Reflection seismic data, acquired across the leading edge of the Alberta Foothills in the Fallen Timber Creek region, have been processed and interpreted to show geometries of frontal structures in the Triangle Zone. The Triangle Zone comprises an antiformal stack of Upper Cretaceous rocks that has been advanced into the foreland basin between upper and lower detachments. A pop-up structure located east of the current antiformal stack indicates the presence of layer-parallel shortening in this region and is interpreted to represent an early stage of the development of a new antiformal stack.
Seismic modelling shows that later undulating events in the seismic sections is attributed to lateral velocity variations within the Triangle Zone. Further modelling analyses indicate that far offsets can be detrimental in stacking. Therefore, the key to optimally image the Triangle Zone is to use small offsets with small shot intervals in data acquisition.
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