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This paper interprets aeromagnetic data for a deep basin section of the Karroo rift in south‐east Tanzania. We use a novel integrated approach involving the application of advanced derivatives to define structure and the tilt‐depth method to determine and map the depth to basement. In the latter case we use the result of both reduced to pole and reduced to equator data to help constrain the shape and depth of the basin. We show that for a reduced to pole aeromagnetic data set, the generalized form of the local phase, called the tilt derivative, is an effective means of providing an initial (first pass) mapping of a sedimentary basin in terms of its fault structure, dip direction of faults and depth to basement. Since the amplitude of the tilt derivative does not contain information on the strength of the geomagnetic field nor magnetization (other than inclination) of the causative body, the susceptibility contrast across faults/contacts is derived from the analytic signal derivative. We also investigate how effective the tilt derivative and tilt‐depth method are for structural and depth to basement mapping in regions close to the magnetic equator, where the reduction to pole transform is often unstable; this is done using the same Tanzania data set transformed to the pole and the equator. We find that the tilt derivative applied to the reduction to equator data cannot be used to map the structure because of the effects of magnetic anisotropy, which results in the magnetic response of structures varying with strike azimuth. To overcome this anisotropy problem the analytic signal and/or local wavenumber derivatives, which are for all practical purposes independent of inclination, provide the best means of defining the major structural trends. We also find that the tilt‐depth method provides coherent depth to basement estimates for both reduced to pole and reduced to equator data. For the deep basin sections of the Karroo rift, there is a sparsity of tilt‐depth results from both the reduced to pole and reduced to equator data sets. However, each set of results has a different spatial coverage, so when combined they provide a better spatial sampling of the long wavelength magnetic character of the basin and thus improve the constraints on the minimum curvature gridding method to map the shape and depth of the basin.

S U M M A R YWe use a multiscale approach as a semi-automated interpreting tool of potential fields. The depth to the source and the structural index are estimated in two steps: first the depth to the source, as the intersection of the field ridges (lines built joining the extrema of the field at various altitudes) and secondly, the structural index by the scale function. We introduce a new criterion, called 'ridge consistency' in this strategy. The criterion is based on the principle that the structural index estimations on all the ridges converging towards the same source should be consistent. If these estimates are significantly different, field differentiation is used to lessen the interference effects from nearby sources or regional fields, to obtain a consistent set of estimates. In our multiscale framework, vertical differentiation is naturally joint to the low-pass filtering properties of the upward continuation, so is a stable process. Before applying our criterion, we studied carefully the errors on upward continuation caused by the finite size of the survey area. To this end, we analysed the complex magnetic synthetic case, known as Bishop model, and evaluated the best extrapolation algorithm and the optimal width of the area extension, needed to obtain accurate upward continuation. Afterwards, we applied the method to the depth estimation of the whole Bishop basement bathymetry. The result is a good reconstruction of the complex basement and of the shape properties of the source at the estimated points.

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We sought to map the depth and density contrast of the Mohorovičić discontinuity (Moho) across the Red Sea area and to model sedimentary thickness from gravity data. The gravity data that are used are a combination of satellite and terrestrial gravity data processed into a Bouguer anomaly grid. A 200-km low-pass filter was used to separate this grid into regional and residual gravity grids. We inverted the regional gravity grid to a Moho depth map based on a density contrast map that is constrained by published seismic results. The interpreted Moho is shallowest ([Formula: see text]) along the axis of the central Red Sea, [Formula: see text] along the axis to the south, and [Formula: see text] in the northern Red Sea. The depth increased to [Formula: see text] at the coast and 35–40 km in the adjacent continents. The residual gravity data provided insights into the tectonic fabric along the whole rift and provided a good correlation with magnetic lineaments where these are available. We used the complete Bouguer anomaly to model sedimentary thicknesses constrained by wells and the interpreted Moho. The modeling results are consistent with the presence of large-scale, ridge parallel tilted fault blocks forming subbasins with a maximum depth of about 6–7 km. Our models suggest that the northern Red Sea has an asymmetric basement surface with the western side deeper than the eastern side. The results indicate the presence of oceanic crust in the central and southern parts of the Red Sea, but not in the north. The very thin crust and interpreted oceanic crustal density in the central Red Sea suggest that this area is fully oceanic—although possibly quite young.