oa Two Methods for Subsurface Velocity and Structure Determination Based on RefiecHon Tomography

Prestack depth migration has become a powerful tool for subsurface structure and velocity determination. We present two tomographic approaches that modify an initial model to produce an updated model which yields flatter prestack migration gathers. The first approach updates a model which consists of closed polygons and is suitable for situations where such a model can be interpreted from the data. The second approach is grid based and can allow a detachment between structure and velocity. Both approaches are derived from the tomographic principle. The spatial discretization yields, in both cases, a set of overdetermined linear equations which are solved by weighted least squares.