The spatial distribution of the seismic activity at Nurek is less

Question

The spatial distribution of the seismic activity at Nurek is less straightforward. Most of the induced earthquakes occur beneath the central part of the reservoir and upstream from it. 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 are 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 permeabilities such structures engender. Immediately upstream from the dam the alternating layers of limestone and gypsum-shale are folded into a V-shape (syncline). Any water entering one of the permeable layers could migrate to the bottom of the basin formed by that layer but would be prevented from moving any further downward by the impermeable rock layer beneath. In this region, therefore, water cannot enter the vast mass of rock below and cannot thereby change the pore pressure. The water in the reservoir here acts only as a load and thus is insufficient to induce seismicity.

Further upstream from the dam, on the other hand, the strata are folded into an inverted V-shape (anticline). In this region water entering a permeable layer can diffuse along with it and thus be carried to various depths without restriction. Here the pore pressure at given depths does change when the water level fluctuates, and this is sufficient to generate seismicity.    1 
 1. 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
(E) water level of the reservoir area behind the dam remains constant

2 
 2. 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, a, 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.
(D) The vertical load exhorted 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.

3 
 3. 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.
(B) An artifact is introduced into a stable environment; the environmental effects of that artifact cannot be separated from general environmental change.
(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.
(D) An artifact creates certain initial effects on its environment; these environmental effects are gradually mitigated by environmental adaptation to the artifact.
(E) An artifact is introduced into an environment; the artifact generates spatially uniform stress but the environment responds differentially to that stress.

4 
 4. 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 with the permeable layer and penetrate into deep rock strata
(E) The structure of limestone strata alternating with shale and gypsum strata in an anticline allows the region to collect handhold water, thus increasing the load on the rocks below.

5 
 5. 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 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

6 
 6. 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.
(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 underlying the reservoir would be less affected by vertical load.

vijayram2496 · Answer

1. 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
(E) water level of the reservoir area behind the dam remains constant

My Answer is  D

As it is mentioned in the last paragraph the more upward from the dam, the shape is inverted V and so it is more frequent when water level in reservoir fluctuates.
That is clearly mentioned in D
A mentions about reservoir filled with capacity ,but there is no information that water filled to capacity can cause seismic waves ,so wrong.
B talks about water level exceptionally low,..but even that point isn't mentioned so ruled out.
C introduces temperature into picture ,but that part is not mentioned .
E does exact the opposite ,if water level is constant there wont be frequent earthquakes.

2.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, a, 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.
(D) The vertical load exhorted 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.

My Answer is  B 
The answer requires some information that says rock strata isn't the culprit for earthquake.

A mentions about two kinds of rock and then mentions one rock strata advantage over other ..this is opposite of what we want .Ruled out
B says that Rock strata is same ,but then still earthquake is experienced in one part but not other. Looks good
C doesn't mention about rock strata at all and adds that earthquake is evenly distributed between dam and the central portion of the reservoir. Nothing about rock strata ..can be ruled out.
D adds that vertical load causes the change ,but then that vertical load can be combined with different rock strata to cause earthquake ..that part is not mentioned. So can be eliminated.
E talks about frequency of earthquake which has no bearing on our answer.

3. 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.
(B) An artifact is introduced into a stable environment; the environmental effects of that artifact cannot be separated from general environmental change.
(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.
(D) An artifact creates certain initial effects on its environment; these environmental effects are gradually mitigated by environmental adaptation to the artifact.
(E) An artifact is introduced into an environment; the artifact generates spatially uniform stress but the environment responds differentially to that stress.

3. 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.
(B) An artifact is introduced into a stable environment; the environmental effects of that artifact cannot be separated from general environmental change.
(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.
(D) An artifact creates certain initial effects on its environment; these environmental effects are gradually mitigated by environmental adaptation to the artifact.
(E) An artifact is introduced into an environment; the artifact generates spatially uniform stress but the environment responds differentially to that stress.

This is the toughest question for me ,
My answer is  E

A says that environment stresses combine to produce an effect and introduction of an artifact(which I suppose water level) restructures the stresses and reduces the incidence of effect. I supposed that this is about V shaped part of under reservoir but it clearly doesn't mention about the other effect. So I eliminated A.
B,C,D talks about general environment changes ,environment adaptations and mitigations but nothing can be compared with data in passage.
 
E is closer to passage as it mentions environment behaves differently with artifacts and that is what I could relate with passage.
Not sure though.

4. 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 with the permeable layer and penetrate into deep rock strata
(E) The structure of limestone strata alternating with shale and gypsum strata in an anticline allows the region to collect handhold water, thus increasing the load on the rocks below.

My Answer is  D 
A mentions that water cannot penetrate into permeable layer ,it is wrong.
B mentions that rock strata causes water to penetrate ,which is also wrong according to passage.
C again mentions that water is not penetrated ,ruled out.
D is correct
E talks about rock strata and wrong.

5. 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 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

My Answer is  E 
A talks about composition of rock strata which allows water to seep-in in anticline so needed.
B talks about structure of rocks ,which is similar to A and needed.
C talks about fluctuations of water level, which is very much needed to predict earthquake.
D talks about load of total mass of water ,which can be relatively of much use .
E is about chemical properties and as per passage there is no mention of earthquake dependence on chemical properties of water .So E is answer

6. 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.
(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 underlying the reservoir would be less affected by vertical load.

My Answer is B

If the rate of change of water level is slow then the seismic activity would not be much frequent as mentioned in 2nd and 3rd paragraphs last lines and so option B is correct.

ElninoEffect · Answer

1. 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
(E) water level of the reservoir area behind the dam remains constant

My Answer is D

As it is mentioned in the last paragraph the more upward from the dam, the shape is inverted V and so it is more frequent when water level in reservoir fluctuates.
That is clearly mentioned in D
A mentions about reservoir filled with capacity ,but there is no information that water filled to capacity can cause seismic waves ,so wrong.
B talks about water level exceptionally low,..but even that point isn't mentioned so ruled out.
C introduces temperature into picture ,but that part is not mentioned .
E does exact the opposite ,if water level is constant there wont be frequent earthquakes.

2.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, a, 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.
(D) The vertical load exhorted 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.

My Answer is B
The answer requires some information that says rock strata isn't the culprit for earthquake.

A mentions about two kinds of rock and then mentions one rock strata advantage over other ..this is opposite of what we want .Ruled out
B says that Rock strata is same ,but then still earthquake is experienced in one part but not other. Looks good
C doesn't mention about rock strata at all and adds that earthquake is evenly distributed between dam and the central portion of the reservoir. Nothing about rock strata ..can be ruled out.
D adds that vertical load causes the change ,but then that vertical load can be combined with different rock strata to cause earthquake ..that part is not mentioned. So can be eliminated.
E talks about frequency of earthquake which has no bearing on our answer.

3. 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.
(B) An artifact is introduced into a stable environment; the environmental effects of that artifact cannot be separated from general environmental change.
(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.
(D) An artifact creates certain initial effects on its environment; these environmental effects are gradually mitigated by environmental adaptation to the artifact.
(E) An artifact is introduced into an environment; the artifact generates spatially uniform stress but the environment responds differentially to that stress.

3. 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.
(B) An artifact is introduced into a stable environment; the environmental effects of that artifact cannot be separated from general environmental change.
(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.
(D) An artifact creates certain initial effects on its environment; these environmental effects are gradually mitigated by environmental adaptation to the artifact.
(E) An artifact is introduced into an environment; the artifact generates spatially uniform stress but the environment responds differentially to that stress.

This is the toughest question for me ,
My answer is E

A says that environment stresses combine to produce an effect and introduction of an artifact(which I suppose water level) restructures the stresses and reduces the incidence of effect. I supposed that this is about V shaped part of under reservoir but it clearly doesn't mention about the other effect. So I eliminated A.
B,C,D talks about general environment changes ,environment adaptations and mitigations but nothing can be compared with data in passage.

E is closer to passage as it mentions environment behaves differently with artifacts and that is what I could relate with passage.
Not sure though.

4. 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 with the permeable layer and penetrate into deep rock strata
(E) The structure of limestone strata alternating with shale and gypsum strata in an anticline allows the region to collect handhold water, thus increasing the load on the rocks below.

My Answer is D
A mentions that water cannot penetrate into permeable layer ,it is wrong.
B mentions that rock strata causes water to penetrate ,which is also wrong according to passage.
C again mentions that water is not penetrated ,ruled out.
D is correct
E talks about rock strata and wrong.

5. 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 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

My Answer is E
A talks about composition of rock strata which allows water to seep-in in anticline so needed.
B talks about structure of rocks ,which is similar to A and needed.
C talks about fluctuations of water level, which is very much needed to predict earthquake.
D talks about load of total mass of water ,which can be relatively of much use .
E is about chemical properties and as per passage there is no mention of earthquake dependence on chemical properties of water .So E is answer

6. 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.
(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 underlying the reservoir would be less affected by vertical load.

My Answer isB

If the rate of change of water level is slow then the seismic activity would not be much frequent as mentioned in 2nd and 3rd paragraphs last lines and so option B is correct.

2) I am thinking of this situation as Standard Deviation so if reduce the gradual change in water level(subtraction) SD should remain the same. (A) Stress patterns in the rock strata beneath the reservoir would be the same as before its construction. We cannot deduce that and even if we can it won't be the same as the condition before the construction. (B) The seismic activity beneath the reservoir would not be very frequent. (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. We cannot deduce that. (E) The stress patterns in the rocks underlying the reservoir would be less affected by vertical load. Stress patterns were not affected by the vertical load previously so it won't really matter when the water level is reduced.

devil.rocx · Answer

In the last question can somebody please explain the difference between B and E. 
What's the difference and from which part of the passage we can draw these inferences.

Hoozan · Answer

Yet both the seismic and aseismic zones are 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?

Sajjad1994  Q5 Why can't (A) be the answer? The passage states that both the zones are "are lithologically similar" so by establishing the lithological composition of the rock strata how can one make an accurate prediction of reservoir-induced earthquake?

Sajjad1994 · Answer

Answer option  (C)  is talking about something not going in the direction of the question while  (B)  is on target. In the last paragraph:

"Here the pore pressure at given depths does change when the water level fluctuates, and this is sufficient to generate seismicity."

The text above suggests that the change in the water level is the reason to generate seismic activity.

The question asks: 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?

Answer: The seismic activity beneath the reservoir would not be very frequent.

Sajjad1994 · Answer

Yes, the passage tells us that "both the seismic and aseismic zones are lithologically similar". For example: The front-end of websites A and B is similar but both are made up of different content management system (cms), different coding is used at the back-end but both look similar. How can we differentiate them? By the different coding used in back-end development. All right the above example may distort things further

Simply remember that both the seismic and aseismic zones are lithologically similar but their composition could be different. And knowing their composition can help to know further about both. PS: By reading the answer option (E) I will not bother reading any option again as (E) is so much out of the scope that it makes the question very easy and straightforward.

NamanPro · Answer

GMATNinja  can you please shed some light on question 3?

Thanks in advance!

GMATNinja · Answer

Question 3 
 
Question 3 asks us "which  sets of causes and effects most closely parallels reservoir-induced seismicity as it is described in the passage." Before diving into answer choices, we first needs to understand the causes and effects in the passage itself. Notice that question 3 specifically asks about "reservoir-induced" seismicity.

So, we can string together this broad series of events:

A reservoir is created. 
 It DOES induce seismic activity under one half of the lake. 
 It DOES NOT induce seismic activity under the other half of the lake.

That pattern aligns nicely with answer choice (E):
 
The "artifact" that is introduced is the reservoir. The water in the reservoir pushes down  equally  on both halves of the lake -- in other words, it puts the rocks below under "uniform stress." However, the two sides of the lake respond to that stress differently. One side experiences seismic activity, and the other does not.

(E) is the correct answer to question 3.

I hope that helps!

The spatial distribution of the seismic activity at Nurek is less

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The spatial distribution of the seismic activity at Nurek is less

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