Earthquakes

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Earthquakes

• Chapter 6

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Just a walk in the park
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Glad to live in Iowa???

• Well, maybe..
• So, whats causing this?
• Friction
• Focus
• Epicenter
• Seismic waves released and cause aftershocks (a
  sort of delayed domino effect)

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How deep is the L-ove ?

• Shallow-focus
• 90 of all earthquakes
• lt 70 km deep
• Intermediate-focus
• b/w 70 and 300 km deep
• Deep-focus
• Occur in subduction zones
• b/w 300 and 650 km under surface
• Inland and under continents little energy left
  at surface
• Why do you suppose there are no earthquakes
  deeper than 650 km?

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The Three Major Earthquake Zones
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Earthquakes this week worldwide
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Mid-Ocean Ridges
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Eurasian - Melanesian
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U.S. Biggest Fault Zone New Madrid (Missouri)
The Big Squeeze!
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Recording Earthquakes

• First device in China around 132 A.D.
• First modern machine 1870
• Seismograph (instrument)
• Equipped with 3 sensing devices
• 1 vertical
• 2 horizontal (N/S and E/W)
• Records by making a tracing on magnetic tape or
  directly into a computer

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Waves from the Focus

• P-waves (or primary)
• Longitudinal waves
• Compression waves (like sound waves)
• Fastest
• First to reach seismograph stations
• Can travel through most solid and liquid
  materials
• S-waves (or secondary)
• Transverse waves
• Side to side waves that look like an S (rope)
• Slower than P-waves and second to reach stations
• Can travel through solid not liquid!

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Surface Waves

• P-waves S-waves
• Originate from epicenter not focus
• Slowest of all wave types
• Last to reach stations, but the biggest tracings
• Very destructive and unpredictable we cannot
  build structures to withstand these waves.

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Seismogram
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P and S-wave behavior thru Earth
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Locating an Earthquake
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Earthquake Measurement

• Magnitude measure of the energy released by an
  earthquake and the amount of ground motion during
  the quake
• gt 7 magnitude is a major earthquake
• Between 6 and 7 moderate quake
• Between 2.5 and 6 minor quake
• lt 2.5 microquake (not felt)

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Measures magnitude
Measures intensity
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Earthquake Damage

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6-story high rise apartment building
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What to do

• Be prepared. Be calm. Be aware.
• Most injuries are due to falling and collapsing
  objects and structures
• Building codes old and new
• Stable ground?
• Tsunamis harbor wave (Japanese)

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Is prediction possible?

• Earliest prediction was animal behavior!
• Past records
• Changes in Earths crust
• Seismic gaps areas where fault line is locked
  and hasnt moved in many years
• Many methods all of which are unreliable at
  best
• Area of Earth Science where much more research is
  needed and has the possibility of saving
  thousands of lives.