Nonlinear Soil Response in the Near-Field of a Vibrator Truck: Application to Land Seismic Surveys

Abstract

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.