The wedge model revisited: A physical modeling experiment

To assess seismic amplitude effects commonly associated with the classic wedge model in geophysics, we built a scaled physical model of a simple high-velocity wedge immersed in water. In addition to demonstrating the well-known tuning effect related to thin beds, a 2D marine zero-offset seismic survey over the physical model shows a surprising number of high-amplitude dipping events corresponding to elastic multimodes, multiples, and mixed-mode reflections having nonreciprocal raypaths. These events cause additional complexities in the amplitudes of the top-wedge and base-wedge reflections that are not observed in simple acoustic seismic responses of the wedge model. Finite-difference, acoustic, exploding-reflector numerical model data, calculated using the same wedge geometry and velocity model, assisted in the identification of these events. It was found that the amplitudes of mixed-mode multiples in data recorded over high-velocity rocks with a wedge-like geometry might be significant. We also discovered that there is a maximum number of zero-offset pure-mode multiples within the wedge for a given wedge taper angle. Conventional P-wave migration of the physical model data confirmed that the multimode reflections degrade the quality of the migrated image.