P-P and P-SV seismic imaging in the Triangle Zone, Canadian Rocky Mountain Foothills

Chakrit Sukaramongkol, Donald C. Lawton

Seismic-reflection data were recorded over the Triangle zone near Sundre by Petrel Robertson in January 1990. The survey line was approximately 15 km. in length covering both the eastern and the western limbs of the Triangle zone structure.

The data were processed with an emphasis on the shallow parts of the data. Attempts were also made to enhance deeper horizons which are of exploration targets. Velocity variations, both laterally and vertically, were observed, specially between the Triangle Zone core, a duplex and its eastern limb. Detailed velocity functions followed by corresponding statics corrections were found to be important factors in improving the stack section's quality. Three migration techniques, i.e., F-K(Stolt) migration, Phaseshift migration and Finite difference(F-D) migration were tested on the stacked data. The resulting migrated sections from these three techniques are of comparable quality. Signal to noise ratio of the final section was enhanced considerably by the applications of a band-pass filter and KLSTAK ( signal-to-noise ratio enhancement via the Karhunen-Love transform ) method.

Using sonic logs of 3 wells from the area and derived synthetic seismograms, geological information was tied to the seismic data. An interpretation of the final section is shown in Figure 6, in which the upper and the lower detachments including the duplex are well defined. Also, a pop-up structure which formed by minor thrust faults associated with the advancement into the foreland basin of an intercutaneous wedge was found below the hanging wall of the upper detachment fault. The presence of the pop-up structure indicates that the Foothills deformation front is not stable but moving toward the foreland.

Modeling studies show that time-structural highs presented at the deep horizons, e.g., Mississippian, Devonian and Cambrian formations are partially attributed to the shallow-lateral velocity variations. Further analysis also indicates that these lateral velocity variations are mild to moderate, and do not produce significant amounts of ray bending as expected.

This study also demonstrates the application of converted-shear wave ( P-SV ) data in structural mapping.