Shallow Qp and Qs estimation from multicomponent VSP data

Michelle C. Montano, Donald C. Lawton, Gary F. Margrave

VSP data give us direct access to the wavelet at different receiver depths without having to include reflections. The down-going wavefield has always been the key to estimate Q and correct the effects of seismic attenuation on the data. In this study we demonstrate that we can also use the up-going wavefield to estimate Q, particularly for the shallow, near-surface layers. Q factors are estimated from synthetic VSP down-going and up-going wavefields by using the dominant frequency matching method (CREWES). We also estimated Q from real VSP data by using the spectral-ratio method (Vista software) as well as the dominant frequency matching method. We found the spectral-ratio method to bemore sensitive to changes in the frequency bandwidth when we compare Q estimation from vibrator to dynamite sources. Also, we found that Q estimation for shallow layers is better using the up-going wavefield than the down-going wavefield. Combining both estimations provides the optimum understanding of Q variation with depth.