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The Leading Edge; August 2001; v. 20; no. 8; p. 854-857; DOI: 10.1190/1.1487294
© 2001 Society of Exploration Geophysicists
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Combined vertical-incidence and wide-angle seismic study of deepwater bright-spot reflections

Christian Müller, Friedrich Theilen and Bernd Milkereit

University of Kiel, Germany

Corresponding author: C. Müller, c.mueller@bgr.de

Editor's note: Christian Müller is now at Germany's Federal Institute for Geosciences and Natural Resources. A version of this paper won the Best Student Poster Presentation award from the 2000 SEG Annual Meeting in Calgary.

The first 20% of the full text of this article appears below.

Ocean island systems such as Hawaii and the Canaries have been built by large volumes of magma intrusions and by lava extrusions based on intraplate volcanism. The Canary Islands, off the Northwest African continental margin (Figure 1), were formed by hot-spot volcanism where subaerial volcanic activity started on Fuerteventura about 20 million years ago.


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  		Figure 1. Map of survey area showing reflection seismic lines and OBH stations acquired by RV Poseidon in 1997 and 1999.

 
During cruises by RV Poseidon in 1997 and 1999, a number of pronounced seismic bright spots were imaged on a dense grid of 2-D reflection seismic lines, 300–800 m below the seafloor at water depths of more than 3800 m in the sedimentary column of the southern Canary Basin.

Bright-spot evaluation using forward modeling, AVO analysis, and true-amplitude data-processing techniques require detailed background P-wave velocity information. However, most seismic surveys in deep water lack wide-angle reflections for velocity analysis. The maximum shot-receiver distances of 800 m at water depths of more than 3600 m in present multichannel seismic (MCS) data do not provide reliable subsurface velocities.

ODP Leg 157, over the submarine flank of Gran Canaria, provided limited stratigraphic and well control to the main bright-spot areas south and southwest of El Hierro (Figure 2). Velocity, density, and porosity logs from these sites are available for the upper 700 m of sediments; the lowermost 300 m mainly comprises volcaniclastic deposits originating from Gran Canaria. Geothermal gradients provide additional constraints for calculation of the stability field of volatiles. To acquire local, subsurface velocity structures in bright-spot areas, 15 ocean-bottom hydrophone (OBH) stations were deployed on the seafloor.


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  		Figure 2. Reconnaissance deepwater seismic line 28/97 showing six prominent bright-spot reflections in the southern Canary Basin. ODP site 956, southwest of Gran Canaria, provides limited stratigraphic and . . . [Full Text of this Article]

 





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