In most earthquakes the Earth’s crust cracks like porcelain. Stress bu

VeritasKarishma carcass AjiteshArun
Can you please explain the Q8 I was confused between A and B
I choose OA as B because Wadii used P and S waves and the researcher before that didn't.
Though A is true as mentioned in the first line of the paragraph 2

The passage says that other people accepted the existence of deep events "only since 1927". It doesn't say (for sure) that they rejected the use of P-S intervals to determine the depths of earthquakes. In the sentence that you are probably looking at:

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.

We know only that they used method X and that Wadati used method Y. This is not enough to say that they rejected method Y. Maybe they just didn't know about it. Maybe Wadati was the first to come up with the idea to apply P-S intervals to this problem. Maybe. The point is that because we don't know any of this for sure, and because we know that what option A says is true as per the passage, we should pick option A over B.

Wonderful topic, very informational and fantastic for everyone. Most seismic tremors had a little zone of extreme shaking, which debilitated quickly with expanding separation from the epicenter, however, others were portrayed by lower top power, felt over a more extensive territory.

Greetings saumyakansal2196,

happy to help.

4. The method used by Wadati to determine the depths of earthquakes is most like which of the following?

Towards the end of para 2, the author harps about the method used by the seismologist.

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.

Since this question is based more on the understanding, so let's delve into the correct option.

- Determining the distance from a thunderstorm by timing the interval between the flash of a lightning bolt and the thunder it produces

On the money!

I am not sure if knowing the fact that light travels faster than sound is necessary to answer this question, but it did help me.

We know, when a thunderstorm occurs, the sound of thunder always comes after a second or two. Now, what the seismologist does is very identical.

He simply measures the time interval between the light (P wave) and the sound wave ( S wave) by the time it reaches us (rupture or focus point)

Also, if this helps, Sound and light do travel at different but constant speeds, making this option an ideal choice.



Let me know if I missed something, would be happy to expand.

Hi VeritasKarishma , GMATNinja

I have doubts regarding the question#2 ...

"Porcelain" has been mentioned here.
"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."
These sentences above describe "shallow event/earthquake".
"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?"
These sentences describe "deep event/earthquake".
" Wadati-Benioff zone" s are where deep events occur.
So I am leaning towards option C.
I understand "Porcelain" has been compared with "crust".
And "mantle" has been compared with "putty".
Still I don't find option E convincing.
Can you please provide some logic in support of option E ?

The author uses porcelain and putty to characterize different parts of the earth. The crust "cracks like porcelain," while the mantle (located beneath the crust) "flows instead of cracking even under stress severe enough to deform it like putty."


The characterizations described above hold true generally -- the crust cracks like porcelain, while the mantle flows like putty. Wadati-Beniof zones, on the other hand, only emerge in specific scenarios (when "one crustal plate is forced under another and descends into the mantle"). If the porcelain/putty analogies "demonstrate[d] the conditions under which a Wadati-Benioff zone form," then these zones would be everywhere, because the analogies describe characteristics of the entire crust and the entire mantle! This is clearly not the case, as earthquakes with an epicenter deep below the surface are relatively uncommon and only occur in specific areas. For this reason, (C) is out.


The author compares the crust and the mantle to well-known substances (porcelain/putty) in order to demonstrate their characteristics to the reader in a familiar way. The specific difference that the author points out is how each piece of the earth reacts to stress -- the crust fractures, while the mantle does not. (E) is the correct answer for question #2.

I hope that helps!

HELP HELP HELP
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.

No one could explain it properly
PLease could you?
A vs C

VeritasKarishma

GMATNinja GMATNinja2

NOTE: The OA for question #3 has been changed from (A) to (C).

From the second paragraph, we know that primary (P) waves and secondary (S) waves both move outward from the focus of an earthquake, traveling at different constant rates. Watadi studied the interval of time between the two type of waves reaching a certain point.

Let's say an earthquake has an epicenter in Paris (sorry, Paris). If you measured the time interval between (P) and (S) waves at a point very close to Paris -- maybe just outside the city -- you would expect the time gap to be very small, because the faster (P) wave hasn't had time to get too far ahead of the slower (S) wave.

What if you measured that time interval at a point far away from Paris -- maybe in Berlin? Now you would expect the time gap to be larger, because the (P) wave has raced ahead of the (S) wave with each passing kilometer.

For most earthquakes, this is exactly what Watadi found!

In a few cases, however, there was a long interval between P and S waves even near the epicenter of the earthquake. What caused this larger gap? For these particular events, the earthquake actually began several hundred kilometers below the surface of the earth (or, the "focus" of the earthquake was several hundred kilometers below the surface). This explains the larger time gap between P and S waves because they still had to cover long distances, giving the P wave time to get well out in front of the S wave. To continue with our example, instead of traveling from Paris to Berlin, the waves traveled UP from deep within the mantle to the surface of the earth.

So if S waves arrive long after P waves, we know that the focus of the earthquake is far away from the point at which the measurement is taken -- whether that distance is horizontal (across the surface of the earth), or vertical (up from within the earth). This fits with answer choice (C), "the earthquake focus was distant."

I hope that helps!

But if the earthquake is a deep event,then the time interval between P and S should be large.Isn't that so?Then why is option A wrong?

If the earthquake is a deep event, then yes, the time interval will always be large. However, that is different than saying that if the time interval is large, the earthquake MUST have been a deep event!

The question asks about a large gap between P and S waves when measured from "a given location." The problem is that we have no idea where that location is in relation to the epicenter of the earthquake. If the location is very close to the epicenter and the gap between P and S waves is large, we can infer that the earthquake was a deep event. However, if the location is far away from the epicenter (e.g., Paris to Berlin), then a large gap could just be the expected result from a regular, more shallow earthquake.

Because we don't how close the "given location" is to the epicenter of the earthquake, we cannot infer that a gap between P and S waves at that point means that the earthquake was a deep event. Eliminate (A).

I hope that helps!

Passage map - overall the passage seeks to describe an explanation and clarification of deep-earth occuring Earth Quakes
p1: Raise a question that the passage seeks to explain
P2: To state the discovery by Wadati in resolution of the question
P3: To explain this discovery
p4: to explain how W's discovery can be supported by - the location of where EQs occur

Q1
A is incorrect - no other methods are described in detail to constitute this.
B is incorrect - he doesnt argue that they are poorly understood, he states that they weren't identified at all
C is incorrect - no revolutionary theory exists. We are simply told of a pre-existing theory.
D is correct - the whole passage is essentially discussing W's theory in an attempt to answer the question raised by the author in P1 "how can.."
E is incorrect - this isn't the main point. Comparisons are made to explain the existence, not as the main point.

Q2
Info contained in first para.
A is incorrect - a comparison to "porcelain" and "putty" is made to illustrate fracturability, not to indicate pressure. The pressure causes the ductility - less ductile = porcelain, more ductile = putty
B is incorrect - this is simply false.
C no - porcelain type earthquakes were already known to researchers before W came along
D absolutely not - we are told they have the similar speeds anyway.
E is correct - putty and porcelain are vivid images that allow the reader to better visualise the susceptibility of the earth to fractures at the crust and not at the mantle.

Q3
P and S waves have similar speeds. Think about this mathematically. So if secondary waves arrive long after primary waves and they are travelling at roughly the same speeds then obviously the distance from the location of the earthquake to the focus must be further.
C is the only thing that can be substantiated.

Q4
The method used by W is discussed in P2 in "W relied on a time difference between P and S waves."
This is most analogous to C - the determining the distance from a thunderstorm by timing the interval..
A is incorrect - Dropping a stone in a well would only produce 1 measurable event. The sound made when it hits the bottom.
B is incorrect - again this is only one measurable event and we have nothing to go by to determine the speed of the movement of the sun.
D is incorrect - there is really only one event or one course of action to determine the movement.
E is incorrect - the speed is controlled. We need two unestimatable events.

Q6
The relationship is largely talked about in P3
A- this is false. By nature, both originate at the focus.
B - false. In p3 we are told that the focus is "several hundred km " below the epicentre
C - no. We are told that the focus is beneath the epicentre "just lay under.."
D - Correct. P3 tells us that in both occurrences the focus is beneath the epicentre, but the distance between the focus and epicentre is further for deep waves
E - no. This cannot be supported. Ref p1

Q6
iii - this is the easiest to support. P1 supports this for surface fractures p4 supports this for other fractures
ii - this is really only discussed in relation to deep fractures. Therefore incorrect.
i. Supported - this is discussed in p1
Therefore D

Q7
Again this can be answered by referring to P3.
W's theory is premised on the fact deep fractures have longer distances between P and S waves- so eliminate (A) and (B)
Next, we are told that "most earthquakes had a small area of intense shaking, which weakened rapidly with increasing distance from the epicentre". Thus, this info is sufficient for us to deduce that the intensity of shaking (or seismic activity) is lower for deep fractures.

Answer choice E

Q8
Quite blatantly answered in sentence 1 of P2 - "that such deep events do occur has only been accepted since 1927" thus, logically, it was not believed that deep events could occur prior to 1927.

Answer choice (A)

Q9
The explanation given by W is spread throughout P2-P3 and some in P4.
A is incorrect - nowhere in the passage are we told about the impact of earthquake influence
B W's theory, per p4, is premised on the fact that "deep events occur in areas where one crustal plate is forced under another..", so if it could be proven that deep events occur in other places other than where crustal plates meet then we would need to explain this with further research and thus it would question the grounds upon which W's theory is supported.
C is incorrect - we are indicated that even at 50km the mantle is too ductile, so logically deeper = more ductile. What's unclear is how this would weaken how the events occur.
D is incorrect - even if they are slightly greater we are still measuring using the same comparative speed. HOWEVER, if this answer choice said "Secondary waves are found to move at irregular speeds" then W's theory is debunked as it removes one significant control.
E is incorrect as we could logically still theory of how deep events occur.

When I attempted this RC, I chose the answer as D. Even I consider that to be the more correct answer. There is nothing revolutionary about the theory. Did you get the explanation on why C is the OA. I went through the entire thread and nobody has explained this question.

(D) is the answer to Question #1, and the OA has been updated accordingly.

I hope that clears it up!

I took 20 mins on this question and got 7/9 right!

Could someone tell me what's the max amount of time I should take to solve a similar passage?

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.

Para2, last sentence
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.


Para3, last sentence
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.


However, someone in the forum also raise doubts the same as me
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.
And the respond to this doubt still confuse me a lot
(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
……..I just don’t know what this explanation means


My way of thinking is that….
In GMAT, we had to choose the option directly related to the vignette, also, about why option (A) is wrong, we can see from the last sentence of Para3, it is that the hypothesis ‘deep event’ will be valid only on the condition that ‘P-S intervals and the intensity patterns’ these two factors establish
is it true or not??

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.---correct
(E) The epicenter is in the crust, whereas the focus is in the mantle.


I’m really confused about option(E)
About option(E), maybe we can infer
from the first sentence of para3

For most earthquakes, Wadati discovered, the interval was quite short near the epicenter, the point on the surface where shaking is strongest.

Also from first & second sentence of para1

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,
-we can infer that ‘’The epicenter is in the crust’’

However, in para1, we know that focus(The focus of an earthquake is the point where the rocks start to fracture. It is the origin of the earthquake.)can be occur both in crust or mantle, if it occur in crust, it’s not far away from epicenter, maybe just a very little distance below epicenter????

carcass Can you help with the following question?

The method used by Wadati to determine the depths of earthquakes is most like which of the following?