A robust Q estimation scheme for adaptively handling asymmetric wavelet spectrum variations in strongly attenuating media

The central frequency shift technique for estimating wave attenuation in seismic exploration assumes a quasi-symmetric amplitude spectrum and has its limitations in low quality factor (Q) regions. The asymmetry of the wavelet amplitude spectrum becomes more pronounced during wave propagation, so using a constant parameter n (the asymmetry index estimated) in the modified frequency-weighted exponential formula method to estimate Q still leads to errors and can degrade the results of inverse Q-filtering. We have derived a new Q-estimation scheme that does not require constant parameter fitting that also works for strongly asymmetric receiver spectra. It is based on forming a synthetic wavelet as the geometric mean of the source spectrum (approximated by the near-source receiver spectrum) and the subsequent attenuated (receiver) wavelet spectrum. The changing centroid frequency and variance of this new wavelet as a function of traveltime can automatically adapt to a changing asymmetric spectrum caused by attenuation. It yields more stable and accurate results, especially in low-Q regions. This adopted approach is successfully applied to synthetic data and vertical seismic profile field survey data and proves to be superior to previous frequency-shift methods.