Summer is Coming! Join the Game of Timers Competition to Win Epic Prizes. Registration is Open. Game starts Mon July 1st.

 It is currently 16 Jul 2019, 11:32

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# In most earthquakes the Earth’s crust cracks

Author Message
TAGS:

### Hide Tags

Senior Manager
Joined: 05 Nov 2012
Posts: 433
Concentration: Technology, Other
In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

17 Jun 2015, 20:57
2
16
Question 1
00:00

based on 541 sessions

33% (02:48) correct 67% (02:54) wrong

### HideShow timer Statistics

Question 2
00:00

based on 508 sessions

80% (00:59) correct 20% (01:24) wrong

### HideShow timer Statistics

Question 3
00:00

based on 524 sessions

40% (01:10) correct 60% (01:17) wrong

### HideShow timer Statistics

Question 4
00:00

based on 497 sessions

77% (01:04) correct 23% (01:11) wrong

### HideShow timer Statistics

Question 5
00:00

based on 493 sessions

57% (01:22) correct 43% (01:33) wrong

### HideShow timer Statistics

Question 6
00:00

based on 460 sessions

48% (00:48) correct 52% (00:57) wrong

### HideShow timer Statistics

Question 7
00:00

based on 445 sessions

67% (01:11) correct 33% (01:27) wrong

### HideShow timer Statistics

Question 8
00:00

based on 405 sessions

79% (00:51) correct 21% (01:09) wrong

### HideShow timer Statistics

Question 9
00:00

based on 428 sessions

59% (01:13) correct 41% (01:07) wrong

### HideShow timer Statistics

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.

An initiative to get official RCs in proper format.
Source:GMATPREP COMPREHENSIVE RC
Intern
Joined: 19 Jan 2016
Posts: 45
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

15 Apr 2016, 02:19
1
This is a passage in Exam Pack 2.
_________________
---------------------------------------------------------
Please kudos me if this helps. Thank you.
Retired Moderator
Joined: 14 Dec 2013
Posts: 2870
Location: Germany
Schools: German MBA
GMAT 1: 780 Q50 V47
WE: Corporate Finance (Pharmaceuticals and Biotech)
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

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.
Current Student
Joined: 28 May 2014
Posts: 518
GMAT 1: 730 Q49 V41
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

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.
_________________

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.
Topic Merged
Manager
Joined: 11 Jun 2017
Posts: 68
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

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.

An initiative to get official RCs in proper format.
Source:GMATPREP COMPREHENSIVE RC

Hi sayantanc2k,

Verbal Forum Moderator
Status: Greatness begins beyond your comfort zone
Joined: 08 Dec 2013
Posts: 2351
Location: India
Concentration: General Management, Strategy
Schools: Kelley '20, ISB '19
GPA: 3.2
WE: Information Technology (Consulting)
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

10 Dec 2017, 09:02
1
Poorvasha wrote:
Hi sayantanc2k,

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) ?
_________________
When everything seems to be going against you, remember that the airplane takes off against the wind, not with it. - Henry Ford
The Moment You Think About Giving Up, Think Of The Reason Why You Held On So Long
+1 Kudos if you find this post helpful
CEO
Joined: 15 Jul 2015
Posts: 2844
Location: India
GMAT 1: 780 Q50 V51
GRE 1: Q170 V169
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

11 Dec 2017, 00:41
1
Poorvasha wrote:
Hi sayantanc2k,

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".
_________________
Manager
Joined: 29 Jan 2015
Posts: 74
Location: India
Concentration: Marketing, Entrepreneurship
GPA: 3.7
WE: Information Technology (Internet and New Media)
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

11 Dec 2017, 23:27
Can anyone please give explanation for question 1? Why is the OA C ? Time consuming passage and relatively tough.
BSchool Forum Moderator
Joined: 05 Jul 2017
Posts: 512
Location: India
GMAT 1: 700 Q49 V36
GPA: 4
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

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
_________________
Board of Directors
Joined: 01 Sep 2010
Posts: 3421
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

10 Jun 2018, 12:49
3
Top Contributor
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
_________________
Manager
Joined: 20 Apr 2018
Posts: 173
Concentration: Technology, Nonprofit
WE: Analyst (Non-Profit and Government)
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

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.
Board of Directors
Joined: 01 Sep 2010
Posts: 3421
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

12 Jun 2018, 00:31
1
Top Contributor
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.

Regards
_________________
Intern
Joined: 08 Dec 2016
Posts: 16
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

21 Jun 2018, 19:13
Hello,

Is this a 700+ level passage?

Thanks.
Manager
Joined: 10 Sep 2015
Posts: 74
Location: India
Concentration: Finance, Human Resources
GMAT 1: 640 Q47 V31
GMAT 2: 660 Q47 V35
GMAT 3: 700 Q49 V36
GPA: 4
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

24 Jun 2018, 00:40
Hi carcass,

Board of Directors
Joined: 01 Sep 2010
Posts: 3421
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

24 Jun 2018, 01:41
Top Contributor
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
_________________
Manager
Joined: 10 Sep 2015
Posts: 74
Location: India
Concentration: Finance, Human Resources
GMAT 1: 640 Q47 V31
GMAT 2: 660 Q47 V35
GMAT 3: 700 Q49 V36
GPA: 4
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

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
Board of Directors
Joined: 01 Sep 2010
Posts: 3421
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

24 Jun 2018, 02:53
3
Top Contributor
1
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
_________________
Manager
Joined: 10 Sep 2015
Posts: 74
Location: India
Concentration: Finance, Human Resources
GMAT 1: 640 Q47 V31
GMAT 2: 660 Q47 V35
GMAT 3: 700 Q49 V36
GPA: 4
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

24 Jun 2018, 04:35
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
Cheers
Intern
Joined: 27 Mar 2018
Posts: 5
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

02 Jul 2018, 04:48
1
1
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?"
CR Forum Moderator
Joined: 25 Apr 2018
Posts: 607
Re: In most earthquakes the Earth’s crust cracks  [#permalink]

### Show Tags

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

_________________

Project CR Butler - 2 CR's everyday
Re: In most earthquakes the Earth’s crust cracks   [#permalink] 12 Jul 2018, 21:59

Go to page    1   2    Next  [ 38 posts ]

Display posts from previous: Sort by