This document provides instructions for using the triangulation method to locate the epicenter of an earthquake using data from three seismic recording stations in the Philippines. Students are given hypothetical data on the arrival times of P and S waves and asked to compute distances, plot circles on a map, and determine where the circles intersect, which would indicate the epicenter. Questions assess the student's understanding of locating the epicenter and importance of determining earthquake epicenters.

1. ACTIVITY NO. 1
FIND THE CENTER

2. OBJECTIVE
Locate the epicenter of
an earthquake using the
triangulation method.

3. MATERIALS
• Hypothetical records of
earthquake waves
• Philippine map
• Drawing compass and
ruler

4. PROCEDURE
1. Study the data showing
the difference in the
arrival time of P-wave and
S-wave on three seismic
recording stations.

5. RECORD
-ING
STATION
TIME
DIFFERENCE
IN THE
ARRIVAL
TIME OF P-
WAVE AND
S-WAVE
(Seconds)
DISTANCE
OF
EPICENTER
FROM THE
STATION
(Km)
COMPUTED
DISTANCE
ON THE
MAP (Cm)
(1 cm : 70
km)
BATANGAS 44.8
PUERTO
PRINCESA
32
DAVAO 38.4

6. 2. Compute the distance of the epicenter
from each of the stations using the
formula:
d= Td x 100 km
8 seconds
Where: d = distance (km)
Td = time difference in the
arrival time of P-wave and
S-wave (seconds)

7. 3. Choose one of the recording
stations and measure the
computed distance on the
map scale ( the scale of the
map is 1 cm: 70 km). Set your
compass for that computed
distance.

8. 4. Center your compass on the
station you have chosen. Draw a
circle.
5. Repeat steps 3 and 4 for the
rest of the stations. You should
get three circles that intersect or
nearly intersect at a point. This
intersection is the epicenter.

9. C:UsersuserDocumentsDownloadsEarthqua
ke Epicenter Triangulation.mp4

10. 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?

11. Distance-Time Graph
0
5
10
15
20
25
30
0 2000 4000 6000 8000 10000
p
s

12. The distance-time graph shows that S-
P interval is about 10 minutes.
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?

13. RECORD
-ING
STATION
TIME
DIFFERENCE
IN THE
ARRIVAL TIME
OF P-WAVE
AND S-WAVE
(Seconds)
DISTANCE OF
EPICENTER
FROM THE
STATION (Km)
COMPUTED
DISTANCE ON
THE MAP (Cm)
(1 cm : 70 km)
BATANGAS 44.8 560 8
PUERTO
PRINCESA
32 400 5.7
DAVAO 38.4 480 6.9
LET’S CHECK YOUR ANSWERS

14. Let’s check your answers!
Q1. Since the three circles drawn
intersect in the sea near Negros, it is
where the epicenter is.
Q2. Assuming that the two circles will
intersect, the circle will intersect at two
points. Therefore, there will be two
locations that could possibly be the
epicenter.

15. Let’s check your answers!
Q3. 9, 000 km
Q4. Locating earthquake epicenters will
pinpoint which fault lines are active.
Usually, the less active fault line stores
great amount of potential energy that
could cause major earthquake once
released. Therefore, places near fault
lines that remain inactive for a long
period of time are due to experience a
major earthquake.