Application of Shallow Vertical Seismic Profiles (VSP) in Interpreting Surface Seismic Data

The vertical seismic profile (VSP) is an efficient and accurate method of tying known geology from a borehole given in depth to the surface seismics ection presentedin time. The VSP enablest he geophysicistt o directly observet he effects of the geology on the seismic wavelet generated at the surface. At each geological interface the resulting transmissionr,e flection, conversion and attenuationc haracteristic of the seismicw avelet can be observed directly from a VSP. Much like common depth point (CDP) reflection techniques VSP’s have been adapted from advances in petroleum exploration. VSP data follows a similar processings equenceto CDP data with stepss uch asg eometiy, first break picks, deconvolution, and stacking. VSP data also has exclusive processing steps such as removal of down going waves and enhancing upgoing waves. WELLPRO, licensed by GENIX Technology Ltd., was used to process the VSP data. Displaying VSP data for interpretation includesm ergingw ell logs (measuredin depth) andt he processedV SP along with a synthetic seismogram into a composite known as an L-plot. VSP data collected by the Geologic Survey of Canada (GSC) as part of a regional hydrogeological investigation of the Oak Ridges Moraine, north of Toronto, Ontario, are used as examples in this paper. Synthetic traces were generated by doing a 140 ms corridor stack of the processedV SP andc an be directly correlated with surfaces eismicd ata acquiredn earby. The VSP verified the existence of three reflectors at approximate depths of 45 metres, 68 metres, and 88 metres and also produced a velocity profile based on depth and one-way travel time, This enables an exact time versus depth interpretation of the surface seismic data at this location.