Self-study
P1
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
Application of method ·
Determine details of past earthquakes, predict future earthquakes
P2
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Intro new method ·
Lichenometry
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
P3
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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
4.
Which one of the following ██████████ ██ ████ ████████ █████████ ██ ███ ████████
a
Lichenometry is less ████████ ████ ███████████ ██████ ██ ██████████ ███ ██████████ ███ ████████ ██ ██████ ████████████
Not supported. The author doesn’t suggest that lichenometry is less accurate than radiocarbon dating in predicting future earthquakes.
b
Radiocarbon dating is ████████ ██ ██ ███████ ██ ██████ ████ ███████████ ████ ████ ██ ████████████ █████ █████ ██████████ ████ █████
c
Radiocarbon dating and ████████████ ███ █████████ ███ ████ ██████ ███████ ██ █████████ ███ ██████ ████ ████████████
We have no reason to think these are the “only” viable methods of dating past earthquakes.
d
Radiocarbon dating is ████ ████████ ████ ████████████ ██ ██████ ███████████ ████ ████████ █████████████ ███ █████ ████
Not supported. Lichenometry is best used on earthquakes within the last 500 years. And, lichenometry can date earthquakes to a more narrow date range than radiocarbon dating can.
e
The usefulness of ████████████ ███ ██████ ███████████ ██ ███████ ██ ██████████ ███████ █████ ███████ ████ ███████ ██ ██████████ ██████ ██████ █████████ ██ ███ ██████
Not supported. Although the author does say that we have to take factors that affect lichen growth rate into account, this does not imply that lichenometry is useful only when factors don’t affect growth rate. Lichenometry can still be useful in these cases as long as we factor in the conditions that affect growth rate.