Epicenter Location Lab

Name______Date______Per_____ St#_____

Purpose:

1. Apply the relationship of P-wave (longitudinal wave) and S-wave (transverse or secondary wave) speeds to estimate the time of arrival of S waves at three seismic stations.

2. Apply the ratio of distance traveled to P-wave arrival time to estimate distances from three seismic stations.

3. Use the distances from the three seismic stations to triangulate the location of the epicenter.

Materials Needed:

Map, Data Sheet, Drawing compass with pencil

Special Instructions:

Since no measurement is exact, a “triangle of uncertainty” is where the epicenter lies. Draw the “triangle of uncertainty” described as that area inside all three circles.

Procedure:

1. Convert the arrival time of P waves to seconds. Record this time in the data sheet.

2. Since the P waves move at 6 km per second in this type of rock, multiply the number of seconds by 6. Record this as the distance from the epicenter using P wave arrival time from #1.

3. S waves move at half the speed of P waves and, therefore, take twice as long to get to each station. Double the arrival times (in seconds) and record in the appropriate Event Data column.

4. Convert the arrival time of the S wave to mixed units by dividing by 60. The remainder from the long division is the number of seconds.

5. To plot the earthquake epicenter on the map of the Lost Continent, the scale distance for the map must be calculated. Copy the “Distance from the Epicenter Using P-wave Time” from your own figures in the “Earthquake Event Data” chart below into the “Distances to be Plotted on the Map” data chart on the next page.

6. Divide the distance by 250 km per inch (100 km per cm, should be 254km/inch, but use 250) in order to find out what measurement on the map represents scale distance to the epicenter.

7. Set a drawing compass to the scale measurement and draw as much of a circle around each station as is possible given the size of the paper.

8. The point that all circles come together is the epicenter.

Earthquake Event Data

Seismic Station / P-wave Arrival Time (mixed units) / P-wave Arrival Time (seconds) / Distance from Epicenter Using P-wave Time (km) / S-wave Arrival Time (seconds) / S-wave Arrival Time (mixed units)
Hightown / 2 min., 29 sec. / 149 Sec
Beach City / 1 min., 24 sec. / 504km
Metropolis / 1 min., 57 sec. / 3 Min
54 Sec

Distances to be Plotted on the Map

Seismic Station / Distance from Epicenter Using P-wave Time / Distance Represented to Map Scale
Hightown
Beach City / (Hint: 5cm is
close)
Metropolis

Questions:

1.  Describe where the epicenter is in terms of the shape of the Lost Continent.

2.  How many seismic stations are necessary to plot the location of an epicenter?

3.  Did you know where the earthquake’s epicenter was after mapping the radius around one city? Why or why not?

  1. Could you have made a better determination of where the earthquake’s epicenter was after mapping the radius around two cities? Why or why not?
  2. After mapping the radius around three cities, how sure are you that you have located the earthquake’s epicenter?
  3. How does including more information help you to gain a better understanding of what is happening?
  4. What are some possible causes for inaccuracy in your triangulation? How could you eliminate or minimize these?
  5. Where is the focus in relationship to the epicenter in this lab/real life?
  6. Is the focus likely to be a small point, or a much larger zone? Explain your answer.
  7. Why is a circle normally drawn around each station?

Web Site Link: http://www.sciencecourseware.org/eec/earthquake/ - complete this activity and print the quiz score for 2 EC points (see my homepage for more info & directions).

Web Site Link for the EC on the Epicenter Location lab: http://www.sciencecourseware.org/eec/earthquake/ - complete this activity and print the quiz score for 2 EC points. Use your first name and last initial, plus your class period as your name. Click the "Demonstration" button to see what to do, then go through "Travel Time" and "Epicenter and Magnitude" lessons, and at some point, you get the quiz. Print the results page, with your name and class period on it, and give it to me by Tuesday, 20 Jan. you can also email the page to me, if you are tech savvy enough to do so.