The Belgica Mound Province, offshore Western Ireland: Results from deep-towed and surface-towed reflection seismic data
Guidard, S.; Henriet, J.-P.; Vanneste, M; Versteeg, W. (2000). The Belgica Mound Province, offshore Western Ireland: Results from deep-towed and surface-towed reflection seismic data. Eos, Trans. (Wash. D.C.) 81(48): F635
In: Eos, Transactions, American Geophysical Union. American Geophysical Union: Washington. ISSN 0096-3941; e-ISSN 2324-9250, more
At present, RCMG is developing a high-resolution deep-tow seismic acquisition system: acoustic pulses are generated by a surface source (very-high-resolution sparker or high-resolution watergun) and recorded by a streamer array towed at submersion depths up to 750 m. Acoustic signals received in the streamer are transmitted through an 1100 m long cable via fibre optic technology and digitized in the acquisition computer. The data are at the same time recorded by a common surface-towed streamer (so-called Jumbo configuration). The objectives for developing such a system are threefold: (1) to improve both the lateral (Fresnel zone) and vertical resolution, (2) to acquire lake-type quality records due to submersion and (3) to obtain a system that is compatible with and complementary to conventionally-used systems. A disadvantage is the necessary application of detailed geometrical corrections.During the R.V. Belgica 16/00 expedition, several seismic profiles have been recorded with the JUMBO configuration in the Belgica Mound Province, offshore Western Ireland. Mound structures appear as nearly transparent patches with only very weak and chaotic internal reflections and diffractions. Their height varies from a few 10 to over 100 m. Some rise above the sea floor while others are buried features. Beneath the erosional base of the mounds, sediment deposition has a sigmoidal configuration with high reflection amplitude. At the sides of a mound structure, some enhanced reflections occur with reversed polarity. Encoded instantaneous frequency displays reveal a sharp decrease of frequency content at exactly the same sub-bottom depths, a feature typical for attenuation. Whether this is attributed to the presence of free gases is unclear. In general, the mound structures itself do not appear as a low-pass frequency filter at the used acquisition frequencies while no significant velocity effects (pull-up, pull-down) are observed beneath the buried mound features.Although the data quality of the deep-tow streamer is not perfect, first results look very promising. Compared to the signals recorded with the surface streamer; the lateral resolution of the deep-tow system is strongly enhanced. The elimination of swell effects furthermore is an important advantage for the overall data quality.
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