A method has been developed for calculating a zero-offset converted-wave synthetic seismograms using a sonic log and a time-variant estimate of the V P /V S ratio. The algorithm is based on the Goupillaud model, where it is assumed that the layer thicknesses are such that all interval times are constant. It is based on the modification of an existing algorithm, used to calculate zero-offset compressional wave synthetic seismograms, by integration of the sonic log in terms of a vertical traveltime for a downgoing compressional wave and an upgoing shear wave, and by introducing incident-angle dependence into the reflection coefficient calculation. This requires knowledge of the total depth to the base of each constant time interval (obtained from the velocity structure), and the source-receiver offset (based on the acquisition parameters).
The algorithm has been tested on a sonic log from central Alberta, and compared to a processed converted shear-wave stacked section.
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