| Abstract: | Three common expressions for the normal moveout of recorded seismic events are investigated by numerical simulation procedures for accuracy in predicting the root-mean-squared (RMS) or mean, as the case may be, subsurface velocity function from seismic data. The principal investigation, for which detailed error curves are shown, was derived for a stochastic subsurface model composed of strata with thicknesses ranging up to 91.4 m (300 ft) and boundary velocity contrasts ranging up to 45.7 m/sec (150 ft/sec); there was a 95 percent chance of velocity increase with increased depth. The effects of changes in the basic statistical subsurface model are discussed. The results appear to confirm the judiciousness of the choices of to and (x/z') as plotting parameters to be used with the respective percent errors in the three expressions, where are, respectively, the zero-offset arrival time of, the offset distance of, and the mean-squared velocity encountered by a seismic ray. Out of the three normal-moveout expressions examined, the “straight-raypath” expression with the RMS velocity substituted as its velocity term proved to be the most accurate in the determination of velocities. |
