Chapter 11 Earthquakes
Earth: An Introduction to Physical Geology, 9e (Tarbuck/Lutgens)
11.1 Multiple-Choice Questions
1) The elastic rebound theory for the origin of earthquakes was first proposed by ________
following the ________ earthquake.
A) Reid; 1906, San Francisco
B) Giuseppe; 1925, Pizza Lake
C) Richter; 1989, Loma Prieta
D) Mohorovicic; 1964, Anchorage
Answer: A
Diff: 1
2) Which one of the following statements concerning foci and epicenters is correct?
A) The focus is the faulted point on the surface directly above the epicenter.
B) The fault first cracks at the epicenter and breaks through to the surface at the focus.
C) The epicenter is at the surface directly above the focus where the earthquake initiates.
D) The earthquake starts at the focus and the rupture extends down to the epicenter.
Answer: C
Diff: 1
3) Which one of the following statements is correct?
A) P waves travel through solids; S waves do not.
B) P and S waves travel through liquids, but P waves do not travel through solids.
C) S waves travel through solids and P waves travel through liquids.
D) P and S waves travel through liquids, but S waves do not travel through solids.
Answer: C
Diff: 1
4) ________ have the highest velocities.
A) Primary waves
B) Secondary waves
C) Surface waves
D) Refracted S waves
Answer: A
Diff: 1
5) The ________ is a direct measure of the distance from a seismic receiving station to the focus
of a distant earthquake.
A) time interval between the first P and S- wave arrivals
B) magnitude of the ground acceleration of surface wave passing a receiving station
C) time elapsed between the first P-wave arrivals from the first and last aftershocks
D) time interval between the first P-wave and the last surface wave
Answer: A
Diff: 1
6) Which one of the following is true regarding tsunamis?
A) They travel as deep-water waves at speeds greater than surface seismic waves but
slower than S waves.
B) Their wave heights decrease and wavelengths increase as they move into shallower
C) They are started by fault-induced, horizontal shifts in the seafloor that suddenly propel
great masses of water in opposite directions.
D) They occur in the open ocean, wavelengths are many miles or kilometers and wave
heights are only a few feet.
Answer: D
Diff: 1
7) On a typical seismogram, ________ will show the highest amplitudes.
A) P waves
B) S waves
C) surface waves
D) body waves
Answer: C
Diff: 1
8) Which of the following foundation materials is most stable during earthquake shaking?
A) bedrock
B) unconsolidated moist soil
C) water-saturate
D) sand and mud
Answer: A
Diff: 1
9) The ________ magnitude scale is a measure of the energy released. It does not directly
measure the extent of building damage.
A) Gutenberg
B) Reid
C) Mercalli
D) Richter
Answer: D
Diff: 1
10) Why was the Marina District, San Francisco, heavily damaged in the 1906 and 1989 quakes?
A) The epicenters of both quakes were right under the district.
B) Shaking was no more extensive than elsewhere in the city, but the whole district
burned following each quake.
C) The area is built on consolidated rock, causing the shaking to be amplified.
D) Liquefaction and foundation failures were common.
Answer: D
Diff: 1
11) Why did the 1988 Armenian earthquake (in the Armenian Republic, then part of the former
Soviet Union) result in an estimated 25,000 deaths?
A) The buildings were constructed on unconsolidated, water-saturated, lakebeds and
foundation failures were common.
B) Numerous, poorly constructed, top heavy, concrete slab buildings collapsed.
C) The quake hit at rush hour; thousands of motorists were killed when freeways
D) The area was densely populated and right at the epicenter of a magnitude 8.5 quake.
Answer: B
Diff: 1
12) ________ is the maximum possible damage designation on the Mercalli scale.
B) 12
C) X
D) 10
Answer: A
Diff: 1
13) Seismic gaps are ________.
A) unusually quiet zones along known active faults
B) slices of land bounded by active, strike-slip faults on all sides
C) inactive faults cutting across high ridges and water gaps
D) segments of active faults with creep rates of up to 2 cm/yr
Answer: A
Diff: 1
14) How was the Turnagain Heights area of Anchorage, Alaska, damaged during the 1964
A) It was hit by a large tsunami and then buried by a rock avalanche.
B) It burned in a fire set off by broken gas lines.
C) A weak, subsurface, clay layer failed, resulting in numerous landslides.
D) all of the above
Answer: C
Diff: 1
15) Approximately how often do locked segments of the San Andreas Fault (California) break,
resulting in major earthquakes?
A) once every six hundred years
B) once every fifteen years
C) once every ten thousand years
D) once every hundred and fifty years
Answer: D
Diff: 1
16) would result in the largest area of ground shaking damage.
A) shallow-focus quake along the Mississippi Valley fault zone
B) deep-focus quake off the coast of North Africa
C) shallow-focus quake along the San Andreas Fault
D) very deep-focus quake beneath the Aleutian Islands
Answer: A
Diff: 2
17) The ________ is the point of origination for an earthquake.
A) fault point
B) focus
C) seismic centroid
D) epizone
Answer: B
Diff: 1
18) Approximately how much more energy is released in a 6.5 Richter magnitude earthquake
than in one with magnitude 5.5?
A) 3000 times
B) 3 times
C) 300 times
D) 30 times
Answer: D
Diff: 1
19) ________ is a widely accepted explanation for the mechanism that generates earthquakes.
A) Dow's recovery theory
B) Dupont's plastic-slip theory
C) Richter's wave-snap theory
D) Reid's elastic rebound theory
Answer: D
Diff: 1
20) P waves ________.
A) propagate only in solids
B) are faster than S waves and surface waves
C) have higher amplitudes than do S waves
D) produce the strongest ground shaking
Answer: B
Diff: 1
21) The Mercalli Scale is a scale from ________.
A) 1 to 12 that rates the energy required for faulting to occur
B) 1 to 10 that rates the energy released by an earthquake
C) I to XII that rates the structural damage due to an earthquake
D) I to X that rates the total energy released during the main quake and all aftershocks
Answer: C
Diff: 1
22) What are the smaller magnitude quakes that follow a major earthquake?
A) exoshocks
B) aftershocks
C) hyposhocks
D) epishocks
Answer: B
Diff: 1
23) The largest lateral, ground displacement is produced by ________.
A) first P arrival reflecting from the inner-outer core boundary
B) the S wave reflected from the core-mantle boundary
C) horizontally vibrating surface waves
D) vertically vibrating P waves refracted across the Moho
Answer: C
Diff: 1
24) The ________ is used to record ground shaking and the earthquake-magnitude scale was
invented by ________.
A) rayoscope; Mercalli
B) vibroscope; Rector
C) polygraph; Freud
D) seismograph; Richter
Answer: D
Diff: 1
25) The epicenter of an earthquake is the ________.
A) point where the fault cracking initiates
B) surface location directly above the point where the fault slip initiates
C) point where the minimum ground shaking is recorded
D) point of most intense, structural damage associated with ground shaking
Answer: B
Diff: 1
26) Energy is stored in rocks adjacent to the site of a future earthquake as ________.
A) elastic strain
B) plastic flow energy
C) thermal energy
D) plastic strain
Answer: A
Diff: 1
27) Why was building damage so extensive in the 1985 Mexico City quake?
A) The epicenter was right in the city.
B) The Richter magnitude was 8.8, and the focus was only 10 miles from the city.
C) Much of the city is built on filled-in, shallow lakes and swampland.
D) The steel frame buildings were rigid and lacked the flexibility to withstand lateral
swaying during even a moderate magnitude quake.
Answer: C
Diff: 1
28) The ________ earthquake was accompanied by major damage from tsunamis and ground
A) San Francisco, CA, 1906
B) Loma Prieta, CA, 1989
C) Northridge, CA, 1994
D) Anchorage, AK, 1964
Answer: D
Diff: 1
29) ________ was struck by three, major earthquakes during the winter and spring months of the
years 1811-1812.
A) New Madrid, Missouri
B) Nome, Alaska
C) Los Angeles, California
D) Charleston, South Carolina
Answer: A
Diff: 1
30) Which one of the following best characterizes tsunamis?
A) They cause the land to ripple and oscillate.
B) They are faster than seismic surface waves.
C) They have relatively small amplitudes compared to their very long wavelengths.
D) They are easily seen at sea but are lost in the swell and breaking waves along a coast.
Answer: C
Diff: 1
31) The ________ earthquake was accompanied by extensive fire damage.
A) Anchorage, 1964
B) San Francisco, 1906
C) Mexico City, 1985
D) Yerevan, Armenia, 1988
Answer: B
Diff: 1
32) ________ refers to the tendency for a foundation material to lose its internal cohesion and fail
mechanically during earthquake shaking.
A) Slurrying
B) Liquefaction
C) Motion slip
D) Seismoflowage
Answer: B
Diff: 1
33) The ________ is directly related to the Richter earthquake-magnitude rating.
A) average of the highest and lowest Mercalli intensity ratings
B) distance between the receiving station and the epicenter
C) time interval between the first P-wave arrival and the first P wave reflected from the
crust-mantle discontinuity
D) amplitude of the seismic waves
Answer: D
Diff: 1
34) Which one of the following regarding the San Andreas Fault in California is true?
A) a sliver of continent west of the fault is moving northward with the Pacific plate
B) a sliver of land west of the fault is sinking under the North American plate
C) continental crust east of the fault is moving east with the North American plate
D) the North American plate is slowly moving northward with respect to the continental
fragment west of the fault
Answer: A
Diff: 2
11.2 Word Analysis Questions
Examine the words and/or phrases for each question below and determine the relationship among the
majority of words/phrases. Choose the option which does not fit the pattern.
1) A) p-wave
B) s-wave
C) surface wave
D) body wave
Answer: surface wave
Diff: 1
2) A) focus
Answer: seismograph
B) seismograph
C) epicenter
D) fault
Diff: 1
3) A) Alaska, 1964
B) San Francisco, 1906 C) Mexico City, 1985 D) New Madrid, 181112
Answer: New Madrid, 1811-12
Diff: 2
4) A) tsunami
Answer: fire
B) fire
C) liquefaction
D) seiche
C) Richter
D) amplitude
Diff: 2
5) Modified Mercalli
B) energy
Answer: Modified Mercalli
Diff: 1
11.3 True/False Questions
1) S waves can travel through solid and liquid media.
Answer: FALSE
Diff: 1
2) The time between the first P-wave and S-wave arrivals is a measure of the distance from a
receiving station to the epicenter of the earthquake.
Answer: TRUE
Diff: 1
3) Earthquakes result from the sudden release of elastic strain energy previously stored in
rocks surrounding a zone of fault movement.
Answer: TRUE
Diff: 1
4) Reid's elastic rebound theory of earthquake generation was based on his studies following
the 1906 San Francisco earthquake.
Answer: TRUE
Diff: 1
5) Following a major earthquake, aftershocks diminish in magnitude but may still be powerful
enough to destroy or further damage weakened buildings.
Answer: TRUE
Diff: 1
6) Horizontal vibrations, such as induced by strike-slip faulting, are generally much more
dangerous to tall buildings than vertical up and down ground shaking.
Answer: TRUE
Diff: 1
7) Tsunamis are caused by sudden displacement of large volumes of seawater.
Answer: TRUE
Diff: 1
8) Because their energy dissipates rapidly in deep ocean waters, tsunamis seldom pose any
danger to coastal areas far away from the causative earthquake.
Answer: FALSE
Diff: 1
9) The Mercalli earthquake intensity scale uses Roman numerals from I to XII, XII being the
highest intensity.
Answer: TRUE
Diff: 1
10) The Richter earthquake magnitude scale is based on the total amount of energy released by
the earthquake.
Answer: TRUE
Diff: 1
11) The epicenter of an earthquake is on the surface of the Earth directly above the focus.
Answer: TRUE
Diff: 1
12) Deep-focus earthquakes are usually very destructive because the seismic shaking is
amplified as the waves approach the surface.
Answer: FALSE
Diff: 1
13) Some large earthquakes are preceded by smaller magnitude foreshocks.
Answer: TRUE
Diff: 1
14) In general, P- and S-wave velocities increase abruptly as the waves pass downward across
the crust-mantle boundary.
Answer: TRUE
Diff: 1
15) Locked fault segments experience slow creep movements, rendering them less likely to host
a large magnitude earthquake.
Answer: FALSE
Diff: 1
16) During the 1906 San Francisco earthquake, fire destroyed many buildings that were
otherwise undamaged or only slightly damaged by the ground shaking.
Answer: TRUE
Diff: 1
17) If the P, S, and surface waves arrive almost simultaneously, the seismic recording station is
virtually at the epicenter of the earthquake.
Answer: TRUE
Diff: 1
18) For shallow-focus earthquakes, surface-wave amplitudes are usually much larger than P and
S-wave amplitudes.
Answer: TRUE
Diff: 1
19) On earthquake distribution maps, the boundaries of the Earth's tectonic plates are shown as
zones of high seismic activity.
Answer: TRUE
Diff: 1
20) Unconsolidated, water-saturated soils or sediments provide good foundation materials for
buildings and other structures.
Answer: FALSE
Diff: 1
11.4 Short Answer Questions
1) The ________ is the site of initial rupturing associated with an earthquake.
Answer: focus
Diff: 1
2) The ________ is the point on the surface directly above the site of initial earthquake rupture.
Answer: epicenter
Diff: 1
3) What instrument is used to record earthquake vibrations?
Answer: seismograph
Diff: 1
4) A ________ is one or more smaller earthquakes that sometimes precede a much larger, main
earthquake event.
Answer: foreshock
Diff: 1
5) ________ is the name of the earthquake-magnitude scale based on the amount of seismic
energy released during the event.
Answer: Richter
Diff: 1
6) What intensity scale describes the extent of structural damage due to earthquake shaking?
Answer: Mercalli
Diff: 1
7) ________ is another name commonly used by scientists to denote seismic sea waves induced
by earthquakes.
Answer: Tsunami
Diff: 1
8) ________ are the first to arrive at distant receiving stations.
Answer: P-waves
Diff: 1
9) An earthquake of magnitude 7.5 releases about how much more energy than one of
magnitude 5.5?
Answer: 900
Diff: 2
11.5 Critical Thinking Questions
Use complete sentences, correct spelling, and the information presented in Chapter 11 to answer the
questions below
1) Tsunamis are only serious threats to coastal areas near an earthquake epicenter because the
waves have lost most of their energy after moving across 100 miles of open water. Is this
statement correct? Why or why not?
Diff: 2
2) Compare and contrast deep-focus verses shallow-focus earthquakes. Include such things as
geologic occurrence, damage potential from ground shaking, size of areas affected by each
one, etc.
Diff: 3
3) Would earthquakes of similar magnitudes in different regions of the Earth cause
approximately the same levels of damage necessarily? In your explanation, consider both
geologic and human-induced factors.
Diff: 3
11.6 Visualization Questions
1) Identify the focus and epicenter on the diagram below.
Answer: See figure 11.2 in chapter 11 of Earth, 9e
Diff: 1
2) Carefully study the seismogram below and note the features labeled A through G. On the
blanks provided beside each item below, note the letter below that corresponds to that item.
An S-wave a) ________
The first S-wave b) ________
The first P-wave c) ________
An L-wave d) ________
A surface wave e) ________
Answer: a) C or D b) D c) G d) B or A e) B or A
Diff: 2
3) Using the time-travel graph below, how long does it take a P-wave to travel 2000 km?
Answer: a) four minutes
Diff: 1
4) Study the cross section below.
Which of these two identical homes would suffer the most damage if an earthquake
occurred along the active fault?
a) ________
Explain your answer
Answer: a) home Y
b) Loose sand under home Y would experience liquefaction during a moderate or
strong earthquake, so home Y would settle down into the sand or fall over (because
the sand grains would vibrate apart in an earthquake).
Diff: 2