AUDIOMAGNETOTELLURIC INVESTIGATIONS OF SHALLOW SEDIMENTARY BASINS IN NORTHERN SUDAN

Audiomagnetotelluric (AMT) investigations were carried out to study sh allow sedimentary basins in northern Sudan and southern Egypt. Unlike recordings in settled areas, the natural variations (atmospherics) in the eastern Sahara were completely unperturbed by cultural noise, usua lly yielding very high data quality. Typical recordings and spectra ar e presented. The atmospherics show distinct daily variations, with max imum amplitudes in the local afternoon/night hours. As a sort of calib ration, AMT measurements together with DC-resistivity and electromagne tic soundings were conducted at several groundwater boreholes. Under f avourable conditions, a vertical anisotropy may be resolved by joint i nversion of DCR and AMT data. The results of a case study in the Es Sa fya basin (NW Sudan) are presented. The investigations were aimed at d etermining basement depths and groundwater levels, as well as the dire ction and dip of major bounding faults. 2-D modelling and inversion re vealed the overall conductivity structure of this shallow graben. The AMT method proved to be a valuable tool for a comparatively swift reco nnaissance study of shallow structures.