Transcript Strike-Slip Faults

6.3 Deforming Earth’s
Crust
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Deformation
• The process by which the shape of a rock changes
in response to stress.
Stress
•The amount of force per unit area on a given
material.
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Describe two ways in which rock layers can
deform when stress is placed on them.
Rock layers can deform by bending and by
breaking.
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Folding
•The bending of rock layers in response to stress in Earths
crust.
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Two types of folds
Anticline
•A fold in which the oldest
rock layers are in the center of
the fold.
•Rock limbs slope down from
the center to form an arch.
Syncline
•A fold in which the youngest
rock layers are in the center of
the fold.
•The limbs slope up from the
center to form a trough.
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Shapes of Folds
•Asymmetrical – rock layers that bend into folds
that are not symmetrical
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•Overturned fold – A fold in which one limb is tilted
beyond 90 degrees.
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Recumbent fold – A fold appears to be
lying on its side.
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Faulting
•The surface along which rocks break and slide past each other is
called a fault.
•The footwall is the block of rock that lies below the plane of the
fault.
•The hanging wall is the block that lies above the plane of the
fault.
Footwall
Hanging wall
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How do faults form?
Faults form when rock is placed under so
much stress that it no longer stretches or
flows, but breaks.
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Normal Fault
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When rocks are pulled apart because of tension (stress that
pulls rocks apart).
The hanging wall moves down relative to the footwall.
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Reverse Faults


When rocks are pushed
together by compression
(stress that pushes rocks
together).
The hanging wall moves
up relative to the
footwall.
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Strike-Slip Faults
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
When rocks are moved
horizontally by opposing
forces due to shearing.
The two fault blocks
move past each other
horizontally.
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Compare how the three types of faults form.
Normal faults form from tension that pulls rocks
apart at divergent boundaries. Reverse faults form
from compression that pushes rocks together at
convergent boundaries. Strike-slip faults form when
shear stress pushes rocks in opposite directions at
transform boundaries.
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Recognizing Faults

Slickensides are grooves,
striations, or polished
surfaces to indicate
where rocks have moved.

Scarp –a row of cliffs
formed by faulting.
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How do mountains form?
Mountains form when tectonic plate motions
crumple and push up the margins of plates.
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Mountain Building
Folded Mountains
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Formed when rock layers
are squeezed together
and pushed upward.
Form at convergent
boundaries where
continents have collided.
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Folded Mountain
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Fault-Block Mountain
•Forms when tension in Earth’s crust causes the
crust to break into a large number of normal faults.
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Fault-Block Mountain
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Volcanic Mountains
•Formed when molten rock erupts onto Earth’s
surface.
•Most volcanic mountains are located at convergent
boundaries.
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Volcanic Mountains
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Review Questions
1.
Why do rocks deform?
Rocks deform when stress is placed on them.
2.
What causes faults to form?
Faults form when so much stress is placed on rock layers
that they break.
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3. For each of the three types of faults, explain the
forces that cause the faults to form.
Normal faults form when tension causes rock to
pull apart and break. Reverse faults form when
compression pushes rocks together and causes
the rock to break. Strike-slip faults form when
shear stress causes rocks to break and to be
pushed in different directions.
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4.
How are mountains related to tectonic plate motion?
Folded mountains occur at convergent plate
boundaries, where compression folds and uplifts rock.
Fault-block mountains occur where divergent plate
motion causes Earth’s crust to break into a series of
normal faults. Volcanic mountains occur at convergent
plate boundaries, where subduction causes the
surrounding mantle rock to melt and magma to rise to
the surface.
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Quiz 6.3 review
•Anticline
•Syncline
•Folded mountains
•Tension
•Compression
•Fault-block mountains
•Normal fault
•Reverse fault
•Molten rock
•Strike slip fault
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