#27 - Concept Reference, Must Be True

[Administrator]

Please post your questions below!

[Lukelee]

D; identified ->earthquakes occurred, we don’t see this firm conditional logic in the passage

E; more likely.. like broad wording, can’t avoid this claim. The larger contact, more earthquakes

Good luck

[lanereuden]

Why is E better than C?

[James Finch]

Hi Lane,

The issue with (C) is that it misstates the reason why "quiet zones" may actually be at risk; it depends on the type of subduction, and how much of the two plates rub up against each other, rather than the gradual buildup and release of energy (a description used in the first paragraph that describes all earthquakes). The second paragraph describes this process: areas where the faster-moving plate is moving the same direction as the slower one and thus has a much steeper descent produce less energy and fewer earthquakes, while areas where two plates are moving in opposite directions see shallower angles of collision and thus more surface area colliding and more energy produced, leading to more earthquakes.

(E) is correct as it represents an inference we can make from the description of the two types of subduction: deeper subduction leads to less energy buildup and fewer earthquakes, while shallower subduction sees more energy produced and more earthquakes.

Hope this clears things up!

[lanereuden]

How do plates move in opposite directions, and then... collide? I do not understand this. This would be like 2 people waking away from each other and somehow they bump into one another?

[Brook Miscoski]

lanereuden, please take another look at the passage. The plates that move in opposite directions are still touching. Think about it this way--you have one very long bus that is going North, and another very long bus that is going South. They're too close--in fact, they're rubbing against each other. Still touching for a very long time. Think about it another way. You've got one very sheet of plastic laying over top another very long sheet of plastic. One is pulled East while one is pulled West. They're still overlapping for a very long time. You can keep going with the concept--it's completely possible for things that are moving in opposite directions to be touching. As I remember, in this passage it's the buses, but you get the idea.

[VamosRafa19]

Hi Lane,

The issue with (C) is that it misstates the reason why "quiet zones" may actually be at risk; it depends on the type of subduction, and how much of the two plates rub up against each other, rather than the gradual buildup and release of energy (a description used in the first paragraph that describes all earthquakes). The second paragraph describes this process: areas where the faster-moving plate is moving the same direction as the slower one and thus has a much steeper descent produce less energy and fewer earthquakes, while areas where two plates are moving in opposite directions see shallower angles of collision and thus more surface area colliding and more energy produced, leading to more earthquakes.

(E) is correct as it represents an inference we can make from the description of the two types of subduction: deeper subduction leads to less energy buildup and fewer earthquakes, while shallower subduction sees more energy produced and more earthquakes.

Hope this clears things up!

I'm not sure I follow the support for E here. Is it because a head on collision between two plates is likely to have a more surface area for each plate get hit, than in a collision where one plate is faster and the 'leading edge' becomes subducted?

[KelseyWoods]

Hi VamosRafa19!

In the second paragraph, the author tells us about a theory by scientists who are trying to explain why there are some areas with high levels of subduction that nevertheless relatively free of earthquakes. The scientists propose that the difference has to do with the direction the plates are moving in. In the areas with lots of earthquakes, the plates move in opposite directions; in the earthquake free zones, the plates move in the same direction.

Why does the direction that the plates are moving in impact the likelihood of earthquakes? The paragraph goes on to state that when the plates are moving in the same direction (relatively few earthquakes) "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." But when the plates are moving in opposite directions (areas with lots of earthquakes), "the subducted plate receives relatively little resistance from the mantle, and so its angle of descent is correspondingly shallow, allowing for a much larger plane of contact between the two plates." So the reason that the directions the plates are moving in affects earthquake likelihood has to do with how large the plane of contact is between the two plates.

All of this suggests that it's the large plane of contact between plates during subduction that makes it more likely for earthquakes to occur.

Hope this helps!

Best,
Kelsey

[gwlsathelp]

What is answer choice A even saying? I think it's using a concept referenced in the stimulus to throw off the test taker when it uses, "in relation to the underlying mantle." It definitely threw me off.

[Adam Tyson]

A is an opposite answer, gwlsathelp, as shown by the descriptions of the two types of subduction zones in the second paragraph. There, we learn that in seismic hot zones (places with a lot of earthquakes) "because the two plates are moving in opposite directions, the subduction zone is relatively motionless relative to the underlying mantle." In contrast, in the places where you have a lot of subduction but few earthquakes, "the collision zone moves with a comparatively high velocity relative to the mantle below."

Answer A mixes those two things up, saying that where you have a lot of motion relative to the mantle you get frequent earthquakes. Nope, that's opposite!