A method of obtaining a velocity‐depth envelope from wide‐angle seismic data

Summary. Due to the non‐uniqueness of traveltime inversion of seismic data, it is more appropriate to determine a velocity‐depth ( v‐z ) envelope, rather than just a v‐z function. Several methods of obtaining a v‐z envelope by extremal inversion have been proposed, all of which invert the data primarily from either x‐p , or T‐p , or both domains. These extremal inversion methods may be divided into two groups: linear extremal and non‐linear extremal. There is some debate whether the linearized perturbation techniques should be applied to the inherently non‐linear problem of traveltime inversion. We have obtained a v‐z envelope by extremal inversion in T‐p with the constraint that the inversion paths also satisfy x‐p observations. Thus we use data jointly in r‐p and x‐p , and yet avoid the linearity assumptions. This joint, non‐linear extremal inversion method has been applied to obtain a v‐z envelope down to a depth of about 30 km in the Baltimore Canyon trough using x‐t data from an Expanding Spread Profile acquired during the LASE project. We have found that the area enclosed by the v‐z envelope is reduced by about 15 per cent using x‐p control on the T‐p inversion paths, compared to the inversion without x‐p control.