Near-surface seismic characterization from a sparsely sampled field data set

Andrew Mills, Kristopher A. Innanen

Multichannel analysis of surface waves (MASW) is a near-surface characterization technique used to estimate shear wave velocities and layer geometries of the shallow subsurface. Typically, MASW uses closely spaced geophones to adequately sample surface waves. In this study, a field data set acquired with greater than ideal receiver separation is used for near-surface velocity inversion.

The least-squares velocity inversion algorithm is developed, for application to shot records containing dispersive ground roll arrivals. The Priddis Thumper Experiment data set, consisting of a 200 m receiver line with 5 m geophone spacing, is used for this study. Individual shot records are stacked, interpolated, and filtered, to reduce spatial aliasing and isolate surface waves. The inversion is then applied to the dispersion curves generated from these processed shot records, producing 1D shear wave velocity profiles. 1D velocity profiles are generated for various source points and combined to produce a 2D velocity profile over the survey line. Bedrock depth is estimated at approximately 20 m, consistent with shallow borehole drill cuttings.