Skip to main content

Advertisement

You are viewing the new article page. Let us know what you think. Return to old version

Article | Open | Published:

Acquisition, processing and analysis of densely sampled P- and S-wave OBS-data on the mid-Norwegian Margin, NE Atlantic

Abstract

This paper describes the processing and analysis of semi-local OBS-data shot along a 122 km profile in the Vøring Basin, NE Atlantic margin, using both a high-frequency/short shot-spacing and a low-frequency/long shot-spacing air-gun source. Spectral analysis of the data reveals that an important difference between the two sources used, is that the low-frequency source generates significantly more energy around 6 Hz. This higher content of very low frequencies allows detection of arrivals to larger offsets for the low-frequency source. For the nearest offsets (0–20 km) the high-frequency source is able to resolve some more details than the low-frequency source, as far as the shallow to intermediate sedimentary levels are concerned. This is mainly caused by the fact that the high-frequency source has a much sharper primary pulse and reduced bubble pulse compared to the low-frequency source. The data quality can be significantly enhanced by use of band-pass filtering, trace mixing, FK (velocity) filtering, minimum phase predictive deconvolution, as well as Radon filtering. Inspection of particle diagrams documents S-wave splitting, interpreted as microcracks aligned vertically in the sedimentary section by the present day (slightly compressive) stress-field.

References

  1. Berg, E. W., L. Amundsen, A. Morton, R. Mjelde, H. Shimamura, H. Shiobara, T. Kanazawa, S. Kodaira, and J. P. Fjellanger, Three component OBS-data processing for lithology and fluid prediction in the mid-Norway margin, NE Atlantic, Earth Planets Space, 53, 75–89, 2001.

  2. Bungum, H., A. Alsaker, L. B. Kvamme, and R. A. Hansen, Seismicity and seismotectonics of Norway and nearby continental shelf areas, J. Geophys. Res., 96(B2), 2,249–2,265, 1990.

  3. Crampin, S., The scattering of S waves in the crust, Pure and Applied Geophysics, 132, 67–91, 1990.

  4. Digranes, P., R. Mjelde, S. Kodaira, H. Shimamura, T. Kanazawa, H. Shiobara, and E. W. Berg, Modelling of shear waves in OBS data from the Vøring Basin (Northern Norway) by 2-D ray-tracing, Pure and Applied Geophysics, 4, 611–629, 1996.

  5. Eldholm, O. and K. Grue, North Atlantic volcanic margins: Dimensions and production rates, J. Geophys. Res., 99, 2,955–2,968, 1994.

  6. Kanazawa, T, Technical Description of TK92-type ocean bottom seismometer, in Investigation of the Central and Northern Part of the Vøring Basin by Use of Ocean Bottom Seismographs, R/V Håkon Mosby 22 Aug.–24 Sept. 1992, cruise report, Statoil report, Mjelde, R. etal, 1993.

  7. Mjelde, R., M. A. Sellevoll, H. Shimamura, T. Iwasaki, and T. Kanazawa, A crustal study off Lofoten, N. Norway by use of 3-C ocean bottom seismographs, Tectonophys., 212, 269–288, 1992.

  8. Mjelde, R., M. A. Sellevoll, H. Shimamura, T. Iwasaki, and T. Kanazawa, Crustal structure under Lofoten, N. Norway, from vertical incidence and wide-angle data, Geophys. J. Int., 114, 116–126, 1993.

  9. Mjelde, R., M. A. Sellevoll, H. Shimamura, T. Iwasaki, and T. Kanazawa, S-wave anisotropy off Lofoten, Norway, indicative of fluids in the lower crust?, Geophys. J. Int., 120, 87–96, 1995.

  10. Mjelde, R., S. Kodaira, H. Shimamura, T. Kanazawa, H. Shiobara, E. W. Berg, and O. Riise, Crustal structure of the central part of the Vøring basin, mid-Norway margin, from three-component ocean bottom seismographs, Tectonophys., 277, 235–257, 1997a.

  11. Mjelde, R., S. Kodaira, P. Digranes, H. Shimamura, T. Kanazawa, H. Shiobara, and E. W. Berg, Comparison between a regional and semiregional crustal OBS-model in the Vøring basin, mid-Norway margin, Pure and Applied Geophysics, 149, 641–665, 1997b.

  12. Mjelde, R., J. P. Fjellanger, P. Digranes, S. Kodaira, H. Shimamura, and H. Shiobara, Application of the single bubble air-gun technique for OBS-data acquisition across the Jan Mayen Ridge, North Atlantic, Marine Geophysical Researches, 19, 81–96, 1997c.

  13. Mjelde, R., P. Digranes, H. Shimamura, H. Shiobara, S. Kodaira, H. Brekke, T. Egebjerg, N. Sørenes, and T. Thorbjørnsen, Crustal structure of the northern part of the Vøring Basin, mid-Norway margin, from wide-angle seismic and gravity data, Tectonophys., 293, 175–205, 1998.

  14. Mjelde, R., J. P. Fjellanger, T. Raum, P. Digranes, S. Kodaira, A. Breivik, and H. Shimamura, Where do PS converions occur? Analysis of OBS-data from the NE Atlantic Margin, First Break, 20, 153–160, 2002.

  15. Neidell, N. S., Land application of S waves, Geophysics: The Leading Edge of Exploration, 11, 32–44, 1985.

  16. Pajchel, J., H. B. Helle, and L. Frøyland, A 2-D seismic Modelling Package, User’s Manual, Geophys. Dep., Norsk Hydro Research Center, Bergen, 1989.

  17. Samson, C, P. J. Barton, and J. Karwatowski, Imaging beneath an basaltic layer using densely sampled wide-angle OBS data, Geophysical Prospecting, 43, 509–528, 1995.

  18. Sellevoll, M. A., H. Shimamura, A. Gidskehaug, and H. Johnsen, Seismiske undersøkelser av Lofoten marginen og refleksjonsseismiske test-målinger på Mohns Rygg, M/S Håkon Mosby, 29. juli-19. august 1988, Cruise report, IFJ, Univ. of Bergen, 1988.

  19. Shiobara, H., A. Nakanishi, H. Shimamura, R. Mjelde, T. Kanazawa, and E. W. Berg, Precise positioning of Ocean Bottom Seismometer by Using Acoustic Transponder and CTD, Marine Geophysical Researches, 19, 199–209, 1997.

  20. Trevorrow, M. V, T. Yamamoto, A. Turget, D. Goodman, and M. Badiey, Very low frequency ocean bottom ambient seismic noise and coupling on the shallow continental shelf, Marine Geophys. Res., 11, 129–152, 1989.

  21. Webb, S. C. and C. S. Cox, Observations and modeling of seafloor microseisms, J. Geophys. Res., 91, 7343–7358, 1986.

Download references

Author information

Correspondence to Rolf Mjelde.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Keywords

  • Radon
  • Seismic Noise
  • Automatic Gain Control
  • Reduction Velocity
  • Ocean Bottom Seismograph