PrepTest 132 - Section 1 - Passage 1 - Question 6

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To study centuries-old earthquakes and the geologic faults that caused them, seismologists usually dig trenches along visible fault lines, looking for sediments that show evidence of having shifted. ███

Intro topic · Methods for studying causes of past earthquakes

Start by looking for buried sediments that shifted during a possible earthquake

Explain method · Use carbon 14 to back-date when material shifted (i.e., when possible earthquake occurred)

Carbon 14 is a radioactive form of carbon that decays (i.e., turns into a different form of carbon) at a known rate, so the amount of carbon 14 left in something can tell us how old that thing is

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Application of method · Determine details of past earthquakes, predict future earthquakes

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Intro new method · Lichenometry

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Explain new method · Use lichen growth to back-date rockfalls in mountain ranges

Lichens begin growing on rocks after an earthquake causes rockfalls; because they grow at a known rate, the size of a lichen patch on a rock can tell us when that rock first fell

Application of new method · If many rockfalls occurred at the same time, that suggests an earthquake

Earthquake was strongest where the most number of rockfalls occurred

Support for lichenometry · over carbon 14 dating

Carbon 14 dating is less accurate because it can be hard to know how much carbon 14 the material started with (just knowing the rate of carbon 14 decay on its own can't tell us how old that material is)

Limitations of lichenometry · Limited time period, complications related to site selection

Passage Style

Single position

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Question Type

Implied

It’s not clear that we can predict the correct answer, but at least we know the correct answer will be supported by the last two sentences: “They note, however, that using lichenometry requires careful site selection and accurate calibration of lichen growth rates, adding that the method is best used for earthquakes that occurred within the last 500 years. Sites must be selected to minimize the influence of snow avalanches and other disturbances that would affect normal lichen growth, and conditions like shade and wind that promote faster lichen growth must be factored in.”

While lichenometry is ████ ████████ ████ ██ ██ ████ ██ ████ ███████████ ████ ████████ ████ ████ ███ █████ ████ ██ ██ █████ ████ ████████ ████ █████ ███████ ███ ██████ ████ ████████████

We have no reason to think, based on the last two sentence, that Bull and Brandon believe lichenometry is more accurate for dating earthquakes more than 500 years ago.

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Nothing in the last two sentences relates to radiation, so we have no reason to think Bull and Brandon assume (B).

Lichens are able ██ ████ ████ ██ ███ █████ ██ █████ ████ ███ ██████ ██ ███████████ ████████

We have no reason to think, based on the last two sentences, that Bull and Brandon believe lichens can grow only on the rocks common in mountainous regions.

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We have no reason to think, based on the last two sentences, that Bull and Brandon believe that the mountain ranges studied in lichenometry are subject to more frequent snowfalls and avalanches than other mountain ranges.

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Bull and Brandon assume (E), because they recommend that we “factor in” conditions “like shade and wind that promote faster lichen growth.” So Bull and Brandon assume that it’s possible to determine how these conditions affect growth rate. If they didn’t think it was possible, it wouldn’t make sense for them to recommend factoring in these conditions.

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PrepTest 132 - Section 1 - Passage 1 - Question 6

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