Over the past year, CREWES designed and built a new shear-wave seismic source for multicomponent near-surface seismic studies. At the heart of the source is a 100 kg hammer that is accelerated by compressed nitrogen over a pressure range from 500 to 2000 psi. The source mast can be operated in a vertical mode for generating P-waves and it can rotate +/- 45 degrees transverse to the longitudinal axis of the trailer, and will generate down-going P-wave and S-waves simultaneously. Pure-mode down-going S-waves are generated by subtracting records taken with the mast rotated in the positive and negative tilt modes. Initial test data generated by this source show that good quality P-wave and S-wave data can be obtained, with source-receiver offsets of several hundred meters. A vertical seismic profile experiment shows high-amplitude energy to the bottom of the well at 149 m depth.
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