Earth Science Chapter 5

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Earth Science Chapter 5

• Earthquakes

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Plate Boundaries
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Pacific-North American Plate Boundary
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Section 5-1 Earths Crust in Motion

• An earthquake is the shaking and trembling that
  results from movement of rock beneath Earths
  surface. Powerful forces caused by movement of
  Earths plates squeeze rock and pull it in
  different directions force that acts on rock to
  change it shape or volume is called stress.

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5-1 Stresses

• There are 3 types of stresses
• Shearing pushes a mass of rock in two opposite
  directions. (Strike-Slip Fault) blocks move
  sideways in opposite direction.

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Strike Slip Fault
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Tension

• 2. Tension pulls on the crust, stretching
  rock. (Normal Faults) - Hanging wall moves
  down.

Foot wall
Hanging Wall
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Tension
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Compression

• 3. Compression squeezes rock until it folds or
  breaks. (Reverse Faults) - hanging wall moves
  up.

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Compression
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Faults - CA
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Faults St. Andreas Fault, Ca.
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Faults

• When stress builds up in rock, it fractures along
  a fault. A fault is a break in Earths crust
  where slabs of crust slip past each other.
• 1. Strike-slip fault the rocks on either side
  of the fault slide past each other sideways with
  little up or down motion. Strike-slip faults are
  caused by shearing.

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Faults

• Normal Fault one block of rock lies above the
  fault while the other block lies below below it.
  Normal Faults are caused by tension.
• Reverse Fault the hanging wall slides upward
  past the footwall. Reverse Faults are caused by
  compression.

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Fault Animations

• http//www.iris.edu/gifs/animations/faults.htm

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Earthquake

• How blocks of rock move along a fault depends on
  how much friction there is between them. If
  friction is low, the blocks slide constantly
  without sticking. If friction is high, the
  blocks lock together. When the amount of stress
  is greater than the amount of friction, the
  blocks unlock, setting off an earthquake.

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Movement Along Faults

• When normal faults uplift a block of rock, a
  fault-block mountain forms.
• A fold is a bend in a rock that forms when
  compression shortens and thickens part of the
  crust.
• A fold that bends upward in an arch is an
  anticline.
• A fold that bends downward in the middle to form
  a bowl is a syncline.
• When a fault pushes up a large, flat block of
  rock, a plateau can form.

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5-2 Measuring Earthquakes

• The point beneath Earths surface where rock
  under stress breaks to cause an earthquake is
  called the focus.
• The point on the surface directly above the focus
  is called the epicenter. During an earthquake,
  vibrations called seismic waves move out from the
  focus in all directions. Seismic waves carry the
  energy of the earthquake away from the focus
  through Earths interior, and across the surface.

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Epicenter
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3 Types of Seismic Waves

• P Waves compress and expand the ground like an
  accordion.
• S Waves vibrate from side to side and up and
  down.
• Surface Waves when P and S waves reach the
  surface, some are changed into Surface waves.
  Surface waves move more slowly, but produce the
  most severe ground movements.

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Tsunamis
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Sumatra Island in Indonesia - Epicenter
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Sumatra Island in Indonesia
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Sumatra Island in Indonesia
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Sumatra Island in Indonesia
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Sumatra Island
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Instruments to Measure Earthquakes.

• Seismograph measure and record the vibrations
  of seismic waves.
• An earthquakes magnitude is a measurement of its
  strength bases on seismic waves. Three scales
• 1. Mercalli Scale rates earthquakes by
  describing their effects on people, buildings,
  and land surfaces.
• 2. The Richter Scale rates earthquakes
  according to the size of the seismic waves as
  measured by the seismograph.
• 3. The Moment Magnitude Scale rates
  earthquakes by estimating the total energy they
  release.

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Earthquake Magnitude
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Earthquake Magnitude
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Seismic Waves
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Seismograph Lab
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Alaska Seismic Map
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5-3 Earthquake Safety

• The severe shaking produced by seismic waves can
  damage or destroy buildings, bridges, topple
  utility poles, and fracture gas and water mains.
  Earthquakes can trigger landslides, mud slides,
  avalanches, and huge water waves called??
• Aftershocks are smaller earthquakes that occur
  after a large earthquake in the same area.

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Safety

• Most deaths and injuries occur from damaged and
  toppled buildings.
• The main danger to people during an earthquake is
  from falling objects and flying glass. The best
  way to protect yourself is to drop, cover, and
  hold.
• If you are indoors when an earthquakes strikes,
  never run outside. Drop, cover, and hold.
  Leaving a building can result in death.
• If you are outdoors, stay in an open area. Do
  not go under trees, buildings, etc. Drop, Cover,
  and hold.

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5-4 Monitoring Faults

• Geologists try to predict when and where an
  earthquake will occur. To observe changes in the
  elevation or tilts of the land, geologists put in
  place instruments that measure stress and
  deformation in the crust.
• Four instruments are used
• Creep meter measure sideways movement of the
  ground.
• Laser-ranging devices measures slight fault
  movements
• Tiltmeters measures how much the ground has
  tipped along a fault.
• Satellites measures radio waves of the ground
  to measure changes in elevation.

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Loma Prieta, CA 1989
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Kobe, Japan - 1995
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Landers, CA 1992
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Niigata, Japan 1964
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Turnnagin Heights,Alaska,1964
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