Earthquake Origin Causes and effects

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Earthquake Origin Causes and effects

• Lab

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goals

• In an earthquake, will all parts of a city suffer
  the same damage?
• What factors may affect the damage caused by an
  earthquake?
• What is the additional hazard of an underwater
  earthquake?
• Describe the effects on life and property from
  consequences of earthquakes such as landslides,
  liquification, surface faulting, and tsunamis.
• Cite ways these hazards can be minimized.
• Describe ways in which people use historical
  data, geologic maps, and technologies to minimize
  earthquake damage.

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Each students gets a white Textbook

• When you learned about the Loma Prieta
  earthquake, you learned about some of the
  destruction around the city. In your textbook,
  turn to page G-158. Look at the three seismograms
  taken from different areas of the city during
  that quake

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Answer the questions in your journal

• At which seismic station was the quake felt most
  intensely? How can you tell?
• At which seismic station was the least intensity
  measured? How can you tell?
• Look at the map next to the seismograms. What is
  the underlying geology at the station registering
  the greatest intensity?
• What is the underlying geology at the station
  registering the least intensity?
• Turn to page G-160 and find the Loma Prieta quake
  in the event column. What geologic changes
  occurred as a result of this earthquake?

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Liquefaction

• Have you ever been to the beach and let the surf
  wash over your feet? As each wave goes out, it
  takes the sand under your feet with it. The sand
  and the water seem to act as one. This is
  similar to the effect that is noted when
  earthquake waves pass through loose soil or sand
  that is saturated with water. The soil and water
  act as a fluid together in an effect known as
  liquifaction

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Results of liquefaction

• This creates an unstable foundation for
  buildings, and is responsible for heavy damage to
  them. Looking back at the Loma Prieta map, you
  can see that the area of artificial fill near the
  waterfront showed the most intense quake, and the
  area of beach dunes showed a similar high
  intensity.

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Part B

• Read pages G-141 to 144 to find out more about
  earthquake intensity measurement and how the
  underlying geology of an area contributes to the
  damage caused by the quake.

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Answer these questions in your journal

• How does the underlying geology of an area affect
  the intensity of an earthquake there?
• Is the Mercalli Scale a good choice for
  scientists? Why/ why not?
• Why do scientists use the Modified Richter scale
  to describe the intensity of an earthquake
  instead of the original Richter scale?
• How is the measured amplitude of a quake with a
  magnitude of 7 different from a quake with a
  magnitude of 5?
• What other factors affect the damage done during
  an earthquake?

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Part C

• Why do buildings break during earthquakes but
  trees do not?
• What can be done to earthquake proof buildings?

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Vibrations and natural frequency

• Lets review some of the things we have learned
  about energy and materials. We have learned
  that everything vibrates at its own natural
  frequency. That frequency depends on the type of
  material and the structure of the object made
  from it. A simple object made from a single
  substance, like a guitar string, can be tuned to
  vibrate at a specific frequency when plucked.
  When objects are made from a variety of materials
  and have complex structures, like buildings, the
  vibrations become far more complex. A building
  may have a natural frequency, or parts of the
  building may have their own natural frequencies.
  The places where pieces join together become an
  important part of the structure, and also affect
  the ability of the whole building to vibrate as a
  unit or in sections.
•  

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Molecular springs

• We have also learned that molecules are held
  together by bonds that resemble tiny springs.
  Some materials have the property we call
  elasticity that enables the bonds to deform and
  return to their original shape. Other materials
  are inelastic. They do not deform readily, and
  are more likely to break if force is applied to
  their bonds. Concrete is an example of a
  material that is inelastic.
•  

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Mass and Motion

• Why do objects move? We know that unbalanced
  forces are needed to begin motion. We know that
  the heavier an object is, the more mass it has,
  and the more force is needed to start it moving.
  We recognize that the mass of an object is the
  property that is important in its ability to
  resist the forces that are applied to it.

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Watch video section

• Engineering segment of the video Shock Waves to
  learn how engineers are developing construction
  methods to reduce the damage to buildings during
  earthquakes.
• As you watch the video, look for specific
  construction techniques used and why they are
  effective.

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Answer these questions in your journal.

• 1. What are three modifications made to existing
  structures to help them withstand earthquakes?
  (How do they help?)
•  
• 2. What are two types of foundation
  modifications for new buildings help prevent
  damage from vibration due to earthquakes?
• 3. In the computer simulation of City Hall, how
  is the building vibration with the isolators
  different from its vibration without them?
•  
• 4. What is the value of a shake table to an
  engineer?
•  
• 5. Why would the gas company replace cast iron
  pipe with plastic pipe?

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Part D Tsunamis

• December 26, 2004 the world is shocked at the
  news of a killer tsunami that engulfed the shores
  of countries along the Indian Ocean. One
  survivors story warmed the hearts of people
  everywhere.
• A school girl from Britain saved numerous lives
  because she recognized the signs of a tsunami and
  got her family and many others to run for safety
  in time.

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What is a Tsunami

• Imagine a very large basin of water that is
  suddenly shaken.
• What will happen to the water?
• It will slosh from side to side.
• When the water level is rising to the edge on one
  side of the basin, it is shallower on the other
  side

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Dec 26, 2004

• Now imagine an incredibly big basin, one the size
  of the Indian Ocean.
• On one side of the ocean, over near Sumatra, a
  750 mile section of the ocean bottom suddenly
  shifted about 50 ft. (about 5 stories on a
  building) due to an earthquake.
• The water in the ocean sloshed from side to side,
  creating an enormous wave known as a tsunami.

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Energy transfer

• The energy that caused the movement of land is
  transferred to the waves it created in the water
• It take enormous energy to move land, so an
  enormous amount of energy is transferred to the
  Tsunami

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Tsunami in the ocean

• Out in the ocean, where the water is deep, the
  water wave generated by an earthquake does the
  same thing. If you are on a ship out in the
  middle of the ocean, you dont notice the
  enormous amount of energy being carried by the
  wave.

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As the Tsunami reaches the shore

• as the wave gets close to shore, it can no longer
  go as deep as it did before. This creates great
  crests that tower over the beaches and crash
  inland. These crashing waves behave like the
  gentle waves you see at the beach, but they carry
  much more energy and do far more damage.

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The force of a Tsunami wave

• If you have ever been knocked down by a wave at
  the beach, you have some understanding of the
  force of a wave. A wave 10 times that size would
  slam you into the beach so hard you would never
  be able to get up again. It would tear up trees
  and knock down buildings. The withdrawing wave
  would drag out to sea anything that was not
  extremely well anchored.

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What not to do if your at the leading edge of a
Tsunami

• Sometimes, people are on the receding side of a
  tsunami before the wave comes in. People have
  gathered on the newly open beach to pick up
  stranded fish and been unable to escape when the
  wave came in. This occurred in Thailand and Sri
  Lanka.

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Secondary effects of Tsunamis

• In addition to the deaths directly caused by the
  tsunami, the devastation to water supplies is an
  invitation to diseases like dysentery and
  cholera. Standing water provides breeding places
  for insects that carry other diseases. Salt
  water inundation of fields causes crop failure.
  While all tsunamis are not as devastating as this
  one was, they are a very serious secondary effect
  of some earthquakes.

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Do all earthquakes create Tsunamis?Are all
Tsunamis created by earthquakes?

• Not every earthquake produces a tsunami, and not
  every tsunami is caused by an earthquake. Any
  major disturbance of the water can cause such a
  wave to develop. Volcanic eruptions like the
  1906 Mount Pelée event create mudslides that
  reach the ocean and cause local tsunamis.