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Densely sampled wide-angle seismic profiles using ocean-bottom seismometers have been used to obtain detailed velocity models of the Shetland-Faeroes Basin in both two and three-dimensions. We demonstrate that the wide-angle (refraction) technique, which employs dense spatial sampling to long offsets, may be successful in areas such as the Atlantic margin, where deep water and/or volcanic horizons mitigate against successful profiling using conventional methods. We employ a series of ray-trace and tomographic inversion procedures on travel time data from profiles across the basin axis to give detailed in situ velocity models and accompanying resolution and uncertainty estimates. Comparison of the in situ velocity of the Mid-Faeroe Ridge with deterministic lithology-velocity data from nearby boreholes strongly implies that CretaceousTertiary shale and sandstone sequences extend to depths of 4.5 km. The presence of pre-Cretaceous sedimentary lithologies at 4.5-8.0 km depth is supported by in situ velocities of 4.0-4.5 km s" 1 which are best explained by well-consolidated sediments and are incompatible with likely constituents of the basement. The southeastern flank of the Mid-Faeroe Ridges is marked by a prominent fault marking a lateral velocity variation of about 0.5 km s" 1 . A rapid increase in velocity at 8 km depth suggests transition into the basement, whose velocity is similar to high-pressure measurements of basalts from the Faeroe Islands. Data from an area] grid of shots and receivers centred over the Mid-Faeroe Ridge have been inverted to give a fully three-dimensional velocity model of a small volume to depths of 10+ km. Variations in the depth of isovelocity surfaces from this model correspond closely with the geometry of the Ridge, and the position of the flanking normal fault and its adjacent basin to the southeast.

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During the Kenya Rift International Seismic Project (KRISP 90) a 450 km long E-W seismic-refractionlwide-angle-reflection profile involving the deployment of 250 instruments was shot across the Kenya Rift. A reflected phase recorded between distances of 260 and 350 km from a 1000 kg shot at the western end of the line in Lake Victoria has been interpreted as originating from about 60 km beneath the western margin of the rift.Detailed processing of this phase has resulted in defining its polarity in relation to the first-arrival diving wave at the same range. Extensive kinematic and dynamic modelling shows there is a high-velocity zone at depths below 60 km under the western flank of the rift. We cannot exclude the presence of a layered alternating high-lowvelocity structure as found in the upper mantle beneath the northern part of the N-S seismic profile along the rift axis.Constraints from xenolith studies indicate that anisotropy may explain the high velocity found beneath the reflecting horizon (2 8.40 km s-'). Petrological modelling shows that if the anisotropy is due to the preferred orientation of olivine crystals, then either a transverse isotropic structure, in which the 'a' and 'c' axes are randomly orientated in the horizontal plane, or an orthorhombic structure, in which the fast 'a' axis is orientated along the direction of the E-W seismic line, is possible. The reflection could also be caused by a pre-rift structure associated with the Proterozoic collisional orogen involving the Mozambique Orogenic Belt and the Archaean Nyanza Craton, whose contact is subparallel to and lies about 70 km to the west of the Tertiary rift. The evidence presented here delimits the lateral extent of the upper-mantle region of anomalously low-velocity material that is confined to below the surface expression of the rift itself at depths below 60 km.

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