Seismic intercept time
= Seismic intercept time
{title2=$\tau=T-px$}
A ray's intercept time subtracts its tangent travel-time contribution at the receiver range. For a smooth branch, $dT/dx=p$ implies $d\tau/dp=-x$. Thus an intercept-time curve encodes range as its negative slope. Separate turning branches around a <low-velocity zone> must be retained rather than joined by fictitious rays.