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# In 1971 researchers hoping to predict earthquakes in the short term by

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In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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Updated on: 29 Jul 2019, 04:12
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OG V 2017 New RC
Line
In 1971 researchers hoping to predict earthquakes in
the short term by identifying precursory phenomena
(those that occur a few days before large quakes
but not otherwise) turned their attention to changes
(5)
in seismic waves that had been detected prior to
earthquakes. An explanation for such changes was
offered by “dilatancy theory,” based on a well-known
phenomenon observed in rocks in the laboratory:
as stress builds, microfractures in rock close,
(10)
decreasing the rock’s volume. But as stress
continues to increase, the rock begins to crack and
expand in volume, allowing groundwater to seep in,
weakening the rock. According to this theory, such
effects could lead to several precursory phenomena in
(15)
the field, including a change in the velocity of seismic
waves, and an increase in small, nearby tremors.

Researchers initially reported success in identifying
these possible precursors, but subsequent analyses
of their data proved disheartening. Seismic waves
(20)
with unusual velocities were recorded before some
earthquakes, but while the historical record confirms
that most large earthquakes are preceded by minor
tremors, these foreshocks indicate nothing about
the magnitude of an impending quake and are
(25)
indistinguishable from other minor tremors that occur
without large earthquakes.

In the 1980s, some researchers turned their
efforts from short-term to long-term prediction.
Noting that earthquakes tend to occur repeatedly in
(30)
certain regions, Lindh and Baker attempted to identify
patterns of recurrence, or earthquake cycles, on which
to base predictions. In a study of earthquake-prone
sites along the San Andreas Fault, they determined
that quakes occurred at intervals of approximately 22
(35)
years near one site and concluded that there was a
95 percent probability of an earthquake in that area
by 1992. The earthquake did not occur within the time
frame predicted, however.

Evidence against the kind of regular
(40)
earthquake cycles that Lindh and Baker tried
to establish has come from a relatively new
field, paleoseismology. Paleoseismologists
have unearthed and dated geological features
such as fault scarps that were caused by
(45)
earthquakes thousands of years ago. They have
determined that the average interval between ten
earthquakes that took place at one site along the
San Andreas Fault in the past two millennia was
132 years, but individual intervals ranged greatly,
(50)
from 44 to 332 years.
(Book Question: 11)
The passage is primarily concerned with

A. explaining why one method of earthquake prediction has proven more practicable than an alternative method
B. suggesting that accurate earthquake forecasting must combine elements of long-term and short-term prediction
C. challenging the usefulness of dilatancy theory for explaining the occurrence of precursory phenomena
D. discussing the deficiency of two methods by which researchers have attempted to predict the occurrence of earthquakes
E. describing the development of methods for establishing patterns in the occurrence of past earthquakes

(Book Question: 12)
According to the passage, laboratory evidence concerning the effects of stress on rocks might help account for

A. differences in magnitude among earthquakes
B. certain phenomena that occur prior to earthquakes
C. variations in the intervals between earthquakes in a particular area
D. differences in the frequency with which earthquakes occur in various areas
E. the unreliability of short-term earthquake predictions

(Book Question: 13)
It can be inferred from the passage that one problem with using precursory phenomena to predict earthquakes is that minor tremors

A. typically occur some distance from the sites of the large earthquakes that follow them
B. are directly linked to the mechanisms that cause earthquakes
C. are difficult to distinguish from major tremors
D. have proven difficult to measure accurately
E. are not always followed by large earthquakes

(Book Question: 14)
According to the passage, some researchers based their research about long-term earthquake prediction on which of the following facts?

A. The historical record confirms that most earthquakes have been preceded by minor tremors.
B. The average interval between earthquakes in one region of the San Andreas Fault is 132 years.
C. Some regions tend to be the site of numerous earthquakes over the course of many years.
D. Changes in the volume of rock can occur as a result of building stress and can lead to the weakening of rock.
E. Paleoseismologists have been able to unearth and date geological features caused by past earthquakes.

(Book Question: 15)
The passage suggests which of the following about the paleoseismologists’ findings described in lines 42–50?

A. They suggest that the frequency with which earthquakes occurred at a particular site decreased significantly over the past two millennia.
B. They suggest that paleoseismologists may someday be able to make reasonably accurate long-term earthquake predictions.
C. They suggest that researchers may someday be able to determine which past occurrences of minor tremors were actually followed by large earthquakes.
D. They suggest that the recurrence of earthquakes in earthquake-prone sites is too irregular to serve as a basis for earthquake prediction.
E. They indicate that researchers attempting to develop long-term methods of earthquake prediction have overlooked important evidence concerning the causes of earthquakes.

(Book Question: 16)
The author implies which of the following about the ability of the researchers mentioned in line 18 to predict earthquakes?

A. They can identify when an earthquake is likely to occur but not how large it will be.
B. They can identify the regions where earthquakes are likely to occur but not when they will occur.
C. They are unable to determine either the time or the place that earthquakes are likely to occur.
D. They are likely to be more accurate at short-term earthquake prediction than at long-term earthquake prediction.
E. They can determine the regions where earthquakes have occurred in the past but not the regions where they are likely to occur in the future.

Originally posted by AbdurRakib on 29 Jul 2016, 02:13.
Last edited by SajjadAhmad on 29 Jul 2019, 04:12, edited 1 time in total.
Updated complete topic (27).
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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11 Apr 2017, 18:16
26
2
Hi stonecold, good question!

Quote:
I have a query regarding the last question in this series.
We are asked about the ability of the researchers in the line 18.
The passage clearly indicates and even mentions -> They were able to predict the timing but not the magnitude." indistinguishable from other minor tremors that occur"

I am still convinced that the OA should be A.

What am i missing.?

P.S-> I have seen the other replies.
without large earthquakes.

Imagine that the researchers recorded 100 large earthquakes of various magnitudes during their study and that nearly all of those large earthquakes were preceded by minor tremors. This might lead us to expect any minor tremor to be followed by a large earthquake, even though we might not know exactly how large that "large" earthquake will be. Thus, choice A is tempting.

Now consider the final fact given in line 23: "these foreshocks... are indistinguishable from other minor tremors that occur without large earthquakes." If instead the passage stated, "these foreshocks are indistinguishable from other minor tremors that occur before small earthquakes", THEN choice A would be defensible... this would imply that after a minor tremor we can expect an earthquake, though we have no idea how small or large it will be. But the passage states that the tremors are "indistinguishable from other minor tremors that occur without large earthquakes." Therefore, the passage implies that a minor tremor could be followed by a large earthquake, a small earthquake, or no earthquake at all; for example, the researchers may have recorded HUNDREDS of minor tremors that were NOT followed by an earthquake.

This explanation is supported by the first sentence starting in line 17: "Researchers initially reported success in identifying these possible precursors, but subsequent analyses of their data proved disheartening." In other words, the researchers were initially successful in identifying earthquake precursors; subsequent analyses proved disheartening, implying that the researchers were not successful in identifying precursors that would predict earthquakes.

I hope that helps!
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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06 Apr 2017, 23:33
23
1
hannahkagalwala wrote:
In the last question, I'm unable to understand why C is correct and A is wrong.

First of all, this is an inference question, right? Because OG has put it under the 'supporting idea' category and the explanation also reads "The question asks for information explicitly stated..."

Quote:
Also, if someone can explain the answer choices A & C as provided by the OG. Thanks!

Hey hannahkagalwala,

It is indeed an inference question, albeit detail oriented, since the question stem clearly asks us to look for an implication of the information given in a particular section of the passage.

Now let's look at choice A:

A. They (1) can identify when an earthquake is likely to occur but (2) not how large it will be.

So, choice A talks about the two things:

1. can identify when an earthquake is likely to occur : Passage states, and I quote, " are indistinguishable from other minor tremors that occur
without large earthquakes
. Basically, this information tells us that yes tremors do happen but the kind of tremors that are followed by earthquakes are not different from the kind of tremors that are NOT followed by earthquakes. Accordingly, if such tremors happen without a resulting earthquake, then the researchers cannot really tell us whether an earthquake is due.

2. not how large it will be. This can be directly understood from this section of the passage "nothing[/b] about the magnitude of an impending quake.

Therefore, since one part can be inferred and one cannot be, this choice is incorrect.

Now, let's take a look at Choice C.

C. They are unable to determine either the time or the place that earthquakes are likely to occur.

When I read this choice initially, the "place" aspect did throw me off a little-bit, but after reading the information one more time and looking at the other answer choices, I went along with Choice C. So, here are my cents on it:

Quote:
Secondly, the passage states the foreshocks are indistinguishable from other minor tremors that occur without large earthquakes. At a stretch, it could mean that they are unsure of the time.

1. unable to determine either the time - This portion, as you agree to an extent, is correct for the reasons explained above (refer to point no. 1 under the explanation for choice A for more detail).

Quote:
But how can they be unsure of the place? The tremors are 'nearby' as stated in the passage.

2. place that earthquakes are likely to occur - Alright, so let's look at how the whole information about tremors observed "nearby" places is given to us. We are basically told that after stress increases beyond a particular point in the rocks, something happens, leading to tremors and other things in the areas nearby to these rocks. Right? But then we are also told that just because these tremors occur, we cannot predict that an earthquake will follow. So, when you combine these two pieces of information, it means that say at place xyz, the researchers observe tremors, but they can't really say that at this place, there will be an earthquake. This is why the whole "place" angle makes sense - even though one is not very comfortable with it in the beginning.

Hope the above explanation helps.

Cheers!
##### General Discussion
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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02 Aug 2016, 09:21
4
alpham wrote:
Can someone explain why the primarily purpose is D and not E? I thought it was more about the development of methods rather than the shortcomings of methods.

The passage discusses two methods for predicting earthquakes and suggests that both the methods are not accurate - Answer has to be D.

Now lets look at why E is wrong:
E. describing the development of methods for establishing patterns in the occurrence of past earthquakes - Are the two methods limited to establishing patterns of past earthquakes? No. Moreover development of methods is a positive tone. But the passage is not too optimistic about the methods suggested. E cannot be the answer.
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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02 Aug 2016, 09:29
1
smartyman wrote:
Please provide OE for Q16. Thanks.

Line 18: Researchers initially reported success in identifying these possible precursors, but subsequent analyses of their data proved disheartening.

The author implies which of the following about the ability of the researchers mentioned in line 18 to predict earthquakes?

A. They can identify when an earthquake is likely to occur but not how large it will be. - Incorrect.
B. They can identify the regions where earthquakes are likely to occur but not when they will occur. - Incorrect.
C. They are unable to determine either the time or the place that earthquakes are likely to occur. - Correct
D. They are likely to be more accurate at short-term earthquake prediction than at long-term earthquake prediction. -Incorrect
E. They can determine the regions where earthquakes have occurred in the past but not the regions where they are likely to occur in the future. - Incorrect

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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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05 Aug 2016, 08:38
Dear Vyshak,
In 1971 researchers hoping to predict earthquakes in the short term by identifying precursory phenomena (those that occur a few days before large quakes but not otherwise) turned their attention to changes in seismic waves that had been detected prior to earthquakes.
Researchers initially reported success in identifying these possible precursors, but subsequent analyses of their data proved disheartening.

Based on these 2 statements:
since subsequent analyses of their data proved disheartening, researchers initially identification of precursor phenomena (those that occur a few days {TIME} before quakes but not otherwise) could be flawed. But the whole passage did not mention that researchers are unable to pinpoint the location of quakes that are likely to occur.

The answer C: They are unable to determine either the time or the place that earthquakes are likely to occur.
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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05 Aug 2016, 09:56
smartyman wrote:
Dear Vyshak,
In 1971 researchers hoping to predict earthquakes in the short term by identifying precursory phenomena (those that occur a few days before large quakes but not otherwise) turned their attention to changes in seismic waves that had been detected prior to earthquakes.
Researchers initially reported success in identifying these possible precursors, but subsequent analyses of their data proved disheartening.

Based on these 2 statements:
since subsequent analyses of their data proved disheartening, researchers initially identification of precursor phenomena (those that occur a few days {TIME} before quakes but not otherwise) could be flawed. But the whole passage did not mention that researchers are unable to pinpoint the location of quakes that are likely to occur.

The answer C: They are unable to determine either the time or the place that earthquakes are likely to occur.

Hi smartyman,

The researchers thought they were successful, but the end result was contrary to what they thought. The premise provides the context, but the conclusion matters the most. And if you read the passage carefully, the whole passage explains the shortcomings of the two methods used to predict earthquakes. They researchers were neither able to predict a place nor the time of earthquakes. The answer can also be obtained through elimination of other choices.
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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07 Nov 2016, 06:58
1
Vyshak wrote:
smartyman wrote:
Dear Vyshak,
In 1971 researchers hoping to predict earthquakes in the short term by identifying precursory phenomena (those that occur a few days before large quakes but not otherwise) turned their attention to changes in seismic waves that had been detected prior to earthquakes.
Researchers initially reported success in identifying these possible precursors, but subsequent analyses of their data proved disheartening.

Based on these 2 statements:
since subsequent analyses of their data proved disheartening, researchers initially identification of precursor phenomena (those that occur a few days {TIME} before quakes but not otherwise) could be flawed. But the whole passage did not mention that researchers are unable to pinpoint the location of quakes that are likely to occur.

The answer C: They are unable to determine either the time or the place that earthquakes are likely to occur.

Hi smartyman,

The researchers thought they were successful, but the end result was contrary to what they thought. The premise provides the context, but the conclusion matters the most. And if you read the passage carefully, the whole passage explains the shortcomings of the two methods used to predict earthquakes. They researchers were neither able to predict a place nor the time of earthquakes. The answer can also be obtained through elimination of other choices.

Researchers initially reported success in identifying
these possible precursors, but subsequent analyses
of their data proved disheartening. Seismic waves

with unusual velocities were recorded before some
earthquakes, but while the historical record confirms
that most large earthquakes are preceded by minor
tremors, these foreshocks indicate nothing about
the magnitude of an impending quake and are

From this statement I marked A as the answer , my line of reasoning is Researchers were not able to find what the shocks meant as the shocks were misleading, they could either indicate a minor or a major earthquake
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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21 Mar 2017, 08:04
In the last question, I'm unable to understand why C is correct and A is wrong.

First of all, this is an inference question, right? Because OG has put it under the 'supporting idea' category and the explanation also reads "The question asks for information explicitly stated..."

Secondly, the passage states the foreshocks are indistinguishable from other minor tremors that occur without large earthquakes. At a stretch, it could mean that they are unsure of the time. But how can they be unsure of the place? The tremors are 'nearby' as stated in the passage.

Answer choice A, on the other hand, is very easily inferable by the line 'these foreshocks indicate nothing about the magnitude of an impending quake'.

Also, if someone can explain the answer choices A & C as provided by the OG. Thanks!

Posted from my mobile device
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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06 Apr 2017, 21:15
16 is ridiculous

it says that seismic waves were recorded before some earthquakes, but while the historical record confirms that most large earthquakes are preceded by minor tremors, these foreshocks indicate nothing about the magnitude of an impeding quake and are indistinguishable from other minor tremors that occur without large earthquakes.

So it should be A not C.... must be a mistake
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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08 Apr 2017, 19:08
Hi Expert

I have a query regarding the last question in this series.
We are asked about the ability of the researchers in the line 18.
The passage clearly indicates and even mentions -> They were able to predict the timing but not the magnitude." indistinguishable from other minor tremors that occur"

I am still convinced that the OA should be A.

What am i missing.?

P.S-> I have seen the other replies.
without large earthquakes.

Regards
Stone Cold
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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16 Apr 2017, 06:22
Hi GMATNinjaTwo,

Can you please explain why choice E is incorrect in question 14 (4)?
My reasoning:
Since paleoseismology provides evidence for regular earthquake cycles on which long term prediction is based. That means related theory written in line 45 are facts on which researchers' theory is based.
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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16 Apr 2017, 15:01
2
1
AR15J,

Quote:
Can you please explain why choice E is incorrect in question 14 (4)?
My reasoning:
Since paleoseismology provides evidence for regular earthquake cycles on which long term prediction is based. That means related theory written in line 45 are facts on which researchers' theory is based.

Referring to line 45, the paleoseismologists "have determined that the average interval between ten earthquakes that took place at one site along the San Andreas Fault in the past two millennia was 132 years, but individual intervals ranged greatly, from 44 to 332 years." This evidence does not suggest that earthquakes occur at regular intervals because the intervals ranged greatly (from 44 to 332 years); in fact, this is evidence against the existence of regular earthquake cycles that could, if they existed, be used in long-term earthquake prediction. If the intervals did not vary greatly (ie if the standard deviation was lower and the interval between most of those earthquakes was very close to the average of 132 years, then this would suggest that earthquakes in that region occur at regular intervals).

Furthermore, the question is asking us to select a fact on which some researchers based their research. Choice E describes data collected by paleoseismologists while conducting their research; thus, choice E describes the research itself, not a fact on which the research was based. Choice C, on the other hand, describes a fact on which some researchers based their research (see line 29: "Noting that earthquakes tend to occur repeatedly in certain regions, Lindh and Baker attempted to identify patterns of recurrence, or earthquake cycles, on which to base predictions."). In other words, Lindh and Baker noted the fact that "some regions tend to be the site of numerous earthquakes over the course of many years," so they began to study those regions to see if they could identify patterns of recurrence on which to base long-term earthquake prediction.
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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13 Aug 2017, 02:07
4
arvind910619 wrote:
Hi Experts

Hi arvind910619 ,

Last question is talking about the ability of the researchers mentioned in line 18.

To answer this question, you must understand the following lines:

"Researchers initially reported success in identifying these possible precursors, but subsequent analyses of their data proved disheartening. Seismic waves with unusual velocities were recorded before some earthquakes, but while the historical record confirms that most large earthquakes are preceded by minor tremors, these foreshocks indicate nothing about the magnitude of an impending quake and are indistinguishable from other minor tremors that occur without large earthquakes."

These lines say they tried recording the Seismic waves of certain regions with the hope that they will determine the place and the time of earthquake occurrence but later they found that we have some places where we can see similar kind of seismic waves but no earth quake is present.

This means what they were thinking is the right approach came out to be irrelevant for them.

Thus, option C is correct. "They are unable to determine either the time or the place that earthquakes are likely to occur."

Let me talk about other options now:

A. They can identify when an earthquake is likely to occur but not how large it will be. --> No where we are given this. As per the meaning, their method was wrong. Hence, they were not able to identify the places or time.

B. They can identify the regions where earthquakes are likely to occur but not when they will occur. --> Same as above. They cannot identify the regions.

C. They are unable to determine either the time or the place that earthquakes are likely to occur.

D. They are likely to be more accurate at short-term earthquake prediction than at long-term earthquake prediction. --> This is not given for these researchers.

E. They can determine the regions where earthquakes have occurred in the past but not the regions where they are likely to occur in the future. --> Again, this is not given

Does that make sense?
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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13 Aug 2017, 03:46
1
GMATNinjaTwo,

How did you infer that those 2 precursors were 'time' and 'place' as mentioned in Option C? In my opinion, A looks to be the clear winner.

Thanks.
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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13 Aug 2017, 05:17
2
KS15 wrote:
GMATNinjaTwo,

How did you infer that those 2 precursors were 'time' and 'place' as mentioned in Option C? In my opinion, A looks to be the clear winner.

Thanks.

Quote:
(Book Question: 16)
The author implies which of the following about the ability of the researchers mentioned in line 18 to predict earthquakes?

A. They can identify when an earthquake is likely to occur but not how large it will be.
B. They can identify the regions where earthquakes are likely to occur but not when they will occur.
C. They are unable to determine either the time or the place that earthquakes are likely to occur.
D. They are likely to be more accurate at short-term earthquake prediction than at long-term earthquake prediction.
E. They can determine the regions where earthquakes have occurred in the past but not the regions where they are likely to occur in the future.

The passage states that "these foreshocks [that precede most large earthquakes] indicate nothing about the magnitude of an impending quake and are indistinguishable from other minor tremors that occur without large earthquakes."

Thus, the researchers cannot use foreshocks (precursory phenomena) to predict earthquakes. A foreshock could be followed by a large earthquake, a small earthquake, or no earthquake at all. Thus, the foreshocks do not give us any information about the time or place that earthquakes are likely to occur.

In other words, if a phenomena gives you no information about whether an earthquake will occur, then obviously it does not give you any information about the time or place that an earthquake will occur. Although "time" and "place" are not specifically cited, we can infer this from the statements in the passage.

Refer to my earlier post for additional analysis of this question and an explanation of why choice (A) is wrong: https://gmatclub.com/forum/in-1971-rese ... l#p1835521.
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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17 Aug 2017, 06:57
1
anuj11 wrote:
Can some one explain question 13 ? I cant distinguish between C and E !! Ended up picking C

Quote:
(Book Question: 13)
It can be inferred from the passage that one problem with using precursory phenomena to predict earthquakes is that minor tremors

A. typically occur some distance from the sites of the large earthquakes that follow them
B. are directly linked to the mechanisms that cause earthquakes
C. are difficult to distinguish from major tremors
D. have proven difficult to measure accurately
E. are not always followed by large earthquakes

The key lies in this portion of the passage:

Quote:
while the historical record confirms
that most large earthquakes are preceded by minor
tremors, these foreshocks indicate nothing about
the magnitude of an impending quake and are
(25)
indistinguishable from other minor tremors that occur
without large earthquakes.

Most large earthquakes are preceded by minor tremors. Does that mean whenever we observe a minor tremor, we can predict that a large earthquake will occur? .... unfortunately not, because those minor tremors are indistinguishable from minor tremors that occur without large earthquakes. In other words, we have no idea whether a minor tremor will be followed by a large earthquake.

As for choice (C), the passage does not say that minor tremors are difficult to distinguish from major tremors. Regardless, unlike choice (E), this does not describe the problem with using precursory phenomena to predict earthquakes.

I hope that helps!
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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15 Dec 2017, 10:41
Nice passage . All correct , Took 11 mins 30 seconds, including 5 mins 30 seconds to read the passage .
AjiteshArun , mikemcgarry ,GMATNinja , ccooley , GMATNinjaTwo , egmat , other experts -- can you please help in Q11(First question)--

I quickly narrowed down to option D and E , but was not confident of the selected answer -- Is option D better because the main intent of researchers has been to predict the occurrence of earthquakes, not establishing patterns in the occurrence of past earthquakes?

D. discussing the deficiency of two methods by which researchers have attempted to predict the occurrence of earthquakes
E. describing the development of methods for establishing patterns in the occurrence of past earthquakes
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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19 Dec 2017, 18:18
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Skywalker18 wrote:
(Book Question: 11)
The passage is primarily concerned with

A. explaining why one method of earthquake prediction has proven more practicable than an alternative method
B. suggesting that accurate earthquake forecasting must combine elements of long-term and short-term prediction
C. challenging the usefulness of dilatancy theory for explaining the occurrence of precursory phenomena
D. discussing the deficiency of two methods by which researchers have attempted to predict the occurrence of earthquakes
E. describing the development of methods for establishing patterns in the occurrence of past earthquakes

Skywalker18 wrote:
Nice passage . All correct , Took 11 mins 30 seconds, including 5 mins 30 seconds to read the passage .
AjiteshArun , mikemcgarry ,GMATNinja , ccooley , GMATNinjaTwo , egmat , other experts -- can you please help in Q11(First question)--

I quickly narrowed down to option D and E , but was not confident of the selected answer -- Is option D better because the main intent of researchers has been to predict the occurrence of earthquakes, not establishing patterns in the occurrence of past earthquakes?

D. discussing the deficiency of two methods by which researchers have attempted to predict the occurrence of earthquakes
E. describing the development of methods for establishing patterns in the occurrence of past earthquakes

We are looking for the primary purpose of the passage, so we need to identify the main intent of the author, not of the researchers. The author describes two failed methods attempted by researchers: one tried in 1971 and the other tried in the 1980s.

As you noted, the goal of those methods (and of the researchers) was to predict earthquakes (the first was geared towards short-term prediction and the other was geared towards long-term prediction). The author explains how those methods failed. Thus, the author's intention was to discuss the deficiency of those two methods.

The second method did involve analyzing patterns in the occurrence of past earthquakes. But did the passage discuss the methods that were used to establish those patterns? No, and even if it did, those patterns do not represent the main purpose of the passage. Rather, the patterns are just background information that the author gives in order to show how that second method failed.

I hope that helps!
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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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01 Oct 2018, 19:17
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P1 - for anticipating earthquake, a theory is given. what it is based on is given.
P2 - above theory is not that effective. reasons are given.
P3 - new theory is given with new aims. this one is also flop.

(Book Question: 11)
The passage is primarily concerned with

A. explaining why one method of earthquake prediction has proven more practicable than an alternative method - no
B. suggesting that accurate earthquake forecasting must combine elements of long-term and short-term prediction - p3 only
C. challenging the usefulness of dilatancy theory for explaining the occurrence of precursory phenomena - p1 + p2
D. discussing the deficiency of two methods by which researchers have attempted to predict the occurrence of earthquakes - best of the lot.
E. describing the development of methods for establishing patterns in the occurrence of past earthquakes - no

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(Book Question: 12)
According to the passage, laboratory evidence concerning the effects of stress on rocks might help account for

According to this theory, such effects could lead to several precursory phenomena in (15) the field, including a change in the velocity of seismic waves, and an increase in small, nearby tremors.

B. certain phenomena that occur prior to earthquakes -

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(Book Question: 13)
It can be inferred from the passage that one problem with using precursory phenomena to predict earthquakes is that minor tremors
P2 - these foreshocks indicate nothing about the magnitude of an impending quake and are (25) indistinguishable from other minor tremors that occur without large earthquakes.

E. are not always followed by large earthquakes -
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(Book Question: 14)
According to the passage, some researchers based their research about long-term earthquake prediction on which of the following facts?
P3 - Lindh and Baker attempted to identify patterns of recurrence, or earthquake cycles, on which to base predictions.

C. Some regions tend to be the site of numerous earthquakes over the course of many years. -

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(Book Question: 15)
The passage suggests which of the following about the paleoseismologists’ findings described in lines 42–50?

40) earthquake cycles that Lindh and Baker tried to establish has come from a relatively new field, paleoseismology. Paleoseismologists have unearthed and dated geological features such as fault scarps that were caused by (45) earthquakes thousands of years ago. They have determined that the average interval between ten earthquakes that took place at one site along the San Andreas Fault in the past two millennia was 132 years, but individual intervals ranged greatly, (50) from 44 to 332 years.
PT - that long term prediction is not useful.

D. They suggest that the recurrence of earthquakes in earthquake-prone sites is too irregular to serve as a basis for earthquake prediction. -
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(Book Question: 16)
The author implies which of the following about the ability of the researchers mentioned in line 18 to predict earthquakes?

C. They are unable to determine either the time or the place that earthquakes are likely to occur. - yes
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Re: In 1971 researchers hoping to predict earthquakes in the short term by   [#permalink] 01 Oct 2018, 19:17

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