Dictionary:Buried-focus effect

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The effect of energy passing through a focal region before it reaches the recording plane. A buried-focus situation commonly causes several branches (usually three) of a reflection to be observable (i.e., several points on the reflector satisfy the law of reflection); see Figure B-11. The portion for which raypaths pass through the focus is called the reverse branch (q.v.) and it involves a phase shift; see Sheriff and Geldart (1995, 155-159). For zero offset and constant velocity, a buried focus occurs if a reflector’s center of curvature lies beneath the recording surface, but less curvature is required for buried-focus effects on offset traces. Hence buried-focus effects are more likely on long-offset traces or deeper in the section. Velocity gradients and curvature of isovelocity surfaces (which are apt to occur in structural areas) affect buried-focus effects. Buried-focus effects can also be produced by local lateral velocity variations that bring about focusing (lens effects).

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