Direct Calculation of Interval Velocities and Layer Thicknesses From Seismic Wide-Angle Reflection Times

Abstract

SUMMARY Wide-angle seismic reflection traveltimes generated by large explosions are used extensively to obtain both velocity and regional structure of the crust and upper mantle. The method most commonly used to calculate interval velocities and thicknesses (layer parameters) of a multilayered earth. supposed to consist of homogeneous, isotropic and horizontal layers, is based on Dix’s ( 1955) interval velocity formula, which needs a prior estimate of the rms velocity and traveltimes at zero offset. Use of Dix’s hyperbolic approximation to the non-hyperbolic wide-angle reflection times causes large errors in the determination of layer parameters. Currently, no direct method exists to extract the velocity information from such wide-angle seismic data. Here we propose a layer-stripping method, using the ray parameter, to calculate the layer parameters directly in a vertically heterogeneous earth from a set of wide-angle seismic reflection data. Synthetic reflection times contaminated by some realistic errors have been used to demonstrate the efficiency and reliability of the algorithms. Field examples using well-identified wide-angle reflection times illustrate the practical feasibility of the proposed method.