DIP-MOVEOUT PROCESSING FOR DEPTH-VARIABLE VELOCITY

In dip-moveout (DMO) processing, the seismic velocity is often assumed to be constant. While several approximate techniques for handling ver tical velocity variation have recently become available, here we propo se a method for computing the kinematically exact DMO correction when velocity is an arbitrary function of the depth. While not known in adv ance, the raypath from source to receiver and the corresponding zero-o ffset raypath satisfy several relationships, which are used to form a system of nonlinear equations. By simultaneously solving the equations via Newton-Raphson iteration, we determine the mapping that transform s nonzero-offset data to zero-offset. Unlike previous schemes that app roximately handle vertical velocity variation, this method makes no as sumptions about the offset, dip, velocity function, or hyperbolic move out. Tests using both synthetic and recorded seismic data demonstrate the effectiveness of this variable-velocity DMO. These tests show this method accurately handles vertical velocity variation, while use of c onstant-velocity DMO can lead to significant errors. Comparing this te chnique to a formulation that approximately handles velocity variation , however, suggests that the improved accuracy of the exact technique may not be justified because of uncertainty in the velocity model and increased cost. While improved accuracy alone may not justify the use of this method in 2-D, its flexibility may in other cases. Changes cou ld be made to handle 3-D DMO, DMO for mode-converted waves, DMO in ani sotropic media, or prestack divergence correction.