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The signal-to-noise ratio of marine wide-angle seismic profiles can be significantly enhanced by stacking multiple shots. Signals detected from airgun shots from a seismic ship repeated many times within a small source area (called “stack shots”) can be stacked in a manner somewhat similar to common-mid-point processing of reflection seismic data. We collected two such “stack shot” profiles across the eastern margin of Newfoundland. At each shooting site, 36 closely spaced airgun shots were fired consecutively, and recorded along a profile made of about 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 technique or “two-pass stack” is the most effective. The traces of each receiver gather are first stacked at an aperture of 0.5 km along a slope of 8 km/s (stacking with linear moveout). The stacked traces are then reordered 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 superior to a direct stack in which all the traces would be stacked in one pass because it allows improvement in the data quality by the various methods designed for each phase of the two-pass stack. Our results show that the “stack shot” technique coupled with the “two-pass stack” is a viable alternative, with less environmental impact, to using large, single explosions at sea.
|Department(s):||Science, Faculty of > Earth Sciences|
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