To the Teacher...

Some of the activities above can stand alone or be skipped without sacrificing lesson continuity. A few others recommend that students complete one or more prerequisite activities first. If the teacher has done some preview ahead of time, he or she can choose which activities or text material to use with a class. A teacher choosing only certain activities should simply preread the sections labeled To do this activity... beforehand. Or a teacher can simply let students browse through lessons on their own.

3. Student Seismosurfing Ideas

1) Find the location, date, and Richter magnitude of the 10 largest earthquakes that occurred in your state or province.
2) How many earthquakes (small or large) have occurred in your locality (county, district, etc.) during the past week? month? year? How large was each of these earthquakes?
3) Following the Loma Prieta quake of 1989, why do geologists expect another major quake to hit the Bay Area of California in the next few years? Which fault is it likely to strike?
4) What information on current earthquake prediction methods can you find on the Internet? Particularly look for information on radon gas, changes in seismic waves speed, and ground water changes. (U.S. Geological Survey may help.)

4. Guide to Activities

Activity: Building Your Own Seismograph

Overview:
Students are presented with two options:
1) Design, build, and demonstrate their own seismograph.
2) Use the given list of materials to build and demonstrate the seismograph shown in the diagram.

Suggestions:

In either option above, students will probably need a few hours outside of class to build the seismograph. The completed seismograph is crude in form, but depending on the care and attention of the student builder, it may be able to register small earthquakes, especially if some sort of motor is included to slowly rotate the adding machine paper roll. (For example, try attaching the second hand of an analog clock to the rotating can.) To get a good drawings, the can should be very smooth and hard, and the writing instrument should write easily under the weight of the brick but should not dry out or break too easily.
Note for the more ambitious student: The March 1995 issue of Science Teacher (page 48) has a more complex home-made seismograph that involves electronics and computer programming. The authorÕs eighth-grade class installed and continually operates it. Materials cost around $200.

Activity: Can You Read a Quake?

Overview:
Students will see simplified versions of eight seismograms from eight locations around the world. All eight seismograms were caused by the same earthquake, though the epicenter of this quake is not revealed (students discover it in the later activity Where Did It Hit?) Students will answer questions regarding these seismograms. Questions focus on identifying the three main types of seismic waves (P, S, and L), observing that not all cities received all three wave types, and beginning to hypothesize why some cities did not get all of the waves.

Suggestions:

Students will probably need help understanding the seismograms. Make sure they clearly understand these points:
1) All recorded waves for all eight locations came from one earthquake (the quake originated in the Asian side of the Pacific Ocean).
2) Although the seismic waves that created the zig-zag lines left the epicenter at exactly the same moment, they arrived at different times in different locations. Cities that were close to the epicenter received waves first; distant cities received waves last.
3) The first wave to arrive is always the Primary (P) wave, (unless the P wave is deflected and never arrives at all).
4) Each city started recording its seismogram at the exact moment the P wave first arrived there. Thus each city started recording at a time of day different from any of the other cities.
For example, if the quake began at 12:00 p.m., Tokyo received the first P waves at about 12:05 (and the first S waves at about 12:09), but Rio received these same P waves at about 12:20. (In this activity, students can determine for themselves which cities are nearest the epicenter.)
What should the student learn in this activity?
The earthquake created at least three types of waves:
1) A first wave (Primary, P) that hit suddenly but with only minor vibrations, and then slowly died out.
2) A second sudden set of small vibrations (Secondary, S) that slowly died out.
3) A final set of very large vibrations (Last, L) that pulsated by growing larger, then smaller, then larger, etc.

Students should also learn that some cities which are relatively near each other (compared to the size of the earth) receive very different waves. One city can receive P, S, and L waves, while a nearby city receives only L waves.

Encourage students to hypothesize why some waves do not show up at certain locations. This answer is found in the layers of the earthÕs interior, as students will find out if they complete Shadows from the Core. Something inside the earth is interfering with the waves that are trying to reach all part of the globe. (If students locate the cities on a map, they may speculate that the oceans cause the wave loss, since liquids always stop S waves. However, P and S waves travel easily through the rock underneath the oceans, and so the oceans are not the cause of the wave loss.)

Activity: Take a Classroom Survey: All Shaken Up.

Overview:
Students can enjoy gathering first hand accounts of peopleÕs experiences in an earthquake anywhere in the world by sending off this survey.

Suggestions:

Be prepared to help students make this survey usable, either by making them a hard paper copy, electronically copying the survey into a file that students can e-mail, or showing students how to do such copying themselves.

Two important considerations:
1) Most people around the world know a bit of English. However, donÕt assume that your survey recipients know English. If you know a local person who speaks another language, you might ask him/her to translate the survey into an appropriate language before you send it. You will get a much more interesting and candid response in the recipientÕs mother tongue.
2) Send your survey with graciousness and patience. Residents of an earthquake site may have many more important concerns on their minds than your survey.

There are many ways to use the survey:
1) Have students fill out the survey themselves before you send it out.
2) Assign to a group of students the task of sending out several mailings to known earthquake sites. Send out several to each site.

Activity: Race of the Waves

Overview:
Students will plot data from a sample earthquake centered in Washington, D.C. The points of this graph will follow two distinct curved lines; any quake on earth would reproduce roughly the same two lines. Students will learn how to use this completed graph and any simple seismogram to determine how far away from an epicenter a seismograph must have been.

Suggestions:

This activity can be done as a homework assignment if class time (especially computer time) is limited. Students will need a copy of the data table. On the other hand, if the teacher and/or students are familiar with a graphing tool on the computer (such as the chart tool in Microsoft Excel), the data can be very quickly plotted and displayed.

As with any graph, remind students to make the graph large and easy to read. They may find their completed graph useful in the later activity ÒWhere Did It Hit?Ó

The central point of this activity: If a distant earthquake occurs in an unknown location and you record an accurate seismogram of the waves you receive, you can determine how far away you were from the quakeÕs epicenter even if no one tells you. Here is how:
S waves usually take the same path deep through the earth that P waves take. Since P waves are faster than S waves, they generally arrive at a location before the S waves. For example, if a city is 3100 km away from an unknown epicenter, the P waves will arrive first, and then the S waves will arrive about 4.2 minutes after the P waves. The time delay is 4.2 minutes no matter in what direction the epicenter is located. For a city 6000 km away from the epicenter, the S waves are 7.5 minutes behind the P waves. A city 8000 km away will have a time delay of 9.5 minutes. Thus more distance = more travel time = more chance to fall behind = longer time delay between S and P waves.

So if a distant earthquake occurs in an unknown location and you have only one good seismogram and your Race of the Waves graph to help you, you can find your distance from the epicenter in two steps:
1) Determine on your seismogram precisely how many minutes the first S waves arrived after the first P wave arrived. This is the time delay for S and P waves.
2) By guess and check, study your graph to find the distance in kilometers that most closely matches your time delay. For example, if your time delay is 4.2 minutes, then the only distance on the graph that has a difference between the S curve and P curve is roughly 3100 km. This is your distance from the unknown epicenter.

Here is an easy method for step two above.
(Suppose again that your time delay is 4.2 minutes.) Lay a piece of scratch paper along side the vertical axis of your graph as if you were going to copy the time divisions (in minutes) onto the scratch paper. Then on the scratch paper draw a line at the graphÕs zero minute mark. Now make a second line on the scratch paper at the 4.2 minute mark. You have just drawn two lines that are 4.2 minutes apart. Making sure you continuously keep the scratch paper lined up vertically parallel with the graph, slide the scratch paper up the S-curve to find where your two drawn lines match up exactly with the S curve and P curve. When you find a perfect match, read directly down (vertically) to determine how many kilometers this 4.2 minute time delay represents. Remember to keep the scratch paper perfectly vertical when you use this method.

Activity: Where Did It Hit?

Suggested Materials:
Compass, ruler, map of the Pacific Ocean region (or world map)

Overview:
Students study three seismograms from three different seismic stations (Tokyo, Sydney, and Hawaii) to determine how far away from the epicenter each one is located. Then students plot these three cities on a map of the Pacific Ocean region, draw a circle around each city representing how far away the epicenter must be, and identify the point on the map where all three circles roughly intersect -- the epicenter.

Suggestions:

Students may need a lot of guidance on the questions of this activity, but the process of discovering the location of the epicenter can be interesting.

The first part of the activity is simply determining the distance from Tokyo, Sydney, and Hawaii to the actual epicenter of the unknown earthquake. (This is the same earthquake that created the seismograms in Can You Read a Quake?, so this activity refers back to the same seismograms.)

In this first part, students should confirm that Tokyo is roughly 3100 km away, and then they should determine that Sydney is roughly 4900 km away and Hawaii is roughly 8600 km away.

The second part of the activity is locating the epicenter on the map. Show students how to understand and use the kilometer (or mile) scale on the Pacific Ocean Map. One way is simply to measure the given map scale in centimeters and then use this measurement as a ratio. For example, if 1000 kilometers on the map is equivalent to 2 centimeters on the ruler, then Tokyo is...
If Map = 1000km, Ruler = 2.0 cm
If Map = 3100 km, Ruler = 6.2 cm
In this example, students would need to draw a circle of radius 6.2 cm around Tokyo. (These calculations are not explained in the activity.)

Students should repeat the same circle-drawing process for Sydney and Hawaii, being careful that in each case they use the seismogram specific to that city. (If Tokyo has a P to S time delay of 4.2 minutes and thus is 3100 km away from the epicenter, its circle on the example map is 6.2 cm in radius. Sydney would have a larger time delay and thus a larger distance and a larger circle.)

Once they have accurately drawn all three circles, most students will find that the three circles do not meet exactly in one point but rather form a small triangle. The epicenter is somewhere inside of this triangle -- near the Philippines.

Activity: Shadows from the Core

Overview:
Students are asked to hypothesize why some seismic waves disappear on their way through the interior of the earth. In the process of answering this question, they will step through a series of clues from seismic waves to determine and draw how the inside of the earth is layered.

Suggestions:

This lesson has several diagrams of the interior of the earth. Some of these diagrams are simple; others may need some helpful interpretation by the teacher. Until they reach the drawing exercise at the end of this activity, students will mostly be reading and studying diagrams.

The student drawings of the interior need not be complicated. They should simply show round (spherical) layering at the five specific depths shown in the P wave reflection diagram.

Perhaps the teacher can add to this exercise by having students color in each layer, identify which layers are solid, and then explain with their diagram why S waves have a shadow zone and why P waves have a shadow zone. The S waves are completely stopped at 2900 km by the molten iron/nickel outer core. The P waves that try to glance through the outer core at an angle are deflected toward the center of the earth at this depth and so they never arrive at the shadow zone region.

Activity: Prediction or Prevention

Overview:
Students are asked to consider some of the more difficult issues regarding predicting and preventing earthquakes.

Suggestions:

This activity can be assigned in several ways:
1) Individual students write their own responses to the issues presented.
2) An individual or a group of students is assigned one of the geologic teams and gives an oral presentation to the class.
3) The class is divided into four groups. Groups A and B debate the Prediction Team issue, and groups C and D debate the Prevention Team issues.

5. Resources

Alaska Earthquake, U.S. Geological Survey, 16 mm, 22 minutes
Earthquakes and Volcanoes. January Productions.
Earthquake Below, NASA, HQ248, 16 mm, 14 minutes
Earthquakes: Exploring EarthÕs Restless Crust. Encyclopedia Britannica Educational Corporation, 21 minutes.
Earthquakes, Lesson of a Disaster, EBE, 16 mm, color, 13 minutes
The San Andreas Fault. Encyclopedia Britannica Educational Corporation, 21 minutes.

Printed Materials:

Bolt, Bruce A. Earthquakes and Volcanoes. W. H. Freeman, 1980.
Brown, Billye Walker, and Walter R. Brown. Historical Catastrophes: Earthquakes. Reading, MA: Addison Wesley.
Brownlee, Shannon. ÒWaiting for the Big One.Ó Discover, July 1986.
Gere, James M. and Haresh C. Shah. Terra Non Firma: Understanding and Preparing for Earthquakes. San Francisco: Freeman, 1984.
Golden, Frederick. The Trembling Earth: Probing and Predicting Quakes. New York: Scribner, 1983.
Mogi, Kiyoo. Earthquake Prediction. Academic Press, 1985.
Science Teacher. March 1995 issue: seismograph
Scientific American. Earthquakes and Volcanoes, 11-article collection. San Francisco: Freeman, 1980.
Southern California Earthquake Preparedness Project. Earthquake Public Information Materials. County Plan Librarians, 1983.
Wood, Robert. Earthquakes and Volcanoes. Weidenfeld, 1987.

Agencies:

United States Geological Survey
Books and Open File Reports Map Distribution Center
Federal Center, Building 41 Federal Center, Building 41 Box 25425 Box 25286
Denver, Colorado 80225 Denver, Colorado 80225
California Division of Mines and Geology
California Earthquake Education Project (CALEEP)

Computer Software:

Earthquakes and Volcanoes. Intellectual Software. Apple and IBM. Quakes. MECC. Apple II+ and Apple IIe

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