Given a scientific passage and an answer, generate a question for the given answer.

[Q]: Passage: A cross section of earthquake epicenters. The depth outlines the subducting plate. There are shallow, intermediate, and deep earthquakes. Answer: earthquake
[A]: Subducting plate and epicenter are terms related to what phenomenon?

[Q]: Passage: The mechanical advantage of a machine is the factor by which the machine changes the input force. It equals the ratio of the output force to the input force. A wheel and axle may either increase or decrease the input force, depending on whether the input force is applied to the axle or the wheel. Answer: mechanical advantage
[A]: What is indicated by the ratio of the output force to the input force in a machine?

[Q]: Passage: Wave amplitude of a transverse wave is the difference in height between a crest and the resting position. Wave amplitude of a longitudinal wave is the distance between particles of the medium where it is compressed by the wave. Answer: a crest
[A]:
Wave amplitude of a transverse wave is the difference in height between what and the resting position?