The time difference, or lag, between the arrival
  of the two waves is important.
• By knowing the time lag, you can tell how far
  away you are from the epicenter.
• The radius of that circle .
• All three circles come together at one point
  (epicenter).

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How Destructive is an Earthquake?

• The height of a wave on the seismograph is a
  measure of the MAGNITUDE.
• Magnitude is the amount of energy released by an
  earthquake.

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Richter vs. Mercalli Scale

• The Richter Scale rates earthquakes from 1 to 10
  according to magnitude.
• Each increase of 1 on the scale means an increase
  of about 30 times the energy released.
• Measures energy
• The Mercalli Scale is based on the amount of
  damage done at a given location.
• Measures effects