Quiz 3 - answers PDF

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Chapter 3 EARTHQUAKES AND THEIR CAUSES MULTIPLE-CHOICE QUESTIONS 1. What is the approximate highest frequency of vibration (of back and forth shaking) in earthquakes? a. 2–3 cycles per minute b. 2–3 cycles per second 20–30 cycles per second c. 2,000–3,000 cycles per second d. 20,000–30,000 cycles per second ANSWER: c [p. 50] Which type of earthquake waves shake with the largest amplitudes (largest range of motion)? a. compressional waves b. shear waves surface waves c. P waves d. S waves ANSWER: c [p. 54] How is the distance to the source of an earthquake determined? a. by calling many seismograph operators to see who felt it most strongly by subtracting the travel times of P and S waves b. by measuring the frequency of the P waves as they arrive at a seismograph c. by measuring the height of the S waves recorded on a seismograph d. by adding the travel times of the L waves and the Raleigh waves ANSWER: b [p. 51] What does the Richter Magnitude Scale depend on? the maximum amplitude of earthquake waves on a seismograph a. the frequency of P waves recorded on a seismograph b. the intensity of shaking during the earthquake c. the amount of destruction by the earthquake d. the distance to the earthquake focus ANSWER: a [p. 53]

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A magnitude 7 earthquake has how much higher ground motion than a magnitude 6 earthquake on a seismogram? twice as high 10 times higher a. 32 times higher b. about 100 times higher c. about 1,000 times higher ANSWER: b [p. 54] Which type or types of earthquake waves move only near the surface of the Earth? all earthquake waves P waves surface waves S waves waves from faults that break near-surface rocks ANSWER: c [p. 50] 2. What kind of material is subject to liquefaction during an earthquake? a. clay saturated with saltwater b. soils that are not saturated with water c. swelling clay saturated with water d. loose sand grains with water between the grains e. poorly compacted artificial fill dumped into the edge of a bay to add usable land ANSWER: d [p. 58] What does the Mercalli Intensity Scale depend on? how much damage occurred in an area the intensity of shaking of the seismograph the amplitude of movement of the seismograph needle the strength of rocks broken along the fault the frequency of the earthquake waves as they reach the seismograph ANSWER: a [pp. 52–53] 3. Why do parking garages often fail and fall during an earthquake? a. Garages fall due to a lack of steel reinforcing bars. b. Garages are made of poor quality concrete. c. Horizontal spans across the large openings are too long to support the weight of vehicles. d. Horizontal support beams shake off their vertical columns because they are often not well braced. e. The vertical concrete supports are too thin to support the load. ANSWER: d [pp. 59–60]

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What is the approximate P-wave velocity through the Earth’s mantle? 8 meters per second 80 meters per second 8 kilometers per second 80 kilometers per second 800 kilometers per second ANSWER: c [p. 52] Which type or types of earthquake waves arrive at a distant seismograph most quickly by traveling by moving through the mantle of the Earth? both P and S waves both P and L waves both S and L waves only S waves only P waves ANSWER: a [p. 52] Which types of earthquake waves do the most damage? compressional waves shear waves body waves P waves surface waves ANSWER: e [p. 50] Which earthquake waves arrive first? P waves S waves L waves shear waves surface waves ANSWER: a [p. 50] Which earthquake waves arrive from the source last? P waves S waves surface waves shear waves body waves ANSWER: c [p. 50]

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Why are surface waves the most destructive type of earthquake waves to buildings? They are compressional waves. They are shear waves. They first compress the material and then pull it apart. They move with the highest velocities. They have larger amplitudes of shaking. ANSWER: e [p. 50] Which waves have the lowest frequencies? P waves S waves surface waves compressional waves shear waves ANSWER: c [p. 50] How much more energy is released in a magnitude 7 earthquake than in a magnitude 6 earthquake? about double about 3 times about 10 times about 32 times about 100 times ANSWER: d [p. 55] Moment magnitude depends on what main factor(s)? total offset distance on the fault during the earthquake total length of the fault ruptured shear strength of the rocks displaced, total surface area of rocks ruptured, and average slip distance on the fault frequency of movement of the earthquake waves and the total time of shaking amplitude of seismograph swing at the first moment of arrival of shaking ANSWER: c [p. 55]

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Between magnitude 7 and magnitude 8 earthquakes, about how much harder is the shaking (how much increase in the acceleration of the ground)? actually less acceleration because the frequency is lower not much twice as hard about 10 times about 32 times ANSWER: b [p. 56] If you find a well-exposed fault that moved before seismographs were available, you can infer the approximate magnitude of earthquake by measuring the __________. largest size tree snapped off by the shaking average size of the largest rocks moved in the earthquake strength of the rocks that the earthquake managed to break total area affected by the tsunami wave produced by the event total length of fault break during the event ANSWER: e [p. 40]

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