NORMAL MOVEOUT STRETCH MUTE ON SHALLOW-REFLECTION DATA

This paper demonstrates the potential consequences of overlooking the significance of allowable stretch ratio when performing normal moveout corrections on shallow-reflection data. Two shallow reflection data sets with drastically different near-surface geologic settings conclusively show the significance of subtle changes in allowable stretch mute. An improper stretch mute can reduce the dominant frequency and bandwidth of a stacked reflection by as much as 50 Hz. The sensitivity of shallow reflections to offset may require allowable stretch selection accuracy to be within +/- 1 percent. It may be necessary to reduce the fold of an individual stacked shallow reflection by as much as 60 percent to avoid excessive degradation of wavelet properties and consequent loss of resolution. A proper normal moveout stretch mute can reduce distortion of reflection wavelet spectra caused by nonvertical incidence recording to less than 10 percent. Stretched reflection wavelets improperly muted can be misinterpreted on CDP stacked sections as stacked refractions or subtle stratigraphic features.