Examining the phase property of the nonstationary vibroseis wavelet

We have observed that Vibroseis wavelets behave very much as if they are minimum phase. This was discovered by applying minimum-phase Wiener deconvolution to the separated vibroseis VSP downgoing waves and observing that the result is effectively a band-limited spike. Motivated by this finding, we simulated a synthetic nonstationary vibroseis wavelet in a constant-Q medium by nonstationary convolution and again we found it to be close to minimum phase. Furthermore, we applied minimum-phase Gabor deconvolution to the sweep-removed vibroseis record and correlated vibroseis data. We obtained very similar results from these two approaches. For the synthetic data, the deconvolved traces from both approaches are consistent with the input reflectivity. For a real shot gather, there are few differences between the deconvolved gathers from these two methods. These comparisons further confirm that the nonstationary wavelet embedded in the correlated surface vibroseis seismic data is approximately minimum phase.