What’S Wrong With Shallow Seismic Refraction Methodology?

The methods currently used to analyse shallow seismic refraction data are inefficient in their use<br>of arrival times for determining shallow velocity structure. A strategy for making more effective<br>use of the data is as follows. Firstly, depths to bedrock or a sub-weathering layer are estimated<br>by a combination of two approaches: the reciprocal (or generalised reciprocal) method and a<br>least-squares difference method. Seismic velocities in each layer are then calculated by<br>constructing a single ‘static-corrected’ travel-time versus distance relation. This is accomplished<br>using a least-squares inversion procedure to correct for baseline differences between shots that<br>have common recording locations, and time reversal to make all seismic energy appear to travel<br>in one direction. The resulting travel-time distance relation is then smoothed to give a preferred<br>velocity solution as a function of position. Hammer seismic surveys provide examples of the<br>effectivenessof the new methodology, and assist in formulating simple guidelines for maximising<br>the resolution of seismic refraction surveys while minimising field costs.