When a seismic common midpoint (CMP) stack or zero-offset (ZO) section is depth or time migrated with different (constant) migration velocities, different reflec- tor images of the subsurface are obtained. If the migra- tion velocity is changed continuously, the (kinematical) migrated image of a single point on the reflector, con- structed for one particular seismic Zo reflection signal, moves along a circle at depth, which we call the Thales circle.
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