Seismic programs in the Alberta foothills area differ from those of a normal plains project in that structural features of a complex tectonic nature are the prime objective. The obstacles are twofold in nature: technical and operational. One of the most serious technical problems in some foothills areas is the difficulty experienced in acquiring usable reflection records, due to: disturbed conditions at reflection horizons depths, rough surface topography, and steeply dipping surface beds. Another serious problem is the influence of rapid lateral variations in vertical velocity caused by excessive thickness of a high or low velocity bed due to repetition by faulting. Wherever the velocity abnormality occurs in the section, all horizons below it will have the reflection time and apparent depth affected. From an operational view, continuous reflection shooting is restricted by limited accessibility can be minimized by the use of the refraction type of shooting. This method requires an essentially straight line which need be accessible at points 1 to 1-1/4 miles apart. The velocity of the Paleozoic limestones are markedly higher than the Mesozoic shales and sands. Therefore, a high speed marker bed exists, overlain by lower speed material. This situation is essential to successful refraction shooting. It is usually impossible to map a bed below the first high speed Paleozoic marker capable of transmitting refraction energy. The refraction method is usually used as a reconnaisance tool with detail being established by reflection shooting.

Abstract by R. R. Williams, P & N G Conservation Board.

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