#26 - Concept Reference, Must Be True

[Jeff Wren]

Hi Brooke,

Please see Robert's previous answer above on the problem with Answer D.

I'll only add that it's important to always focus on the "big picture" ideas/main point of the passage even when answering detail questions like this one.

In the first paragraph, it mentions that most earthquakes are found in "hot zones," regions with high levels of subduction but and this is the critical point of the passage, there are regions of high levels of subduction that don't have earthquakes. So the reason that the passage is written is to try to explain what else is going on. In other words, to explain why only some of the areas with high levels of subduction have earthquakes while some do not.

The final sentence of paragraph one poses a question that the rest of the passage goes on to answer. As a general rule of thumb, when you come across the author raising a question, take note of it because the answer to it will often be a central idea in the passage. Here the question raised was "how can often intense subduction take place at certain locations with little or no seismic effect?" (lines 19-21).

The following paragraph explaining the differences between shallow and deep descents provides the answer to this question. In this context, shallow descents result in more and larger earthquakes and deep descents result in little or no earthquakes. The deep descents explain why there are regions with intense subduction that have little or no seismic effect (i.e. earthquakes).

Here's one final observation that may be helpful with science passages in general. Most of these passages follow a pattern where a new theory helps explain a puzzling fact (which happens here) or a new study sheds light on a previous theory, etc.. Usually, but not always, the passage agrees with the new theory, so it's important to understand the author's take on the different theories/viewpoints.

In this passage, the traditional theory fails to explain this odd fact while the new theory does offer a plausible explanation, and the author agrees with this new theory. If you check the correct answer to the Main Point question in question 22, it can be helpful in answering some of the other questions.

[mollylynch]

Hi, I am confused about where this is supported in the passage. I feel like so many things about subduction and plates moving toward each other are being said. That is why I chose E. How do we know that shallow angles are where most earthquakes are?

[Jeff Wren]

Hi Molly,

The key paragraph that compares/contrasts the two different kinds of plate collisions is the second paragraph. In this paragraph the word "quiet" (lines 23, 30) refers to subduction zones with little or no earthquakes. These quiets zones are contrasted with "normal" zones (for lack of a better word) that do produces earthquakes.

One of the tricky parts of this paragraph is that it first describes the "normal" zones in lines 24-29, then it describes the quiet zones in lines 30-44, and then goes back to describing the "normal" zones in lines 45-51.

The normal zones (that produce earthquakes) have plates moving in opposite directions. (This is why Answer E is wrong.) You may be wondering, how can we tell that lines 24-29 are referring to the normal, earthquake producing zones? Starting in line 29-30, the words "In contrast, the plate collisions in the quiet zones" (my emphasis) have plates moving in the same direction. So we know that what was just described in lines 24-29 are the non-quiet, normal zones that produce earthquakes.

Lines 30-44 describe the features of the quiet zones, such as great resistance from the mantle (line 39) and steep descent (line 40). These descriptions also eliminate Answers A and B since these answer are describing feature of the quiet (no earthquake) zones and are therefore opposite answers.

Starting in line 44 with the words "On the other hand" the passage goes back to the normal, non-quiet zones that produce earthquakes. We know that the passage is now describing the normal zones due to the contrasting words "on the other hand" and the description of "collisions in which the plates move toward each other" (line 45), which is a description of the normal zones as already discussed in line 24-29. These normal zones create shallow descents (lines 47-48). This feature on the normal, non-quiet earthquake producing zones is correctly captured in Answer C.