Inversion of Rayleigh wave group velocities from high-explosive tests

Rayleigh-wave group-velocity have been obtained by the moving window analysis of high-explosive ground motion records at McCormick Ranch, Kirtland AFB. Fundamental mode velocities (225 to 264 m/s) were determined for the period range 50-160 ms at a recording distance of 229 m. Also, higher mode dispersion was observed for periods 25-60 ms with group velocities of 280 - 305 m/s. Possible spall phase dispersion was observed at distances of 11-36 m. Seismic refraction surveys provided initial model parameter for the test site. An iterative inversion method was used to estimate the shear velocity distribution. Constant layer thickness and attenuation values equal 50-100 were additional initial constraints. Inversion results yielded a shear-wave velocity model of 245-610 m/s to a depth of 24 m at McCormick Ranch.