Optimum pseudo-random sweeps for vibratory surveys to reduce risk of damaging buildings

Abstract

Optimized pseudo-random sequences are calculated and tested for the purpose of reducing possible damage to buildings by vibratory sources during seismic reflection acquisitions. The common linear sweeps used at vibratory measurements cause resonance in infrastructure, hence the potential for damage increases. Pseudo-random sweep signal can be a natural choice to decrease resonance effects, but the sequences produced by simple random number generators have disadvantages. In this paper requirements are set and an optimization process is employed for producing pseudo-random sweeps to achieve satisfactory results. Two strategies are considered for pre-processing: autocorrelation and deconvolution. Analysis of optimum sweep examples shows, that the peak energy is increased, while side-lobe energy is decreased compared to a simple pseudo-random sweep. Field tests reveal, that the peak particle velocity values are reduced substantially, while correlated and deconvolved records are of similar quality to a linear sweep driven record.