Constant phase rotations and constant time shifts are the constant and slope of a polynomial approximation to the seismic wavelet phase. Errors in the estimation of either one cause a bias in the subsequent estimation of the other. It follows that estimations of time-shifts followed by subsequent phase estimates, as is commonly done in well tying, is subject to this bias meaning that alignment errors cause compensating phase errors and a very questionable solution. A strategy is presented to overcome this bias whereby the alignment is estimated though correlation of trace envelopes and it is demonstrate that this is much more accurate. This strategy is then extended to the nonstationary case where, in a series of numerical experiments, it is demonstrated that nonstationary phase rotations and time delays can be reliably measured with good quality data.
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