Unit 8 Notes

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Earthquakes
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What is an Earthquake?

• Earthquakes Vibrations (seismic waves) within
  Earth materials are produced by the rapid release
  of energy
• Earths crust is in constant motion because of
  tectonic forces
• Earths crust can store elastic energy
• When forces exceed the elastic limits and
  structural strength of the rocks, the rocks will
  break and/or move producing vibrations that
  travel outward in all directions

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Earthquakes

• The actual place underground where the rocks
  break producing vibrations is called the focus.
• The place on the surface directly above the focus
  is called the epicenter.

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What types of forces are created?

• Tension Force/Stress
• stretching or pulling force
• Makes a normal fault

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Normal Fault
http//www.geo.uib.no/jordskjelv/index.php?topice
arthquakeslangen
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What types of forces are created?

• Compression Force/Stress
• force pushing something together
• Makes a reverse fault

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Reverse Fault
http//www.geo.uib.no/jordskjelv/index.php?topice
arthquakeslangen
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What types of forces are created?

• Shear Force
• a system of forces that operates against a body
  from different sides
• Makes a strike-slip fault

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Strike-Slip Fault
http//www.geo.uib.no/jordskjelv/index.php?topice
arthquakeslangen
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What causes Earthquakes?

• Movement along faults occurs when the energy
  exceeds the friction holding the sides of the
  fault together and is suddenly released.
• Movement of magma (volcanic)
• Volcanic eruptions

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Fault lines Earthquakes
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Seismic Waves

• Originate at the focus and travel outward in all
  directions
• Foreshocks small earthquakes that come before a
  major earthquake
• Aftershocks Are adjustments in the crust after
  in earthquake
• Smaller than main earthquake, but can cause as
  much or more damage. They can continue for weeks
  to months. Not every earthquake produces
  aftershocks

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Seismic Waves
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3 Types of seismic Waves

• P waves (primary waves) Compressional wave
• Particles move back and forth in the same
  direction as the wave
• Travels the fastest
• Can pass through solids and liquids (gases also)
• Does not cause damage

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Types of Waves

• S wave (secondary wave, shear wave)
• Waves move at up and down and side to side.
• Travels slower than P waves.
• Can pass through solids only.
• Part of the body wave that will eventually
  cause damage.

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Types of Waves

• L wave (long wave, surface wave, ground wave)
• Particles move in elliptical orbit
• Originates on the surface after the P and S waves
  go straight up from the focus and reach the
  surface
• The L wave causes the damage and will be the
  strongest at the epicenter
• Travels the slowest

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How do we Measure Earthquakes?

• Earthquake waves are recorded by a seismograph
  and the recording of waves on paper is called
  seismogram

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How do we Measure Earthquakes?

• Intensity a measure of the effects on an
  earthquake at a particular location
• Magnitude a measure of the strength or amount
  of energy released during an earthquake

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How do we Measure Earthquakes?

• Richter Scale Measures the amplitude of
  earthquake waves on seismograms
• Scale from 1-10
• Each number is 10 times the amplitude of the
  number below
• More precise and accurate

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Modified Mercalli Scale

• Modified Mercalli scale An estimate of the
  intensity based on observation of actual damage.
• Usually represented by Roman Numerals (i.e. II)
• Very dependent upon the quality of structures

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Locating the Origin of Earthquake Activity

• Locating the epicenter
• Lag time between the arrival of the P wave and
  the S wave to the seismograph station is
  converted to a distance (miles or km).
• A circle with a radius that equals the distance
  is drawn around the station.
• Two stations can narrow down the location to two
  places where the two circles intersect
• Locating the focus the lag-time of the L wave
  will determine the depth of the focus

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Earthquake Dangers

• Most injuries and deaths are caused by falling
  objects and most property damage results from
  fires that start
• Tsunami seismic sea wave sometimes generated
  when an earthquake originates on the ocean floor

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TsunamiDecember 2004
http//www.bedford.k12.ny.us16080/flhs/science/im
ages/tsunami2004/
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Tsunami ClipDiscovery School
Tsunami by Brainpop
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Earthquake Dangers

• Liquefaction unconsolidated materials that are
  water saturated may turn to a fluid causing some
  underground objects such as storage tanks to
  float to the surface

Ground fissures caused by liquefaction near the
mouth of the Pajaro River in California during
the 1989 Loma Prieta earthquake. When the surface
of the ground oscillates, wet, sandy, and muddy
soils can flow like a liquid. This is
liquefaction. You can liquefy wet sand at the
beach by pumping it up and down with your feet.
Photo courtesy of the Loma Prieta Collection,
Earthquake Engineering Research Center, UC
Berkeley.
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Earthquake Dangers

• Landslides

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Earthquake Safety

• Protect yourself from falling objects (GET UNDER
  SOMETHING) or stand in a hallway or doorway
  (watch out for a swinging door)
• Do not try to go outside during the earthquake
• After the earthquake and before the aftershocks,
  go outside
• Do not return to the building until it has been
  inspected

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