Unplugged Practice Test: Reading Comprehension, Passage 3
Taking the test? Finish it first. This page shows the answers.
- Read for the author's position and each paragraph's job before the questions; most wrong answers on this passage misassign a view to the wrong speaker or overstate a claim.
- Every credited answer below is settled by specific words in the passage, quoted in the walkthrough.
- Every passage on this test is original, and Steve checked every one himself before release.
The passage
Geophysicists long treated a fault as a locked seam that gives way all at once, shedding stored strain in a rupture recorded hundreds of miles off. Read that way, six decades of records had a hole. Surveying found strain piling up on faults that registered nothing for decades, then broke violently. Where did the motion of those quiet decades go, and why should a fault's quiet end when it does? When Ilse Renquist announced in 1984 that resurveyed benchmark lines along the Talmage Fault, a Serrano Basin fault quiet since 1931, recorded slip still under way, her colleagues dismissed it. Nobody then accepted that a fault could move without giving off waves an instrument would register. Renquist had observed that the quiet stretches ran longest on faults sealed beneath thick, impermeable beds of saturated clay, and proposed that slip continued there too slowly to shake the ground.
Minor earthquakes on the neighboring Callis Fault gave her a test. Into boreholes along both she lowered a new device: a fluid-filled cylinder cemented into bedrock, so that a contraction of the surrounding rock forces fluid through a narrow channel, recording the displacement. Along the Talmage Fault it tracked steady slip for months with no earthquake on any segment. In a later survey of 49 segments in another range, her devices caught slip on 47; conventional seismometers over the same months caught 9.
Her later work explained the mismatch. Slip on a fault, like deformation in certain other solids under load, can proceed in a creeping mode where the enclosing rock is weak and the fluid pressure within it stays high and steady. The slipping surface advances about a millimeter a day rather than a meter in seconds, its energy spread over weeks. Waves of that kind are too faint and too low in frequency for a standard seismometer to separate from background noise. This silent mode, Renquist argues, is no curiosity: it is the ordinary behavior of many faults, letting strain bleed away for years while every instrument reports calm. Some faults, she grants, stay locked and rupture from rest.
What ends the quiet follows the calendar. In the Serrano Basin the annual maximum in groundwater recharge, when meltwater off the range drives a pulse down to the fault, disturbing the steady pressure creep depends on, arrives within a few weeks of the yearly peak in recorded tremor, the two tracking each other through 23 years of records. Renquist reads that as the answer to the older question: a fault's quiet ends in the season the pulse reaches it, and beneath the basin's impermeable clay caps, where the water never gets down and the pressure never changes, the quiet has never ended. Her answer opens a further one. Nobody has established how the water does its work, whether the abrupt rise in pressure alone unclamps the slipping surface or whether the warmth the water carries into the fractured rock returns a fault's motion to a rate fast enough to shake the ground.
Question 15: Detail
15. The passage supplies an answer to which one of the following questions?
- (A)Which other solids deform in the creeping mode that Renquist describes?
- (B)Does cementing a device into bedrock alter the behavior of the fault beneath it?
- (C)Do episodes of silent slip damage structures standing above them?
- (D)How does Renquist intend to determine what brings a fault's silent phase to an end?
- (E)What led Renquist to propose that faults registering no earthquakes were nonetheless moving?
EWhy (E) is correct
The passage answers this exact question in its opening move: surveys turned up strain piling up on faults that registered nothing for decades and then broke violently, and then Renquist's resurveyed benchmark lines along the Talmage Fault, quiet since 1931, recorded slip still under way. That's the evidence, unexplained strain buildup plus directly measured ongoing motion, that led her to propose these silent faults were moving all along even though no instrument had picked up shaking.
Why the other answers are wrong
AWhy (A) is wrong
(A) asks which other solids share the creeping mode, but the passage only says the fault behaves like "certain other solids under load" without naming any of them.
BWhy (B) is wrong
(B) asks whether cementing the device into bedrock changes the fault's own behavior, a question the passage never raises about its recording instrument.
CWhy (C) is wrong
(C) wonders whether silent slip damages structures above it, which the passage never mentions at all.
DWhy (D) is wrong
(D) is about her method for finding what ends the quiet, but the passage reports her finding, the recharge pulse tracking the tremor peak, and leaves what the water actually does as an open question, not a method she's pursuing.
Question 16: Inference
16. According to the passage, Renquist's colleagues dismissed her finding of slip along the Talmage Fault because they assumed that
- (A)any movement on a fault gives off waves strong enough for an instrument to register
- (B)slip on a fault can proceed too slowly to shake the surrounding ground
- (C)a fault in its creeping mode cannot be registered by a conventional seismometer
- (D)the surveying methods available to Renquist were too imprecise to show slip
- (E)the only motion in the Serrano Basin occurred beneath thick sediment cover
AWhy (A) is correct
The passage says Renquist's colleagues turned aside her report of ongoing slip along the Talmage Fault because nobody then accepted that a fault could move without giving off waves an instrument would register. Their skepticism rested on the assumption that any real movement on a fault must produce shaking strong enough to show up on a seismometer, exactly what (A) states, so continuing slip that no instrument caught looked impossible to them.
Why the other answers are wrong
BWhy (B) is wrong
(B) states Renquist's own proposal, that slip can go too slowly to shake the ground, which is what she argued against her colleagues, not what they assumed.
CWhy (C) is wrong
(C) describes a distinction her later work established, between creeping and seismometer-visible slip, not the belief her colleagues held in 1984.
DWhy (D) is wrong
(D) misplaces the objection: the colleagues doubted whether silent slip was possible at all, not whether her survey technique was precise enough.
EWhy (E) is wrong
(E) invents a claim about where all Serrano Basin motion occurred that the passage never attributes to her colleagues.
Question 17: Inference
17. Based on the passage, which one of the following best accounts for the gap between the two results the second paragraph closes with?
- (A)The borehole device's sensitivity to very slow deformation of the surrounding rock is limited.
- (B)Motion on a fault does not always shake the ground vigorously enough to be caught seismically.
- (C)Slip on a fault responds mainly to seasonal changes in the rate of groundwater recharge.
- (D)Slip cannot be caught on segments where the sediment above the fault has been drained of water.
- (E)Bedrock ordinarily contains fluid-filled channels whose motion a seismometer can register.
BWhy (B) is correct
The second paragraph reports that Renquist's borehole devices caught slip on 47 of 49 segments while ordinary seismometers over the same months caught only 9. The third paragraph explains why: creeping fault motion advances a slipping surface about a millimeter a day, spreading its energy over weeks instead of releasing it in seconds. Waves that slow and that faint are too weak and too low in frequency for a standard seismometer to pull out of background noise, even though the borehole device, built to register that same slow displacement directly, catches it. So most of that motion never shook the ground hard enough to register on a seismometer at all.
Why the other answers are wrong
AWhy (A) is wrong
(A) This is backward: the borehole device is the instrument that caught nearly every segment, so its sensitivity to slow deformation isn't what's limited.
CWhy (C) is wrong
(C) Seasonal recharge explains what ends a fault's quiet stretch, in the fourth paragraph, not why one instrument caught more segments than another in the second paragraph.
DWhy (D) is wrong
(D) The passage never says slip on drained segments goes uncaught; the clay-capped segments discussed later are ones where the quiet itself never ends, a different claim entirely.
EWhy (E) is wrong
(E) The fluid-filled channel described is the borehole device Renquist lowered into the rock, not a feature bedrock ordinarily contains that a seismometer could register.
Question 18: Analogy/Application
18. Suppose that silent slip missed by conventional seismometers invariably produced an ordinary earthquake once the slipping surface reached shallow, well-drained rock. The passage suggests that which one of the following would most likely be true?
- (A)Borehole devices cemented into shallow rock would fail to track the slip preceding such earthquakes.
- (B)Fluid pressure at depth would have to equal the pressure found in shallow rock for slip to speed up.
- (C)Such earthquakes would mark the end of a fault's creeping mode rather than a release of strain by a fault at rest.
- (D)Faults that produced such earthquakes would have ruptured violently at some earlier time.
- (E)A fault in its creeping mode can keep moving through rock from which water has been removed.
CWhy (C) is correct
The passage's mechanism has creeping slip proceeding where a fault sits in weak rock under steady, high fluid pressure, moving too slowly and too faintly for an instrument to register, until something disturbs that pressure. If silent slip always turned into an ordinary earthquake once it reached shallow, well-drained rock, that earthquake would mark the moment the slip stopped being the slow creeping process and started moving fast enough for an instrument to catch it. That's a fault leaving its creeping mode, not a fault that had been sitting locked and finally ruptures from rest, which is exactly (C).
Why the other answers are wrong
AWhy (A) is wrong
(A) isn't implied: the device tracks displacement through fluid pressure mechanically, and nothing in the hypothesis says it would stop working in shallow rock.
BWhy (B) is wrong
(B) is far more specific than the passage supports; nothing sets a value requiring depth pressure to equal shallow-rock pressure before slip speeds up.
DWhy (D) is wrong
(D) doesn't follow; a fault known only for creeping isn't thereby known to have ruptured violently earlier.
EWhy (E) is wrong
(E) contradicts the mechanism, since creeping mode depends on the surrounding rock holding fluid at high, steady pressure, not on rock the water has left.
Question 19: Inference
19. Which one of the following is most strongly supported by the passage?
- (A)Faults in the Serrano Basin become likelier to rupture when fluid pressure at depth falls.
- (B)Faults can creep silently only after a violent rupture nearby has disturbed them.
- (C)Motion caught by conventional seismometers is harder for borehole devices to track than fault motion beneath thick basin sediment is.
- (D)In the Serrano Basin, fault motion is likelier to be caught by conventional seismometers in the months when groundwater recharge is greatest.
- (E)Borehole devices are less sensitive to a fault's motion while it creeps than they are while it ruptures.
DWhy (D) is correct
The fourth paragraph ties the annual maximum in groundwater recharge to the yearly peak in recorded tremor, arriving within a few weeks of it and tracking together through 23 years of records in the Serrano Basin, and reads that pulse as what ends a fault's quiet stretch. Recorded tremor is what a standard seismometer catches, so when recharge peaks and disturbs the steady pressure, the passage supports (D): the months of heaviest recharge are also the months when conventional seismometers are likelier to catch fault motion.
Why the other answers are wrong
AWhy (A) is wrong
(A) has it backward, since the passage ties the ending of a quiet stretch to a rise in fluid pressure from groundwater recharge, not a fall.
BWhy (B) is wrong
(B) claims creep needs a violent rupture nearby first, a link nothing in the passage states.
CWhy (C) is wrong
(C) draws a comparison between seismometers and motion beneath thick basin sediment that the passage never makes; it only compares seismometers to borehole devices generally.
EWhy (E) is wrong
(E) reverses the actual pattern, since the borehole devices are built to catch the slow creeping mode that seismometers miss, not the other way around.
Question 20: Primary Purpose
20. The final paragraph functions mainly to
- (A)name the directions research in the field will take and the obstacles it will have to get past
- (B)assess how a technique described earlier is likely to change the research that follows it
- (C)recommend further uses for a technique described earlier in the passage
- (D)list the effects of the physical process the third paragraph describes and mark the limits of what is currently known about it
- (E)settle a question posed earlier in the passage while introducing findings that raise questions of their own
EWhy (E) is correct
The final paragraph ties the yearly peak in groundwater recharge to the yearly peak in recorded tremor across 23 years, and that timing match settles the question posed early on, why a fault's quiet ends when it does. In the same paragraph, a new question opens up: whether the pressure rise alone unclamps the fault or whether the warmth the water carries does the work. So the paragraph both closes one puzzle and raises another, which is (E).
Why the other answers are wrong
AWhy (A) is wrong
(A) treats the paragraph as a general map of research directions and obstacles, but it settles a specific question first rather than surveying a field's future.
BWhy (B) is wrong
(B) makes it a judgment about how the borehole technique will shape later research, when it's the seasonal timing data, not the device, doing the settling here.
CWhy (C) is wrong
(C) has the paragraph recommending new uses for the device, something it never does.
DWhy (D) is wrong
(D) leaves it as a list of effects with a note on limits, which misses that it answers a question raised earlier rather than just cataloguing outcomes.
Question 21: Inference
21. Which one of the following views about faults does the passage suggest Renquist holds?
- (A)Borehole devices, had they been placed along the Talmage Fault when she first announced slip there, would have tracked it.
- (B)On most faults strain does not build toward a rupture at all, since silent slip bleeds it away as fast as it accumulates.
- (C)A fault returns from creeping to rupture only when an earthquake on a nearby fault disturbs it.
- (D)No earthquake ever begins the release of strain on a fault; each one is simply motion already under way, sped up.
- (E)Borehole devices placed on any fault in any range would register some amount of silent slip.
AWhy (A) is correct
(A) follows from how her later devices behaved once she built them. She believed slip was continuing quietly along the Talmage Fault back when she announced the resurveyed benchmark lines in 1984, and when she later lowered her borehole devices into that same fault, they tracked steady slip for months with no earthquake anywhere on the segments. Since the device caught exactly the kind of motion she had claimed was there all along, it would have caught that same motion had it existed on the Talmage Fault back when she made her original announcement.
Why the other answers are wrong
BWhy (B) is wrong
(B) reaches past what the passage supports. The passage grants that some faults stay locked and rupture from rest instead of releasing strain slowly through silent slip.
CWhy (C) is wrong
(C) reverses the actual trigger, since what ends the quiet in the Serrano Basin tracks the seasonal groundwater pulse, not an earthquake on a neighboring fault.
DWhy (D) is wrong
(D) overstates the case, since a fault that stays locked until it ruptures from rest, which the passage allows for, is exactly a case where an earthquake begins the release rather than merely speeding up motion already under way.
EWhy (E) is wrong
(E) generalizes past the specific test, moving from the 49 segments in one range to every fault in every range.
