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SEG HL Lecture presented by ASEG Queensland Branch
The lecture will be presented by Greg Beresford. Please RSVP to Megan Nightingale by 24 March if you plan to attend.
Talk Overview:
The recording of seismic data on the seafloor commenced in the late 1980s to allow acquisition in areas where towed streamers could not be deployed. The use of ocean-bottom cables (OBCs) provided the opportunity for geophysicists to measure the conjugate fields of pressure and particle velocity and theoretically to remove the surface ghost from marine data. Under certain approximations, it also allowed (in theory at least) the removal of water-column reverberations, a very exciting prospect indeed for marine acquisition. There is some very nice physics in OBC acquisition: phase shifts between pressure and vertical particle velocity because of surface ghosts; separation of upgoing and downgoing waves; depiction of waves just above and just below the seafloor boundary; the role of the subseafloor elastic profile in generating guided waves in the water column. There is also the difficult geophysical estimation problem of geophone coupling, which can make that nice physics inapplicable, especially in areas of shallow water.
What are the physical conditions at the seafloor that make the processing of OBC data difficult? How strong can horizontally propagating (guided) waves be relative to the primary reflections we are trying to measure? How do we quantify and recognize the noise on OBC data when we record in two or four components? In what ways can the geophones on the seafloor misbehave? What esoteric seismic domains can we invent to take advantage of full-azimuth recordings with a high density of sources? There is a lot of fun to be had by the processing geophysicist! What are some of the insights gained when the geophysicist is given the opportunity to design experiments and analyze data at the start of OBC surveys?
In recent years, there have been many developments in the technology associated with seafloor acquisition, and this has been covered thoroughly in the SEG honorary lecture of 2012, “Ocean bottom acquisition: Past, present and future.” Here, I will restrict my lecture to exploring some of the fundamental concepts and challenges that are associated with this area of geophysics.
About the Speaker:
Greg Beresford is a self-employed consulting geophysicist working in seismic acquisition and processing. He has a D.Phil. from Oxford University, where he studied guided waves for in-seam fault detection. He worked for G.S.I. research in Dallas in the early 1980s and returned to Australia in 1986 as senior lecturer in the School of Earth Sciences at the University of Melbourne. His interests include signal-to-noise enhancement, near-surface geophysics, elastic modelling for AVO and for converted waves, and shallow-water ocean-bottom cable (OBC). He has 44 publications to his credit.
Beresford has a keen interest in teaching and has presented numerous industry courses in the Pacific South and Asian regions. These included invited courses on OBC acquisition and processing. He has processed full OBC surveys on ProMAX and has been involved in numerous in-field testing programs for OBC and transition-zone data acquired in diverse regions around the world: the Gulf of Khambhat in India, north-eastern Brazil, the Gulf of Suez, the Nile Delta, Sumatra, Kalimantan, Papua, the Browse Basin in Australia, and Bangladesh.
