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

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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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New post 11 Apr 2017, 18:16
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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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New post 06 Apr 2017, 23:33
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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! :)
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New post 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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New post 13 Aug 2017, 02:07
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arvind910619 wrote:
Hi Experts
Please explain the answer of the last question ?


Hi arvind910619 ,

Let me help you. :)

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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New post 16 Apr 2017, 15:01
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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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New post 02 Aug 2016, 09:29
2
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

Answer: C
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New post 13 Aug 2017, 05:17
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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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New post 17 Aug 2017, 06:57
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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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New post 12 Jun 2019, 16:43
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Hi everyone! At this point, I think maybe it would be wise for me to change my user name to "NotAnExpert" because I always start off my posts with a disclaimer that I am indeed 'not an expert'. However, for the purposes of full disclosure, I always just want to make clear I'm a just a person studying for the GMAT and looking to use this forum as a place of learning and nothing else. I encourage everyone to contribute because without contributors, you would have nothing to read! =)

It seems like the final question of this passage is giving everyone the most trouble; a rather 'controversial question'. Lol. I'll give my take on it and hopefully if you are/were still struggling on having the 'ahh' moment, this may help you out. Although I may not be smiling any new tea, I often find that when I am having difficulty learning any concept, I just need to hear it explained multiple ways before I click with one.

Quote:
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.

Step 1. I always, always, always rephrase the passage as I read. Make sure that this is an instinctive reaction as you read the passage. You should be continuously reading and rephrasing -i.e. comprehending - as you go. By the end of the passage, you should always be aiming to understand "what is the point of this passage?" which is the exact same question as "what is the passage primarily concerned with?"

Step 2. For every question, always go back to the passage. The question we're looking at is an inference question and so I immediately direct my eyes to the relevant portion of the passage and scan at the specific content +/- one sentence. For this, the work is already done for you as the question states to look at line 18, so just read the sentence before and after.

Step 3. Always find 4 wrong answers!
    (A) They can identify when an earthquake is likely to occur but not how large it will be. - Oh wow, already I am so very tempted. I am going to focus on explaining this answer choice because (1) I actually got this question wrong and fell into this trap, and (2) it seems to be the choice most people are grappling with.

    What made me fall for this was that it was half right and I really hung on to the fact - yes, it is true that 'researchers cannot predict how large it will be'. In addition, I think my mind mashed together the two parts of this “dilatancy theory,” regarding how stress fractures in rocks could lead to "such effects could lead to several precursory phenomena".

    I missed the causation and hence I was not able to distinguish between cause and effect; the cause (cracks in rocks) would tell you where the earthquakes are going to occur and the tremors that the are caused by said cracks (i.e. pressure) were 'supposed' to tell you how strong the quake would be. But none of that theory worked out: "Line 18: Researchers initially reported success in identifying these possible precursors, but subsequent analyses of their data proved disheartening".

    So while the passage may very explicitly say "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.", it looks to me that I just misunderstood/misread the earlier part discrediting the other part of answer choice (A).

    (B) They can identify the regions where earthquakes are likely to occur but not when they will occur. Ironically, I was able to knock this guy out right away. Line 18 +/-1 state that the researcher's cannot identify neither when nor where where earthquakes are likely to occur.

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

    (D) They are likely to be more accurate at short-term earthquake prediction than at long-term earthquake prediction.There is mention of the words "short-term" in the next few lines; however, you can quickly see that it is not in the context of the researchers targeted in our question stem.

    (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. Careful not to try and bring outside information into this. While it seems redundant to say researchers can find something that has already occurred, but not see what is going to happen in the future, this is not what is stated in the line 18. I think it's fairly straight forward that the passage does not state this so I'll leave this one without lengthy explanation.

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New post 19 Jun 2020, 03:32
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Hello, SkR1. I enjoyed reading your thorough analysis. I feel honored to have been mentioned alongside the others you named. I typically add my two cents when I feel a more thorough treatment of a question may be warranted, or if a user brings up a specific point that has not been addressed. I do this out of respect for my fellow GMAT Clubbers, Experts and students alike. In this case, I see that the top two posts in the thread address this very question. If you have read through the analyses by GMATNinjaTwo, neetis5, smartyman, Kurtosis, abhimahna, sahilbhatia21 at the top of page 2, and Chelsea212 and the question still does not make sense, then feel free to ask again for help. I guess I am having trouble understanding any lingering doubts you may have. (And, to be honest, I feel I have little to add in the way of insight that the posts above by the aforementioned members have not already touched on.)

Thank you for tagging me. I hope you find the answer you are looking for.

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New post 21 Jun 2020, 04:12
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saby1410 wrote:
VeritasKarishma GMATNinja
can u explain last question and also this line(earthquakes, but while the historical record confirms
that most large earthquakes are preceded by minor
tremors,) why 2 contradictory words are used together.
In 5 question if option d wasn't mentioned can we say E option be correct though it isn't mentioned whether they looked or not looked on causes of earthquake ,but paleoseismologists looked at the causes.



Yes, question no 6 is certainly a bit tricky and it took me a couple of reads before I settled on (C).

Lines of interest:
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...

...

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.



So in 1971, researchers thought of predicting earthquakes in short term by identifying precursory phenomena (such as, rain before a rainbow).
They observed some changes in seismic waves before large earthquakes. Initially, they reported success (say, they observed that before every large earthquake, these seismic waves changed) but later were disappointed. They observed these changes in seismic waves before small earthquakes as well as without any earthquakes. So now can they predict when an earthquake will happen based on changes in seismic waves? No. Some times these changes lead to large earthquakes, sometimes to small earthquakes and sometimes to no earthquake. So if we see these changes, can we say whether an earthquake will happen? No.
In 1980s, some researchers turned away from predicting short term and tried to predict long term earthquakes. After this we have the discussion on places that are earthquake prone etc.

6. 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.

Changes in seismic waves can take place even without earthquakes. Apparently they are frequent enough to make researchers consider it a failure and turn away. Hence, they cannot identify when an earthquake is likely to occur.

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

Correct. The researchers mentioned in line 18 give no lead on predicting earthquakes in any way.

Answer (C)
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New post 07 Nov 2016, 06:58
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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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New post 13 Aug 2017, 03:46
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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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New post 19 Dec 2017, 18:18
1
2
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

Skywalker18, your reasoning looks good!

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.

Choice (D) the best answer.

I hope that helps!
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New post 27 Jun 2019, 10:34
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Hi PriyankaPalit7 - I'm NotAnExpert but I'll try to see if I can help before one of the Ninjas have a minute to respond.

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

I've underlined the word 'long-term' because it is the key part of identifying the correct answer. While the statement made in answer choice (D) is a completely true statement made in the passage (see the second underlined set of words I've highlighted in red below), it is a statement that is made with respect to short, not long-term earthquakes. The correct answer - answer choice (C) - is supported by the text that I've highlighted in green.

Hope this helps!

Quote:
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. 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, 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 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 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.

In the 1980s, some researchers turned their efforts from short-term to long-term prediction. 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 a study of earthquake-prone sites along the San Andreas Fault, they determined that quakes occurred at intervals of approximately 22years 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 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 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, from 44 to 332 years

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New post 11 Mar 2020, 13:50
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RitujaBasu wrote:
Please explain the answer for the 6th question in this RC. I chose A but the answer is C.

Hello, RitujaBasu. I would suggest reading the earlier response by GMATNinjaTwo to this very question. If you still have questions after that, feel free to post your specific query again. (It appears you are in good company with choice (A), which has snagged over 50 percent of question-answerers on this site as of this writing.)

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New post 21 Jun 2020, 04:20
1
saby1410 wrote:
VeritasKarishma GMATNinja
can u explain last question and also this line(earthquakes, but while the historical record confirms
that most large earthquakes are preceded by minor
tremors,) why 2 contradictory words are used together.
In 5 question if option d wasn't mentioned can we say E option be correct though it isn't mentioned whether they looked or not looked on causes of earthquake ,but paleoseismologists looked at the causes.



As for your 'but while' question, notice the structure of the sentence:

Clause A - Seismic waves with unusual velocities were recorded before some earthquakes.

Clause B - 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.

'But' joins these two contrasting independent sentences.

Clause A, but Clause B
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New post 21 Jun 2020, 04:23
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saby1410 wrote:
VeritasKarishma GMATNinja
can u explain last question and also this line(earthquakes, but while the historical record confirms
that most large earthquakes are preceded by minor
tremors,) why 2 contradictory words are used together.
In 5 question if option d wasn't mentioned can we say E option be correct though it isn't mentioned whether they looked or not looked on causes of earthquake ,but paleoseismologists looked at the causes.


As for question 5, option (E) is not correct and will not be. The passage doesn't suggest it. No one suggests anything about 'causes of earthquakes'.
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New post 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] 05 Aug 2016, 08:38

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