USING GUIDED P-WAVES TO OBTAIN A HIGH RESOLUTION P-WAVE VELOCITY MODEL OF THE NEAR SURFACE

A 2D P-wave velocity model of the near surface was created from fundamental mode dispersion curve trends of guided P-wave phase velocities. The fundamental mode of the dispersion curve trends was identified at a majority of geophone locations in our data set. Each of these geophones was selected as the central geophone within an optimum window (aperture), providing a laterally varying set of phase velocities that was used to image the dispersive properties of the underlying strata. A user defined 1D P-wave velocity model was created and forward modeled to obtain a theoretical/calculated phase velocity trend at each location. The calculated trend was compared to the observed phase velocity trend at each central geophone location and the geologic model was run through an iterative inverse procedure until the norm of the difference between the calculated and observed phase velocity trends reached a minimum. The resulting suite of 1D P-wave models was then combined to form a 2D P-wave velocity model of our study area. Our inverted P-wave velocity model was then compared to a seismic refraction model to check the accuracy of our results. We show that it is possible to create a high resolution P-wave velocity model of the near surface by using guided P-waves, but did observe large variations in our velocity values and depth to reflectors when comparing our results to a seismic refraction model. The large variations we observed can be explained by difficulties in our dispersion curve identification due to weaker guided P-wave energy and modal jumps within this data set