Answer:
Friction plays a key role in how ruptures unzip faults in the earth's crust," says Vito Rubino, research scientist at Caltech's Division of Engineering and Applied Science (EAS). "Assumptions about dynamic friction affect a wide range of earthquake science predictions, including how fast ruptures will occur, the nature of ground shaking, and residual stress levels on faults. Yet the precise nature of dynamic friction remains one of the biggest unknowns in earthquake science."
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