Velocity for inversion of 3D seismic surveys

Abstract

Abstract In the paper ‘Revisiting Dix’s RMS Velocity’ (James, 2018) it was shown that there is no single velocity function that will accurately correct NMO for all the offsets in a seismic shot record. For the simplest possible model, with more than one layer NMO, velocity is not hyperbolic. Therefore, since the idea that ‘NMO velocities can be approximated by RMS averages of interval velocities’ is pervasive in seismic data processing we need some adjustment to our procedures. The impetus to study RMS velocities came from the practice of muting far offsets when performing AVA/AVO analysis and the far offsets were not flat in time after NMO. With the muting, the information at far offsets was discarded. Historically NMO velocities were picked directly and so it was never necessary to have reflections that were not flat after correction. Muting for NMO was restricted to the region where refractions and or reflections interfered with each other.