#21 - Nuclear reactors are sometimes built in "geologically quiet" regions,

[jiyounglee]

Hello powerscore,

I do not understand why E cannot be a correct answer.
Applying assumption negation technique, E could be rephrased as "Earthquake faults in geologically quiet regions do not produce earthquakes at least once in 100,000 years"

Therefore, earthquake may not happen at all in 100,000 years.

In this case, those (nuclear reactor site) that are least likely to be struck by an earthquake are ones located near a fault that earthquake may not happen at all.

Is it because the answer choice does not include "nuclear reactor site"?

Thank you for your help,
Young

[Jonathan Evans]

Hi, Young,

Good question. Let's recap the specifics of this argument:

Premise:

(1) In a geologically quiet region, no minor fault produces an earthquake more than once every 100,000 years.

Conclusion:

In a geologically quiet region, the sites that are least likely to be struck by an earthquake are close to a fault that has recently produced an earthquake.

Discussion:

It follows that such a fault will not produce another earthquake within 100,000 years. We have to determine whether it is possible that there be anywhere less likely to produce an earthquake within a geologically quiet region. The key is whether the reactor need be close to any fault at all.

The author assumes that the only potential sites for nuclear reactors in geologically quiet regions are close to faults. Were this not the case, his conclusion would not make sense because he would have failed to consider that sites within geologically quiet regions distant from any fault might be even less likely to experience a quake. Hence, answer choice (C) is credited.

Now let's discuss answer choice (E), and as you suggest, let's employ the Assumption Negation Test. If it were not true that "Earthquake faults in geologically quiet regions produce earthquakes at least once in 100,000 years," could it still be true that the places least likely to be struck by an earthquake are those close to a fault that has recently produced an earthquake?

Yes, this could still be true because the premises still holds that such a location could not be expected to experience another quake within 100,000 years, even if (per the above negation) such a fault may not produce any earthquake at all within the next 100,000 years.

I hope this explanation helps to clear up this problem for you.

[jiyounglee]

Yes! It is more clear now!
Thank you.

[bluebell]

I'm still a bit confused as the stimulus states that geologically quiet regions contain only minor faults which led me to infer that the minor faults are already present in all geologically quiet regions. Please explain.

[KelseyWoods]

Hi bluebell!

It would help if you could be a little more specific about what you find confusing--are you unsure why (C) is an assumption necessary for the argument? Are you unsure why another answer choice is incorrect? Are you unsure how to approach an Assumption question? I'll try to answer based on what I think you might be getting at--but let us know if your confusion lies somewhere else!

We know from the stimulus that geologically quiet regions only have minor faults but we don't know how widespread minor faults are within those regions. Basically, geologically quiet regions are regions that don't have major faults. But that doesn't necessarily mean that they have to have a whole bunch of minor faults. So just because a nuclear reactor site is in a geologically quiet region, that doesn't necessarily mean that it is near a minor fault. Thus, answer choice (C) has not been directly stated in the stimulus.

Necessary Assumptions are basically things that must be true for the argument to stand. Sometimes these assumptions feel like they have already been stated. But if you look at the precise wording of the stimulus, they haven't been directly stated, only assumed by the author.

Hope this helps!

Best,
Kelsey

[bluebell]

Hi Kelsey,
I was just confused because it seemed to me that answer choice C was restating a premise in the argument because we are already told that geologically quiet regions contain minor faults which would mean that all geologically quiet regions contain minor faults. Am I correct in understanding it that way and is C correct because of the word "near"? All geologically quiet regions could have minor faults, however, the nuclear reactors don't have to be built near them.

[KelseyWoods]

Exactly, bluebell. Geologically quiet regions may have minor faults, but just because you're in a geologically quiet region, that doesn't necessarily mean that you are near a minor fault.

[MeliXi]

Hi, I've read the explanations multiple times, but I don't know why I'm still not getting it.
I really do not understand why C is the answer.
If we negated C: "In a geologically quiet region, not every potential nuclear reactor site is near at least 1 minor fault." - AKA some potential nuclear reactor sites aren't near any minor faults.
How does that weaken the argument that "the potential nuclear reactor sites in a geologically quiet region that are least likely to be struck by an earthquake are ones located near a fault that has produced an earthquake within living memory"??
Isn't it possible for both statements to be true? In a geologically quiet region, some potential nuclear reactor sites could be far away from any minor fault, but the ones that are near a fault that's produced an earthquake within living memory, are least likely to be struck by an earthquake. So the ones that aren't near faults that have produced an earthquake within living memory are more likely to be struck by an earthquake - & these can be located near no faults.
I don't see anything wrong with those statements???

[KelseyWoods]

Hi MeliXi!

This is definitely a difficult question!

Great job trying out that Assumption Negation Technique--you negated the answer choice correctly!: "In a geologically quiet region, NOT every potential nuclear reactor site is near at least one minor fault." In other words, some nuclear reactor sites are not near any faults in these regions (these regions only have minor faults so if they're not near a minor fault, then they're not near any fault!).

If there are some nuclear reactor sites that are not near any faults, then those sites would be the ones that are least likely to be struck by an earthquake. This might require a little bit of deduction from what they say in the stimulus (which is part of what makes this question so hard!), but basically earthquakes can only occur along fault lines. If there are no fault lines, there are no earthquakes. So if you are not near any fault lines, then you can't be struck by an earthquake.

Therefore, nuclear sites that are not near any fault lines would be less likely to be struck by an earthquake than nuclear sites that are near minor fault lines which have had a recent earthquake. That directly contradicts the conclusion that the nuclear sites near fault lines that have had recent earthquakes would be the least likely to be struck by an earthquake. Thus, answer choice (C) is necessary for the argument.

Hope this helps!

Best,
Kelsey

[Morgan2cats]

Hi PS,

Thanks for your response! I didn’t fully understand C until I read your latest explanation.

I noticed you mentioned "fault lines." Is the idea here that understanding fault lines helps us realize that not being near them is safer than being near one? But since this isn’t explicitly mentioned in the argument, how can we know for sure when it’s appropriate to bring in outside knowledge like this? In what situations should we rely on additional knowledge?

Thanks in advance!

but basically earthquakes can only occur along fault lines.