Geology review CH. 8

Chapter 8 Geology review

· Correct Answer is highlighted in Bold.

  • 1. A 7.2 magnitude earthquake

o Topic: n/a

o a. would be so large that a quake this size would occur only once a century.

o b. would have surface waves 10,000 times the amplitude of a 4.2 quake.

o c. would release approximately 33,000 times the energy of a 4.2 quake.

o d. is one of the largest possible and is classed as a great quake.

o e. would logically have a reading of about XII on the Mercalli scale.

o Feedback/Reference: There’s a three-step difference between a 4.2 and 7.2 quake. The difference in ground shaking (amplitude) for
this would be 10 x 10 x 10 = 1,000. The energy difference would be approximately 32 x 32 x 32, which is almost 33,000.

Section: 8.5, p. 230

  • 2. Which statement is TRUE?

o Topic: n/a

o a. P, S, L, and R are all body waves that pass through the Earth’s interior.

o b. The hypocenter (focus) is the point on the Earth’s surface directly above the epicenter.

o c. Governments are supportive of the worldwide seismic network because it can detect nuclear bomb tests as well as natural earthquakes.

o d. Water leakage from reservoirs cannot trigger quakes.

o e. S-waves travel twice as fast as P-waves.

o Feedback/Reference: L and R are surface waves; the epicenter is above the focus; water leakage can trigger quakes; and S-waves
travel at 60% the speed of P-waves. The epicenter is the point on Earth’s surface above the hypocenter—the location of fault rupture.

Section: 8.4, p. 226

Resources: see also section 8.3.

  • 3. A tsunami

o Topic: n/a

o a. is a special kind of tidal wave caused by the gravitational attraction of the Sun, not the Moon.

o b. can get big but never larger than 30 feet high.

o c. is dangerous near its source but dies out within about 200 miles.

o d. may be just a low and very broad wave at sea but both slows in speed and grows in height as it approaches shore.

o e. All the possible answers are correct.

o Feedback/Reference: Tsunamis are caused by volcanic or seismic activity or by undersea landslides, can get tens of meters high, and
can cross entire ocean basins.

Section: 8.7, p. 241

Resources: Figure 10.30; Flashcards

  • 4. Which process would not cause an earthquake?

o Topic: n/a

o a. the rapid alteration of atoms in a mineral in response to pressure changes in the mantle

o b. the lithification of sediment

o c. the violent, sudden eruption of a volcano

o d. the impact of a large meteorite

o e. an underground nuclear bomb test

o Feedback/Reference: Earthquakes are generally caused when the stress (“pent-up energy”) on a rock system exceeds the physical
ability of the rock system to contain it—and so the rock breaks. Less common, yet real causes of earthquakes include: phase changes of atoms in
minerals as pressure changes (e.g., the transformation of various forms of SiO2 from one to another), volcanic eruption, meteorite impacts, and nuclear

Section: 8.2, p. 218-219

  • 5. Earthquake prediction is not highly reliable, but geologists do know that

o Topic: n/a

o a. quakes will never happen in seismic gaps.

o b. short-term predictions usually do turn out to be correct.

o c. northern California, not southern California, is the area most likely to have the “Big One.”

o d. more earthquakes happen along plate boundaries than at intraplate locations.

o e. All the possible answers are correct.

o Feedback/Reference: Seismic gaps are areas of high seismic risk; accurate short-term predictions are rare; and nobody knows where
the “Big One” will strike.

Section: 8.6, p. 236; Fig. 8.14, p. 231

  • 6. Which of the following statements is FALSE regarding the 2010 Haiti earthquake?

o Topic: n/a

o a. The event was so destructive because of poor construction standards.

o b. Faulting occurred along a transform plate boundary.

o c. The earthquake generated a tsunami that was responsible for the majority of the lives lost.

o d. The earthquake was due to interactions between the Caribbean and North American plates.

o e. The likelihood of an earthquake was great because stress had been building on the fault for over 200 years.

o Feedback/Reference: No tsunami was generated by the Haiti earthquake. The high loss of life was due to the collapse of buildings
that were not built to resist shaking.

Section: Box 8.1, The Haiti Catastrophe of 2010, p.234

Resources: Box 8.1

  • 7. Which statement is TRUE?

o Topic: n/a

o a. Earthquakes in California are the result of reverse faulting along the San Andreas Fault.

o b. Earthquakes in California are the result of widening along the San Andreas Fault, which will eventually cause western California to sink into the

o c. Earthquakes in California are commonly above magnitude 7.5 because the San Andreas is such a large fault.

o d. Faults that have not pierced or ruptured the earth’s surface are not hazardous.

o e. All types of building construction are equally vulnerable to earthquake damage.

o Feedback/Reference: Faults that have not yet pierced the Earth’s surface cannot be visually identified or mapped by geologists, and
can only be detected by drilling or geophysical studies. Because of this they may be undetected until slip occurs along them, damaging structures that
were inadvertently built over them.

Section: 8.2, p. 220

Resources: n/a

  • 8. Which statement is TRUE? Liquefaction

o Topic: n/a

o a. can cause clay-rich sediment to turn into an unstable slurry of clay and water.

o b. is the sudden loss of strength of some soils that happens because of earthquake shaking.

o c. caused great damage in the Alaska quake of 1964.

o d. can affect sand layers below ground surface and cause them to erupt as sand volcanoes or sand boils.

o e. All the possible answers are correct.

o Feedback/Reference: All the possible answers are correct.

Section: 8.7, p. 238; Fig. 8.23, p. 241

Resources: Flashcards

  • 9. The displacement of a fault is the distance between two features along it that a geologist believes were once located directly next to one

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Geologists look for unusual and unique rock formations or structures along the two opposing sides of a fault to
reliably estimate total (or cumulative) offset.

Section: 8.2, p. 220; Fig. 8.4, p. 220

  • 10. Which statement is TRUE?

o Topic: n/a

o a. R- and L-waves are surface seismic waves.

o b. S-waves are compressional body waves; P-waves are shear body waves.

o c. Surface waves are the first to show up on a seismogram recording of a quake.

o d. Shallow-focus quakes do less damage than deep-focus quakes.

o e. All the possible answers are correct.

o Feedback/Reference: P-waves are compressional body waves that arrive first, followed by S-waves (shear body waves), and then by R-
and L(surface)-waves. Shallow-focus waves cause the most damage because they don’t lose much energy before reaching the surface.

Section: 8.3, p. 224; Fig. 8.7, p. 225

  • 11. Most major earthquakes and volcanic eruptions occur

o Topic: n/a

o a. in similar locations.

o b. along all three types of plate boundaries.

o c. within the continental lithosphere.

o d. along convergent plate boundaries.

o e. along divergent and convergent plates.

o Feedback/Reference: You may have to recall an earlier chapter to realize that volcanoes occur at only some convergent boundaries and
at few transform boundaries. Earthquakes occur at all three boundaries.

Section: 8.6, p. 232.

Resources: Fig. 10.18

  • 12. Which statement concerning tsunami events is FALSE?

o Topic: n/a

o a. The velocity of a tsunami wave increases when the wave moves from open ocean into shallower water.

o b. Tsunamis may be generated by underwater earthquakes, landslides in coastal mountain ranges, or submarine landslides.

o c. The interval between waves varies from about 15 minutes to an hour, and wave action may continue for several hours.

o d. Upthrust of the sea floor along a fault can displace huge amounts of water and result in giant tsunami waves.

o e. Tsunamis can travel as fast as jet planes (several hundred mph).

o Feedback/Reference: The wave slows down due to friction, and this causes the water to pile up higher and produce a taller wave.

Section: 8.7, p. 241

  • 13. Identify the FALSE statement. The Richter scale

o Topic: n/a

o a. measures the size of a quake in terms of the damage it does (its intensity).

o b. measures the amplitude of the largest deflection on a seismogram in response to specifically defined seismic waves at a specifically defined distance
and depth.

o c. is today termed a local magnitude reading (Mz).

o d. works well only for shallow, nearby earthquakes.

o e. requires use of a particular design of seismograph.

o Feedback/Reference: It measures quake size in terms of the ground motion it generates (its magnitude).

Section: 8.5, p. 229

Resources: Flashcards

  • 14. The primary reason that earthquake aftershocks occur is

o Topic: n/a

o a. the sudden dewatering of nearby seafloor sediments as they respond and re-equilibrate to new conditions following a main shock.

o b. a semi-self-sustaining “triggering event” of recrystallization of minerals into denser polymorphs, triggered by the shock waves of a large earthquake.

o c. fault creep.

o d. magmatic movement along newly created or newly weakened faults.

o e. stress that has not been fully released and/or was created by a main shock.

o Feedback/Reference: Aftershocks generally occur as newly shifted rock makes minor adjustments to altered stresses.

Section: 8.2, p. 224

Resources: Flashcards

  • 15. Identify the FALSE statement. Seismographs

o Topic: n/a

o a. may be of the mechanical type, consisting of a weight, spring, frame, pen, and revolving cylinder.

o b. may be electronic, consisting of a heavy cylindrical magnet, coil of wire, spring, and computer readout of the voltage generated.

o c. are sensitive enough to record ground movements down to only about one millimeter.

o d. located throughout the world contribute to a seismic network whose data is available worldwide.

o e. operate because of inertia; one part of the instrument remains motionless while the recording device moves in response to seismic waves.

o Feedback/Reference: A seismograph can detect ground motion down to a mere millionth of a millimeter—a sensitivity that is far
greater than can be felt by humans.

Section: 8.4, p. 226

  • 16. Identify the FALSE statement.

o Topic: n/a

o a. Normal faults result from stretching the Earth’s crust, thrust faults from squeezing it horizontally.

o b. The modern description of earthquake size is complex; it includes surface-wave magnitude, body-wave magnitude, local magnitude, and moment magnitude

o c. Moment magnitude (Mw) rating is the number now used for the official (archival) record.

o d. All earthquake magnitude scales are logarithmic, which means a difference of one unit in magnitude reading represents a ten-fold difference in ground

o e. The energy released from a magnitude 6.6 earthquake is 10 times greater than the energy released from a magnitude 5.6 earthquake.

o Feedback/Reference: The energy release that corresponds to a difference in magnitude increase of 1.0 is approximately 32; it is the
ground amplitude of passing earthquake waves that is 10 times greater, for a magnitude increase of 1.0.

Section: 8.5, p. 230

  • 17. Identify the FALSE statement.

o Topic: n/a

o a. Seismic waves become smaller in amplitude with increasing distance from the epicenter.

o b. Earthquake magnitude is based on ground motion recorded by a seismograph; intensity is based on the amount of damage produced.

o c. Contour lines representing Mercalli values are used to delimit zones of quake intensity; the greater the quake the higher the intensity values and the
wider the zones.

o d. The moment magnitude scale takes into account the size of the affected area and characteristics of the rock affected.

o e. Earthquakes do not occur at depths greater than about 100 km (60 miles).

o Feedback/Reference: Earthquakes can commonly occur as deep as 660 km (about 400 miles).

Section: 8.6, p. 232; Fig. 8.17(a), p. 235

  • 18. Which of the following is NOT a good technique for building earthquake-resistant structures?

o Topic: n/a

o a. Allow some degree of flexibility.

o b. Bolt bridge spans to the top of support columns.

o c. Wrap bridge supports with steel cables.

o d. Use supports that are capable of holding more than the static (unmoving) weight of the building.

o e. Use concrete-block rather than wood-frame construction.

o Feedback/Reference: Concrete blocks crack and tumble; wood-frame construction flexes and has a better chance of surviving quake

Section: 8.9, p. 247-248

  • 19. Identify the TRUE statement.

o Topic: n/a

o a. P- and L-waves are both surface waves.

o b. S- and P-waves are both surface waves.

o c. Surface waves originate at a hypocenter (focus) within the Earth.

o d. L- and R-waves are body waves.

o e. Surface waves arrive later and are generally more damaging than body waves.

o Feedback/Reference: Earthquake waves tend to arrive in order of increasing damage. P-waves (arriving first) generally alarm people
but cause little damage. S-waves (arriving next) are more alarming and more damaging. Surface waves (arriving last) tend to be the most destructive.

Section: p.224

  • 20. Identify the FALSE statement. Long-term earthquake predictions

o Topic: n/a

o a. are statements of the likelihood of an earthquake happening in some particular area within the next thousand years.

o b. are based on the identification of seismic zones.

o c. are based on the study of historic recurrence intervals.

o d. involve looking for sand volcanoes and disrupted bedding in the area.

o e. involve looking for young fault scarps in the area.

o Feedback/Reference: Long-term predictions range from a few decades to centuries.

Section: 8.8, p. 245-46

  • 21. If an S-wave arrives 5 minutes and 38 seconds (5’38″) after a P-wave, how far away is the epicenter from the point where the time difference in
    wave arrival was measured?

o Topic: n/a

o a. 1,000 km

o b. 2,000 km

o c. 4,000 km

o d. 600 km

o Feedback/Reference: Based on the average first-arrival times for P- and S-waves after a large earthquake, the distance from the
epicenter to the observation point (a seismographic station) would be 4,000 km, as shown in Figure 8.10 (b) and (c), p. 246. There’s a pretty good
chance you’ll have a problem to solve using a graph like this if you’re taking a geology lab while you’re reading for this class.

Section: Fig. 8.10, p. 228

  • 22. If a P-wave arrives 3 minutes 19 seconds (3’19″) before an S-wave, how far away is the epicenter from the point where the time-difference in
    wave arrival was measured?

o Topic: n/a

o a. 1,000 km

o b. 2,000 km

o c. 3,000 km

o d. 4,000 km

o e. 5,000 km

o Feedback/Reference: Look at Figure 8.10 (b). If 3 minutes and 19 seconds elapses from the first “shake” of a P-wave until the first
“shake” of an S-wave, the estimated distance that the waves have traveled from the epicenter is 2,000 km, based on average velocities for these types
of waves.

Section: Fig. 8.10, p. 228

  • 23. The intensity of earthquake damage is calculated by comparing measurements by seismographs.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Intensity (the damage from an earthquake) is determined by reviewing the damage at a location. Intensity depends
on where you measure it. A large earthquake is likely to have a high intensity (great damage) at its epicenter, and no intensity (no damage) on the
opposite side of the planet.

Section: 8.5, p. 229; Table 8.1

  • 24. The Richter scale of magnitude is more accurate and has replaced the moment magnitude scale of magnitude.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: The Richter scale of magnitude was developed primarily from a catalog of shallow earthquakes in Southern
California, and it underestimates deeper and stronger earthquakes such as those at subduction zones.

Section: 8.5, p. 229-30

Resources: Topic: n/a

  • 25. Which term does NOT denote a pattern of motion of the Earth during an earthquake?

o Topic: n/a

o a. foreshocks

o b. aftershocks

o c. InSAR

o d. elastic rebound

o e. stick-slip

o Feedback/Reference: InSAR (Interferometric Synthetic Aperture Radar) is an instrument that detects subtle ground-surface distortions
associated with earthquakes. Foreshocks and aftershocks are small quakes that precede and follow major quakes; elastic rebound is the overall theory of
how earthquakes occur; stick-slip refers to the start-stop movement on a fault.

Section: 8.2, p. 221

  • 26. Which of the following earthquake phenomena has killed the fewest number of humans?

o Topic: n/a

o a. ground shaking

o b. landslides and avalanches

o c. tsunami

o d. fire

o Feedback/Reference: People can generally withstand the small amount of g-force involved without serious injury; the other phenomena
are more likely to injure or kill.

Section: 8.7, p. 237

  • 27. Identify the FALSE statement. Short-term earthquake prediction

o Topic: n/a

o a. is being worked on but is far from being a successful procedure.

o b. may involve interpretation of swarms of foreshocks.

o c. may involve precise laser survey of the ground, looking for small distortions.

o d. may be improved by use of computer modeling of stress buildup patterns.


e. depends heavily on studying precursor phenomena such as changes in water level in wells, gases, electrical conduction of rock, and animal behavior.

o Feedback/Reference: Believers say these clues suggest cracking in the crust preceding quakes; skeptics are very skeptical.
In short, short-term prediction by any method has a long way to go.

Section: 8.8, p. 246

  • 28. Identify the FALSE statement. The tsunami event of December 26, 2004,

o Topic: n/a

o a. involved a monstrous magnitude 9.3 earthquake that lasted 9 minutes.

o b. was first noticed as a withdrawal of the sea along the beachfront.

o c. consisted of local tsunamis that affected the island of Sumatra and later tsunamis that struck all along the Indian Ocean coast.

o d. created a wide swath of elevated water that moved inland and submerged broad areas.

o e. was caused by a massive earthquake along a transform fault.

o Feedback/Reference: No warning system existed for the Indian Ocean area, and no affected towns had evacuation plans. Efforts are
currently being made to establish these.

Section: 8.7, p. 240

  • 29. The reading XIX is logical for a moderate-sized quake on the Mercalli intensity scale, which runs from X to XXX.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: The Mercalli scale runs from I (little damage) to XII (total destruction); moderate would be in the VI-to-VII

Section: 8.5, p. 229

Resources: Tables 8.1

  • 30. Plotting the hypocenters (foci) of earthquakes, showing their progression from shallow to intermediate to deep as you move eastward across
    South America, is really drawing the profile of a subducting ocean plate.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Earthquake hypocenters (foci) lie on the plane between the subducting Pacific Plate and the overriding South
American Plate, and this plane reaches deeper as it extends eastward.

Section: 8.6, p. 231; Fig. 8.14, p. 231; Fig. 8.17, p. 235

  • 31. Major weather events such as hurricanes and tornadoes release as much energy as the great earthquakes.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Hurricanes and tornadoes have the approximate energy releases of magnitude 6.5 and 4 earthquakes, respectively.
These magnitudes are much less than those of great earthquakes.

Section: Fig. 8.13 p.231, Table 8.2, p. 230

Resources: Flashcards

  • 32. Examining sedimentary bedding in a geologic study reveals disrupted layers formed 260, 820, 1,200, 2,100, and 2,300 years ago. What is the
    recurrence interval of the earthquakes that caused the disruption?

o Topic: n/a

o a. 200 years

o b. 380 years

o c. 510 years

o d. 560 years

o e. 900 years

o Feedback/Reference: The recurrence interval is the average spacing between events. Calculating the difference in ages between each
disrupted layer and averaging those values gives a recurrence interval of 510 years.

Section: 8.8, p. 245

Resources: Figure 10.33 (d); Flashcards

  • 33. Roughly 80% of the earthquake energy released on Earth comes in the continental collision zone where the Himalayas are still growing; the
    remaining 20% is scattered at random locations worldwide.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: About 80% of energy is released by the plate boundary quakes of the Pacific Rim; most of the remaining 20% is
released in the continental collision area north of Africa and the Indo-Australian plate.

Section: 8.6, p. 235

  • 34. Although the risk is small, disastrous earthquakes can happen in regions that are not seismic zones.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Although disastrous quakes are more common in seismic zones, they can happen anywhere.

Section: 8.6, p. 231; Fig. 8.19, p. 237

  • 35. It takes less energy to activate an old fault than to create a comparably sized new one, so old faults must still be treated as areas of
    weakness vulnerable to earthquakes.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Faults are zones of weakness that can be reactivated by relatively little new stress.

Section: 8.2, p. 220

  • 36. If a rock undergoes enough stress to produce elastic strain, an earthquake always happens.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: A rock must be strained beyond its elastic limit before there is any potential for rupture and earthquake.

Section: 8.2, p. 220

  • 37. Friction occurs along fault surfaces within geologic materials because no solid geologic surface is perfectly smooth; all contain small bumps
    or protrusions.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: There are no perfectly smooth surfaces, so friction always occurs when surfaces move against each other.

Section: 8.2, p. 221

Resources: Fig. 10.7

  • 38. The New Madrid, Missouri, quakes of 1811–1812 and the Charleston, South Carolina, quake of 1886 were both large intraplate quakes.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Although most quakes occur at plate boundaries, major quakes like the New Madrid quake and the Charleston quake
have occurred far from plate boundaries.

Section: 8.6, p. 236

  • 39. Intermediate and deep-focus quakes occur in the Wadati-Benioff zone of a divergent plate boundary.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Wadati-Benioff zones do contain intermediate and deep earthquakes, but these zones are associated with
subduction, which occurs at convergent boundaries, not divergent boundaries.

Section: 8.6, p. 233; Fig. 8.17 (a), p. 235

Resources: Fig. 10.20; Flashcards

  • 40. Rayleigh seismic waves cause the Earth’s surface to move vertically; low seismic waves cause the ground to ripple back and forth, creating a
    snakelike movement of the surface.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: These are the motion patterns of surface seismic waves.

Section: 8.3, p. 224 Fig. 8.7, p. 225

  • 41. Because intraplate earthquakes are infrequent and tend to have shallow hypocenters, they have had little effect on human society.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: They are infrequent, but quakes with shallow hypocenters generally do the most surface damage, and strong
intraplate rock transmits seismic energy well and thus can strongly affect large areas.

Section: 8.6, p. 236

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