Inverting the head wave coefficient with multi-fold near-surface seismic refraction data

Summary The head wave coefficient (HWC), the refraction analogue of the reflection coefficient, is a complex function of the densities and the P- and S-wave velocities in both the weathered and sub-weathered regions. In general, the HWC increases with increasing P- and S-wave velocities in the weathered layer, but it decreases with increasing P- and S-wave seismic velocities in the sub-weathered layer. Unscaled S-wave velocities in the weathered and sub-weathered regions can be computed with the HWCs for each interface and the detailed P-wave seismic velocities in each layer, using various approximations for the HWC. In general, there is excellent agreement between the measured and computed HWCs. However, some form of traveltime-based estimate of the S-wave velocities is required to calibrate the amplitude-based estimates.