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 22 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 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. 1 (Book Question: 11) 1. 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 2 (Book Question: 12) 2. 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 3 (Book Question: 13) 3. 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 4 (Book Question: 14) 4. 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. 5 (Book Question: 15) 5. 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. 6 (Book Question: 16) 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. 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.

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

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Hi RonTargetTestPrep KarishmaB GMATNinjaTwo ReedArnoldMPREP GMATNinja : quick question on 6, answer (E) specifically.

I dont see why the first half (in green) is wrong.

Quote:

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.

We should be able to "infer" the green font half in (E) becuase of the following lines in the passage

Line 21 : ...............but while historical record confirms that most large earthquakes are preceded by minor tremors....

If Line 21 is true - that MUST MEAN that researchers ** can determine ** the regions where earthquakes have occured in the past.

Why ?

Well, because there are historical records of past earthquakes.

So the Researchers **CAN** Determine the regions where earthquakes have occured in the past.

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jabhatta2

Hi RonTargetTestPrep KarishmaB GMATNinjaTwo ReedArnoldMPREP GMATNinja : quick question on 6, answer (E) specifically.

I dont see why the first half (in green) is wrong.

Quote:

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.

We should be able to "infer" the green font half in (E) becuase of the following lines in the passage

Line 21 : ...............but while historical record confirms that most large earthquakes are preceded by minor tremors....

We are talking about the researchers in line 18 and their ability to predict earthquakes.

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

The passage does not mention or imply that these researchers had the ability to "determine the regions where earthquakes have occurred in the past."

The passage says that 'historical record confirms that most large earthquakes are preceded by ...' so we can say that this implies that we do know about past earthquakes but who determined the regions where they took place etc is not given to us. Who determined the regions and other info about these earthquakes and made records is not known. There is no reason to assume that it was determined by these researchers.

Besides, we are talking about the ability of these researchers in the case of predictions (earthquakes in future) so a discussion about the past is irrelevant.

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26 Jun 2023, 09:22

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1. The passage is primarily concerned with

A. explaining why one method of earthquake prediction has proven more practicable than an alternative method
Both the methods ie, dilatancy theory (analyses of foreshocks) and earthquake cycles suffer from glaring deficiencies. No evaluations amongst the two methods has been presented in the passage

B. suggesting that accurate earthquake forecasting must combine elements of long-term and short-term prediction
Such a suggestion by author is not mentioned in the passage

C. challenging the usefulness of dilatancy theory for explaining the occurrence of precursory phenomena
dilatancy theory's usefulness has been challenged in only the 2nd paragraph. Too limited in scope

D. discussing the deficiency of two methods by which researchers have attempted to predict the occurrence of earthquakes
The main point of the passage is : 'Both the methods ie, dilatancy theory (analyses of foreshocks) and earthquake cycles suffer from glaring deficiencies'.

E. describing the development of methods for establishing patterns in the occurrence of past earthquakes
no description of timeline in the development of methods can be found in the passage

The correct option is (D)

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Updated on: 28 Jun 2023, 06:22

Originally posted by rn1112 on 26 Jun 2023, 09:58.
Last edited by rn1112 on 28 Jun 2023, 06:22, edited 1 time in total.

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2. According to the passage, laboratory evidence concerning the effects of stress on rocks might help account for

A. differences in magnitude among earthquakes
No such claims regarding magnitude linked to the laboratory evidence in the passage

B. certain phenomena that occur prior to earthquakes
the passage highlights that the effects of stress lead to precursory phenomena in the form of minor tremors

C. variations in the intervals between earthquakes in a particular area
these pertain to earthquake cycles method of predicting earhquakes !!

D. differences in the frequency with which earthquakes occur in various areas
Similar to (C) above. such an argument has been presented while discussing the earthquake cycles method of predicting earhquakes .

E. the unreliability of short-term earthquake predictions
laboratory evidence focusses on the effects of stress lead to precursory phenomena, not on the the unreliability of short-term earthquake predictions

The correct option is (B)

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3. 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
no such fact presented in the passage

B. are directly linked to the mechanisms that cause earthquakes
foreshocks are not always followed by earthquakes -- as highlighted in the passage

C. are difficult to distinguish from major tremors
no such comparisons not drawn in the relevant portion of the passage

D. have proven difficult to measure accurately
difficulty in measurement for the minor tremors has not been discussed in the passage

E. are not always followed by large earthquakes
In paragraph 2 (lines 22-27) of the passage, the author alludes to the fact that 'these foreshocks indicate nothing about the magnitude of an impending quake and are indistinguishable from other minor tremors that occur without large earthquakes' -- highlights that such minor tremors are not always followed by earthquakes

The correct answer is (E)

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4. 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.
opposite to this stem has been highlighted in the passage ie, precursory shocks are similar to other minor tremors that occur without large earthquakes.

B. The average interval between earthquakes in one region of the San Andreas Fault is 132 years.
That's just a fact presented in the passage. The research work was not based on this fact.

C. Some regions tend to be the site of numerous earthquakes over the course of many years.
ines 27-31 (2nd paragraph) clearly highlight : 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,

D. Changes in the volume of rock can occur as a result of building stress and can lead to the weakening of rock.
mechanism described in these lines. Not used as a fact by the researchers for research about long-term earthquake prediction

E. Paleoseismologists have been able to unearth and date geological features caused by past earthquakes.
The work of palaeoseismologists have not been shown to assist research regarding preciction about long-term earthquake prediction

The correct option is (C)

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5. 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.
'irregular' recurrence has been highlighted. There is no mention of decreasing trend.

B. They suggest that paleoseismologists may someday be able to make reasonably accurate long-term earthquake predictions.
No such prediction inferred from the particular extract of the passage concerning paleoseismologists

C. They suggest that researchers may someday be able to determine which past occurrences of minor tremors were actually followed by large earthquakes.
The paleoseismologists have not deliberated upon the past occurrences of minor tremors in connection with 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.
Lines 48-50 (last paragraph) highlights the view of paleoseismologists : 'individual intervals ranged greatly from 44 to 332 years' --- highlighting evidently that the paleoseismologists thought 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.
There is no mention of evidence related to the causes of earthquakes in the particular extract of the passage .

The correct option is (D)

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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.
Clearly highlighted in line 24 of the passage that 'foreshocks indicate nothing about the magnitude of an impending quake'

B. They can identify the regions where earthquakes are likely to occur but not when they will occur.
If the foreshocks are indistinguishable from other minor tremors that occur without large earthquakes (as highlighted in the passage), then the location can also not be determined.

C. They are unable to determine either the time or the place that earthquakes are likely to occur.
Lines 23-26 of the passage mention that such researchers' analyses later proved that the foreshocks are indistinguishable from other minor tremors that occur without large earthquakes -- if that be so, then it can be inferred that the researchers will be 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.
No such comparisons drawn regarding accuracy of short-term earthquake prediction over 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.
Determination of the regions where earthquakes have occurred in the past -- not discussed in connection with such researchers

The correct option is (C)

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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!

Hi,
I had the same confusion as stonecold and I went through the explanation which largely makes sense, however, the option talks about them being able to identify when an earthquake is likely to occur and not that the earthquake occurs for sure. Wouldn't this make A more defensible?

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Question 6

sectan

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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.

Hi,

I had the same confusion as stonecold and I went through the explanation which largely makes sense, however, the option talks about them being able to identify when an earthquake is likely to occur and not that the earthquake occurs for sure. Wouldn't this make A more defensible?

The word "likely" does soften (A) to some degree. However, we still can't say that the researchers in question are "likely" to identify when an earthquake will occur. Let's say that they record some "possible precursors" to an earthquake -- is that earthquake then likely to occur at some predictable time in the near future?

Sadly, it is not. These possible precursors are "indistinguishable" from other events that are not followed by an earthquake at all. So the researchers are left in the dark -- maybe an earthquake will occur, maybe it won't.

Given this, we can't say that it is "likely" that the researchers can identify when an earthquake will occur. Eliminate (A) for question 6.

I hope that helps!

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