Faults
Grade 8 Earth and Space Science
LEARNING OUTCOMES
At the end of the lesson, you should be able to:
1
2
3
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describe the appearance of a fault;
explain how a fault forms using the concept of the
Elastic Rebound Theory;
explain how faults generate earthquakes; and
identify the different types of faults.
ENGAGE
Multiple Choice: Choose the letter of the best answer.
1
Based on the map, the areas marked with
1red color are called______________.
A. The Intertropical Convergence zone
(ITCZ)
B. The Pacific Ring of fire
C. The Bermuda Triangle
D. Typhoon prone areas
Multiple Choice: Choose the letter of the best answer.
2 1
The areas marked with red color is called
The Pacific Ring of Fire because _______.
A. it has the greatest number of volcanic
activities in the world.
B. it has a long chain of mountain ranges.
C. it surrounds the Pacific ocean.
D. this is where most of the typhoons are
formed.
Multiple Choice: Choose the letter of the best answer.
3 1
Based from the figure, the Philippines is
located within the Pacific Ring of Fire. How
does this affect us?
A. Our country is more prone to typhoons
B. Our country experiences cold weather
C. Our country has a lot of active
volcanoes and fault lines
D. Our country is safe from natural
disasters
ENGAGE
How do faults produce quakes?
EXPLORE
Damages of an
Earthquake
Find out how destructive
an earthquake can be.
Interactive
EXPLAIN
EXPLAIN
1. According to the news,
where is the epicenter of
the earthquake found?
Interactive
EXPLAIN
2. What was the cause of
the earthquake?
Interactive
EXPLAIN
3. Describe the damages
in areas located along the
faults and compare it with
those that are away from
the faults.
Interactive
EXPLAIN
4. How is energy stored in
rocks?
Interactive
EXPLAIN
5. What happens when the
stored energy in the rocks
released?
Interactive
An earthquake is a
vibration of the Earth due
to the rapid release of
energy.
A fault is a break in the
Earth’s crust, and along
the break, significant
movement takes place.
EXPLAIN
You can see the fault in the Earth’s crust,
and along the break, significant movement
has taken place.
The accumulated energy grows strong
enough, the plates break free.
Interactive
EXPLAIN
These faults were not always there. Beneath
the earth, there are forces that move the
earth’s plates. The processes happening
below the earth will be discussed in details
in your Grade 10 Science.
Interactive
EXPLAIN
But to simply explain how energy is stored in
rocks and how energy is released during an
earthquake, there is the Elastic Rebound
Theory
Interactive
Elastic Rebound Theory
 Most earthquakes are produced by the rapid release of
elastic energy stored in rock that has been subjected to
great forces.
 When the strength of the rock is exceeded, it suddenly
breaks, causing the vibrations of an earthquake.
EXPLAIN
When too much bending occurs and the
limit is reached, the rocks suddenly snap.
The bent rocks straighten out and vibrate.
The vibrations travel in all directions and
people in different places will feel them as a
quake.
Interactive
EXPLAIN
There are different faults based on the
relative movement of the blocks on either
side of the fault. The rocks on both sides of
a fault can move up or down or sideways.
Interactive
EXPLAIN
But before you understand these, you
should be able to determine first which
is the hanging wall and the foot wall of
the fault:
Interactive
A foot wall is a
block of crust that lies underneath
a fault plane.
A hanging wall is a block of crust
that is located above a fault
plane.
Its shape rests or hangs on the
foot wall.
Types of Faults
UNMOVED CRUST
Types of Faults
REVERSE FAULT
Reverse faults form when the hanging wall
moves up The forces creating reverse faults
are compressional, pushing the sides
together.
Types of Faults
NORMAL FAULT
Normal faults form when the hanging wall
drops down. The forces that create normal
faults are pulling the sides apart, or
extensional.
Types of Faults
STRIKE- SLIP FAULT
Strike-slip faults have walls that move
sideways, not up or down
ELABORATE
FRICTION ALONG FAULTS
Over many years, rocks on
the opposite side of the faults
move, but friction on fault locks it
and prevents slip.
How rocks move along a fault
depends on how much friction there
is between the opposite sides of the
fault.
ELABORATE
If you can recall from your
Physics lessons, Friction is the
force that opposes the motion
of one surface as it moves
across another surface.
Friction exists because
surfaces are not perfectly
smooth.
ELABORATE
Where friction along a fault is
low, rocks on both sides of the
fault slide by each other
without much sticking. Where
friction is moderate, the sides
of the fault jam together. Then
from time to time they jerk
free, producing small
earthquakes.
ELABORATE
Where friction is high, the
rocks lock together and do not
move. In this case, stress
increases until it is strong
enough to overcome the
friction force.
ELABORATE
Going back to the real scenario
given at the start of the lesson, here
in our country, the fault line that is
found in Cebu which resulted in a
7.3 magnitude earthquake is just
one example of a fault that may
have stored its energy for years,
until it breaks and resulted into a
strong vibration or earthquake
ELABORATE
Explore the online map made by
PHILVOCS that shows the
distribution of active faults in the
Philippines.
A. See if your location is near
along a fault line.
B. Identify at least 3 cities near
you that lie along a fault line.
EVALUATE
Multiple Choice: Click on the letter of the correct
answer.
1 1 It is a break in the earth’s crust where
significant movement occurred
A. Focus
B. Epicenter
C. Fault
Multiple Choice: Click on the letter of the correct
answer.
2 1 A vibration due to the rapid release of
energy is known as ___________.
A. Tidal wave
B. Earthquake
C. Focus
Multiple Choice: Click on the letter of the correct
answer.
Earthquakes are common in the Philippines
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3
because it is in an area called ______
A. Southeast Asia
B. Pacific ring of fire
C. Pacific ocean
Multiple Choice: Click on the letter of the correct
answer.
A block of rock that forms the upper half of a
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fault is called ______.
A. Friction
B. Foot wall
C. Hanging wall
Multiple Choice: Click on the letter of the correct
answer.
5 1 Which of the following shows a Normal fault?
A.
B.
C.
Write True if the statement is True, otherwise write
False.
1 1
San Andreas Fault is an example of transform
fault.
Write True if the statement is True, otherwise write
False.
2 1
Normal Fault is formed when the hanging
wall moves up.
Write True if the statement is True, otherwise write
False.
3 1
A foot wall is a block of crust that lies
underneath a fault plane.
Write True if the statement is True, otherwise write
False.
4 1
When fault moves, it causes earthquakes.
Write True if the statement is True, otherwise write
False.
5 1
Reverse faults have walls
sideways, not up or down
that
move