Near surface S-wave seismic reflection profiling– new approaches and insights

Multi-component high resolution seismic reflection profiling has been extensively tested over a wide variety of ground surfaces across the southern provinces of Canada, showing new potential for applications of the method in groundwater and natural hazards research. The near-surface shear-wave reflection method using vibratory sources and short spacing land streamers equipped with three-component receivers is an excellent tool for accurately characterizing shear-wave velocities and recording optimal, non-aliased shear-wave data in the most polarized direction. A small portable multi-component vibrator developed at the Geological Survey of Canada (GSC) named ‘Microvibe’ provides higher frequency S-wave and P-wave signals than can be acquired with a Minivib I. In this paper we show that the shear-wave polarization can vary with depth and it may be necessary to combine multiple components together to achieve an optimized stacked section. Significant velocity anisotropies of up to 15% have been observed between the horizontal and vertical directions when using this multicomponent Microvibe source. We make key recommendations based on time and space sampling recording windows for successful near surface PP-wave, PS-wave and SS-wave seismic reflection surveys. Using field examples and velocity measurements, we show the complexity of velocities in non-homogeneous media in the near surface.