Experimental and theoretical evidence is presented to show that a strong seismic event, occurring late in a record and at distances beyond the critical distance, is a wide angle reflection and not a refraction from a high velocity limestone formation. The evidence includes studies of the effects of anisotropy on the velocities along reflected and refracted paths and of the variation of amplitude of the event with distance. The paper also describes how the results of broadside wide angle reflection shooting may be combined with normal reflection shooting to map strongly dipping limestone structures. An application to a profile through a foothills well in western Canada is included.

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