Shallow P and S velocity structure, Red Deer, Alberta

Donald C. Lawton, Meredith A. McArthur, Rachel T. Newrick, Sarah E. Trend

A multioffset vertical seismic profile was acquired at a site near Red Deer, Alberta, using a compressional minvibe source. A five-level, three-component VSP tool with a 15 m receiver spacing was used for data acquisition over a vertical aperture from surface to 300 m depth. First arrivals of offset data revealed the presence of turning rays for both Pwaves and S-waves. Traveltimes and incident angles were inverted to yield a five-layer isotropic P-wave velocity model. P-wave velocity gradients of 10 s-1 and 5 s-1 were derived for the top two layers, respectively, and weak anisotropy ( = 0.02 and = 0.02) was deduced for the two shallowest layers. Direct S-waves were also recorded in the walk-away data. First-arrival traveltime and incident angle analysis yielded SV-wave velocity gradients up to18 s-1.