EQ-14: Seismograph Accessories
Materials List
Tupperware:
wooden rulers (7)
compasses w/ pencils (11)
Baggie:
Extra pens and paper rolls for EQ 15 - Seismograph
Jumprope
Laminated seismograph reading (large)
Slinkies (2)
Pendulum, lead ball on string
Directions to change roll of paper (on machine, and separate)
Baggies of popcorn to show magnitudes (4)
Books: 1) Susan van Rose
2) USGS (2)
3) Northridge
copies of Fig 3 SF Bay Area map (one per child)
copies of Fig 2 graph (if doing all steps with class)
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Seismograph
EQ 14-15
page 1
SEISMOGRAPH
EQ – 14-15
Source: Bobbie Callison/Tony Kramer
Objectives:
Understand how a seismograph records energy waves as they travel through the earth.
Locate the epicenter of an earthquake from seismographic readings.
Science Themes:
Energy
Patterns of change
Scale and structure
Systems and interactions
Process Skills:
Observing
Inferring
Applying
Communicating
Grade Levels:
5–8
New Words:
Seismograph, primary (P) and secondary (S) waves, Richter and Mercalli scales,
magnitude, amplitude, epicenter, focus
Background information:
Introduce this station using basic information from "The Inside Story" (in script notebook).
Earthquake damage can be assessed by two different methods, magnitude and intensity.
Magnitude is determined by the energy released from shock waves traveling through the
earth. Charles Richter of Cal Tech invented the Richter scale for measuring the amount of
energy released from seismograph readings. It indicates the strength or power of an
earthquake on a logarithmic scale ranging from 1 to 10. Intensity is a measure of the local
effects of an earthquake obtained from reports or observed effects on structures. The
Mercalli Scale is used to represent intensity, and is based on a Roman numeral scale from I
to XII; it measures the magnitude of damage.
The focus of an earthquake is below the surface of the earth where rocks first fracture due
to increased pressure. The epicenter is the place on the earth's surface directly above the
focus. Waves of energy radiate out from the focus which can be recorded on a
seismograph. There are three wave types, primary (P), secondary (S), and surface( L)
waves. The P and S waves travel through the earth's interior while the L waves travel on
the surface of the earth. There are differences in wave action and impact on rock material.
The P wave or compression (hard snap) wave is first, followed by an undulating S wave.
Primary waves travel about 1.7 times faster than secondary waves (different rock types
may alter the velocity). The epicenter of an earthquake is determined by measuring the
time difference between the arrival of the first P wave and the first S wave at a seismograph
station.
Primary waves travel through all types of matter, solid or liquid, pushing material in the
direction of the wave's path. A slinky can be used to demonstrate the P waves. These
waves can change the volume and shape of the material they pass through.
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Seismograph
EQ 14-15
page 2
Secondary waves shake particles at right angles to the secondary waves; they only change
the shape of the materials. A rope can be used to demonstrate S waves. Fluids will resist
change in shape, so S waves can not pass through fluids such as the inner cor e of the earth.
Slinky toy demonstrates P waves
Rope demonstrates S waves
One way to describe P and S waves to children is to have them relate the waves to thunder
and lightening, making sure they understand that the sound is traveling through a
different media (air). The P wave represents lightening that is seen while thunder
represents the S wave. Lightening is seen first, followed by the sound of thunder.
The epicenter of the earthquake can be determined by establishing the time intervals
between the arrival of the first P wave and the arrival of the first S wave at three different
recording stations.
The L wave is the surface wave that travels along the ground's surface, causing it to swell
like ocean waves. Surface waves can also travel from side to side. These cause most of the
structural damage to buildings. Surface waves retain a higher amplitude for a longer
period because they are confined to a narrower area than are primary or secondary waves.
Students can determine the epicenter of an earthquake from actual seismograph readings
which are on the next page – directions are included. Or a master copy of this exercise can
be left with the teacher to be completed later.
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Seismograph
EQ 14-15
page 3
Activities:
Demonstrating Energy Waves
Energy moves through waves. P (pounding or percussion) waves can be illustrated by
putting an ear to the table while pounding the table. S waves (snaky) are slower. Or use the
Slinky to show both types of waves. Have one student hang on to the end of the Slinky
while you move the other end to produce the desired type of wave. Show the P wave by
making one hard snap and an S wave by slowly undulating the Slinky.
Making Your Own Seismogram
Let each child make his/her energy waves using the seismograph in the following manner.
One student pulls the paper tape slowly and evenly while you or another student holds the
pen in the correct position so that it records on the paper. Make a P wave by pounding on
the table -"hen-peck line." Make an S wave by pushing the table back and forth.
Locating the Epicenter of an Earthquake Using S and P waves
There are two ways to approach this activity, the long form or the short form. The long
form is explained in detail in the following paragraphs and will take the students about
fifteen to twenty minutes to complete, requiring use of a compass and graphing.
Emphasize the importance of taking accurate measurements and why certain professions
strive for perfection with measurements. To use the short form, you as the teacher, do steps
1, 2 and 3 ahead of time so that the compasses are preset for students to locate the epicenter
as described in Step 4. In this procedure students still get the idea as to how the epicenter
is determined, but math skills are not emphasized.
Steps
1. Observe Figure 1, indicating three seismographs of the same earthquake that occurred
in the Bay Area on March 1958. Each seismograph was taken from a different station,
Palo Alto, San Francisco and Lick Observatory. The beginning of the S and P waves
are marked on each recording. Each seismograph is scaled so that 1 millimeter
represents 1 second.
2. Take a millimeter ruler and measure the distance between the P and S waves in Figure
1 on each seismograph recording. You can place your ruler above the graph lines for
easier reading. Record your data:
(a) San Francisco Station 5 mm or 5 seconds.
(b) Lick Station 6 mm or 6 seconds.
(c) Palo Alto Station 5 mm or 5 seconds.
3. Using the graph in Figure 2, plot the above data in seconds on the S-P black line,
making a small dot for each reading. Determine the number of kilometers
represented by each dot.
(a) San Francisco Station____________kilometers from the focus to this station
(b) Lick Observatory ____________kilometers from the focus to this station
(c) Palo Alto Station____________kilometers from the focus to this station
Environmental Volunteers
Seismograph
EQ 14-15
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4. Using the map in Figure 3, determine the epicenter of this earthquake.
Starting with the San Francisco Station, place your compass point on the zero on the
map scale, measure out the number of kilometers you calculated in Step 3. Take your
compass and place the compass point on the dot for the San Francisco Station. With
the pencil end of the compass, draw a circle around this station. Repeat this
procedure for Lick and then the Palo Alto stations.
5. Find the place where all three circles intersect. This is the epicenter of the earthquake.
If the lines do not perfectly intersect, it means measurements were not 100% accurate.
Use the closest area of intersection as the epicenter. Why is it important to have
accurate measurements? Why might the original data be inaccurate?
SEISMOGRAPH READINGS
SAN FRANCISCO STATION
LICK OBSERVATORY
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PALO ALTO STATION
Seismograph
EQ 14-15
page 5
Figure 1
Note: 1 millimeter = 1 second
Class discussion
Was the epicenter on or near an active fault______
If yes, which fault__________
?
?
Can you estimate the extent of damage from this earthquake?
How large an area would feel this earthquake?
Some Things to Ponder:
1. What type information does a seismograph tell you about an earthquake?
Ans: Power of an earthquake, how long the earthquake lasted, and location of the quake.
2. Who invented a scale to measure the magnitude of an earthquake?
Ans: Dr. Charles Richter of the California Institute of Technology
3. How much stronger is a magnitude 7 earthquake than a magnitude 6 earthquake?
Ans: Wave amplitude (height) is 10 times stronger but energy released is 31 times greater (not
measurable).
4. Does a seismograph reading indicate damage caused by an earthquake?
Ans: No, a Mercalli scale is used for that information
5. Can a P wave travel through the core of the earth?
Ans: Yes, but an S wave cannot.
6. Figure out the strength (wave amplitude) on a logarithmic scale of an earthquake with
a magnitude 3.
Ans: 10x 10x 10x = 1000
7. Now compute the strength of a magnitude 5 earthquake.
Ans: 10x 10x 10x 10x 10x = 100,000
8. What is the energy released for each of the above magnitudes (You may use a
calculator)?
There is no term given for energy released such as pounds or tons.
Ans: 31x 31x 31x = 29,791 for magnitude 3
Ans: 31x 31x 31x 31x 31x = 28,629,151 for a magnitude 5
9. Compare the effects of a magnitude 5 earthquake with a magnitude 3 earthquake on
the basis of potential damage to structures.
Ans: On a logarithmic scale, a magnitude 5 earthquake releases much more energy, therefore
the potential for damage is considerably greater.
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Seismograph
EQ 14-15
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This activity was modified for elementary grades from Physical Experiments in Geology,
Laboratory Course (1967), Gilbert C.M. & Christensen, M.N., Mc Graw Hill.
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Seismograph
EQ 14-15
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