Where Do Those Squiggles Come From?

This activity is designed to help students understand how a seismograph records the ground motion that accompanies an earthquake and other events that cause ground shaking.

Concepts and learning outcomes	Students will understand that: Seismographs are used to measure the movement of the Earth. An earthquake is the sudden slip at a fault. Earthquakes release energy in the form of seismic waves, which cause the ground to shake. The amplitude of the seismic wave recorded by a seismograph is related to the magnitude of the earthquake. The duration of an earthquake can be inferred from a seismogram. The arrival of P, S, and surface waves can be identified in a seismogram: the P wave arrives first, followed by the S wave, and then the surface wave.
Appropriate for	Grades 6-8
Time requirements	20 minutes in class, much more depending on which extensions you use.
Vocabulary	seismogram seismograph P wave S wave surface wave epicenter amplitude
Prerequisites	No prior knowledge needed
Background for teachers	This lesson contains ideas for introducing or reinforcing earthquake science using real events, and learning about some of the ways that scientists measure and study earthquakes. For information on: How do I read a seismogram What are seismic waves How a seismograph works

Materials / Preparation

Student worksheet (Pdf) with instructions and questions for the students
A long strip of paper (adding machine or cash register paper is ideal if you have it, but regular unlined paper will work if you tape together several sheets), pencils, ruler
Copies of a recent earthquake seismogram from the Rapid Earthquake Viewer - either save it as a PDF and make a copy for each group or show the REV website using an LCD projector. Directions are under the Procedures section below.
Pencil/pen for each student group
Thick book (to represent the Earth's surface) for each student group

Grouping

Groups of four

Teacher tips

If you want to do this lesson but no major earthquakes have recently been reported, you can use an archived one (see directions below). If you do not have computers in the classroom, access REV and print out the seismogram for students to review prior to doing the activity.

You will be using the Rapid Earthquake Viewer (REV) for this activity. If you want to become familiar with it (or have your students do so) before doing the activity, go through the Rapid Earthquake Viewer Tutorial.

Procedures

(Before class) How to print out seismograms:

Go to Rapid Earthquake Viewer (REV). On the left side is a list of the most recent earthquakes.
Click on the earthquake you want to explore. A new window will open which notes the location of the earthquake on a world map and displays seismic activity recorded at stations of varying distance from the earthquake.
Notice the colored triangles above the seismograms. These correspond to the stations listed at the bottom of the page. Click on a station between 2 and 10 degrees from the epicenter to access more detailed data for this station. Vertical, north-south, and east-west components of the movement recorded at that site will be shown. Note: Modern seismograph stations have three separate instruments, one to record motion in a north-south direction, another to record east-west motion, and one which records vertical ground motion.
If you plan to cover P waves and S waves with your students click on the “overlay estimated P/S wave arrival times” box. This will overlay flags that identify the approximate arrival of the P and S waves at this station. If the P and S waves are very close and hard to distinguish you might want to try a different station. Note: These flags are estimated by a computer model and may be a little off as the model assumes a “perfect Earth”, meaning that it does not take into account differences in materials within the structure of the Earth the waves are traveling through. These variations in material density can cause the actual travel times to be different than the computer model.
Click the “Save the seismogram as a PDF” button just below the seismogram. You can print this and give copies to the students, make an overhead, or just to have it as a quick reference to refer to when using the LCD projector. Note: If you plan to cover P and S waves you will need to hand-draw the flags showing the estimated time for P and S wave arrival times. Do this for your reference but make copies of the seismograms without these flags for students to use to do their own evaluation of the seismograms.

Introduction to lesson:

Did anyone hear about the earthquake in ____________? Show a newspaper headline, or online news clip etc., and ask students what they have heard about it.
How do scientists study earthquakes? Answers may include the use of seismographs or estimates of damage.
What type of technologies do scientists use to study earthquakes? Answers may include GPS, seismographs, tilt meters, or strainmeters.
What type of information can scientists gather by looking at a seismogram? Answers may include strength or magnitude, length of shaking, distance from the earthquake.
Hand out the preprinted copies of the seismograms or go to the REV website find the recent earthquake in the left side bar and click on it.
Explain that these are seismograms from the current earthquake. The class will try to recreate them with a simple hand-made seismograph.

Recreating the seismogram:

Hand out the student worksheet.
Place the strip of blank paper on a book.
Have one student hold the pencil stationary over the midpoint of the paper, a second student will push the book back and forth while the third student pulls the paper across the book, creating a record of this movement that is analogous to a seismogram. The fourth student records the time the “earthquake” lasted.
Allow for several trials to perfect the technique and produce a seismogram that is similar to the real one.

Note: See Extensions below for other approaches to this activity using free Macintosh software or a more complex manipulative.

Questions to think about while recreating the seismogram:

What is your “seismograph” recording?
What happens to the amplitude (size of the wave) when you increase the amount of energy (shaking)?
What other factors affect how the seismogram looks? Think of the tasks each of your teammates did to make the seismogram.

Discussion questions for after the activity:

What did you have to do in order to make your seismogram look similar to one for this earthquake?
Looking at the seismogram for the actual earthquake, how long did the shaking occur? Time is recorded in hours, minutes and seconds; HH.MM.SS. This can be determined by consulting the “Time since the earthquake” axis on the seismogram. How does this compare to the length of time the “earthquake” you created lasted?
Would the seismogram look different if the shaking lasted longer? The “squiggles” would last for a longer time as referenced by the “Time since the earthquake” axis.
What happens to the amplitude (size of the wave) when you increase the amount of energy (shaking)? Students should understand that they have to move the book more to create larger amplitudes on the seismogram, which is analogous to the Earth shaking more vigorously during this period of time.
To introduce P and S wave arrivals explain that earthquakes produce different types of seismic waves and that these can be identified in the seismograms. P and S waves are body waves that travel through the interior of the Earth (they do not travel on Earth’s surface). P waves travel faster than S waves and generally arrive at and are recorded on the seismograms first. S waves move slower and are more destructive since they move in an undulating fashion. Since S waves arrive later, they appear later on the seismogram and are usually seen as a second pulse. Have students view the following animations to see how the waves move through the Earth. They can also refer to the REV glossary for more information.

P wave animation
S wave animation
Surface or L wave animation, another type of seismicwave
Why are there three seismograms for each station? What do you think is meant by vertical, north-south, and east-west motion? The REV Glossary explains this under “Orientation” . Different instruments on the seismograph measure the three types (or components) of motion (vertical, north-south, east-west). Seismologists use this and other information to determine the general direction of the seismic wave source, the magnitude at its source, and the character of the wave motion. The following animation provides a visualization of this concept.
Have students consult How to Read a Seismogram and then examine the seismogram printed out or on-line to identify where these waves are recorded in the “squiggly line” or waveform. If you have time, students can view data from additional stations for this earthquake and practice identifying these two types of seismic waves.

Assessment

Optional.

Post magnitude and duration of shaking data for two earthquakes on the board. An example of this would be:

Earthquake #1: Magnitude 4.7, duration of shaking 30 seconds
Earthquake #2: Magnitude 9.1, duration of shaking 4 minutes

You can show real-world examples by looking in REV . Have students draw what the 2 different seismograms might look like if recorded at the same station. They should understand that Earthquake #1 would have a smaller amplitude and the movement recorded in the seismogram would be shorter in length (thus duration) than Earthquake #2.

Extra credit option: Draw what the seismogram would look like for a station that is farther away. Would the amplitude diminish? Answer: The time at which the P and S waves arrived would be later, and the amplitude would decrease. Duration becomes harder to assess at greater distances because of scattering of the signal.

Extension

Have students go through the Rapid Earthquake Viewer Tutorial to better understand how to interpret real-time earthquake data.
If you have a Macintosh laptop, you can download free software (SeisMac 2.0) to turn your laptop into a seismograph. Students can shake and impact the surface on which the laptop sits to observe and identify the different movement components of seismic waves (vertical, north-south, east-west). IRIS has developed activities that use this software. Go to IRIS lessons and look for one titled: SeisMac Activity.
See how to make a simple model of a seismometer out of ordinary materials or students can build their own seismograph using materials such as: ring stands and a variety of attachments, adding machine tape, tape, pens or markers, string, something for weight (coins, rubber stoppers, erasers, etc) paperclips, rubber bands.
To see a video that shows how a seismograph works. Click on View, then the Take a test drive button, click on View again and the video will launch.
Highway Seismograph This is an activity that students can do at home - actually, in the car. Students create a seismogram of the motion of the car as it moves down the road. The second part of the lesson involves measuring the amplitude of the motion recorded, conversion of units and using a logarithmic scale.
Students can simulate P and S waves.
Hear seismic waves converted into a sound which humans can hear. Click here to just listen to the sound!