A comparison of the methods of engineering seismic refraction analysis and generalized linear inversion for deriving statics and shallow bedrock velocities.

摘要

Refracted first arrivals recorded in high resolution seismic surveys contain key information for deriving statics and are important for improving the resolution of reflections. They may also be useful for estimating shallow bedrock velocities as an aid to interpreting bedrock geology below the weathered layer. Two different techniques to estimate near-surface information are described in this thesis: one is a generalized linear inversion (GLI) technique that uses damped least squares to estimate statics and Occam's method to estimate lateral variations in the bedrock layer for interpretation of geology; the other employs the reciprocal method and the smoothing of forward and reverse apparent velocity profiles in the analysis. A comparison is made between the effectiveness of these techniques for a synthetic data set and 3 high resolution data sets collected at two mine sites in central Newfoundland for mining exploration purposes.;For these data there was no discernible difference in the quality of the stacked seismic sections for the data sets processed with statics derived using GLI compared with the reciprocal method. Lateral variations in bedrock seismic velocity are resolved to the same degree by both direct smoothing and Occam's technique, resulting in similar geological interpretations. The resolution of the bedrock velocities in both methods depends on the acquisition parameters, the signal-to-noise ratio in the field, and the amount of smoothing applied to the data. Future work may be to use a more efficient numerical procedure in GLI to handle sparse matrices and to make a comparison of these techniques for the case of diving raypaths.