Inside Earth: Chapter 2 Earthquakes

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Inside Earth Chapter 2- Earthquakes

• Section 1 Earths Crust In Motion

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Guide For Reading

• How does stress forces affect rock?
• Why do faults form and where do they occur?
• How does movement along faults change Earths
  surface?

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Earthquakes

• Earthquake The shaking that results from the
  movement of rock beneath Earths surface

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Earths plates create powerful forces that ___ or
___ the rock in the crust.

• squeeze
• pull

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Stress

• Stress A force that acts on rock to change its
  shape or volume

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What is Volume?

• The amount of space an object takes up

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Energy is stored in rock until the rock
______________.

• either breaks or changes shape

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Shearing

• Shearing Stress that pushes a mass of a rock in
  opposite, horizontal directions

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Tension

• Tension Stress that stretches rocks so that it
  becomes thinner in the middle

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Compression

• Stress that squeezes rock until it folds or breaks

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Figure 2 If shearing continues to tug at the
slab of rock in B, what will happen to the rock?

• The rock will break the two parts will move in
  opposite directions

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Deformation

• Deformation A change in the volume or shape of
  Earths crust
• Most changes in the crust occur so slowly that
  they can not be observed directly

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Checkpoint (Page 55) How does deformation change
Earths surface?

• It causes it to
• Bend
• Stretch
• Break
• Tilt
• Fold
• Slide

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Guide For Reading How does stress forces affect
rock?

• The three kinds of forces that affect rock are
• Shearing
• The rocks break and slip apart
• Tension
• The rock stretches and becomes thin in the middle
• Compression
• The rock squeezes until it folds or breaks
• These stresses work over millions of years to
  change the shape and volume of rock

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Faults

• A break in the Earths crust where slabs of rock
  slip past each other
• Faults occur when enough stress builds up in rock
• Rocks on both sides of the fault can move up or
  down, or sideways

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Strike-Slip Faults

• A type of fault where rocks on either side move
  past each other sideways with little up-or down
  motion.
• Shearing causes these types of faults

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Normal Faults

• A type of fault where the hanging wall slides
  downward
• Tension forces cause normal faults

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Hanging Wall Footwall

• Hanging wall The block of rock that forms the
  upper half of a fault
• Footwall The block of rock that forms the lower
  half of a fault

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Reverse Faults

• A type of fault where the hanging wall slides up
• Compression forces cause reverse faults

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Figure 5 Which half of the reverse fault slid up
and across to form this mountain, hanging wall or
the footwall? Explain.

• The hanging wall slipped up and across. If the
  footwall had moved up, the fault would be called
  a normal fault

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Guide For Reading Why do faults form and where
do they occur?

• Faults usually occur along plate boundaries,
  where the forces of plate motion compress, pull,
  or shear the crust so much that the crust breaks

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Checkpoint (Page 57) What are the three types of
fault? What force of deformation produce each?

• Strike-slip faults
• Produced by shearing
• Normal faults
• Produced by tension
• Reverse faults
• Produced by compression

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What is friction?

• A force that opposes the motion of one surface as
  it moves across another surface

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Friction exists because

• surfaces are not perfectly smooth.

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Describe what occurs when the friction along a
fault line is low.

• The rocks on both sides of the fault slide by
  each other without much sticking

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Describe what occurs when the friction along a
fault line is moderate.

• The sides of the fault jam together
• From time to time they jerk free
• Small earthquakes occur

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Describe what occurs when the friction along a
fault line is high.

• Both sides of the fault lock together and do not
  move
• The stress increases until it is strong enough to
  overcome the force of friction
• Larger and/or more frequent earthquakes will occur

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The San Andreas fault in California is a
transform boundary that contains ___ stress.

• high

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Fault-Block Mountain

• A mountain that forms where a normal fault
  uplifts a block of rock

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How does the process of a fault-block mountain
begin?

• Where two plates move away from each other,
  tension forces create many normal faults
• When two of these normal faults form parallel to
  each other, a block of rock is left lying between
  them
• As the hanging wall of each normal fault slips
  downward, the block in between moves upward
• When a block of rock lying between two normal
  faults slides downward, a valley forms

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Folds

• A bend in rock that forms where part of Earths
  crust is compressed

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How does the compression of two plates cause an
earthquake?

• The collisions of two plates can cause
  compression and folding of the crust
• Such plate collisions also lead to earthquakes,
  because folding rock can fracture and produce
  faults

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Anticline

• Anticline An upward fold in rock formed by
  compression of Earths crust

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An example of an anticline is the _________.

• Black Hills of South Dakota

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When and how did this location form?

• Black Hills began to form about 65 million years
  ago

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Syncline

• Syncline A downward fold in rock formed by
  tension in Earths crust

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An example of a syncline is the _____.

• Illinois Basin

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This syncline stretches _____ from the western
side of _____ through the state of _____.

• 250 kilometers
• Indiana
• Illinois

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Plateaus

• A large area of flat land elevated high above sea
  level

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Guide For Reading How does movement along faults
change Earths surface?

• Over millions of years, fault movement can change
  a flat plain into a towering mountain range
• Mountain ranges can form from
• Fault block mountain
• Folding
• Anticlines Synclines
• Plateaus