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# Because of its accuracy in outlining the Earth's subsurface, the seism

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Because of its accuracy in outlining the Earth's subsurface, the seism  [#permalink]

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Updated on: 15 Oct 2019, 23:08
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New Project RC Butler 2019 - Practice 2 RC Passages Everyday
Passage # 287, Date : 24-Aug-2019
This post is a part of New Project RC Butler 2019. Click here for Details

Because of its accuracy in outlining the Earth's subsurface, the seismic-reflection method remains the most important tool in the search for petroleum reserves. In field practice, a subsurface is mapped by arranging a series of wave-train sources, such as small dynamite explosions, in a grid pattern. As each source is activated, it generates a wave train that moves downward at a speed determined uniquely by the rock's elastic characteristics. As rock interfaces are crossed, the elastic characteristics encountered generally change abruptly, which causes part of the energy to be reflected back to the surface, where it is recorded by seismic instruments. The seismic records must be processed to correct for positional differences between the source and the receiver, for unrelated wave trains, and for multiple reflections from the rock interfaces. Then the data acquired at each of the specific source locations are combined to generate a physical profile of the subsurface, which can eventually be used to select targets for drilling.

Spoiler: :: OA
A

1. The passage is primarily concerned with

(A) describing an important technique
(B) discussing a new method
(C) investigating a controversial procedure
(D) announcing a significant discovery
(E) promoting a novel application

Spoiler: :: OA
C

2. According to the passage, in the seismic-reflection method all of the following have a significant effect on the signal detected by the seismic instruments EXCEPT the

(A) presence of unrelated wave trains
(B) placement of the seismic instruments
(C) number of sources in the grid pattern
(D) nature of the reflectivity of the rock interfaces
(E) properties of rocks through which the wave train has traveled

Spoiler: :: OA
C

3. It can be inferred from the passage that the seismic-reflection method would be likely to yield an inaccurate physical profile of the subsurface in which of the following circumstances?

(A) If the speed at which the wave train moved downward changed
(B) If the receiver were not positioned directly at the wave-train source
(C) If the rock on one side of a rock interface had similar elastic characteristics to those of the rock on the other side
(D) If the seismic records obtained for the different sources in a grid were highly similar to each other
(E) If there were no petroleum deposits beneath the area defined by the grid of wave-train sources

Spoiler: :: OA
C

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

(A) A method is criticized, and an alternative is suggested.
(B) An illustration is examined, and some errors are exposed.
(C) An assertion is made, and a procedure is outlined.
(D) A series of examples is presented, and a conclusion is drawn.
(E) A hypothesis is advanced, and supporting evidence is supplied.

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Originally posted by carcass on 22 Aug 2019, 08:49.
Last edited by SajjadAhmad on 15 Oct 2019, 23:08, edited 2 times in total.
Updated - Complete topic (1020).
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Re: Because of its accuracy in outlining the Earth's subsurface, the seism  [#permalink]

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24 Aug 2019, 23:42
+1 Kudos to posts containing answer explanation of all questions
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Re: Because of its accuracy in outlining the Earth's subsurface, the seism  [#permalink]

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26 Aug 2019, 21:59
1
Summary - Author is talking about Seismic-Reflection method and its importance. Then he/she provides details of the method and how it deals with various factors affecting its accuracy.

1. The passage is primarily concerned with

(A) describing an important technique – CORRECT.
(B) discussing a new method – WRONG. Not a ‘New’ method as its not mentioned in the passage that it’s new.
(C) investigating a controversial procedure – WRONG. This option is incorrect for the reason that author is not investigating any controversial procedure.
(D) announcing a significant discovery – WRONG. No author does not say anything about significant discovery.
(E) promoting a novel application – WRONG. No option is given by author.

2. According to the passage, in the seismic-reflection method all of the following have a significant effect on the signal detected by the seismic instruments EXCEPT the

After POE eliminated A, D and E. Got stuck with B and C and eliminated C for the reason that passage mentions ‘each’ n lne-3 “As each source is activated, it generates a wave train that moves… “. Assumed that ‘each’ plays a role in locating every seismic instrument.

(A) presence of unrelated wave trains – WRONG. Mentioned in passage.
(B) placement of the seismic instruments
(C) number of sources in the grid pattern
(D) nature of the reflectivity of the rock interfaces – WRONG. Refer line-4 of passage.
(E) properties of rocks through which the wave train has traveled – WRONG. ‘Rock characteristic’ mentioned in passage.

3. It can be inferred from the passage that the seismic-reflection method would be likely to yield an inaccurate physical profile of the subsurface in which of the following circumstances?

Again using POE eliminated A B and E. Stuck with C and D chose D over C with a reasoning that different sources with similar seismic records would mislead the method to generate similar profile thus inaccuracy.

(A) If the speed at which the wave train moved downward changed – WRONG. Opposite to what we require to infer. Change is necessary for a unique profile
(B) If the receiver were not positioned directly at the wave-train source – WRONG. Not mentioned.
(C) If the rock on one side of a rock interface had similar elastic characteristics to those of the rock on the other side
(D) If the seismic records obtained for the different sources in a grid were highly similar to each other
(E) If there were no petroleum deposits beneath the area defined by the grid of wave-train sources – WRONG. No deposits would also have some unique profile.

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

After POE eliminated A B and D. After a brief thought mistook in the thick of moment elements of the method as evidence to mark E the wrong answer as correct.

(A) A method is criticized, and an alternative is suggested. – WRONG. There’s no author’s opinion.
(B) An illustration is examined, and some errors are exposed. – WRONG. Author describes and nowhere examines to expose errors.
(C) An assertion is made, and a procedure is outlined.
(D) A series of examples is presented, and a conclusion is drawn. WRONG. No conclusion is drawn.
(E) A hypothesis is advanced, and supporting evidence is supplied.
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Re: Because of its accuracy in outlining the Earth's subsurface, the seism  [#permalink]

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27 Aug 2019, 03:52
please explain Q2 & Q3.
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Re: Because of its accuracy in outlining the Earth's subsurface, the seism   [#permalink] 27 Aug 2019, 03:52
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# Because of its accuracy in outlining the Earth's subsurface, the seism

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