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605-655 Level|   Long Passage|   Science|                        
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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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Chelsea212
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
Chelsea212, your explanation looks great! Nicely done. PriyankaPalit7, just let us know if that doesn't resolve your doubts.
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HI SajjadAhmad, workout

Can you please remove those numbers beside the para and keep the passage parawise. I understand that passage is according to OG but in the actual Prep there will be no numbers and that makes easy to read and practice.
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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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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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got 5 out of 7 correct . last question was toughest . how can it be of 600 level .
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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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jayarora
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

Hi Jay

I think you refer to Q5 and not Q4.

Option (A) states that "frequency with which earthquakes occurred at a particular site decreased significantly over the past two millennia". There are several problems with this:

1) The passage suggests that Lindh and Baker's predictions did not pan out.
2) Recent findings of paleoseismologists show a greater gap between earthquakes.

The recent findings seem to overturn the earlier suggestions ie; it is the research findings that have changed the time interval - the actual time interval would have been the same irrespective of the research findings. Therefore it would be inaccurate to say, based on these statements, that the "frequency of earthquakes...has decreased" as option (A) does. We can also surmise this from the statement, " 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 implies that there was no regular trend in the time interval between successive earthquakes - there has been variation but there is nothing to suggest whether the time interval has been increasing or reducing.

Hope this helps.
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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.
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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.

in E option:
but not the regions where they are likely to occur in the future.= TRUE
They can determine the regions where earthquakes have occurred in the past =?

Quote:
Statement1: . 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
.
>> They can only determine if they know where these earthquakes have occurred
Quote:
Statement2:In a study of earthquake-prone sites along the San Andreas Fault, they determined that quakes occurred at intervals of approximately 22 years near one site and concluded that there was a 95 percent probability of an earthquake in that area by 1992
>> They determined where these earthquakes occurred
atleast they have some ability to determine the earth quake location where it occured . it could be anywhere between 0.xx% to 99.xx%

The long term prediction analysis is based on history of these earthquake occurrences ,so we can't determine that they have no ability.


If i see the question:
Quote:
about the ability of the researchers mentioned in line 18 to predict earthquakes
In 1971 researchers hoping to predict earthquakes - researchers A
In the 1980s, some researchers turned their efforts from short-term to long-term prediction.- Some researchers subset of A
so could be same researchers


Quote:
C. They are unable to determine either the time or the place that earthquakes are LIKELY to occur.
LIKELY- it doesn't say MUST BE.
Likely could be anywhere between 0.xx-99.xx%.

After this detailed understanding, why would i chose answer C?
GMATGodGMATNinja @GMATNinjaTwo neetis5 Kurtosis abhimahna Skywalker18 aragonn MentorTutoring CrackVerbalGMAT VeritasKarishma
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Did not understand question 6. Why is the answer C and not A when it is clearly mentioned in the passage that the researchers could not identify the magnitude of the earthquake. We have to stick to the location. Please explain it properly.
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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.

- Andrew
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saby1410
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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saby1410
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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saby1410
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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My passage summary:
1. Introduce researcher's objective of predicting earthquakes thru precursory phenomena (short term prediction)

2. Dilatancy Theory was used to predict precursors before a large tremor

3. Initial Success in identifying precursors

4. But precursors unable to identify the diff between regular small tremors Vs small tremors that occur before a big tremor

5. researchers changed their efforts from short term to long term prediction by decoding past patterns

6 New study proved that no pattern can be proved

Mainpoint: Author discusses two methods researchers used to predict earthquakes and highlighted how neither of them was successful in its objective
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neetis5
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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! :)

Hi Neetis5,
"Without large earthquakes" can mean that earthquakes do occur, but are not necessarily large?
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