| Summary: | The nonlinear behavior of soils can significantly modify the wavelet radiated from
vibrator trucks. In this paper, we describe a field experiment designed to measure the
nonlinear response of a natural soil formation in the near-field of a vibrator truck. A 267-kN
(30-ton) vibrator truck performed a step-sweep through a set of 201 discrete frequencies from
50-Hz to 10-Hz, which was repeated at 11 increasing source amplitudes. Steady-state
amplitude spectra for the source output measured on the vibrator truck are significantly
different than amplitude spectra for receivers located immediately adjacent to the vibrator
truck. Spectral ratios between the source and adjacent receivers show a systematic decrease
in peak frequency as the source amplitude is increased. Near-field measurements from
vibrator trucks provide a more accurate measurement of the source wavelet that includes soil
nonlinearity, and may ultimately lead to a method for optimizing the transmission of energy
through an arbitrary soil formation.
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