Using Variations in Amplitude With Offset and Midpoint to Constrain Tomographic Inversion

Seismic amplitudes are shown to provide useful information about rapid lateral velocity changes. Inversion of seismic amplitude data is used to constrain conventional traveltime tomographic inversion, producing an improved velocity field. Amplitude measurements recorded over a time gate, and normalised for each offset, can be assumed to be influenced solely by absorption in the overlying rocks. A normalised image of seismic velocity can be produced by using this simplification to invert seismic amplitudes. Lateral velocity gradients calculated from the amplitude inversion are used as a filter to constrain the traveltime solution. This approach results in sharper resolution of lateral velocity variations. This technique is applied to a model of a surface reef from the Northwest Shelf of Australia.