Finding the Epicenter

Triangulation Method

by Romelyn Belmonte

Multiple Choice

The list below shows the summary of different steps in the triangulation method. Arrange them in the correct order.

I.Identify the intersection of the circles.

II.Convert the distance of the epicenter of the earthquake from the seismic station to the scale of the map.

III.Identify the distance of the epicenter of the earthquake from the seismic station to the scale of the map.

IV.Draw circles around the seismic station using the scaled distance as the radius.

• I, II, III, IV

• IV, III, II, I

• IV, I, III, II

• III, II, IV, I

Multiple Choice

The following materials and tools are necessary to locate the epicenter of an earthquake except one. Which is NOT a necessary material or tool?

• Data from the seismic stations.

• Map

• Compass

• Ruler

Multiple Choice

You have been quietly studying your lesson when suddenly, you felt that the ground is shaking. Being observant, you have watched the clock for the difference in the time of arrival of the P and S –waves. If the time difference you have observed is approximately 3 minutes, what will be your rough estimate of the earthquake’s epicenter distance from your location?

• 800 km

• 2400 km

• 1600 km

• Incomplete data

Multiple Choice

Which of the following BEST explains why it is necessary to identify the location of the earthquake’s epicenter?

• To distinguish the possible cause of the earthquake.

• To know if there will be a landslide.

• To identify the intensity of the earthquake.

• To avoid experiencing earthquakes again.

Multiple Choice

Your friend was a victim of a deadly earthquake. With that, she worked hard to be able to migrate to a place where there will be the least possibility of an earthquake occurring. The following countries are her options.  If she will ask for your advice, which of the following countries will you suggest to her?

• Indonesia

• France

• Cuba

• Australia

Triangulation Method

LOCATING THE EPICENTER OF AN EARTHQUAKE​

​Introduction

​The epicenter is the point on Earth's surface directly above an earthquake. Seismic stations detect earthquakes by the tracings made on seismographs. Tracings made at three separate seismic stations are needed to locate an earthquake epicenter.

​Objective

​To identify the location of an earthquake epicenter using a travel time graph and three seismograph tracings

​Materials

​a. Ruler

b. map

c. safety drawing compass

d. calculator

Procedure

1. Using the seismograms, determine the arrival time of the P-wave and S-waves for the Corvallis Oregon, Cathedral Carves Missouri, and Albuquerque, New mexico stations. Record the measurements in the data table.

Fill in the Blanks

What is the time of arrival of P waves in COR?

Fill in the Blanks

What is the time of arrival of S waves in COR?

Fill in the Blanks

What is the time of arrival of P waves in ANMO?

Fill in the Blanks

What is the time of arrival of S waves in ANMO?

Fill in the Blanks

What is the time of arrival of P waves in CCM?

Fill in the Blanks

What is the time of arrival of S waves in CCM?

Procedure

2.Once you have the measurements for P and S waves, calculate the difference by subtracting the P-wave arrival time from the S-wave arrival time. Record the measurements in the table..

Procedure

3. Using the difference in arrival time, determine the distance from the seismic station of the earthquake for each city. Record the distances.

​for COR

Fill in the Blanks

What is the distance of the earthquake epicenter from COR?

​for CCM

Fill in the Blanks

What is the distance of the earthquake epicenter from CCM?

​for ANMO

Fill in the Blanks

What is the distance of the earthquake epicenter from ANMO?

Procedure

4. Draw a circle around each station, using the distance of the earthquake as a radius.

Procedure

5. Find the point where all three of the circles intersect. That point is the estimated epicenter of the earthquake. Record the epicenter of the earthquake.

Poll

Were you able to get to the same epicenter?

• Yes

• No

• Did not finishd the activity

Open Ended

What were your difficulties in doing the activity?

Guide Questions​

​

Open Ended

1. Why would geologists need seismic data from three stations in order to calculate the epicenter of an earthquake? Why would they not be able to only use two stations?

Open Ended

2. Would you predict more earthquakes in areas where the Earth’s tectonic plates are moving towards each other or where the plates are moving apart? Explain your reasoning.

Open Ended

3. Seismologists and geologists are not the only scientists who interpret seismic data. What other professions would used seismic data? What could they use it for?