Stacked Data

 

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Figure 2 Stacked section after full processing and prestack migration.

 

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Figure 3 Zoomed and gained stacked section after full processing and prestack migration.

A stacked section of the data after prestack migration and full processing can be seen in Figure . A gained and windowed stacked section is shown in Figure . The seafloor reflection occurs at about 4.3 s two-way travel time, indicating a water depth of over 3 km, and decreases in depth gradually along the line. It is followed by a strong bottom simulating reflection at a distance between 25 km and 52 km, suggesting the presence of methane hydrates in this region. In a small region above the BSR, there is a ``quiet'' zone where no diffractions or reflections are visible. Dillon et al. 1993 connected this zone, which is present above most of the BSRs in the region of the Blake Outer Ridge, to the presence of hydrate in the sediment. A fairly bright ``flat spot'' reflection is apparent beneath the BSR at approximately 5.4 s two-way traveltime, which does not parallel the seafloor or BSR reflection events. No BSR is visible in the first half of the seismic line, between 0 and 25 km distance, and the sediment structure appears fairly uniform. The maximum dips of the events throughout the entire length of the data are less than 2$^{^{\circ}}$, thus representing simple geological structures.

The zoomed and gained part of the stacked section, as shown in Figure , furthermore enhances the structure above and below the BSR. It clearly displays some events cutting across the BSR. Since the BSR is not a lithological but a phase boundary, such crossing of events can often be observed. It is a characteristic by which BSRs can be easily recognized.