PT151.S1.P4.Q23 > Analytics

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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

23.

According to the passage, what ███████ ████ ███ ██████ ██████ ██ ███ ████ █████████ ████████

Question Type

Stated

The author tells us what happens in the middle of P2: “In contrast, the plate collisions in the quiet subduction zones occur between two plates that are moving in the same general direction—the second plate's motion is simply faster than that of the first, and its leading edge therefore becomes subducted. But in this type of subduction, the collision zone moves with a comparatively high velocity relative to the mantle below. Thus, rather like an oar dipped into the water from a moving boat, the overtaking plate encounters great resistance from the mantle and is forced to descend steeply as it is absorbed into the mantle. The steep descent of the overtaking plate in this type of collision reduces the amount of contact between the two plates, and the earthquake-producing friction is thereby reduced as well.”

The trailing edge ██ ███ █████████████ █████ ██ █████████ █████ ███ █████████████ ██████

The leading edge of the faster-moving plate is subducted under the trailing edge of the slower plate. So the trailing edge of the slower plate isn’t subducted under faster plate.

The leading edge ██ ███ █████████████ █████ ██ █████████ █████ ███ █████████████ ██████

The leading edge of the faster-moving plate is subducted under the trailing edge of the slower plate. The leading edge of the slower-moving plate isn’t subducted under anything.

10%

The leading edge of the faster-moving plate is subducted under the trailing edge. It’s not the trailing edge of the faster plate that’s subducted; it’s the leading edge of that plate.

Stated in the middle of P2: “In contrast, the plate collisions in the quiet subduction zones occur between two plates that are moving in the same general direction—the second plate's motion is simply faster than that of the first, and its leading edge therefore becomes subducted.”

80%

The leading edge ██ ███ ███████ █████ ██ █████████ █████ ███ ██████ ██████

The author doesn’t discuss smaller vs. larger plates. What matters is what’s faster-moving and slower-moving.

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PrepTest 151 - Section 1 - Passage 4 - Question 23

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PrepTest 151 - Section 1 - Passage 4 - Question 23

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