An interface inversion has been tested and applied to wide-angle reflection data from the 1986 PASSCAL Ouachita experiment. An interface corrugation with a relief of 10 km and a width of 30 km was successfully imaged in a test of the interface inversion. Velocity-depth curves derived for shot points 14--19 using the tau-sum method are similar to an average one-dimensional velocity model from forward modeling using travel time correlations from southern profiles 14--19. The similarity of these velocity-depth curves positioned over the southern half of the PASSCAL experiment suggests that crustal structure in this region is approximately laterally homogeneous. Lower crustal velocities are not well resolved due to the recording on most profiles of only small segments of the travel time triplications. A two-dimensional velocity structure was derived by using the average one-dimensional velocities for the deeper crustal layers and formally inverting for depth to interfaces. The final inversion model is found to be consistent with previous refraction interpretations south of the Ouachita orogenic trend and concurrent interpretations of the PASSCAL data set.

Inversion results for the central and southern portion of the PASSCAL profile indicate a depth of 10--12 km for a midcrustal layer which thins southward from approximately 10 km to about 4 km. A lower crustal layer with an average thickness of 12 km and a Moho depth of approximately 29.5 km are also determined. Interference depths are in agreement with a normal moveout stack of the PASSCAL data set. In particular, the shallowing of the Moho to a depth of 30 km over the northern 50 km of the profile matches previous interpretations of the data set and has been interpreted here and in previous studies as the location of the Paleozoic continental margin. Geophysical studies of the modern Atlantic continental passive margin provide the simplest comparison to the crustal structure derived here. The lower crustal layer found south of the shallowing of the Moho to 30 km beneath the PASSCAL profile is analogous in thickness and position to rift stage lower crust. However, other tectonic interpretations are possible given the uncertainties in velocity and lithology relationships. ¿ American Geophysical Union 1990