LITHOSPHERIC WIDE-ANGLE SEISMIC PROFILES USING STACKED AIRGUN SHOTS

The signal-to-noise ratio of marine wide-angle seismic profiles can be significantly enhanced by stacking multiple shots. Signals detected f rom airgun shots from a seismic ship repeated many times within a smal l source area (called ''stack shots'') can be stacked in a manner some what similar to common-mid-point processing of reflection seismic data . We collected two such ''stack shot'' profiles across the eastern mar gin of Newfoundland. At each shooting site,:36 closely spaced air un s hots were fired consecutively, and recorded along a profile made of ab out 400 land receivers at offsets of 100 to 455 km. While the data can be stacked in several different ways we show that a two-step techniqu e or ''two-pass stack'' is the most effective. The traces of each rece iver gather are first stacked at an aperture of 0.5 km along a slope o f 8 km/s (stacking with linear moveout). The stacked traces are then r eordered by increasing offset and stacked a second time along the same slope and with an aperture of 0.5 km or less. This technique is super ior to a direct stack in which all the traces would be stacked in one pass because it allows improvement in the data duality by the various methods designed for each phase of the two-pass stack. Our results sho w that the ''stack shot'' technique coupled with the ''two-pass stack' ' is a viable alternative. with less environmental impact, to using la rge, single explosions at sea.