Seismologists use triangulation to locate an earthquake's epicenter using data from at least three seismic stations. They determine the time difference between the arrival of P and S waves from each station. This time difference is used to calculate the distance from the station to the epicenter. Circles are drawn around each station marking this distance. Where the circles intersect is the epicenter location. Locating the epicenter helps determine which fault lines were active and increases understanding of hazards in the area.

6. Locating
the
Epicenter

8. 1. What is the exact location of the
epicenter on the surface of the Earth?
A. Beneath where the earthquake starts.
B. Directly above where the earthquake
starts.
C. Located at the center where the
earthquake starts.
D. Right beside where the earthquake starts

9. 2. What will be the starting point to be
traced to locate the epicenter of an
earthquake?
A. First P wave and the first S wave
B. Second P wave and the second S
wave
C. Third P wave and the third S wave
D. Fourth P wave and the fourth S wave

10. 3. The significance of locating an earthquake’s
epicenter is to ______________.
A. identify the fault that did not rupture
causing the earthquake.
B. increase the confidence in the hazard
exhibiting in the area.
C. locate the epicenter that can be used as
plate boundary.
D. lessen the confidence in the hazard
exhibiting in the area.

11. 4. What method do seismologists
use in locating an epicenter?
A. Focus Group Discussion
B. Interview
C. Observation
D. Triangulation

12. 5. Given the diagram below, where
does the epicenter occur?
A. 1 B. 2 C. 3 D. 4

13. Arrange the letters to form a word
related to the lesson. Write your
answers on you SCIENCE-EXCEL
I R I A N T N O L G U A T
T_ _ _ _ _ U L _ _ _ O N
1

14. Arrange the letters to form a word
related to the lesson. Write your
answers on you SCIENCE-EXCEL
C F S U O
_ _ _ U _
2

15. Arrange the letters to form a word
related to the lesson. Write your
answers on you SCIENCE-EXCEL
E N E I R P C T E
_ _ I _ _ _ _ E _
3

16. Arrange the letters to form a word
related to the lesson. Write your
answers on you SCIENCE-EXCEL
U T F L A
_ A _ _ _
4

17. Arrange the letters to form a word
related to the lesson. Write your
answers on you SCIENCE-EXCEL
A E A Q E R H K T U
_ _ _ _ _ _ _ A _ E
5

18. Location of an Epicenter

19. How to locate the earthquake
epicenter?
• Determine the time interval between
the arrival of the P and S waves (the S-
P interval) on the seismograms from at
least three different stations.

20. • The distance between the beginning of
the first P wave and the first S wave
tells you how many seconds the waves
are apart.
• Locating the epicenters will determine
which fault lines are active.

21. Seismologists can locate the epicenter of an
earthquake by using TRIANGULATION
METHOD.
When seismic data is collected from at least three
(3) different locations, it can be used to determine
the epicenter of an earthquake by where it
intersects. Hence, scientists need at least three
(3) seismic stations to clearly identify the location.

22. How to compute the distance of the epicenter from
each of the stations
Where: d = distance (km)
Td = time difference in the arrival time of P-
wave and S-wave (seconds)
This formula is suited because 8 seconds is the interval
between the times of arrival of the P-wave and S-wave at a
distance of 100 km.

23. Activity 1
Find the Center
Objective:
Locate the epicenter of an earthquake using the triangulation method.
Procedure:
1. Study the data showing the difference in the arrival time of P-wave
and S-wave on three seismic recording stations.

25. 2. Choose one of the recording stations and
measure the computed distance on the
map scale. Set your compass for that
computed distance.
3. Center your compass on the station you
have chosen. Draw a circle. You should
get three circles that intersect or nearly
intersect at a point. This intersection is the
epicenter.

28. Guided Questions
Q1. Where is the epicenter of this
hypothetical earthquake?
Q2. What difficulty will you encounter if you
only have data from two recording
stations?

29. In the previous activity, the hypothetical
earthquake happened locally, that is why
we use the formula stated in the
procedure.
But, if the earthquake took place at a far
greater distance, seismologists use the
DISTANCE-TIME GRAPH

31. Guided Questions
Q3. What is the distance of the epicenter
from the seismic station?
Q4. What do you think is the importance of
determining the epicenter of an
earthquake?

33. 1. What is the exact location of the
epicenter on the surface of the Earth?
A. Beneath where the earthquake starts.
B. Directly above where the earthquake
starts.
C. Located at the center where the
earthquake starts.
D. Right beside where the earthquake starts

34. 2. What will be the starting point to be
traced to locate the epicenter of an
earthquake?
A. First P wave and the first S wave
B. Second P wave and the second S
wave
C. Third P wave and the third S wave
D. Fourth P wave and the fourth S wave

35. 3. The significance of locating an earthquake’s
epicenter is to ______________.
A. identify the fault that did not rupture
causing the earthquake.
B. increase the confidence in the hazard
exhibiting in the area.
C. locate the epicenter that can be used as
plate boundary.
D. lessen the confidence in the hazard
exhibiting in the area.

36. 4. What method do seismologists
use in locating an epicenter?
A. Focus Group Discussion
B. Interview
C. Observation
D. Triangulation

37. 5. Given the diagram below, where
does the epicenter occur?
A. 1 B. 2 C. 3 D. 4

38. SEE YOU NEXT
TIME