Download Earthquake

Earthquakes
Earth’s Crust In Motion
Guide For Reading
• How does stress forces affect
rock?
• Why do faults form and where do
they occur?
• How does movement along faults
change Earth’s surface?
Earthquakes
• Earthquake: The shaking that results
from the movement of rock beneath
Earth’s surface
Earth’s plates create powerful
forces that ___ or ___ the
rock in the crust.
• squeeze
• pull
Stress
• Stress: A force that acts on rock to
change its shape or volume
What is Volume?
• The amount of space an object takes
up
Energy is stored in rock until
the rock ______________.
• either breaks or changes shape
Shearing
• Shearing: Stress that pushes a mass of
a rock in opposite, horizontal directions
Tension
• Tension: Stress that stretches rocks
so that it becomes thinner in the
middle
Compression
• Stress that squeezes rock until it
folds or breaks
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
Deformation
• Deformation: A change in the volume
or shape of Earth’s crust
• Most changes in the crust occur so
slowly that they can not be observed
directly
Checkpoint How does
deformation change Earth’s
surface?
• It causes it to:
•
•
•
•
•
•
Bend
Stretch
Break
Tilt
Fold
Slide
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
Faults
• A break in the Earth’s 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
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
Normal Faults
• A type of fault where the hanging
wall slides downward
• Tension forces cause normal faults
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
Reverse Faults
• A type of fault where the hanging
wall slides up
• Compression forces cause reverse
faults
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
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
Checkpoint: 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
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.
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
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
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
The San Andreas fault in
California is a transform
boundary that contains ___
stress.
• high
Fault-Block Mountain
• A mountain that forms where a
normal fault uplifts a block of rock
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
Folds
• A bend in rock that forms where part
of Earth’s crust is compressed
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
Anticline
• Anticline: An upward fold in rock
formed by compression of Earth’s
crust
An example of an anticline is
the _________.
• Black Hills of South Dakota
When and how did this
location form?
• Black Hills began to form about 65
million years ago
Syncline
• Syncline: A
downward fold in
rock formed by
tension in Earth’s
crust
An example of a syncline is
the _____.
• Illinois Basin
This syncline stretches _____
from the western side of
_____ through the state of
_____.
• 250 kilometers
• Indiana
• Illinois
Plateaus
• A large area of flat land elevated
high above sea level
Guide For Reading: How does
movement along faults
change Earth’s 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