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Deforming Earth’s Crust
Deforming the Earth’s Crust
Deformation is the process of changing
the shape of rock because of stress.
Stress - A force that acts on rock to
change its shape or volume
►
Layers of rock bend when enough stress is applied
to them.
►
They can eventually reach their elastic limit and
break.
There are 3 types of stress:
1.
2.
3.
Compression
Tension
Shearing
1) Compression occurs when two tectonic
plates collide or are squeezed together.
►When
compression occurs at
convergent boundaries, large mountain
ranges can form.
2.) Tension occurs when forces act to
stretch on object.

This occurs at divergent boundaries.
3.) Shearing: Stress that pushes a mass of
a rock in opposite, horizontal directions.
► This occurs at transform boundaries
►
►
►
Some rocks break when stress is applied
to them.
The surface along which rocks break and
slide past each other is called Fault.
A fault is classified as a hanging wall or
foot wall when it is not vertical.
A hanging
wall is the
block of rock
above the fault.
A foot wall is
the block below
the fault.
3 Types of Faults
►
Reverse
►
Normal
►
Strike-slip
2.) Reverse Faults
• A type of fault where the hanging wall
slides up
• Compression forces cause reverse
faults
http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
2.) Normal Faults
• A type of fault where the hanging wall
slides downward
•Tension forces cause normal faults
http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
3. 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
http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
Summary: 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
Checkpoint: What are the three types of
fault? What force of deformation produces
each? (tension, compression or shearing?)
► Strike-slip
faults
►Produced
► Normal
by shearing
faults
►Produced
► Reverse
by tension
faults
►Produced
by compression
What is friction?
►A
force that opposes the motion of one
surface as it moves across another surface
► Friction
exists because… surfaces are not
perfectly smooth.
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
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
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
Checkpoint: The San Andreas fault in
California is a transform boundary
that contains _?__ stress.
 high