Inversion of ground roll dispersion for near-surface shear-wave velocity variations

Multicomponent and shear wave seismic surveys are becoming increasingly more common in today's exploration world. They offer additional information about the subsurface not available from conventional P-wave surveys. However, because it is often difficult to make accurate measurements of shear wave refracted events in shot gathers, reasonable estimates of the near-surface shear wave velocity field for static calculations are hard to make. An alternative method for determining the near-surface shear wave velocity profile is described which makes use of the information contained within ground roll, energy which is normally considered to be a nuisance in seismic data. Ground roll propagates dispersively, this dispersion is principally a function of the nearsurface shear wave velocity field. Linear inverse theory is employed to extract estimates of the nearsurface shear wave velocity profile from measurements of the dispersion in source generated ground roll. Similar techniques have been used by earthquake seismologists to extract shear wave velocity profiles of the Earth's crust and mantle from measurements of the dispersion in surface waves generated by earthquakes.