Predicting rugged water-bottom multiples through wavefield extrapolation with rejection and injection

Predicting rugged water-bottom multiples and peg-legs

Wave equation multiple modeling consists of downward wavefield extrapolation from the sea surface to the sea floor and upward wavefield extrapolation from the sea floor to the sea surface. In general, the water velocity and the water-bottom elevation can be measured with relative ease by field survey or estimated from seismic data. It is relatively difficult or expensive to get an accurate interval velocity of the subsurface by seismic velocity analysis when the lateral velocity varies strongly. Therefore, if I can use only the water velocity and water-bottom elevation to predict the water-bottom multiples and peg-legs, the efficiency will be improved.

One of the solutions to the above-mentioned issue is to make an approximation to the rugged water bottom. The approximation depends on which algorithm I choose. For example, if the wavefield extrapolation is based on the Kirchhoff integral algorithm, a dipping flat surface can be selected to approximate the rugged water bottom, so that the calculation of the Green’s function does not involve the subsurface velocity. Similarly, if the wavefield extrapolation is based on the phase shift or finite difference algorithm, a horizontal flat surface can be chosen. Obviously, these approximations to the real water bottom will sacrifice effectiveness for efficiency.

To improve the efficiency without loss of effectiveness, I present a so-called wavefield extrapolation with rejection and injection.

Predicting rugged water-bottom multiples through wavefield extrapolation with rejection and injection