A fault, designated the Katdoornbosch-Witpoortjie Thrust, was traced in the field continuously from the area north of Klerksdorp to the West Rand. It is shown that the Katdoornbosch Thrust and the Witpoortjie Fault form elements ofthe same structure. Evidence is presented why the Witpoortjie Fault should be designated a thrust. Thrust faults related to the Vredefort Event are recognized mainly by their 2 Ga, post-Transvaal age, their concentric arrangement around the centre of the structure, and their centrifugal vergence, away from the centre. Where chert beds ofthe Malmani Subgroup were intersected, thrust faults of Vredefort Event age can be recognized by a unique type of brecciation, displaying chocolatetablet-type boudinage, with fracturing having taken place in three dimensions. The brecciation is confined uniquely to the ramp zones and was probably formed during the release of three-dimensional, hydrostatic stress, when fault detachment took place. The recognition of this type ofbrecciation along the planes of the thrust faults associated with the stage of centrifugally directed movement, during the formation of the Vredefort Structure, provides an important criterion in their recognition. The Katdoornbosch-Witpoortjie Thrust is one of a set of similarly orientated, time-related thrusts, formed during the Vredefort impact event.
Late 2001 SERCEL conducted an experiment with a solid streamer system, which amongst others included a section with single hydrophones at an interval of 1.5 m. CGG together with SERCEL performed additional tests in 2003 in an operational environment for the duration of 2-3 months. Shell UK as operator for these surveys, allowed the insertion of some sections with single hydrophones in one of the deployed streamers. The duration of this field experiment allowed for exposure to any weather condition including the acquisition of seismic data with the operational qualification Not To Be Processed (NTBP). The field geometry allowed for direct comparison of the single hydrophones with groups in the solid section in front and with groups in the liquid section just behind, and with solid and liquid groups in the adjacent streamers. Summary Solid streamers are less sensitive to weather-related noise than liquid streamers. Hence, with the solid streamers the operational weather window can be extended. In addition solid streamers can be towed shallower without a prohibitive increase in noise. The application of noise filters on single hydrophones in a solid streamer only yields marginal improvements over application of the same filters on hydrophone groups. These improvements do not justify the introduction of single hydrophone recording. For reduction of weather noise a hydrophone spacing of 3 m may be adequate for solid streamers. However, the reduction from 16 to 8 hydrophones per 12.5 m groups shows an increase in flow noise. This flow noise will further increase with only 4 hydrophones at 3.125 m per 12.5 m group. Field experiment 1-Solid streamers and liquid streamers CGG acquired seismic data offshore Morocco using traditional liquid Syntrak streamers and full offset solid streamers. This allowed for comparison of signal and noise and operational performance of both streamer systems. In a good weather period the movement of the streamer through the water controls the minimum broadband noise level. This flow noise was measured at 5 microbar (with 3 Hz low-cut) for the solid streamer and 3 microbar for the liquid streamer. The increased flow noise in the solid streamer is caused by (1) the reduced number of hydrophones per 12.5 m group (8 instead of 16), (2) the location of the hydrophones closer to the skin, (3) a reduced hydrophone aperture and (4) the smaller streamer diameter.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.