Migrated 3D seismic reflection data from the same acquisition program used in this study were discussed in (48). As part of the processing of the reflection seismic data, amplitude normalization was performed, such that the highest observed reflection amplitude had a value of unity. Geologic horizons shown in Figs. 2 and 3 were based on a calibration well that was drilled to a total vertical depth of 3607 m from a surface elevation of 890.9 m (48). The top of Precambrian basement is deeper than local well control and so was correlated using a nearby Lithoprobe deep reflection survey, which has synthetic ties to Precambrian well penetrations (49).

Images extracted from the 3D seismic volume can be used to investigate structural features within the region at various depths. We first flattened the reflections at the Wabamun Formation top to highlight geological features that were present before and during deposition of this layer. Figure 2B shows a cross section through the 3D seismic volume displaying seismic amplitudes as a function of depth, which can also be used to visualize structural features, as well as stratigraphy. Figure 3 (A and B) shows a horizontal slice through the 3D seismic volume at a depth of 3386 m, with the positive and negative seismic amplitudes highlighting various structural features discussed below.

Although cumulative fault displacement is inferred to be dominantly perpendicular to the horizons, subvertical faults can nevertheless be identified on the basis of localized curvature anomalies (50) or changes in apparent dip of reflections that mark the locations of hinge lines (49). Channel and reef edge features can also be identified in Fig. 2 in a similar manner; however, the interpreted fault strands span multiple stratigraphic horizons and correlate with the linear features in Fig. 3. Our estimate for maximum post–mid-Devonian fault displacement was constrained by the lack of a discernible lateral offset on the reef edge. Figure 3A shows that there is little discernible offset of the mid-Devonian Swan Hills reef margin where it is intersected by the observed faults. Some seismicity forms a cluster aligning parallel to the reef edge (17), suggesting that higher mechanical strength of the reef facies relative to the off-reef facies may have influenced faulting. The theoretical resolution limit for migrated seismic data is equal to the spatial sampling interval; thus, based on the common midpoint interval for the data of 30 m, we estimated that the offset on the reef margin can be no greater than 50 m (allowing for some uncertainty).

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