Abstract

A critical parameter in interpreting seismic refraction data with the generalized reciprocal method (GRM) is the reciprocal time, which must be available for each layer from which refracted rays return to the surface. The reciprocal time can be measured in the field, but this requires special equipment or procedures. Shooting to obtain the reciprocal time from each layer along a long seismic line may be operationally impractical. However, the method of phantoming arrivals overcame the problems. In phantoming, a reciprocal time is actually measured along any length of the seismic refraction line for any refractor and that value can be used as the reciprocal time in GRM processing if the first-break arrival times are phantomed properly. Realizing that the reciprocal time may be extracted from overlapping normal forward and reverse shots and phantoming the data accordingly will save much field time and expense. An example shows the results of using a reciprocal time measured across one spread for simultaneously processing and interpreting collinear, overlapping spreads.

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