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In most earthquakes the Earth’s crust cracks

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In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 17 Jun 2015, 20:57
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In most earthquakes the Earth’s crust cracks like porcelain. Stress builds up until a fracture forms at a depth of a few kilometers and the crust slips to relieve the stress. Some earthquakes, however, take place hundreds of kilometers down in the Earth’s mantle, where high pressure makes rock so ductile that it flows instead of cracking, even under stress severe enough to deform it like putty. How can there be earthquakes at such depths?

That such deep events do occur has been accepted only since 1927, when the seismologist Kiyoo Wadati convincingly demonstrated their existence. Instead of comparing the arrival times of seismic waves at different locations, as earlier researchers had done. Wadati relied on a time difference between the arrival of primary (P) waves and the slower secondary (S) waves. Because P and S waves travel at different but fairly constant speeds, the interval between their arrivals increases in proportion to the distance from the earthquake focus, or rupture point.

For most earthquakes, Wadati discovered, the interval was quite short near the epicenter, the point on the surface where shaking is strongest. For a few events, however, the delay was long even at the epicenter. Wadati saw a similar pattern when he analyzed data on the intensity of shaking. Most earthquakes had a small area of intense shaking, which weakened rapidly with increasing distance from the epicenter, but others were characterized by a lower peak intensity, felt over a broader area. Both the P-S intervals and the intensity patterns suggested two kinds of earthquakes: the more common shallow events, in which the focus lay just under the epicenter, and deep events, with a focus several hundred kilometers down.

The question remained: how can such quakes occur, given that mantle rock at a depth of more than 50 kilometers is too ductile to store enough stress to fracture? Wadati’s work suggested that deep events occur in areas (now called Wadati-Benioff zones) where one crustal plate is forced under another and descends into the mantle. The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture.


1. The passage is primarily concerned with
(A) demonstrating why the methods of early seismologists were flawed
(B) arguing that deep events are poorly understood and deserve further study
(C) defending a revolutionary theory about the causes of earthquakes and methods of predicting them
(D) discussing evidence for the existence of deep events and the conditions that allow them to occur
(E) comparing the effects of shallow events with those of deep events


2. The author uses the comparisons to porcelain and putty (lines 2 and 8) in order to
(A) explain why the Earth’s mantle is under great pressure
(B) distinguish the earthquake’s epicenter from its focus
(C) demonstrate the conditions under which a Wadati-Benioff zone forms
(D) explain why S waves are slower than P waves
(E) illustrate why the crust will fracture but the mantle will not


3. It can be inferred from the passage that if the S waves from an earthquake arrive at a given location long after the P waves, which of the following must be true?
(A) The earthquake was a deep event.
(B) The earthquake was a shallow event.
(C) The earthquake focus was distant.
(D) The earthquake focus was nearby.
(E) The earthquake had a low peak intensity.


4. The method used by Wadati to determine the depths of earthquakes is most like which of the following?
(A) Determining the depth of a well by dropping stones into the well and timing how long they take to reach the bottom
(B) Determining the height of a mountain by measuring the shadow it casts at different times of the day
(C) Determining the distance from a thunderstorm by timing the interval between the flash of a lightning bolt and the thunder it produces
(D) Determining the distance between two points by counting the number of paces it takes to cover the distance and measuring a single pace
(E) Determining the speed at which a car is traveling by timing how long it takes to travel a known distance


5. The passage supports which of the following statements about the relationship between the epicenter and the focus of an earthquake?
(A) P waves originate at the focus and S waves originate at the epicenter.
(B) In deep events the epicenter and the focus are reversed.
(C) In shallow events the epicenter and the focus coincide.
(D) In both deep and shallow events the focus lies beneath the epicenter.
(E) The epicenter is in the crust, whereas the focus is in the mantle.


6. The passage suggests that which of the following must take place in order for any earthquake to occur?
I. Stress must build up.
II. Cool rock must descend into the mantle.
III. A fracture must occur.
(A) I only
(B) II only
(C) III only
(D) I and III only
(E) I, II, and III


7. Information presented in the passage suggests that, compared with seismic activity at the epicenter of a shallow event, seismic activity at the epicenter of a deep event is characterized by
(A) shorter P-S intervals and higher peak intensity
(B) shorter P-S intervals and lower peak intensity
(C) longer P-S intervals and similar peak intensity
(D) longer P-S intervals and higher peak intensity
(E) longer P-S intervals and lower peak intensity


8. The passage suggests which of the following about the views held by researchers before 1927?
(A) Some researchers did not believe that deep events could actually occur.
(B) Many researchers rejected the use of P-S intervals for determining the depths of earthquakes.
(C) Some researchers doubted that the mantle was too ductile to store the stress needed for an earthquake.
(D) Most researchers expected P waves to be slower than S waves.
(E) Few researchers accepted the current model of how shallow events occur.


9. The author’s explanation of how deep events occur would be most weakened if which of the following were discovered to be true?
(A) Deep events are far less common than shallow events.
(B) Deep events occur in places other than where crustal plates meet.
(C) Mantle rock is more ductile at a depth of several hundred kilometers than it is at 50 kilometers.
(D) The speeds of both P and S waves are slightly greater than previously thought.
(E) Below 650 kilometers earthquakes cease to occur.




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Re: In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 15 Apr 2016, 02:19
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This is a passage in Exam Pack 2.
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Re: In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 30 Jan 2017, 03:05
1
oasis90 wrote:
Hi Sayantanc2k,

I am having trouble disecting the information for Question 7 of the RC on the link below. I am usually pretty good with RC but I found this one very challenging.

https://gmatclub.com/forum/in-most-eart ... 00099.html

Question 7.

Regards,
Humam


Epicenter is the point on the earth surface directly above the location of seismic activity (i.e., the focus or rupture point).

If the seismic activity is shallow, then the epicenter is close to the focus, implying the P-S interval will be short. On the other hand if the activity (focus) is deep down, then the distance between the focus and the epicenter is high, implying a longer P-S interval. Thus choices A and B can be eliminated.

Now whether the peak intensity at the epicenter for a a deep activity would have similar / higher / lower peak intensity compared to a shallow activity depends on the distance of the epicenter from the focus. Because the deep activity is farther away from the epicenter than a shallow activity is, the intensity would be lower at epicenter for a deep activity.

Thus we arrive at the following combination: Longer P-S interval and lower intensity. Hence option E is correct.

(In summary, once you realise that the P-S interval at a point increases as the distance of the point from the focus increases, and the intensity at a point decreases as the distance of the point from the focus increases, then it is not diffcult to determine what would happen when the epicenter ( the point under consideration) is far away (i.e. in case of a deep activity) from the focus, compared to an epicenter nearby (i.e. in case of a shallow activity) to the focus.

Please let me know if you still have doubts.
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Re: In most earthquakes the Earth’s crust cracks  [#permalink]

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New post Updated on: 13 Nov 2017, 23:50
In most earthquakes the Earth’s crust cracks like porcelain. Stress builds up until a fracture forms at a depth of a few kilometers and the crust slips to relieve the stress. Some earthquakes, however, take place hundreds of kilometers down in the Earth’s mantle, where high pressure makes rock so ductile that it flows instead of cracking, even under stress severe enough to deform it like putty. How can there be earthquakes at such depths?

That such deep events do occur has been accepted only since 1927, when the seismologist Kiyoo Wadati convincingly demonstrated their existence. Instead of comparing the arrival times of seismic waves at different locations, as earlier researchers had done. Wadati relied on a time difference between the arrival of primary (P) waves and the slower secondary (S) waves. Because P and S waves travel at different but fairly constant speeds, the interval between their arrivals increases in proportion to the distance from the earthquake focus, or rupture point.

For most earthquakes, Wadati discovered, the interval was quite short near the epicenter, the point on the surface where shaking is strongest. For a few events, however, the delay was long even at the epicenter. Wadati saw a similar pattern when he analyzed data on the intensity of shaking. Most earthquakes had a small area of intense shaking, which weakened rapidly with increasing distance from the epicenter, but others were characterized by a lower peak intensity, felt over a broader area. Both the P-S intervals and the intensity patterns suggested two kinds of earthquakes: the more common shallow events, in which the focus lay just under the epicenter, and deep events, with a focus several hundred kilometers down.

The question remained: how can such quakes occur, given that mantle rock at a depth of more than 50 kilometers is too ductile to store enough stress to fracture? Wadati’s work suggested that deep events occur in areas (now called Wadati-Benioff zones) where one crustal plate is forced under another and descends into the mantle. The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture.

The author’s explanation of how deep events occur would be most weakened if which of the following were discovered to be true?
(A) Deep events are far less common than shallow events.
(B) Deep events occur in places other than where crustal plates meet.
(C) Mantle rock is more ductile at a depth of several hundred kilometers than it is at 50 kilometers.
(D) The speeds of both P and S waves are slightly greater than previously thought.
(E) Below 650 kilometers earthquakes cease to occur.

The method used by Wadati to determine the depths of earthquakes is most like which of the following?
(A) Determining the depth of a well by dropping stones into the well and timing how long they take to reach the bottom
(B) Determining the height of a mountain by measuring the shadow it casts at different times of the day
(C) Determining the distance from a thunderstorm by timing the interval between the flash of a lightning bolt and the thunder it produces
(D) Determining the distance between two points by counting the number of paces it takes to cover the distance and measuring a single pace
(E) Determining the speed at which a car is traveling by timing how long it takes to travel a known distance

Information presented in the passage suggests that, compared with seismic activity at the epicenter of a shallow event, seismic activity at the epicenter of a deep event is characterized by
(A) shorter P-S intervals and higher peak intensity
(B) shorter P-S intervals and lower peak intensity
(C) longer P-S intervals and similar peak intensity
(D) longer P-S intervals and higher peak intensity
(E) longer P-S intervals and lower peak intensity

The passage supports which of the following statements about the relationship between the epicenter and the focus of an earthquake?
(A) P waves originate at the focus and S waves originate at the epicenter.
(B) In deep events the epicenter and the focus are reversed.
(C) In shallow events the epicenter and the focus coincide.
(D) In both deep and shallow events the focus lies beneath the epicenter.
(E) The epicenter is in the crust, whereas the focus is in the mantle.
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Originally posted by saswata4s on 13 Nov 2017, 21:15.
Last edited by Vyshak on 13 Nov 2017, 23:50, edited 1 time in total.
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Re: In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 18 Nov 2017, 16:01
JarvisR wrote:
In most earthquakes the Earth’s crust cracks like porcelain. Stress builds up until a fracture forms at a depth of a few kilometers and the crust slips to relieve the stress. Some earthquakes, however, take place hundreds of kilometers down in the Earth’s mantle, where high pressure makes rock so ductile that it flows instead of cracking, even under stress severe enough to deform it like putty. How can there be earthquakes at such depths?
That such deep events do occur has been accepted only since 1927, when the seismologist Kiyoo Wadati convincingly demonstrated their existence. Instead of comparing the arrival times of seismic waves at different locations, as earlier researchers had done. Wadati relied on a time difference between the arrival of primary (P) waves and the slower secondary (S) waves. Because P and S waves travel at different but fairly constant speeds, the interval between their arrivals increases in proportion to the distance from the earthquake focus, or rupture point.
For most earthquakes, Wadati discovered, the interval was quite short near the epicenter, the point on the surface where shaking is strongest. For a few events, however, the delay was long even at the epicenter. Wadati saw a similar pattern when he analyzed data on the intensity of shaking. Most earthquakes had a small area of intense shaking, which weakened rapidly with increasing distance from the epicenter, but others were characterized by a lower peak intensity, felt over a broader area. Both the P-S intervals and the intensity patterns suggested two kinds of earthquakes: the more common shallow events, in which the focus lay just under the epicenter, and deep events, with a focus several hundred kilometers down.
The question remained: how can such quakes occur, given that mantle rock at a depth of more than 50 kilometers is too ductile to store enough stress to fracture? Wadati’s work suggested that deep events occur in areas (now called Wadati-Benioff zones) where one crustal plate is forced under another and descends into the mantle. The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture.


1. The passage is primarily concerned with
(A) demonstrating why the methods of early seismologists were flawed
(B) arguing that deep events are poorly understood and deserve further study
(C) defending a revolutionary theory about the causes of earthquakes and methods of predicting them
(D) discussing evidence for the existence of deep events and the conditions that allow them to occur
(E) comparing the effects of shallow events with those of deep events


2. The author uses the comparisons to porcelain and putty (lines 2 and 8) in order to
(A) explain why the Earth’s mantle is under great pressure
(B) distinguish the earthquake’s epicenter from its focus
(C) demonstrate the conditions under which a Wadati-Benioff zone forms
(D) explain why S waves are slower than P waves
(E) illustrate why the crust will fracture but the mantle will not


3. It can be inferred from the passage that if the S waves from an earthquake arrive at a given location long after the P waves, which of the following must be true?
(A) The earthquake was a deep event.
(B) The earthquake was a shallow event.
(C) The earthquake focus was distant.
(D) The earthquake focus was nearby.
(E) The earthquake had a low peak intensity.


4. The method used by Wadati to determine the depths of earthquakes is most like which of the following?
(A) Determining the depth of a well by dropping stones into the well and timing how long they take to reach the bottom
(B) Determining the height of a mountain by measuring the shadow it casts at different times of the day
(C) Determining the distance from a thunderstorm by timing the interval between the flash of a lightning bolt and the thunder it produces
(D) Determining the distance between two points by counting the number of paces it takes to cover the distance and measuring a single pace
(E) Determining the speed at which a car is traveling by timing how long it takes to travel a known distance


5. The passage supports which of the following statements about the relationship between the epicenter and the focus of an earthquake?
(A) P waves originate at the focus and S waves originate at the epicenter.
(B) In deep events the epicenter and the focus are reversed.
(C) In shallow events the epicenter and the focus coincide.
(D) In both deep and shallow events the focus lies beneath the epicenter.
(E) The epicenter is in the crust, whereas the focus is in the mantle.


6. The passage suggests that which of the following must take place in order for any earthquake to occur?
I. Stress must build up.
II. Cool rock must descend into the mantle.
III. A fracture must occur.
(A) I only
(B) II only
(C) III only
(D) I and III only
(E) I, II, and III


7. Information presented in the passage suggests that, compared with seismic activity at the epicenter of a shallow event, seismic activity at the epicenter of a deep event is characterized by
(A) shorter P-S intervals and higher peak intensity
(B) shorter P-S intervals and lower peak intensity
(C) longer P-S intervals and similar peak intensity
(D) longer P-S intervals and higher peak intensity
(E) longer P-S intervals and lower peak intensity


8. The passage suggests which of the following about the views held by researchers before 1927?
(A) Some researchers did not believe that deep events could actually occur.
(B) Many researchers rejected the use of P-S intervals for determining the depths of earthquakes.
(C) Some researchers doubted that the mantle was too ductile to store the stress needed for an earthquake.
(D) Most researchers expected P waves to be slower than S waves.
(E) Few researchers accepted the current model of how shallow events occur.


9. The author’s explanation of how deep events occur would be most weakened if which of the following were discovered to be true?
(A) Deep events are far less common than shallow events.
(B) Deep events occur in places other than where crustal plates meet.
(C) Mantle rock is more ductile at a depth of several hundred kilometers than it is at 50 kilometers.
(D) The speeds of both P and S waves are slightly greater than previously thought.
(E) Below 650 kilometers earthquakes cease to occur.




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Hi sayantanc2k,

Can you please help with question 1 and 9 ?
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Re: In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 10 Dec 2017, 09:02
Poorvasha wrote:
Hi sayantanc2k,

Can you please help with question 1 and 9 ?


Hi Poorvasha,

9. The author’s explanation of how deep events occur would be most weakened if which of the following were discovered to be true?
The question remained: how can such quakes occur, given that mantle rock at a depth of more than 50 kilometers is too ductile to store enough stress to fracture? Wadati’s work suggested that deep events occur in areas (now called Wadati-Benioff zones) where one crustal plate is forced under another and descends into the mantle. The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture.

(A) Deep events are far less common than shallow events. -- Incorrect -- frequency is irrelevant as to how deep events occur
(B) Deep events occur in places other than where crustal plates meet. - Correct -- If this is true , then the explanation in highlighted part will be weakened .
(C) Mantle rock is more ductile at a depth of several hundred kilometers than it is at 50 kilometers - Incorrect
(D) The speeds of both P and S waves are slightly greater than previously thought. -- Incorrect -- actual speeds do not matter
(E) Below 650 kilometers earthquakes cease to occur. -- Incorrect -- there is no mentioned depth after which quakes ceases to occur



AjiteshArun , mikemcgarry ,daagh ,egmat , GMATNinja , sayantanc2k , RonPurewal , other experts -- can you please help with Question 1(primary purpose) ?
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Re: In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 11 Dec 2017, 00:41
Poorvasha wrote:
Hi sayantanc2k,

Can you please help with question 1 and 9 ?
Skywalker18 wrote:
AjiteshArun , mikemcgarry ,daagh ,egmat , GMATNinja , sayantanc2k , RonPurewal , other experts -- can you please help with Question 1(primary purpose) ?
The OP says that this is a GMATPrep question, but I don't like the OA (C). I'd much rather go for option D.

In the current OA, C, we have
JarvisR wrote:
defending a revolutionary theory about the causes of earthquakes and methods of predicting them
I can understand the revolutionary (for the time) and possibly the theory bit (for Wadati’s work suggested that deep events occur in areas... where one crustal plate is forced under another and descends into the mantle), but there is no defense (defending), and no mention whatsoever of anything supporting "predicting them".

Option D says
JarvisR wrote:
discussing evidence for the existence of deep events and the conditions that allow them to occur
This option looks much better. Here we have evidence, not a theory. Evidence fits much better with Kiyoo Wadati convincingly demonstrated their existence. The whole thing, evidence for deep events, is well supported by that such deep events do occur has been accepted only since 1927, when the seismologist Kiyoo Wadati convincingly demonstrated their existence. The rest of it (the conditions that allow them to occur) also seems to work with how the passage discusses how these earthquakes are possible even though "rock is so ductile".
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Re: In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 11 Dec 2017, 23:27
Can anyone please give explanation for question 1? Why is the OA C ? Time consuming passage and relatively tough.
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In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 10 Jun 2018, 11:24
Hello GMATNinja , Skywalker18 , AjiteshArun

Can you explain the below question?
Quote:
The passage supports which of the following statements about the relationship between the epicenter and the focus of an earthquake?
(A) P waves originate at the focus and S waves originate at the epicenter.
(B) In deep events the epicenter and the focus are reversed.
(C) In shallow events the epicenter and the focus coincide.
(D) In both deep and shallow events the focus lies beneath the epicenter.
(E) The epicenter is in the crust, whereas the focus is in the mantle.

According to me , the answer should be C but the OA is D

the passage mentions the below lines
Quote:
the more common shallow events, in which the focus lay just under the epicenter, and deep events, with a focus several hundred kilometers down.


In shallow events --> focus and epicenter are very close
in deep events --> the focus and epicenter are very far

Hence i selected C. Kindly let me know where i am going wrong
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Re: In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 10 Jun 2018, 12:49
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Quote:
the more common shallow events, in which the focus lay just under the epicenter, and deep events, with a focus several hundred kilometers down.


(C) In shallow events, the epicenter and the focus coincide.

They overlap, perfectly. Nowhere in the passage is mentioned this kind of overlapping

(D) In both deep and shallow events, the focus lies beneath the epicenter.

The green part of the sentence implies that in both kind of events (shallow and deep) the focus and the epicenter are still one on top of the other. They could be a little shifted as circles (if we wanna imagine this way).

Hope this helps
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Re: In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 11 Jun 2018, 20:06
carcass why is the answer to question 1 (C) defending a revolutionary theory about the causes of earthquakes and methods of predicting them
and not (D) discussing evidence for the existence of deep events and the conditions that allow them to occur

Nowhere does the author discuss anything about predicting earthquakes. D is a better fit? Please clarify.
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Re: In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 12 Jun 2018, 00:31
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Quote:
For most earthquakes, Wadati discovered, the interval was quite short near the epicenter, the point on the surface where shaking is strongest. For a few events, however, the delay was long even at the epicenter.Wadati saw a similar pattern when he analyzed data on the intensity of shaking.


Quote:
The question remained: how can such quakes occur, given that mantle rock at a depth of more than 50 kilometers is too ductile to store enough stress to fracture? Wadati’s work suggested that deep events occur in areas (now called Wadati-Benioff zones) where one crustal plate is forced under another and descends into the mantle.


The red part is a new approach related to his discoveries.

Hope this helps.

Ask for further assistance

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Re: In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 21 Jun 2018, 19:13
Hello,

Is this a 700+ level passage?

Thanks.
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Re: In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 24 Jun 2018, 00:40
Hi carcass,

Could you please explain the OA for 3rd que. I selected 'c' but OA is 'A'. Please help me.
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Re: In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 24 Jun 2018, 01:41
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Fact 1

Quote:
Wadati relied on a time difference between the arrival of primary (P) waves and the slower secondary (S) waves. Because P and S waves travel at different but fairly constant speeds, the interval between their arrivals increases in proportion to the distance from the earthquake focus, or rupture point.


Fact 2


Quote:
Both the P-S intervals and the intensity patterns suggested two kinds of earthquakes: the more common shallow events, in which the focus lay just under the epicenter, and deep events, with a focus several hundred kilometers down.


C says that the waves are distant from focus, which is not true. What is true is that their arrivals difference increases in proportion to the distance from the earthquake focus.

If the EQ is shallow then the difference could be really tiny if no difference at all, if the EQ is deep then the difference is remarkable.


Hope this helps
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Re: In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 24 Jun 2018, 02:31
Hi carcass,

Quote:
C says that the waves are distant from focus, which is not true. What is true is that their arrivals difference increases in proportion to the distance from the earthquake focus.

If the EQ is shallow then the difference could be really tiny if no difference at all, if the EQ is deep then the difference is remarkable.


Not sure where C told that waves are distant from focus, it is just saying that the 'focus is distant' which is supposed to be true in case of deep events. The same is mentioned in following:
Quote:
two kinds of earthquakes: the more common shallow events, in which the focus lay just under the epicenter, and deep events, with a focus several hundred kilometers down.

As per my understanding option A as well as C are saying one and the same thing, if deep event then focus is distant and if focus is distant thet means deep event. I am confused in this.
PLease correct me if my understanding is wrong or if i missed out any point.
TIA :)
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Re: In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 24 Jun 2018, 02:53
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3. It can be inferred from the passage that if the S waves from an earthquake arrive at a given location long after the P waves, which of the following must be true?

(A) The earthquake was a deep event.
(B) The earthquake was a shallow event.
(C) The earthquake focus was distant.
(D) The earthquake focus was nearby.
(E) The earthquake had a low peak intensity.

(A) The earthquake was a deep event.

Because P and S waves travel at different but fairly constant speeds, the interval between their arrivals increases in proportion to the distance from the earthquake focus, or rupture point.

This is because the EQ is deep in the crust.

(C) The earthquake focus was distant.

This actually means NOT deep in terms of profundity but in terms of distance on a flat plan or distance. I.E. the focus happens in Tokio and the arrival point of the waves is in Osaka. Point A to B not as point A over B.

Hope this helps
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In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 24 Jun 2018, 04:35
Oh got your point now.
I did not notice that. It was mentioned just in the same para:
Quote:
Instead of comparing the arrival times of seismic waves at different locations, as earlier researchers had done.

Thanks a lot carcass
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Re: In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 02 Jul 2018, 04:48
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For Q 6 the correct answer, option D, suggests that both stress and fracture must take place in order for ANY earthquake to occur. But the following lines suggest that in case of the less common earthquakes fracture doesent occur. So If my understanding is correct, the answer should be A (only Stress).

"where high pressure makes rock so ductile that it flows instead of cracking" &
"how can such quakes occur, given that mantle rock at a depth of more than 50 kilometers is too ductile to store enough stress to fracture?"
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Re: In most earthquakes the Earth’s crust cracks  [#permalink]

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New post 12 Jul 2018, 21:59
Hi GMATNinja,

Can you please help in explaining why is the OA C for this one.I feel like D is more appropriate here.

Thanks!

Quote:

1. The passage is primarily concerned with
(A) demonstrating why the methods of early seismologists were flawed
(B) arguing that deep events are poorly understood and deserve further study
(C) defending a revolutionary theory about the causes of earthquakes and methods of predicting them
(D) discussing evidence for the existence of deep events and the conditions that allow them to occur
(E) comparing the effects of shallow events with those of deep events




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