FIG. T-1. Tau-p (τ-p) mapping. (a) An end-on seismic record is f(x,t) where x=source-geophone distance (offset) and t=arrival time. (b) Its tau-p transform is F(τ,p) where p=dt/dx=1/Va and τ=intercept time at x=0. The reciprocal of the apparent velocity, p, is called slowness. Hyperbolic reflections transform into ellipses, straight events into points (the direct wave into P1, the head wave into P2).