Thin-Bed Interval Velocity Inversion

For an isolated thin layer producing a composite seismic event exhibiting an apparent RMS velocity, the RMS velocities of the top and base reflectors, and thus the reflector time locations as a function of offset, can theoretically be determined if the zero- offset time thickness is known. For layers in the vicinity of tuning, the time thickness can be inferred using spectral decomposition. Thus, the interval velocity of the layer can be determined from its moveout curve, even when top and base reflectors cannot be resolved. This extends the range of layer thicknesses over which interval velocities can be measured using moveout from above to somewhat below tuning. It also provides a framework for simultaneous full-waveform inversion of thin layers for multiple offsets.

The interval velocity determination has been applied to single-layer synthetic seismic data derived from a range of different models. Results obtained under favorable conditions show a high degree of accuracy ranging from ninety-seven to ninety-nine percent in estimating the interval velocity of a thin layer, while those obtained in the presence of noise show a large degree of variability and accuracy ranges from forty-eight to eighty-five percent.