Datum Shift and Velocity Estimation
, by Jon F. Claerbout
I derive an equation for a family of hyperbolas with various datums,
each member of the family having a different asymptote velocity
but the same rms velocity. Nonhyperbolic traveltime is readily mimicked by such datum-shifted hyperbolas. Datum adjustment was installed in the Overlay program. Dragging the mouse up and down changes the datum of the overlay hyperbola (after NMO it is a difference of two hyperbolas).
Two of the Yilmaz field profiles gave datums of 120-220ms. An Alberta profile was found to be a textbook quality example.