PrepTest 151 - Section 1 - Passage 4 - Question 24

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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

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Details of hypothesis · Collision causes subduction which causes earthquakes

Explains seismic hot zones: high levels of subduction produce many earthquakes

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Phenomenon · But subduction can also occur without causing earthquakes

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Hypothesis · Type of collision makes a difference

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Collision type 1 · Plates moving toward each other

Occurs in seismic hot zones (many earthquakes)

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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

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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.

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Analogy · Collision type 1 behaves like sheets of sandpaper

Colliding plates slide across each other; high resistance (friction)

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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

24.

Which one of the following, ██ █████ █████ ███████ ███ ████████ █████████ ██ ███ ███ ████████ ████████ ███ ██████ ██ ███████ ████████ ██ ███ ████ ██ █████████ ███████ ████████ ███████

Question Type

WSE (RC)

The new proposal is that the direction of plate collision influences earthquake frequency. In particular, when plates move in opposite direction, earthquakes are more likely. But when plates move in the same direction, earthquakes are less likely. This is described in P2.

To challenge this proposal, let’s look for an answer that presents evidence to the contrary. For example, evidence that there are no earthquakes even when plates collide in the opposite direection. Or evidence that there are many earthquakes even when plates collide in the same direction.

Some regions where ███████ ████████ ██ ██████████ ███ ██████████ █████████ ██████ ███ ███████ ██ █████ ███ █████████ ██████ ████ ██████ ███ ██████ ██ ███ ████ ██████████

This is consistent with the theory, because same-direction collections are supposed to produce few earthquakes.

10%

There are areas ██ █████ ██████ ███████ ███ ██ █████ █████ ██ ██████ ██ ██ ███████ █████████

This is consistent with the theory, because these plate collisions could be in the same direction. If so, we’d expect few earthquakes.

There are areas █████ █ █████ ███ █████████ ██ █ ███████ █████ ██████ ██████████ ███ █████ █████ ████ ████ ████ ██ ████ ████████████

Plates descend at a shallow angle when they collide in opposite directions. If plates collide in opposite directions, we’d expect many earthquakes. So (C) undermines the proposal by showing that there aren’t many earthquakes in a zone with opposite-direction collisions.

66%

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This is consistent with the proposal. The scientists never suggest that there must be more factors in the size of the plane of contact besides the angle of subduction. So if it turns out that the size of the plane of contact is related only to the angle of subduction, this doesn’t undermine the proposal.

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This is consistent with the proposal. Plates descending at a steep angle occur when the plates collide in the same direction. When plates collide in the same direction, we expect few earthquakes.

PrepTest 151 - Section 1 - Passage 4 - Question 24

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