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

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

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New post 20 Feb 2019, 00:50
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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Re: In 1971 researchers hoping to predict earthquakes in the short term by  [#permalink]

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New post 12 Jun 2019, 17:43
1
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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Big Fat Disclaimer: I am NotAnExpert, but rather, merely a person that is studying for the GMAT and wants to make the best of, and take the most out of this forum. My only goal is to contribute to the community from the which I have taken so much, and ultimately help make the GMAT Club forums a better place to learn. In my posts, I share my learning outcomes by verbalizing how I solved problems, and hope that the added perspective can help anyone achieve an 'ah-hah' moment.

Sometimes it takes a concept being explained in 15 different ways to achieve an 'ah hah' breakthrough moment and I am here to contribute one, of hopefully many, unique perspectives. I do not encourage or participate in posts that simply state "that was easy", or "relevant, out of scope, correct". I find that people - myself included - often have a difficult time truly understanding the fact that in CR/RC questions, there will be one very definitively black and white correct answer, just a there is in Quant. As a result, my posts are exclusively focused on CR and RC. There is no such thing as a 'kinda right' question and because of this, I contribute detailed posts on how I came to my answer in hopes that it will connect with someone.

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

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New post 27 Jun 2019, 04:34
(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.

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New post 27 Jun 2019, 11:34
1
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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Big Fat Disclaimer: I am NotAnExpert, but rather, merely a person that is studying for the GMAT and wants to make the best of, and take the most out of this forum. My only goal is to contribute to the community from the which I have taken so much, and ultimately help make the GMAT Club forums a better place to learn. In my posts, I share my learning outcomes by verbalizing how I solved problems, and hope that the added perspective can help anyone achieve an 'ah-hah' moment.

Sometimes it takes a concept being explained in 15 different ways to achieve an 'ah hah' breakthrough moment and I am here to contribute one, of hopefully many, unique perspectives. I do not encourage or participate in posts that simply state "that was easy", or "relevant, out of scope, correct". I find that people - myself included - often have a difficult time truly understanding the fact that in CR/RC questions, there will be one very definitively black and white correct answer, just a there is in Quant. As a result, my posts are exclusively focused on CR and RC. There is no such thing as a 'kinda right' question and because of this, I contribute detailed posts on how I came to my answer in hopes that it will connect with someone.

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

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New post 29 Jun 2019, 14:47
Chelsea212 wrote:
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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Re: In 1971 researchers hoping to predict earthquakes in the short term by   [#permalink] 29 Jun 2019, 14:47

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