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605-655 (Medium)|   Long Passage|   Science|                        
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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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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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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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Question 6:

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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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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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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anuj11
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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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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Skywalker18
(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
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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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

----------------------------------------------
(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 -

----------------------------------------------
(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 -
----------------------------------------------
(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. -

----------------------------------------------

(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. -
----------------------------------------------

(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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My Take on Question no. 16:

Portion of the RC:

"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."

Takings:
Foreshocks :
1. Cannot indicate the magnitude of upcoming quake
2. are indistinguishable from minor tremors that ocur without large quakes

Process of Elimination:

A. They can identify when an earthquake is likely to occur but not how large it will be. (They cannot identify the likely occurance as these were indistinguisable from minor tremors without large earthquakes ;Therefore, they cannot identify the earthquakes)

B. They can identify the regions where earthquakes are likely to occur but not when they will occur. (Cannot Determine the place, Explanation in option C explanation)

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

Cannot Determine Time: As They cannot determine the earthquake because " Fore shocks are indistinguishable from minor tremors that occur without large quakes"
Cannot Determine Place: Because of
1) Unusual Velocities of Sesmic waves: "precursory phenomena in the field, including a change in the velocity of seismic waves " in the text since Change in velocity is different from unusual velocities, this implies that field cannot be determined
2) Foreshocks are indistinguishable from other minor tremors:"nearby tremors" in the text are precursory phenomena, since these precursory phenomena tremors are indistinguishable from OTHER tremors ; Therefore, Earthquakes cannot be determined thereby place cannot be determined.


D. They are likely to be more accurate at short-term earthquake prediction than at long-term earthquake prediction. (Out of scope, this was some other researcher's issue discussed later in the passage)

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. (No such information is there to indicate about regions where the earthquakes have occured in the past)
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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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(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.

I need help with this question.
Why is option D incorrect? Some researchers in 1971 base their research on In 1971 researchers hoping to predict earthquakes in dilatancy theory.

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. -> this was explained by dilatancy theory.

GMATNinjaTwo, GMATNinja, abhimahna
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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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RitujaBasu
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Please explain the answer for the 6th question in this RC. I chose A but the answer is C.
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RitujaBasu
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.)

- Andrew
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Hi, could someone help explain Question 4 please?

The relevant portion of the passage:

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.
Now if the time period has increased from 22 years(as predicted by L and B) to 132, why cannot we infer that the frequency has significantly reduced? Wouldn't choice A be a correct answer?

Thanks in advance
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