Velocity-independent Layer Stripping of Pp and Ps Reflection Traveltimes

Building accurate interval velocity models is critically important for seismic imaging and amplitude inversion. Here, we adapt the so-called “PP+PS=SS” method to devise an exact technique for constructing the interval traveltime-offset function in a target zone beneath a horizontally layered overburden. The algorithm is designed for arbitrarily anisotropic target layers, but the overburden is assumed to have a horizontal symmetry plane (i.e., up-down symmetry). Important advantages of this layer-stripping technique compared to the existing Dix-type equations include the ability to handle the asymmetric moveout of mode-converted waves and laterally heterogeneous target layers with multiple curved reflectors. Also, our method is entirely data-driven and does not require knowledge of the velocity field anywhere in the medium. The computed interval moveouts of PPand PS-waves can be used to estimate the interval parameters of transversely isotropic layers with a tilted symmetry axis (TTI), which is essential for accurate imaging in fold-and-thrust belts (e.g., the Canadian Foothills) and near flanks of salt domes. Other applications include the dip-moveout inversion for the P-wave time-processing parameter η and stable computation of interval long-spread (nonhyperbolic) moveout for purposes of anisotropic velocity analysis.