Grade 8 Science

2. How does this affect us?

6. Magnitude 6.4
October 25, 2022
(Tuesday)

7. Do you know why do
earthquakes occur?
After going through this
module, you are expected to:
1. Describe what a fault is
using models or illustrations;
2. Explain how movements
along faults generate
earthquakes

8. -is an event of ground shaking usually
caused by the rapturing of fault within
Earth
- Most earthquakes occur at boundary.
-An earthquake occurs when movement
along fault zone results in a sudden
release of built up strain energy in the
lithosphere.

9. Why do Earthquakes
occur?
Earthquakes occur due to:
*Sudden formation of a new fault
(fracture on which sliding
occurs)
*Sudden slip on an existing fault
*Sudden change in the arrangement
of atoms in the minerals of rock
*Movement of magma in a volcano
*Giant landslides
*Meteorite impact
*Underground nuclear bomb tests

10. FAULT is a fracture or break in
Earth’s lithosphere along which block of
rock move past each other. Sudden
movements in faults cause earthquakes.

12. Activity 1. Where’s the Fault?
Carefully observe the figures below. Answer the questions that
follow and write your answer on separate sheet.

13. Figure 2A is the starting point. The two parallel
lines are there so that it is clear for you to observe the
events. Figure 2B, 2C and 2D shows how a crack forms in
the sand.

14. Q1. What is formed as the sand in Figure 2 moves in opposite direction?
Q2. What happens to the lines?
Q3. Compare what you see in the picture in Figure 1 and what you see in
the activity. Do you see anything similar?

15. Q1. What is formed as the sand in Figure 2 moves in opposite direction?
Q2. What happens to the lines?
Q3. Compare what you see in the picture in Figure 1 and what you see in
the activity. Do you see anything similar?

16. Q1. A crack “line” or break is formed
Q2. The lines are shifted or displaced
Q3. The cracks in figure 2 are similar to the break
across the road in figure 1.

17. An Earthquake occurs
somewhere on this planet
every 30 seconds, day after
day. Most of these are so weak
they go unnoticed without the
use of sensitive modern
instruments called
seismographs.

18. Seismograph

19. STRESS IN EARTH’S CRUST
STRESS
- is a force that squeezes
rocks together, stretches or
pulls them apart, or pushes
them in different directions.

20. *As tectonic plates move, they cause
stress in the crust, which in turn
produces faults and folds.

22. Why do earthquakes occur?
What is the relationship between
earthquakes and faults?

23. On July 16, 1990, a
strong earthquake hit
Luzon.
During that
earthquake, many people
lost their lives and many
more were injured.

24. - A lot of buildings and other
structures were either damaged or
destroyed.
-The earthquake had a magnitude
of 7.8 and its epicenter was
located in Nueva Ecija.
-According to scientists, the
earthquake was caused by
movement along the Philippine
Fault..

25. Seismologists are scientists
who study earth movement.
They work in seismographic
stations throughout the world.
When these stations detect
earth movement, they compare
their records of the time and
type of waves and, from that
information, determine the
epicenter of an earthquake.

26. The epicenter is the point on the
Earth’s surface directly above the
focus.

27. Fault
Epicenter
Magnitude

28. Earthquakes are
associated with
faults.

29. When a fault suddenly moves, an
earthquake occurs.

31. Normal fault is one in
which an upper block
of rock, separated by a
fault from a lower
block, moves
downward relative to
the lower block.
Normal faults occur
where tectonic plates
are moving apart,
such as in the Great
Rift Valley in Africa.

33. Reverse fault is one in
which an upper block of
rock slides over a lower
block which is
separated from it by the
fault. A low-angle
reverse fault is called a
thrust fault. An
example includes the
Himalaya Mountains
where the Indian Plate
is pushing into the
Eurasian Plate.

35. Strike-slip fault is a
fault along which
motion is mostly in a
horizontal direction.
This may cause roads
and river banks to
change their position.
The San Andreas
Fault in California is a
strike-slip fault.

38. Materials Needed:
• Two small boxes (fruit juice box, shoe box)
• Masking tape or scotch tape
• Rubber band or garter
• Paper clip
• Toy house or anything that is placed on the
top of the box

41. ENERGY from inside the Earth
make the ground move. There is no
movement right away because of the
FRICTION. Friction held the rocks
together. Once the friction is overcome,
the ground will move and the
earthquake will occur.

42. --- is the place where the first break
happens, where the fault starts to slip,
where first movement takes place. It is
the starting point of the earthquake.
--- is the spot directly above the focus
on the surface of the Earth.

44. An earthquake may be described in two ways:
1. Intensity
- effects on people or Surroundings
2. Magnitude
- energy released
*The intensity of an earthquake gives us an
idea of how strong or weak the shaking is.

47. Intensity and Magnitude
A measurement of an earthquake’s
intensity describes how much ground
motion was felt at a specific location. For a
single earthquake, the amount of ground
motion will be different at different
locations. Often, the highest intensity is
closest to the earthquake. You do not feel
earthquakes that are very far away, but that
doesn’t mean they are small! The intensity
at your location is just very low. Intensity is
measured based on what people felt and
what was damaged.

48. Intensity
Mercalli Intensity Scale defines the
intensity of an earthquake by the amount of
damage it does and how much shaking is felt. It
is denoted by roman numerals- I, II,III...XII.
-determined by observing the effects of
the earthquake in different places.
Houses, buildings, and other
structures are inspected.
People are interviewed about
-what they saw
-how they felt or
-what they did

49. 1. When an earthquake occurs, where would
shaking be greater? Near the epicenter or away
from the epicenter? Why?
2. Where would damage be more? Near the
epicenter or away from the epicenter? Why?
3. Based on your answers to Questions A and B,
where would the intensity be higher? Near the
epicenter or away from the epicenter?
4. Suppose an earthquake occurred in Luzon.
Would the intensity be the same all over the
Philippines? Why?

50. Obviously, the greater the
magnitude, the stronger the earthquake.
To distinguish the two, intensity is
expressed using Roman numerals (I, II,
III) while magnitude uses Hindu-arabic
numerals (2, 3, 4).
Earthquakes with a magnitude of 2
may or may not be felt. Those that are felt
by most people have a magnitude of 4.
Magnitude 6 quakes can lead to a lot of
damage in highly populated areas.

52. SEISMOGRAPH –
device that can detect
and record seismic
waves.
The record of an
earthquake on a
seismograph is
called
seismogram.

53. -- rates EQs
based on
measurement
of the times and
amplitudes of
seismic waves
by certain
seismograph.

54. -- gives measure of the amount of energy
released by an earthquake.

55. -- rates the effects of
earthquakes, which ranges
from 1- 12, is based on
observations of the
intensity of ground
shaking and damage in the
areas affected by an
earthquake.

56. DO YOU
LIVE NEAR
AN ACTIVE
FAULT?

57. It is one that has moved in the
past
and is expected to move again.
It has generated earthquakes
before and is capable of
causing more in the future.

61. But along some faults, the
effects may be dramatic. Suppose
a house was built on a fault. As
the ground shifts little by little,
parts of the house will be affected.
The floor will crack, doors will
not close, and the roof may start
to leak.

64. Earthquakes
and
Tsunamis

75. When a fault at the bottom of
the sea suddenly moves, the water
above it can be affected.
A sudden push from an
underwater fault can produce a
wave called a tsunami.

76. Unlike a wave that is formed
by the wind, a tsunami is so much
more powerful. Wind waves are
just sea-surface waves. In
comparison, a tsunami involves the
whole depth of the sea, from the
seafloor to the surface.

77. So, how are earthquakes related to
tsunamis?

78.  As an earthquake occurs, seismic waves
move out in all directions from the focus.
 The energy released during an
earthquake is carried by vibrations called
SEISMIC WAVES.
 As the rocks break and move, potential
energy is transformed into kinetic energy in
the form of seismic waves.

79. Mechanical vibrations that occur inside
the Earth (along fault lines) which is
caused by the breakage of rocks
Main Types
Surface
Waves
Body Waves
Sub - Types Sub - Types
Love Waves
Rayleigh
Waves
Primary
Waves
Secondary
Waves
-Travel along the
surface of the Earth
from the point
directly above the
epicenter
-travel only through
the lithosphere that
cause ripples on the
surface
-most damaging
type
-Travel along the free
surface of an elastic solid
such as the Earth
-their motion is a
combination of
longitudinal compression
and dilation that results in
an elliptical motion of
points on the surface
-spread out most in time,
producing a long wave
duration on seismographs
-Compressional Waves
-Longitudinal Waves
-The particles vibrate
parallel to the
direction where the
wave is travelling
-Can travel through
solids, liquids and gas
-Transverse Waves
-The particles
vibrate
perpendicular to
the direction
where the wave is
travelling
-Slower than P-
waves
-Can travel
through solids only

81.  fastest waves
 travel through solids, liquids, or gases
 compressional wave, material
movement is in the same direction as
wave movement

82.  slower than P waves
 travel through solids only
 shear waves – move material
perpendicular to wave movement

83.  Slowly than P
and S waves, but
usually produce
larger ground
movements and
greater damage.