Earthquakes occur along the fault lines on the Earth’s crust

Question

Earthquakes occur along the fault lines on the Earth’s crust. It is believed that earthquakes relieve stress on theses faults, making the faults more stable. Therefore, the portion of a fault that has just experienced an earthquake is relatively safe and unlikely to rupture again for a substantial time.

Which of the following, if true, most strongly supports the argument above?

A. Most aftershock activity following the main earthquake occurs on the margins of the area where the faults slipped a lot during the main earthquakes.
B. Stress reduction during a major earthquake is large and pervasive over the ruptured surface of the fault.
C. Data on earthquakes indicate that the area that has just slipped is actually more likely to have another failure.
D. If unusually intense aftershock activity is observed within the high-slip zone, a larger earthquake in the immediate vicinity of the first event might still be possible.
E. Many faults are so weak that they experience a series of earthquakes, both major and minor within a few days of the main earthquake.

Ekens · Answer

B. The argument gives a causal link which is:belief that earthquakes relive stress across faultlines therefore faults which have just experienced earthquakes are safe.

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frankgraves · Answer

Why the answer is A?
I think B is the correct answer.
If I quote option B, "Stress reduction during a major earthquake is large and pervasive over the ruptured surface of the fault"
There is a large stress reduction after an earthquake, thus making the fault more stable.

elavendan1 · Answer

The conclusion here is,  the portion of a fault that has just experienced an earthquake is relatively safe and unlikely to rupture .
Assuming you eliminated C,D,E, we can compare A and B.

A says that Most aftershock activity occurs in the margins, not in the faults. In other words, option A says that once the main earthquake event is complete, even the aftershock activity doesn't happen along the fault lines. It occurs in the margin area. So these faults will be saved from the aftershock activity.

Meanwhile, we have couple of reasons to eliminate B. 
1. Stress reduction is large over the ruptured surface of the fault. In my opinion, option B just restates the premises with additional adjectives. i.e, stress release is 'large' over the ruptured surface.
2. option B talks about  major earthquakes , while the conclusion addresses earthquakes in general. 
3. The unstated assumption here is stress reduction on the fault lines is enough to make these faults stable.

Option B relies on the same assumption that the argument depends, while option A eliminates one potential cause that might destabilize the faults. That is why option A is answer.

Hope this helps.

guddo · Answer

Earthquakes occur along the fault lines on the Earth’s crust. It is believed that earthquakes relieve stress on theses faults, making the faults more stable. Therefore, the portion of a fault that has just experienced an earthquake is relatively safe and unlikely to rupture again for a substantial time. 
 
Which of the following, if true, most strongly supports the argument above?

The argument says: earthquakes reduce stress on the ruptured part of a fault, so that specific portion is safer for a while. The best support will directly back the link “earthquake reduces stress on the ruptured surface” and make “less likely to rupture again soon” more credible.

A. Most aftershock activity following the main earthquake occurs on the margins of the area where the faults slipped a lot during the main earthquakes.

This supports the idea that the high slip zone (the part that just ruptured a lot) is relatively quiet afterward, which fits “safe for a while.” It is supportive, but it is indirect because it uses aftershock locations as a proxy.

B. Stress reduction during a major earthquake is large and pervasive over the ruptured surface of the fault.

This directly confirms the key mechanism the conclusion relies on: the ruptured surface experiences substantial stress relief. If stress really drops across that surface, it is more reasonable that it is  unlikely to rupture again soon .  This is the strongest support.

C. Data on earthquakes indicate that the area that has just slipped is actually more likely to have another failure.

This contradicts the conclusion, so it weakens, not supports.

D. If unusually intense aftershock activity is observed within the high-slip zone, a larger earthquake in the immediate vicinity of the first event might still be possible.

This introduces an exception that suggests the recently slipped zone might still be risky in some cases. That undercuts the “relatively safe” claim.

E. Many faults are so weak that they experience a series of earthquakes, both major and minor within a few days of the main earthquake.

This also undercuts the conclusion, since it says repeat quakes can happen soon.

Answer: (B)

Earthquakes occur along the fault lines on the Earth’s crust

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Earthquakes occur along the fault lines on the Earth’s crust

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

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My Rewards