integrated Seismic Imaging and Modelling of Margins - the towed streamer surveys.
Zoë Lunnon1,2, Alan W. Roberts1, Philip Christie2, Robert White1, Nick Kusznir3 and Alan Roberts4
1
Cambridge University Earth Sciences, Bullard Labs, Madingley Road, Cambridge CB3 0EZ.
2
Schlumberger Cambridge Research, High Cross, Madingley Road, Cambridge CB3 0EL.
3
Department of Earth Sciences, Liverpool University, 4 Brownlow Street, Liverpool L69 3GP.
4
Badley Technology Ltd., North Beck House, North Beck Lane, Hundleby, Spilsby, Lincs. PE23 5NB.
This abstract outlines one of a two-part poster presentation describing the four year iSIMM project. iSIMM
seeks to model the evolution of magmatic margins and their basins using seismic imaging with integrated towed
streamer and ocean bottom seismometer (OBS) data. This poster focuses on the towed streamer data.
Intracratonic basin models can successfully predict heat-flow and subsidence from basin stretching. However,
these models cannot easily be extended to magmatic margins due to melt underplating and extrusion (i.e. crustal
non-conservation), and depth dependent stretching1. The North Atlantic continental margin was formed by
continental break-up in the early Tertiary above the Iceland mantle plume. This led to stretching and thinning
of the continental lithosphere, accompanied by massive magmatism, producing flood basalts and extensive
igneous intrusion2. The seismic components of iSIMM seek to develop a structural model from seabed to Moho
to image the stretched crust and the extruded, intruded and under-plated igneous material, and to use these
constraints in magmatic margin basin modelling.
Basalt flows present a challenge to seismic imaging. Flows are highly heterogeneous with large impedance
contrasts, and while they may have a low intrinsic attenuation, the strong multiples generated often mask the
little energy penetrating to the base of the basalt and the sub-stratum. The Faroes Large Aperture Research
Experiment3 used two ships to acquire 38km steamer data which penetrated the flood basalts, but did not image
the Moho, or provide sufficient data to estimate the magmatic under-plating, both of which are key aims of
iSIMM. Recent analyses of the Lopra borehole seismic data (Christie et al., submitted), and of wide-angle
seismic data4, have defined, at least locally, certain basalt flow propagation characteristics and have assisted the
survey design. A low frequency source design aids basalt penetration. Synthetic seismogram modelling prior to
the acquisition was used to select shot interval and record length.
In summer 2002, iSIMM surveyed two continent-ocean transitions (COT), one close to the Faroes, the other
west of Rockall-Hatton Bank (RHB). Both acquired OBS and towed streamer data: 12km Q-streamer for the
near-Faroes survey and a 3km NERC streamer for RHB. Early data samples are displayed on the poster.
The Q-Marine acquisition aims to image, where possible, to the basement below the basalt. Q-Marine5
provides long offset (12km) data with high density, single sensor sampling and shot-by-shot signature
monitoring. Unlike conventional streamer data, Q-data can be grouped after acquisition. A multi-streamer
swath also allows some cross-line protection. Ultimately the streamer and OBS data will be integrated for deep
velocity analysis and for identification of seismic mode conversions. We will follow the method of Fleidner &
White6 in using pre-stack depth migration to optimise the crustal image using both streamer and OBS data.
iSIMM’s long term goal is to develop a rifted margin basin model. OBS and streamer data integration will
provide an image from sea-floor to Moho and will demonstrate the applicability of Q-Marine to probe beneath
basalt. iSIMM investigators are Liverpool and Cambridge Universities, Badley Technology and Schlumberger,
supported by NERC, Agip UK, BP, Amerada Hess, Anadarko, Conoco, Phillips, Shell, Statoil, and
WesternGeco.
1) Davis, M. & Kusznir N.J., Depth-dependent lithosphere stretching at rifted continental margins. Earth Plan. Sci. Let., In review.
2) White, R. & McKenzie, D., Magmatism at rift zones: the generation of volcanic continental margins and flood basalts. Journal of Geophysical Research, 94, 76857729, 1989.
3) White, R.S., Fruehn, J., Richardson, K.R., Cullen, E., Kirk, W., Smallwood, J.R., & Latkiewicz, C., Faroes Large Aperture Research Experiment (FLARE): imaging
through basalt. Petroleum Geology of Northwest Europe: Proceedings of the 5 th Conference, 1243-1252, 1999.
4) Richardson, K.R., White, R.S., England, R.W., & Fruehn, J., Crustal structure of the Faroe Islands: mapping sub-basalt sediments using wide angle seismic data.
Petroleum Geoscience, 5, 161-172, 1999.
5) Martin, J., Özbek, A., Combee, L., Lunde, N., Bittlestone, S., & Kragh, E., Acquisition of marine point receiver seismic data with a towed streamer. Annual Meeting
Abstracts, Society of Exploration Geophysicists, paper ACQ-3.3, 2000.
6) Fliedner, M.M., & White, R.S., Sub-basalt imaging in the Faeroe-Shetland Basin with large-offset data. First Break, 19, 247-252, 2001.