Refraction traveltime curves (time-distance plots) showed a three-layer case for P-wave data and a two-layer case for S-wave data. The extra layer exhibited by the P-wave results was produced by the interface representing the seismic water table, a horizon apparently invisible to S waves. Data from both P and S surveys revealed a high-speed layer thought to be bedrock at a depth of 9 to 11 meters. However, the bedrock surface interpreted from the P-wave data was unreasonable undulatory.
The following recommendations resulted from this study. The Tt/T (transverse/transverse) shear-wave procedure, with 75 percent overlap and interpreted with both ABC and SIP methods, will map the depth to bedrock surface. If greater depth precision is required, surface-to-borehole seismic surveys should be run at carefully selected sites. Hammer impact can produce high-quality data in this area.
Jason Masoner