PGP Practice Test

1Single Choice

A seismic refraction survey is performed over a two-layer earth in which the deeper layer has a higher P-wave velocity than the shallower layer. Which statement correctly describes the head-wave (refracted) arrival recorded at geophones offset beyond the crossover distance?

A.It travels along a direct path through the upper layer at the velocity of the upper layer.
B.It travels downward and upward entirely within the lower layer, obeying Snell's law at the refracting interface.
C.It travels along the top of the lower layer at the velocity of the lower layer, with energy continuously refracted back to the surface along the interface.
D.It is always the first arrival regardless of source-to-receiver offset.

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