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555-605 Level|   Long Passage|   Science|         
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agrasan
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In spite of early doubts, it is now well established that large reserv 04 May 2025, 05:59
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Hi experts KarishmaB GMATNinja MartyMurray

In question-9, I am unable to eliminate option D, could you please help?

My reasoning is: D seems correct as the oversimplification is mentioned in para-2 as "...But now there are no doubts, for well-documented examples of reservoir-induced seismicity are known throughout the inhabited continents. In general terms, what happens is that the huge mass of water in a reservoir changes the stress patterns in the underlying rocks..."

BUT para-3 says "...In this case, the timing of the induced seismicity is directly related not to the absolute amount of water present but to variations in that amount."

Clearly, water variations poses a challenge to oversimplification mentioned earlier.
Please let me know what is wrong with my reasoning here.
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In spite of early doubts, it is now well established that large reserv 20 Sep 2025, 06:05
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"3) understanding of paragraph - contrast word ""Yet"" and question asked ?
“Lithologically similar” = The rock types (composition) in both areas (the one that has earthquakes and the one that doesn’t) are the same.
Those rocks include:Limestone = fractured and permeable.
Shale and gypsum = less permeable
So basically: both areas have a mix of the same kinds of rocks.
But only one of the areas has earthquake activity (seismic), and the other doesn’t (aseismic), even though the rock composition is the same.

9) advancing a theory :The passage discusses an already accepted idea (reservoirs can cause earthquakes), and gives evidence.It doesn’t propose a new theory.
resolving a dispute :The passage mentions there was skepticism in the past, but that’s no longer the case.There’s no ongoing dispute being settled here.
author is explaining a relationship: Between the structure of rock layers (folds) and the occurrence of reservoir-induced earthquakes."
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In spite of early doubts, it is now well established that large reserv 27 Sep 2025, 03:21
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Your first question answer is incorrect. The correct answer is C. In the very First paragraph, it is mentioned that "detailed records of the pre-reservoir seismic background were incomplete at best". This means we didn't know before constructing the reservoir in that location, what was the rate of seismic activities and all. Thus we didn't have enough data for scientific rigorous examination.

Oppenheimer1945
1. The passage suggests that the author would regard which of the following as most important for a "scientifically rigorous examination" (Highlighted) of the hypothesis that large reservoirs can induct earthquakes?

(A) Systematic surveys of seismic activity under a reservoir after filling began (True)
what happens is that the huge mass of water in a reservoir changes the stress patterns in the underlying rocks.

(B) Detailed geological maps of the composition of rock strata underlying a reservoir
- this is not specific to impact of reservoirs on earthquake
(C) Comparable records of seismic activity in the area of a reservoir prior to and after construction and filling of the reservoir-
Intersting but not suggested in passage
(D) Precise calculation of the amount of vertical pressure exerted by the reservoir's water load
- water cannot enter the vast mass of rock below and cannot thereby change the port pressure.
(E) Accurate records of the rate of increase in pore pressure in the rock strata underlying the reservoir
-the pore pressure at given depths does change when the water level fluctuates, and this is sufficient to generate seismicity.(change in pore pressure is important and not increase in pressure)

2. According to the passage, earthquake activity in the area of the Nurek reservoir is most frequent when the

(A) reservoir is filled to capacity
(B) water level in the reservoir is exceptionally low
(C) reservoir is subjected to sudden drops in temperature
(D) water level in the reservoir fluctuates (True)
(E) water level of the reservoir area behind the dam remains constant

Nurek reservoir in the Soviet Union, which has been generating seismic activity since filling began in the early 1970's. In this case, the timing of the induced seismicity is directly related not to the absolute amount of water present but to variations in that amount. Bursts of seismic activity are triggered when the water level changes, with the frequency of the activity increasing as the rate of level change increases.


3. According to the passage, which of the following proves that earthquake activity in the area of the Nurek reservoir cannot be accounted for exclusively by the composition of the rock strata underlying the reservoir?

(A) There are two kinds of rock underlying the reservoir, but only the shallow-water limestones are permeable.
(B) The same rock strata underlie the whole reservoir area, but only one part of the area is subject to earthquake activity.
(C) The earthquake activity in the area is evenly distributed between the regions behind the dam and the central portion of the reservoir.(True)
(D) The vertical load exerted by the water in the reservoir has different effects on shallow-water limestones than on mixed shale and gypsum_
(E) When the frequency of earthquake activity increases, the locations of such activity become more diffuse.

The region containing that half of the reservoir immediately behind the dam, on the other hand, is almost completely aseismic. Yet both the seismic and aseismic zones arc lithologically similar, consisting largely of shallow-water limestones, which are highly fractured and thus relatively permeable, interbedded with mixed components of low-permeability shale and gypsum. What, then, governs the location of the induced seismicity?

The answer lies in the varying structures of the rock strata and the different permcabilities such structures engender. Immediately upstream from the dam the alternating layers of limestone- and gypsum-shale arc folded into a V-shape (syncline). Further upstream from the darn, on the other-hand, the strata arc folded into an inverted V-shape (anticline)


4. Which of the following best describes the organization of the passage?

(A) An assertion is made, briefly explained, and then an illustrative example is examined in detail. (This is the right flow)
(B) A hypothesis is advanced, carefully qualified, and then supporting data are presented. (no data is presented)
(C) A scientific dispute is introduced and the c:asc for one side is analyzed and illustrated_ (case for one side is not presented)
(D) A generally accepted principle is stated in order to introduce a detailed examination of a case that violates the principle
In general terms, what happens is that the huge mass of water in a reservoir changes the stress patterns in the underlying rocks. The water load exerts a simple vertical pressure on the rocks immediately, while the pore pressure in the rocks increases gradually as the water infiltrates at a rate that depends on their permeability and prior water content.

One such example is the Nurek reservoir in the Soviet Union, which has been generating seismic activity since filling began in the early 1970's. In this case, the timing of the induced seismicity is directly related not to the absolute amount of water present but to variations in that amount. Bursts of seismic activity are triggered when the water level changes, with the frequency of the activity increasing as the rate of level change increases.


(E) A theory is explained and a recent example that makes the theory obsolete is presented. (example of Nurek doesn't make the theory obsolete)

5. Which of the following sets of causes and effects most closely parallels reservoir-induced seismicity as it is described in the passage?

(A) Environmental stresses in an area combine to produce an effect; the introduction of an artifact to that area restructures the stresses and reduces the incidence of the effect. (stresses in an area combine is wrong)
(B) An artifact is introduced into a stable environment; the environmental effects of that artifact cannot be separated from general environmental changes.(the reservoir is built, the effects of earthquake becomes a normal phenomena) - True
(C) An artifact is introduced into an environment; local conditions peculiar to that environment have little impact on the effects generally produced by such artifacts.
(local conditions do have impact )
(D) An artifact creates certain initial effects on its environment; these environmental effects are gradually mitigated by environmental adaptation to the artifact.
(Mitigation is not dicussed in passage)
(E) An artifact is introduced into an environment; the artifact generates spatially uniform stress but the environment responds differentially to that stress.
(env responding diff is not correct)




6. Which of the following best describes the interaction of water and rock strata in the region of the anticline under the Nurek reservoir?

(A) Shale and gypsum form the top layer of rock in an anticline and thus the water cannot penetrate to the permeable limestone layer.
(B) Fractured and highly permeable limestone forms a basin in an anticline through which water penetrates to the rock below.
(C) The shale and gypsum layer beneath the permeable limestone basin in an anticline prevents water from penetrating to deeper rock strata.
(D) The shape of an anticline allows water to travel along the permeable layer and penetrate into deep rock strata. (True)
(E) The structure of limestone strata alternating with shale and gypsum strata in an anticline allows the region to collect and hold water, thus increasing the load on the rocks below.

shallow-water limestones, which are highly fractured and thus relatively permeable, interbedded with mixed components of low-permeability shale and gypsum. the strata arc folded into an inverted V-shape (anticline). In this region water entering a permeable layer can diffuse along it and thus be carried to various depths without restriction

7. It can be inferred from the passage that an accurate prediction of reservoir-induced earthquake activity at the site of the Nurek reservoir prior to its construction would have required all of the following data EXCEPT

(A) a general geological survey of the area, establishing the lithological composition of the rock strata
(B) a detailed examination of the structure of the rock strata underlying the site of the reservoir
(C) a projection of the number and magnitude of the fluctuations in the level of the water in the reservoir
(D) an estimate of the load that would be created by the total mass of water in the reservoir
(E) a determination of the chemical properties of the water that would be used to fill the reservoir (This is not given in the passage)

8. The passage implies that which of the following would be true in the area of the Nurek reservoir if the rate of change in the water level in the reservoir were very gradual?

(A) Stress patterns in the rock strata beneath the reservoir would be the same as before its construction.
(B) The seismic activity beneath the reservoir would not be very frequent. (True)
(C) The spatial distribution of seismic activity beneath the reservoir would be altered.
(D) The rate of infiltration into rock strata below the reservoir would increase.
(E) The stress patterns in the rocks under-lying the reservoir would be less affected by vertical load.

Bursts of seismic activity are triggered when the water level changes, with the frequency of the activity increasing as the rate of level change increases.

9. The author of the passage is primarily concerned with

(A) advancing a theory (author puts efforts to explain the cause )
(B) resolving a dispute (Author clarifies the true reason for seismic activity is change in water level and not the huge mass of reservoir exerting pressure in rocks )
(C) explaining a relationship (this is the part of passage)
(D) correcting an oversimplification (no correction is posed by the author)
(E) reinterpreting data (no data is reinterpretter here)
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