Introduction:

Your task will be to locate the epicenter for the earthquake using the arrival time of P-waves and S-waves from several seismic stations. Upon completion of the virtual lab, you will write a laboratory report of your results.

Problem:

How can we use seismic waves to determine the epicenter of an earthquake?

Hypothesis:

Review the Introduction tab of the pre-lab within the lesson. Hypothesize how seismographs will be used to pinpoint the epicenter of the Earthquake.

Materials:

Use the reference image in the Reading Seismographs tab of the pre-lab to identify the S-P Time interval of a seismograph reading. Use the Determining Distance to an Epicenter tab and the Locating an Epicenter tab of the pre-lab as practice before completing the procedures below.

Procedures:

Examine the reference image under Materials to learn to identify the S-P time interval of a seismograph reading.

Under Data and Observations, determine the S-P time intervals of all three stations using the time scale under the seismograph readings. For example, if P wave arrives at 2:02 pm and the S wave arrives at 2:27 pm, the total S-P time interval is 25 minutes.

Record the time interval for each station in Table 1 under Data and Observations.

To determine the distance from each seismograph to the epicenter, you multiply the S-P time interval by 10. For example, if the time interval is 25 minutes, 25 x 10 = 250 kilometers.

Record the calculated distance to each station from the epicenter in Table 1 under Data and Observations.

Next, use the distance scale under Data and Observations to measure the three circles provided, each with a radius that equals the distance of each station. To measure, place the center of each circle at zero. An example measurement is shown below for a 75 km radius.

Place each of the measured circles around the station on the map that they represent. All three circles should have one intersecting point that matches the epicenter.

Complete the Questions and Conclusion section and Reflection Questions section of the lab report.

Variables:

For this investigation, list the independent, dependent, and controlled variables.

Data and Observations:

S-P Time Intervals

Table 1: Seismograph Data

Based on your results, were you able to locate the epicenter of this earthquake?

Station

S-P Interval Time (min)

Distance (km)

1

2

3

Distance Scale:Place each station on the map below to find the epicenter.

Station 1

Station 2

Station 3

Questions and Conclusion

Why are earthquakes monitored worldwide instead of in earthquake-prone areas only?

How many seismographs are needed to find the epicenter of an earthquake? Why is this number significant?

What is the relationship between S- and P-waves?

How did the study of earthquake waves lead to a greater understanding of the interior structure of Earth?

Not all earthquakes are felt by people; however, such earthquakes are often detected on seismographs. Why?

How did your hypotheses about the use of seismographs compare to your experimental results? Were you able to find the epicenter of the earthquake using this method?

If you were unsuccessful in locating the epicenter, describe how you could modify seismograph resources to find the epicenter successfully.

Reflection Questions

What are the necessary criteria for proper measurement of an epicenter location? Are there any limitations in this virtual lab that make finding the exact epicenter of an earthquake more difficult?

How will knowledge of an earthquake epicenter help emergency management teams make better earthquake response plans?

If seismographs showed a specific region as earthquake prone, what proposed solutions could lessen the damage of potential earthquakes? (Describe at least two.)

What are some costs and benefits of one of your proposed solutions?

What variables could you change in the virtual lab that would allow you to evaluate the strength of your solutions and any proposed emergency response plans?

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