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## B. Two-layer media

Let the first layer with horizontal bedding z=h1 have the velocity v1, and the second layer with the dipping bed

have velocity v2. Time-migration is performed in homogeneous model with velocity .

First step:

Second step: :

Third step: imaging (from the condition (74)):

After substitution , we obtain location of reflector image in the time section:
 (75)

Let us perform time-to-depth migration in true two-layer model with the help of Hubral's technique (Hubral, 1977). This technique consists of transmission of amplitudes along image rays, which satisfy Snell's law and approach the surface vertically. But in this simple example all image rays are vertical in both layers. So the location of the reflector's image in depth-section will be derived from the equation:

where t must be expressed according to equation (75). After simple manipulation we derive

that differs from true position of the reflector.

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Stanford Exploration Project
1/13/1998