ISSN:
1365-2478
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Geosciences
,
Physics
Notes:
The idea of imaging beneath a high-velocity layer using converted waves has been popular since 1990. Because these wave types have their maximum amplitudes at mid- to far-offsets, the search for pure P-waves at the highly multiple-contaminated near-offsets can be avoided. For the Atlantic Margin, with buried thin-layered basalts, our quantitative study shows that the initial single-layered approach is not viable. Even in an unrealistic ideal geological setting, the amplitude of the symmetrical PSP-mode is far too weak to be recognized on towed streamer data. Furthermore, in the far-offset window, where locally converted waves have their strongest amplitudes, there is a multitude of other reflections, refractions and interbedded multiples, which have similar moveouts and, often, higher amplitudes. Without the removal of these events, a reliable image of the subsurface cannot be produced. We show that even if this problem were solved, it would be far easier to use the P-wave reflection from beneath the basalt at near-offsets. Our study shows that this wave type is by far the strongest response. A borehole-derived model using a thin-layered basalt sequence reveals that the strongest locally converted wave has an asymmetrical path and is 10 times weaker. All our results indicate that the pure P-modes provide the best chance of imaging sub-basalt sedimentary interfaces.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1046/j.1365-2478.2003.00367.x
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