The Marine VHR 2.5-D Seismic Brute Stack Cube as a Feasible Tool for Low Budget Investigation and Research
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Ó Springer 2005
The marine VHR 2.5-D seismic brute stack cube as a feasible tool for low budget investigation and research Christof Mu¨ller Institute of Geosciences, Department of Geophysics, Kiel University, Otto-Hahn-Platz 1, D-24118 Kiel, Germany; (Phone: +49-431-880-3901; Fax: +49-431-880-4432; E-mail: [email protected]) Received 26 January 2004; accepted 25 April 2005
Key words: Baltic Sea, gas, Holocene, marine 3-D seismics, multichannel Boomer seismics, very high resolution (VHR)
Abstract Between 1997 and 1999 several marine seismic surveys were carried out in Kiel Bay aimed towards the development of a threedimensional acquisition and interpretation technique for small scale subsurface structures using high-frequency sources and multichannel streamers. The data set was recently revisited by the author and reprocessed to obtain a multichannel stacked seismic data cube. Nominal hydrophone positions are deduced by determining offsets from first arrival times and estimating the hydrophone positions under consideration of the ships track. Processing towards a ‘seismic cube’ mainly comprised CMP sorting, constant velocity NMO correction and stacking. The resulting VHR 3-D seismic ‘brute stack cube’ reveals rich structural details. The fluvial Pleistocene channel system already documented in an earlier publication was tracked further to the north. It is situated below a flat cover of gasbearing Holocene sediments, which locally constitute the seafloor. This till-horizon is superimposed on a second till layer showing strong topographic variations. Seismic signal phase and shielding effects indicate the possible presence of gas in these formations. This case history demonstrates that the VHR 3-D seismic method is a feasible tool for low budget investigation and research.
Abbreviations: AGC: Automatic gain control; BSH: German Federal Maritime and Hydrographic Agency; CMP: Common-midpoint; DFG: German Research Foundation; NMO: Normal moveout; SNR: Signal to Noise Ratio; VHR: Very High Resolution
Introduction Very high resolution (VHR) 3-D seismic acquisition has been lately gaining attention in the geophysical community. This is in part due to the increasing capability of computers to handle large datasets, but it is also due to the broad and affordable availability of high precision differential GPS. Most applications are in the field of engineering and archaeological geophysics where the three-dimensional imaging of small scale structures is of great interest and the possibilities offered by the method are highly attractive (Scheidhauer et al., 2001; Missiaen et al., 2002). Small in this respect refers to magnitude of the seismic signal’s dominant wavelength, i.e. a few decimeters. This defines the term ‘VHR’ and demands for the deployment of
sources with a signal pulse length of a few tenths of a microsecond. The term ‘2.5-D’ describes all survey types, including the case discussed here that only sufficiently samples the Fresnel zone in one horizontal direction and provides dense parallel profiles to generate a cohe
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