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CHAPTER 3
EARTHQUAKES AND THEIR DAMAGES: SHAKING GROUND,
COLLAPSING BUILDINGS
Correct answers are indicated by an asterisk, both in short answer and multiple choice questions.
True or False questions can be easily prepared from multiple choice questions
Web Sites:
http://earthquake.usgs.gov/
http://eqhazmaps.usgs.gov/
http://geopubs.wr.usgs.gov/prof-paper/pp1623
http://neic.usgs.gov/
http://neic.usgs.gov/neis/pANDs/neic_maps.html
http://nisee.berkeley.edu/
http://pubs.usgs.gov/gip/earthq1/
http://pubs.usgs.gov/gip/earthq3/
http://pubs.usgs.gov/gip/earthq4/severitygip.html
http://quake.abag.ca.gov/
http://quake.geo.berkeley.edu/cnss/
http://quake.wr.usgs.gov
http://quake.wr.usgs.gov/info/eqlocation/
http://quake.wr.usgs.gov/prepare/ncep/a_andreas.html
http://quake.wr.usgs.gov/QUAKES/FactSheets/BetterDesign/
http://quake.wr.usgs.gov/QUAKES/FactSheets/PacNW/
http://seismo.berkeley.edu/
http://www.anatolianquake.org
http://www.avo.alaska.edu/Seis/.
http://www.data.scec.org/
http://www.geohaz.org/radius.html
http://www.geol.binghamton.edu/faculty/jones/
http://www.iris.edu/seismon/
http://www.iris.washington.edu/about/ENO/
http://www.nasa.gov/centers/goddard/earthandsun/0930_earthquake.html
http://www.sciencecourseware.com/eec/Earthquake/
http://www.seismic.ca.gov/
http://www.trinet.org/shake
http://wwwneic.cr.usgs.gov/neis/general/seismicity/seismicity.html
Videos:
Video: NOVA - The day the earth shook
Video: NOVA - Killer quake
Video: NOVA - Earthquake!
Video: NOVA - San Francisco: The City that waits to die. Annenberg/CPB Collection; P.O. Box 1922,
Santa Barbara, CA
Video: Gould Media: Earthquakes, Mount Vernon, NY
Video: Gould Media, Inc.: The 1989 San Francisco Bay Area Earthquake, Mount Vernon, NY
Video: Quake! Our trembling Earth. Geoscience Resources, Burlington, NC
Video: The walls came tumbling down; Earthquake history of the Holy Land: Amos Nur, Dept. of
Geophysics, Stanford, CA
Video: PBS – The Great San Francisco Earthquake: American Experience Series
Geologic Hazards Slide Sets: Earthquakes (14 sets) National Geophysical Data Center, NOAA, Dept. 930,
325 Broadway, Boulder, CO 80303
References:
Blais-Stevens, A., J.J. Clague, P.T. Bobrowsky, and R.T. Patterson, 1997, Late Holocene sedimentation in
Saanich Inlet, British Columbia, and its paleoseismic implications: Canadian Jour. Earth Sciences, vol.
34, p. 1345-1357.
Dolan, J.F. and others, 1995, Prospects for larger or more frequent earthquakes in the Los Angeles
metropolitan region: Science, v. 267, p. 199-205.
Eckel, E., and others, 1970, The Alaska earthquake, March 27, 1964, lessons and conclusions: U.S. Geol.
Survey Prof. Paper 546, 57 p.
Hamilton, R. and A. Johnson, 1990, Tecumseh's prophecy: preparing for the next New Madrid earthquake:
U.S. Geol. Survey Circular 1066.
Hartzell, S.H., and others, 1996, Site response for urban Los Angeles using aftershocks of the Northridge
earthquake: Seismological Soc. of Amer., v. 86, p. S168-S192.
Heaton, T.H., J.F. Hall, D.J. Wals, and M.W. Halling (1995) Response of high-rise and base-isolated
buildings to a hypothetical Mw 7.0 blind thrust earthquake: Science, vol. 267, p. 206-211.
Hough, S.E., 1995, Earthquakes in the Los Angeles metropolitan region: A possible fractal size distribution
of rupture size: Science, vol. 267, p. 211-213.
Hylland, M.D., B.D. Black, and M. Lowe, 1997, Geologic hazards of the Wasatch Front, Utah: Field guide,
Geol. Soc. America Ann. Mtg., Salt Lake City, p. 299-324.
Hyndman, R.D., 1995, Giant earthquakes of the Pacific Northwest: Scientific American, Dec. 1995, p. 6675.
Jacoby, G.C., D.E. Bunker, and B.E. Benson, 1997, Tree-ring evidence for an A.D. 1700 Cascadia
earthquake in Washington and northern Oregon: Geology, p. 999-1002.
Johnson, A.C. and E.S. Schwieg, III, 1996, The enigma of the New Madrid earthquakes of 1811-1812:
Annual Review of Earth and Planetary Sciences, v. 24, p. 339-384.
Lawson, A.C., chairman, 1908,The California Earthquake of April 18, 1906: Report of the State
Earthquake Investigation Commission: Carnegie Institution of Washington Publication 87, 2 v.
Reiter, L., 1994, Earthquake hazard analysis: Columbia Univ. Press, 461 p.
Rogers, A.M., T.J. Walsh, W.J. Kockelman, and G.R. Priest, 1996, Assessing earthquake hazards and
reducing risk in the Pacific Northwest; Volume 1, U.S. Geol. Survey Prof. Paper 1560, 306 p.
Vallance, J.W. and K.M. Scott, 1997, The Osceola mudflow from Mount Rainier: Sedimentology and
hazard implications of a huge clay-rich debris flow: Geol. Soc. America Bull. v. 109, p. 143-163.
Yeats, R.S., K. Sieh, and C.R. Allen, 1997, Geology of Earthquakes: Oxford Univ. Press, 576 p.; Seismic
Hazard Assessment, p. 445-472.
Wallace, R.E., editor, 1990, The San Andreas Fault system, California: U.S. Geol. Survey Prof. Paper
1515, 283 p.
CHAPTER 3: End of chapter answers
1. What is the approximate highest frequency of vibration (of back and forth shaking) in
earthquakes?
* 20-30 cycles/second
2. Which type or types of earthquake waves move only near the surface of the earth?
* Surface waves
3. Which type of earthquake waves shake with the largest amplitudes (largest range of
motion)?
* Surface waves
4. Where is the safest place to be in an earthquake?
* outside (with nothing overhead)
5. What is meant by the “elastic rebound theory”?
* Rocks across a fault are stressed and bent elastically. Ultimately they fracture during
an earthquake and the two sides straighten out, leaving them offset across the fault.
6. How is the distance to an earthquake determined?
 Knowing the velocity of travel of P- and S-waves, the difference between P- and Swave arrival times is converted to a distance.
7. What does the Richter Magnitude Scale depend on?
* maximum amplitude of earthquake waves on a seismograph (of a specific type)
8. A magnitude 7 earthquake has how much higher ground motion than a magnitude 6
earthquake on a seismogram?
* 10 times higher
9. In addition to ground motion along a fault and shaking of a building, what types of
ground failure can lead to severe damage of a building?
* liquefaction – compaction and flow of the ground, from rearrangement from loose
packed grains to closer-packed grains.
* quick clays – clays arranged as “a house of cards” can collapse and flow if shaken.
10. What kinds of structural materials make dangerously weak walls during an
earthquake?
* bricks, concrete blocks, stone, or adobe (mud)
11. What type of wall strengthening is commonly used to prevent a building from being
pushed over laterally during an earthquake?
* diagonal cross braces in the walls
* sheets of plywood well anchored to the walls.
12. Why do the floor or deck beams of parking garages and bridges sometimes fail and
fall during an earthquake?
* The ends of the beams rest loosely on ledges to permit heat expansion. Flexing of the
support posts can pull the beams off their ledges.
13. Where a tall building is right next to a short building, why is the tall building often
damaged? Why does the damage occur and where in the building?
* Different frequencies or periods of oscillation of the tall and short buildings (they sway
at different frequencies) so they bang into one another.
* The tall building sometimes collapses at the height of the short building.
14. What type of feature is commonly used to prevent a building from shaking so much
during an earthquake?
* base isolation, for example, rubber pads between the building and its foundation.
15. If a building is to be built on bedrock, it that good or bad? Why?
* Good. Bedrock shakes at a high frequency and a tall building flexes at a low frequency
so they do not shake in resonance during an earthquake.
Short answer questions (Ch 3):
1. What type of wall strengthening is commonly used to prevent a building from being
pushed over laterally during an earthquake?
* diagonal beams
2. Why do the floor or deck beams of parking garages and bridges sometimes fail and
fall during an earthquake?
* The horizontal beams, resting on a sliding surface designed to permit thermal
expansion and contraction, shake completely off their ledges
3. Where a tall building is right next to a short building, why is the tall building often
damaged? Why does the damage occur and where in the building?
* Tall buildings sway at a lower frequency than short buildings so the buildings bang
into one another. The tall building breaks at the top of the short building.
4. What type of feature is commonly used to prevent a building from shaking so much
during an earthquake?
* Base isolation pads – essentially shock absorbers between the building and its
foundation.
5. Name the three main types of earthquake waves.
* primary, secondary, surface (or) P, S, surface
6. What is the approximate P-wave velocity through the Earth? Indicate whether your
answer refers to the earth’s crust or mantle.
* 5-6 km/sec in continental crust; 8 km/sec in mantle
7. Which type or types of earthquake waves arrive at a distant seismograph most quickly
by traveling through the mantle of the earth?
* P- and S-waves
8. Which type of earthquake waves do the most damage?
* Surface waves
9. Which earthquake waves arrive first?
* P-waves
10. Which earthquake waves arrive last?
* Surface waves
11. Which of the three main types of earthquake waves tend to be most destructive to
buildings?
* Surface waves
12. Why are surface waves the most destructive type of earthquake waves (2 quite
different reasons)?
* larger amplitude of shaking (greatest ground motion)
* closer to surface of earth and thus closer to building
13. Why are building fires so hard to fight after an earthquake?
* broken water mains
14. Why do so many people in certain regions get sick and often die from sickness after
an earthquake?
* broken sewer lines contaminate water supplies
15. Which waves have the lowest frequencies?
* S-waves
16. What does the Mercalli Intensity Scale depend on?
* how much damage occurred and how strongly people feel the earthquake
17. How much more energy is released in a magnitude 7 earthquake than in a magnitude
6 earthquake?
* about 32 times
18. What are the three main factors that affect moment magnitude?
* shear strength of the rocks displaced
* total surface area of rocks ruptured by the fault movement
* average slip distance on the fault
19. Between magnitude 7.0 and magnitude 8, about how much harder is the shaking (how
much increase in the acceleration of the ground) during an earthquake?
* not much
20. In addition to amount of damage, increases in what factors go along with increase in
earthquake magnitude? List several.
* fault offset
* length of fault ruptured
* acceleration of the ground
* time of shaking
* velocity of motion of the ground
21. If you find a well exposed fault that moved before seismographs were available, how
can you infer the approximate magnitude of earthquake generated by the movement?
(2 quite different ways)
* measure the offset distance (distance moved) during the event
* measure the total length of fault break during the event
22. List 3 characteristics of the ground that would increase or amplify the ground shaking
and destruction of a building during an earthquake.
* soft mud amplifies shaking relative to bedrock
* loose sand filled with water causing liquefaction
* waves are focused by synclines in bedrock below the ground surface.
23. Do folds in layers of rocks under a building have any effect on the degree of shaking
and damage to the building? If so, how would it work?
* building over a syncline (downfold) can focus the earthquake waves to concentrate
them under the building.
24. Since most deaths in earthquakes are caused by buildings and other structures falling
on people, what building materials are most susceptible to collapse?
* masonry (brick, stone), adobe
25. Since most deaths in earthquakes are caused by buildings and other structures what
types of construction or design are most likely to cause building collapse?
* unbraced (weak) ground-floor garages (or store-fronts)
* too many windows on any floor
* walls not well secured to floors
26. Since most deaths in earthquakes are caused by buildings and other structures what
sometimes causes collapse of a mid-floor of a building (e.g.: 3rd floor of a 7-story
building) when the other floors remain standing?
* building oscillates at same frequency as the ground during an earthquake
27. Are wood-frame houses safe or unsafe for the occupants in a moderately strong
earthquake? Why?
* Safe for the occupants though the house may be severely damaged.
* Wood structures are flexible and will not generally collapse.
28. In some buildings, often a single floor will collapse. What characteristics of a
building will lead to such a single-floor collapse?
* Weak floors: Too many windows on a certain floor Garages or storefronts on the
ground floor
29. In many old brick or stone buildings how are the floors held up?
* The wood floor beams rest loosely in notches in brick or stone walls.
30. What is unsafe about old brick or stone construction in an earthquake?
* Flexing of the walls can permit the beams to pull out and the floors to fall.
31. If the electricity goes out at night during an earthquake, why should matches or
candles not be used to provide light?
* They can ignite gas in the air.
32. If a building is to be built on soft sediment, is a short or tall building safer? Why?
* A short building. Soft sediment shakes at a low frequency and a short building shakes
at a high frequency so they do not shake in resonance during an earthquake.
33. Why are structures on soft sand or mud often destroyed in an earthquake, when
nearby structures on bedrock remain essentially undamaged?
* bedrock shakes with small amplitude vibrations
* soft sediment shakes with stronger (large amplitude) vibrations/ greater back and forth
distances.
34. Why did the double-deck freeway at the east edge of San Francisco Bay, collapse in
the 1989 Loma Prieta earthquake, while nearby structures in low hills to the east
suffered little damage?
* sediment shakes more violently (larger amplitudes) during an earthquake than bedrock.
35. Which is more likely to be damaged during an earthquake, a building down on low,
flat ground next to a bay or on top of a hill nearby (ignore the possibility of any
landsliding) and why?
* On low, flat ground next to a bay, soft sediment would shake more violently (larger
amplitudes) during an earthquake than harder rock on a hilltop nearby.
36. Draw simple sketches of a seismograph record of an earthquake (assuming the same
earthquake and the same distance from the earthquake):
a. on bedrock
b. on nearby soft
sediment
37. Why are strong concrete structures sometimes destroyed in a large earthquake,
whereas nearby homes built with frame construction (wood lumber) are little
damaged?
* concrete is rigid so it will crack and break rather than bending or flexing during
earthquake shaking
* wood is flexible and will bend or flex but not break during earthquake shaking
38. List the characteristics of brick walls in buildings 100 to 200 years old that make
them vulnerable to collapse during an earthquake. Assume the bricks and the mortar
between them are still of good quality.
* Brick walls are rigid and will crack and break rather than flex during an earthquake.
* Old brick walls are structural brick with no internal reinforcing (e.g.: rebar) and no
internal frame structure (structural wood walls).
39. Why is it advisable to keep well away from an old brick building during an
earthquake, even if the walls do not collapse or crumble and the windows do not
break?
* Many have overhanging brick parapets (brick roof overhangs) that break off and fall,
crushing anything below.
40. If you were sitting in a parked car next to an old brick building in Boston, St. Louis,
or Seattle, what would you do if an earthquake begins shaking violently – and why?
Assume that you cannot merely drive away.
* Immediately get out of the car and away from the building because brick walls or
parapets can fall and crush the car and any occupants.
41. Seismic waves travel at different velocities.
a. Which waves travel fastest and how fast do they move through the Earth’s mantle?
* P-waves. They travel at about 8 km/sec.
b. Which waves travel next fastest and how fast?
* S-waves. They travel at about 5 or 6 km/sec.
c. Which waves come next and how fast do they travel?
* Surface waves. They travel at about 2 or 3 km/sec.
d. Why are surface waves so much slower?
* They travel through near-surface rocks.
e. Which waves travel through solid rocks?
* P, S, and surface waves (or all earthquake waves)
42. Which seismic waves do not travel through liquids?
* S-waves
43. What is the motion of P-waves?
* compressional (or) compressing and stretching particles in the direction of wave travel.
44. What is the motion of S-waves?
* up and down shear motion of particles
45. What is the motion of surface waves?
* rolling like water particles in a water wave
46. What are the main types of fault motion? Provide the name and type of motion.
* strike-slip: lateral slip of one block past the other
* normal: steep fault with the block above the fault moving down
* reverse: steep fault with the block above the fault moving up
* thrust: gently-sloping fault with the block above the fault moving up
47. Extension of the Earth’s crust generally causes what type of fault or faults?
* normal faults
a. What type of plate boundary would produce such a fault or faults?
* rift (or spreading)
b. Compression of the Earth’s crust generally causes what type of fault or faults?
* reverse or thrust faults
c. What type of plate boundary would produce such a fault or faults?
* ocean-continent or continent-continent collision
48. What is the difference between elastic deformation and plastic deformation?
* Rocks subjected to stress involving elastic deformation return to their original form
after the stress is relieved; the deformation is reversible.
* Rocks subjected to plastic deformation do not return to their original shape but remain
deformed after the stress is relieved.
49. How do seismologists determine how far away an earthquake was from their
seismograph?
* They determine the time lag between the P- and S-wave arrival and, knowing the
different velocities of those waves, calculate the distance. The time lag increases the
farther they are from the earthquake.
50. How do seismologists determine the location of an earthquake?
* They determine the distance of the earthquake from at least 3 seismographs of quite
different locations and draw circles of distance from each seismograph.
* The earthquake was at the intersection of the 3 distance circles.
51. What is the difference between the epicenter and the focus of an earthquake?
* The focus is the point of origination of the earthquake (generally below the Earth’s
surface). The epicenter is the point on the Earth’s surface directly above
the
focus.
52. What does earthquake wave frequency mean?
* the number of wave crests (or cycles) to pass a location per second.
53. How is the Richter Magnitude Scale measured?
* the logarithm (to the base 10) of the amplitude of a set of earthquake waves on a
seismograph
54. How much greater amplitude of earthquake waves is a magnitude 6 earthquake than a
magnitude 5 earthquake?
* 10 times
55. How much greater energy is released by a magnitude 6 earthquake than a magnitude
5 earthquake?
* about 32 times
56. How much greater energy is released by a magnitude 7 earthquake than a magnitude
5 earthquake?
* 32 x 32 = 1024 times (more than 1000 times).
57. Which waves are used to determine earthquake magnitude?
* Any of them, P-, S-, or surface waves. The numbers are only a little different.
58. What can you conclude from the Gutenberg-Richter Frequency-Magnitude
relationship?
* There are frequent small earthquakes, fewer moderate-size and only rarely large
earthquakes.
a. What is the largest possible earthquake magnitude? Why?
* about magnitude 10 because the longest fault length that could be broken is the
circumference of the Earth, about 40,000 km.
b. What is the largest earthquake ever recorded since modern seismographs were
invented – or in the last 100 years?
* about 9.5
c. Where and when was that largest earthquake ever recorded?
* in Chile, 1960
59. Consider a magnitude 7 earthquake, near its source:
a. What is the likely amount of damage? Provide examples.
* most masonry structures destroyed.
b. What is the approximate rate of acceleration during the earthquake, in terms of
percentage of the acceleration of gravity or as a multiple of the acceleration of
gravity?
* generally > 80 percent of g.
c. What is the approximate time of shaking?
* 20-30 seconds (almost a half minute)
d. What is the approximate distance of offset?
* 2-3 meters
e. What is the approximate length of fault broken during the earthquake?
* 50-80 km
60. What is the relationship between the magnitude of an earthquake and the
displacement or offset on the fault causing the earthquake?
* A larger magnitude earthquake is generated by a larger fault offset.
61. Provide an example of the amount of fault offset and the magnitude of earthquake
generated.
* A 2-3 meter offset would generate a magnitude 7 earthquake.
62. What is the relationship between the magnitude of an earthquake and the total length
of fault broken?
* A larger magnitude earthquake is generated by a larger length of fault broken.
63. Provide an example of the amount of fault offset and the magnitude of earthquake
generated.
* A total break of 50-80 km length of fault broken would generate a magnitude 7
earthquake.
64. What is a sand boil?
* a low pile of sand
65. What causes formation of a sand boil? Be clear and to the point.
* Liquefaction and compaction of sand at depth expels the excess water to the
surface, carrying sand with it.
66. What is liquefaction?
* Earthquake shaking of loose water-bearing sand causes settling and compaction of the
sand and expulsion of the water.
67. What hazard does liquefaction pose, and for who or what?
* Differential settling of the ground can collapse or topple buildings.
68. Bedrock structures below ground can influence the strength of shaking of the ground
surface in an earthquake, which can affect damage to a building above such
structures. Explain how that works.
* Above an anticline (upfold), energy is dissipated and there is less damage.
* Above a syncline (downfold), energy is concentrated and there is more damage.
69. Apartment buildings with ground-floor garages are often heavily damaged during a
strong earthquake. What is the main damage and why?
* Ground-floor garages lack much lateral support because of their wide openings for car
entry so that floor falls over laterally.
70. Sometimes a single floor of a building (above the ground floor) collapses in an
earthquake, even though the rest of the building is relatively undamaged. What aspect
of the design of the building often leads to that collapse?
* A floor with too many windows lacks lateral (or diagonal) support.
71. Sometimes a single floor of a tall building (above ground floor) collapses in an
earthquake even though the floors have identical construction. Why?
* The frequency of shaking of the ground matches the frequency of shaking of the
building.
72. What aspect of building design can help keep an intermediate floor of a building
from falling over or collapsing in a strong earthquake?
* diagonal braces or shear walls
73. Although single-story frame (wood construction) houses don’t often collapse in an
earthquake, they are sometimes severely damaged. What is the most common cause
of such damage and how could it have been prevented?
* They shake off their foundations.
* The house should be well bolted to the foundation.
74. What are some inexpensive ways to minimize earthquake damage to a single-story
frame (wood construction) house?
* Anchor the floor to the foundation.
* Install diagonal braces or sheets of plywood along walls.
* Anchor loose, heavy objects to the floor and walls – for example, water heaters,
refrigerators, book cabinets, TV sets
75. Why do the wood floors in old brick buildings sometimes collapse in a strong
earthquake, even though the brick walls do not? Be specific.
* The joists (horizontal wood floor beams) often rest loosely in slots in the brick walls.
Lateral shaking of the walls can shake the floor beams out of the slots and permit
them to fall.
76. Parking garages with strong reinforced concrete uprights and strong reinforced
concrete horizontal support beams often fail in a strong earthquake, even though the
concrete does not crumble? Why? Be specific.
* The welds that hold the horizontal beams to the vertical supports often crack, or the
sliding joints that permit thermal expansion and contraction, slide off during
earthquake shaking.
77. Sometimes a tall, strongly constructed newer building next to a shorter, older building
will be severely damaged in an earthquake. Explain briefly and concisely the nature
of the damage and why it occurs.
*Different frequencies of shaking of the tall and shorter building cause them to bang into
one another. That causes the tall building to collapse at the height of the shorter
building.
78. Buildings of different heights shake back and forth at different frequencies. Which
shake at higher frequencies, short buildings or tall buildings?
* short buildings
a. What is the approximate frequency of shaking, or back and forth sway, of a typical 2story building?
* 5-10 back and forth motions per second (= 5-10 Hz) or 1/5 -1/10 second per back and
forth motion.
b. What is the approximate frequency of shaking, or back and forth sway, of a typical 20story building?
* 0.2 back and forth motions per second (= 0.2 Hz) or 5 seconds per back and forth
motion.
79. What can be done to a building, either during construction, or after, to reduce the
shaking of a building during an earthquake, and therefore reduce the possibility of
severe damage?
* Use base isolation pads between the building and its foundation.
a. How does this work?
* The base isolation pads act as shock absorbers to minimize transfer of ground shaking
to the building.
Chapter 3 - 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
c. * 20-30 cycles per second
d. 2000-3000 cycles per second
e. 20,000-0,000 cycles per second
2. Which type of earthquake waves shake with the largest amplitudes (largest
range of motion)?
a. Compressional waves
b. Shear waves
c. * Surface waves
d. P-waves
e. S-waves
3.
a.
b.
c.
d.
e.
Which of the following would be the safest place to be in an earthquake?
In bed
In a brick building
In a building with concrete walls
* In a frame (wood) house
In a building with stone walls well cemented together
4. How is the distance to the source of an earthquake determined?
a.
b.
c.
d.
e.
by calling many seismograph operators to see who felt it most strongly
* by subtracting the travel times of P- and S-waves.
by measuring the frequency of the P-waves as they arrive at a seismograph
by measuring the height of the S-waves recorded on a seismograph
by adding the travel times of the L-waves and the Raleigh waves.
5.
a.
b.
c.
d.
e.
What does the Richter Magnitude Scale depend on?
* the maximum amplitude of earthquake waves on a seismograph
the frequency of P-waves recorded on a seismograph
the intensity of shaking during the earthquake
the amount of destruction by the earthquake
the distance to the earthquake focus
6. A magnitude 7 earthquake has how much higher ground motion than a
magnitude 6 earthquake on a seismogram?
a. twice as high
b. * 10 times higher
c. 32 times higher
d. about 100 times higher
e. about 1000 times higher
7. Which type or types of earthquake waves move only near the surface of the
earth?
a. all earthquake waves
b. P- waves
c. * surface waves
d. S-waves
e. waves from faults that break near-surface rocks
8.
a.
b.
c.
d.
e.
What kind of material is subject to liquefaction during an earthquake?
clay saturated with salt water
almost any mix of sand and clay with water between the grains
swelling clay saturated with water
* loose sand grains with water between the grains
poorly compacted artificial fill dumped into the edge of a bay to add usable land
9.
a.
b.
c.
d.
e.
Which of the following make the safest house walls during an earthquake?
four inches of concrete
stone blocks well cemented together
bricks tightly mortared together
adobe
* two by four inch lumber covered with plywood
10. Which of the following is most likely to fail in an earthquake?
a. * a 5-story and a 10-story building of identical construction set 30 centimeters apart
b. a 5-story building and a 10-story building of identical construction set 4 meters apart
c. two identical 10-story buildings set 30 centimeters apart
d. two identical 30-story buildings set 30 centimeters apart
e. two identical 100-story buildings set 10 centimeters apart
11. Most of the deaths in the 1989 Loma Prieta earthquake in the San Francisco Bay
area were:
a. from collapse of buildings in San Francisco
b. from collapse of a section of the suspension bridge crossing the bay to Oakland
c. from collapse of old brick buildings in the area
d. * from collapse of an elevated reinforced concrete freeway
e. from collapse of a high-rise building constructed on San Francisco Bay fill
12. Parking garages often fail and fall during an earthquake for what reason?
a. lack of steel reinforcing bars
b. 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 support ledge because they are often not
tightly bolted to that ledge.
e. The vertical concrete supports are too thin to support the load
13. What is the approximate P-wave velocity through the Earth’s mantle?
a. 8 meters per second
b. 80 meters per second
c. * 8 kilometers per second
d. 80 kilometers per second
e. 800 kilometers per second
14. Which type or types of earthquake waves arrive at a distant seismograph most
quickly by traveling by moving through the mantle of the Earth?
a. * both P- and S-waves
b. both P- and L-waves
c. both S- and L-waves
d. only S-waves
e. only P-waves
15. Which type of earthquake waves do the most damage?
a. compressional waves
b. shear waves
c. body waves
d. P-waves
e. * Surface waves
16. Which earthquake waves arrive first?
a. * P-waves
b.
c.
d.
e.
S-waves
L-waves
shear waves
surface waves
17. Which earthquake waves arrive from the source last?
a. P-waves
b. S-waves
c. * Surface waves
d. shear waves
e. body waves
18. Surface waves are the most destructive type of earthquake waves to buildings
because they:
a. are compressional waves.
b. are shear waves.
c. first compress the material and then pull it apart
d. move with the highest velocities.
e. * have larger amplitudes of shaking.
19. Which waves have the lowest frequencies?
a. P-waves
b. S-waves
c. * surface waves
d. compressional waves
e. shear waves
20. What does the Mercalli Intensity Scale depend on?
a. * how much damage occurred in an area
b. the intensity of shaking of the seismograph
c. the amplitude of movement of the seismograph needle
d. the strength of rocks broken along the fault
e. the frequency of the earthquake waves as they reach the seismograph.
21. How much more energy is released in a magnitude 7 earthquake than in a
magnitude 6 earthquake?
a. about double
b. about 3 times
c. about 10 times
d. * about 32 times
e. about 100 times.
22. Moment magnitude depends on what main factor or factors?
a. total offset distance on the fault during the earthquake
b. total length of fault ruptured
c.
* shear strength of the rocks displaced, total surface area of rocks ruptured, and
average slip distance on the fault
d. frequency of movement of the earthquake waves and the total time of shaking
e. the amplitude of seismograph swing at the first moment of arrival of the shaking.
23. Between magnitude 7.0 and magnitude 8 earthquakes, about how much harder
is the shaking (how much increase in the acceleration of the ground)?
a. actually less acceleration because the frequency is lower
b. * not much
c. twice as hard.
d. about 10 times
e. about 32 times
24. If you find a well exposed fault that moved before seismographs were available,
you can infer the approximate magnitude of earthquake by:
a. measuring the largest size tree snapped off by the shaking
b. measuring the average size of the largest rocks moved in the earthquake
c. measuring the strength of the rocks that the earthquake managed to break
d. measuring the total area affected by the tsunami wave produced by the event
e. * measuring the total length of fault break during the event
25. Which of the following characteristics of the ground under a building would not
increase the danger of its destruction during an earthquake.
a. soft mud rather than bedrock
b. loose sand filled with water
c. syncline (downfold) in bedrock below the ground surface
d. * an anticline (upfold) in bedrock below the ground surface
e. layers oriented parallel to the hillside on which the building sits.
26. Which factor is not likely to contribute to building collapse in an earthquake?
a. ground-floor garages
b. many windows on any floor
c. walls loosely anchored to floors to provide flexibility
d. building oscillation frequency similar to the earthquake vibration frequency
e. building oscillation frequency quite different than the earthquake vibration frequency
27. Since most deaths in earthquakes are caused by buildings and other structures,
what sometimes causes collapse of a mid-floor of a building (e.g.: 3rd floor of a 7story building) when the other floors remain standing?
a. * building oscillates at similar frequency as the ground during an earthquake
b. building oscillates a frequency quite different than that of the ground in earthquake
c.
higher levels of many buildings are more-lightly built because they don’t have to
carry
the load of as many floors above
d. many buildings have more windows on higher floors where the views are better
e. most buildings bend more at half their height because that is their point of inflexion
28. Which of the following is not true? During a moderately strong earthquake
a.
b.
c.
d.
e.
wood-frame houses:
rarely have any measurable damage.
are flexible and will not generally collapse
may be shaken off their foundations but not crush their occupants
* are generally safe for the occupants though the house may be severely damaged.
are generally not strongly reinforced and people inside are often killed
29. In many old brick or stone buildings:
a. the floor beams are supported by separate vertical wood posts
b. the floor beams are anchored to the walls by steel angle irons
c. * the floor beams rest loosely in notches in the walls
d.
brick or stone on the walls is merely for appearance. The internal structure
provides the strength.
e.
brick or stone was erected by old-style craftsmen who took the time to make them
strong enough to survive most earthquakes.
30. Which of the following is not true of many old brick or stone buildings in an
earthquake?
a. Flexing of the walls can permit the floor beams to pull out and the floors to fall.
b.
Brick walls in old buildings are often three bricks thick and can withstand a
strong earthquake.
c. * Because of its mortar brick walls can flex enough to withstand most earthquakes.
d. Bricks falling from buildings often crush cars which would often kills passengers.
e.
Stone walls are no better than brick walls in an earthquake.
31. Which of the following is not true? Structures on soft sand or mud are often
destroyed in an earthquake, when those on nearby bedrock are nearly
undamaged because:
a. bedrock shakes with small amplitude vibrations
b. * soft sediment transmits earthquake waves at higher velocities.
c. soft sediment shakes with large amplitude vibrations
d. soft sediment can liquefy
e. soft sediment can landslide
32. The double-deck freeway at the east edge of San Francisco Bay collapsed in the
1989 Loma Prieta earthquake because:
a. it was too tall for its height
b. it lacked steel reinforcing bars
c. strong shaking lasted for more than the 30 minutes it was designed for
d. * it was built across soft muds
e. water from San Francisco Bay rotted the foundation material, weakening it
33. It is advisable to keep well away from an old brick building during an
a.
b.
c.
d.
e.
earthquake, because:
old brick walls are generally not well anchored to the ground and often topple over
the ornamental brick of the walls is not firmly attached to the main structure of
the building and they easily separate and fall.
the frequency of earthquake shaking matches the frequency of flexure of brick
walls, they buckle in the middle, and fall
the mortar in old brick walls is generally crumbly, permitting groups of bricks to
shake out and fall
* overhanging brick parapets often break off and fall.
34. What is the motion of P-waves?
a. straight line without any up and down or lateral motion
b. * compressing and stretching particles in the direction of wave travel.
c. up and down motion in a vertical plane, in the direction of wave travel
d. circular motion in a vertical plane, like a water wave
e. circular motion in a horizontal plane
35. What is the motion of S-waves?
a. straight line without any up and down or lateral motion
b. compressing and stretching particles in the direction of wave travel.
c. * up and down motion in a vertical plane, in the direction of wave travel
d. circular motion in a vertical plane, like a water wave
e. circular motion in a horizontal plane
36. What is the motion of surface waves?
a. straight line without any up and down or lateral motion
b. compressing and stretching particles in the direction of wave travel.
c. up and down motion in a vertical plane, in the direction of wave travel
d. * circular motion in a vertical plane, like a water wave
circular motion in a horizontal plane
37. Extension of the Earth’s crust generally causes what type of fault or faults?
a. * normal faults
b. reverse faults
c. thrust faults
d. transform faults
e. strike-slip faults
38. Compression of the Earth’s crust generally causes what type of fault or faults?
a. normal faults
b. * reverse faults
c. transform faults
d. strike-slip faults
e. gravitational faults
39. What is the “elastic rebound” theory?
a.
b.
c.
d.
e.
Rocks along a fault slowly bend, then snap back during an earthquake, so that
afterwards rocks across the fault show no offset.
Rocks of the Earth’s crust bend down under the load of a mountain range, then
rebound quickly after the mountain is eroded away.
Certain peculiar types of rocks flex elastically when they are dropped on a hard
surface.
Rocks are compressed elastically as earthquake waves pass, then rebound to their
original positions.
* Rocks slowly bend until they break and snap back during an earthquake
40. What is meant by plastic deformation? Rocks deformed plastically:
a. flow like fluids.
b. can bend back and forth many times without breaking or losing shape.
c. return to their original shape after the stress is relieved; the deformation is
reversible.
d. * do not return to their original shape but remain deformed after the stress is
relieved.
e. crack and break under small stresses.
41. Seismologists determine the location of an earthquake by:
a. comparing the strength of the P- and S-waves.
b. sensing the direction of the earthquake source from their seismograph
c. calling the seismograph operator closest to the earthquake.
d. using their seismograph with a method called triangulation
e. * drawing circles of distance from at least three different seismographs locations
42. The epicenter of an earthquake is the:
a. center of a great-circle arc the fault traces on the surface of the Earth
b. subsurface geometric center of the whole area of rocks broken in the fault.
c. central position along the Earth’s surface of the total length of fault broken
d. * point on the Earth’s surface directly above the point of initial fault breakage
e. point, below the surface, at which the earthquake-generating fault begins to break
43. What does earthquake wave frequency mean?
a. how often an earthquake strikes a certain area.
b. * the number of wave crests to pass a location per second
c. the total number of waves generated by an earthquake
d. the number of crests of an earthquake wave from the source to your seismograph.
e. the number of back and forth motions of building sway during an earthquake
44. Which waves are used to determine earthquake magnitude?
a. only the P-waves
b. only the S-waves
c. either the P- or the S-waves
d. only the surface waves.
e. * Any of them, P-, S-, or surface waves
45. What can you conclude from the Gutenberg-Richter Frequency-Magnitude
relationship?
a. large earthquakes are frequent
b. large earthquakes have high frequency
c. large earthquakes shake buildings with high frequency
d.
There are twice as many small earthquakes as moderate-size earthquakes and
twice as many moderate-size earthquakes as giant earthquakes.
e.
* There are numerous small earthquakes, fewer moderate-size and only rarely
large earthquakes
46. What is the largest possible earthquake magnitude, and why?
a.
* about 10 because the longest fault length that could be broken is the
circumference of the Earth
b. 9, since that is the upper end of the scale to which all others are compared
c. about 14 since the Earth would split in half with anything larger
d. about 10 since no rocks are strong enough to withstand a larger event
e. about 10 since that is the largest event ever recorded.
47. What is the largest earthquake ever recorded since modern seismographs were
invented – or in the last 100 years? And where was it?
a. * about 9.5, in Chile
b. about 9, in Sumatra in 2004
c. over 9, in Alaska in 1964
d. over 9, in the Himalayas in the 1920s
e. over 9, off the coast of Madagascar in the 1920s
48. For a magnitude 7 earthquake, the approximate time of shaking is:
a. 2 seconds
b. 6 or 7 seconds
c. * 20 or 30 seconds
d. 2 minutes
e. 20-30 minutes
49. For a magnitude 7 earthquake, the approximate amount of fault offset is:
a. 2-3 centimeters
b. 20-30 centimeters
c. * 2-3 meters
d. about 50 meters
e. It depends on how strong the rocks are that are broken along the fault
50. For a magnitude 7 earthquake, the approximate length of fault broken is:
a. 5-8 meters
b. about 50 meters
c. 50-80 meters
d. * 50-80 kilometers
e. 800-1000 kilometers
51. What is a sand boil and how is it formed?
a. * a low pile of sand formed by an earthquake shaking sand into a smaller space
b. a low pile of sand formed by thermal swelling of sand from friction during an
earthquake.
c. boiling of water in sand by friction between grains from violent earthquake shaking
d. a boil-like bulge of the ground caused by interference of earthquake waves
an underground cavity formed by earthquake shaking
52. Why do freeway overpasses often collapse in a strong earthquake, even though
their supports are concrete.
a. the overpasses are too long to be without additional supports
b. the overpasses lack internal reinforcing rods.
c. poor quality concrete was used in construction
d. heavy concrete in the roadways shakes back and forth, breaking the supports at their
bases
e. * earthquake shaking crumbles the concrete so the rebar buckles
53. Why does a single floor of a building (above the ground floor) collapse in an
earthquake, even though the rest of the building is relatively undamaged.
a. A floor without an internal shear wall because of internal design requirements.
b. * The frequency of shaking of the building matches that of the ground
c. The frequency of shaking of the building is much greater than that of the ground.
d. The frequency of shaking of the building is much lower than that of the ground.
e. Poor linkage of reinforcing bars in concrete supports between floors
54. What commonly causes severe damage in single-story frame (wood construction)
houses in an earthquake?
a. They bounce up and down so much that the internal plaster or sheetrock crumbles.
b. They bounce up and down so much that the nails pull out of the wood supports.
c. The shaking shatters the windows so the glass cuts up everything.
d. * They shake off their foundations.
e. They totally collapse.
55. What is ineffective in reducing the possibility of earthquake damage to a
building?
a. using base isolation pads between the building and its foundation.
b. using diagonal bracing in the walls
c. add sheets of plywood to the walls
d. anchoring the building to its foundation
e. * loading the ground floor with heavy weights to prevent it from moving so much.
56. Buildings sway back and forth in an earthquake. A 20-story building oscillates:
a. 5 times per second
b. once per second
c. * once per 5 seconds
d. once per minute
e. once per 5 minutes
57. What is a common back and forth distance of shaking at the top of a modern 20story structural steel building in a magnitude 7 earthquake?
a. 3-4 centimeters
b. 30-40 centimeters
c. * 3-4 meters
d. 30-40 meters
e. 3-4 kilometers
58. Why do freeway overpasses often collapse in a strong earthquake, even though
their supports are concrete.
a. the overpasses are too long to be without additional supports
b. the overpasses lack internal reinforcing rods.
c. poor quality concrete was used in construction
d. heavy concrete in the roadways shakes back and forth, breaking the supports at their
bases
e. * earthquake shaking crumbles the concrete so the rebar buckles
59. Why does a single floor of a building (above the ground floor) collapse in an
earthquake, even though the rest of the building is relatively undamaged.
a. A floor without an internal shear wall because of internal design requirements.
b. * The frequency of shaking of the building matches that of the ground
c. The frequency of shaking of the building is much greater than that of the ground.
d. The frequency of shaking of the building is much lower than that of the ground.
e. Poor linkage of reinforcing bars in concrete supports between floors
60. What commonly causes severe damage in single-story frame (wood construction)
houses in an earthquake?
a. They bounce up and down so much that the internal plaster or sheetrock crumbles.
b. They bounce up and down so much that the nails pull out of the wood supports.
c. The shaking shatters the windows so the glass cuts up everything.
d. * They shake off their foundations.
e. They totally collapse.
61. What is ineffective in reducing the possibility of earthquake damage to a
building?
a. using base isolation pads between the building and its foundation.
b. using diagonal bracing in the walls
c. add sheets of plywood to the walls
d. anchoring the building to its foundation
e. * loading the ground floor with heavy weights to prevent it from moving so much.
62. Buildings sway back and forth in an earthquake. A 20-story building oscillates:
a. 5 times per second
b. once per second
c. * once per 5 seconds
d. once per minute
e. once per 5 minutes
63. What is a common back and forth distance of shaking at the top of a modern 20story structural steel building in a magnitude 7 earthquake?
a. 3-4 centimeters
b. 30-40 centimeters
c. * 3-4 meters
d. 30-40 meters
e. 3-4 kilometers
64. Which type of fault would result from tensional stresses?
a. * normal
b. reverse
c. thrust
d. transform
e. strike-slip
65. Along the San Andreas Fault in California, how many magnitude 7 earthquakes
would it take to relieve the same stress in the rocks as one magnitude 8
earthquake?
a. just 1
b. about 3
c. about 10
d. * about 32
e. about 300
66. The San Fernando Valley and Northridge earthquakes were both about
magnitude 6.7; both caused significant damage in the Los Angeles area. How
many magnitude 6.7 earthquakes would it take to relief the rock stress of one
magnitude 7.7 earthquake?
a. just 1
b. about 3
c. about 10
d. * about 32
e. about 300