Cross-hole seismic tomography for engineering site investigation

Abstract

Abstract The results of cross-hole seismic tomography at sites where there is good geological control are presented. Comparisons have been made between the tomograms and the geological cross sections in order to assess the technique under in situ conditions. It is shown that while the geological sections do not contain velocity information they have provided structural constraints which provided fresh insight when interpreting the seismic tomograms. Processing artefacts in field-data tomograms, particularly when the angular ray coverage is incomplete, have been identified using ‘synthetic’ tomograms based on the geological section. In addition, velocity anisotropy and critically refracted arrivals were identified as likely causes of differences between ‘synthetic’ and ‘field data’ tomograms, given a knowledge of the geological section. It is proposed that cross borehole tomographic surveys should not be taken immediately at their face value in the absence of geological control.