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three days. After an earthquake, fires can be caused
by ruptured gas lines, damage to fuel storage tanks,
and downed power lines.
Pages 107–109: Class Activity
(Reinforcement)
To reinforce earthquake safety procedures, write the
headings “Before,” “During,” and “After” on the
chalkboard. Have students list the safety actions to
follow in the event of an earthquake.
Pages 108–109: Career Focus
You may wish to contact the U.S. Geological Survey
or a nearby university for the location of the nearest
seismograph station. Request a copy of a seismogram to show to the class.
Small-Scale Investigation
Seismographic Record (p. 105)
Science Process Skills: constructing models,
observing, comparing, describing
Answers to Critical Thinking
1. The elastic rebound theory states that rocks
deform when under stress, then rebound, or
bounce back, to their original shape during an
earthquake, causing the ground to shake.
2. The seismograph is located on the opposite side
of the earth from where the earthquake occurred.
3. The city with earthquake intensity of IV is farther from the epicenter than the city with earthquake intensity of VI.
4. no; because tsunamis form only when earthquakes occur on or near the ocean floor
Answers to Application
1. Is the soil loose or firm? Are there faults nearby?
Have earthquakes occurred nearby in the past? Is
the soil likely to shift after a heavy rain?
2. because doorways have frames, which provide
extra support, and because the top of a door
frame might deflect falling objects
3. When local P waves are slower than normal, it
may mean that the area will experience a major
earthquake, usually soon after the P waves return
to normal speed.
Answers to Analysis and Conclusions
1. energy release
2. different types of crustal material
3. For a given mass, the box filled with sand shows
less displacement than the box containing sand
and newspaper. The box filled with sand is more
rigid and thus vibrates less.
4. Increased vibration produces more-erratic lines,
which suggests greater energy release.
Alternative Lab: Seismograph Model—WARD’S
80 M 5720
Chapter 6 Review
Answers to Review
1. b
2. a
3. d
4. b
5. c
6. c
7. d
8. d
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Chapter 6
9. c
10. a
11. a
12. a
13. d
14. a
In-Depth Investigation
Earthquake Waves (pp. 114–115)
Approximate time: 1 class period
Objective: to find the location of an earthquake’s
epicenter
Skills: interpreting data and models, observing,
measuring
Prelab Discussion
Before students begin the investigation, use a world
map to point out where the majority of earthquakes
occur. Have students discuss the significance of the
pattern in these occurrences. Ask why scientists
must find the epicenters of earthquakes.
Teaching Strategies
1. Before students begin the investigation, be sure
that they understand the difference between the
focus and the epicenter of an earthquake. The
focus is the point on a fault at which movement
occurs and an earthquake begins; the epicenter is
directly above the focus and is where the surface
waves begin to move.
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2. Be sure that students understand how to calculate
the distance from each city to the epicenter of the
earthquake in Step 2 of the procedure. These figures must be correct to accurately determine the
epicenter of the earthquake on the map.
3. Emphasize to students that the circles on the map
must intersect in order to determine the epicenter
of the earthquake. If the circles do not intersect,
tell students that they must check their calculations in both the prelab preparation and the
procedure.
4. To extend the investigation, have interested students contact a nearby college or university to
obtain seismographic tracings. The tracings can
be studied and discussed by the class.
2. Other than in fault or rift zones, an earthquake
could result from old buried faults or the
rebounding of land, such as in New England after
the ice retreated during the last ice age.
Answers to Prelab Preparation
Visit go.hrw.com for study aids matched to your textbook. Type in the following keyword: HQ2 HOME.
Alternative Labs: Horizontal Seismograph—
WARD’S 13 M 4100; Earthquake Watch Lab
Activity—WARD’S 36 M 4130; Earthquakes and
Plate Boundaries Activity—WARD’S 34 M 1207;
Plate Boundaries and Earthquake Prediction—
WARD’S 34 M 1222
More Technology Resources
Internet
2. a. 16.4 seconds; 32.8 seconds
b. 24.4 seconds; 48.8 seconds
c. 8.0 seconds; 16.0 seconds
Visit www.scilinks.org to find up-to-date Internet
resources. Use the sciLINKS codes in your textbook.
Answers to Procedure
Visit www.si.edu/hrw for on-line materials from one
of our nation’s premier science museums.
1. Austin: 150 s; Bismarck: 168 s; Portland: 120 s
2. Austin: 1,875 km; Bismarck: 2,100 km; Portland:
1,500 km
4. The circles should all intersect near San Diego,
California.
Answers to Analysis and Conclusions
1. San Diego, California
2. To ensure that the location is accurate. Sometimes the first two circles intersect in more than
one place. The third circle intersects both of the
other two circles in only one place.
Visit www.cnnfyi.com for late-breaking news and
current events stories.
One-Stop Planner with Test Generator
Use this CD-ROM to generate customized lesson
plans and tests, to print out worksheets, to link to the
above Internet sites, and more.
Holt Earth Science Interactive Tutor
Use the animations, movies, and projects in this
CD-ROM to help students explore and investigate
earth science. For Chapter 6, use the lesson Volcanoes
and Earthquakes.
Answers to Extensions
1. Near California’s San Andreas Fault, the Pacific
Northwest, or Alaska the probability is high.
Elsewhere in the United States, the chances are
much lower.
Commentary and Answers
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