# Inside Earth Chapter 2- Earthquakes

Shared by:
Categories
-
Stats
views:
32
posted:
4/7/2010
language:
English
pages:
41
Document Sample

```							Inside Earth: Chapter 2- Earthquakes

Section 1: Earth’s Crust In Motion

• 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 (Page 55): How
does deformation change
Earth’s surface?

• It causes it to:
•   Bend
•   Stretch
•   Break
•   Tilt
•   Fold
•   Slide
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
up, the fault would
be called a normal
fault
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 (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
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