Download Skinner Chapter 5

Fall 2000
Lohrengel
Geology 1013 -Earth System Science
Chapter 5 Study
Instructions:
Read each question carefully before answering. Work at a steady pace, and you should
have ample time to finish.
_____________________________________________
1. How are seismic waves used to learn about the internal structure of
the Earth?
2. Describe how the method of triangulation is used to locate the
epicenter of an earthquake. Support you answer with a neat,
well- labelled diagram.
3. What does it mean when we say that the lithosphere is in isostatic
balance on the asthenosphere? How does glacier ice provide a
demonstration of the principle of isostasy? Support your answer with
neat, well- labelled diagrams.
4. Explain how you could use a gravimeter to demonstrate the principle
of isostasy.
5. What is an S-wave shadow zone? How have S-waves helped scientists to
learn about the Earth's core? Support your answer with a neat,
well- labelled diagram.
6. Sometimes the largest earthquakes (such as the M 8.4 Good Friday
earthquake in Anchorage, Alaska, 1964) cause fewer deaths than
smaller earthquakes (such as the M 6.8 earthquake of December, 1988
in Armenia). Why do you think this is?
7. What is isostasy? What does isostasy tell us about the relationship
between the lithosphere and the asthenosphere?
8. Long-term earthquake forecasting has been much more successful than
short-term prediction and early warning. Why?
9. The outer core is inferred to be molten because it does not transmit
seismic waves.
10. When slippage of rock occurs along a fracture in a rock, the
fracture is called an earthquake.
11. The epicenter of an earthquake is the point where the earthquake's
energy is first released.
12. The point on the Earth's surface directly above the focus is called
the epicenter.
13. The point on the Earth's surface directly above the epicenter is
called the focus.
14. Seismic waves travel through the Earth at uniform velocities,
spreading out in all directions.
15. P waves are compressional/expansional waves that can pass through
gases, liquids and solids.
16. S waves travel more slowly than P waves through the same material.
17. Surface waves are the first seismic waves to be recorded by the
seismograph in the event of an earthquake.
18. The moho is the seismic discontinuity that marks the boundary
between the core and mantle of the Earth.
19. The amount of energy released by a Richter magnitude 7.5 earthquake
is approximately _________ times greater than the energy released by
a magnitude 5.5 earthquake.
a. 30
b. 60
c. 100
d. 900
20. Transform plate boundaries are characterized by
a. earthquakes.
b. volcanic activity.
c. mountain building.
d. All of these are true.
21. Earthquakes are
a. restricted to plate boundaries.
b. most common along plate boundaries.
c. evenly distributed across plates.
d. most common in ocean basins.
22. The term epicenter refers to
a. the focus of an earthquake.
b. the point from which an earthquake's energy originates.
c. the point on the Earth's surface directly above the focus of an
earthquake.
d. the point of failure of rocks in the elastic rebound theory.
23. The term seismic gap refers to
a. a region where no seismic activity occurs.
b. the point of rupture of stressed rocks deep in the Earth (in the
elastic rebound theory).
c. a method for predicting seismic sea waves (tsunami).
d. a segment of a seismically active fault along which no large
earthquakes have occurred recently.
24. An instrument that measures ground vibrations is a
a. gravimeter.
b. seismogram.
c. geodolite.
d. seismograph.
25. The Richter magnitude of an earthquake
a. is measured on an instrument called a Richter scale.
b. is measured by the amplitude of seismic waves recorded by
seismographs.
c. is determined by the area over which it is felt.
d. depends on how near the recording instrument is to the epicenter.
26. Which one of the following is not a danger closely associated with
earthquakes?
a. fires
b. seismic sea waves
c. quicksand
d. surface rupturing
e. heating of the ground surface
27. The most intense earthquakes to jolt North America in the past 200
years were centered in
a. California.
b. New York.
c. South Carolina.
d. Missouri.
28. Research into the short-term prediction of earthquakes currently
focuses on observations of changes that may signal an impending
earthquake, such as
a. swarms of tiny earthquakes.
b. changes in magnetism.
c. tilting of the land surface.
d. All of these are true.
29. The focus of an earthquake is
a. the point on a fault surface where seismic energy is first
released.
b. the point on the Earth's surface where seismic energy is first
released.
c. the region of greatest damage during an earthquake.
d. the point on the Earth's surface above the epicenter.
30. Which one of the following does not belong with the others?
a. gravimeter
b. seismogram
c. seismograph
d. magnetometer
31. The S-wave shadow zone assisted scientists in determining that
a. the core of the Earth is composed primarily of metallic iron and
nickel.
b. the asthenosphere is a weak layer of anomalously low seismic
velocity.
c. the outer core of the Earth is molten.
d. All of these are true.
32. An increase of 1 on the Richter magnitude scale for earthquakes
corresponds to an increase in released energy of approximately
a. 10-fold.
b. 20-fold.
c. 30-fold.
d. 100-fold.
33. An increase of 1 on the Richter magnitude scale for earthquakes
corresponds to an increase in maximum seismic wave amplitude of
a. 10-fold.
b. 20-fold.
c. 30-fold.
d. 100-fold.
34. Tsunamis
a. are also called "seismic waves."
b. are sometimes incorrectly called tidal waves, but have nothing to
do with tides.
c. travel very slowly across the open ocean, but hit the shore as
enormous breakers.
d. All of these are true.
35. The asthenosphere
a. is a zone of anomalously low seismic velocity.
b. underlies the lithosphere.
c. is a zone of plastic deformation within the upper part of the
mantle.
d. All of these are true.
36. Which one of the following is not use d by scientists to predict
earthquakes?
a. foreshocks
b. seismic gaps
c. isostasy
d. strange animal behavior
37. The flotational balance among segments of the lithosphere is
referred to as
a. gravity.
b. isostasy.
c. density.
d. seismicity.
38. The asthenosphere is the zone in which
a. seismic wave velocities are highest.
b. rocks are very ductile.
c. all earthquakes originate.
d. All of these are true.
39. Vibrations sent out by earthquakes are measured with an instrument
called a ________________.
40. Energy released at an earthquake's focus radiates outward as two
kinds of body waves: _______________ waves and _______________
waves.
41. The pronounced seismic discontinuity that marks the mantle-crust
interface is called the ____________________.
42. Seismic waves that do not pass through the body of the Earth are
called _______________.
43. The asthenosphere is a zone of anomalously ______________
seismic-wave speed.
44. The _______________ scale is used to calculate the amount of energy
released during an earthquake, on the basis of the recorded
amplitude of the seismic waves.
45. The Earth's core has a high density and is inferred to consist
primarily of _______________ and a small amount of ________________.
46. The flotational balance maintained by large segments of the
lithosphere that "float" on the underlying asthenosphere is referred
to as __________________.
47. The scale that measures earthquake intensity on the basis of felt
vibration and extent of damage to buildings is called the
__________________ scale.
48. Rocks can be elastically deformed by seismic body waves in two ways:
(1) by a change in ___________________ or (2) by a change in
__________________.
49. What are six different ways earthquakes cause damage?
50. What is a seismic gap? Why are seismic gaps so important in
earthquake prediction?
51. How did S-waves reveal that the Earth's outer core is liquid?
52. What does the elastic rebound theory suggest?
53. Explain how a bent piece of wood can be an analogy for an
earthquake.
54. What is the difference between the focus and epicenter of an
earthquake? When new reporters give the "location" of an earthquake,
which one are they actually referring toƒƒthe epicenter or the
focus?
55. What are the most important differences between S waves and P waves?
56. What are the main differences between seismic body waves and surface
waves?
57. What, exactly, is the moho?
58. A single earthquake has only one magnitude on the Richter scale, but
it may have numerous magnitudes on the modified Mercalli intensity
scale. How can that be?
_____________________________________________
Fall 2000
Lohrengel
Geology 1013 -Earth System Science
Answer Key: Chapter 5 Study
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9. F
10. F
11. F
12. T
13. F
14. F
15. T
16. T
17. F
18. F
19. D
20. A
21. B
22. C
23. D
24. D
25. B
26. E
27. D
28. D
29. A
30. B
31. C
32. C
33. A
34. B
35. D
36. C
37. B
38. B
39. seismograph
40. (P...S) OR (primary...secondary) OR (compressional...shear)
41. (Mohorovicic discontinuity) OR (M-discontinuity) OR (moho)
42. surface waves
43. (low) OR (slow)
44. Richter magnitude
45. iron...nickel
46. (isostasy) OR (isostatic equilibrium) OR (isostatic balance)
47. (modified Mercalli) OR (modified Mercalli intensity)
48. shape...volume
49. Earthquakes cause damage by (1) ground motion; (2) faulting and
surface rupturing; (3) fires; (4) land movement and slope collapse;
(5) liquefaction; and (6) tsunami.
50. Seismic gaps are places along seismically active faults where, for
one reason or another, earthquakes have not occurred for a long time
and where elastic strain is increasing. Seismic gaps receive a lot
of attention because they are considered the place most likely to
experience large earthquakes.
51. S-waves cannot be transmitted through liquids. S-waves are
transmitted through the crust and mantle (solid) but not through the
outer core (liquid).
52. The elastic rebound theory suggests that, if fault surfaces lock
rather than slip easily past one another, the rocks on either side
of the fault will bend and in bending they will store elastic strain
energy. When the fault finally does slip and the bent rocks rebound
to their original shapes, an enormous amount of energy is released
as an earthquake.
53. When you bend a thin piece of wood, the energy from your muscles is
stored in the wood in the form of elastic strain energy. If you
release the wood, this stored energy will return it to its former
shape. However, if you bend the wood too far it will break, and the
stored elastic energy will be suddenly converted to heat energy,
sound energy (the snapping of the wood), and vibrations in the wood.
The same is true of rocks: when they are deformed by movement along
a fault, they build up elastic strain energy. When the rock finally
breaks and slippage occurs along the fault, the stored energy will
be released all at once in the form of an earthquake (elastic
rebound theory).
54. The focus is the point (or, sometimes, the area) where energy is
first released, which generally lies at some depth below the
surface. The epicenter is the location on the surface of the Earth
that immediately overlies the focus. When the "location" of an
earthquake is reported on the news, it is with reference to the
epicenter of the quake, not the focus.
55. P waves travel more quickly (through the same material) than S
waves. S waves cannot be transmitted through fluids. P waves are
compression/expansion waves; S waves are shear waves.
56. Surface waves travel more slowly than body waves, and they travel
along or closely to the surface of the Earth, rather than through
it; they are the last waves to be detected by a seismograph. Surface
waves tend to have very long wavelengths and high amplitudes;
therefore, they often cause significant damage.
57. "Moho" is short for "Mohorovicic discontinuity (or M-discontinuity).
It is a pronounced seismic discontinuity that marks the base of the
crust (i.e., the top of the mantle, or the crust-mantle boundary).
58. The calculation of Richter magnitude takes into account the distance
of the seismic station from the earthquake's epicenter; the modified
Mercalli scale does not. In other words, the strength of an
earthquake on the Mercalli scale depends on distance from the
epicenter: the closer you are, the stronger the shaking and the
higher the magnitude on the Mercalli scale.