Near surface characterization using a 9-component refraction survey: Cochrane, Alberta

Darryl G. Parry, Donald C. Lawton

A 9-component refraction survey was undertaken in the town of Cochrane. The investigated stratigraphy includes fluvial deposits of the Bow River and bedrock. The source employed for this experiment was a wooden beam stuck by a large hammer. This source suffers in the SV mode from abundant generation of horizontal P-waves. The first break data were obtained by stacking and subtracting same polarity and opposite polarity records, giving a suite of traveltime data. Traveltime data have been interpreted to yield a velocity/depth structure for the survey location. P-wave data imaged the water table at about 14 m depth (VP = 910 & above ad 2660 m/s below). SH-wave data do not show the water table, but show the bedrock at about 26 m (VSH = 520 m/s above the bedrock and 1000 m/s within it). A more complete survey would include more shot offsets in order to apply more sophisticated interpretation schemes.