Within the Margins of Africa theme within the framework of Inkaba Ye Africa (IyeA) and as part of the Agulhas-Karoo onshore/offshore geoscience transect, Near Vertical Reflection (NVR) seismic data was collected in South Africa from Oct - Dec 2005.

The 800 km Agulhas-Karoo Transect runs from the Kaapvaal Craton southward, across the Karroo basin, the Cape Fold Belt and the southern continental margin of Africa, to the Agulhas Fracture Zone and adjacent Plateau in the southern Indian Ocean. The transect crosses the Beattie Magnetic Anomaly (BMA the world's largest such crustal anomaly, within Cape Conductivity Zone and Namaqua-Natal Metamorphic Belt, beneath the Karoo Basin. The NVR experiment that ran for a ~100km section near the centre of the profile, across the BMA. The goals are to investigate the seismic image of the BMA and to integrate this with findings of the complementary Magnetotellurics (MT) and Wide Angle onshore-offshore refraction/reflection data (WRR).

In the NVR seismic experiment, 182 boreholes were drilled to a depth of ~12m and at a spacing of ~500m. The Boreholes were charged with ~15kg explosives (sources). An 18km array of 20x3 channel recording stations and vertical component geophones every 100m, recorded the energy reflections in the vertical component (receivers). This delivered a high quality NVR seismic dataset - suitable for creating a ~100 km long image of the crustal reflectivity and deep crustal structures down to a depth of >40km.

The preliminary processing show a shallow strong flat lying feature at ~5-8km along most of the profile, contrasted by complex underlying structures at the expected location of the BMA and further complex crustal structures down to 30-40km depth that image the region adjacent to the Moho. The findings correspond to anomalies in similar regions found by the experiments of the MT and WRR groups.

Principal Investigators

• Trond Ryberg (GFZ Potsdam)
• Albrecht Schulze
• Klaus Bauer (GFZ Potsdam)
• Michael Weber (GFZ Potsdam)

Publications

• Lindeque, A. S., Ryberg, T., Stankiewicz, J., Weber, M. H., & de Wit, M. J. (2007). Deep Crustal Seismic Reflection Experiment Across the Southern Karoo Basin, South Africa. South African Journal of Geology, 110(2-3), 419-438. doi:10.2113/​gssajg.110.2-3.419.