DIRECT CALCULATION OF INTERVAL VELOCITIES AND LAYER THICKNESSES FROM SEISMIC WIDE-ANGLE REFLECTION TIMES

Wide-angle seismic reflection traveltimes generated by large explosion s are used extensively to obtain both velocity and regional structure of the crust and upper mantle. The method most commonly used to calcul ate interval velocities and thicknesses (layer parameters) of a multil ayered earth, supposed to consist of homogeneous, isotropic and horizo ntal layers, is based on Dir's (1955) interval velocity formula, which needs a prior estimate of the rms velocity and traveltimes at zero of fset. Use of Dir's hyperbolic approximation to the non-hyperbolic wide -angle reflection times causes large errors in the determination of la yer parameters. Currently, no direct method exists to extract the velo city information from such wide-angle seismic data. Here we propose a layer-stripping method, using the ray parameter, to calculate the laye r parameters directly in a vertically heterogeneous earth from a set o f wide-angle seismic reflection data. Synthetic reflection times conta minated by some realistic errors have been used to demonstrate the eff iciency and reliability of the algorithms. Field examples using well-i dentified wide-angle reflection times illustrate the practical feasibi lity of the proposed method.