WEEKLY LEARNING ACTIVITY SHEETS

Science 8, Quarter 2, Week 2A

Epicenter & Focus, and Intensity & Magnitude

Name: ____________________________________ Section: ____________________

Learning Objective

By the end of this science lesson, you shall enable to differentiate the:
a. epicenter of an earthquake from focus; and
b. intensity of an earthquake from its magnitude. (S8ES-IIa-15)

Time Allotment: 2 hours

Key Concepts

• Earthquakes start beneath Earth’s surface.

• The focus (also termed as hypocenter) of an earthquake is the point
underground where rocks first begin to move. Seismic waves travel
outward from the earthquake’s focus.
• The epicenter (EHP-ih-SEHN-tuhr) is the point on Earth’s surface
directly above the focus. Note that the prefix epi- comes from a Greek
word meaning “on top of.” Hence, an earthquake’s epicenter is directly
over its focus. Scientists name an earthquake after the city or
municipality that is closest to its epicenter.
• In general, if two earthquakes of equal strength have the same
epicenter, the one with the shallower focus causes more damage.
Seismic waves from a deep-focus earthquake lose more of their energy
as they travel farther up to Earth’s surface.

Figure 1. Seismic waves

spread out from the focus
of an earthquake. The
earthquake begins at the
focus. The epicenter is the
point on the surface
directly above the focus.

Source: meritnation

• An earthquake may be described in two ways: intensity and magnitude.

The intensity of an earthquake gives us an idea of how strong or weak
the shaking is. The effect of an earthquake on the Earth’s surface is
called the intensity. The intensity scale consists of a series of certain
key responses such as people awakening, movement of furniture,
damage to chimneys, and finally - total destruction.

KENNY JAMES A. CUBERO

Surigao del Norte National High School
kennyjames.cubero@deped.gov.ph | 0950-568-8010
 • The Philippine Institute of Volcanology and Seismology (PHIVOLCS)
uses the following scale to describe the intensity of earthquakes in the
Philippines. The lower numbers of the intensity scale generally deal
with the manner in which the earthquake is felt by people. The higher
numbers of the scale are based on observed structural damage.
Structural engineers usually contribute information for assigning
intensity values of VIII or above.

Intensity
Shaking Description/Damage
Scale

Perceptible to people under favorable

Scarcely circumstances. Delicately balanced objects are
I
Perceptible disturbed slightly. Still water in containers
oscillates slowly.

Felt by few individuals at rest indoors. Hanging

II Slightly Felt objects swing slightly. Still water in containers
oscillates noticeably.

Felt by many people indoors especially in upper

floors of buildings. Vibration is felt like one
passing of a light truck. Dizziness and nausea are
III Weak
experienced by some people. Hanging objects
swing moderately. Still water in containers
oscillates moderately.

Felt generally by people indoors and by some

people outdoors. Light sleepers are awakened.
Vibration is felt like a passing of a heavy truck.
Hanging objects swing considerably. Dinner,
Moderately plates, glasses, windows and doors rattle. Floors
IV
Strong and walls of wood framed buildings creak.
Standing motor cars may rock slightly. Liquids in
containers are slightly disturbed. Water in
containers oscillate strongly. Rumbling sound
may sometimes be heard.

Generally felt by most people indoors and

outdoors. Many sleeping people are awakened.
Some are frightened, some run outdoors. Strong
shaking and rocking felt throughout building.
Hanging objects swing violently. Dining utensils
V Strong
clatter and clink; some are broken. Small, light
and unstable objects may fall or overturn.
Liquids spill from filled open containers.
Standing vehicles rock noticeably. Shaking of
leaves and twigs of trees are noticeable.

VI Very Strong Many people are frightened; many run outdoors.

Some people lose their balance. motorists feel like
KENNY JAMES A. CUBERO
Surigao del Norte National High School
kennyjames.cubero@deped.gov.ph | 0950-568-8010
 driving in flat tires. Heavy objects or furniture
move or may be shifted. Small church bells may
ring. Wall plaster may crack. Very old or poorly
built houses and man-made structures are
slightly damaged though well-built structures are
not affected. Limited rockfalls and rolling
boulders occur in hilly to mountainous areas and
escarpments. Trees are noticeably shaken.

Most people are frightened and run outdoors.

People find it difficult to stand in upper floors.
Heavy objects and furniture overturn or topple.
Big church bells may ring. Old or poorly-built
structures suffer considerably damage. Some
well-built structures are slightly damaged. Some
VII Destructive cracks may appear on dikes, fish ponds, road
surface, or concrete hollow block walls. Limited
liquefaction, lateral spreading and landslides are
observed. Trees are shaken strongly.
(Liquefaction is a process by which loose
saturated sand lose strength during an
earthquake and behave like liquid).

People are panicky. People find it difficult to

stand even outdoors. Many well-built buildings
are considerably damaged. Concrete dikes and
foundation of bridges are destroyed by ground
settling or toppling. Railway tracks are bent or
broken. Tombstones may be displaced, twisted or
overturned. Utility posts, towers and monuments
mat tilt or topple. Water and sewer pipes may be
Very
VIII bent, twisted or broken. Liquefaction and lateral
Destructive
spreading cause man-made structure to sink, tilt
or topple. Numerous landslides and rockfalls
occur in mountainous and hilly areas. Boulders
are thrown out from their positions particularly
near the epicenter. Fissures and faults rapture
may be observed. Trees are violently shaken.
Water splash or stop over dikes or banks of
rivers.

People are forcibly thrown to ground. Many cry

and shake with fear. Most buildings are totally
damaged. bridges and elevated concrete
IX Devastating structures are toppled or destroyed. Numerous
utility posts, towers and monument are tilted,
toppled or broken. Water sewer pipes are bent,
twisted or broken. Landslides and liquefaction
with lateral spreadings and sandboils are

KENNY JAMES A. CUBERO

Surigao del Norte National High School
kennyjames.cubero@deped.gov.ph | 0950-568-8010
 widespread. the ground is distorted into
undulations. Trees are shaken very violently with
some toppled or broken. Boulders are commonly
thrown out. River water splashes violently on
slops over dikes and banks.

Practically all man-made structures are

destroyed. Massive landslides and liquefaction,
large scale subsidence and uplifting of land forms
Completely
X and many ground fissures are observed. Changes
Devastating
in river courses and destructive seiches in large
lakes occur. Many trees are toppled, broken and
uprooted.

Table 1. PHIVOLCS Earthquake Intensity Scale

Source: Philippine Institute of Volcanology and Seismology

• The intensity of an earthquake is determined by observing the effects

of the earthquake in different places. Houses, buildings, and other
structures are inspected.
• Another way of describing the strength of an earthquake is by
magnitude. Recall that as rocks bend along a fault, energy is stored
little by little. When the rocks suddenly snap, the stored energy is
released. The released energy can be calculated by scientists and is
called the magnitude of an earthquake. Obviously, the greater the
magnitude, the stronger the earthquake is.
• The Richter magnitude scale, also known as the local magnitude (M)
scale, assigns a number to quantify the amount of seismic energy
released by an earthquake. It is a base-10 logarithmic scale.

Richter
Description Earthquake Effect
Magnitude

<2.0 Micro Micro earthquakes, not felt

2.0-2.9 Minor Generally not felt, but recorded

3.0-3.9 Minor Often felt, but rarely causes damage

Noticeable shaking of indoor items,

4.0-4.9 Light rattling noises. Significant damage
unlikely

Can cause major damage to poorly

constructed buildings over small regions.
5.0-5.9 Moderate
At most slight damage to well-designed
buildings

Can be destructive in areas up to about

6.0-6.9 Strong 160 kilometers (100 miles) across in
populated areas

KENNY JAMES A. CUBERO

Surigao del Norte National High School
kennyjames.cubero@deped.gov.ph | 0950-568-8010
 Can cause serious damage over larger
7.0-7.9 Major
areas

Can cause serious damage in areas

8.0-8.9 Great
several hundred miles across

Devastating in areas several thousand

9.0-9.9 Great
miles across

10.0+ Epic Never recorded

Table 2. Richter Magnitude Scale

Source: GNS Science, Te Pū Ao

• 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. Earthquakes with a
magnitude of 7 can cause severe damage. A magnitude 8 or 9 quake
results in widespread destruction, especially near the epicenter.
Luckily, only one or two occur every year.
• The instrument used to record earthquakes is called a seismograph.
The first seismographs were designed by British scientists working in
Japan between 1880 and 1890. The most famous of these early
seismographs was a horizontal pendulum model built by John Milne.
Pendulum seismographs rely on a simple principle of physics, the
principle of inertia. A heavy weight that is allowed to move freely will
tend to remain in its original position when the ground beneath it
begins to move in response to earthquakes waves.

Figure 2. Basic
Seismograph. A
seismograph is an
instrument which is used
to measure the strength,
direction, and duration of
an earthquake, volcano
eruption, explosion, etc.

Source: AZO Sensors

• Mechanical or electrical devices can be used to sense the motion of the

ground relative to the heavy pendulum of the seismograph.
Up-and-down or sideways ground motion sends a mechanical or
electrical signal to a pen attached to a paper-covered drum. As the
drum turns, the pen wiggles, producing an amplified recording of the
ground motion. This recording is called a seismogram. Scientists use
the amplitudes of earthquake waves recorded as seismograms to
determine the magnitude ratings of earthquakes.

KENNY JAMES A. CUBERO

Surigao del Norte National High School
kennyjames.cubero@deped.gov.ph | 0950-568-8010
Activity 1. Multiple-Choice Questions

What you need: pen and paper

What to do: Choose the letter of the best answer. Write your answers on a
separate sheet of paper.
1. What refers to the point on Earth’s surface directly above the origin of an
earthquake?
A. Focus
B. Intensity
C. Epicenter
D. Magnitude

2. When the rocks suddenly snap, the stored energy is released. What does the
given scenario pertain to?
A. Focus
B. Intensity
C. Epicenter
D. Magnitude
3. An earthquake jolted 17 km northeast of Z City. During the interview by a
local reporter, a resident there described the disaster where vibration was felt
like a passing of a heavy truck. In relation to the scenario, what was the
intensity value of the quake?
A. II
B. IV
C. VI
A. VIII
4. Maria, a registered geologist, has been working at PHIVOLCS for 28 years.
Just right after a strong quake measuring 7 on the Richter scale jolted X
province, her team was then delegated by the department to give an official
name for the earthquake. In what way did the team of Maria name the quake?
A. They named the earthquake after the city/municipality that was closest
to its focus.
B. They named the earthquake after the city/municipality that was closest
to its epicenter.
C. They named the earthquake after the person that was closest to its
focus.
D. They named the earthquake after the person that was closest to its
epicenter.
5. During their earth science class, Juana and Enzo were tasked by their
teacher to correctly describe the strength generated by most earthquakes.
Which would be the statement to be set out by the said students?
A. If two earthquakes of equal strength have the same epicenter, the one
with the shallower focus causes less damage.
B. If two earthquakes of equal strength have the same epicenter, the
one with the deeper focus causes less damage.
C. If two earthquakes of equal strength have the same epicenter, the one
with the shallower focus causes less damage.

KENNY JAMES A. CUBERO

Surigao del Norte National High School
kennyjames.cubero@deped.gov.ph | 0950-568-8010
 D. If two earthquakes of equal strength have different epicenters, the one
with the shallower focus causes less damage.
Activity 2. True or False

What you need: pen and paper

What to do:

1. In the table displayed below, check (✓) column 2 if the statement(s)

is/are true.
2. Mark wrong (✗) in column 3 if the statement(s) is/are false, and then
rewrite or rephrase to make it/them true.
3. Copy and answer on a separate sheet of paper.

Statement True False

1. Seismic waves travel outward from the

earthquake’s focus.
2. Based on the Richter magnitude scale,
magnitude 5.6 is a light earthquake.
3. Intensity I may be bent, twisted or broken
water and sewer pipes.
4. Seismograph is the instrument used to
record earthquakes.
5. A magnitude-13 earthquake struck
Antartica in the late 19 century.
th

Activity 3. Matching Type

What you need: pen and paper

What to do: Match Column A with the correct answer in column B. Choose
the letter of teh best answer. Copy and on a separate sheet of paper.
Column A Column B
(Magnitude/Intensity Value) (Damage/Effect)
A. Felt by many people indoors especially in
______ 1. Magnitude 9.4
upper floors of buildings
B. Can be destructive in areas up to about 160
______ 2. Intensity III kilometers (100 miles) across in populated
areas

C. Standing motor cars may rock slightly and

______ 3. Intensity X
liquids in containers are slightly disturbed.

D. Massive landslides and liquefaction, large

______ 4. Magnitude 6.8 scale subsidence and uplifting of land forms
and many ground fissures are observed.

KENNY JAMES A. CUBERO

Surigao del Norte National High School
kennyjames.cubero@deped.gov.ph | 0950-568-8010
______ 5. Intensity IV E. Devastating in areas several thousand miles
across

F. Can cause serious damage in areas several

hundred miles across

Guiding Questions:
Q1. What practical applications why scientists want to measure how
strong an earthquake is?

Q2. What is perhaps the benefit of using or depending on an “intensity”

scale for earthquakes, instead of a “magnitude” scale?

Activity 4. Essay
What you need: pen and paper

What to do: Explain with a strong, supporting statement. Before you begin
writing, read the questions carefully and plan what you will say. Your essay
should be as well organized and as carefully written as you can make it. Note
that your output for this activity is rated against the given rubric. Write your
5-sentence answer on a separate sheet of paper.
1. What is the difference between focus and epicenter? What makes them
distinct from each other?

___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
2. Discuss at least three (3) differences between magnitude and intensity.
What are their unique properties?

___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
Reflection

What is your most memorable earthquake experience? How did you

overcome it? And, what life-lesson have you learned from that experience?
Write your 5-sentence answer on a separate sheet of paper.

Rubric for Essay and Reflection

KENNY JAMES A. CUBERO

Surigao del Norte National High School
kennyjames.cubero@deped.gov.ph | 0950-568-8010
 Name: _______________________________________ Section: ________________

Category Excellent (15) Very Good (10) Average (5) Score

Practical application Practical application is Practical application
is scientifically scientifically explained is explained
explained consistent consistent to the consistent to the
Content
to the concepts, and concepts, but with concepts, but with
has no minimal misconceptions.
misconception. misconception.
The organization Words are mostly Sentences within
enhances and organized, in order, paragraph make
Organization showcases the and makes sense to the sense, but the order
central idea or theme reader. of paragraphs does
not.
All sentences are Most sentences are Sentences sound
well-constructed and well-constructed, but awkward, are
have varied structure they have a similar distractingly
and length. The structure and/or repetitive, or are
leaner makes no length. The learner difficult to
Spelling and errors in grammar, makes several errors in understand. The
Grammar mechanics, and/or grammar, mechanics, learner makes
spelling. and/or spelling that numerous errors in
interfere with grammar,
understanding. mechanics, and/or
spelling that interfere
with understanding.
TOTAL

Comments:
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________

References for Learners

Books

Department of Education, Science 8 Learner’s Module: Earth and Space, 1st

ed. (Vibal Publishing House, Inc., 2013), 125-130.
McDougal Littell, McDougal Littell Science Grade 8: Unit 2: The Changing Earth,
South Carolina ed. (Houghton Mifflin Company, 2007), 228.

KENNY JAMES A. CUBERO

Surigao del Norte National High School
kennyjames.cubero@deped.gov.ph | 0950-568-8010
Websites
Philippine Institute of Volcanology and Seismology. “PHIVOLCS Earthquake
Intensity Scale (PEIS).” phivolcs.dost.gov.ph.
https://www.phivolcs.dost.gov.ph/index.php/earthquake/earthquake-in
tensity-scale (accessed November 6, 2020).

GNS Science, Te Pū Ao. “What is the Richter Magnitude Scale?” gns.cri.nz.

https://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/
Monitoring-Earthquakes/Other-earthquake-questions/What-is-the-Richt
er-Magnitude-Scale (accessed November 6, 2020).

Image Credits
Fig. 1. Jain, Purya. Difference between epicenter and focus. Meritnation.
Accessed November 6, 2020.
https://s3mn.mnimgs.com/img/shared/content_ck_images/images/Epi
cen tre%20and%20focus(1).jpg
Fig. 2. Kaur, Kalwinder. Application of Seismometers in the Measurement of
Earthquakes. AZO Sensors. Accessed November 6, 2020.
https://www.azosensors.com/images/Article_Images/ImageForArticle_7(
2).jpg

Answer Key
5. B
4. B
3. B
2. D
1. C

Activity 1. Multiple-Choice Questions

KENNY JAMES A. CUBERO

Surigao del Norte National High School
kennyjames.cubero@deped.gov.ph | 0950-568-8010
 kennyjames.cubero@deped.gov.ph | 0950-568-8010
Surigao del Norte National High School
KENNY JAMES A. CUBERO
Activity 4. Essay
1. Answers may vary. Sample answer: The focus is the actual point of rock breakage or
movement. the focus is usually located far below the surface of the Earth. The epicenter is
the point on the surface of the Earth directly above the focus.
2. Answers may vary. Sample answer: Intensity is the severity of earthquake shaking is
assessed using a descriptive scale – the Modified Mercalli Intensity Scale. While in
magnitude, earthquake size is a quantitative measure of the size of the earthquake at its
source. The Richter Magnitude Scale measures the amount of seismic energy released by
an earthquake.
Activity 3. Matching Type
1. E
2. A
3. D
4. B
5. C
Guiding Questions:
Q1. Answers may vary. Sample answer: So they can help make buildings, roads, bridges,
etc., strong enough to survive earthquakes of varying strengths.
Q2. Answers may vary.
Sample answers:
(A) Intensity scale is laid out in a detailed discussion wherein clear representation of the
earthquake is being emphasized.
(B) Since earthquake energy dissipates with distance from the epicenter, the intensity of
the earthquake also dissipates. Therefore, on a map of intensities, one may locate the
approximate epicenter of the earthquake at the most intense place.
Activity 2. True or False
Statement True False
1. Seismic waves travel outward from the
earthquake’s focus.
✓
2. Based on the Richter magnitude scale, ✗
magnitude 5.6 is a light earthquake.
3. Intensity I may be bent, twisted or broken water ✗
and sewer pipes.
4. Seismograph is the instrument used to record
earthquakes.
✓
5. A magnitude-13 earthquake struck Antartica in ✗
the late 19th century.
2. False. Based on the Richter magnitude scale, magnitude 5.6 is a moderate earthquake.
3. False. Intensity VIII may be bent, twisted or broken water and sewer pipes.
5. False. Earthquakes of magnitude 10 or larger cannot happen. No fault long enough to
generate a magnitude 10 earthquake is known to exist, and if it did, it would extend around
most of the planet.