Self-study
P1
According to the generally accepted theory of plate tectonics, the earth's crust consists of a dozen or so plates of solid rock moving across the mantle—the slightly fluid layer of rock between crust and core. ████ ███████████ ███ ████ ██ █████████ ██ █ ██████ ██ ███ ████████ ██ █████ ██████ ███████ ███ ███████ ██ ████ ████████ ███
Phenomenon & hypothesis ·
Earthquakes explained by plates colliding
Details of hypothesis ·
Collision causes subduction which causes earthquakes
Explains seismic hot zones: high levels of subduction produce many earthquakes
Phenomenon ·
But subduction can also occur without causing earthquakes
P2
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Hypothesis ·
Type of collision makes a difference
Collision type 1 ·
Plates moving toward each other
Occurs in seismic hot zones (many earthquakes)
Collision type 2 ·
Plates moving in same direction
Occurs in quiet zones (few earthquakes)
Analogy ·
Collision type 2 behaves like boat's oar
Collision zone moving across mantle (fluid layer) like boat over water; subducting plate descends steeply into mantle like oar in water
Evidence for hypothesis ·
Collision type 2 involves little contact (friction) between plates
Less friction means less likely to cause earthquake
Evidence for hypothesis ·
Collision type 1 involves more contact (friction) between plates
Collision zone not moving across mantle, so colliding plates remain in contact with each other. More friction means more likely to cause earthquake.
Analogy ·
Collision type 1 behaves like sheets of sandpaper
Colliding plates slide across each other; high resistance (friction)
P3
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Implication ·
of hypothesis
Regions with little subduction (plate collision) could still cause earthquakes, depending on collision type (collision type 1 causes greater risk)
Passage Style
Phenomenon-hypothesis (RC)
Single position
25.
Based on the information in ███ ████████ █████ ███ ██ ███ █████████ █████████ █████ ████ █████████ ████████ ███ ████ ██████████
Question Type
Implied
Let’s keep in mind the point made at the very end as well as the overall point of the passage. The point at the very end is that the scientists’ theory described in P2 offers a “warning.” Places with low levels of subduction might in fact be a significant risk of earthquakes, depending on the type of subduction. Notice that the author hasn’t connected the dots on exactly why these areas might be at significant risk of earthquakes. One way to logically complete the passage would be to articulate why these zones are at risk. For example, “If these zones have plates that collide in the opposite direction, their risk of earthquakes is increased despite a low level of subduction.”
a
Depending on the ████████████ ███████ █████ ████████ ███ ███████ █████ ██ ██████ ███ ███████████ ████ █████ ████████ █████ █████████
This doesn’t fit, because we have no reason to think there’s “always a possibility plate velocity could increase.” The author never suggested anything that implies plate velocity can always increase. Since (A) isn’t supported, it wouldn’t be a logical completion.
b
The lower the █████ ██ ██████████ ██ ██ █████ ███ ███████ ███ ███████████ ████ ███ ██████████ █████ ██ █████████ ██ █ ███████ ██████
This doesn’t fit, because it’s unsupported. The author never suggests that lower levels of subduction imply higher chance of shallow subduction angles. The author never presents a correlation between amount of subduction and angle of subduction.
c
Any region where ██████████ ██████ █████ ██████ ██ ████████ ██ ███ █████ ██ ██████████ ███ █ ██████████ ████████ ██ ███████ █████████
This doesn’t fit, because the author’s emphasis at the end is on the “nature of the subduction” taking place — the direction of the plates that collide. The author doesn’t suggest that subduction might always increase and that this is why there might be risk in low subduction zones.
d
Even at low ███████ ███ ███████ █████ ██ ██████████ ██████████ ███████ ██ █ ███████████ ██████ ██ ███████ █████████
This doesn’t fit, because it’s not supported. The author doesn’t suggest that subduction at low levels “inevitably” (always) results in a lot of seismic activity. The angle of subduction matters.
e
Even in such █ ███████ █ █████ ██████████ ██ █ ███████ █████ ██ ██████ ██ █████ █ █████ ████ ██ ████████████████████ █████████
This fits at the end, because this helps explain why regions with low levels of subduction may be at risk of earthquakes. If a plate in a collision descends at a shallow angle — meaning,