6th Edition Marshak Test Questions & Answers

Interlude D: The Earth’s Interior Revisited: Insights from Geophysics

LEARNING OBJECTIVES

ID A. Explain how seismic waves behave as they pass through the Earth’s interior.

ID B. Describe how the study of seismic waves can tell us about layering inside the Earth.

ID C. Characterize the Earth’s internal layers.

ID D. Provide a model illustrating how the surface elevation of the lithosphere generally represents the consequences of Archimedes’ principle.

ID E. Explain how gravitational attraction varies with location, and what these variations mean.

ID F. Explain why the Earth’s magnetic field exists, and why its strength varies with location.

MULTIPLE CHOICE

1. The subdiscipline of geology that investigates the Earth’s physical characteristics such seismic waves, gravity, and magnetism is termed _______.

2. Which of the following best describes how scientists study the interior of the Earth?

3. The time it takes for a seismic wave to travel from the focus of an earthquake to a seismometer is called the ________.

4. Seismic waves travel ________ in solids than in liquids; however, unlike P-waves, S-waves ________ travel through liquids.

5. If a P-wave is traveling through the Earth and encounters a molten magma chamber, what will happen to the velocity of the P-wave?

6. If an S-wave is traveling through rock when it encounters a molten magma chamber, what will happen to the velocity of the S-wave?

7. If a S-wave is traveling through sandstone and then encounters peridotite, the S-wave will ________.

8. What behavior will seismic waves exhibit when traveling from a lower-velocity material into a high-velocity material?

9. Which layer of the Earth has the highest density?

10. The core consists of two layers: a(n) ________ inner core and a(n) ________ outer core.

11. What causes the velocity of a P-wave to increase when it enters the inner core?

12. You are studying the seismic data from Mars when you notice that there are no S-waves recorded from 130° through 180° on the opposite side of the planet. What does this information tell you about the interior of Mars?

13. Using the graph below, why is the outer core liquid, but the inner core solid?

14. The graph below shows the change in velocity of seismic waves with depth in the crust. Why does the velocity of the P-wave drop drastically at the core-mantle boundary?

15. In the following graph, why does the line for S-waves NOT appear in the outer core?

16. In the picture below, when the ship is filled with cargo it sinks into the water until the mass of water displaced is equal to the mass of the cargo. The ship is then said to be ________.

17. If a ship weighs 52,000 tons and is in isostatic equilibrium when 6,000 tons of cargo is added, what is the total mass of water that will be displaced by the ship after the cargo is added?

18. The Earth’s gravity is best represented by an equipotential surface that contains bumps and depressions where areas of higher or lower gravity appear over the Earth. This representation is called the ________.

19. If a gravity anomaly is negative, what does that imply about the material underground?

20. A mountain range made of high-density basalt would produce a(n) ________ gravity anomaly compared to a mountain range of lower-density sedimentary rocks.

21. Why would the gravity anomaly over a deep-ocean trench be negative?

22. The Earth’s magnetic field is produced in the ________.

23. A positive magnetic anomaly is produced when the measured magnetic field strength is ________ the expected magnetic field strength.

24. If you measure the magnetization of an area of igneous rocks and find a large negative anomaly, what does that imply about the rocks?

25. Why are magnetic anomalies of continental crust so much more complicated than those of oceanic crust?

1. If a P-wave is traveling up toward Earth’s surface from a layer of mantle peridotite to a layer of limestone crust, what will happen to the P-wave in terms of speed and direction of motion? Why?

2. Using the image below, explain why the P-wave velocity drops drastically at the outer core-mantle boundary. Also, explain why the P-wave velocity speeds up at the inner core–outer core boundary.

3. During the last ice age, continental glaciers covered significant portions of the North American continent. In the context of Archimedes’ principle, what effect would these glaciers have had on the lithosphere relative to the asthenosphere? How was isostatic equilibrium achieved?

4. Imagine that you are an economic geologist, trying to find copper resources. How might gravity anomalies help you?

5. Kilauea Volcano in Hawaii has been erupting large volumes of basaltic lava over the past few decades. Would the magnetic anomaly associated with this recent volcanism be positive or negative? Why?