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For much of the twentieth century, seismologists operated on the princ
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Updated on: 07 Aug 2026, 10:57
Updated on: 07 Aug 2026, 10:57
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For much of the twentieth century, seismologists operated on the principle that the gradual accumulation of strain along a fault line was the most reliable indicator of an impending earthquake's likely magnitude. The greater the strain buildup, the more violent the expected rupture. This conviction held until the 2004 Sumatra-Andaman earthquake, a massive event that originated on a fault segment where strain accumulation had been unremarkable. In the aftermath, a competing hypothesis gained ground: that the absolute level of stress already present in the crust, independent of its rate of increase, could be the decisive factor. The two views carry opposite implications for hazard assessment, since a region with slow strain accumulation might still be primed for a catastrophic release if absolute stress is high. A recent evaluation of eleven leading earthquake-forecasting models underscored the practical consequences of this theoretical split. When the models were asked to predict quake probabilities using only strain-rate data, their outputs clustered within a narrow range. Once absolute stress estimates were incorporated into the simulations, however, the forecasts scattered so widely that they became virtually useless for setting building codes or insurance premiums. The discrepancy leaves emergency planners in an untenable position: they must prepare for a worst-case scenario that existing models cannot even agree upon.
1. The author of the passage is primarily concerned with
A. advocating for the superiority of one earthquake-forecasting approach over another
B. accounting for the unexpected severity of the 2004 Sumatra-Andaman earthquake
C. explaining why a once-dominant theory has been abandoned
D. detailing the practical difficulties that arise from unresolved scientific disagreement
E. comparing the methodologies employed by eleven different earthquake models
2. It can be inferred that one reason the eleven models described in the passage produced widely scattered forecasts when absolute stress estimates were included was that
A. absolute stress data are inherently less reliable than strain-rate measurements
B. the models were constructed using outdated information about fault mechanics
C. the researchers who built the models held differing views on how absolute stress influences earthquake likelihood
D. the models were designed to prioritize strain-rate data and could not properly integrate additional variables
E. the absolute stress levels varied so greatly from one fault to the next that no single model could account for all cases
3. The information in the passage suggests that emergency planners would be in a better position to set building codes if researchers could first answer which of the following questions?
A. What is the maximum possible magnitude of an earthquake on a fault with slow strain accumulation?
B. Which of the two competing hypotheses—strain accumulation or absolute stress—is more consistent with the data from the 2004 Sumatra event?
C. How can strain-rate data be used to estimate absolute stress levels in the crust?
D. To what extent does the inclusion of absolute stress estimates alter the forecasts produced by a typical earthquake model?
E. What is the relative importance of strain accumulation versus absolute stress in determining the magnitude of an earthquake rupture?
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Originally posted by Carcass on 04 Aug 2026, 23:26.
Last edited by GeminiHeat on 07 Aug 2026, 10:57, edited 1 time in total.
Last edited by GeminiHeat on 07 Aug 2026, 10:57, edited 1 time in total.
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GRE Prep Club Team Member
Joined: 20 Feb 2017
Posts: 2932
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Re: For much of the twentieth century, seismologists operated on the princ
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07 Aug 2026, 11:17
07 Aug 2026, 11:17
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Explanation
2. It can be inferred that one reason the eleven models described in the passage produced widely scattered forecasts when absolute stress estimates were included was that
The passage states:
"A recent evaluation of eleven leading earthquake-forecasting models underscored the practical consequences of this theoretical split."
Then it says:
"When the models were asked to predict quake probabilities using only strain-rate data, their outputs clustered within a narrow range. Once absolute stress estimates were incorporated, however, the forecasts scattered so widely..."
The author explicitly links the divergence in forecasts to the theoretical split between the two competing hypotheses. The most reasonable inference is that the different models implemented or weighted absolute stress differently because their creators had different assumptions about its role in earthquake prediction.
Thus, C best explains why adding absolute stress caused the forecasts to diverge.
A. The passage never says the data are less reliable. It attributes the disagreement to the competing theories, not to poor data quality.
B. No evidence supports this. The passage never suggests the models are outdated.
D. The passage doesn't say the models were incapable of incorporating absolute stress. It says they produced different results when they did.
E. The forecasts differed because the models treated absolute stress differently, not because stress varied across faults. The passage discusses one simulation exercise, not variation across many faults.
Answer: C
2. It can be inferred that one reason the eleven models described in the passage produced widely scattered forecasts when absolute stress estimates were included was that
The passage states:
"A recent evaluation of eleven leading earthquake-forecasting models underscored the practical consequences of this theoretical split."
Then it says:
"When the models were asked to predict quake probabilities using only strain-rate data, their outputs clustered within a narrow range. Once absolute stress estimates were incorporated, however, the forecasts scattered so widely..."
The author explicitly links the divergence in forecasts to the theoretical split between the two competing hypotheses. The most reasonable inference is that the different models implemented or weighted absolute stress differently because their creators had different assumptions about its role in earthquake prediction.
Thus, C best explains why adding absolute stress caused the forecasts to diverge.
A. The passage never says the data are less reliable. It attributes the disagreement to the competing theories, not to poor data quality.
B. No evidence supports this. The passage never suggests the models are outdated.
D. The passage doesn't say the models were incapable of incorporating absolute stress. It says they produced different results when they did.
E. The forecasts differed because the models treated absolute stress differently, not because stress varied across faults. The passage discusses one simulation exercise, not variation across many faults.
Answer: C
GRE Prep Club Team Member
Joined: 20 Feb 2017
Posts: 2932
Given Kudos: 1268
GPA: 3.39
Re: For much of the twentieth century, seismologists operated on the princ
[#permalink]
07 Aug 2026, 11:27
07 Aug 2026, 11:27
1
Expert Reply
Explanation
3. The information in the passage suggests that emergency planners would be in a better position to set building codes if researchers could first answer which of the following questions?
The passage identifies an unresolved scientific disagreement:
Hypothesis 1: The rate of strain accumulation is the key predictor of earthquake magnitude.
Hypothesis 2: The absolute stress in the crust is the decisive factor.
This disagreement causes earthquake models to produce dramatically different forecasts once absolute stress is included, leaving emergency planners unable to rely on them for building codes.
If researchers could determine how important each factor really is relative to the other, models would likely converge on more reliable forecasts, making it easier to set building codes.
Thus, E addresses the central unresolved issue in the passage.
A. This concerns one specific scenario. The planners' problem is broader: they don't know which physical factor governs earthquake magnitude in general.
B. The 2004 earthquake triggered the debate, but the passage is about the broader scientific uncertainty. Even if Sumatra favored one hypothesis, researchers would still need to understand the overall relationship between strain and stress across earthquakes.
C. The issue is not how to estimate stress; it's whether and how stress should influence forecasts.
D. The passage already answers this: including absolute stress makes forecasts scatter so widely that they become virtually useless. Knowing this more precisely would not resolve the underlying disagreement.
Key idea
The planners' problem stems from uncertainty about which physical quantity actually determines earthquake magnitude. Resolving the relative importance of strain accumulation and absolute stress would make forecasts more consistent and useful.
Answer: E
3. The information in the passage suggests that emergency planners would be in a better position to set building codes if researchers could first answer which of the following questions?
The passage identifies an unresolved scientific disagreement:
Hypothesis 1: The rate of strain accumulation is the key predictor of earthquake magnitude.
Hypothesis 2: The absolute stress in the crust is the decisive factor.
This disagreement causes earthquake models to produce dramatically different forecasts once absolute stress is included, leaving emergency planners unable to rely on them for building codes.
If researchers could determine how important each factor really is relative to the other, models would likely converge on more reliable forecasts, making it easier to set building codes.
Thus, E addresses the central unresolved issue in the passage.
A. This concerns one specific scenario. The planners' problem is broader: they don't know which physical factor governs earthquake magnitude in general.
B. The 2004 earthquake triggered the debate, but the passage is about the broader scientific uncertainty. Even if Sumatra favored one hypothesis, researchers would still need to understand the overall relationship between strain and stress across earthquakes.
C. The issue is not how to estimate stress; it's whether and how stress should influence forecasts.
D. The passage already answers this: including absolute stress makes forecasts scatter so widely that they become virtually useless. Knowing this more precisely would not resolve the underlying disagreement.
Key idea
The planners' problem stems from uncertainty about which physical quantity actually determines earthquake magnitude. Resolving the relative importance of strain accumulation and absolute stress would make forecasts more consistent and useful.
Answer: E
