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 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 5. c 9. c 13. d 2. a 6. c 10. a 14. a 3. d 7. d 11. a 4. b 8. d 12. a 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. 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. T48 Chapter 6

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. Answers to Prelab Preparation 2. a.16.4 seconds; 32.8 seconds b. 24.4 seconds; 48.8 seconds c. 8.0 seconds; 16.0 seconds Answers to Procedure 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. 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. 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. 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 Visit go.hrw.com for study aids matched to your textbook. Type in the following keyword: HQ2 HOME. Visit www.scilinks.org to find up-to-date Internet resources. Use the scilinks codes in your textbook. Visit www.si.edu/hrw for on-line materials from one of our nation s premier science museums. 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. Commentary and Answers T49