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Modern methods of predicting earthquakes recognize that quakes, far fr

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Modern methods of predicting earthquakes recognize that quakes, far fr  [#permalink]

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Updated on: 15 Oct 2019, 23:29
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Modern methods of predicting earthquakes recognize that quakes, far from being geologic anomalies, are part of the periodic accumulation and discharge of seismic energy. As continents receive the horizontal thrust of seafloor plates, crustal strains develop. Accumulation of strain can take anywhere from 100 years in certain coastal locations to over a millennium in some inland regions before a critical point is reached and a rupture occurs. In both areas, the buildup of strain is accompanied by long- and short-range precursory phenomena that are crucial to earthquake prediction. Quakes along active faults—like those along the Pacific coasts—are usually frequent; scientists designate such areas as quake-prone. However, when the time interval between quakes is great, as in inland regions, locating active faults is only a beginning. Geological scars of past subsidence, cracks, and offsets are useful in determining potential quake locations, as are seismicity gaps, areas where no small quakes have been recorded. Seismologists may also consult the historical record. Primary sources range from eyewitness accounts of ancient quakes to recent official documentation of quake-related damage.

Once the perimeters of a quake-prone zone are established, a network of base stations can monitor precursory phenomena. Stations must extend over a wide area yet be placed at measured intervals to obtain precise readings. Changes in geochemical readings (electric currents, radon concentrations) and in groundwater levels, as well as the occurrence of microearthquakes, are valuable precursors. Crustal movements—tilting, rising, and expansion or contraction of the ground’s surface—can be read through triangulation and leveling surveys taken over the course of decades. Theoretically, if an area’s critical strain—the magnitude of strain necessary to produce a rupture—is known, subtracting the measured accumulated crustal strain from the critical strain will indicate a time frame for an impending quake.

Violent tilting and foreshocks are among phenomena classified as short-term precursors. Many are still being identified as new quakes occur. Such precursors are valuable since their appearance can permit prediction of a quake to within hours of the primary rupture. Here, too, historical documents are useful. Seismologists recognized the liquefaction of sand as a precursor after a 1964 quake in Japan.

1. According to the passage, a major difference between coastal regions and inland regions is that in coastal regions

A) crustal strain does not occur.
B) earthquakes are less numerous.
C) critical points are reached more quickly.
D) precursory phenomena are seldom observed.
E) seafloor plate action is less powerful.

2. The primary purpose of the passage is to

A) clarify the way in which earthquakes develop in inland locations.
B) show that earthquakes are a result of the normal accumulation and discharge of seismic energy.
C) discuss the accumulation of crustal strain in coastal regions.
D) argue that precursory phenomena should be disregarded in attempts at quake prediction.
E) describe methods of earthquake prediction and explain the importance of precursory phenomena.

3. The primary function of the third paragraph is to

A) explain the relationship between accumulated and critical strain.
B) describe the use of precise intervals in establishing networks of base stations.
C) summarize the differences between earthquakes in coastal and inland regions.
D) outline some of the methods used by seismologists to predict earthquakes.
E) suggest that critical strain is not spread evenly along most major fault lines.

4. According to the passage, knowledge of an area’s critical strain can help seismologists

A) estimate the date of a future earthquake.
B) calculate the severity of an initial rupture.
C) measure the seismic force along a fault.
D) revise the distances between base stations.
E) predict the rate of future crustal movement.

89

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Last edited by SajjadAhmad on 15 Oct 2019, 23:29, edited 1 time in total.
Updated - Complete topic (1035).
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Re: Modern methods of predicting earthquakes recognize that quakes, far fr  [#permalink]

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16 Dec 2018, 05:25
Hey dude ...great passage
I just have one small doubt ...is the 3rd paragrapagh located correctly because in the question of function of 3rd para the OA says "some methods" plral...but in last para only 1 such method is given...
I think some part of the 2nd para is of the 3rd para ...to be precise the ". Crustal movements—tilting, rising, and expansion or contraction of the ground’s surface—can be read through triangulation and leveling surveys taken over the course of decades....."
The tilting isthen continued in the supossedly last para...could you please check....I could be wrong...but please check

I have checked, there is no such issue.

Official Explanation

1. According to the passage, a major difference between coastal regions and inland regions is that in coastal regions

Difficulty Level: 700

Explanation:

Paragraph 1 contrasts coastal regions, where crustal strains build rapidly, with inland regions, where strains build more slowly. (C) paraphrases that distinction. (A) flatly contradicts the passage—the first paragraph states that crustal strain is great in coastal regions. (B) contradicts the passage—quakes are less numerous in inland areas. (D) also contradicts the passage—you can infer that in coastal areas, which experience frequent quakes, precursory phenomena must be common. (E) contradicts the passage—paragraph 1 indicates that coastal regions confront thrusting sea floor plates.

2. The primary purpose of the passage is to

Difficulty Level: 550

Explanation:

Choice (E) encompasses the passage’s topic and scope plus the content of all four paragraphs—the importance of precursors. (A) is too narrow—the passage says little about earthquakes in inland areas. (B) mentions introductory information in paragraph 1, but it neglects the passage’s topic—methods of earthquake prediction. (C) has the same problem as (A)—it’s too narrow. Coastal regions are only part of the picture in this passage. (D) is also too narrow, and it’s inconsistent with the passage. Precursory phenomena are key to earthquake prediction.

3. The primary function of the third paragraph is to

Difficulty Level: 550

Explanation:

Paragraph 3 lists a lot of details that are useful for predicting when an earthquake will strike. That fits very nicely with (D). (A) and (B) are the sorts of answers you can fall for if your reading becomes too detail oriented. They both represent details in paragraph 3 but not the main function of the paragraph. (C)addresses details in paragraphs 1 and 2. The paragraph never suggests “that critical strain is not spread evenly along most major fault lines,” (E).

4. According to the passage, knowledge of an area’s critical strain can help seismologists

Difficulty Level: 600

Explanation:

“Strain” is mentioned in paragraph 1, but the question asks about “critical strain,” which is discussed only at the end of paragraph 3. There, you read “critical strain will indicate a time frame for an impending quake.” That fits perfectly with (A). There is nothing anywhere about calculating “the severity of an initial rupture,” (B). It’s unclear what the term seismic force means, so (C) is no good. (D) refers to an unrelated detail from the beginning of the paragraph. (E) is tempting because “crustal movement” is discussed in the context, but it is ultimately wrong because it leaves out the idea of predicting a time frame for the next earthquake.

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Re: Modern methods of predicting earthquakes recognize that quakes, far fr  [#permalink]

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14 Dec 2018, 02:36
1
Hey dude ...great passage
I just have one small doubt ...is the 3rd paragrapagh located correctly because in the question of function of 3rd para the OA says "some methods" plral...but in last para only 1 such method is given...
I think some part of the 2nd para is of the 3rd para ...to be precise the ". Crustal movements—tilting, rising, and expansion or contraction of the ground’s surface—can be read through triangulation and leveling surveys taken over the course of decades....."
The tilting isthen continued in the supossedly last para...could you please check....I could be wrong...but please check
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Re: Modern methods of predicting earthquakes recognize that quakes, far fr  [#permalink]

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14 Dec 2018, 04:52
An easy one.....by GMAT standards....

Dint calculate the time but never paused either during passage reading or question solving....

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Re: Modern methods of predicting earthquakes recognize that quakes, far fr  [#permalink]

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16 Dec 2018, 13:37
could anyone explain the 1st? "However, when the time interval between quakes is great, as in inland regions, locating active faults is only a beginning. " referring the greater time intervals in inland regions, I conclude the number of earthquake... so I went for B.
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Re: Modern methods of predicting earthquakes recognize that quakes, far fr  [#permalink]

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16 Dec 2018, 17:52
We have to differentiate between coastal and inland by referring to what is the special feature of coastal.B might have been the answer had the question just asked us to differentiate between coastal and inland.C is the correct answer.

Regards.
Re: Modern methods of predicting earthquakes recognize that quakes, far fr   [#permalink] 16 Dec 2018, 17:52