Logical Reasoning

PT17 · S2 · Q21 Nuclear reactors are sometimes

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Nuclear reactors are sometimes built in “geologically quiet” regions, so called by geologists because such regions are distant from plate boundaries and contain only minor faults.

Conclusion

Of all the potential nuclear reactor sites in a "quiet" region, the ones near a fault that has produced a quake within the last 100 years (living memory) are the ones least likely to be struck by an earthquake.

Evidence

These faults (minor faults in a "quiet" region) never produce an earthquake more often than once in any given 100,000 year period.

Evaluate

This is a really tough argument to argue with. At first it seems like a Gambler's Fallacy issue, where we're told that . If that were what was said, then we can't act, as the author is, like just because a fault had a recent earthquake, we shouldn't expect another earthquake there for 100,000 years.

That would be interpreting the average / probability too literally.

However, this was not a case of taking an average or a probability and treating it overly literally. The evidence actually establishes that you never have 2 or more quakes from the same minor fault within a 100,000 year time span.

So the author is correct to think that if there's been a quake in living memory at any of these faults, then that fault will not produce another quake for at least 99,900 years (I was just subtracting 100 years of "living memory" from 100,000).

Okay, then how could her conclusion be wrong? How could putting a reactor near a minor fault that has quaked in the past 100 years (and thus won't quake for the next 100,000 years) not be putting the reactor where an earthquake is least likely?

Well, the evidence doesn't say that . It says that you'll have at most one earthquake every 100,000 years.

Maybe some of these minor faults have never had an earthquake, and thus we don't really expect them to ever have an earthquake. They might still be less likely to be struck by an earthquake than the sites that have 1 every 100,000 years.

Goal

- Is there a Missing Link? Sure, I guess we're assuming that . (i.e. all other sites are more likely to have an earthquake within the next 99,900 years)

But this seems like an unlikely type of correct answer to me, so I would be listening instead for a Defender answer. It will be ruling out an objection.

If we negate the correct answer, it should give us a way to object to the Conclusion, to argue that some other site would be even less likely to have an earthquake than would these sites the author is endorsing.

For example, the author is assuming, There are not minor faults in this region that are believed to only have 1 earthquake every 1 million years".

21.

Which one of the following is an assumption on which the argument depends?

  1. Geologically quiet regions are the

    Too Strong: least dangerous

    This argument is only talking about the safest spots within a geologically quiet region to put a reactor. The argument never compares geologically quiet regions to any other type of region, so we can't say she must have been assuming that they're the least dangerous of all possible regions. (It's possible that other regions are more prone to earthquakes, but far less prone to tornados / hurricanes / floods / power surges / etc. So there's no reason we should assume that geologically quiet zones are the least dangerous areas)

    6% picked this

  2. For any potential nuclear reactor

    Too Strong: primary

    Just because likelihood of being hit by an earthquake is the only type of safety risk being discussed in this paragraph doesn't mean that the author believes it's the #1 risk. If we negated this answer, we could say that "being struck by an earthquake isn't the primary determinant, but it's the second most important." The argument wouldn't be changed in any way by demoting it from #1 to #2, so it's unnecessary for the author to believe that it's the #1 risk. The author's conclusion doesn't advocate that we put a reactor near a minor fault that has recently produced a quake. If she had recommended that, then we would care about other potential risks, in evaluating her plan. But her conclusion is just a statistical one, not a prescriptive one. She's merely trying to establish a factual claim that sites near a recently-quaked minor fault would be least likely to be struck by an earthquake.

    8% picked this

  3. Correct

    In a geologically quiet region,

    Why this is right

    This seems way too extreme at first blush: every potential site is near at least one minor fault? But if we have a flexible mindset (which we should, since we came to these answers relatively cluelessly), we can negate this and ask if it would weaken. Would it hurt the argument to say, in these quiet regions, there is at least one potential reactor site that isn't near any minor faults ? Yes! That seems to give us a way to fight the author's conclusion. She thinks that a site near a recently-quaked minor fault would be the least likely to be struck by an earthquake. But if there are potential sites that aren't near any minor faults, wouldn't those be even less likely to be struck by an earthquake? The sites near recently-quaked minor faults are likely to be struck by an earthquake again in 100,000 years or so. But a site that isn't near any fault lines at all is unlikely to ever by be struck by an earthquake. (note the outside knowledge needed to understand this answer: earthquakes only occur at fault lines between tectonic plates) The author was mentally comparing potential reactor sites thinking they all had a "1 quake every 100,000 years" cycle and simply saying that the most-recently quaked sites would have the longest duration before another earthquake struck. That means the author was assuming that "every site is near a minor fault. So let me figure out which minor fault would be least likely to be struck." Negating this answer gives the objection of, "wait, why are you assuming it has to be near a minor fault at all? Can't we just put it in the middle of nowhere, far from any minor fault, and have even less risk of being struck by an earthquake?"

    Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.

    45% picked this

  4. Nuclear reactors that are located

    Out of Scope

    Out of Scope: built to withstand one The author hasn't insinuated that a nuclear reactor can withstand one earthquake. She might believe that an earthquake would totally destroy a nuclear reactor. We're talking about building a reactor at a site that wouldn't have an earthquake for almost 100,000 years, so the author could just be thinking, "Yeah, at that point the earthquake will destroy the reactor, but who knows if humanity will still even exist at that point? If we do, we'll have moved on from this technology. Or if we haven't, at least we got a good 100,000 years out of the site before an earthquake destroyed the reactor."

    10% picked this

  5. Earthquake faults in geologically quiet

    Too Strong

    Too Strong: at least once every 100k This is tempting, because the author is definitely failing to consider that under the definition of "no more than 1 every 100,000 years", there could still be WIDE variation in terms of how frequently each minor fault in a quiet region produces earthquakes. But she's definitely not forced to believe there MUST be at least one earthquake per fault per 100,000 years, If we negate this answer, we get "at least one fault in a quiet region does not produce at least one quake every 100,000 years". That is not any kind of objection because the author is only saying that there can't be more than one quake every 100,000, not that all of them reliably give you exactly one quake every 100,000.

    31% picked this

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