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.
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