Velocity imaging by tau–<i>p</i> transformation of refracted seismic traveltimes

Abstract

ABSTRACT We present a new method for producing a ‘brute’ velocity image rapidly and automatically from traveltimes picked from densely sampled refraction data. The procedure involves imaging by data transformation from the time–offset domain into the tau– p (intercept–slope) domain, and does not include conventional modelling steps. Differences in apparent velocity and tau along reciprocal paths in the up‐ and downdip directions allow the estimation of the true velocity and geometrical position of the ray turning points. The tau–velocity–turningpoint ( τ – ν – x ) map distributes phases automatically on the basis of geometry and velocity to give a two‐dimensional representation of subsurface structure. This map may be converted simply to depth and two‐way‐time images. Such images have potential for direct geological interpretation, for use as a starting model for seismic inversion, for superimposition on to conventional reflection images, or for input into prestack depth migration and other processing routines.