Scientists use data from at least three seismic stations collected at different locations to triangulate the epicenter of an earthquake. The time difference between the P and S waves recorded at each station is used to compute the distance from the station to the epicenter. Circles are drawn on a map centered at each station with radii equal to the computed distances. The intersection of the three circles identifies the epicenter location.

1. Scientists use triangulation to find the
epicenter of an earthquake. When seismic
data is collected from at least three
locations, it can be used to determine the
epicenter by where it intersects. Every
earthquake is recorded on
numerous seismographs located in different
directions.

2. FIND
THE

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

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

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

6. RECORD
-ING
STATION
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
TIMEDIFFERENCE
IN THE ARRIVAL
TIME OF P WAVE
AND SWAVE
(seconds)

7. 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)

8. 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

9. 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.

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 SP
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. Let’s check your
answers!