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A quantitative study on the use of converted waves for sub‐basalt imaging
Author(s) -
Hanssen Peter,
Ziolkowski Anton,
Li XiangYang
Publication year - 2003
Publication title -
geophysical prospecting
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.735
H-Index - 79
eISSN - 1365-2478
pISSN - 0016-8025
DOI - 10.1046/j.1365-2478.2003.00367.x
Subject(s) - geology , amplitude , basalt , reflection (computer programming) , borehole , regional geology , offset (computer science) , sedimentary rock , surface wave , igneous petrology , economic geology , mineralogy , geophysics , seismology , optics , engineering geology , paleontology , physics , metamorphic petrology , tectonics , volcanism , computer science , programming language
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.