Abstract
The multistreamer Side-Looking Seismic system presented in this paper makes a sonograph of uncovered or buried crustal topography, thus revealing the structural fabric of the oceanic basement, even when this is covered with a sedimentary layer. Major elements of the system are an airgun as a sound source, five single-channel parallel streamers and two minicomputers for signal capture and processing.
The system is used simultaneously for enhanced single-channel seismic profiling and for side-looking seismics. A vertical section with an improved signal-to-noise ratio and a suppression of side-echoes is produced on a digital seismic recorder. Primary side-looking seismic output in the form of 5 profiles with different angles of incidence is obtained within 10 seconds. This part of the processing can be done in real time.
In sediment-covered areas the low frequencies used cause the slanted profiles (the side beams in the primary output) to be side-looking sonar images of buried topography. The projection process yielding final side-looking output corrects for slant range deformation caused by the water column and, if necessary, for deformation caused by refraction within the sedimentary column. The result approaches a conformal map of the structure of the traversed basement. Swath width is mainly determined by water depth and refraction effects in the sediment. In Madeira abyssal plain a swath width of 8000 m was attained in a water depth of 5000 m.
Within the swath, oceanic basement structures are recognized in the form of elongate more or less parallel reflectors. They are interpreted as buried spreading topography. The lack of side-echoes within fracture zones combined with typical wall signatures can be used to trace fracture zones. These features are demonstrated for an area in Madeira abyssal plain.
Similar content being viewed by others
References
Albers, V. M.: 1965, ‘Underwater Acoustics Handbook—II’, Pennsylvania State University Press.
Ballard, R. D. and Van Andel, T. H.: 1977, ‘Morphology and Tectonics of the Inner Rift Valley at Lat 36°50′ N on the Mid-Atlantic Ridge’, Geol. Soc. America Bull. 88, 507–530.
Bracewell, R. N.: 1978, ‘The Fourier Transform and Its Applications’, 2nd edition, McGraw-Hill, New York.
Collette, B. J., Slootweg, A. P., Verhoef, J., and Roest, W. R.: 1984, ‘Geophysical Investigations of the Floor of the Atlantic Ocean Between 10° and 38° N (Kroonvlag project)’, Proc. Kon. Ned. Ak. Wet. Series B, 87(1), 1–76.
Denham, C.: in press, ‘Fourier Downward Continuation of Echosoundings’, J. Geophys. Res.
Doornbos, D. J.: 1978, ‘On Seismic-Wave Scattering by a Rough Core-Mantle Boundary’, Geophys. J. R. Astr. Soc., 53, 643–662.
Fornari, D. J., Ryan, W. B. F., and Fox, P. J.: ‘Sea MARC 1 Side-Scan Sonar Imaging Near the East Pacific Rise’, Eos Trans. AGU 64, 482.
Hamilton, E. L.: 1980, ‘Geoacoustic Modeling of the Sea Floor’, J. Acoust. Soc. Am. 68(5), 1313–1340.
Hanrahan, J. J.: 1980, ‘A Perspective on Bottom Reflectivity and Backscattering’, in Kuperman, W. A. and Jensen, F. B. (eds.), Bottom-interacting Ocean Acoustics, NATO Conference series IV, Vol. 5, Plenum, New York.
Harris, F. J.: 1978, ‘On the Use of Windows for Harmonic Analysis with the Discrete Fourier Transform. Proc. IEEE 66, 51–83.
Houtz, R. E.: 1980, ‘Comparison of Velocity-Depth Characteristics in Western North Atlantic and Norwegian Sea Sediments’, J. Acoust. Soc. Am. 68(5), 1409–1414.
Hussong, D. M. and Fryer, P.: 1983, ‘Back-Arc Seamounts and the Sea MARC II Seafloor Mapping System’, Eos Trans. AGU 64, 627–632.
Laughton, A. S.: 1981, ‘The First Decade of Gloria’, J. Geophys. Res. 86, 11511–11534.
Luyendyk, B. P. and Macdonald, K. C.: 1977, ‘Physiography and Structure of the Inner Floor of the Famous Rift Valley: Observations with a Deep-Towed Instrument Package’, Geol. Soc. Am. Bull. 88, 648–663.
Matthews, D. J.: 1939 (reprinted 1970), ‘Tables of the Velocity of Sound in Pure Water and in Sea Water, for Use in Echo Sounding and Sound Ranging’, Second edition, British Admiralty Hydrographic Department, No. 282.
McCord, H. L.: 1978, ‘Synthetic Aperture Radar Systems’, ICS course 475.
Papoulis, A.: 1962, ‘The Fourier Integral and its Applications’, McGraw-Hill, New York.
Ramberg, I. B., Gray, D. F., and Raynolds, R. G. H.: 1977, ‘Tectonic Evolution of the FAMOUS Area of the Mid-Atlantic Ridge, lat 35°50′ to 37°20′ N’, Geol. Soc. Am. Bull. 88, 609–620.
Schouten, H. and Denham, C.: in press, ‘Estimating the Roughness of Sea Floor’, J. Geophys. Res.
Searle, R. C. and Laughton, A. S.: 1977, ‘Sonar Studies of the Mid-Atlantic Ridge and the Kurchatov Fracture Zone’, J. Geophys. Res. 82, 5313–5328.
Sinclair, J. E. and Bhattacharya, G.: 1980, ‘Interaction Effects in Marine Seismic Source Arrays’, Geophys. Prosp. 28, 323–332.
Slootweg, A. P.: 1980, ‘Multiple Beam Generation with a Digital Computer for Echosounding at Low and High Frequencies’, Ph.D. Dissertation, Geologica Ultraiectina, No. 24.
Slootweg, A. P. and Collette, B. J.: 1985, ‘Crustal Structure and Spreading History of the Central North-Atlantic in the Cretaceous Magnetic Quiet Period (African Plate)’, Proc. Kon. Ned. Ak. Wet. Series B, 88(3), 251–302.
Spiess, F. N. and Tyce, R. C.: 1973, ‘Marine Physical Laboratory Deep Tow Instrumentation System’, Scripps Inst. Oceanog. Reference 73–74, 1–37.
Taylor, T. T.: 1955, ‘Design of Line-Source Antennas for Narrow Beamwidth and Low Side-Lobes, IRE Trans. on Ant. and Prop. AP-3, 16–28.
Wang, H. S. C.: 1975, ‘Amplitude Shading of Sonar Transducer Arrays’, J. Acoust. Soc. Am. 57, 1076–1084.
Whitmarsh, R. B. and Laughton, A. S.: 1976, ‘A Long-Range Sonar Study of the Mid-Atlantic Ridge Crest near 37°N (FAMOUS Area) and its Tectonic Implications’, Deep-Sea Res. 23, 1005–1023.
Wolff, C. J. M.: 1976, ‘A Parallel Analog Fourier Transformer for Acoustic Underwater Holography and Sector Scanning Sonar’, paper presented at the Conference on Recent Developments in Underwater Acoustics, Portland (GB).
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Slootweg, A.P. Basement imaging with Side-Looking Seismics. Marine Geophysical Researches 8, 149–174 (1986). https://doi.org/10.1007/BF00338226
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00338226