Seismic Surveys in Central West Antarctica: Data and Processing Examples from the ANTALITH Field Tests (1994-1995)

During the austral summer of 1994-95, the University of Texas at Austin, in collaboration with the Pennsylvannia State University and the British Antarctic Survey, collected a 60 km multichannel seismic reflection profile along with two smaller profiles and two wide-angle profiles over the Byrd subglacial basin in central-west Antarctica. The primary aim of the field season was investigating the requirements of conducting long traverses over the ice sheet as a pre-requisite to any regional traverse that may span continental Antarctica in the future. A secondary aim was obtaining a shallow to mid-crustal section of the lithosphere below the Byrd subglacial basin. Analysis of the multichannel seismic data resulted in an image of the base of ice as well as shallow sub-ice reflections and also revealed intra-ice reflections that (with minor exceptions) conform to the ice-floor topography. The rest of the CMP crustal section is transparent with no major recorded reflections. However, a shorter wide-angle survey conducted using larger charges over part of the same traverse revealed a deep crustal reflection at 4.9 s of two-way traveltime. A one-to-one comparison of the multichannel and wide angle data indicates that the high energy, low frequency seismic energy generated by the larger charges of the wide angle data was more successful in imaging the deep crustal section. This comparison also revealed that the crust in this area is indeed transparent from just below the ice floor to the 4.9 s reflection recorded by the wide angle data. Along the main traverse, the base of ice has siginificant topographical undulation in both inline and crossline directions with the highest elevations being nearly 750 m above the average depth of the ice-floor. There is ample evidence of faulting at the base of ice and several half grabens and localized basins can be identified. However, if there is sediment beneath the ice in these basins, it is not of significant thickness as indicated by the lack of events in the seismic reflection data. Nevertheless, these findings are in broad agreement with the idea that ice streams generally originate in fault-bounded sedimentary basins (Blankenship et al., 1997).