: Click Play and wait for the vibrations to stop. Suppose you were at the recording station when the earthquake hit. Based on the pattern of waves on the seismogram, what did you experience during the earthquake? 4. Explore: Click Reset, and drag the recording station closer to the epicenter. Click Play.

A. How does this seismogram differ from the one you first investigated?
B. What would this earthquake feel like?

Activity B:

Distance to the epicenter Get the Gizmo ready:
● Click Reset.
● Place the recording station 300 km from the epicenter. (Does not have to be exact.)

Question: How can you determine how far you are from the center of an earthquake?

1. Observe: Click Play, and observe the P- and S-waves. Which waves are faster?

2. Measure: Wait until the seismogram is complete. Turn on Show time probe. Place the left (green) probe on the first P-wave, and the right (blue) probe on the first S-wave. (See example at right.)
What is the Time difference (∆t) between the P- and S-waves?

3. Predict: How do you think the time difference between the first P-wave and the first S-wave will change as the distance to the epicenter increases?

4. Gather data: Place the recording station at each of the following distances to the epicenter. (Does not need to be exact.) Measure the P- and S-wave time difference (∆t) on the seismogram at each distance, and record the values in the table on the left.

Distance (km) ∆t (s)
100
200
400
600
800
1000

5. Make a graph: Plot your data on the graph to the right of the data table. ✏️ Draw a line to connect the points in order. What does this graph show?

6. Draw conclusions: How does the time difference (∆t) between the first P-wave and the first S-wave relate to the distance to the epicenter?

7. Apply: Suppose a recording station was located 500 km from the epicenter.

What will be the time difference (∆t) between the first P-wave and the first S-wave? Check your answer using the Gizmo. Were you correct?
Anyone know these?

8. Practice: On each of the seismograms below, label ( ✏️) the first P-wave and the first S-wave. Estimate the time difference (∆t), and then use your graph to find the distance to the epicenter. (As in the Gizmo, each vertical line represents 50 seconds.)