A &tgr;-P slant stack algorithm is applied to shot point 16 of the 1986 PASSCAL Ouachita experiment to determine the optical one-dimensional velocity structure. Several enhancements to a standard slant stack algorithm are used to image a one-dimensional velocity function from the shot point gathered data. Because only postcritical reflections and refractions are needed to image a velocity function, significant muting of precritical energy is performed, which reduces the effect of noise in calculating the stack. For data sets with long offsets, scaling the data by a factor equal to or greater than offset distance compensates for the effects of geometrical spreading and attenuation. This enhances imaging of the deeper regions of the velocity model and balances amplitudes across the shot point gather. Finally, ray parameter-depth images can have difficulty imaging higher velocities, since for higher velocities, a small change in ray parameter results in a large increment in velocity. This problem is overcome by slant stacking in equal increments of velocity instead of ray parameter.

The enhanced slant stack algorithm is applied to shot point 16 of the 1986 PASSCAL Ouachita data set, which sufficiently satisfies the assumption of lateral homogeneity based on previous studies of the region. Other velocity models are found to be consistent with the envelope of velocity function imaged by the slant stack method. Maximum amplitudes on the &tgr;-P image are used as a constraint to delineate a more detailed velocity model. A seven-layer velocity model is derived for shot point 16 which is found to be similar to those of others who have studied the area. The top three layers are sediments associated with the gulf coastal plain, followed by a thick layer derived from sedimentation associated with the closing of the proto-Gulf of Mexico and the associated Ouachita orogeny. The determination of a more detailed velocity function from the envelope suggests somewhat higher velocities in the lower crustal layer than previous studies. However, given the one-dimensional assumptions of the method, as well as the signal to noise ratio of the data, the velocity envelope is the most important constraint on the velocity models and tectonic interpretation provided by this analysis. ¿ American Geophysical Union 1990