Earth's Crust in Motion Earthquakes So . What is an

1
Earth's Crust in Motion
2
Earthquakes

• So.
• What is an Earthquake?
• And
• What are some things that can cause them?

3
Stress in the Crust

• An earthquake is the shaking that results from
  the movement of rock beneath Earth's surface.
• This is a super powerful force!!!
• These forces are examples of stress.
• Stress is a force that acts on rock to change its
  shape or volume.

4
Types of Stress

• There are three different kinds of stress that
  occur in the Earths crust
• Shearing
• Tension
• Compression
• All of this stress works over millions of years
  to change the shape of rock.
• SoAny change in the shape of Earth's crust is
  called deformation.

5
Shearing

• Stress that pushes a mass of rock in two opposite
  directions is called shearing.
• Shearing can cause two slabs of rock to slip past
  each other like the picture below.
• What feature in California is an example of this?

6
Tension

• Tension is a stress that pulls on the crust,
  stretching rock so that it becomes thinner in the
  middle.
• Tension occurs where two plates are moving apart.
• Think of pulling a Milky Way candy bar apart.
• What ocean feature is this an example of?

7
Compression

• Compression is a stress force that squeezes rock
  until it folds or breaks.
• One plate pushing against another plate can
  compress rock easily.
• Almost like Mr. Wises strength!!!

8
Kinds of Faults

• When enough stress builds up in rock, the rock
  can break, creating a fault.
• A fault is a break in the crust where two slabs
  of crust slip past each other.
• The rocks on both sides of a fault can either
  move up or down or sideways.
• Faults usually occur along plate boundaries
• There are three main types of faults
• Strike-slip faults
• Normal faults
• Reverse faults

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Strike-Slip Faults  

• Shearing creates strike-slip faults.
• In a strike-slip fault, the rocks on either side
  of the fault slip past each other sideways
• A strike-slip fault that forms the boundary
  between two plates is called a transform
  boundary.
• What fault in California is an example of this?

10
Normal Faults  

• Tension forces in Earth's crust cause normal
  faults.
• In a normal fault, the fault is at an angle, so
  one block of rock lies above the fault while the
  other block lies below the fault.
• Tension forces create normal faults where plates
  diverge, or pull apart.
• What ocean feature is an example of this?

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Normal Faults
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Reverse Faults  

• Compression forces produce reverse faults.
• A reverse fault has the same structure as a
  normal fault, but the blocks move in the opposite
  direction.
• What geologic feature is an example created by
  compression?

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Reverse Faults
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Mountain Building

• The forces of plate movement can build up Earth's
  surface.
• Over millions of years, fault movement can change
  a flat plain into a towering mountain range

15
Mountains Formed by Faulting

• When normal faults uplift a block of rock, a
  fault-block mountain forms.

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Mountains Formed by Folding

• Under certain conditions, plate movement can
  cause crust to fold.
• Folds are bends in rock that form when
  compression shortens and thickens part of Earth's
  crust.
• The collisions of two plates can cause
  compression and folding of the crust.
• Some of the world's largest mountain ranges, such
  as the Himalayas and the Alps, formed when pieces
  of the crust folded during the collision of two
  plates.
• Such plate collisions also lead to earthquakes!

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Mountains Formed by Folding
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Anticlines and Synclines  

• A fold in rock that bends upward into an arch is
  an anticline.
• A fold in rock that bends downward in the middle
  to form a bowl is a syncline.
• Anticlines and synclines are found on many parts
  of Earth's surface where compression forces have
  folded the crust.