Research:

As rocks are deformed by tectonic movements, an enormous amount of energy is stored in the rock. During an earthquake, this energy is released and causes p and s wave vibrations to travel outward in all directions through the planet. The P ans S wave vibrations from earthquakes are recorded by seismographs.

A seismograph works by isolating a drawing device such as a pen from vibrations of the ground. This pen draws a line onto a moving surface that is not isolated from vibrations. The moving surface may be paper, photographic film or in computer memory. If the surface vibrates, the movements of the ground are drawn as zig-zags in the continuous line from the pen.

The seismograph record shows the exact time that the two types of waves reached the machine. The farther from the earthquake, the greater difference in arrival times because the P-wave moves faster than the S-wave.

This time lag between the arrival of the two waves indicates the distance to the epicenter of the earthquake.

Materials:
Seismograph record, spreadsheet program. Below is some data that you collected at seismograph station over several years. As a seismologist you noted the arrival times of P and S waves from many earthquakes, then when you found out later where and when the earthquake was, you noted the distance to that quake and how many minutes it took for the vibrations to reach your machine.

1. Make a graph that shows both a curve for the S-wave travel times and a curve for the P-wave travel times.

Excel Instructions: To do this on a computer,
1. First highlight the data below (include headings).
2. Then start your spreadsheet program, and click in A1 to set it as the upper left location for your data.
3. Then choose "Edit", then "Paste Special", choose "Text", and "OK". This should paste each number and word into its own cell.
4. If you graph the data now, you'll probably get garbage. You first have to put the data in an order that the computer can understand. Look at the data and see what the relationships are between the columns; does the value in each column increase with distance?
5. Highlight the data (numbers only) then choose "Data", then sort. Choose which column to sort by, then "OK". Check the results against the original data to make sure the proper times stayed with the right distances.
6. Now you can graph the data. Highlight the distances, p-wave travel times, and s-wave travel times.
7. Choose "Insert", then "Chart" (or click the chart button) then choose the appropriate graph. Follow the chart process, including adding proper data labels and titles with your name on the chart.
8. Note gap between travel times. Does it get larger with distance from the quake or smaller?
9. When you have a graph that can be used to find epicenter distances from the lag time between p and s-wave arrival times, print the chart to include in your lab report.

2. Determine the lag times for each earthquake, which is the difference in travel times. Make a graph for this to include in your lab report, and print the completed data table for your lab report.

3. The section of a seismogram below shows that a P-wave arrived at your seismograph at 14:58:20 and the S-wave at 15:03:20 :

1. Determine the distance to this quake using your graphs.
2. Describe how you did this.
3. Describe how you could determine the distance to the quake with only the two travel time graphs if you did not have the lag time graph.
4. Describe what other information you would need to determine the actual location of the quake.

Seismogram record:

Earthquake data:

Earthquake  Epicenter  S-wave       P-wave       Lag 
Number      Distance   Travel time  travel time  time
            (km)       (minutes)    (minutes)	

1	1500	6.18	3.38	       2.80
2	2500	8.90	5.03	
3	500	2.38	1.25	
4	2250	8.25	4.64	
5	7750	20.18	11.38	
6	7000	18.90	10.70	
7	8750	21.80	12.20	
8	4750	14.19	8.10	
9	4000	12.50	7.20	
10	7250	19.33	10.93	
11	9750	23.18	12.78	
12	10000	23.50	12.90	
13	3500	11.35	6.50	
14	5500	15.83	8.95	
15	5000	14.75	8.40
16	1750	6.89	3.81
17	6000	16.90	9.50
18	9000	22.20	12.40
19	1000	4.75	2.50
20	4500	13.63	7.80
21	250	1.19	0.63
22	7500	19.75	11.15
23	3250	10.78	6.15
24	750	3.56	1.88
25	2750	9.55	5.41
26	0	0.00	0.00
27	8000	20.60	11.60
28	9500	22.85	12.65
29	3000	10.20	5.80
30	1250	5.46	2.94
31	8500	21.40	12.00
32	5750	16.36	9.23
33	6250	17.40	9.80
34	9250	22.53	12.53
35	4250	13.06	7.50
36	6500	17.90	10.10
37	6750	18.40	10.40
38	3750	11.93	6.85
39	2000	7.60	4.25
40	5250	15.29	8.68
41	8250	21.00	11.80

Data Addenda: 2 graphs, completed data table.

Conclusion:

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