Name
Date
Class
Earthquakes and Seismic Waves
Inquiry Warm-Up, How Do Seismic Waves Travel Through Earth?
In the Inquiry Warm-Up, you investigated how waves move through matter. Using what
you learned from that activity, answer the questions below.
1. OBSERVE In Step 3, how does the direction in which the disturbance in
the spring forms compare to the position of the spring?
2. OBSERVE In Step 4, how does the direction in which the disturbance in
the spring forms compare to the position of the spring?
3. PREDICT In Step 4, you moved the spring from side to side. How else
might you move the spring to produce a similar kind of wave?
4. APPLY CONCEPTS Where else have you seen waves like the one you
created in Step 4?
117A
Name
Date
Class
Earthquakes and Seismic Waves
What Are Seismic Waves?
1a. REVIEW The energy released by an earthquake moves out from the
earthquake’s
in the form of seismic waves.
b. PREDICT Small earthquakes occur along a certain fault several times
a year. Why might geologists worry if no earthquakes occur for
25 years?
I get it! Now I know that seismic waves are
I need extra help with
How Are Earthquakes Measured?
2a. IDENTIFY The
scale rates earthquakes based on
the amount of energy that is released.
b. INFER Suppose the moment magnitude of an earthquake is first
thought to be 6, but is later found to be 8. Would you expect the
earthquake damage to be more or less serious? Why?
I get it! Now I know that to measure earthquakes, geologists use seismic waves to
determine
I need extra help with
117B
Name
Date
Class
Earthquakes and Seismic Waves
How Is an Epicenter Located?
3a. REVIEW Geologists use
earthquake’s epicenter.
to locate an
b. IDENTIFY What can geologists measure to tell how far an earthquake’s
epicenter is from a particular seismograph?
c. APPLY CONCEPTS Suppose an earthquake occurs somewhere in
California. Could a seismograph on Hawaii be used to help locate the
epicenter of the earthquake? Why or why not?
I get it! Now I know that geologists can locate an earthquake’s epicenter by using
I need extra help with
117C
Name
Date
Class
Earthquakes and Seismic Waves
On a separate sheet of paper, identify the three types of seismic waves and how seismic
waves are used to locate the epicenter of an earthquake.
117D
Name
Date
Class
Earthquakes and Seismic Waves
Understanding Main Ideas
Read pages 110-117 in your text. Then, answer the questions below.
1. What are seismic waves? _______________________________________________________
_________________________________________________________________________
2. In what order do the three types of seismic waves arrive at a seismograph?
1st: ______________________
2nd: ______________________
3rd: ______________________
3. Which type of seismic wave produces the most severe ground movement?
_________________________
4. What three scales are used to measure earthquakes?
 Amount of shaking: ____________________________
 Magnitude (size): ______________________________
 Total energy released: __________________________
5. Why do geologists try to locate the epicenter of an earthquake? ___________________________
________________________________________________________________________________
Building Vocabulary
Match each term with its definition by writing the letter of the correct definition in the
right column on the line beside the term in the left column.
6.
focus
a. records ground movements caused by seismic waves as they
move through Earth
7.
epicenter
b. slowest seismic waves
8.
surface waves
c. the point beneath Earth’s surface at which rock under stress
breaks and triggers an earthquake
9.
seismograph
d. the point on the surface directly above the point at which an
earthquake occurs
117E
Name
Date
Class
Earthquakes and Seismic Waves
Read the passage and look at the table below it. Then use a separate sheet of paper to
answer the questions that follow the table.
Comparing the Richter and Moment Magnitude Scales
The Richter scale rates earthquakes based on the size of their seismic waves, as
measured by seismographs. The moment magnitude scale rates earthquakes based
on the total amount of energy they release. To determine the moment magnitude
rating, seismologists measure the surface area of the ruptured fault and how
far the land moved along the fault. An earthquake’s Richter rating and moment
magnitude rating are not always the same. The table below shows the ratings on
both scales of some famous earthquakes.
Magnitude
Date
Location
1906
1960
Richter scale
Moment
magnitude scale
San Francisco, CA
Arauco, Chile
8.3
8.3
7.7
9.5
1985
Mexico City, Mexico
8.1
8.1
1989
1999
2003
2004
San Francisco, CA
Izmit, Turkey
Bam, Iran
Sumatra-Andaman Islands
7.1
7.4
6.5
9.1
7.2
7.4
6.6
9.3
2005
2008
Pakistan
Eastern Sichuan, China
7.6
8.0
7.6
7.9
1. Which earthquake was strongest according to the Richter scale?
Which was strongest according to the moment magnitude scale?
2. Which earthquakes had the same ratings on both scales?
3. Which earthquake was rated more than 0.5 stronger on the moment
magnitude scale than it was rated on the Richter scale?
4. Which earthquakes were rated stronger on the Richter scale than
they were rated on the moment magnitude scale?
5. Why can the same earthquake have different ratings on the two
scales?
117F
Name
Date
Class
Earthquakes and Seismic Waves
If the statement is true, write true. If the statement is false, change the underlined word
or words to make the statement true.
1.
The shaking and trembling that results from movement of rock
beneath Earth’s surface is called an earthquake.
2.
Earthquakes are caused by the forces of mountain movement.
3.
The epicenter of an earthquake is below the focus.
4.
P waves can become surface waves when they reach Earth’s
surface.
5.
The Modified Mercalli scale rates the amount of damage from
an earthquake.
6. To locate the epicenter of an earthquake, geologists need data from two or more
seismographs.
Fill in the blank to complete each statement.
7. Seismic waves are
8. The
begins to break or move.
that are similar to sound waves.
of an earthquake is the point where rock under stress
9. The seismic waves that move fastest are
.
10. Geologists use the moment magnitude scale to rate the total
released by an earthquake.
117G
Earthquakes and Seismic Waves
Answer Key
6. c
7. d
1. The disturbance is in the same direction as the
8. b
position of the spring.
9. a
2. The disturbance is at right angles to the
position of the spring.
3. The spring could be jerked up and down
instead of to the side.
1. Richter scale: Sumatra-Andaman Islands at 9.1;
4. water waves
moment magnitude scale: Arauco, Chile at 9.5
2. Mexico City, Mexico; Izmit, Turkey; Pakistan
3. Arauco, Chile
Seismic waves spread out from the focus of the
earthquake. P waves are primary waves. They
compress and expand the ground. S waves are
secondary waves. They move the ground from
side to side or up and down. Surface waves form
when P waves or S waves reach the surface. They
cause the ground to move up and down.
4. San Francisco, CA; Eastern Sichuan, China
5. Magnitude based on the moment magnitude
and Richter scales are different because
each scale uses different types of data. The
Richter scale rates an earthquake based on
the size of its seismic waves as measured by
a seismograph. The moment magnitude scale
uses additional data to rate the total energy
released by an earthquake.
1. Seismic waves are vibrations that travel
through Earth, carrying the energy released
during an earthquake.
2. P waves, S waves, surface waves
1. true
2. plate
3. surface waves
3. above
4. true
4. The moment magnitude scale provides an
5. shaking
6. three
7. vibrations
8. focus
9. P waves
10. energy
estimate of the total energy released by an
earthquake. It can be used to rate earthquakes
of all sizes, regardless of whether they occur
close by or far away.
5. Geologists measure the difference between
the arrival times of P waves and S waves at
three or more seismographs. Using these
differences, they determine the distance of the
epicenter from each seismograph and plot the
distances as circles on a map. The epicenter is
located where the three circles intersect.
117H